Presentation type:
TS – Tectonics & Structural Geology

EGU23-1798 | Orals | TS1.7 | Arne Richter Award for Outstanding Early Career Scientists Lecture

Episodic delocalization in the upper crust: Implications for earthquake forecasting 

Jessica McBeck, Francois Renard, and Yehuda Ben-Zion

The progressive localization of deformation has long been recognized as a fundamental phenomenon of the macroscopic failure of rocks. Our recent analyses using X-ray tomography during triaxial compression indicate that fractures and higher magnitudes of shear and dilative strain spatially localize as rocks are driven closer to macroscopic failure. Similarly, geophysical observations of low magnitude seismicity in southern and Baja California show that deformation localizes toward the future rupture plane of M>7 earthquakes. These sets of observations indicate that deformation can increase in localization toward failure, and that deformation can temporarily decrease in localization (delocalize) during this overall increase. These observations indicate that the spatial organization of deformation may be used to recognize the acceleration of the precursory phase leading to large earthquakes and the macroscopic, system-scale failure of heterogeneous materials. However, such efforts will require identifying the conditions that promote phases of delocalization, and how these perturbations in the overall trend of increasing localization influence the timing of macroscopic failure. In this presentation, I will describe these analyses, and new work that aims to identify which characteristics of the fracture networks determine the localization at a particular level of stress, and the change in localization from one stress step to the next in triaxial compression experiments at the confining stress conditions of the upper crust.

How to cite: McBeck, J., Renard, F., and Ben-Zion, Y.: Episodic delocalization in the upper crust: Implications for earthquake forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1798, https://doi.org/10.5194/egusphere-egu23-1798, 2023.

EGU23-4551 | Orals | MAL29 | Stephan Mueller Medal Lecture

Neotectonic Rates of Motion Between Hotspots 

Richard Gordon, Kevin Gaastra, Gregory Mifflin, and Chengzu Wang

Hotspots, sites of mid-plate or excessive volcanism, overlie plumes of hot rock that rise in the solid state from Earth’s deep mantle. Estimated rates of lateral hotspot motion since Late Cretaceous time have been as low as ≈3 mm/yr to as high as ≈80 mm/yr. We focus on geologically current (i.e., neotectonic) motions because the precision and accuracy of relative plate motions in the MORVEL set of relative plate angular velocities (DeMets et al., 2010) are an order of magnitude greater than plate motion estimated for earlier time intervals.  Prior efforts to estimate neotectonic relative motion between hotspots from trends of hotspot tracks found no significant difference from zero motion (i.e., they are consistent with fixed hotspots) and no useful upper bound on the rate of motion (e.g., Minster et al., 1974; Gripp & Gordon, 1990, 2002).

Our recent analysis builds on methods to objectively estimate the uncertainty of hotspot trends. We use the uncertainties estimated by Gripp & Gordon (2002) and by Wang et al. (2019a) for the hotspot trend data set of Morgan & Morgan (2007).  The objectively estimated uncertainties tend to be larger than those assigned by Morgan & Morgan (2007), especially for slow moving plates.  In a global inversion of the observed trends, a chi‐square test indicates that the trends and adopted uncertainties are consistent with fixed hotspots (p=0.08; p < 0.05 would indicate significance). When we conduct a two‐tier analysis, however, the motion between groups of hot spots is significant. The group‐means of trend‐perpendicular component of velocity range in nominal magnitude from 0 to 6 mm/a with a median of ≈3 mm/a.  Wang et al. (2019b) applied these data and uncertainties to investigate how well the hotspot motion predicted by Doubrovine et al (2012) in their Global Moving Hotspot Reference (GMHRF) fit the observations.  Surprisingly the GMHRF fits the observed trends much worse than they are fit assuming fixed hotspots.

The key to our newest analysis, which attains far higher resolution than before, is the novel use of Monte Carlo inversion to find directions and rates of hotspot motion that misfit the observed trends by angles consistent with the uncertainties in the trends. We obtained one million pseudorandom realizations of the direction of motion of each of 53 hotspots and inverted for the rate of hotspot motion that best fits the observed hotspot trend data.  We examined speeds ranging from 0 to 15 mm/yr in increments of 1 mm/yr.  For 60% of the realizations the best-fitting hotspot speed is 0 mm/yr, i.e., no motion between hotspots. Forty per cent of the realizations are fit better with some motion between hotspots with merely 2% of the realizations being fit acceptably close to the misfit expected given the size of the uncertainties.  No realizations gave an acceptable fit with motion less than 2 mm/yr or with motion exceeding 8 mm/yr; the 95% confidence interval is 2–4 mm/yr, significantly different from zero, but low enough to strongly support the use of the fixed hotspot approximation.

How to cite: Gordon, R., Gaastra, K., Mifflin, G., and Wang, C.: Neotectonic Rates of Motion Between Hotspots, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4551, https://doi.org/10.5194/egusphere-egu23-4551, 2023.

TS1 – Deformation mechanisms and rheology

Natural faults host various types of migrating slow earthquake phenomena, with migration speeds much lower than seismic wave speeds and different moment-duration scaling from regular earthquakes. To advance the obtained quantitative understanding of the migration process and long duration of slow earthquakes,  I study a chain reaction model in a population of brittle asperities based on a rate- and state-dependent friction on a 3-D subduction plate boundary. Simulation results show that the migration speed is quantitatively related to frictional properties by an analytical relation derived here. By assuming that local pore water in front of the migration drives rapid tremor reversal and is so local as to hold a constant stress drop, the application of the analytical solution to observational results suggests that (i) the temporal changes of observed migration speeds for the rapid tremor reversal could be explained by about 70% reduction of the effective normal stress; (ii) effective normal stress for the deeper extension of seismogenic segment in the western part of Shikoku is about 1.5 times greater than that in the central part. Applying rupture time delay between slow earthquake asperities for a duration longer than the regular earthquake, I also conclude that (iii) the characteristic slip distance of rate-and-state friction for low-frequency earthquakes is roughly between 30 μm and 30 mm; (iv) the stress and strength drops of very low-frequency earthquakes is much smaller than 1 MPa.

References:

Ariyoshi, K. (2022). Extension of aseismic slip propagation theory to slow earthquake migrationJournal of Geophysical Research: Solid Earth127, e2021JB023800. https://doi.org/10.1029/2021JB023800

How to cite: Ariyoshi, K.: Physical interpretation of slow earthquake migration process based on a friction law, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-204, https://doi.org/10.5194/egusphere-egu23-204, 2023.

With the growing need for CO2 storage, risk management is essential to secure the storage sites; these risks include fault reactivation, ground surface deformation/sea-bottom (uplift), well and caprock integrity, and CO2 leakage; managing these risks could be achieved by understanding the hydromechanical behaviors of rock induced by the reservoir pressure build-up caused by CO2 injection. However, this remains a crucial challenge because the rock's mechanical and hydraulic properties are poorly constrained. Moreover, the conventional monitoring methods usually consider CO2 plume migration only, which is not enough to understand the induced pressure front that occurs far beyond the real pressure plume. Although several techniques could image the geomechanical deformation and investigate the surface deformation well, these monitoring methods do not provide a complete image regarding the deformation migration from the subsurface to the surface due to the limited measurement points in addition to the cost issue.

 In this paper, we will introduce Rayleigh scattering-based Distributed Optical Fiber Strain Sensing (DFOSS) as an effective tool for subsurface and surface geomechanical monitoring to track the dynamic responses at each spatial location along the cable due to the deformation caused by injection; this technology could overcome other conventional methods' limitations including continual spatiotemporal measurements, cost-effective installation: vertically along the wellbore and horizontally into the ground surface, covered area and sea bottom. We will review several laboratory and field experiments from our previous studies. First, we will show the laboratory results from the first laboratory test to track the movement of the CO2 plume as it enters the clay-rich critical regions in the reservoir–caprock system using DFOSS and monitoring of the injected water in a sandstone sample using DFOSS in the second test. Both results demonstrated that DFOSS could provide high-resolution information on deformation and fluid activity. Next, we will show our subsurface monitoring field results, where we conducted several water injection tests in a shallow well. We monitored the injection process by installing DFOSS in a monitoring well. Our outcome confirmed that DFOSS could provide critical information for rocks' properties and fluid migrations by geomechanical monitoring, and it could be a real-time and permanent monitoring tool for wellbore, caprock integrity, and CO2 leakage. Finally, we will show the surface deformation monitoring results, where we installed the fiber cable into the surface horizontally in a shallow trench; the airbag inflation and deflation tests were conducted under the fiber cable to simulate uplift and subsidence caused by the fluid injection and production in the subsurface. The results suggested that DFOSS could locate any anomaly along the cable.

 Our results demonstrate that installation of DFOSS in fiber cables horizontally into the surface around the injection site and vertically in a well to incorporate well-based strain sensing with surface monitoring, allowing geomechanical monitoring (horizontally into the surface and vertically in the subsurface) in three dimensions via a cost-effective, real-time and permanent monitoring system.

How to cite: Amer, R., Xue, Z., and Hashimoto, T.: Geomechanical Monitoring at CO2 storage sites with Distributed Fiber Optic Strain Sensing: Insights from laboratory and Field experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1507, https://doi.org/10.5194/egusphere-egu23-1507, 2023.

EGU23-1637 | ECS | Posters on site | TS1.3

Numerical simulation provides conditions for interpreting the groundwater response to Earth tides 

Jose Bastias, Gabriel Rau, and Philipp Blum

Earth tides exert small gravitational variations in the subsurface which lead to pore pressure changes and water level fluctuations in groundwater monitoring wells. This groundwater response to Earth tides has been used to estimate subsurface hydraulic and geomechanical properties. However, existing approaches are based on simplifying assumptions and their reliability has not been tested for realistic conditions. To simulate how Earth tides affect the subsurface, we developed and verified a numerical model that couples hydraulic and geomechanical theories. We modelled the response of a semi-confined aquifer which exchange water with an observation well for the dominant M2 Earth tide component. We reveal that undrained (i.e., groundwater does not flow in response to stress) and confined (i.e., groundwater is under pressure) conditions are necessary for the analytical solution to be valid. For the M2 frequency we assess that this occurs at depths ≤ 50 m and requires specific storage at constant strain sε ≥ 10-6 m-1, hydraulic conductivity of the aquitard kl ≤ 5 • 10-5 ms-1 and aquifer kl ≥ 1 • 10-4 ms-1, respectively. Further, we illustrate that established analytical solutions are valid in unconsolidated systems, whereas consolidated systems require additional consideration of the compressibility ratio between the porous medium and the porous skeleton (i.e., inclusion of the Biot coefficient). Overall, we find that a priori knowledge of the subsurface system increases the reliability of the groundwater response interpretation. Our results improve understanding of the effect of Earth tides on groundwater systems and provide a framework for evaluating subsurface properties.

How to cite: Bastias, J., Rau, G., and Blum, P.: Numerical simulation provides conditions for interpreting the groundwater response to Earth tides, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1637, https://doi.org/10.5194/egusphere-egu23-1637, 2023.

EGU23-2823 | ECS | Posters on site | TS1.3

Experimental evidence for viscous deformation and strain localization in fractured granitoid rocks 

Natalia Nevskaya, Weijia Zhan, Holger Stünitz, Alfons Berger, and Marco Herwegh

According to well-established hypotheses based on field observations of natural faults, viscous deformation may localize following pre-existing brittle fractures. The weak behaviour can be explained by brittle grain size reduction and phase mixing, which may activate grain size sensitive processes in the viscous field. To prove this hypothesis, it is necessary to perform experiments to observe the strain and stress evolution in faulted and non-faulted rocks. Pec et al. (2012) performed experiments on granitic rocks by shearing manually crushed granitic powder between coarse solid granitic forcing blocks. However, in their study, there are unavoidable boundary conditions between the forcing blocks and the gouge, and a comparison to an intact rock without fracture is difficult.

In our study, we reduce the boundary conditions to a minimum and can directly compare the stresses and microstructural evolution during deformation of intact and fractured granitic ultramylonites at 650°C, confining pressure of 1.2GPa, and a constant displacement rate of 10-8m/s. We perform these experiments on initially solid cylindrical samples in two experimental sets: In set A, we slowly apply the load and confining pressure, to ensure an intact rock sample is deformed. In set B, we create fractures before the experiment starts but already in the closed system of the experimental setup. Once experimental P/T conditions are reached, both experimental sets are deformed to different finite strains to investigate the associated microstructural evolution. The deformation is disseminated in the set A experiments, but localizes strongly along the fracture in experimental set B. The strain is accommodated by viscous granular flow incorporating an impressive grain size reduction of up to 1000x and dissolution/precipitation processes. In addition, the stress records show that in experiments A, initially a 30% higher yield stress has to be overcome before steady state flow, while in set B steady state flow is reached directly without a strain softening increment. In both sets, steady state stresses range around 300MPa, i.e. far below the confining pressure.

Applying microstructural observations and mechanical data of our experiments to deformation of granitoid crust in nature reveals that fractures serve to reach mechanical steady state earlier compared to non-fractured crust. As a matter of strain, however, both settings may yield at the same mechanical strengths of resulting shear zones. It is important to note that polymineralic fine-grained ultramylonites are up to four times weaker than monomineralic quartz, presenting an important behaviour of efficient strain localization and rheological properties substantially below those of the end member minerals.

 

Pec, M., Stünitz, H. and Heilbronner, R., 2012. Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures. Journal of Structural Geology, vol. 38, pp. 200-221. https://doi.org/10.1016/j.jsg.2011.09.001

How to cite: Nevskaya, N., Zhan, W., Stünitz, H., Berger, A., and Herwegh, M.: Experimental evidence for viscous deformation and strain localization in fractured granitoid rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2823, https://doi.org/10.5194/egusphere-egu23-2823, 2023.

The present mean convergence rate of Himalaya is ~ 15 mm/year. In comparison to the convergence and stress accumulation, only few stress release events represented by greater than M5+magnitude earthquakes in the Himalayan region have been observed. Understanding the constraints leading to the disparity in stress accumulation and stress release, is crucial to understand the stress accommodation mechanism and seismicity in the Himalayas. The current active subduction boundary is marked by Main Frontal Thrust separating the sub-Himalayas and the Gangetic alluvial plains. The rock types within the Main Frontal Thrust sheet show two primary types of sandstone protoliths, and gouges exhibiting cataclastic to foliated microstructural features. In this study, we have performed rotary-shear velocity step experiments on the powdered samples of the sandstone within the Main Frontal Thrust to determine their frictional properties at slow (creep) to fast (seismic) velocity under 10 MPa effective normal stress condition.  We discuss these results and their implications on seismic nucleation in Himalayan Main Frontal Thrust.

How to cite: Sarkar, D. P. and Hirose, T.: Frictional properties of sandstone gouges within Himalayan Main Frontal thrust: constraints on seismicity of shallow crustal deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3062, https://doi.org/10.5194/egusphere-egu23-3062, 2023.

EGU23-3401 | ECS | Posters on site | TS1.3

Ambient Stress in Subduction Forearcs Constrained by Numerical Models and Earthquake Static Stress Drop Values 

Gian Maria Bocchini, Armin Dielforder, Kilian B. Kemna, Rebecca M. Harrington, Andrea Hampel, and Onno Oncken

Stress in active subduction forearcs is controlled primarily by friction along the megathrust and the gravitational force. The competing deviatoric compressive and tensional stresses generated by megathrust friction and gravity, respectively, are of the same order of magnitude and result in very low deviatoric stress in the forearc. The near neutral stress state in subduction forearcs is supported by observations of stress reversal, that is a change from deviatoric compression to deviatoric tension, caused by very small megathrust shear stress drops (<10MPa) after recent large megathrust earthquakes. However, studies that quantify and compare the stress state in subduction forearcs at various stages of the seismic cycle are still limited. Here, we use two-dimensional finite-element force-balance models to quantify and constrain forearc stresses at different locations along the Chilean and Japanese subduction margins that are at different stages of the seismic cycle. The models consider forearc topography, slab geometry, crustal thickness, and water load to quantify the elastic stress in the forearc due to gravity and friction along the megathrust. The models indicate low deviatoric stress values (10s of MPa) in the subduction forearcs, which imply a weak forearc crust in areas of active seismic deformation. We validate the model results by estimating seismic stress drop values of forearc earthquakes from high-quality seismic waveform recordings. We estimate spectral corner frequency using both single-spectrum and spectral-ratio estimates and depth-dependent shear-wave velocity models. Spectral-ratio estimates provide more robust corner-frequency estimates that we employ to validate and interpret the increasing stress drop trend down to depths of ~50-60 km. The slight depth dependency of seismic stress drop values is consistent with depth dependency of deviatoric stress obtained from the finite-element models. Moreover, we find that average seismic stress drop values are systematically lower or similar to maximum deviatoric stress obtained from our models, which is consistent with a partial stress release during earthquakes in the forearc. Our results suggest a relation between seismic stress drop values and ambient stress in subduction forearcs.

How to cite: Bocchini, G. M., Dielforder, A., Kemna, K. B., Harrington, R. M., Hampel, A., and Oncken, O.: Ambient Stress in Subduction Forearcs Constrained by Numerical Models and Earthquake Static Stress Drop Values, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3401, https://doi.org/10.5194/egusphere-egu23-3401, 2023.

EGU23-4865 | ECS | Posters on site | TS1.3

Rotation of borehole breakouts by the effect of fractures/faults: observation and numerical model study 

Minzy Kang and Chandong Chang

Borehole breakouts, rock compressive failure at the wellbore wall, are one of the most widely utilized stress indicators, providing useful site-scale in situ stress states for a variety of geo-engineering projects. A 1 km deep vertical borehole drilled to study earthquakes in southeast Korea showed borehole breakouts rotated in azimuth at several depths by as much as 35° from the average azimuth, enlarging uncertainty in representative stress orientation. These breakouts developed in a highly fractured tuffaceous rock at a depth range from 840 m to 1000 m and breakout rotation always occurred adjacent to fractures and faults. While breakout rotation adjacent to fractures/faults has often been observed previously, there are several issues that have to be addressed regarding such a rotation, that is, would it be a local perturbation associated with drilling that can be ignored when assessing representative in situ stress states?; what aspect of fracture perturbs the stress indicator? To address these questions, we carried out a series of 3D finite element modeling, in which the rock mass consists of a single competent rock type (metamorphosed tuff) with a thin and soft planar fracture crossing the model. A borehole penetrates the center of the model vertically. The fracture orientation was varied from model to model for a given far-field boundary stress condition. The model results show that the rotation of breakouts increases generally (but with wide scattering) with an increase in slip tendency of the fracture. A more detailed analysis shows that the azimuthal rotation of breakouts tends to increase in a clearer manner with an increase in the horizontal shear displacement (or shear strain) component along fracture having relatively high slip tendency. For the reasonable values of mechanical properties assumed in the model, the breakout rotation can be as high as ~34° from the boundary stress orientation imposed in the model. Such stress rotation occurs throughout the extent of the fracture and is reflected in breakout rotation. The model results are quite comparable to the breakout rotations observed in the borehole. Our study suggests that breakout rotation is not just a local feature around the borehole but reflects a site-scale stress rotation associated with the presence of fractures having specific orientations and slip direction.

How to cite: Kang, M. and Chang, C.: Rotation of borehole breakouts by the effect of fractures/faults: observation and numerical model study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4865, https://doi.org/10.5194/egusphere-egu23-4865, 2023.

We explore the strength of the lithosphere beneath the Graham Land region (Antarctic Peninsula) using numerical modeling which simulate lithospheric deformation as a function of geological and geophysical parameters. First, we process 21 GNSS time series data spanning 1997–2022 provided by the Nevada Geodetic Laboratory, to produce a robust tectonic velocity solution and calculate a new geodetic strain rate model using an optimal mesh grid definition of 0.5 x 0.5 degrees that best fits our study area. Second, we combine our new geodetic strain rate model with the Moho depth and rheological parameters such as geothermal heat flow (GHF), heat productions and thermal conductivity previously published in the literatures to determine yield strength envelope (YSE) along three profiles (A, B and C respectively) beneath Graham Land. The lithospheric strength values are in a range from 0 to 500 MPa and depend more on strain-rates at the surface and thermal regime (GHF) than on crustal thickness. The highest values for the crust (500 MPa) are mostly concentrated in the profile A, near Cape Alexander, where the second invariant of the strain rate present the smaller value (5-15 μstrain/yr) and the principal strain rates are compressive approximately in the N-S directions. In contrast, the highest values for the mantle mainly depend on the thermal structure of the lithosphere and Moho depth and the highest values are concentrated in the profiles B (297 MPa) and C (279 MPa), in the Trinity Peninsula. Here, the second invariant of the strain rates, present the larger value (50-80 μstrain/yr) and the principal strain rates are extensive in the W-E directions, with a maximum value of 30 μstrain/yr. The results of our study demonstrate that both “jelly sandwich” and “crème brûlée” models are valid for the Graham Land lithosphere, depending on specific thermal and rheological conditions considered.

How to cite: Linsalata, F. and Spada, G.: Strength of the lithosphere derived by geological and geophysics data: the Graham Land (Antarctic Peninsula) case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5060, https://doi.org/10.5194/egusphere-egu23-5060, 2023.

EGU23-5935 | ECS | Posters on site | TS1.3

A stress field model for the Unterhaching geothermal plant: Challenges and solutions in local model calibration 

Sophia Morawietz, Moritz Ziegler, Karsten Reiter, Oliver Heidbach, Inga Moeck, Ingmar Budach, Hartwig von Hartmann, and Jennifer Ziesch

The stress field of Earth's upper crust is crucial for geodynamic processes and of key importance in planning and managing the utilization of the subsurface, such as geothermal energy extraction, stimulation of enhanced geothermal systems, or safety assessment of deep geological repositories. The contemporary 3-D stress state also provides the basis to assess the impact of induced stress changes which can lead to the reactivation of pre-existing faults, the generation of new fractures, or subsidence due to long-term depletion.

However, information on the stress state of Earth's crust is sparse and often not available for the areas of interest. So far, the stress tensor orientations and stress regimes have been systematically compiled and provided by the World Stress Map (WSM) project in a public-domain database. Yet, the acquisition of stress tensor orientations is not necessarily accompanied by the determination of the stress magnitudes, which, however, are required when investigating questions related to stability and hazard mitigation strategies of georeservoirs. To estimate the 3-D stress state, geomechanical-numerical modelling is applied. For the calibration of such models, stress magnitude data are essential. A major challenge is to bridge the scale gap between the widely scattered data that is required for model calibration and the high-resolution small-scale geological model in the target area. Ziegler et al. (2016) presented a multistage approach to resolve this challenge. For this, two successively calibrated models are created – one large-scale model with coarse resolution but available stress magnitude data for calibration, and one local model with fine resolution, e.g., based on a 3-D seismic survey of the target area, but without any stress data. Synthetic data obtained through the large-scale model is used to calibrate the small-scale local model.

First, we validated the multistage approach by means of generic models to rigorously quantify the associated introduced uncertainties. For this purpose, we implemented a highly simplified model lithology with only vertical stratification and no lateral changes. In a second step, we applied the multistage approach in a real-world setting and demonstrated the applicability on a local model of Unterhaching, south of Munich/Germany, where a geothermal district heating plant is located. Here, a local high-resolution model based on a 3-D seismic survey (Budach et al., 2018) has been successfully calibrated on a regional-scale stress model of the Bavarian Molasse Basin. The results of the local-scale model agree with the large-scale model. At the same time, stress change due to rock property variability, only resolved in the local-scale model, is shown.

How to cite: Morawietz, S., Ziegler, M., Reiter, K., Heidbach, O., Moeck, I., Budach, I., von Hartmann, H., and Ziesch, J.: A stress field model for the Unterhaching geothermal plant: Challenges and solutions in local model calibration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5935, https://doi.org/10.5194/egusphere-egu23-5935, 2023.

EGU23-6297 | ECS | Posters on site | TS1.3

New steps toward estimating the driving and resistive forces on the Eurasian plate 

Renato Gutierrez Escobar, Candela Garcia Sancho, and Rob Govers

We aim to quantify the likely ranges of magnitudes and directions of forces that may explain present-day natural stresses within the Eurasian plate. We first focus on one of the driving forces, horizontal gravitational stresses (HGSs) resulting from lateral variations in gravitational potential energy, which are particularly relevant in the context of the Eurasian plate because there are no major slabs attached to it (i.e., no slab pull force). We show that different published models of lithospheric density including lateral variations in the lithosphere-asthenosphere boundary result in significantly different HGSs. Other driving forces are mantle convective tractions including dynamic topography, and plate interaction tractions with bounding plates. Second, we include observed major faults into a 2D spherical cap elastic model of the Eurasian plate. We show results of forward FEM calculations based on the best model parameters of Warners et al. (2013) and compare them with observed stress directions. We propose different objective functions that quantify the (relative contributions to the) misfit of the modelled and observed stresses, fault slip directions, and magnitudes, the deviation of the net torque on the plate from zero, and the model representation error. Our study represents a stepping stone towards a Bayesian inference workflow to constrain the dynamics of the Eurasian plate of which we show preliminary results.

Warners-Ruckstuhl, K. N., R. Govers, and R. Wortel, 2013, Tethyan collision forces and the stress field of the Eurasian Plate: Geophys. J. Int., v. 195, no. 1, p. 1–15, doi:10.1093/gji/ggt219.

How to cite: Gutierrez Escobar, R., Garcia Sancho, C., and Govers, R.: New steps toward estimating the driving and resistive forces on the Eurasian plate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6297, https://doi.org/10.5194/egusphere-egu23-6297, 2023.

EGU23-6615 | ECS | Posters on site | TS1.3

Weakening of granitoid gouge in hydrothermal ring shear experiments 

Weijia Zhan, Natalia Nevskaya, André Niemeijer, Alfons Berger, Chris Spiers, and Marco Herwegh

Fault gouges of granitoid composition represent the principal non-cohesive tectonites within fault zones in the continental crust. The spatial distribution and strength of granitoid fault gouges is therefore crucial for understanding how weak the upper continental crust could be due to the formation of fault zones. Although several laboratory investigations reported the mechanical weakening of granitoid gouges in shear experiments, the deformation mechanism responsible for such behavior remains not well understood.

To address this issue, we conducted two series of shear experiments on granitoid gouges by using a ring shear apparatus. The starting gouge powders were derived from crushed granitoid mylonite with a median grain size of 45 μm. In a first set of experiments, gouges were sheared at a sliding velocity of 100 μm/s for a displacement of 15 mm. Temperatures explored ranged from 20°C to 650°C in order to determine the temperature dependence of gouge strength. The second set of experiments is identical to the first ones, except that the applied sliding velocity was set at 1 μm/s to study how fault slip rate influences the strength of gouges.

We observe that differences in gouges strengths as a function of sliding velocity and temperature: At a sliding velocity of 100 μm/s, the steady-state shear stress (τ) remains relatively constant at τ=76-82 MPa over the entire temperature range. Contrastingly, at a sliding velocity of 1 μm/s the steady-state shear stress remains temperature-insensitive with τ≈75 MPa up to tempertures of 450°C, but decreases then to τ≈50 MPa at 650°C (Fig.1 a). Furthermore, the amount of decrease of shear stress is strain dependent (Fig.1 b). At even slower sliding velocity of 0.1 µm/s, the shear stresses decrease further to τ≈38 MPa.

Microstructurally, all gouges deformed at T≦450°C show typical cataclastic features, where angular clasts with grain size of ~10 μm are surrounded by a fine-grained matrix. Intergranular fracture arrays in Riedel- and Y-shears are well developed over the entire cross section, indicating homogeneous bulk deformation. In contrast, gouges sheared at 650°C with τ≈50 MPa show strain localization in a principal slip zone. It is shear plane parallel with widths up to ~50 µm. Inside the principal slip zone, all grains are dramaticly reduced to nm-size and tightly packed. No intergranular fracture arrays are observed. Outside the principal slip zone, rounded grains with size of ~5 μm are loosely packed, with meniscus cement growing in between. The aforementioned strain localization is enhanced at temperature above 450°C and slip rate below 1μm/s, suggesting that viscous creep mechanisms (e.g. pressure solution) control the deformation process at slow sliding velocities, which is not the case in fast rate experiments. Our results show that the activation of viscous creep mechanisms leads to significant fault zone weakening, while contrasts in grain size keep deformation localized.

Figure 1 Shear stress plotted as a function of temperature. Shear stress data collected at (a) 15mm displacement in steady-state, and at (b) 5mm displacement.

How to cite: Zhan, W., Nevskaya, N., Niemeijer, A., Berger, A., Spiers, C., and Herwegh, M.: Weakening of granitoid gouge in hydrothermal ring shear experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6615, https://doi.org/10.5194/egusphere-egu23-6615, 2023.

The North Alpine Thrust Front (NATF) is an example of the classical onshore fold-and-thrust belt and foreland system [1]. There are ongoing heat production projects in this area. However, complex compaction and stress fields require detailed investigation for safe and economical drilling activities. Previous field investigation of the wedge and foredeep shed light on the possible driving mechanisms for overpressure generation in the wedge, foredeep and footwall in the SE of Germany. To do this, 20 deep wellbores are selected in this area and their geophysical and drilling data are investigated [2]. This study is a complementary work to find possible explanations for observations through numerical modeling. Examining the mechanics behind these complex deformations is beyond the capabilities of the critical taper theory. However, a large strain geomechanical numerical simulator coupled with critical state soil mechanics constitutive model can provide useful insights in this regard. Geomechanical forward modeling requires boundary conditions at far distances. Also, except some basic geometrical features, other deformations are not predefined and they are developing during the simulation. Therefore, it is not only insightful regarding the final shape of the system, but also progressive development of the deformations is trackable [3].  A plane-strain framework is implemented to simulate the interested processes through the Elfen software [4]. A quasistatic criterion is assumed throughout the simulation to decrease the possible boundary effects of the loading. Adaptive-remeshing helps to capture the large-strain behavior of the system in a reasonable computational time. Data from different sources of the drilling, geophysical tools and field observation is used to tune the model and test the capability of the model to estimate the required properties. Numerical simulations result in a similar geometry which is observed in the field works. Obtained stress values and pore pressure are comparable to the field data.  The differences between the simulation results and field observations can be attributed to the assumptions which were made during the simulation. For example, thermal impacts and possible diagenetic processes are neglected during the simulation. Also, a homogeneous material is assumed for the different layers, while in the real case, there are heterogeneities inside the layers.

1. Pfiffner, O, A. (1986) “Evolution of the North alpine Foreland Basinn in the central Alps”, Foreland Basins, 219-228.

2. Drews, M., Duschl, F. (2022) “Overpessure, vertical stress, compaction and horizontal loading along the North Alpine Thrust Front, SE Germany”, Marine and Petroleum Geology, 143, 105806.

3. Albertz, M., Sanz, P, F. (2012) “Critical state finite element models of contractional fault-related folding: Part 2. Mechanical analysis”, Tectonophysics, 150-170

4. Rockfield (2017) “Elfen explicit manual (Version 4.10)”, Swansea, UK, Rockfield Software.

How to cite: Mahmoodpour, S., Drews, M., and Duschl, F.: Geomechanical forward modeling of the stress field, pore pressure and compaction in the North Alpine Thrust Front, SE Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7038, https://doi.org/10.5194/egusphere-egu23-7038, 2023.

EGU23-7497 | Orals | TS1.3

Shear resistance and near-field stresses on rough faults 

Yuval Tal and Lior Wise

Natural faults are rough at all scales and can be described with fractal geometry. This deviation from planarity results in geometric asperities and a heterogeneous stress field. Analytical and numerical studies have shown that roughness introduces additional shear resistance on the fault and promotes failure in the medium surrounding the fault because of the elevated stresses. These studies generally assume a small slip on the fault, i.e., much smaller than the minimum roughness wavelength, λmin. It is important to examine the effects of roughness on shear resistance and near-fault stresses at large sliding, as well as the assumptions incorporated in the derivation of the analytical solutions.

In this study, we examine the effects of fault geometry on the shear resistance and near-fault stresses at large sliding numerically, using a method that is based on the mortar finite element formulation, in which non-matching meshes are allowed across the fault, and the contacts are continuously updated. This enables modeling slip larger than λmin and the overriding of asperity contacts. We begin with simulations of an elastic medium and show that, indeed, the roughness results in large and heterogeneous stresses on and off the faults, which increase with the roughness level. However, except for small slip values, the increase of shear resistance with slip is much smaller than the linear increase predicted by the analytical models, which assume small and uniform slip. For self-similar geometry, with Hurst exponent of H = 1, the average shear resistance increases with slip at a decreasing rate. For self-affine geometry, with H < 1, it initially increases with slip, then decreases at a slip larger than λmin /2. Although overriding of asperities is allowed in the simulations, as slip increases, significant stress concentrations are developed on the fault, which may not be realistic for natural rock surfaces. To account for that, we implement wear laws into the method and model the evolution of stresses during a quasistatic slip and cycles of dynamic earthquakes. The wear process redistributes and bounds the stresses on the fault and allows a more realistic characterization of stress distribution near the fault.

How to cite: Tal, Y. and Wise, L.: Shear resistance and near-field stresses on rough faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7497, https://doi.org/10.5194/egusphere-egu23-7497, 2023.

EGU23-8377 | ECS | Orals | TS1.3

Structural and frictional control on the transient deepening of the seismogenic zone following major earthquakes in Central Italy 

Giuseppe Volpe, Maria Eugenia Locchi, Giacomo Pozzi, Elisa Tinti, Marco Scuderi, Chris Marone, and Cristiano Collettini

After many large earthquakes aftershocks activity can reach depths greater than the base of the seismogenic zone that is defined by background seismic activity. This observation is generally explained by strain rate induced embrittlement associated with the increase of post-mainshock strain rate, which favors a transition from ductile to brittle behavior. However, the underlying physical processes are not well understood. Here we integrate geological and geophysical data for the 2016–2017 Central Italy seismic sequence with laboratory experiments to provide a geological and physical interpretation for the post-mainshock transient deepening of the base of the seismogenic zone.

The base of the seismogenic zone in the central-northern Apennines is set typically at 9-10 kilometers and corresponds to the top of the phyllitic basement. Structural studies on exhumed basement rocks highlight a heterogeneous basement fabric consisting of competent, 10 to 200 m wide, quartz-rich lenses surrounded by an interconnected and frictionally weak phyllosilicate-rich matrix. The matrix controls the overall rheology of the basement due to its interconnectivity, and promotes aseismic deformation because its rate-strengthening behavior.

Following each major (Mw > 5.5) event of the 2016–2017 sequence, a dramatic and abrupt increase in seismic rate is observed below 10 km, hence within the basement. Here we document the presence of seismicity clusters made of more than 4 earthquakes and characterized by small magnitude (Mw < 2.5), small dimensions (< 500 meters), small temporal duration (< 14 days) and a swarm-like behavior. Furthermore, these clusters are often represented by multiple or repeating earthquakes with a cross correlation coefficient higher than 0.7 for all the three components. These observations suggest that the increase of shear stressing rate within the basement is responsible for deepening of seismicity. To further explore this idea, we performed laboratory experiments on rocks from exhumed outcrops of basement rocks. We found that shear stressing rate promotes accelerated creep on the phyllosilicate-rich matrix and dynamic instabilities on the quartz-rich gouge belonging to the lenses.     

Our integrated analysis suggests that the mainshocks of the 2016-2017 seismic sequence promoted an increase of shear stressing rate within the basement allowing the phyllosilicate-rich matrix to creep faster hence favoring the loading and the repeated failures of locked seismogenic patches represented by the quartz-rich lenses.

How to cite: Volpe, G., Locchi, M. E., Pozzi, G., Tinti, E., Scuderi, M., Marone, C., and Collettini, C.: Structural and frictional control on the transient deepening of the seismogenic zone following major earthquakes in Central Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8377, https://doi.org/10.5194/egusphere-egu23-8377, 2023.

EGU23-8980 | ECS | Orals | TS1.3

Continental lithosphere deformation is a response to its thermodynamically controlled critical crustal thickness 

Ajay Kumar, Mauro Cacace, and Magdalena Scheck-Wenderoth

We study the present-day thermo-mechanical state of the Alpine Himalayan Collision Zone to understand the physics controlling the observed crustal differentiation and the underlying continental-wide geodynamics. We found that the stability of the lithosphere is regulated by a thermodynamically controlled critical crustal thickness (Cr), which is close to the average thickness of the continental crust. Regions with thickness higher than Cr, representing orogenic lithosphere, and higher than average potential energy undergo weakening and dissipate the acquired internal energy, compared to their foreland lithospheres that have crustal thickness close to Cr. A weaker orogenic lithosphere deforming in a dissipative mode to release the acquired potential energy manifests as zones of diffused rather than focused deformation. We additionally find that the energy dissipation path that the orogenic lithosphere takes to either attain Cr (cratonization) or to undergo runaway instability (rifting) is modulated by the feedback between the thermal and mechanical relaxation of the lithosphere. The internal energy stored in the crust from heat-producing elements, fastens the dissipation of the acquired potential energy.

How to cite: Kumar, A., Cacace, M., and Scheck-Wenderoth, M.: Continental lithosphere deformation is a response to its thermodynamically controlled critical crustal thickness, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8980, https://doi.org/10.5194/egusphere-egu23-8980, 2023.

EGU23-10150 | ECS | Orals | TS1.3

SpannEnD – Prediction of the recent crustal stress state of Germany using a 3D geomechnical-numerical model 

Steffen Ahlers, Karsten Reiter, Tobias Hergert, Andreas Henk, Luisa Röckel, Sophia Morawietz, Oliver Heidbach, Moritz Ziegler, and Birgit Müller

For the safe usage of the subsurface the stress state is of great importance, e.g., for borehole stability, mitigation of induced seismicity or the search and long-term safety of a high-level nuclear waste deposit. However, the state of knowledge concerning the stress state in Germany is limited as only unevenly distributed stress measurements are available which frequently provide only one component of the stress tensor. The SpannEnD (Spannungsmodell Endlagerung Deutschland) project aims to improve this knowledge with the help of a 3D geomechanical-numerical model. The model is calibrated on available stress magnitudes and enables a continuum-mechanics based prediction of the stress state and its local variability for Germany.

The 3D geomechanical-numerical model comprises the upper lithosphere and contains 22 lithological units parametrized with individual mechanical properties (Young’s modulus and Poisson’s ratio) and densities. Linear elasticity is assumed and the finite element method (FEM) is used to solve the equilibrium of forces. Overall, the model contains about 11 million hexahedral elements resulting in a lateral resolution of 2.5 x 2.5 km2 and a vertical resolution of up to 250 m. The model is calibrated by adaptation of displacement boundary conditions with magnitudes of the minimum (Shmin) and maximum horizontal stresses (SHmax). The model results show an overall good fit with these stress magnitudes used for calibration indicated by a mean of the absolute stress differences of 4.6 MPa for Shmin and 6.4 MPa for SHmax. Furthermore, the results agree well with additional data sets excluded from calibration but used for validation, e.g., with a mean of the absolute stress differences of 1.1 MPa for vertical stress magnitudes and an absolute mean deviation of the orientation of SHmax with regard to World Stress Map data of 11.9°.

How to cite: Ahlers, S., Reiter, K., Hergert, T., Henk, A., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., and Müller, B.: SpannEnD – Prediction of the recent crustal stress state of Germany using a 3D geomechnical-numerical model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10150, https://doi.org/10.5194/egusphere-egu23-10150, 2023.

An essential feature of plate tectonics is that lithospheric deformation is localized at plate boundaries with substantially larger magnitude than that in plate interiors, suggesting that lithospheric rheology is weaker at plate boundaries than in plate interiors. Numerous mantle convection modeling studies that approximate this empirically derived lithospheric rheology using different formulations or proxies (e.g., pre-existing weak zones, faults, reduced coefficient of friction or yield stress, …) have largely reproduced the observed features of lithospheric deformation. While the rheological formulations in theoretical modeling studies have become increasingly more sophisticated often with an expressed goal to understand the cause of plate tectonics and initiation of subduction, it is important to place constraints on lithospheric rheology using in-situ observations including flexural (i.e., vertical motion) and seismic response to different forcings. Laboratory studies indicate that lithospheric deformation is controlled by frictional sliding, low-temperature plasticity (LTP) and high-temperature creep with increasing temperature. Observations of lithospheric flexure and seismicity at Hawaiian Islands (i.e., plate interior setting) in response to volcanic construction suggest that internal frictional coefficient µf is 0.25, while LTP is significantly weaker than that derived from laboratory studies [e.g., Mei et al., 2010], based on modeling studies of loading response of Hawaiian lithosphere with realistic elasto-frictional-plastic-viscous rheology [Zhong and Watts, 2013]. Further studies [Bellas and Zhong, 2021; Bellas et al., 2020; 2022] showed that µf is 0.3 and activation energy of LTP needs to be reduced from laboratory derived value of 320 KJ/mol to 190 KJ/mol to fit the flexural and seismic deformation at Hawaii, and that the same rheological parameters reproduce the observed elastic thickness at other oceanic islands and seamounts on lithosphere of different ages. The Japan subduction zone shows characteristic features of subducting lithosphere with its outer rise and trench topography and transition from shallow normal/extensional faulting to deep reverse/compressional faulting seismic deformation (i.e., neutral plane) [e.g., Craig et al., 2014]. Dynamic deformation models of subduction have been formulated, using realistic slab buoyancy force and elasto-frictional-plastic-viscous rheology, to interpret the observations of trench-outer rise topography and neutral planes [Han et al., 2022]. The modeling indicated that the observed neutral plane in the Japan subduction zone is consistent with the rheology for subducting lithosphere with LTP activation energy of ~220 KJ/mol and µf~0.3, which are similar to that inferred for the plate interior at Hawaii. The modeling also found that µf<0.1 that is required to generate mobile-lid or plate tectonic convection in mantle convection models [e.g., Moresi and Solomatov, 1998] would not generate the extensional to compressional stress transition (i.e., neutral plane) in the Japan subducting lithosphere, further suggesting the importance of in-situ observational constraint on lithospheric rheology and dynamics of plate tectonics. 

How to cite: Zhong, S., Han, S., and Bellas, A.: Constraints of Flexural and Seismic Observations on Lithospheric Rheology at Plate Interior and Plate Boundary Settings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11786, https://doi.org/10.5194/egusphere-egu23-11786, 2023.

EGU23-12847 | ECS | Posters on site | TS1.3

Slip tendency analysis of 3D faults in Germany 

Luisa Röckel, Steffen Ahlers, Sophia Morawietz, Birgit Müller, Karsten Reiter, Oliver Heidbach, Tobias Hergert, Moritz Ziegler, Andreas Henk, and Frank Schilling

For many underground operations such as geothermal energy exploitation, mining, oil and gas production or the storage of high-level radioactive waste, active tectonic or induced seismicity is of concern. Seismicity usually occurs on pre-existing faults that are reactivated under adequate stress conditions. Thus, an assessment of the reactivation potential of faults can aid in the identification of areas particularly prone to the occurrence of seismic events or such areas where adequate geotechnical measures have to be taken to avoid anthropogenic fault reactivation. A tool for the assessment of the fault reactivation potential is the so called slip tendency, which is the ratio between the maximum resolved shear stress on the fault plane and the normal stress. Such an analysis requires information about the stress field acting on the fault plane and information about the fault geometry, fault orientation and frictional properties. Information about these parameters can be very limited, since 3D fault geometries are often only extrapolated from geological surface data. Furthermore, stress data is usually sparse, only available pointwise and unevenly spatially distributed. Geomechanical-numerical modelling can be used to derive a spatially comprehensive description of all six independent components of the stress tensor from the available stress data.   

For Germany, an estimate of the stress tensor is provided by the geomechanical-numerical model by Ahlers et al. (2022). Furthermore, fault geometries as part of geological models of the German federal states are available for large parts of Germany. We use both the stress data derived from the geomechanical-numerical model and the fault geometry data from the federal state models to calculate slip tendencies for more than 10.000 faults and fault segments. The resulting slip tendency is generally the highest in the northern Upper Rhine Graben area where it routinely reaches values of 0.7 and more. In the Alpine and Alpine Foreland region the slip tendency is generally the lowest with values only very rarely exceeding 0.3. In North Germany slip tendency values range mainly between 0.3 and 0.6 but with both higher and lower values being fairly common. In general, faults striking in NNE-SSW direction and NW-SE direction display the overall highest slip tendencies whereas faults striking in ENE-WSW direction show very low slip tendencies. With increasing depth slip tendencies generally decrease strongly. However, there are still major areas in Germany where either no fault geometries or only insufficient fault geometries are available. Furthermore, pore pressure has a major influence on the slip tendency. For our calculations, we assume hydrostatic pore pressure. While overpressured pore fluid is documented for example for the Molasse Basin in South Germany, no spatially comprehensive pore pressure data set is currently available for the whole of Germany.

How to cite: Röckel, L., Ahlers, S., Morawietz, S., Müller, B., Reiter, K., Heidbach, O., Hergert, T., Ziegler, M., Henk, A., and Schilling, F.: Slip tendency analysis of 3D faults in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12847, https://doi.org/10.5194/egusphere-egu23-12847, 2023.

EGU23-13718 | Posters on site | TS1.3

If you get the stress data, you've always asked for 

Karsten Reiter, Oliver Heidbach, Moritz Ziegler, Silvio Giger, Rodney Garrard, and Jean Desroches

The upper Earth crust is increasingly used by mankind, to extract, transport, store or dispose materials, energy, or waste. Regardless of the objective, long term safety and stability is essential and thus, the contemporary stress state of the upper crust is one of the key variables. To estimate a continuous description of the 3‑D stress tensor, geomechanical numerical models are used. The most important parameters to set up such models are the knowledge of the underground structures, the distribution of rock properties as well as the stress data, on which the models are calibrated. In the model, the vertical stress results from the gravitational volume forces due to the density distribution and the horizontal stresses from the Poisson effect as well as appropriate lateral displacement boundary conditions. The latter are determined by finding a best-fit with respect to given stress magnitude data of the maximum and minimum horizontal stress SHmax and Shmin, respectively.

A unique dataset of stress magnitude data has been recently acquired within the exploration phase for deep geological repository of radioactive waste in Switzerland. Nine cored boreholes in three potential siting areas have been drilled and besides a wide range of logging runs, and laboratory tests of rock properties, more than 120 Mini-Hydraulic Fracturing (MHF) and Sleeve Re-Opening (SR) tests were successfully performed in different stratigraphic units to estimate the magnitudes of Shmin and SHmax

Here, we present a 3‑D geomechanical-numerical model that shows both, the best-fit to the measured stress magnitudes as well as the range of stress magnitude variability in the volume of the different stratigraphic units. This variability results from MHF/SR measurements uncertainties and from the variation of rock properties within the lithologies. Furthermore, one has to assess how representative each MHF/SR measurement is for a larger rock volume. To represent the stress variability within the lithologies, many model simulations that cover the distribution of possible rock parameters were performed. The distribution is given by the cumulative density function (CDF) for the Youngs modulus and the Poisson number for each stratigraphic unit. Based on the range of model simulations we visualize the variation of the stress components along virtual well paths in analogy to the statistical variation. Such plots allow to quantify and visualize the potential variation of the present-day stress state within the stratigraphic column because of the petro-physical variability within the stratigraphic units. Furthermore, using the CDF, we can assign to each model simulation a probability that allows us also to estimate a probability distribution of the stress variability in the different units.

How to cite: Reiter, K., Heidbach, O., Ziegler, M., Giger, S., Garrard, R., and Desroches, J.: If you get the stress data, you've always asked for, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13718, https://doi.org/10.5194/egusphere-egu23-13718, 2023.

EGU23-13795 | Orals | TS1.3

Integrated stress determination at the KTB deep crustal laboratory 

Carolin Boese, Marco Bohnhoff, Oliver Heidbach, and Georg Dresen

One main goal of the Continental Deep Drilling Program (KTB) of the Federal Republic of Germany was to establish a continuous stress profile from the surface to the final drilling depth of 9.1 km. To characterize stresses with depth, several independent methods were applied: analyses of borehole failure such as borehole breakouts/drilling-induced tensile fractures; hydraulic fracturing mini-tests at several intervals ≤3 km depth as well as two modified hydraulic tests at 6 and 9 km depth; and core disking and strain retardation of core samples. Focal mechanisms of induced seismic events from fluid injection experiments were inverted for stress estimates at different depths. Since then, the KTB is known as a world-class site with regard to crustal stress data. In particular, stress magnitude estimates are still among the deepest and fewest high-quality estimates derived at crustal depth.

The GEOREAL fluid injection experiment aims to characterize the geothermal potential at the KTB site at 4 km depth and to refine the adaptive reservoir stimulation concept employing near-real-time microseismic monitoring with direct feedback on hydraulic parameters. Additionally, a goal of GEOREAL is to investigate spatial and temporal stress variations at this depth. We noticed new borehole breakouts in the open hole section of the pilot well KTB-VB, likely due to the massive fluid production and injection experiments between 2002 and 2005. Together with new logging and seismic data from GEOREAL, these stress estimates will be used to further characterize the stress field from the borehole to the reservoir scale.

The GEOREAL hydraulic stimulation will include a series of hydraulic tests at ≥3.9 km to investigate the effect of pressure build-up and release, the role of continuous and periodically varying flow rates, the effect of relaxation phases and maximum injection pressure on the spatio-temporal propagation of induced seismicity. Induced events will be monitored with high precision using a 12-level geophone chain in the KTB main hole at only ~300 m distance to the stimulation interval. This will be used to determine stress estimates from focal mechanism inversion of induced events on a 100-m source scale.

To better understand the role of the local stress field we use a 3-D geomechanical-numerical model (10 x 10 x 10 km3) of the KTB. This offers a unique opportunity to utilize the detailed knowledge of the subsurface at the KTB site, in particular due to the existing 3-D structural model, high-quality rock property estimates from laboratory work, high-quality stress magnitude data, and new information from GEOREAL. The model provides a continuous description of the 3-D stress field including its changes due to the variability of rock properties to assess the in-situ stability of the intact rock mass and faults. This allows for further detailed studies that require the undisturbed in-situ stress state as one key observable and input parameter to characterize deep geothermal reservoirs and associated processes such as induced seismicity.

How to cite: Boese, C., Bohnhoff, M., Heidbach, O., and Dresen, G.: Integrated stress determination at the KTB deep crustal laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13795, https://doi.org/10.5194/egusphere-egu23-13795, 2023.

EGU23-13955 | Posters on site | TS1.3

The 3D stress field of Nordland, northern Norway - insights from numerical modelling 

Sofie Gradmann, Marie Keiding, Odleiv Olesen, and Yuriy Maystrenko

The Nordland area in NW Norway is one of the tectonically most active areas in Fennoscandia. It exhibits patterns of extension, which are in contradiction to the first-order regional stress pattern that reflects compression from ridge-push. The regional stress field stems from the interaction of ridge push and GIA (glacial isostatic adjustment); the local stress field mainly results from gravitational stresses, as well as the flexural effects of sediment erosion and re-deposition.

We develop 3D finite element numerical models of crustal scale, using existing geometric constraints from previous geophysical studies. Internal body forces, induced by variations in density, topography or Moho depth, already yield significant deviatoric stresses, which are often omitted in stress models. We show that these can strongly influence the near-surface stress regime, in particular for the continental-margin setting we are considering. Similarly, existing weakness zones (such as faults) control the local stress field.

We apply the far-field stress fields (GIA, ridge-push, sediment redistribution) as effective force boundary conditions to the sides or base of the model. This way, we can account for all stress sources at once, but can also vary them separately in order to examine their relative contributions to the observed stress and strain rate fields.

We compare our models to the stress and strain observations derived from different recent seismological and geodetic data sets. These point to a correlation of seismicity with major changes in the crustal geometry.

How to cite: Gradmann, S., Keiding, M., Olesen, O., and Maystrenko, Y.: The 3D stress field of Nordland, northern Norway - insights from numerical modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13955, https://doi.org/10.5194/egusphere-egu23-13955, 2023.

EGU23-14316 | Posters virtual | TS1.3

Lithospheric rheology and strength in La Palma Island (Canary archipelago) 

Silvia Martín-Velázquez, David Gomez-Ortiz, Tomás Martín-Crespo, Cristina De Ignacio, José Arnoso, and Fuensanta G. Montesinos

The Canary Islands are an archipelago of eight islands and several islets in the Atlantic Ocean that have been built up by intraplate magmatism. The more recent subaerial eruption took place in La Palma Island during the last four months of 2021 (September 19th to December 13th). This volcanic activity formed the Tajogaite volcanic vent and several minor vents following an eruptive fissure roughly trending N310ºE. The eruption was preceded by intense shallow (<12 km depth) volcanotectonic activity that continued during the whole eruptive process, reaching more than 11,000 earthquakes located. After the first shallow pre-eruptive seismic swarm, the seismicity was mainly located at two different depth levels with hypocenters located at 10-15 and 30-40 km depth.

Seismicity record in the island for previous historical eruptions is very scarce and we have used this seismic episode to explore the lithospheric strength in this intraplate geodynamic setting corresponding to an old (~156 Ma) oceanic lithosphere. Geotherms and brittle and ductile rheological laws with different thermo-mechanical properties have been used to calculate strength envelopes. We have combined the study of the lithospheric strength and the vertical distribution of the seismicity from that period to estimate the extension of the brittle mechanical layer that conditioned the hypocentral locations.

How to cite: Martín-Velázquez, S., Gomez-Ortiz, D., Martín-Crespo, T., De Ignacio, C., Arnoso, J., and Montesinos, F. G.: Lithospheric rheology and strength in La Palma Island (Canary archipelago), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14316, https://doi.org/10.5194/egusphere-egu23-14316, 2023.

EGU23-14361 | ECS | Posters on site | TS1.3

Evidence of Synorogenic Extension in the Upper-Middle Crust in Central Taiwan  

Olivia Lozano Blanco, Björn Lund, Puy Ayarza, Joaquina Álvarez-Marrón, Dennis Brown, and Yih-Min Wu

The active Taiwan mountain belt is located in a complex geodynamic setting that involves two subduction processes. To the northeast, the Philippine Sea Plate subducts northward beneath the Eurasian Plate at the Ryukyu Trench, while in the southwestern part, the Eurasian Plate subducts eastward under the Philippine Sea Plate, where it obliquely collides with the Luzon Volcanic Arc. The Taiwan thrust-and-fold belt is created as a result of this ongoing arc-continent collision. Regardless of the predominance of compression in the overall structure of the island, several studies have also reported normal faulting. This study aims to estimate the local and regional stress field using earthquake focal mechanism data to contribute to a better understanding of crustal deformation in the complex tectonic setting of Taiwan.

Manually clustered earthquake focal mechanisms are inverted to obtain an estimate of the principal stress (σ1, σ2, σ3) orientations and the stress ratio (σ12)/(σ13), from which the direction of the maximum horizontal stress (SH) is calculated. The initial data set contains 11,587 earthquake focal mechanisms compiled from several sources dating between 1990 and 2020. All deep earthquakes in the Ryukyu subduction zone were removed from the data set. The Chi-Chi 1999 and other major earthquakes and aftershocks were also removed as they may reflect a distorted stress field. After preprocessing, a database consisting of 8,510 events with focal depths between 1-144 km and magnitudes ML=0.7-5.9 was used in the inversion. Depth division was performed in a regular 7 km grid up to 28 km depth, all events deeper than 28 km being considered in the same layer.

Preliminary results show that, to the southwest, the notable clockwise rotation of SH from SW-NE to a W-E direction and a change in the fault type from strike-slip to reverse to the east coincides with the interaction between the ENE-striking reactivated inherited structures of the Eurasian continental margin and the NNE-striking thrust faults of the foreland thrust-and-fold belt. To the centre-east, results show normal faulting in the upper crust, which changes to reverse faulting with depth, suggesting that there is a stress transition at approximately 14 km. Beneath that depth, there is a general state of compression. Ongoing research aims at integrating these results with those of numerical modelling and with field data in an effort to understand the locus of deformation and the occurrence of extensional tectonics in compressional settings, here and in other mountains belts worldwide.

This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency of the Ministry of Science and Innovation of Spain. Olivia Lozano acknowledges funding from the same agency through contract PRE2019-091431. Funding from SERA European Union H2020 INFRAIA-2016-2017 Agreement, 170522 is also acknowledged.

 

How to cite: Lozano Blanco, O., Lund, B., Ayarza, P., Álvarez-Marrón, J., Brown, D., and Wu, Y.-M.: Evidence of Synorogenic Extension in the Upper-Middle Crust in Central Taiwan , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14361, https://doi.org/10.5194/egusphere-egu23-14361, 2023.

EGU23-15990 | ECS | Orals | TS1.3

Flooding Induced Seismicity in the Ruhr Area – a geomechanics numerical modelling approach 

Thomas Niederhuber, Martina Rische, Thomas Röckel, Birgit Müller, and Frank Schilling

The Ruhr region is characterized by centuries of coal mining at depths reaching more than 1000 meters. After the closure of the last mines, their controlled flooding started. The Floodrisk project investigates ground uplift, stress changes due to pore pressure changes and the reactivation potential of faults to explain induced seismicity. We focused on monitoring the eastern Ruhr area and are investigating in detail the relationship between mine water rise, tectonic stress and induced seismicity in the Haus Aden drainage area.

In the region of the former "Bergwerk Ost", which had the highest seismicity in the Ruhr area during active mining, the RUB has installed a network of up to 30 short-period seismic stations. Continuous monitoring of seismicity and mine water levels is available for this region from the active mining phase through the post-mining phase to flooding. The temporal evolution of the mine water level after the pumps were shut down in mid-2019 shows a strong correlation with the temporal evolution of the observed microseismicity. Over 2200 induced events have been located since the beginning of flooding, showing spatial clustering. A comparison of the mine galleries, which today serve as the main underground waterways, with the localizations of the events shows that most of the events occur about 300 m below the main pillars located between the longwall panels.

This study provides a compilation of the regional stress state in the eastern Ruhr area based on the mine measurements, which were re-evaluated to derive the regional stress component and compared with stress orientations from independent sources (information on stresses in deep boreholes and earthquake focal mechanisms). The spatial distribution of stress orientations in the Ruhr region shows a rather homogeneous stress pattern with only very few locations where stress orientations differ significantly from the average.

Based on the geometry of the pillars, shafts and longwall panels, a generic numerical FE-model was developed using the compiled stress data for model calibration. The results indicate increased vertical stresses within and below the pillars as a result of stress arching. The horizontal stress changes are minor, thus differential stress increases in the vicinity of the event localizations.

How to cite: Niederhuber, T., Rische, M., Röckel, T., Müller, B., and Schilling, F.: Flooding Induced Seismicity in the Ruhr Area – a geomechanics numerical modelling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15990, https://doi.org/10.5194/egusphere-egu23-15990, 2023.

Bavali Shear Zone (BSZ), the western extension of the Moyar Shear Zone (MSZ), located between the Coorg Block in the north and Nilgiri Block in the south is a 100 km long, steep-dipping and WNW-striking dextral shear zone, which is a less studied part of the MSZ. The majority of the rocks in the BSZ are schistose, including hornblende-biotite±epidote schist, garnet-biotite-sillimanite±muscovite±chlorite schist and talc-tremolite-actinolite-chlorite schist. The gneissic varieties comprise of amphibolite gneiss, granulite gneiss, quartz-feldspar gneiss, hornblende-biotite gneiss, and garnet-biotite gneiss. Other rock types include high-grade metamorphic rocks such as pyroxene granulite and charnockite, banded magnetite quartzite, micaceous quartzite with/without sillimanite, metapyroxenite, amphibolite and mylonite. Several felsic intrusive like granite, diorite, syenite, quartz-feldspar leucosomes and mafic/ultramafic intrusive such as gabbro and anorthosite are found in some places.

The dominant structural trend of the BSZ is WNW with strikes varying between 110⁰N and 130⁰N. The steep-dipping and variably oriented pre-shear zone fabrics are preserved in low-strain domains. The BSZ is steep dipping and characterized by steeply-plunging stretching lineation with a persistent dextral sense of shear. The shear zone shows N-down kinematics in vertical sections perpendicular to the shear zone fabrics. The β-axis of poles to the shear zone fabric and the orientations of the hinges of the folds related to shearing share low-angle obliquities with the stretching lineations. It indicates that the shear-related folds have a reclined to steeply-inclined geometry, and the fold hinges are broadly collinear with the stretching direction. The last deformation in the BSZ with down-dip stretching lineation clearly shows the features of the transpressional shear zone with a dextral sense of movement and top-to-the-north kinematics.

U-Th-(total) Pb monazite chemical dating was performed on structurally constrained monazites from the BSZ. Monazites from one garnet-biotite-sillimanite-chlorite schist, one garnet-biotite gneiss and one mylonite close to the BSZ were dated. The monazite hosted in the garnet-biotite-sillimanite-chlorite schists provide prominent ages of 751±40 Ma, the garnet-biotite gneiss yielded a peak at 742±15 Ma and the single mylonite sample collected close to the BSZ yield a distinct age peak at 745±67 Ma. All the metamorphic monazites from the BSZ show a prominent mid-Neoproterozoic age, lacking in the adjoining Coorg Block, Nilgiri Block and Western Dharwar Craton. We, therefore, assign this mid-Neoproterozoic metamorphic chemical ages retrieved from monazites to the ductile deformation in the BSZ that reoriented all the pre-shearing fabrics and speculate that the BSZ collision orogeny preceded the eventual integration of the Greater India landmass with the Gondwanaland during the early-Palaeozoic.

How to cite: Nanda, S. and Rekha, S.: Structure and monazite geochronology along the Bavali Shear Zone, the western extension of the Moyar Shear Zone, southern India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-281, https://doi.org/10.5194/egusphere-egu23-281, 2023.

Partial melting often occurs alongside sites of rapid deformation in the Earth’s mantle and crust. Microstructural molten and crystalline components align in response to deformation, leading to anisotropies in mechanical, transport, and seismic properties detectable by remote sensing. Here, we investigate the co-evolution of melt, shape, and crystallographic preferred orientations (MPOs, SPOs & CPOs) at early stages of experimental shear deformation, constraining their contribution to observable signatures. We characterized the microstructures of partially molten (2-4 wt% melt) olivine-basalt aggregates deformed in general shear at a temperature of 1250°C under a confining pressure of 300 MPa, at shear stresses of τ = 0-175 MPa and shear strains of γ = 0-2.3. We then used the Gassman poroelastic differential effective medium method to calculate resultant seismic anisotropy.

The grain-scale network of melt pockets developed a strong preferred orientation parallel to the maximum principal stress at γ < 0.4. At higher strains, the orientation of the grain-scale melt pockets remained parallel to the maximum principal stress, but incipient, sample-scale melt bands formed at ~25° antithetic to the direction of shear.  While the orientation of individual melt pockets evolved quickly, grain SPOs and CPOs required larger strains (γ > 2) to strengthen and change. A weak SPO and CPO were induced during sample preparation, with grain long axes oriented perpendicular to the direction of maximum principal stress and a- and c-axes girdled perpendicular to the long axis of the sample. At the highest explored shear strain, a strong SPO was established and the girdled a-axes of the CPO rotated to align nearly parallel to the shear plane, developing clusters parallel to the shearing direction.  

These results yield two key conclusions about the orientation of melt networks in deforming partially molten rocks. First, the grain-scale and sample-scale alignments of melt pockets are distinct. At the grain scale, melt pockets align approximately parallel to the maximum principal stress, but the en echelon arrangement of melt pockets yields a sample-scale MPO at ~25o to the maximum principal stress (20o to the shear plane). Second, the relative timescales of melt and solid microstructural evolution are different, and are directly reflected in changes to seismic anisotropy. The grain-scale MPO reacts to a change in the orientation of the maximum principal stress after only a small amount of strain; in contrast, CPOs and SPOs require much higher strains before responding to a change in stress conditions. Seismic anisotropy is greatest when olivine a-axes and the grain-scale orientation of melt pockets are in relatively close alignment, so anisotropy will quickly decrease with any change in the orientation of the stress field that results in a rotation of the MPO away from the orientation of olivine a-axes. Perturbations to a local stress field can thus be observed almost immediately due to a rapidly reorienting melt network, making MPOs a more valuable predictor of instantaneous change than CPO-driven anisotropies.

How to cite: Seltzer, C., Peč, M., Zimmerman, M., and Kohlstedt, D.: Co-evolution of melt and crystal phases in experimentally sheared partially molten rocks and generation of seismic anisotropy during rapid deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-539, https://doi.org/10.5194/egusphere-egu23-539, 2023.

EGU23-878 | Posters on site | TS1.5

Seismic induced anisotropy and kinking in quartz 

Michel Bestmann, Giorgio Pennacchioni, Bernhard Grasemann, Rüdiger Kilian, Luiz F.G. Morales, John Wheeler, and Andreas Bezold

Recognition of seismically induced microstructures is important to unravel the different deformation processes during seismic cycles, especially at the base of the upper crust where many earthquakes nucleate. Deformed quartz veins related to a strike-slip shear zone within the Schobergruppe (Austroalpine Crystalline Complex, Eastern Alps) contain intense kinking in elongated quartz grains. The kink band boundaries are inclined into the general dextral sense of shear. Cathodoluminescence (CL) images reveal that the entire thin section contains a very high density of intragranular, sub-planar microstructures developed as thin dark CL lamellae accompanied with nanometre-scale fluid inclusions. Based on the oscillating orientation variation across low angle boundaries (misorientation angle 1-9°) these lamellar microstructures are referred as short-wavelength undulatory extinction microstructures - SWUE (Trepmann and Stöckhert, 2013, Solid Earth, 4). Only grains with SWUE, orientated parallel to the foliation, are kinked. In general, kinked microstructures mainly develop in strongly anisotropic material or within lamellar minerals, i.e. micas. Deformation at high stresses (e.g. at greenschist conditions or during coseismic loading) can produce a strong anisotropic microstructure in quartz by the development of deformation lamellae. Trepmann and Stöckhert (2013) showed in deformation experiments of quartz that SWUE preserve evidence of an earlier coseismic stress peak, even when overprinted during subsequent crystal plastic creep deformation at lower stress. The SWUE in the deformed Schober quartz veins are interpreted in a similar way. These microstructures were primary deformation lamellae developed during coseismic loading. Pseudotachylyte veins within the analysed shear zone next to the sample give evident for a seismic event. Subsequent overprint by ongoing creep at lower stresses is recorded by the vein quartz mylonites. The densely spaced sub-planar microstructures cause a high anisotropy of the quartz grains, which finally were kinked. Electron Backscatter diffraction data give evidence of different slip system active in the formation of the deformation lamellae/SWUE and the subsequent kinking. The opposite direction of the Burges vectors (based on Weighted Burges Vector analysis, Wheeler et al., 2009, Journal of Microscopy, 233) in the kink band domain is consistent with sinistral shearing along the anisotropic deformation lamellae/SWUE in the dextral sheared kink band. Kinked micas (muscovite and biotite) in the mica-rich host rock, next to the kinked quartz vein sample, point to seismic induced kinking. However, the question arise if the kinking of micas and quartz was caused instantaneously during the same seismic event or if the quartz kinking is related to post-seismic creep at transient high stresses during ongoing deformation at lower greenschist facies conditions under dextral sense of shear (Bestmann et al., JGPR – Solid Earth, 126).

How to cite: Bestmann, M., Pennacchioni, G., Grasemann, B., Kilian, R., Morales, L. F. G., Wheeler, J., and Bezold, A.: Seismic induced anisotropy and kinking in quartz, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-878, https://doi.org/10.5194/egusphere-egu23-878, 2023.

EGU23-1582 | ECS | Posters on site | TS1.5

Insights into microstructural and petrophysical properties of deformation bands in porous sandstone, Kachchh (Kutch) Rift Basin, India 

Mohamedharoon Shaikh, Soumyajit Mukherjee, Sudipta Dasgupta, David Rajkhowa, Deepak Maurya, and Laxman Chamyal

The study addresses how the deformation mechanisms influence the microstructural properties of deformation bands developed in high-porosity sandstones of the Kachchh (Kutch) Rift Basin (KRB), India. The KRB located at the western continental margin of the Indian plate is neotectonically active and is affected by the periodic reactivation of multiple ~W-striking dip-slip/strike-slip faults. We investigated the porous sandstones of Bhuj and Jhuran Formation, which contain cataclastic shear bands, disaggregation bands, and cementation bands. High-resolution optical and scanning electron microscopy images were used to analyze the microstructures, grain size and shape, and porosity for both the host rock and deformation bands. The cataclastic bands display preferential alignment of elongated grains parallel to the boundaries of deformation bands. The mechanisms of deformation are dominated by varying degrees of cataclasis and pressure solution that have caused grain reorganization, rolling, flaking of grain edges, and intragranular and transgranular fracturing. This resulted in grain size and porosity reduction within the deformation bands. The porosity loss in deformation bands is of three to five orders of magnitude compared to the host rock. The grain size distribution results are consistent with a power-law model that have low exponent (D) values between 0.89 and 1.00 for deformation bands. Our findings suggest that cataclasis within deformation bands appears to be dominant in the extensional stress state, however shear-related disaggregation of grains is observed in both extensional and compressional stress regimes.

 

How to cite: Shaikh, M., Mukherjee, S., Dasgupta, S., Rajkhowa, D., Maurya, D., and Chamyal, L.: Insights into microstructural and petrophysical properties of deformation bands in porous sandstone, Kachchh (Kutch) Rift Basin, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1582, https://doi.org/10.5194/egusphere-egu23-1582, 2023.

EGU23-2302 | Orals | TS1.5

The record of ductile strain by Raman spectroscopy of carbonaceous material – deformation experiments and applications to the brittle-ductile régime 

Hugues Raimbourg, Moris-Muttoni Benjamin, Augier Romain, Lahfid Abdeltif, and Champallier Rémi

Raman spectroscopy on carbonaceous material (RSCM) is a method widely used to infer the temperature of metamorphism in metasediments. Furthermore, anomalies in the Raman signature of carbonaceous particles contained in fault zones have been interpreted as reflecting short-lived heating events due to friction during earthquakes. These applications of RSCM rely all on the assumption that temperature is the main factor controlling the reorganization of carbonaceous material (CM) and its expression by Raman spectroscopy. Nonetheless, few examples of natural fault zones and shear zones recently raised questions about the possible role of strain in such reorganization.

In this work, we studied the influence of deformation on the Raman spectra of CM. We carried out experiments of deformation on low-grade shales in the Paterson and Griggs-type rigs, corresponding to low and high pressure conditions, for variable conditions of temperature and strain rates, simulating deformation at the brittle-ductile transition. In parallel, we examined in these experiments the evolution of CM using the intensity ratio (IR), defined as the intensity ratio of the Defect band over the Graphite band of the Raman spectrum.

Deformation proceeded as a combination of slip on discrete planes, corresponding to macroscopic stick-slip events, and of ductile shear in few hundreds of µm’s-thick zones. The effect of stick-slip events on RSCM signal is unclear, principally because the deformed layers are too thin to contain CM to be analyzed. In contrast, in zones of distributed strain we observed a systematic and significant increase in IR compared to undeformed domains, reflecting an enhancement in the structural organization of CM. On the basis of additional experiments of static heating we carried out in parallel, we show that the IR increase cannot be connected to local and transient increase in temperature during the experiment, and has therefore to be connected to strain itself.

The zones of concentrated ductile strain are characterized by comminution of the clasts of quartz and feldspar initially present, accompanied by the development of a porosity at the submicron-scale. Chemical analysis revealed that along with intense grain-size reduction, the chemical composition of the feldspar was modified. On the basis of these microstructural and chemical evidence, it appears that the elementary processes behind ductile deformation include intense mechanical fracturing and mass transfer along the grain boundaries.

As a conclusion, it appears that strain has an undisputable effect to increase IR of . When applied to nature, the relevant temperature and mechanical realm of these experiments is the brittle-ductile transition, for temperature of the order or below 300°C. These conditions are also the ones corresponding to seismic deformation. Therefore we show here that Raman spectra in fault zones reflect not only the temperature history (including coseismic flash-heating), but also, and to a large extent, the strain history of the rock.

How to cite: Raimbourg, H., Benjamin, M.-M., Romain, A., Abdeltif, L., and Rémi, C.: The record of ductile strain by Raman spectroscopy of carbonaceous material – deformation experiments and applications to the brittle-ductile régime, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2302, https://doi.org/10.5194/egusphere-egu23-2302, 2023.

To understand the deformation microstructures and seismic properties at the top of a subducting slab in warm subduction zones, deformation experiments of epidote blueschist were conducted in simple shear by using a modified Griggs apparatus. Deformation experiments were performed under high pressure (0.9–1.5 GPa), temperature (400–500 °C), shear strain (γ) in the range of 0.4–4.5, and shear strain rate of 1.5×10-5–1.8×10-4 s-1. After experiments, crystallographic preferred orientations (CPOs) of minerals were determined by electron backscattered diffraction (EBSD) technique, and microstructures of deformed minerals were observed by transmission electron microscopy (TEM). Seismic velocity and anisotropy of constituent minerals and whole rocks were calculated using the CPOs and elastic constants of each mineral. The CPO of glaucophane showed the [001] axes aligned subparallel to shear direction and the (010) poles aligned subnormal to the shear plane at low shear strain (γ ≤1), while the [100] axes aligned subnormal to the shear plane at high shear strain (γ >2). The CPO of epidote showed non-systematic fabric at a shear strain of γ <2, but it showed the (010) poles aligned subparallel to shear direction and the [100] axes aligned subnormal to the shear plane at a shear strain between 2< γ <4. At a high shear strain of γ =4.5, the alignment of the (010) epidote poles had altered from subparallel to subnormal to the shear plane, while the [001] axes were aligned subparallel to shear direction. TEM observations and EBSD mapping revealed that the CPO of glaucophane was developed by dislocation creep, somewhat affected by the cataclastic flow at high shear strain. On the other hand, the CPO development of epidote was considered to have been affected by dislocation creep under a shear strain of 2< γ <4, but the CPO was highly affected by cataclastic flow with rigid body rotation under a high shear strain (γ >4). The average seismic velocity of P-wave (Vpaver) and S-wave (Vsaver) of whole rocks (epidote blueschists) were in the range of 7.19–7.63 km/s and 4.22–4.47 km/s, respectively, and the AVp (seismic anisotropy of P-wave) and Max.AVs (maximum seismic anisotropy of S-wave) were in the range of 4.5–11.0% and 3.91–6.40%, respectively. The Vpaver and Vsaver of experimentally deformed epidote blueschist were reduced about 8–13% and 6–11%, respectively, compared to the seismic velocities of lithospheric mantle surrounding the slab. The delay time of S-wave calculated from subducting oceanic crust composed of epidote blueschist was generally increased with increasing the subducting angle of the slab and volume proportion of glaucophane. Our experimental results indicate that the magnitude of shear strain and rheological contrast between component minerals plays an important role on the formation of CPOs of glaucophane and epidote. In addition, our calculational results of seismic properties suggest that volume proportion of constituent minerals, CPO types of glaucophane and epidote, and the subducting angle of the slab are important factors to control seismic velocity and anisotropy observed in warm subduction zones.

How to cite: Park, Y. and Jung, H.: Deformation microstructures and seismic properties of experimentally deformed epidote blueschist and implications for seismic velocity and anisotropy in warm subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3196, https://doi.org/10.5194/egusphere-egu23-3196, 2023.

EGU23-3794 | Posters on site | TS1.5

Slip localization by cataclasis and fluid-rock interaction in seismogenic crustal faults (Gole Larghe Fault, Italy) 

Silvia Mittempergher, Giulio Di Toro, Stefano Aretusini, Jean-Pierre Gratier, Andrea Bistacchi, and Tommaso Giovanardi

At nucleation depths of earthquakes in the continental crust (7-15 km), cataclastic processes and fluids interact in a complex way, affecting the mechanical properties, deformation mechanisms and fabric of fault rocks. In this study, we analyzed the effects of cumulative displacement, fault orientation and slip localization on the fabric of low-displacement cataclasite-pseudotachylyte-bearing faults in granodiorite and discuss the feedbacks between deformation mechanisms potentially controlling the transition to unstable slip.

The samples were stem from a well-exposed outcrop of the Gole Larghe Fault Zone (Southern Alps, Italy), which was active 30 Ma ago as a dextral transpressive fault at depths of earthquake nucleation (9-11 km, 250-280°C). Faults and shear fractures were digitized from an orthorectified photomosaic over an area of about 65 m2 to quantify their spatial arrangement. Samples were stem from faults and shear fractures which accommodated increasing cumulative displacements from 0 to 4.8 m, with strikes ranging from N074 to N125. Samples were characterized by means of microstructural (field emission scanning electron microscope, optical cathodoluminescence), mineralogical (X-Ray powder diffraction), geochemical (Energy Dispersive X-Ray Spectroscopy, EMPA) and image analysis (clast size distribution and shape parameters) investigations.

Although fractures are uniformly distributed in the analyzed outcrop, 69% of the total displacement is accommodated along two main pseudotachylyte-bearing fault strands. Cataclasites consist of fragments of the wall rock (quartz, plagioclase and K-feldspar), in a matrix of K-feldspar, chlorite and epidote. With increasing displacement, the average grain size of quartz and plagioclase clasts decreases, the fractal dimension of the clast size distribution increases (from 1.6 to 2.8 in two dimensions) and the faults develop multiple domains of foliated cataclasites and non-foliated, highly comminuted ultracataclasites. If ultracataclasites or pseudotachylytes are present in the fault rocks, an increase of the displacement/thickness ratio suggests strain localization. The boundaries of quartz and plagioclase clasts in cataclasites are generally jagged, and clasts with equivalent diameters of less than 5 μm are rare, suggesting partial corrosion of the clast’s boundaries and dissolution of the smallest fragments. Elongated clasts are often oriented at an acute angle with fault boundaries, forming foliated cataclasite domains. Their iso-orientation is more intense in faults having a higher resolved normal stress (assuming a constant far-field stress tensor), i.e., the P-shears. Foliation is associated with an incipient mineral segregation of the matrix minerals, with epidote and titanite aligned along the foliation surfaces and K-feldspar and chlorite in low-strain sites.

In agreement with experimental results, once slip localizes along highly comminuted horizons, slip appears to be further localized along it, suggesting slip weakening behavior associated with cataclastic flow. Diffusive mass transfer processes enhanced by comminution and fluid ingression allow a residual part of the displacement to be accommodated by frictional-viscous mechanisms (creep), especially at high driving stresses. 

How to cite: Mittempergher, S., Di Toro, G., Aretusini, S., Gratier, J.-P., Bistacchi, A., and Giovanardi, T.: Slip localization by cataclasis and fluid-rock interaction in seismogenic crustal faults (Gole Larghe Fault, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3794, https://doi.org/10.5194/egusphere-egu23-3794, 2023.

EGU23-5111 | ECS | Orals | TS1.5

Fluid-assisted deformation processes at the roots of oceanic transform faults. 

Manon Bickert, Mary-Alix Kaczmarek, Marcia Maia, and Daniele Brunelli

Oceanic Transform Faults (OTFs) are major plate boundaries that regularly offset the axis of Mid-Oceanic Ridges and are able to generate Mw 7 earthquakes. Yet, very little is known on the evolution of fault slip mechanics at depth, mainly due to rare exposures of deep sections at the seafloor. The Atobá Ridge is one of the rare structures where the roots of an active transform fault are exposed and accessible. This transpressive ridge is part of the northern transform fault of the St. Paul transform system in the Equatorial Atlantic (Maia et al., 2016). There, ultramafic mylonites are tectonically exhumed along the inner thrust faults of a positive flower structure.

Here we study the deformation mechanisms in ultramafic mylonites and ultramylonites sampled at the Atobá ridge. We show that all samples experienced ductile deformation at 750-900°C in the spinel stability field, resulting in a pervasive grain size reduction. We propose fluid-assisted dissolution-precipitation creep as the main deformation mechanism, leading to dissolution of orthopyroxene and formation of lens-shaped olivine and interstitial minor phases’ neoblasts (pyroxenes, spinel, and amphibole). Orthopyroxene neoblasts formed by this mechanism mimic the Crystallographic Preferred Orientation of the olivine neoblasts. Fluid-assisted dissolution-precipitation creep allows deformation of stiff minerals at significant lower stresses and temperatures than dislocation creep, possibly leading to an intense strain localization. This mechanism, previously reported in ophiolites and orogenic contexts (Hidas et al., 2016; Prigent et al., 2018), is described for the first time in the oceanic transform environment. Similar microstructures have been observed in mylonites from other OTFs, suggesting that this mechanism could be more widespread and could even represent one of the main deformation law in the lower oceanic lithosphere, with important implications on the mechanics and structures of (oceanic) transform faults and long-lived detachments.

This work is supported by PRIN2017KY5ZX8.

REFERENCES

Maia, M., Sichel, S., Briais, A., Brunelli, D., Ligi, M., Ferreira, N., Campos, T., Mougel, B., Brehme, I., Hémond, C. and Motoki, A., 2016. Extreme mantle uplift and exhumation along a transpressive transform fault. Nature Geoscience, 9(8), pp.619-623.

Hidas, K., Tommasi, A., Garrido, C. J., Padrón-Navarta, J. A., Mainprice, D., Vauchez, A., Barou, F., & Marchesi, C. (2016). Fluid-assisted strain localization in the shallow subcontinental lithospheric mantle. Lithos, 262(October), 636–650. https://doi.org/10.1016/j.lithos.2016.07.038

Prigent, C., Guillot, S., Agard, P., & Ildefonse, B. (2018). Fluid-assisted deformation and strain localization in the cooling mantle wedge of a young subduction zone (Semail ophiolite). Journal of Geophysical Research: Solid Earth, 123. https://doi.org/10.1029/ 2018JB015492

How to cite: Bickert, M., Kaczmarek, M.-A., Maia, M., and Brunelli, D.: Fluid-assisted deformation processes at the roots of oceanic transform faults., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5111, https://doi.org/10.5194/egusphere-egu23-5111, 2023.

EGU23-5451 | ECS | Orals | TS1.5

Dynamic evolution of porosity in lower crustal faults during the earthquake cycle 

Stephen Paul Michalchuk, Sascha Zertani, François Renard, Oliver Plümper, Alireza Chogani, and Luca Menegon

In the dry lower crust, earthquake-induced fracturing can increase permeability for fluids to infiltrate and flow, thus facilitating fluid-rock interactions, and potentially altering the strength and rheology of fault systems. Understanding the mechanisms that create and reduce porosity requires a detailed microstructural analysis. Here, we analyze microstructures that have recorded primary and secondary porosity generated by the dynamic rupture propagation of a lower crustal earthquake, and that were subsequently reworked during post- and interseismic viscous creep.

An exhumed lower crustal section comprised largely of anhydrous anorthosites cross-cut by a coeval network of pseudotachylytes (solidified melts produced during seismic slip) and mylonitized pseudotachylytes (overprinted during the post- and interseismic viscous creep), is found at Nusfjord, Lofoten, Norway. We study the microstructures using synchrotron X-ray microtomography (SμCT), focused ion beam scanning electron microscopy (FIB-SEM) nanotomography, electron backscatter diffraction (EBSD) analysis, and SEM imaging.

SμCT data reveals that porosity is dispersed and poorly interconnected within a pseudotachylyte vein (0.16 vol% porosity overall), and noticeably increased along the grain boundaries of garnet grains (1.07 – 1.87 vol%). The increased porosity around garnet is formed due to a net negative volume change (-DV) during garnet growth, as there is a localized increase in density of ~1.00 g/cm3 when a recrystallizing garnet overgrows a pseudotachylyte matrix (plagioclase + amphibole). Efficient healing of the earthquake damage zone (0.03 vol% porosity) resulted in the preservation of only a few but relatively large interconnected primary pores along fractures in the anorthosite. Fractures were healed by the growth of plagioclase neoblasts nucleated from extremely comminuted fragments of the host anorthosite, and by the precipitation of barium-enriched K-feldspar filling intragranular pores. Fluid-rock interaction was so efficient at sealing the porosity that a FIB-SEM transect along one of these microfractures revealed a myrmekite intergrowth replacing K-feldspar.

Porosity is dramatically decreased in the mylonitized pseudotachylyte (0.03 vol% overall), and focused mainly within monomineralic domains of plagioclase (0.07 – 0.11 vol%). These are interpreted as recrystallized and sheared survivor clasts of wall-rock fragments, while the polymineralic domains are primarily derived from the overprint of the original pseudotachylyte veins. The plagioclase grains in both domains are more-or-less equant, very fine grained (< 25 μm), lack a crystallographic preferred orientation, grain boundaries occasionally aligned to form quadruple junctions, and are well-mixed amongst the hydrous phases (polymineralic domain), suggesting that both domains deformed primarily by grain-size sensitive diffusion creep and viscous grain boundary sliding. The polymineralic domain has the least porosity (~0.01 vol%), which reflects the efficient precipitation of phases (amphibole, biotite, and feldspars) into transient pores during creep cavitation.

A porosity reduction on the order of 90% from a pristine to a mylonitized pseudotachylyte may eventually result in shear zone hardening, and development of new pseudotachylytes overprinting the mylonites. Therefore, earthquake-induced rheological weakening of the lower crust is intermittent, occurs when a fluid can infiltrate a transiently permeable shear zone, and may stop when the porosity becomes clogged.

 

How to cite: Michalchuk, S. P., Zertani, S., Renard, F., Plümper, O., Chogani, A., and Menegon, L.: Dynamic evolution of porosity in lower crustal faults during the earthquake cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5451, https://doi.org/10.5194/egusphere-egu23-5451, 2023.

EGU23-6483 | ECS | Orals | TS1.5

A non-hydrostatic stress state forms fabrics during metamorphic reactions 

James Gilgannon, Damien Freitas, Roberto Rizzo, John Wheeler, Ian Butler, Sohan Seth, Federica Marone, Christian Schlepütz, Gina McGill, Ian Watt, Oliver Plümper, Lisa Eberhard, Hamed Amiri, Alireza Chogani, and Florian Fusseis

Many metamorphic rocks have a fabric. What is often not clear is how much deformational or metamorphic processes contributed to the formation of these fabrics. Are foliations always the result of strain? When does intrinsic crystallographic anisotropy alone lead to the formation of structural elements? Understanding the relative contributions of deformation and metamorphism in rock fabrics is fundamentally important because it is foundational to understanding the role of stress in reacting and deforming rocks.

To this end, we make a major advance in our understanding of fabric development in reacting rocks by showing in time-resolved (4D) synchrotron microtomography (µCT) experiments that when a gypsum dehydration reaction occurs in a differentially stressed sample the reaction products develop orthogonally to the largest principal stress. This is an important finding because we can show with our µCT data that this preferred orientation forms early in the reaction and at very small strains (<1%). Using a simple kinematic model we can demonstrate that it cannot have formed because of reorientation during mechanical compaction. It remains to be established if it is nucleation or growth of bassanite that is being affected by the stress or both. Our experiments suggest that metamorphic transformations may be inherently anisotropic when reacting under the influence of a non-hydrostatic stress state. 

The consequences of this are many. For example, there will be cases in natural rocks where the interpretation of a lineation, foliation or crystallographic preferred orientation as formed by strain may be incorrect. Moreover, the physical properties (e.g. hydraulic and mechanics) of metamorphic rocks could also be significantly anisotropic from early in a transformation. Mass transport pathways might initialise as channelled or partitioned conduits which would have an impact during subduction and in thin-skinned tectonics. Our data reveal a critical new finding related to the very common geological occurrence of reacting rocks experiencing a differential stress.

How to cite: Gilgannon, J., Freitas, D., Rizzo, R., Wheeler, J., Butler, I., Seth, S., Marone, F., Schlepütz, C., McGill, G., Watt, I., Plümper, O., Eberhard, L., Amiri, H., Chogani, A., and Fusseis, F.: A non-hydrostatic stress state forms fabrics during metamorphic reactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6483, https://doi.org/10.5194/egusphere-egu23-6483, 2023.

EGU23-6569 | ECS | Orals | TS1.5

Deep crustal dynamics driven by local and transient transformation weakening 

Mathieu Soret, Holger Stünitz, Jacques Précigout, Florian Osselin, Amicia Lee, and Hugues Raimbourg

Mechanisms driving the long-term dynamics of plate interfaces remain poorly-constrained. To date, the rheology of the crust is considered to be controlled by solid-state diffusion processes such as crystal plastic deformation (dislocation creep). Yet, most minerals formed at high-pressure conditions are mechanically very strong (garnet, omphacite, glaucophane, zoisite, kyanite) and can only be deformed plastically at unrealistically high stresses or temperatures. A growing number of studies point to the crucial role of fluid-rock interactions and mineral transformations in the development of crustal shear zones of low viscosity. The rock weakening is interpreted as being induced by dissolution and precipitation processes at grains boundaries in chemical disequilibrium. Here, we tackle the eclogite rheology conundrum by performing the first deformation experiments at high-pressure conditions (> 2 GPa) on a two-phase aggregate representative of the lower crust.

Shear experiments were performed in a new generation of Griggs-type apparatus (Univ. Orléans) at 850°C, 2.1 GPa and a shear strain rate of 10⁻6 s⁻¹. The starting material consists of mixed powders of plagioclase and clinopyroxene separated from an undeformed gabbro (Kågen, Norway) and hot-pressed with a grain size lower than 100 µm. Experiments have been conducted with 0.2% added water.

Mechanical data indicate that the samples are first very strong with a peak differential stress between 1.0 and 1.4 GPa. Then, a significant weakening is observed with a stress decrease of 0.5 GPa. The high-strain samples are characterized by a strain gradient and a reaction gradient, both increasing toward the center of the shear zone. The nucleation of new phases leads to a drastic grain size reduction and phase mixing. The intensities of both are positively correlated with the strain intensity. The nature, distribution and fabric of the reaction products vary also progressively with strain intensity. At the peak stress, the reaction products are restricted to grain boundaries where they form corona structures, while in the high-strain samples, they occur throughout the sample replacing most of the starting material. The primary plagioclase and clinopyroxene grains show incipient dynamic recrystallization, whereas reaction products never do. The nano-porosity reported in the samples attests to the presence of free-fluid phase along the reactive grain boundaries, despite the high-pressure conditions. This nano-porosity requires grain boundary sliding (GBS) processes to form, as indicated by the spatially associated quadrupole junctions.

Our results show that strain at eclogite-facies conditions is preferentially localized by GBS-accommodated dissolution and precipitation creep in reactive zones. We suggest that this dominant deformation process take place in rock at chemical disequilibrium in the presence of a free-fluid phase. Therefore, deformation along deep plate interfaces should be initiated and governed by transient and local transformation weakening, allowing long-term deformation at far lower stresses than dislocation creep.

How to cite: Soret, M., Stünitz, H., Précigout, J., Osselin, F., Lee, A., and Raimbourg, H.: Deep crustal dynamics driven by local and transient transformation weakening, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6569, https://doi.org/10.5194/egusphere-egu23-6569, 2023.

EGU23-7017 | Posters on site | TS1.5

Hydrocarbon-bearing fluid migration produces brecciation at high pressure condition in subduction 

Francesco Giuntoli, Luca Menegon, Guillaume Siron, Flavio Cognigni, Hugues Leroux, Roberto Compagnoni, Marco Rossi, and Alberto Vitale Brovarone

It has been recently proposed that high-pressure genesis of abiotic hydrocarbon can lead to strain localization in subducted carbonate rocks1. However, the mechanical effects of the migration of these hydrocarbon-bearing fluids on the infiltrated rocks still need to be constrained.

In this study, we investigate omphacitite (i.e. omphacite-rich rock) adjacent to a high-pressure methane-rich fluid source from the Western Italian Alps (Italy) using a multiscale and analytical approach including petrographic, microstructural, X-ray compositional mapping and electron backscatter diffraction analyses (EBSD). In the field, omphacitite bands are 1-5 metres thick and tens of metres long and are adjacent to carbonate rocks affected by high-pressure reduction and methane-rich fluid production.

Hand specimens and thin sections display a brecciated structure, with omphacitite fragments ranging in size from a few microns to several centimetres, surrounded by a matrix of jadeite, omphacite, grossular, titanite, and graphite. X-ray compositional maps and cathodoluminescence images highlight oscillatory zoning and skeletal textures in jadeite, omphacite and garnet in the matrix, suggesting a fast matrix precipitation under plausible disequilibrium conditions. CH4 and H2 are found in fluid inclusions in the jadeite grains. This feature suggests a potential link between the genesis of CH4 in the adjacent carbonate rocks and the brecciation event.

EBSD analysis was performed on omphacitite clasts close to their borders, where omphacite grain size varies between a few microns and a maximum of 100 microns. Those omphacite grains display no crystallographic preferred orientation, abundant low angle boundaries and low (< 5°) internal lattice distortion. We interpret these textures as formed by pervasive and diffuse micro-fracturing related to the brecciation occurring at high pore fluid pressure, reaching sub-lithostatic values. This study suggests that at high-pressure conditions in subduction zones, the genesis and migration of hydrocarbon-bearing fluids can trigger fracturing in adjacent lithotypes.

 

1 Giuntoli, F., Vitale Brovarone, A., Menegon, L., 2020. Feedback between high-pressure genesis of abiotic methane and strain localization in subducted carbonate rocks. Sci. Rep. 10, 9848. https://doi.org/10.1038/s41598-020-66640-3

 

This work is part of project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 864045).

 

How to cite: Giuntoli, F., Menegon, L., Siron, G., Cognigni, F., Leroux, H., Compagnoni, R., Rossi, M., and Vitale Brovarone, A.: Hydrocarbon-bearing fluid migration produces brecciation at high pressure condition in subduction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7017, https://doi.org/10.5194/egusphere-egu23-7017, 2023.

EGU23-7120 | ECS | Orals | TS1.5

Deep learning and chemical constraints allow accurate segmentation of µCT data from metamorphic rocks 

Roberto Emanuele Rizzo, Damien Freitas, James Gilgannon, Sohan Seth, Ian B. Butler, John Wheeler, Federica Marone, Christian Schlepuetz, Gina McGill, Olivier Plümper, and Florian Fusseis

X-ray tomographic imaging has become a very valuable tool for the analysis of (rock) materials, both for visualising complex 3D microstructures and for imaging internal features such as damage, mineral reaction, and fluid/rock interactions quantitatively. The validity of the results derived from X-ray tomography, however, hinge on the  accuracy of the image segmentation. There are many methods for image segmentation (from simple manual thresholding to machine learning and deep learning approaches), which can produce a high range of variability in the segmentation results. Accuracy of segmentation results is seldom checked and thus calling the reproducibility of the results into question. In this contribution we show how metamorphic reactions themselves can be used to constrain accuracy and highlight the benefits of deep learning methods to extend this over many large datasets efficiently.

Here, we demonstrate a methodology that uses deep learning to achieve reliable segmentation of time-series volumetric images of gypsum dehydration reaction, on which standard segmentation approaches fail due to insufficient contrast. We implement 2D U-net architecture for segmentation, and, to overcome the limitations of training data obtained experimentally through imaging, we show how labelled data obtained via machine learning (i.e., Random Forest Classification) can be used as input data and enhance the neural network performances. The developed deep learning algorithm proves to be incredibly robust, as it is able to consistently segment volume phases within the whole suite of experiments. In addition, the trained neural network exhibits short run times (<7 minutes for ~250 MB of image volumes) on a local workstation equipped with a GPU card.  

To confirm the precision achieved by our workflow, we consider the theoretical and measured molar evolution of gypsum (CaSO4.2H2O) to bassanite (CaSO4.½H2O) during the dehydration. Within all time-series experiments, errors between the predicted theoretical and the segmented volumes fall within the 5% confidence intervals of the theoretical curves. Thus, the segmented CT images are very well suited for extracting quantitative information, such as mineral growth rate and pore size variations during the reaction. To our knowledge, this is the first time an internal standard is used to unequivocally measure the accuracy of a segmentation model.  Being able to accurately and unambiguously measure the volumetric evolution during a reaction enables high-level modelling and verification of the physical (hydraulic and mechanical) properties of rock materials involved in tectono-metamorphic processes.

How to cite: Rizzo, R. E., Freitas, D., Gilgannon, J., Seth, S., Butler, I. B., Wheeler, J., Marone, F., Schlepuetz, C., McGill, G., Plümper, O., and Fusseis, F.: Deep learning and chemical constraints allow accurate segmentation of µCT data from metamorphic rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7120, https://doi.org/10.5194/egusphere-egu23-7120, 2023.

EGU23-8015 | ECS | Orals | TS1.5

Syn-kinematic porosity evolution during nucleation and growth of stylolites (Eilean-Dubh limestone, NW Scotland) 

Zhaoliang Hou, Florian Fusseis, Martin Schöpfer, and Bernhard Grasemann

Stylolites are common microstructures in rocks, where mineral dissolution in a fluid localises in more or less discrete seams. Stylolite formation strongly affects rock porosity, pore connectivity and thus fluid flows. However, details of porosity evolution associated with stylolite nucleation, propagation and growth remain unclear, leading to the debate whether stylolites are conduits or barriers for fluids.

In this contribution, we use an exceptionally large high-resolution SEM-BSE mosaic (102,600 × 18,239 pixels, 0.17µm/pixel) to investigate the detailed microstructures of stylolites from the Eilean Dubh limestone of the NW Highlands in Scotland. Advanced image analyses indicate that porosity self-organises systematically around stylolites suggesting a four-stage growth process for stylolites: In stage 1, primary pyrites in the rock matrix concentrate stress and dissolution, leading to the formation of porosity. In stage 2, the dissolution porosity self-organises, triggering a chemical-hydraulic-mechanical feedback loop that facilitates further dissolution. In stage 3, the porous zones enlarge and grow along the direction of the smallest principal stress (process zone), concentrating the synkinematic precipitation of pyrites from an external fluid in the core (core zone). In stage 4, the isolated domains connect forming a stylolite with a core zone in the center (highest porosity) surrounded on both sides by a process zones (higher-than-matrix porosity), suggesting a conduit phase during stylolite formation. Since the stylolite-hosting Eilean-Dubh limestones were episodically imbricated below the Ullapool thrust and the stylolites formed sub-parallel to the internal thrust planes, we speculate that synkinematic fluids during the stylolite formation were pumped episodically into the rock during activity of the Ullapool thrust. The detailed stylolite microstructures and the proposed process for stylolite growth suggest that stylolite in carbonate may act as a conduit for a fluid flow.

How to cite: Hou, Z., Fusseis, F., Schöpfer, M., and Grasemann, B.: Syn-kinematic porosity evolution during nucleation and growth of stylolites (Eilean-Dubh limestone, NW Scotland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8015, https://doi.org/10.5194/egusphere-egu23-8015, 2023.

The VPFFT-ELLE numerical scheme is a micro-dynamic approach able to simulate the microstructure evolution of polycrystalline and polyphase aggregates during deformation and recrystallisation (www.elle.ws). The approach has been widely used to simulate the dynamic recrystallisation of ice, halite and olivine aggregates, among others. A limitation of this numerical scheme is that is limited to viscoplastic deformation by dislocation glide. However, at homologous high temperatures and low stresses, point-defect mediated mechanisms such as dislocation climb and diffusion creep are important in order to accommodate plastic deformation in polycrystalline aggregates.

We present an update of the approach by incorporating a new scheme able to simulate dislocation climb and diffusion creep in an elasto-viscoplastic regime. The approach is based on a previously small-strain version of a formulation based on the fast Fourier transforms (FFT) for the prediction of micromechanical fields in polycrystals (Lebensohn et al., 2012). The new approach integrates a rate-sensitivity, crystallographically-based constitutive model of a single crystal deforming by climb and glide, combined with an isotropic, linear model for the parametric simulation of active diffusion within grains and at grain boundaries.  

An overview of the theoretical basis of the approach is presented with some benchmarks and applications to the prediction of the effective behaviour and evolution of crystallographic-preferred orientation of highly anisotropic minerals. As expected, the incorporation of both new mechanisms produces a relaxation of differential stresses and the integration of additional scale lengths in the models. However, challenging features are remaining, such as an efficient integration with the recrystallisation processes (grain boundary migration and nucleation of new grains), or appropriate incorporation of transient creep processes.

 

Lebensohn et al (2012) An elasto-viscoplastic formulation based on fast Fourier transforms for the prediction of micromechanical fields in polycrystalline materials, International Journal of Plasticity, 32–33, 59–69. 

How to cite: Griera, A. and Lebensohn, R.: A full-field approach to simulate microstructure evolution during high-temperature deformation of polycrystalline aggregates including dislocation (glide and climb) and diffusion creep mechanisms.  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8486, https://doi.org/10.5194/egusphere-egu23-8486, 2023.

EGU23-9254 | Orals | TS1.5

Micro- to nanostructural analysis of deformation along the Muddy Mt. thrust, Nevada, U.S.A. 

Joseph Clancy White, Samuel Luke Merrithew, and Noah John Phillips

The Muddy Mt. thrust, Nevada, U.S.A, is an iconic contractual fault juxtaposing Paleozoic carbonates onto the autochthonous Mesozoic Aztec sandstone.  The minimum thickness of the thrust sheet is estimated at 4-5 km.  In contrast to many thrusts that exhibit shale-carbonate interfaces, the Muddy Mt. thrust has a mineralogically simple bimaterial interface defined by the carbonate-silicate interface.  The deformation associated with the thrust exists as a variable cataclastic zone on the order of 10-100m. Previous work has documented the extensive evidence of brittle deformation at a range of scales.  Questions at hand during such studies have included the systematic variation in fracture intensity; the contribution of fluid pressure, if any, to the thrust mechanics; the nature of deformation and permeability changes in the footwall porous sandstone and measurement of temperature transients along discrete slip surfaces.

Structures within the deformation zone, and along the thrust interface provide evidence of both seismic and interseismic displacements.  The latter comprise simple fracture, brecciation, shattered dolomite, extensive and cyclic cataclasis and fragment reduction producing tectonic foliation with evidence of cannibalized fragment, gouge injection, discrete slip surfaces and, notably, intracrystalline (plastic) deformation of carbonate aggregates.  Given that macroscopic structures, such as those listed, ultimately depend on atom-to-grain scale processes, this contribution examines the fine-scale textural attributes of aggregates proximal to the thrust interface that in many cases have grain/particle sizes sizes less than a micrometre.  The objective is to extract micromechanical behaviour that can be relevant to the displacement record of crustal-scale faults.  The microstructures and microfabrics of the interface rocks have been examined by analytical STEM, EBSD of samples prepared by focussed ion-beam techniques, with longer range elemental variations determined by mXRF.

How to cite: White, J. C., Merrithew, S. L., and Phillips, N. J.: Micro- to nanostructural analysis of deformation along the Muddy Mt. thrust, Nevada, U.S.A., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9254, https://doi.org/10.5194/egusphere-egu23-9254, 2023.

The subduction interface is characterized by downdip changes in seismic and aseismic behavior that is controlled by metamorphic reactions, deformation conditions, rheological properties, and fluid sources and pathways. Recent seismological evidence shows that a mixture of brittle-ductile deformation at the downdip limit of the seismogenic zone is responsible for producing slow slip and very low-frequency earthquakes. One way to address the possible mechanics and causes behind this dual deformation behavior is by observing exhumed rocks that provide us with the opportunity to make direct geological observations for microstructure and deformation mechanism analysis. Our project aims to understand the deformation mechanism hosted in the dominant mineral phases of metacherts and blueschist from an exhumed paleomegathrust in the Franciscan Subduction Complex. 

The Mesozoic Franciscan Subduction Complex consists mostly of underplated clastic sediment-rich terranes that are metamorphosed from prehnite-pumpellyite to blueschist facies. Angel Island, in the San Francisco Bay, is composed of blueschist facies metasedimentary and metabasic rocks containing potential paleo-megathrust faults that correlate to the source depths of slow slip earthquakes. Subduction-related faults and shear zones crop out in sea cliffs around the perimeter of the island and enable us to observe deformation features in characteristic subduction zone lithologies. We focus on a proposed subduction-related shear zone in blueschist-facies metachert juxtaposed against mafic/ultramafic rocks. Centimetric-scale field maps show coeval brittle-ductile features such as mutually cross-cutting extension fractures, kink folds, veins, and mylonitic foliations hosted in a wide variety of rheologically distinct lithologies. These lithologies contain synkinematic sodic amphibole and stilpnomelane demonstrating that this fault was active at blueschist facies. The main deforming mineral phases are sodic amphiboles, phyllosilicates, and quartz. The structural fabric comprises of shear fabrics, kink folding, dismembered veins, flattened grains, solution seams, and compositional layering. Amphiboles and phyllosilicates define the foliation of these rocks whereas quartz exhibits evidence of dislocation creep. Using EBSD-generated phase maps, we try to determine the deformation mechanisms hosted within the metacherts and blueschists along the paleomegathrust. Paleostress during megathrust creep will be constrained using EBSD-generated grain size statistics. Our study highlights the complexity of deformation within these lithologies while presenting evidence for possible deformation mechanisms witnessed at slow slip depths.

How to cite: Das, M., Rowe, C., and Mookerjee, M.: Microstructural investigations along a blueschist facies paleomegathrust: Implications for deformation mechanisms for deep slow slip behavior, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10817, https://doi.org/10.5194/egusphere-egu23-10817, 2023.

EGU23-11375 | Posters on site | TS1.5

Microscale deformation of a Proterozoic Granite near the nexus of the Mid-Continent Rift and Nemaha Uplift, SE Nebraska, USA 

Caroline Burberry, R Matt Joeckel, and Michele Waszgis

Deformation microstructures can be used to decipher multiple stages of deformation in ancient terranes through the assessment of classical high-temperature minerals, fabrics, and textures (e.g., alteration minerals, reduction of grain size) as well as low-temperature cross-cutting features (e.g., brittle fracture).  Microstructural studies are typically necessary, in conjunction with hand-sample and/or outcrop work, to fully characterize the spectrum of deformation events and mechanisms in a system and to understand the impact that future deformation events may have on similar rock masses.  

In this study, we focus on samples from SE Nebraska, where crystalline basement, chiefly the Central Plains orogeny, dates from the Proterozoic assembly of the central craton of North America. This basement was deformed by the evolution of two major features: (1) the 1.1 Ga Mid-Continent Rift System (MCRS) and (2) the >300 Ma Nemaha Uplift (NU). Due to the uplift on the flanks of the MCRS and the NU, ~60 m of these basement rocks were recovered in a fragmented small-diameter core. This so-called “Capitol/Capital Beach core”, one of exceedingly few basement cores in SE Nebraska, was drilled in 1887 as part of an unsuccessful search for rock salt or brine. Pieces of it were distributed as souvenirs, then painstakingly reclaimed and rearticulated by the state geologist. We present a first-ever textural and microstructural analysis of the basement rock from this historic core.

Preliminary thin section petrography indicates that the groundmass of the basement rock is primarily quartz, twinned feldspar, mica and some opaques (zircon?) with remnant intergrowths and textures consistent with cooling from a melt; therefore, we consider the basement in this area to be granitic. Under crossed polars, we observe undulose extinction in the quartz grains, implying high strain. Quartz grains also show subgrain development at grain boundaries. Thin sections and hand samples also reveal the development of phyllosilicate shear zones, altered from the precursor micas that are folded and kinked themselves. Furthermore, we note at least two generations of brittle fracture in quartz and feldspar grains, some of which propagate through and displace the phyllosilicate shear zones and are filled with alteration minerals, including possible epidote.

Our microstructural data implies that the granitic basement has undergone no less than four discrete phases of deformation since accretion. We associate two of these phases with the evolution of the MRCS and NU evolution, but other two phases of deformation occurred earlier, probably during the Cambrian to Mississippian, an interval about which little in terms of regional tectonism and deformation is known.  Our work highlights the importance of cratonic uplift events in the fracture of rock masses, even on the microscopic scale, during basement evolution.  It also portends important insights from continued investigation.

How to cite: Burberry, C., Joeckel, R. M., and Waszgis, M.: Microscale deformation of a Proterozoic Granite near the nexus of the Mid-Continent Rift and Nemaha Uplift, SE Nebraska, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11375, https://doi.org/10.5194/egusphere-egu23-11375, 2023.

Subducted metabasic rocks play an important role in defining the rheology of the subduction zone interface and are believed to be the primary source of volatiles for arc magmatism and fluid-induced seismicity. The rheology of metabasic rocks along the subduction zone interface are typically modeled based on the strength of omphacite, however metabasic rocks are made up of a variety of different minerals. In this study we present a detailed microstructural analysis of zoisite from an eclogite collected on Kini beach in Syros, Greece and make the argument that

 zoisite may be important in defining the rheology of metabasic rocks along the subduction zone interface.The studied sample is a prograde blueschist to eclogite facies rock primarily containing glaucophane, omphacite, zoisite, and garnet with minor amounts of chlorite retrogression at the rims of large omphacite grains. A hand sample (~12 cm in diameter) was polished and several thin sections were made for analyses. The hand sample shows strain is primarily localized into zoisite-rich layers suggesting zoisite was the weakest mineral when the sample was deforming. Backscatter electron images of the zoisite layers show a homogeneous mixture of zoisite and clinozoisite, where clinozoisite makes up ~10% of the zoisite layers. Zoisite grains are on average twice as large as clinozoisite with an average grain size of 61 μm, whereas clinozoisite has an average grain size of 36 μm. Both phases have strong shape and crystallographic preferred orientations. Both phases show poles to (100) maxima roughly orthogonal to the reference foliation, while poles to (010) develop a girdle sub-parallel to the foliation plane, and poles to (001) are uniformly distributed. EBSD analysis shows that a few zoisite and clinozoisite grains develop subgrain boundaries, suggesting dislocation related mechanisms played a minor role. Based on our analysis, zoisite is interpreted to have deformed primarily by a combination of rigid body rotation and dissolution-precipitation, which lead to the precipitation of clinozoisite. Further analyses will be conducted on zoisite as well as other common minerals within the sample.

How to cite: Morales, L. F. G., Tokle, L., and Salvadori, L.: Microstructural analysis of zoisite from a naturally deformed eclogite (Syros, Greece): Implications on the rheology of metabasic rocks along the subduction zone interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11713, https://doi.org/10.5194/egusphere-egu23-11713, 2023.

Amphibole is a hydrous mineral form under metamorphic conditions of the lower crust and in subduction zones. Despite its abundance and ubiquitous texture, the deformation mechanisms of amphiboles are not well understood. We characterize the microstructure of three amphibolites with a high modal fraction of hornblende or actinolite (≥70%) that were deformed under different conditions of pressures and temperatures. We investigated three natural amphibole samples from different localities in India: amphibolite from the Chitradurga shear zone (CSZ) with P-T conditions of ~5 kb and ~600 ºC, hornblendite from the Mayodiya Ophiolite Complex (MOC) from NE Himalaya, with P-T conditions of 7.8-8.2 kb, and 770-820 ºC, and hornblendite from the Koraput Alkaline Complex (KAC) with P-T conditions of 7.6-8.4 kb, and 860-883 °C. To depict the deformation and recrystallization mechanism/s we used electron backscatter diffraction (EBSD) to analyze the grains’ shape, orientation, and the small, intragrain misorientations. The CSZ exhibits elongated actinolite grains with sharp boundaries, tabular shape, and areas of localized deformation illustrated by high-amplitude ‘V-shaped’ kinking of the actinolite grains. The MOC hornblendite exhibits wedge-like elongated grains with crosscutting relations and twinning in the hornblende grains. The KAC hornblendite exhibits very large grains (several mm) with smaller grains at their periphery and highly lobate grain boundaries. MOC and KAC hornblendites show large porphyroblast grains with high intragrain misorientations surrounded by smaller matrix grains and low intragrain misorientations, consistent with a recrystallization fabric. In addition, in the MOC sample, the orientation of grains away from the porphyroblasts shows the continuous spread of their orientation compared with the porphyroblast. Relying on the microstructural observations, we interpret that the CSZ sample was deformed under brittle kinking and the MOC and KAC samples (with elevated P-T conditions) were deformed and recrystallized under temperature-dependent mechanism (e.g., dislocation creep, diffusional processes). Interestingly, although the apparent difference in deformation mechanism, all samples show the same [001] alignment of their intragrain misorientation axis, which does not fit with the common (100)[001] slip system for amphiboles. The different deformation mechanisms will be discussed in light of the microstructural observations and the ability to use the intragrain misorientation axis as a proxy for assessing the deformation mechanism and/or slip system.

How to cite: Meher, B. and Boneh, Y.: Delineating microstructural features of deformation and recrystallization of Ca-rich amphibole from naturally deformed amphibolites , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11779, https://doi.org/10.5194/egusphere-egu23-11779, 2023.

EGU23-12331 | ECS | Posters on site | TS1.5

The interplay of deformation and devolatilization – texture evolution during subduction of meta-ophicarbonates 

Manuel D. Menzel, Károly Hidas, and José Alberto Padrón-Navarta

A key characteristic of subduction zones is that lithologies in slabs undergo prograde devolatilization while simultaneously being subject to deformation. A growing number of studies suggest that dissolution-precipitation creep may be the dominant deformation mechanism when fluid is present [1] and that the related fabric development and weakening are most pronounced during metamorphic reaction [2]. Here we investigate the microstructural and textural evolution of meta-ophicarbonate lenses hosted in Atg-serpentinite and Chl-harzburgite of the Milagrosa and Almirez ultramafic massifs in the Nevado-Filábride Complex (Betic Cordillera, S. Spain), which record high-pressure alpine subduction metamorphism. Similar rocks typically occur along tectonized lithological contacts between peridotite and mafic or sedimentary units, thus they can be ideal archives of focused deformation, prograde devolatilization and large scale fluxing by fluid from high-P serpentinite dehydration in subduction zones. In Milagrosa, serpentinite-hosted ophicarbonates —formed after variable mixtures of Ca-carbonate and serpentine— underwent prograde metamorphism to foliated antigorite-diopside-dolomite rocks and Ti-clinohumite-bearing diopside marbles (550 – 600 °C, 1.0 – 1.4 GPa). In Almirez, ophicarbonates were transformed to high-grade assemblages of Ti-clinohumite, olivine, diopside, chlorite, aragonite and dolomite (650 – 680 °C, 1.7 – 1.9 GPa) [3]. We combine microstructural and textural data obtained from electron backscatter diffraction (EBSD) and optical cathodoluminescence (CL) imaging to investigate the relationship between deformation and metamorphic devolatilization during prograde metamorphism. In Milagrosa, Atg-serpentinites show a fabric with a crystallographic preferred orientation (CPO) of antigorite typical of high-P Atg-serpentinites in subduction zones. Antigorite in antigorite-diopside-dolomite rocks displays the same fabric, with a c-axes maximum coinciding with the pole to the foliation, and diopside c-axes parallel to lineation. Dolomite and calcite in the Milagrosa meta-ophicarbonate lenses have a consistent CPO with their c-axes orientated subparallel to that of antigorite, which correlates with the poles to (100) of diopside. In foliated meta-ophicarbonates at Almirez, diopside, dolomite and calcite show a very similar distribution of their crystallographic axes with respect to foliation. CL imaging reveals concentric core-rim zoning of diopside and dolomite in both localities. Clusters of aragonite inclusions indicate that all zoning generations in diopside formed at high-P by growth and/or dissolution-reprecipitation.

These zoning patterns and low intra-grain misorientations point to diffusion creep by dissolution-precipitation as the dominant deformation mechanism. The strong correlation of diopside, carbonate and antigorite CPOs may have been caused by oriented crystal growth under differential stress and anisotropic fluid flow in the reacting ophicarbonate. We infer that antigorite dehydration in meta-ophicarbonate at 580 – 600 °C is related to transient ductile deformation enhancing fluid drainage, followed by compaction and an increased bulk rock strength once all antigorite devolatilizes. This causes deformation and fluid flow during dehydration of the host serpentinite at 650 °C to focus around the meta-ophicarbonate lenses, shielding carbonate from dissolution at subarc conditions.

 

[1] Malvoisin & Baumgartner (2021) G³; https://doi.org/10.1029/2021GC009633

[2] Stünitz et al. (2020) JSG; https://doi.org/10.1016/j.jsg.2020.104129

[3] Menzel et al. (2019) JMG; https://doi.org/10.1111/jmg.12481

M.D.M acknowledges funding of Junta de Andalucía (Postdoc_21_00791)

How to cite: Menzel, M. D., Hidas, K., and Padrón-Navarta, J. A.: The interplay of deformation and devolatilization – texture evolution during subduction of meta-ophicarbonates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12331, https://doi.org/10.5194/egusphere-egu23-12331, 2023.

EGU23-12383 | ECS | Orals | TS1.5

Effect of stress biaxiality on fracture energy and microstructures of tensile cracks 

Antoine Guggisberg, Mathias Lebihain, Jo Moore, and Marie Violay
The onset of crack propagation is often described with a unique threshold and intrinsic material property, the fracture energy. However, in geomaterials, this parameter varies with environmental and loading conditions (e.g., temperature, confining pressure, humidity, loading rate, etc.). This can be explained by more elaborate models in which the fracture energy is set by the weakening mechanisms at stake during material breakdown. Variations in fracture energy may then be attributed to a change in the failure mechanisms occurring in a dissipative region located very near the crack tip. Here, we show how stress biaxiality can cause a shift in the mechanisms dictating crack propagation and how they consequently affect the fracture energy.
 
To this end, we performed modified ring tests (MRT) and wedge splitting tests (WST) on Carrara marble. These tests were selected for their stable configurations, while they have opposite stress biaxiality levels; -8 and +5 MPa respectively for MRT and WST. These tests also allow continuous fracture energy measurements thanks to a compliance method previously calibrated on PMMA experiments. We halted crack propagation and extracted thin sections at the tip, on which we acquired backscatter electron (BSE) and electron backscatter diffraction (EBSD) maps using a scanning electron microscope.
 
These experiments showed that the fracture energy is test dependent: it ranges between 20 to 30 J/m2 on the MRT, and 20 to 80 J/m2 on the WST, depending on the crack tip position. Interestingly, the variations of fracture energy seem correlated with variations of stress biaxiality and associated microstructures. The BSE and EBSD scans show that the crack is mostly intra-granular and straight at a negative stress biaxiality level on the MRT. While at a positive level on the WST, the crack travels through grain boundaries with significant branching and higher tortuosity. These observations are in good agreement with theoretical studies on crack path in heterogeneous materials. However, one may expect that a shift from inter-granular (WST) to intra-granular (MRT) fracture would be associated with higher fracture energy, as the crack crosses through tough grains rather than weak grain boundaries. The opposite is measured as “en-passant” cracks occasionally form on the crack path during wedge-splitting tests. It creates bridging patches that oppose crack opening and double the fracture energy. These microstructures might be key to large variations of tensile fracture energy observed in geomaterials, whose fracture behavior is strongly influenced by stress biaxiality.

How to cite: Guggisberg, A., Lebihain, M., Moore, J., and Violay, M.: Effect of stress biaxiality on fracture energy and microstructures of tensile cracks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12383, https://doi.org/10.5194/egusphere-egu23-12383, 2023.

EGU23-14135 | ECS | Posters on site | TS1.5

Semi-brittle deformation of Carrara marble: snapshots during strain accumulation 

Tongzhang Qu, Nicolas Brantut, David Wallis, and Christopher Harbord

Semi-brittle deformation arises as the manifestation of combined microphysical mechanisms dominated by pressure (including dilation, fracturing, frictional sliding) and temperature (including intragranular diffusion of matters, dislocation motion and annihilation, twinning, and grain-boundary sliding). Although each of the deformation mechanisms is individually relatively well understood, the combination and interaction between the two sets of processes remain poorly known.

In order to have a better understanding of the semi-brittle behavior in the lithosphere, we conducted a series of uniaxial compression experiments on samples, cored from Carrara marble – polycrystalline calcite with low porosity and isotropic texture, at confining pressure of 400 MPa in gas pressure medium, temperature of 200 ºC and constant strain rate of 1 × 10-5 /s. Ultrasonic waves were transmitted through the specimen by a pair of piezoelectrical crystals to monitor the in-situ microstructural states of the sample. The focus of this work is to investigate the contribution of each mechanism as a function of strain accumulation. Accordingly, deformation is ceased at a different stage in each experiment, including the onset of inelastic behavior (at ~0.3% strain) and yield point (at ~1.1% strain) and stages after the yield point (at 1.8%, 3.8% and 7.5% strains).

The mechanical testing results from the 5 runs are essentially reproducible before yielding, and after yielding the difference among the experiments is at most ~20 MPa in stress at the same strain. Strain hardening occurred in the later three specimens deformed to relatively large extent with stress increasing, for example, from 140 to 300 MPa in the sample deformed by 7.5%. The wave velocity, occasionally increasing at the start of deformation in some experiments, generally decreases with increasing strain. Preliminary observations by scanning electron microscopy and EBSD on deformed samples show pervasive distribution of fractures, twins and high misorientation within individual grains, confirming that all the aforementioned mechanisms in semi-brittle regime have potentially contributed to the deformation at such experimental conditions. Further analysis quantifying the evolution of fracture density, twin density and intracrystalline plastic strain with increasing deformation is currently being undertaken.

How to cite: Qu, T., Brantut, N., Wallis, D., and Harbord, C.: Semi-brittle deformation of Carrara marble: snapshots during strain accumulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14135, https://doi.org/10.5194/egusphere-egu23-14135, 2023.

EGU23-14287 | Posters on site | TS1.5

Microstructure and paleotemperature record of the upper Cretaceous rocks from the Alpine collision in the western Pyrenean Axial Zone (Eaux-Chaudes fold nappe). 

Norbert Caldera, Albert Griera, Marco A. López-Sánchez, Marc Guardia, Pierre Labaume, Abdeltif Lahfid, and Antonio Teixell

The Alpine collisional deformation of the upper Iberian margin in the western Axial Zone of the Pyrenees occurred under conditions of moderate paleotemperature (Caldera et al., 2021). Carbonates from the upper Cretaceous of the Eaux-Chaudes fold nappe (ECFN) preserve evidence of ductile deformation at both large- and microscale under greenschist facies. The ECFN provides evidence of high ductile strain achieved under considerable burial conditions (ca. 10 km), contrasting with the standard view of near-surface Alpine deformation of the upper part of the Iberian collided margin. The mylonites observed in the km-scale overturned limb of the ECFN feature strong shear deformation characterized by intrafolial folds, S-C fabrics, mineral lineation and boudinaged, asymmetric dolomite bodies.

Microscale observations by EBSD indicate that grain-shape and crystallographic preferred orientations (CPO) are well-developed in calcite aggregates. Deformation is mild in the normal fold limb, with spaced pressure solution seams. CPO and inverse pole figure (IPF) results from high-strain zones advocate for dislocation creep as the main deformation mechanism by basal-slip along the a- and m- axis. Dynamic recrystallization is also observed as well as local four-node.

In general, calcite-rich aggregates are characterised by fine recrystallized matrix, ranging in grain size between 12-30 µm, and therefore indicating relatively low-stress conditions (20-60 MPa) using the more common piezometers. The spatial distribution of the secondary phase content, such as dolomite and quartz, conditioned the strain partitioning in the polymineralic mylonites. On one hand, grain size reduction of the calcite phase was favoured in areas between small, spaced dolomite grains. On the other hand, calcite grain growth was favoured in shadow zones of large dolomite porphyroclasts. Dolomite phase shows dominant ductile-brittle behaviour expressed by low internal crystal plasticity developing weak CPO and featuring extensional fractures along grain boundaries. Quartz is the less common mineral phase and also affected by ductile-brittle deformation with occasional undulose extinction.

Complementing the microstructural results, we delve deeper into alpine paleotemperatures along the ECFN by Raman spectroscopy of carbonaceous material (RSCM) and microprobe analysis using Powell et al. (1984) and Covey-Crump (1989) methods. Results from all methods are consistent with the ductility observed. The higher values are obtained in the mylonites of the autochthon and overturned limb ranging 340-360ºC. On the other hand, the normal limb features paleotemperatures in a lower range of 300-330ºC. Those temperatures are in accordance with the deformation mechanisms observed.

The microfabrics and paleotemperature results here documented from the Eaux-Chaudes Massif show for the first-time ductile mechanisms of deformation in Alpine mylonites derived from post-Variscan sedimentary rocks during the Alpine orogeny in the Pyrenees.

 

Caldera, N., Teixell, A., Griera, A., Labaume, P. & Lahfid, A. (2021). https://doi.org/10.1111/ter.12517

Covey-Crump, S.J. & Rutter, E.H. (1989). https://doi.org/10.1007/BF00387202

Powell, R., Condliffe, D. M. & Condliffe, E. (1984). https://doi.org/10.1111/j.1525-1314.1984.tb00283.x

How to cite: Caldera, N., Griera, A., López-Sánchez, M. A., Guardia, M., Labaume, P., Lahfid, A., and Teixell, A.: Microstructure and paleotemperature record of the upper Cretaceous rocks from the Alpine collision in the western Pyrenean Axial Zone (Eaux-Chaudes fold nappe)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14287, https://doi.org/10.5194/egusphere-egu23-14287, 2023.

EGU23-14586 | ECS | Orals | TS1.5

Effect of phlogopite on the strength of mica-quartz assemblage and underlying chemical processes 

Lalla Khadija Alaoui, Laura Airaghi, Holger Stünitz, Hugues Raimbourg, and Jacques Précigout

While mineral plasticity is often seen as the most important process to deform rocks in the deep, viscous realm, but an increasing number of studies is highlighting the contribution of mineral reactions and chemical processes to bulk strain. This issue is especially acute at the brittle-viscous transition, where plasticity is hampered by the low temperature conditions. In this work, we studied the deformation processes operating in mica+quartz assemblages, representative of greenschist to amphibolite-facies mylonites, with a special focus on the respective contributions of plasticity and dissolution-precipitation processes.

Assemblages made of phlogopite (Phl) and quartz (Qz) were experimentally deformed in simple shear (Griggs-type apparatus) at 800°C, 10kbar, shear strain rate ~10-5 s-1 and 0.1 wt. % added H2O.  For well-constrained grain sizes (63μm < Phl < 125μm, 10μm < Qz < 20μm), we varied the phase proportions of phlogopite (10, 20, 30, 50, 70 and 100% vol. Phl).

Mechanical results indicate at first order a decrease in strength as the proportion of mica is increased. Samples for 10% vol. Phl deform at differential stresses of ∼1200 and at 20% Phl at ~900MPa, while 100% vol. Phl sample deform for differential stresses as low as ~300MPa. However, the weakest behavior is observed for 30% vol. of mica. The strength of the latter sample lies well out of the iso-strain/iso-stress curves, pointing to the fact that the assemblage does not behave as a simple mechanical mixture of the two end-member mineral phases.

In all samples, an important grain size reduction is noticeable for mica flakes. Grain size reduction is also present for quartz grains, especially with decreasing proportion of mica in the assembly. Most of the strain is accommodated by quartz as an interconnected network in Phl-poor samples, while in Phl-rich samples, phlogopite grains are interconnected. In quartz, a weak intragrain deformation is observed for most samples with no evidence for dynamic recrystallization Quartz is largely reworked as attested by trace element variations, with the reworked quartz proportion decreasing with increasing abundance of phlogopite Only the 10% vol. Phl sample is characterized by incipient polygonal subgrains between parent quartz grains (Qz1). Quartz is reworked mainly by dissolution-precipitation, with newly formed product (Qz2) surrounding original, inherited quartz grains. Qz2 is characterized by a large microporosity, and is enriched in aluminum compared to Qz1. The contribution of dissolution-precipitation seems to be maximal in the weakest sample (30% vol. Phl). Therefore, our study shows that dissolution precipitation processes are instrumental to weaken the two-phase material and that bulk strength strongly deviates from composite flow laws in case of a purely mechanical mixing.

How to cite: Alaoui, L. K., Airaghi, L., Stünitz, H., Raimbourg, H., and Précigout, J.: Effect of phlogopite on the strength of mica-quartz assemblage and underlying chemical processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14586, https://doi.org/10.5194/egusphere-egu23-14586, 2023.

EGU23-14690 | ECS | Posters on site | TS1.5

Particle alignment during sedimentation – a 4D approach 

Rebecca Kühn, Rüdiger Kilian, Dustin Lang, Luiz Morales, Ola Grendal, and Michael Stipp

The microstructural evolution of clay-rich sedimentary rocks starts with the settlement and alignment of particles. With the accordance between shape preferred orientation and crystallographic preferred orientation (CPO) in the case of disk-like clay particles, the parallel alignment can be quantified measuring the clay CPO.

In order to quantify the influence of the sedimentation conditions on the CPO of primary layering we performed sedimentation experiments combined with in-situ synchrotron diffraction measurements. The experimental procedure involved a sediment suspension drip inserted at the top of a 30 cm water column at regular intervals. The fluid in the column was either deionized water or seawater, and the sediment suspension contained either kaolinite with of disk-like particle shapes or a mixture of kaolinite and polycrystalline illite, the latter with more compact particle shapes. Time-resolved CPO development in the experiments was measured at ESRF, beamline ID22.

The formation of a CPO is readily observed at the water-sediment interface with an initially higher CPO strength in deionized water experiments than in seawater. The resulting sediment shows a pronounced layering in both fluids when using pure kaolinite. In the layered sediments in deionized water the CPO strength varies strongly between different layers. At some measurement positions, a high initial CPO strength drops fast in the first 150 minutes, interpreted to result from dewatering-related reorganisation of the microstructure. A stable CPO strength can be observed after ~200 min. In the seawater experiments the CPO strength does not vary in different layers and increases slowly but constantly with time and overburden indicating a successive rotation of particles. CPO in kaolinite experiments is higher than in kaolinite + illite experiments as compact particles locally inhibit the alignment.

The evolution of clay particle orientation and therefore microstructure can be quantified in space and time. It is suggested that the initial microstructure is crucial for the progressive development of the rock during diagenesis and hence e.g. resulting physical properties. 

How to cite: Kühn, R., Kilian, R., Lang, D., Morales, L., Grendal, O., and Stipp, M.: Particle alignment during sedimentation – a 4D approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14690, https://doi.org/10.5194/egusphere-egu23-14690, 2023.

EGU23-14897 | ECS | Posters virtual | TS1.5

Clay mineral alignment during early stages of burial 

Dustin Lang, Rebecca Kuehn, and Rüdiger Kilian

The formation of crystallographic preferred orientations (CPO/texture) in sediments is often attributed to rigid grain rotation of minerals and aggregates, plastic-brittle deformation and dissolution-precipitation processes. Due to their platy habit, clay minerals have a large shape anisotropy and are expected to develop a CPO most readily under favorable conditions. Here, we present an experimental approach in order to quantitatively explore the influence of particle settling and subsequent compaction in an undisturbed, ideal environment.

For the experiments, a powder of idiomorphic kaolinite grains (texture-forming components) was mixed with a fine-ground, illite aggregates (texture-inhibiting components) in mass proportions of 0, 30, 50, 70 and 100 %. The illite aggregates have compact shapes and are built up of submicron-sized crystallites. The modal particle size of both components is about 5 µm. Particles were mixed with artificial seawater and the resulting sludge was left to settle in 80 cm high acrylic tubes. For each composition three samples were produced: Sedimentation-only and two drained compaction experiments. The latter were carried out in a in a mechanical press, progressively applying a uniaxial load up to 0.4 MPa and 4 - 8 MPa, respectively. Compaction resulted in a volume decrease of 30 and 60 vol-%. The CPO of clay minerals was measured using high energy X-ray diffraction at beamline P07b at Deutsches Elektronen-Synchrotron (DESY) in Hamburg and pole figure data was directly extracted using single peak evaluation.

The results show that sedimentation alone, can yield a strong texture of the clay minerals. In the compaction experiments, texture strength is logarithmically related to the applied load, i.e. increase of texture strength is decreases at higher loads. Texture strength is linearly related to shortening and porosity reduction. In all cases, kaolinite texture strength is inversely correlated with illite aggregate content.

The results indicate that only a fraction of clay minerals is deposited flat on the sediment surface. Further, alignment during settling is hampered in the presence of particles with compact shapes. It is interpreted that rigid body rotation is limited to the very initial stages of settling and compaction. Additional texture strengthening is hampered by the lack of particles prone to rotate. Sediment surface processes as well as rigid body rotation during initial loading in the first few centimeters of burial are thus the most important processes in the formation of a CPO in clay rich sediments. Subsidence history beyond principal porosity elimination does not have a strong impact on the CPO. Therefore, the texture strength of a fine-grained sedimentary rock can be indicative of settling and early compaction conditions. In return, texture-related properties of artificial clays can be regulated by controlling those conditions.

How to cite: Lang, D., Kuehn, R., and Kilian, R.: Clay mineral alignment during early stages of burial, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14897, https://doi.org/10.5194/egusphere-egu23-14897, 2023.

EGU23-15284 | Posters on site | TS1.5

Orientation-dependent recrystallization and extreme ductility in a sheared quartz vein 

Rüdiger Kilian and Michael Stipp

Microstructures in quartz are widely used to draw inferences on conditions and history of deformation. In particular quartz recrystallization microstructures are often assumed to provide an interdependent information on e.g., deformation temperatures, strain rates or grain boundary mobility. Piezometric approaches attempt to relate a given recrystallized grain size or low angle boundary (LAB) structure to differential stress during deformation.

Here, a decimeter-scale, sheared quartz vein from the Central Pyrenees hosted in phyllites of the Hospitalet Massif was studied by means of EBSD. The sheared part of the vein consists of a mm-scale, planar, parallel layering representing an estimated shear strain > 5. The layering is defined by domains of different crystal orientations and a pronounced contrast in recrystallization behavior. Domains with the c-axis about normal to the kinematic section consist of almost single grains which stretch to aspect ratios > 40, show a very homogeneous LAB pattern, little dynamic recrystallization (< 20 vol%) and recrystallized grain sizes have a volume weighted mode of ~8 µm. Based on boundary misorientations and microstructure, recrystallization is inferred to proceed predominantly by a combination of subgrain rotation, and geometric recrystallization. The second type of domains consists of non-recrystallized remnants of old grains with low aspect ratios, a very heterogeneous LAB structure and c-axes within the kinematic plane, for example normal to the foliation. Recrystallization at overall > 50 vol% proceeds in localized, often conjugated bands. Bands and c-axes of recrystallized grains within those bands are inclined in mutually opposite directions, unrelated to the host crystal orientation. The grain size varies systematically for different band types, e.g. bands in a C' orientation contain the largest recrystallized grain size (~12 µm). Recrystallization is inferred to proceed, at least partially, by nucleation and local grain boundary migration. The third type of domain shows mixed behavior, whereat more highly sheared parts correlate with a smaller recrystallized grain size and c-axis directions changing towards the normal of the kinematic section.

Neither the dependence of grain size on recrystallization processes, nor the orientation-dependent recrystallized grain sizes and LAB structure are easily compatible with a single controlling factor, i.e. flow stress. The data suggest that especially the orientation of host grains plays a non-negligible role in controlling recrystallization mechanisms, LAB structure and dynamically recrystallized grain sizes. This relationship needs to be considered when investigating highly deformed rocks which usually exhibit a strong degreee of preferred orientation.

How to cite: Kilian, R. and Stipp, M.: Orientation-dependent recrystallization and extreme ductility in a sheared quartz vein, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15284, https://doi.org/10.5194/egusphere-egu23-15284, 2023.

EGU23-15498 | Orals | TS1.5

Direct Observation of Grain Boundary Sliding in Forsterite Bicrystals 

Shobhit Pratap Singh, Christopher Thom, Lars Hansen, Katharina Marquardt, John Wheeler, Elisabetta Mariani, and Julian Mecklenburgh

Olivine is the most abundant mineral in Earth’s mantle, and its rheology is likely to control upper-mantle convection. While the rheology of olivine is widely studied, little is known about the rheology of olivine grain boundaries and their effect on deformation in the mantle. Forsterite bicrystals, synthesized by direct bonding of highly polished single-crystal plates, were tested in this study to investigate sliding along the single grain boundary at high temperature (1300°C). Prior to deformation, the bicrystals were polished and scratch markers were scribed perpendicular to the grain boundary to track grain-boundary sliding. Bicrystals were deformed in shear loading between two alumina pistons in a uniaxial creep apparatus at 1 atm with applied axial stress ranging from 1 to 30 MPa. The specimen deformation was measured in real time using a high-resolution (~1 μm) linear variable differential transducer. Each test was carried out until attainment of a quasi-steady state deformation rate to determine the creep parameters. Post-deformation microstructural analysis was conducted using a scanning electron microscope (SEM) and electron backscattered diffraction. Our study established that the creep-rate law for bicrystals is different than single and polycrystalline forsterite. Bicrystals are weaker and shows up to 1 order of magnitude higher deformation rates. SEM microstructures reveal the sliding of scratch markers, which is direct evidence of grain-boundary sliding in forsterite. However, the strain geometry is complex, and further experiments are necessary to determine the overall strain distribution in the sample. Here we present the rationale of our research, and we compare our results on grain-boundary sliding in forsterite with the earlier literature.

How to cite: Singh, S. P., Thom, C., Hansen, L., Marquardt, K., Wheeler, J., Mariani, E., and Mecklenburgh, J.: Direct Observation of Grain Boundary Sliding in Forsterite Bicrystals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15498, https://doi.org/10.5194/egusphere-egu23-15498, 2023.

In the southern Apennines, Mesozoic carbonates are characterized by the superimposition of different brittle deformation structures formed during different phases of rifting, orogenic shortening and post-orogenic extension. In the western Matese area, fault zones developed in the Triassic dolostones commonly exhibit the complex juxtaposition of different fault rocks, wide damage zones and pulverized dolomite rocks. Significantly, pulverization causes a drastic change in the petrophysical behavior of deformed rock masses through dynamic shattering. For these reasons, a better description of the processes that steer the “dolomite flour” spatial distribution through fault zones represents a fundamental aspect of the mechanical stratigraphy assessment related to subsurface infrastructure building and of the fault zone hydraulic behavior.

In this work, we present a multi-scalar and multi-methodological approach to provide a possible structural evolutionary scenario for the Matese Triassic dolostones. We analyzed fault zones outcropping along the eastern side of the Telese plain in the Ailano and Alife area. The fault zones consist of mature damage zones where pulverized rocks occur in patches of variable size (10s 100s of meters) immediately adjacent to the fault core. The fault zones show complex arrays of slip surfaces, including a major N-S normal fault crosscut and reactivated by NE-SW and NW-SE strike-slip faults. Extensive powder bodies are heterogeneously distributed within the damage zone and adjacent to the fault cores of both systems of faults. Fault zone architecture is associated with different brittle structural facies: i) cataclastic to ultra-cataclastic facies; ii) wide volumes of pulverized “dolomite flour”; iii) foliated cataclasite; iv) cataclastic shear bends; v) hydrothermalized dolomite; vi) unstrained lithons.

Fault analysis suggests that the N-S normal fault systems accommodated extension during the Mesozoic passive margin extensional phases. The NE-SW and NW-SE strike-slip fault systems developed in a successive phase of orogenic shortening. The shortening-related strike-slip faults propagation overprint the inherited Mesozoic fault zone through extensive pulverization processes of dolostones with the formation of a wide volume of “dolomite flour”.

How to cite: Diamanti, R., Camanni, G., and Vitale, S.: Structural evolution of long-lasting fault zones developed in dolostones in the south-western Matese area (southern Apennines, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15512, https://doi.org/10.5194/egusphere-egu23-15512, 2023.

EGU23-15541 | Orals | TS1.5

The effect of earthquake rupture on the brittle-viscous flow of olivine 

Elisabetta Mariani, Heath Bagshaw, Matt Bilton, and Joe Gardner

Earthquakes are triggered by the sudden release of strain energy accumulated in the Earth’s crust and mantle. Around 55 earthquakes are located every day around the world, and 16 large earthquakes of magnitude greater than 7 are expected in any given year. These events are responsible for many deaths and for major natural disasters. The periodicity of rupture events is controlled by complex variables such as fault surface roughness, fault geometry, fluid-rock interactions, fluid pressure oscillations and the mechanics of the fault rock. Seismology, rock mechanics experiments and modelling have provided vital insights into the behaviour and frictional properties of faults, but the brittle-viscous response of rock to earthquake rupture and the passage of shock waves is currently not understood.

Natural olivine exposed at the Earth surface, but derived from Earth’s upper mantle, display microstructures where brittle, frictional and viscous deformation coexist. Here we study the microstructures and textures locked in the geological record of the Premosello peridotite to understand the transient brittle-viscous deformation mechanisms triggered during large earthquakes, and their contribution to energy dissipation and build-up during the earthquake cycle.

In this study we use electron backscatter diffraction (EBSD) in the SEM, as well as TEM analyses, to detail the micron to nanoscale structures of olivine in samples from the shallow upper mantle, collected near thick pseudotachylytes in proximity of the Mohorovičić discontinuity, which juxtaposes these peridotites with the lower crustal granulites of the Ivrea-Verbano Zone.

How to cite: Mariani, E., Bagshaw, H., Bilton, M., and Gardner, J.: The effect of earthquake rupture on the brittle-viscous flow of olivine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15541, https://doi.org/10.5194/egusphere-egu23-15541, 2023.

EGU23-15832 | ECS | Orals | TS1.5

Rheology and Deformation Processes of Fine-grained Quartz Aggregate 

Subhajit Ghosh, Holger Stünitz, Hugues Raimbourg, and Jacques Précigout

Grain size is a critical parameter for viscous deformation processes and controls the rheological behaviour (weakening and strain localizations in mylonites) of polycrystalline aggregates. Recently,  Ghosh et al., (2022) used Tana quartzite (~200 μm) to develop a new grain-size-insensitive flow law (stress exponent, n = 2; activation energy, Q = 110 kj/mol). The n = 2 is interpreted to indicate the serial operation of grain interior (dislocation glide) and grain boundary (dissolution-precipitation, DPC + Grain boundary sliding, GBS) accommodation processes. It is shown that all the previous results obtained from coarse-grained (∼100 - 200 μm) quartz aggregates (high total strain, significant recrystallization) plot within a factor of ∼5 times the strain rate predicted by this flow law. Moreover, a number of earlier studies with fine-grained (3.6 to 12 μm) quartz reported an n-value range of 1.7 to 2.5 (Kronenberg and Tullis 1984; Fukuda et al., 2018), similar to the values obtained from coarse-grained samples. A deviation from the grain-size-insensitive creep-dominated process is expected at those grain-size ranges and poses the question: how much weakening is possible by grain-size-reduction within the continental crust?

Using a Griggs-type apparatus, we deformed fine-grained (~ 3-4 μm) as-is and 0.1 wt.% H2O-added novaculites, representing a fully recrystallized shear zone material, at the same condition as coarse-grained Tana quartzite (~200 μm). The as-is novaculite is ~3.5 times stronger than the H2O-added novaculite. A similar strength difference (~4 times) was also observed between the as-is and H2O-added Tana quartzite. The H2O-added novaculite is ~4 times weaker than the H2O-added Tana. The as-is novaculite is ~4.5 times weaker than the as-is Tana quartzite. Thus, the addition of 0.1 wt.% H2O causes a similar order of weakening as the smaller grain size; the as-is novaculite has a similar strength as the data predicted from the H2O-added Tana flow law. The maximum strength difference (more than an order of magnitude) arises between the end-member samples i.e., the as-is Tana and H2O-added novaculite, which indicate the combined effect of grain size and H2O. The n (1.91 to 2.19) and Q (118 kj/mol) values measured from novaculites are similar to the Tana and the Tana flow law can express all the novaculite data within the error associated with the Griggs-type apparatus, only by manipulating the A-value of the flow law. Therefore, the n and Q values are largely grain-size-insensitive, while the strength differences due to grain size and added-H2O can be expressed by varying the A-value. Further, the similarity in the n and Q values indicates that the same deformation mechanisms (i.e., dislocation creep accommodated by grain boundary processes) operate in both materials. Microstructural analysis of the novaculite reveals the development of a core-shell structure of individual grains due to grain boundary migration (GBM). A combination of deformation mechanisms (dislocation glide, GBM, GBS) are mutually dependent and interact to achieve the bulk sample strain. The variations in A-value may reflect the efficiency of the GBS mechanism depending on grain size and H2O content. Finally, the implications of these results on crustal strength will be discussed.

How to cite: Ghosh, S., Stünitz, H., Raimbourg, H., and Précigout, J.: Rheology and Deformation Processes of Fine-grained Quartz Aggregate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15832, https://doi.org/10.5194/egusphere-egu23-15832, 2023.

EGU23-16744 | Orals | TS1.5

Raman based crystallographic orientation mapping with qRICO: first applications for geological materials characterisation 

Jacob Bowen, Mario Heinig, Peter Reischig, Florian Bachmann, Oleksii Ilchenko, Yuriy Pilgun, and Olivia Barbee

The relationship between Raman peak intensity and crystal orientation via knowledge of the: Raman tensor of a given vibrational mode, incident laser light and Raman scattered light polarisation vectors is well established. Thanks to Loudon’s work in 1964 the Raman tensor structure is known for all 32 crystal classes[1]. Many researchers have exploited this to determine Raman tensor coefficients to study the nature of semiconductor and covalently bonded materials e.g.[2,3] using polarised Raman microscopy with the aim to determine crystal orientation locally.

In 2019 Ilchenko et al. demonstrated the feasibility of quantitatively mapping crystallographic orientation of polycrystalline materials in 2D, and in 3D exploiting the confocal nature of a Raman microscope[4]. The novelty of this work overcomes the need to serially collect Raman spectra at each map pixel for multiple combinations incident and scattered polarization needed to compute the local crystal orientation. A new generation of this technology, quantitative Raman imaging of crystallographic orientation (qRICO), rapidly collects Raman spectra of up to 20 combinations of incident and scattered polarization in a simultaneous manner.

Development work using ideal semiconductor materials has demonstrated that qRICO delivers the ability to produce crystallographic images of sample microstructures with sample stage step / pixel sizes down to 0.5 µm, contiguous scanning areas on the order of 10 x 10 cm and crystal orientation accuracy better than 2°. Thus, qRICO provides access to a very wide range of the microstructure length scales seen in geological materials and is amenable to typical geological specimen dimensions and shapes. Fundamentally qRICO is not limited to polished planar sample surfaces and is not restricted to surface studies for transparent materials.

In this work, in addition to non-natural polycrystalline materials, we will present high resolution as well as large area map examples of orientation mapping results on natural diamonds containing defect structures, polycrystalline quartz particles and multiphase petrographic thin slices. These examples will be used to illustrate the potential of qRICO for understanding geological materials in terms of grain boundaries, phase boundaries, orientation gradients, and crystallographic orientations and texture in relation to the conventional information contained in the underlying Raman spectra such as chemical gradients and internal stress.

[1]  R. Loudon, The Raman effect in crystals, Adv. Phys. 13 (1964) 423–482. https://doi.org/10.1080/00018736400101051.
[2]  C. Kranert, C. Sturm, R. Schmidt-Grund, M. Grundmann, Raman tensor elements of β-Ga2O3, Sci. Rep. 6 (2016) 35964. https://doi.org/10.1038/srep35964.
[3]  X. Zhong, A. Loges, V. Roddatis, T. John, Measurement of crystallographic orientation of quartz crystal using Raman spectroscopy: application to entrapped inclusions, Contrib. Mineral. Petrol. 176 (2021) 89. https://doi.org/10.1007/s00410-021-01845-x.
[4] O. Ilchenko, Y. Pilgun, A. Kutsyk, F. Bachmann, R. Slipets, M. Todeschini, P.O. Okeyo, H.F. Poulsen, A. Boisen, Fast and quantitative 2D and 3D orientation mapping using Raman microscopy, Nat. Commun. 10 (2019) 5555. https://doi.org/10.1038/s41467-019-13504-8.

How to cite: Bowen, J., Heinig, M., Reischig, P., Bachmann, F., Ilchenko, O., Pilgun, Y., and Barbee, O.: Raman based crystallographic orientation mapping with qRICO: first applications for geological materials characterisation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16744, https://doi.org/10.5194/egusphere-egu23-16744, 2023.

EGU23-17008 | ECS | Orals | TS1.5

Grain growth of polycrystalline ice doped with soluble impurities 

Qinyu Wang, Sheng Fan, and Chao Qi

The grain size of polycrystalline ice affects key parameters related to planetary evolution such as the rheological and dielectric properties of Earth's glaciers and ice sheets as well as the ice shells of ice satellites. Although past experiments have studied the grain growth of pure water ice as well as polycrystalline ice doped with air bubbles and insoluble particles, the effect of soluble ions, such as Cl- and SO42-, which are commonly found in glaciers, on the growth of polycrystalline ice is not clear. To investigate the effect of soluble impurities on the grain growth kinetics of polycrystalline ice, we conducted annealing experiments on polycrystalline ice samples doped with different concentrations of KCl (10-2, 10-3, 10-4, 10-5 mol/L) and MgSO4 (10-2, 10-5 mol/L), respectively. Ice powders were obtained by spraying a fine mist of solution (ultra-pure water + KCl or MgSO4) into liquid nitrogen. The powders were then dried and uniaxially pressed into a cylinder at 30 MPa and -30°C and then hydrostatically pressed into a cylindrical ice sample at 100 MPa and -30°C for 15 min. The samples were annealed for a maximum of 320 h at a hydrostatic pressure of 20 MPa (corresponding to about 2 km glacier depth) and different constant temperatures (-5, -10, -15, -20, -25°C). After each experiment, we took microscopic images of the polished sample surface using an optical microscope equipped with a cold stage. Machine learning methods combined with human quality check were utilized on the images to distinguish the grain boundaries. Then a grain size was measured as the average equivalent grain diameter with a geometry factor applied. For KCl, at -5°C (the eutectic point of KCl solution is -10.7°C), lowest-concentration-doped ice (10-5 mol/L) grew slightly faster than higher-concentration-doped ice (10-2, 10-3, 10-4 mol/L), and both are faster than pure ice; at -10°C and -15°C, there was no significant difference between the growth rates of both doped ice with different concentrations and pure ice; while at -20°C and -25°C (well below the eutectic point of ice and KCl), the growth rates of higher-concentration-doped ice (10-2, 10-3 mol/L) were slower than those of pure ice and lower-concentration-doped ice (10-4, 10-5 mol/L), which are similar to each other. For MgSO4, at -5°C (the eutectic point of MgSO4 solution is -3.6°C), the growth rates of doped ice with different concentrations are not significantly different from that of pure ice; while at -10°C and lower temperatures, the growth rates of doped ice are slower than that of pure ice. We propose that at temperatures well above the eutectic point, grain growth may be largely influenced by partial melts and temperatures well below the eutectic point, soluble impurities impede grain growth. These results help quantifying the contribution of different creep mechanisms, grain-size sensitive and insensitive, under natural conditions and will contribute to future estimation of the rheological strength of glaciers and ice shells.

How to cite: Wang, Q., Fan, S., and Qi, C.: Grain growth of polycrystalline ice doped with soluble impurities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17008, https://doi.org/10.5194/egusphere-egu23-17008, 2023.

Junggar Basin, located in the northern Xinjiang, is one of the most important oil and gas bearing sedimentary basins in China. Zhong-4 Block, located in Fukang Sag at the southern edge of the basin, is rich in oil and gas resources but low in exploration. Strike slip faults in the study area play an important role in controlling the distribution of oil and gas. Based on seismic and logging data, the static characteristics of strike slip faults are determined, the formation mechanism of strike slip faults is clarified, and the relationship between strike slip faults and oil and gas distribution is clarified. The results show that: (1) North east trending R-type shear fault, northwest trending P-type shear fault and north-south trending T-type extension fracture fault are developed in Zhong-4 block. The cross section of the strike slip fault is steep, with flower like structure, and obvious dolphin effect and ribbon effect can be seen; On the plane, it is characterized by segmented development, consisting of oblique overlapping segment, linear segment and braided structure segment; (2) The faults in Zhong4 Block are generally strike slip faults formed under the single shear mechanism consisting of NWW, NE and NS directions. According to the comprehensive geometric and kinematic characteristics, the fault zone in the work area mainly follows the rightward Riedel single shear mode. The included angle between R shear fault, P shear fault and main fault is mostly 15 °~25 °, which is widely developed in the work area. There are two stages of strike slip activities in the study area. The first stage is left strike slip in the west of Dong 6 well area in the early Jurassic, and the second stage is right strike slip in the whole study area in the late Jurassic; (3) The fault block traps developed in the strike slip fault oblique overlap zone are the main places for oil and gas enrichment in the study area, while the vertical sealing of the fault controls the oil and gas enrichment horizon. When the normal stress of the section is large and the vertical sealing of the fault is strong, oil and gas are enriched in the deep Sangonghe Formation; When the vertical sealing of the fault is poor, oil and gas are distributed in deep Sangonghe Formation and shallow Toutunhe Formation.

How to cite: xiulin, L. and youlu, J.: Characteristics of Jurassic Strike-slip Faults in Block 4 in Junggar Basin and Their Relationship with Hydrocarbon Distribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1023, https://doi.org/10.5194/egusphere-egu23-1023, 2023.

EGU23-1686 | ECS | Orals | TS1.7

Upper Miocene to Present fault architecture and fluid pathways in the Val d’Agri basin (Southern Italy) 

Giulia Schirripa Spagnolo, Fabrizio Agosta, Luca Aldega, Andrea Billi, Stefano Bernasconi, Giacomo Prosser, Luca Smeraglia, and Eugenio Carminati

Structural analysis coupled with geochemical study of syn-tectonic mineralizations unraveled the role of fluids during the polyphase tectonic evolution of the Val D’Agri, a seismically-active intermontane basin located in the Southern Apennines fold and thrust belt, hosting the largest onshore oil field in western Europe. In this basin, the structural control on present-day fluid circulation is still not well constrained. For this reason, the aim of this work is to reconstruct the Val d’Agri fault system (VAF) architecture and paleo-fluid circulation during the basin tectonic evolution. The VAF evolution was caused by non-coaxial polyphase stress regimes that can be summarized in: 1) Upper Miocene-Lower Pliocene compressional regime; 2) Upper Pliocene-Lower Pleistocene late orogenic strike-slip regime 3) Early Pleistocene-Present post-orogenic extensional regime. Based on new field work, mapping, and structural analysis, we recognized that the VAF is organized in different oriented faults sets. The main sets are N-S-, NE-SW-, and ESE-WNW-striking faults, where the last one has the higher degree of maturity. U-Pb dating of calcite slickenfibres highlighted the long-term tectonic history of these fault sets, with episodes of activation and reactivation of inherited faults. In particular, we recognize: N-S-striking normal faults that reactivated inherited Upper Miocene-Lower Pliocene thrusts; Upper Pleistocene NE-SW-striking normal-lateral faults; one Miocene ESE-WNW-striking normal-lateral fault, with also evidence of reactivation in more recent time. Clumped isotopes analysis together with optical and cathodoluminescence observations of about 50 syn-tectonic calcite mineralizations allowed us to link specific fluid pathways to the different stress regimes. Indeed, bed-parallel veins and mineralizations sampled along transpressive, transtensive, and normal fault sets show that: 1) during the Upper Miocene-Lower Pliocene compressive tectonic phase, fluid circulation occurred in a closed system, characterized by host-rock buffered fluids; 2) during Upper Pliocene-Lower Pleistocene late orogenic phase, fluid circulation occurred in an open system, characterized by meteoric water with low to moderate residence time; 3) during the Lower Pleistocene-Present extensional phase, fluid circulation occurred in an open system, characterized by the mixing of meteoric water and uprising deep high temperature fluids. We highlight that the reconstruction of paleo to present-day fluid circulation is a valid tool for assessing natural and induced seismic hazard in seismically active areas where hydrocarbons are exploited and fluids are injected into the crust, such as in the Val d'Agri basin.

How to cite: Schirripa Spagnolo, G., Agosta, F., Aldega, L., Billi, A., Bernasconi, S., Prosser, G., Smeraglia, L., and Carminati, E.: Upper Miocene to Present fault architecture and fluid pathways in the Val d’Agri basin (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1686, https://doi.org/10.5194/egusphere-egu23-1686, 2023.

EGU23-1798 | Orals | TS1.7 | Arne Richter Award for Outstanding Early Career Scientists Lecture

Episodic delocalization in the upper crust: Implications for earthquake forecasting 

Jessica McBeck, Francois Renard, and Yehuda Ben-Zion

The progressive localization of deformation has long been recognized as a fundamental phenomenon of the macroscopic failure of rocks. Our recent analyses using X-ray tomography during triaxial compression indicate that fractures and higher magnitudes of shear and dilative strain spatially localize as rocks are driven closer to macroscopic failure. Similarly, geophysical observations of low magnitude seismicity in southern and Baja California show that deformation localizes toward the future rupture plane of M>7 earthquakes. These sets of observations indicate that deformation can increase in localization toward failure, and that deformation can temporarily decrease in localization (delocalize) during this overall increase. These observations indicate that the spatial organization of deformation may be used to recognize the acceleration of the precursory phase leading to large earthquakes and the macroscopic, system-scale failure of heterogeneous materials. However, such efforts will require identifying the conditions that promote phases of delocalization, and how these perturbations in the overall trend of increasing localization influence the timing of macroscopic failure. In this presentation, I will describe these analyses, and new work that aims to identify which characteristics of the fracture networks determine the localization at a particular level of stress, and the change in localization from one stress step to the next in triaxial compression experiments at the confining stress conditions of the upper crust.

How to cite: McBeck, J., Renard, F., and Ben-Zion, Y.: Episodic delocalization in the upper crust: Implications for earthquake forecasting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1798, https://doi.org/10.5194/egusphere-egu23-1798, 2023.

EGU23-4374 | ECS | Orals | TS1.7

Python toolbox for fracture stratigraphy quantification and mechanical interface characterization 

Paul Joseph Fimbiyaha Namongo Soro, Juliette Lamarche, Sophie Viseur, Fateh Messaadi, and Pascal Richard

Modelling Discrete Fracture Networks (DFN) in naturally fractured reservoir (NFR) implies identifying and understanding the fracture spatial distribution and relationships to stratigraphic interfaces (crosscutting or abutment) in 3D. However, capturing fracture geometric parameters in the subsurface has always been a challenging task. To palliate the lack of data, and to better constrain modelling inputs, outcrop analogs are often used. While Simonson (1978) showed that mechanical contrasts at bed interfaces are essential to control fracture abutment, Cooke (2006) showed that bed/inter-bed thickness ratio is also an important parameter to account for.

Our goal is to predict fracture network geometry in stratified sedimentary rocks. To this purpose, we present a new original python toolbox. We performed an integrated approach that quantifies and automatically computes the bed interface’s compliance to let fractures go through (or not). Accounting for abutment, cross-cutting relations and bed thickness data, a compliance value is calculated for each interface using 1D scanline or 2D outcrop photograph. The process comprises (1) a field survey data or a digitized image (stratigraphy and fracture pattern) and (2) the processing of the data. First, we applied the method to existing classification and quantification from other authors as case study to check the feasibility of the code. Second, we applied the method to naturally fractured and stratified carbonates located in SE France and Centre Albania.

How to cite: Namongo Soro, P. J. F., Lamarche, J., Viseur, S., Messaadi, F., and Richard, P.: Python toolbox for fracture stratigraphy quantification and mechanical interface characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4374, https://doi.org/10.5194/egusphere-egu23-4374, 2023.

Modern concepts of fault strength account for compositional and hence rheological heterogeneity of natural fault zones. An important implication of heterogeneity is strain partitioning between stronger and weaker phases and a gradual transition from brittle to ductile deformation. While a broader brittle-ductile transition zone is consistent with deformation fabrics in fault zones, it remains uncertain how broad the transition zone is and whether deformation fabrics record truly simultaneous brittle-ductile deformation or successions of brittle and ductile deformation driven by temporal changes in temperature, strain rate, and/or pore fluid pressure. Here we present data from a major fault zone of the Permo-Triassic Khao-Khwang fold-and-thrust belt, Thailand. The fault zone is located in marine calcareous shales with Permian limestones in the foot- and hanging wall. Thrusting occurred at peak temperatures of ~200°C. Deformation fabrics document frictional sliding, cataclasis, mineral veining, and pressure solution in the main fault zone and local mylonitization at the base of the hanging wall limestone. Thus, the fault zone records competing brittle and ductile deformation and incipient strain partitioning between the shales and limestones, consistent with a broad brittle-ductile transition zones due to rheological heterogeneity. Radiogenic strontium isotope ratios (87Sr/86Sr) of syntectonic vein carbonates and calc-mylonites, tell, however, a slightly different story. Vein carbonates from the fault zone all have Permian seawater-like 87Sr/86Sr ratios documenting a rock-buffered pore fluid during brittle deformation. By comparison, the calc-mylonites record less radiogenic 87Sr/86Sr ratios hinting at a mantle source. The Sr ratios are similar to those of syntectonic mafic dykes that intruded Khao-Khwang fold-and-thrust belt. We interpret the distinct Sr ratios of the calc-mylonite to document that mylonitization was triggered by migration of hot magmatic fluids. In this case, strain partitioning between the shales and limestone were likely insignificant without the impact of the hot fluids, although the limestones were already close to the brittle-ductile transition at ambient temperatures of ~200°C. Taken together, our findings suggest that the transition from frictional deformation and pressure solution in shales to ductile shearing in limestones might be rather abrupt than gradual.

How to cite: von Hagke, C., Dielforder, A., Glodny, J., and Morley, C. K.: Is mixed brittle-ductile deformation simultaneous or successive? Insights from the strontium isotope systematics of deformation structures in a heterogenous fault zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4874, https://doi.org/10.5194/egusphere-egu23-4874, 2023.

EGU23-4909 | ECS | Posters on site | TS1.7

The usage of open-source aerial images for the characterisation of a fracture network. Insights from a multi-scale approach in the Zagros Mts. 

Marco Mercuri, Stefano Tavani, Luca Aldega, Fabio Trippetta, Sabina Bigi, and Eugenio Carminati

The characterisation of the fracture network is a fundamental step for modelling the circulation of different types of geofluids at multiple scales, including at the reservoir scale. Due to the difficulty of sampling the fracture network with a spatial continuity, fracture networks are often derived from a stochastic approach applied to ground truth parametrized datasets. Classical field methods for collecting and analysing fracture data sets (i.e., scan-lines or scan-areas) have limited sample area and the results might be affected by local factors (e.g., facies variations and faults). In poorly- to non-vegetated regions, field-derived data can be integrated with satellite and aerial images providing a “big-picture” of the study area. The availability of open-source, high-resolution aerial and satellite images (e.g., Google Maps, Bing Maps) coupled with the development of specific software and tools (e.g., NetworkGT; FracPaQ) allow to digitize and analyse very large and spatially continuous data sets of fractures at multiple scales for a single case study.

In this work, we test the use of Bing Maps imagery for the analysis of the fracture network affecting the Kuh-e-Asmari anticline, in the Zagros fold-and-thrust belt. The Kuh-e-Asmari anticline is considered as an outcropping analogue of fractured reservoirs and is in a scarcely vegetated area, covered by high resolution open-source aerial images (~2.6 m/pixel). We obtained three different image-derived fracture data sets by manually digitizing the fracture network at three different scales (1:50000, 1:5000, and 1:500) in QGIS. Each data set has been analysed using the NetworkGT plugin within QGIS. In detail, we analysed the orientation, length distribution, abundance, and topology of each fracture network data set, and we have compared the results with structural data from scan-lines performed in the field on the same anticline.

Results proved to be scale-dependent, with each scale having its pros and cons, as follows. The 1:50000 data set is the only spatially continuous data set, allows to rapidly map the main tectonic features (e.g., major faults and fracture corridors) but it is not accurate enough in terms of the definition of orientation sets and length analyses. The 1:5000 data set is potentially spatially continuous and allows to analyse fracture and connectivity distributions with high detail, by highlighting strongly fractured/connected elongated zones, possibly representing damage zones of known, previously mapped, fault strands. The 1:500 scale cannot guarantee the spatial continuity of the data set but, if applied to a small area, provide reliable results.

Results obtained in this work suggest that the manual interpretation of open-source aerial images is a viable way for the characterization of fracture networks in poorly vegetated areas only if the right scale is chosen. For the case study presented here we suggest interpreting the fracture network at 1:5000 or similar scales. A successful testing of semi-automatic or automatic algorithms for lineament detection is required to perform a spatially continuous interpretation and analysis at the highest possible resolution, and/or to analyse the fracture dataset at multiple scales (more than the 3 investigated here).

How to cite: Mercuri, M., Tavani, S., Aldega, L., Trippetta, F., Bigi, S., and Carminati, E.: The usage of open-source aerial images for the characterisation of a fracture network. Insights from a multi-scale approach in the Zagros Mts., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4909, https://doi.org/10.5194/egusphere-egu23-4909, 2023.

EGU23-5184 | Orals | TS1.7

Internal architecture of the frontal part of subduction accretionary prism: the role of folding in brittle diffuse deformation 

Francesca Remitti, Andrea Festa, Giuseppe Nirta, Edoardo Barbero, and Silvia Mittempergher

Studies of the shallow part (Tmax< 150°C) of ancient and active prisms documents that ductile (e.g., folds), brittle and localized (e.g., faults) deformation, and diffuse deformation (e.g. scaly fabric), likely contemporaneous at the scale of geological time, may occur in the same outcrop. Moreover, the source areas of precisely located shallow slow earthquakes (downdip locating the transition from brittle to ductile deformation) span a range of depths from <1 to ~15 km below the seafloor, overlapping the temperature range of megathrust earthquake rupture in some convergent margins (e.g. Nankai and Japan Trench), and propagating up to the seafloor in other ones (e.g. Costa Rica). This implies that the shallow part of the accretionary prisms cannot be uniquely defined as characterized by ductile/brittle behavior or as prone to localization or de-localization of deformation.

To better understand how deformation affects the frontal part of accretionary prisms, the general architecture and internal structure of the frontal part of accretionary prisms need to be considered.  Field evidence of the deformational structures occurring in the frontal part of active and ancient accretionary prisms from the mesoscale to the regional scale suggests that recumbent and isoclinal folding are frequent in the shallow part of accretionary prisms, developing in pre-lithification to poorly metamorphosed rocks. In this framework, diffuse scaly fabric and pervasive boudinage, traditionally considered as evidence of shear delocalization, could be alternatively seen as the result of the progressive deformation envisioned in literature for the formation of recumbent folds i.e.: buckling with the development of an overturned fold limb and subsequent kinematic amplification by coaxial strain components with vertical maximum shortening. However, the plethora of brittle structures accommodating the change in shape on the hinge and limbs of the folds, have a different distribution in space and accommodate a different strain than brittle fracture associated with faults and/or thick shear zone. Therefore, this interpretation has implications in terms of the distribution in space of brittle structures and in the distribution of shear strain in the frontal part of subduction zones.

How to cite: Remitti, F., Festa, A., Nirta, G., Barbero, E., and Mittempergher, S.: Internal architecture of the frontal part of subduction accretionary prism: the role of folding in brittle diffuse deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5184, https://doi.org/10.5194/egusphere-egu23-5184, 2023.

EGU23-5306 | Posters on site | TS1.7

Deformation pattern, paleostress, and paleofluid evolution in the Pag anticline, External Dinarides of Croatia 

Alessio Lucca, Silvia Mittempergher, Andrea Succo, Andrea Bistacchi, Marco Meda, and Fabrizio Storti

The NW-SE striking Pag anticline, in the External Dinarides fold and thrust belt, provides an appropriate field site for studying fold- and fault-related deformation patterns at different scales in a transpressional setting due to outstanding exposures. We performed a multiscale structural analysis together with petrographic and isotopic characterization of syntectonic calcite cements. Results indicate that the Pag anticline, is a box fold developed mainly by detachment folding in response to NE-SW oriented compression. Depth-to-detachment calculation indicates that the basal thrust of the anticline is located in the Upper Jurassic evaporitic complex, at a depth of about 2.5 km. The geometry of the fold is strongly controlled by the interaction and overstepping of a major thrust-backthrust fault pair. In the northern sector, backthrust activity produced a northeastern facing, steeply dipping to near vertical backlimb. Moving southward, the forelimb gradually becomes vertical to overturned and fold asymmetry switches to a southwestward facing. Late- to post-folding tightening resulted in non-cylindrical and compartmentalized deformation by near vertical N-S right-lateral, and E-W, left-lateral, strike-slip faults trending oblique to the fold axis. These fault sets make a wider angle than expected for transversal conjugate strike-slip faults commonly associated with folding, possibly due to lateral propagation from inherited, folded soft-sediment extensional faults. Paleostress analysis indicates that the evolution of the Pag anticline occurred in a stress field that switched from contractional to transpressional configuration, maintaining a N40-50° oriented major stress axis. Petrographic and isotopic data support infiltration of meteoric fluids into exposed carbonates in the pre-folding stage, followed by mixing with marine fluids during folding at shallow burial conditions and, eventually, meteoric fluid circulation along strike-slip faults in the late to post-folding stage. Stable isotope ratios suggest that fluid flow evolved from a bedset confined system to an open one in the late to post-folding stage. As such, a major role to control paleofluid flow is played by the transversal sets of low-displacement near orthogonal strike-slip faults. This suggests that, in reservoir structural characterization, particular attention should be paid to the presence of low-displacement strike-slip faults because of their role to enhance fluid flow mixing and channeling. The presence and, particularly, the abundance of such deformation features are difficult to constrain in buried fractured reservoirs by seismic reflection imaging because of low displacement values. We, consequently, stress the importance of studying field analogues by multidisciplinary approaches for better understanding the relationships between folding, faulting, the associated incremental deformation patterns, and the impact on fluid flow.

How to cite: Lucca, A., Mittempergher, S., Succo, A., Bistacchi, A., Meda, M., and Storti, F.: Deformation pattern, paleostress, and paleofluid evolution in the Pag anticline, External Dinarides of Croatia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5306, https://doi.org/10.5194/egusphere-egu23-5306, 2023.

EGU23-5630 | ECS | Orals | TS1.7

The role of pressure solution in the evolving fracture stratigraphy properties of Mesozoic platform carbonates 

Canio Manniello, Simona Todaro, Ian Abdallah, Giacomo Prosser, and Fabrizio Agosta

The study carbonates are exposed in the axial zone of the southern Apennines ftb, Italy. These rocks form a natural laboratory to investigate the time-dependent variation of primary heterogeneities and both dimensional properties and distribution of high-angle joints, veins, and shear fractures. We integrate field-based stratigraphic and structural analyses of the platform carbonates with both petrographic and microstructural investigations of selected specimens to unravel their depositional setting and diagenetic evolution. Furthermore, we focused on the modalities of pressure solution-assisted deformation of bed interfaces and single beds to investigate their possible control on the geometry, distribution, and relative timing of the high-angle fractures. The platform carbonate succession includes a Pliensbachian in age, well-layered, lagoonal carbonate unit including both mud-and grain-supported limestone beds, and a Toarcian in age oolithic carbonate unit. Our results showed that pressure solution mainly localized within bed-parallel interfaces and within the grain-supported limestone beds. During early-to-burial diagenesis, precipitation of calcite rims and blocky calcite cements predominantly occurred in the latter beds, in which ghosts of meniscus cements associated to the earliest diagenetic stages are documented. The fracture intensity (P10) computed for the earliest high-angle fracture set shows the highest values in correspondence of the grain-supported beds. During the Oligo-Miocene Apennine orogeny, the mechanical layering of the carbonates evolved due to flexural slip of the layered carbonates, and formation of intra-carbonates thrust faults with flat-ramp-flat geometries were documented. Specifically, there formed s-c-c’ tectonites along the primary interfaces juxtaposing the single bed packages, and oblique-to-bedding reverse faults offsetting the single beds developed due to pressure-solution assisted deformation.The Plio-Quaternary transtension dissected the platform carbonates, and caused both their uplift and exhumation from shallow crustal depths. By computing the fracture density (P20) and intensity (P21) associated to transtension, the highest values were calculated within the coarser grained carbonate beds. Independently from their thickness, these carbonate beds are the most fractured ones in the study succession. These results hence showed that the platform carbonates acquired the mechanical properties during early-to-burial diagenesis, that later permitted strain clustering within the stiffer, grains-supported beds. We invoke that chemical/physical compaction and diffuse cementation of these carbonate beds were responsible for the Plio-Quaternary fracture distribution throughout the platform carbonates. Moreover, we also documented similar P20 and P21 variations, which are consistent with the profound control exerted by primary mechanical interfaces on vertical growth of transtensional fractures. Indeed, we interpreted the similar P20 and P21 variations as a result of shear stress localization along per-existing, stratabound fractures, which ruptured these interfaces forming small-scale process zones (high P20 values) at their extensional quadrants (high P21 values). Ongoing petrophysical analysis will shed lights on the dimension, distribution, and overall connectivity of the pore system aiming at assessing the overall control exerted by bed-parallel stylolites and pressure solution seams on the efficiency of the mechanical interfaces abutting the stratabound transional fractures.

How to cite: Manniello, C., Todaro, S., Abdallah, I., Prosser, G., and Agosta, F.: The role of pressure solution in the evolving fracture stratigraphy properties of Mesozoic platform carbonates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5630, https://doi.org/10.5194/egusphere-egu23-5630, 2023.

EGU23-6476 | ECS | Orals | TS1.7

Fluid-rock chemical-physical equilibrium/disequilibrium inferred from tectonic carbonates in the Apennines (Italy): an advanced approach to track seismic cycles and earthquakes 

Manuel Curzi, Luca Aldega, Andrea Billi, Chiara Boschi, Eugenio Carminati, Gianluca Vignaroli, Giulio Viola, and Stefano Bernasconi

Geofluids play an important role to seismic faulting both at hypocentral depth during earthquake nucleation and at shallower crustal levels during seismic rupture propagation. Pre- to co-seismic anomalies of crustal fluid circulation have thus far been identified by hydrogeochemical and seismological (Vp/Vs) monitoring and are generally interpreted as potential precursors, triggers, and/or facilitators of large magnitude earthquakes. Structural and geochemical studies on syn-tectonic mineralizations have highlighted different patterns of fluid ingress, circulation and fluid-rock interaction during the seismic cycle of thrusts and normal faults. Understanding fault rock-fluid relationships in exhumed faults is useful for revealing the role of fluids also in still ongoing seismic cycles from different tectonic settings. We present a review of published studies and original data on the chemical-physical characteristics of syn-tectonic mineralizations formed by fluids that assisted fault-related deformation in the Apennines (Italy). We use our data to build a general model of fluid circulation during thrusting and normal faulting during the seismic cycle, and define a multi-technique workflow to identify tectonic-related physical/chemical equilibria/disequilibria in fluid-rock systems. The proposed workflow relies upon multiscale structural analysis, stable C, O, and clumped isotope analysis, radiometric dating and burial-thermal modeling. The chosen study area is the Central Apennines fold-and-thrust belt, where post-orogenic extensional deformation, characterized by numerous Mw ≥ 6.5 earthquakes, currently overprints Neogene-Quaternary folds and thrusts. We show that thrusting mostly develops in closed fluid systems where fluid and host rock are close to chemical equilibrium. Subsequent normal faulting is characterized by a dominant upward and/or downward open fluid circulation system with an overall range of δ18O of paleofluids from -10‰ to +13.5‰ (V-SMOW). Isotopic and thermal fluid-rock disequilibria are particularly evident during pre-/ and co-seismic extensional deformation with mineralizations that are up to 30° C warmer and 16° C colder than the host rock and are associated with the ingress of exotic (meteoric or deep crustal) fluids.

How to cite: Curzi, M., Aldega, L., Billi, A., Boschi, C., Carminati, E., Vignaroli, G., Viola, G., and Bernasconi, S.: Fluid-rock chemical-physical equilibrium/disequilibrium inferred from tectonic carbonates in the Apennines (Italy): an advanced approach to track seismic cycles and earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6476, https://doi.org/10.5194/egusphere-egu23-6476, 2023.

EGU23-6717 | Orals | TS1.7

The growth of fault damage zones; field data and analogue modelling 

Roger Soliva, Sylvain Mayolle, Stéphane Dominguez, and Christopher Wibberley

The study of faults in the upper crust has generated interests in modelling their impact on fluid flow and the mechanical behavior of the earth's crust. Fault damage zones are important structures with multiple implications for resource management and earthquake studies. This work aims to characterize the distribution and growth of damage around faults, and to study its impact on the Displacement - Damage thickness (D-T) scaling law. Two complementary approaches of field analyses and analog modelling of normal faults are developed to answer this question. We presents new results of fault damage mapping, D-T scaling in carbonate rocks and the first analog modelling experiments of fault damage zones inspected in-plane. The results show a heterogeneous and asymmetric distribution of damage around faults, mainly influenced by fault interactions during their growth (segmentation, conjugate faults). A D-T law specific to wall damage is established and shows a normal correlation between D and T for less than c. 100 m of fault displacement, and also confirms the existence of a damage thickness threshold after c. 100 m of displacement. To explain this law, we propose a damage zone growth model controlled by the interaction and coalescence of fault segments. Analogue modelling shows a failure mode transition during fault growth, from a segmented dilatational-shear mode to a localized compactional-shear mode. They also demonstrate that initiation of segmentation, segment activity selection, interaction and coalescence processes control the development of fault damage zones and the D-T law. Furthermore, the thickness of the faulted brittle layer is a main controlling parameter of segmentation, strain localization and the fault damage thickness threshold observed.

How to cite: Soliva, R., Mayolle, S., Dominguez, S., and Wibberley, C.: The growth of fault damage zones; field data and analogue modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6717, https://doi.org/10.5194/egusphere-egu23-6717, 2023.

EGU23-6753 | ECS | Orals | TS1.7

Fault damage zone growth in analog models: typology and segment selection process into fault corridors 

Sylvain Mayolle, Roger Soliva, Stéphane Dominguez, and Christopher Wibberley

A better understanding of stress perturbation around faults, strain propagation, and fluid flow in the upper crust require characterization of the evolution of fault damage zones. Numerous studies provide significant amounts of data and description from a broad variety of faults, however, fault damage evolution is not clearly understood.

In this study, we investigate experimentally damage zones dynamic evolution during normal faults population growth. With this aim, we used a sandbox type device and multilayered analog model, monitored by high-resolution cameras. Several types of damage zones are evidenced and we performed an accurate description of their growth from initiation to mature damage. New damage types including conjugate link damage and graben damage are described for the first time and show similarities with observations in nature. We highlight the new concept of “fault system damage” as the increase of deformation and secondary fault density by the interaction of major faults. We also show that fault damage zones grow by segment linkage into corridors of fault segments formed in the first stages of model deformation. Based on these observations, we propose and discuss the new concept of “segment selection in corridors” as the process of the onset of fault maturation and their damage zone development.

How to cite: Mayolle, S., Soliva, R., Dominguez, S., and Wibberley, C.: Fault damage zone growth in analog models: typology and segment selection process into fault corridors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6753, https://doi.org/10.5194/egusphere-egu23-6753, 2023.

Hydrothermal veins can form when pre-existing anisotropy gets dilated by increase in fluid pressure (Pf). In addition fluctuation in Pf can result in the deposition of economically important deposits, such as gold in veins. Therefore, statistical analysis of dilational quartz veins can help to identify the mineralization potential of an area. This present study is focused on this aspect. The metavolcanic rocks of Dharwar Craton (Southern India) are replete with quartz veins, but mineralization is restricted to certain domains in the vicinity of Gadag, Hutti, and Kolar. To study the topological importance in mineral exploration, an experiment is carried out in different parts (e.g., Gadag, Hutti, Raichur, Gadwal) of Dharwar Craton. Orientation of dilational quartz veins, thickness, and spacing data are collected from different transects of the above-mentioned areas. Variations in driving pressure ratio (ΔRʹ), fractal dimension (Dc), Weibull modulus (α), vein intensity (Vi), and coefficient of vein spacing (Cv(S)) are calculated from vein data of each transect. These parameters are integrated to plot a three-axes “mineralization potential plot”, also known as P-D-F plot (Lahiri et al., 2020). The distance between the origin (0,0,0) and the point representing the transect in the P-D-F plot gives the “mineralization potential parameter” (Md). It is established that a transect in mineralized zone is represented by a point that lies closer to origin than non-mineralized zone. However, it is our observation that the points representing mineralized zone show more clustering on the P-D-F plot, whereas the points representing non-mineralized zone are dispersed.  We infer that in order to identify a zone as having high mineralization potential, the Md value should not only be lower but also the clustering should be higher.

How to cite: Biswas, S. and Mamtani, M. A.: Mineralization potential from vein statistics at regional scale – an example from the Dharwar Craton (Southern India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7033, https://doi.org/10.5194/egusphere-egu23-7033, 2023.

EGU23-7298 | ECS | Posters on site | TS1.7

New constraints from structural data and U-Pb calcite geochronology on La Collada fluorspar ore body (Asturian basin, NW Spain) 

Pablo Granado, Jonas B. Ruh, Marcel Guillong, and Luis Rodríguez-Terente

The Permian–Mesozoic Asturian (NW Spain) hosts a series of world-class fluorspar deposits - a critical raw material for the EU - with more than 15 Mt. extracted to date. Asturian fluorspar deposits are hosted in silicified Paleozoic and Triassic carbonate rocks, spatially associated with the fault-bound margins of the basin. The Asturian fluorspar deposits show an important structural and lithological control, being hosted in fault-fill veins, jogs and breccias associated with steeply-dipping extensional faults and related folds, and strata-bound bodies replacing carbonate rocks. The general paragenesis comprises fluorite, calcite, quartz, (±) barite, and minor sulfides including pyrite, sphalerite, chalcopyrite, (±) galena. Formation of these fluorspar deposits has been assigned to the Permian volcanic activity during the extensional event following the Variscan orogeny, or the Mesozoic opening of the Atlantic realm.

For this study, we have sampled and measured the orientation of the main ore body at La Collada underground works. The ore body is hosted in a fault-fill vein moderately dipping to the SSW (mean plane is 214/47; n=41), ranging in thickness from a few meters to 15m. Observed sub-vertical veins of calcite are kinematically compatible with the main SSW-dipping fault-fill vein, and suggest concomitant ore deposition and extensional faulting. Laminated textures and localized high-dilation breccias in the main fault-fill vein suggests multi episodic fault activity associated with fluid overpressures (fault-valving?). S/C structures and fault slickensides (n=6) indicate oblique right lateral reactivation. Three representative samples from the main fault-fill vein were taken for U–Pb dating by LA-ICP-MS. Calcite spot analysis yielded two age populations (155Ma, 131Ma.) thus suggesting multiepisodic precipitation of calcite, and a potential open system. Obtained radiometric ages are consistent with rift initiation in the Asturian basin, and opening of the Bay of Biscay since Upper Jurassic times. Coupled with structural geology and textural analysis, LA-ICP-MS U-Pb dating of hydrothermal calcite aids in constraining the timing of fluid-flow events and fault activity responsible for ore deposit formation and re-mobilization, and refines the regional context of the Asturian fluorspar deposits.

How to cite: Granado, P., Ruh, J. B., Guillong, M., and Rodríguez-Terente, L.: New constraints from structural data and U-Pb calcite geochronology on La Collada fluorspar ore body (Asturian basin, NW Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7298, https://doi.org/10.5194/egusphere-egu23-7298, 2023.

Under diagenetic conditions between ca. 50 ℃ to 250 ℃ the systematics of cement precipitation and differential infill makes network porosity, and thus permeability and strength, scale and thermal history dependent. Using examples of regional opening-mode fractures in sandstones from the Cambrian Flathead Formation, Wyoming, a low-enthalpy geothermal outcrop analog, we show that quartz deposits preferentially fill fractures up to ca. 0.05 mm wide with a transition from mostly sealed to mostly open fractures over a narrow size range of opening displacements from 0.05 to 0.1 mm. Scale- and diagenesis- dependent connectivity can be described using use rule-based node descriptions to rapidly measure diagenesis sensitive connections within the context of current field practice.  In our example, although networks have trace connectivity, effective connectivity for fluid flow is greatly reduced by quartz cement. Near some faults, trace connectivity increases as initially wide porous fractures preferentially shear and wing cracks form, increasing fracture intersections (Y-nodes). However, pore space is lost due to the development of quartz-cemented microbreccia. Macro-scale trace connectivity increases, but porous connectivity diminishes and thus potential for fluid flow is markedly lower. We illustrate how diagenesis-sensitive contingent nodes can be used to extrapolate permeability estimates to locations having different thermal histories.

How to cite: Laubach, S. and Forstner, S.: Scale-dependent fracture patterns and flow in low-enthalpy geothermal targets: the role of diagenesis and contingent nodes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8776, https://doi.org/10.5194/egusphere-egu23-8776, 2023.

EGU23-8940 | Orals | TS1.7

Scaling, connectivity and correlation length of stylolite, fracture and fault networks 

Daniel Koehn, Daniel Hafermaas, Saskia Köhler, Jürgen Lang, Bakul Mathur, Rahul Prabhakaran, and Ruaridh Smith

Stylolite, fracture and fault networks are important fluid pathways, especially in low permeable rocks such as limestone and therefore important for subsurface applications including geothermal energy production. These systems grow in both time and space and have a given correlation length. Below the correlation length the system becomes saturated and shows a given scaling, for example in roughness for stylolites. Whereas above the correlation length the roughness or width of the growing system becomes constant. The position of this length varies with time and space whilst also being influenced by the system size. This becomes important when the systems connect, for example fractures that grow and merge together such that they have a given size. In this contribution we show with numerical simulations and natural examples how stylolite, fracture and fault networks scale in time and space, how their correlation length is evolving and how they become connected. We discuss the implications for scaling of larger networks as well as implications for deformation and fluid flow.

How to cite: Koehn, D., Hafermaas, D., Köhler, S., Lang, J., Mathur, B., Prabhakaran, R., and Smith, R.: Scaling, connectivity and correlation length of stylolite, fracture and fault networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8940, https://doi.org/10.5194/egusphere-egu23-8940, 2023.

EGU23-8991 | Posters on site | TS1.7

Modelling of Fragmentation Process in Deformation Bands and Faults 

Bakul Mathur, Daniel Koehn, and Ruaridh Smith

Fragmentation in deformation bands and faults is relatively complex with multiple fracture sets breaking single grains into anisotropic splinters. An understanding of the development of deformation bands and faults and the associated mechanical and permeability evolution is important for many applications including treatment of faults in reservoir models, flow properties of faults in geothermal systems and CCS (Carbon Capture and Storage), and seismic hazards. Various mathematical models have been developed to capture rock fragmentation process at single and multi-grain scale as well as to study the hydraulics in large scale geological discontinuities. However a multi-scale approach is needed to understand the implications of the changes in mechanical properties and permeability due to small scale rock fragmentation on the large scale bands, faults and fractures. This study aims to employ an extended Discrete Element Method (DEM) approach with multi-scale aggregates to model the evolution of deformation bands in porous sandstones.

Grain failure in rocks can be caused by different loading conditions, such as compressive loading, shear displacement, thermal, hydraulic or chemical effects. In this study, simulation of the comminution  process of the polyhedral shaped grains is achieved under compressive and shear loading. Single grain fragmentation is realised with the Mohr-Coulomb approach, which is a classical failure criterion for brittle particle systems. The failure criterion is combined with the Weibull statistical distribution that captures the grain size effect. A multiple grain model is simulated with DEM combined with the Mohr-Coulomb-Weibull concept. The computations are carried out with an open-source discrete numerical modelling framework YADE. The study sheds light on the influence of initial rock properties (porosity, grain size and shape) and deformation mechanism (compaction, shearing and combinations) on the development of deformation bands and faults.

How to cite: Mathur, B., Koehn, D., and Smith, R.: Modelling of Fragmentation Process in Deformation Bands and Faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8991, https://doi.org/10.5194/egusphere-egu23-8991, 2023.

EGU23-9301 | ECS | Orals | TS1.7

Rigid rotation of quartz grains in a low-porosity calcarenite: an indicator of early deformation?  

Maria Eleni Taxopoulou, Marine Lartigau, Charles Aubourg, Nicolas Beaudoin, Elli-Maria Charalampidou, and Jean-Paul Callot

Reservoir rocks, such as carbonates, are rapidly becoming key elements for the energy transition. The damage of these reservoir rocks when placed under a stress field must be characterized, to better predict storage capacity distribution. In the shallow subsurface, carbonate rocks accommodate the stress by developing structures at the mesoscale, such as fractures, deformation bands or stylolites, depending on porosity or fluid content. Those are localized, showing a finite damaged area, outside which the relative host rock can accommodate the applied stress in a different way, usually overlooked in low temperature and pressure conditions.

In this study, we highlight a new marker of accommodation of shortening, characterized by heterogeneous quartz grain rotation in non-porous carbonate matrix. The studied rock is an upper Cretaceous bioclastic calcarenite from the Cotiella Massif (Spain). This rock is composed of 85% carbonate (micrite and recrystallized microsparite), 10% quartz, and <5% of nanometric porosity. It hosts a fracture pattern including fractures, stylolites and deformation bands that correspond to different tectonic stages. However, we focus on investigating the quartz grain orientation in the grains outside the deformation bands, in both the far-field and near-field host rock. We investigated the fabric (typology, distribution and orientation) of thousands of quartz grains using X-ray microtomography on cylindrical cores of 8-26 mm diameter. Each segmented quartz grain is approximated with a best-fit ellipsoid whose major axis (L1) and minor axis (L3) give us information about the average orientation of the quartz grain. We show that the typology of the quartz grains, namely the size and average shape is similar in all our samples.

The average orientation of all quartz grains at the core scale reveals subtle preferences, without clear correlation to the orientation of neither the stylolites nor the deformation bands. We observe that in half of the samples studied, the quartz grain fabric is not controlled by the bedding. Instead, there are two distinct patterns of grain orientation, with the quartz grain fabric either reflecting the early burial stage or revealing a later reorientation perpendicular to one of the major shortening directions. These directions are either striking parallel to the local shortening flow (NE-SW) or to the regional orogenic flow (N-S), that is attributed to the Pyrenean orogeny. Evidence of dissolution-recrystallization are observed in quartz, but the diagenetic conditions constrainthis mechanism from being a robust hypothesis to explain the change of quartz fabric, but rather favour the rigid rotation of quartz in a micritic matrix. The examination of both the quartz grains and the carbonate matrix with EBSD suggests a local strain accumulation within the carbonates in the vicinity of quartz grains. Although the mechanisms causing this rotation need to be better understood, measuring the grain typology and orientation on a considerable number of grains with the aid of X-ray microtomography could result in a new method of deformation quantification in carbonate rocks.

How to cite: Taxopoulou, M. E., Lartigau, M., Aubourg, C., Beaudoin, N., Charalampidou, E.-M., and Callot, J.-P.: Rigid rotation of quartz grains in a low-porosity calcarenite: an indicator of early deformation? , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9301, https://doi.org/10.5194/egusphere-egu23-9301, 2023.

EGU23-9680 | Posters on site | TS1.7

Numerical and analytical modelling of bending-induced tensile fractures 

Martin Schöpfer, Bernhard Grasemann, and Ralph Hinsch

Although the origin of outer-arc extension fractures in folded sequences is well-understood and documented in many natural examples, geometric and geomechanical factors controlling their spacing are hitherto unexplored. This study investigates the formation of bending-induced tensile fractures during constant-curvature forced folding using two-dimensional Distinct Element Method (DEM) numerical modelling. The DEM model comprises a central brittle layer embedded within elastic layers; the layer interfaces are cohesionless. Folding of this three-layer system is enforced by a velocity boundary condition at the model base, while a constant overburden pressure is maintained at the model top.

The models illustrate several key stages of fracture array development: (i) Prior to the onset of fracture, the neutral surface is located midway between the layer boundaries, consistent with pure bending; (ii) Once the outer-fibre stress equals the tensile strength of the layer, fractures nucleate and propagate through the brittle layer; (iii) The rate of fracture formation as a function of curvature decreases nonlinearly, with new fractures developing approximately midway between two existing fractures; (iv) Eventually no new fractures form, irrespective of any further increase in fold curvature, a state referred to as fracture saturation.

On the basis of these numerical model results, an approximate analytical solution for fracture spacing based on classic beam theory is developed. The predicted range of fracture spacing as a function of fold curvature is in good agreement with the numerical model results. Importantly, the analytical solution reveals which geometric and geomechanical factors control fracture spacing, namely layer thickness, radius of curvature, Young’s modulus, tensile strength and confining pressure. The fracture spacing to layer thickness ratio at saturation however depends only (nonlinearly) on the ratio of tensile strength to overburden pressure.

The numerical model results are qualitatively compared with field observations at outcrops located in the Montpellier Fold region. The folded lithologies are of Jurassic age and comprise (brittle) limestones, with (ductile) marl intercalations. Fracture-bound limestone blocks located within the fold hinges and observed on the fold-profile plane are laterally bound by V-shaped veins that thin towards the fold core. In the inner-arc of each vein-bound limestone block, the marl interbed thickens towards the veins, whereas in the outer-arc it thins towards the veins. Clearly, the thickness distribution of the marl interbeds reflects non-uniform loading, which is consistent with the loading conditions hypothesised on the basis of the theoretical models.

How to cite: Schöpfer, M., Grasemann, B., and Hinsch, R.: Numerical and analytical modelling of bending-induced tensile fractures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9680, https://doi.org/10.5194/egusphere-egu23-9680, 2023.

EGU23-9789 | ECS | Posters on site | TS1.7

Structural investigations and U/Pb dating in the southern Paris basin do not record any Alpine deformation 

Stephen Brown, Yves Missenard, Philippe Robion, Laurent Beccaletto, Cécile Allanic, and Frédéric Haurine

Deformation of intraplate sedimentary basins essentially results from tectonic stresses that propagate from plate boundaries. Yet, the detailed characteristics of this far field propagation are often poorly constrained, especially in age. Recent developments of U/Pb dating of calcite precipitations in fault planes and veins hopefully greatly help to frame the schedule of deformation. This is the case for the Meso-Cenozoic Paris basin, liable to have recorded several Cenozoic events due to its location in the western Eurasian plate, like Pyrenean and Alpine collisions and Oligocene extension (ECRIS).

Our study focusses on the southern Paris basin area, north of the Morvan massif, where Alpine deformations are expected. Field data reveal almost exclusively strike-slip deformations with variable σ1 direction. These results are about to be confirmed at the microscopic scale using Anisotropy of Magnetic Susceptibility and of P-Wave Velocity methods. Associated U-Pb dating of synkinematic calcites from Jurassic strata indicates distributed Eocene deformation and an absence of Oligocene or Miocene ages. Such ages suggest the record of Pyrenean and possibly ECRIS tectonic events. Strikingly, Alpine deformation and especially stress propagation leading to the growth of the Jura fold-and-thrust belt during Miocene does not imprint the studied area although the Alpine orogen is located closer than the Pyrenean belt.

How to cite: Brown, S., Missenard, Y., Robion, P., Beccaletto, L., Allanic, C., and Haurine, F.: Structural investigations and U/Pb dating in the southern Paris basin do not record any Alpine deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9789, https://doi.org/10.5194/egusphere-egu23-9789, 2023.

Long-lived, mature faults can be architecturally complex. The in-depth unravelling of their complexity, including understanding the dynamic and multiscalar evolution of their mechanical properties, requires detailed multidisciplinary studies. Indeed, an integrated approach is the only viable solution to the deconvolution of the at times very complex internal architecture of brittle fault zones, which represents a phenomenal archive of faulting history and conditions through time and in space. Fault zone architectures are commonly characterized by the spatial juxtaposition of “brittle structural facies” (BSFs), which progressively form and continuously evolve during faulting. The mutual spatial and temporal relationships of BSFs impact directly on the bulk static and dynamic permeability structure of fault zones. The permeability structure, in turn, plays a significant role on the distribution of georesources and on seismogenesis in the brittle upper crust, where both natural and induced seismicity are often associated with fluid migration and overpressure. Detailed models of the complexity of fault zones and of their static and dynamic permeability structure are thus necessary to refine our understanding of fluid pathways and of the mechanisms leading to fluid compartmentalization and possible overpressure in the crust. We present a multidisciplinary workflow to decipher exhumed complex fault zones by integrating detailed structural analyses with geochronological dating of the deformation events recorded by the constituent BSFs and systematic in-situ permeability measurements to connect deformation structures to deformation age and hydraulic properties. The absolute dating of BSFs constrains how fault hydraulic properties change not only through space but also in time (during seismic or orogenic cycles, for example) as the fault architecture (and permeability structure) progressively develop. As a case study, we apply this workflow to the Zuccale Fault in the northern Apennines (Italy), a major low-angle fault that formed and was repeatedly reactivated during a time interval spanning at least the last 22 Myr. A stark spatial heterogeneity of its present-day permeability (up to four orders of magnitude) emerges as a key structural and hydraulic feature, even for tightly juxtaposed BSFs. Results show how complex fault architectures steer the 3D hydraulic structure of the brittle upper crust with direct implications on styles and modes of fluid ingress and flow.

How to cite: Viola, G., Curzi, M., Giuntoli, F., and Vignaroli, G.: Structural-, in-situ permeability- and K-Ar geochronological constraints from complex and heterogeneous fault zones: new perspectives on fluid circulation and seismogenesis in the upper crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12282, https://doi.org/10.5194/egusphere-egu23-12282, 2023.

EGU23-14635 | ECS | Orals | TS1.7

Growth of normal faults in flexural foreland basins: a case study of the Northern Alpine Foreland Basin 

Lucas Eskens, Nevena Andrić Tomašević, Matthias Müller, and Rolf Herrman

The nucleation and subsequent vertical and lateral growth of normal faults have been the focus of many studies in extensional settings as these are important conduits for heat or fluid transfer. However, little attention has been attributed to normal fault growth in flexural foreland basins. The flexural downbending of the foreland plate generates extensional stresses, leading to the formation of normal faults in flexural foreland basins. Therefore, besides having an important role for subsurface fluid flow, normal faults in foreland basins are a fingerprint of the tectonic events associated with the downbending of the lower plate during collisional tectonics. In this study, we quantify the Oligocene to Early Miocene spatial and temporal evolution of the normal faults and their growth styles in the Northern Alpine Foreland Basin (NAFB). For this approach we use two 3D seismic volumes in the depth domain, located in the German part of the NAFB, to interpret both normal faults and prominent seismic horizons. This allows us to construct throw-depth and throw-length profiles to quantify changes in fault-parallel and down-dip throw patterns. This analysis allows us to reconstruct how the normal faults in our study area grew in 3D over time. Throw-depth profiles of the faults generally record throw maxima for either the foreland unconformity reflector or Oligocene aged reflectors, subsequently decreasing both up-and downward. This implies that following nucleation, the faults grew both upward into the syn-flexural fill of the basin and downward into the pre-flexural basement. Furthermore, comparing throw-depth and throw-length profiles of the faults in both seismic volumes shows that lateral fault growth is coupled with the fault tip moving towards younger stratigraphy. This is highlighted in the eastern German NAFB, where the vertical linkage between a lower segment that nucleated in the Eocene-Rupelian and an upper segment that nucleated in the Late Chattian is observed. To summarize, the observations imply that normal faults in the German NAFB were newly formed during flexural downbending of the European plate, preferably nucleating at the top of the plate before growing downward. This is different from fault growth observed in purely extensional settings, where faults typically grow upward instead of downward. Finally, the variable normal fault activity in the different seismic volumes in the German NAFB point out basin-parallel variations in flexural subsidence, possibly driven by spatiotemporal variations in Alpine frontal thrusting and/or slab pull.

How to cite: Eskens, L., Andrić Tomašević, N., Müller, M., and Herrman, R.: Growth of normal faults in flexural foreland basins: a case study of the Northern Alpine Foreland Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14635, https://doi.org/10.5194/egusphere-egu23-14635, 2023.

EGU23-14859 | ECS | Posters virtual | TS1.7

To what extent does U-Pb geochronology of calcite cements help to constrain the sequence of fracture development in folded strata? The Mirabeau Anticline (SE France) as a case study. 

Aniès Zeboudj, Olivier Lacombe, Nicolas Beaudoin, Jean-Paul Callot, Juliette Lamarche, and Abel Guihou

Folded sedimentary layers usually exhibit brittle mesostructures such as faults, joints, veins, and stylolites which accommodate the internal strain of strata during folding but also before strata started to be tilted, i.e. during Layer Parallel Shortening (LPS), and after tilting, i.e. during late stage fold tightening (LSFT) when shortening can no longer be accommodated by fold growth. We have established a fracture sequence in the Mirabeau anticline (SE France) using orientation data and relative chronology with respect to bedding attitude, which comprises the early-, syn- and late-folding fractures related to the folding event (1). This field-based approach is compared to 12 ages out of 32 samples analyzed by LA-ICP-MS U-Pb geochronology of selected syn-kinematic calcite, in order to provide an absolute time frame for the fracture development, along with a potential validation of the sequence of deformation. Along a section across the fold strike axis, the deformation related to the contraction lasted at least 12 Ma (or 26 Ma with uncertainties), bracketed between 52 Ma (± 8 Ma) and 40 Ma (± 6 Ma), indicating that the fold developed in response to the so-called Pyrenean-Provençal phase. In depth however, the sequence of deformation as inferred from the structural study of the fracture network is challenged by the absolute age of the syn-kinematic calcite: syn-folding flexural-slip surfaces are dated from 52 Ma (± 8 Ma), i.e. older than early-folding reverse faults associated to LPS (46 ± 4 Ma).  

 

In order to better constrain the onset of Layer-Parallel Shortening (LPS), we further analyzed the bedding parallel sedimentary stylolites through the inversion of their roughness to better define the burial depth range during which the Jurassic and Upper Cretaceous formations of interest were submitted to a vertical stress σ1. Once projected on the burial-time model of the investigated strata, the depth range, going up to 3 km, constrains the time at which σ1 presumably switched from vertical to horizontal in response to the onset of tectonic loading. Altogether, this work questions the limits of absolute dating in understanding fold-fracture relationships, and forewarn of potentially misleading interpretation of absolute ages when associated with deformation features. The example of the Mirabeau Anticline enables a discussion about the compatibility and complementarity of different approaches to date mesoscale and macroscale deformation features in fold-and-thrust belts where the sedimentary record is not well preserved.

 

Keywords : Absolute dating, fracturation, fold, carbonates

 

(1) Lacombe O., Beaudoin N., Hoareau G., Labeur A., Pecheyran C. & Callot J.P., 2021. Dating folding beyond folding, from layer-parallel shortening to fold tightening, using mesostructures : Lessons from the Apennines, Pyrenees and Rocky Mountains.  Solid Earth, 12, 10, 2145-2157

How to cite: Zeboudj, A., Lacombe, O., Beaudoin, N., Callot, J.-P., Lamarche, J., and Guihou, A.: To what extent does U-Pb geochronology of calcite cements help to constrain the sequence of fracture development in folded strata? The Mirabeau Anticline (SE France) as a case study., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14859, https://doi.org/10.5194/egusphere-egu23-14859, 2023.

EGU23-15471 | ECS | Posters virtual | TS1.7

Paleostress evolution in the South Pyrenean fold and thrust belt based on the structural analysis of fractures and U-Pb dating of carbonates 

David Cruset, Daniel Muñoz-López, Jaume Vergés, and Anna Travé

Structural analyses of vein and faults related with the growth of the South Pyrenean fold and thrust belt are coupled with the U-Pb ages of fracture-filling calcites compiled in Cruset et al. (2020) and Muñoz-López et al. (2022). Fractures include conjugated vein systems and reverse, strike-slip and normal faults cemented by calcite. The results reveal the orientation of tectonic stresses during the Pyrenean compression and their spatial and temporal evolution since the Late Cretaceous.

 Late Cretaceous to late Palaeocene U-Pb dates between 70.6 and 55.3 Ma registered compressional deformation in the inverted Mesozoic salt-related extensional basins corresponding to the Bóixols and Upper Pedraforca thrust sheets. Calculated paleostresses show a predominant N-S direction of tectonic transport, with more pronounced NW-SE directions in the western termination of the Bóixols and in the northern sector of the Upper Pedraforca.

Fracture data and U-Pb ages between 47.9 and 42.3 Ma measured in the Lower Pedraforca thrust sheet reveal N-S and NW-SE directions of tectonic transport during the middle Eocene, similar to those in the Bóixols and Upper Pedraforca thrust units. Contrarily, younger late Eocene to Oligocene U-Pb ages between 36.2 and 28.4 Ma measured in the lowermost Cadí thrust sheet reveal an homogeneous N-S trend during the emplacement of this unit.

Fractures cutting the Bóixols and Upper Pedraforca thrust sheets, and filled with cements yielding U-Pb ages from 48.8 to 25.68 Ma, show the same directions of tectonic transport than those measured for the Late Cretaceous-Paleocene. These Eocene and Oligocene ages also register the post-emplacement deformation of upper tectonic units on top of the Lower Pedraforca, Cadí, Montsec and Serres Marginals lower thrust sheets.

This research was funded by the project ALORBE (PIE-CSIC-202030E310), DGICYT Spanish Projects PID2021-122467NB-C22 and PGC2018-093903-B-C22 Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación/Fondo Europeo de Desarrollo Regional, Unión Europea. David Cruset acknowledges the Spanish Ministry of Science and Innovation for the "Juan de la Cierva Formación” contract FJC2020-043488-I AEI/10.13039/501100011033.

References

Cruset, D. et al., 2020. Quantifying deformation processes in the SE Pyrenees using U-Pb dating of fracture-filling calcites. Journal of the Geological Society, 177: 1186-1196.

Muñoz-López, D., et al. 2022. Spatio-temporal variation of fluid flow behavior along a fold: The Bóixols-Sant Corneli anticline (Southern Pyrenees) from U–Pb dating and structural, petrographic and geochemical constraints. Marine and Petroleum Geology, 143: 105788.

How to cite: Cruset, D., Muñoz-López, D., Vergés, J., and Travé, A.: Paleostress evolution in the South Pyrenean fold and thrust belt based on the structural analysis of fractures and U-Pb dating of carbonates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15471, https://doi.org/10.5194/egusphere-egu23-15471, 2023.

EGU23-16265 | Posters on site | TS1.7

Depicting the fluid system evolution in a major thrust and associated fracture network, from layer parallel shortening to today: the Sierra de Orba anticline, Jaca basin, Spain. 

Nicolas Beaudoin, Anne Battani, Irène Aubert, Antoine Léon, Charles Aubourg, Laurent Emmanuel, and Finlay Stuart

The evolution of deformation structures and associated past fluid flow is a key to better appraise both the reservoir properties of a rock and the regional evolution of an area. Indeed, the meso-scale fracture network often develops over a long period of time, granting access to a long term evolution of a past fluid system (i.e. the temperature, origin and migration pathways of the fluids) on the one hand. On the other hand, major thrusts are believed to enable episodic fluid migrations on larger spatial scales, in relation to their activity calendar, whether this activity is over or ongoing. It is seldom however to reconstruct both the past fluid flow and the present-day fluid flow on the same structure, yet it can be very enlightening about the evolution of the thrust connectivity at depth since before a fold developed over it.

In this study we reconstructed the deformation pattern and associated past fluid system related to the development of the Sierra de Orba Anticline (Spain), and we compare it to the current-day fluids resurging in the vicinity of the fault. The Sierra de Orba anticline is part of a fault-propagation fold system that developed in the northern part of the Jaca Basin, Southern Pyrenean foreland, Spain. This fold affects the sedimentary succession including the Triassic decollement level, the Upper Cretaceous to Paleocene carbonate strata and the Middle Eocene marls. The N110 striking major thrust, where the Upper Cretaceous Marboré Fm. lies unconformably onto the Eocene marls, was sampled, along with the fracture network in the hangingwall and the footwall of the thrust. The fracture network includes a sequence of prefolding sets of joints and veins, striking E-W and N060 and flexural-slip related reverse faults. Then, the network encompasses the orogeny history since likely the forebulge development until the strata tilting during folding. Syn-kinematic calcite cements were characterized petrographically in both joints and faults, then studied by means of oxygen and carbon isotopic measurements coupled with fluid inclusion microthermometry. Results highlight that the fluid system recorded an alternation between meteoric fluids (δ18O signature of the fluid: -5‰ SMOW) heated up at 70-80°C, and evolved seawater (δ18O signature of the fluid: +5 to +10‰SMOW) heated up at 70-100°C. That past fluid system around the main thrust did not record any deep-sourced fluids, unlike similar structures in the southern Pyrenean foreland. The major gas content of current day fluids was analysed from a resurgence in the footwall of the thrust. This gas is especially nitrogen-rich (>86%), and is characterized by an heavy δ13C signature of the methane content (4‰PDB). Both these features could relate to deep processes, such as an oxidation of a potential abiotic carbon that can be related to a serpentinization process. This hypothesis needs to be further evaluated by means of a study of noble gas content. Beyond regional implications, this case study illustrate how a combination of geochemical proxies can help to unravel the evolution of a fluid system at a fold-thrust scale, from its onset to today.

How to cite: Beaudoin, N., Battani, A., Aubert, I., Léon, A., Aubourg, C., Emmanuel, L., and Stuart, F.: Depicting the fluid system evolution in a major thrust and associated fracture network, from layer parallel shortening to today: the Sierra de Orba anticline, Jaca basin, Spain., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16265, https://doi.org/10.5194/egusphere-egu23-16265, 2023.

EGU23-16523 | Orals | TS1.7

Basal Décollement Splaying characterizes Mid-Crustal Deformation and Exhumation of orogenic cores in an intracontinental orogen 

Yang Chu, Zhentian Feng, Wei Lin, Lingtong Meng, and Guangyao Xin

Mid-to-lower crustal rock exhumation is common in orogenic belts, but the deformation process exposing these rocks remains debated. Distributed deformation in low viscous crust extruding mid-to-lower crustal rocks as channel flow and localized deformation along shear zones imbricating rigid blocks are two end-members that account for crustal thickening and unroofing. At the northwest of the Early Paleozoic orogenic belt in the South China Block, the Jiuling Massif includes orogenic root rocks exhumed from deep crustal level. Their structural pattern and exhumation history can improve our understanding on how continental mid-to-lower crust is deformed, thickened, and finally transported to the surface. Structural analysis reveals that two major mid-crustal ductile shear zones and their splays are developed at temperatures of ∼350°C–550°C. Anisotropy of magnetic susceptibility (AMS) shows that the Southern Jiuling Batholith has a modified AMS pattern by syn-orogenic compression, suggesting a gradually deformed rigid block. Combining surface geological evidence and deep structures by gravity modeling, we find shear zones rooted in basal décollement incrementally stacked the rigid granitic blocks. Along strike, the major shear zones evolved differently with more splays at their eastern portions. Thus, tectonic imbrication gradually evolve to pervasive flow-like deformation as shear zones continue to splay and form an anastomosed shear zone system. The complexed structures by splayed shear zones segmenting and imbricating small rigid blocks may correspond to the geophysically low-velocity zone in the crust, so shear zone splaying is a linking mechanism between tectonic imbrication and viscous flow deformation of the crust, and reconcile these two end-members.

How to cite: Chu, Y., Feng, Z., Lin, W., Meng, L., and Xin, G.: Basal Décollement Splaying characterizes Mid-Crustal Deformation and Exhumation of orogenic cores in an intracontinental orogen, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16523, https://doi.org/10.5194/egusphere-egu23-16523, 2023.

EGU23-16602 | Orals | TS1.7

Long time degassing of crustal fluids along inactive fault in an intracratonic basin (Morvan, France) 

Anne Battani, Domokos Gyore, Benjamin Brigaud, Alexis Bernard, Philippe Sarda, and Finlay Stuart

Helium-rich gases (up to 6%) upwell along a fault that bounds the western edge of the granitic Morvan Massif (northeastern part of the French Massif Central) and the sedimentary rocks of the southeastern edge of the Paris Basin. The sampled gas is mainly composed of nitrogen (90 %.). The radiogenic 3He/4He (0.02 Ra, where Ra is the atmospheric ratio) and nucleogenic 21Ne/22Ne (0.031) imply that the gas is basement-derived, in good agreement with the presence of granite in the area. The high radiogenic He concentration can be explained by a rock/ water system isolated over geological time scales and might be linked with the presence of a close-by fluorite ore deposit, dated 130 Ma, located above the fault and at the basement/sediment unconformity in Pierre-Perthuis, formed by leaching of granite (Gigoux et al., 2015).

The possible link between the fluorite ore and the He-rich gases should imply that groundwater in which He released from U and Th in granite was trapped for several millions of years in the granite or in the permeable basement/sediment unconformity reservoir, below the sedimentary cover probably reaching 1.5 km in the area at the end of the Cretaceous. Deep groundwaters trapped in the reservoir accumulated helium before tectonic exhumation of the Morvan Massif and remobilization of fluids to the surface through the Bazois fault, whose onset began 40 My ago (Lenoir et al., 2021). Mixing between old deep crystalline-water with superficial water is evidenced by the presence of high amount of atmosphere-derived nitrogen.

The high chloride content of the waters may originate from the marine water trapped in the Early Jurassic clays, and released by faulting, or by water-rock interaction and hydrolysis of minerals, reinforcing the link between chlorine, fluorine, and water from granite.

This geological example shows that in quiescent area, inactive fault can act as a fluid pathway over long time scale.

How to cite: Battani, A., Gyore, D., Brigaud, B., Bernard, A., Sarda, P., and Stuart, F.: Long time degassing of crustal fluids along inactive fault in an intracratonic basin (Morvan, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16602, https://doi.org/10.5194/egusphere-egu23-16602, 2023.

EGU23-236 | ECS | Orals | GMPV5.1

Computer modeling of mineral dendrite growth 

Dawid Woś and Piotr Szymczak

Mineral dendrites are an example of a pattern which forms in rocks when they are infiltrated by the hydrothermal, manganese-rich fluids. As these fluids mix with other oxygenated fluids within the fractured rock, manganese oxide is formed. The oxide then precipitates, forming intricate, branched patterns. Several models of this process have been proposed, which vary in complexity. One model assumes crystallization of manganese oxides directly on the surface of the growing dendrite, causing it to elongate. Another model involves an initial growth of small nanoparticles of manganese oxide, which then aggregate into larger structures. The evolution of the system in both models is described by the system of reaction-diffusion equations.

 

We study this process using lattice-Boltzmann method to track the evolving concentrations of the species involved in reaction. Next, we analyze the dependence of the morphology of the resulting patterns on the physical parameters characterizing the reaction and growth, such as initial concentrations of manganese ions and oxygen molecules, reaction rates, nucleation thresholds or surface energy of the dendrites. Our study has been focused on planar structures, growing along fractures or bedding planes. We have investigated the impact of multiple infiltrations of manganese-bearing fluid on the morphology of the dendrites. We compare the numerical results to the morphologies of the real systems with the aim of reconstructing the hydrochemical conditions prevailing during their growth

How to cite: Woś, D. and Szymczak, P.: Computer modeling of mineral dendrite growth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-236, https://doi.org/10.5194/egusphere-egu23-236, 2023.

EGU23-275 | ECS | Orals | GMPV5.1

Effects of mixing at pore intersections on large-scale dissolution patterns 

Rishabh Prakash Sharma, Peter K. Kang, and Piotr Szymczak

Dissolution of carbonate rocks is a complex process in which the interplay of flow, transport, reaction, and geometric evolution plays an important role. The nonlinear couplings between these processes may lead to the formation of intricate patterns, including spontaneously formed channels (wormholes) [1].  It has been long established that the shapes of the dissolution patterns depend on fluid flow and mineral dissolution rates [2]. Recently, it also has become increasingly clear that pore-scale processes can impact large-scale morphologies [3,4]. However, the effects of pore-scale mixing on large-scale patterns remain unclear.

In this work, we investigate the effect of pore-scale mixing processes on the evolution of dissolution channels. Pore space is represented by a network of cylindrical tubes with the diameter of each segment increasing in proportion to the local reactant consumption. The inlet concentration of each pore is controlled by local mixing rules. Two different mixing protocols are considered: full mixing, in which the incoming reactant fluxes are assumed to be completely mixed at the intersection, and streamline routing, where the tracer follows the streamlines into the outgoing pores. We found that streamline routing enhances the flow focusing particularly strongly in moderate Damköhler number regimes where relatively wide dissolution channels appear spontaneously in the system. With the same initial conditions as the full mixing case, the winning channels obtained with streamline routing not only propagate faster but also could grow at a different location in the system. The enhanced flow focusing caused by streamline routing produces thinner wormholes and leads to shorter breakthrough times. Lastly, the evolution of velocity distribution is also found to be distinctive depending on the mixing rule.

[1] Hoefner, M. L. and Fogler,  H. S. AIChE J. 34: 45–54, 1988

[2] Golfier, F., et al.  J. Fluid. Mech. 457: 213-254, 2002

[3] Li, L., Peters, C. A., & Celia, M. A. Adv. Water Res., 29: 1351–1370, 2006

[4] R. Roded, P. Szymczak, R. Holtzman, Geophys. Res. Lett. 48:e2021GL093659, 2021

How to cite: Sharma, R. P., Kang, P. K., and Szymczak, P.: Effects of mixing at pore intersections on large-scale dissolution patterns, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-275, https://doi.org/10.5194/egusphere-egu23-275, 2023.

EGU23-463 | ECS | Orals | GMPV5.1

Experimental Measurements of Micron-thick Interphase Thermodynamics along a Water-Rock Interface 

Armin Mozhdehei, Lionel Mercury, and Aneta Slodczyk

Water-rock interaction determines how the geochemical cycles evolve from Earth surface to the deep interior, related to the fluxes, time, and reactivity between fluid phases and solids. Thus, quantifying mass balances from the global scale to the local one, for understanding planetary geodynamics as well as optimizing geothermal doublets, require understanding how the driving force is controlled between solids and dissolved phases [1, 2]. As a consequence, water-rock budget has a major role to drive the porosity accessible to flow. The standard approach is to consider the chemical potentials of the bulk phases assuming the interface to be infinitely thin and therefore thermodynamically negligible, except with highly divided materials and/or super-confined solutions. Our work is based on previous investigations evidencing the formation of an interphase layer/domain, up to one micron thick, having distinct thermodynamic features with respect to the bulk phase properties [3].  

Herein, diffraction limited FTIR micro-spectroscopy in transmission mode, based on confocal microscope coupled to broadband supercontinuum laser or synchrotron beam, was employed as an energetic probe to monitor the thermodynamic characteristics of liquid water as a function of beam location in a synthetic fluid inclusion (one pore micro-scale closed cavity). FTIR hyperspectral data was recorded to illustrate distance-dependent vibrational energy (absorption signatures) at room and homogenization temperatures. The vibrational energy was transformed to Gibbs free energy using a partition function [4].

The results showed that Gibbs free energy changes by 600 to 1000 J/mol up to 1μm far from the water-quartz interface. This variation indicates a significant change in the chemical reactivity of liquid water over a thick domain, rather defining an “interphase” instead of an “interface.” We observed that the thermodynamic property of this interphase domain has a thermal dependency, and by increasing the temperature the chemical potential has a higher value. The Gibbs free energy variation with T can be interpreted by either an enthalpic or an entropic contribution, or a combination of both. This surprising discovery calls for a shift in the paradigm of the bulk phases dominance in water-rock interaction.

References

1. Putnis, A., Fluid–Mineral Interactions: Controlling Coupled Mechanisms of Reaction, Mass Transfer and Deformation. Journal of Petrology, 2021. 62(12): p. egab092.

2. Putnis, A., J. Moore, and H. Austrheim, Fluid-rock reaction mechanisms and the inevitable consequences for mass transport and texture formation. 2022, Copernicus Meetings.

3. Bergonzi, I., et al., Oversolubility in the microvicinity of solid–solution interfaces. Physical Chemistry Chemical Physics, 2016. 18(22): p. 14874-14885.

4. Bergonzi, I., et al., Gibbs free energy of liquid water derived from infrared measurements. Physical Chemistry Chemical Physics, 2014. 16(45): p. 24830-24840.

 

How to cite: Mozhdehei, A., Mercury, L., and Slodczyk, A.: Experimental Measurements of Micron-thick Interphase Thermodynamics along a Water-Rock Interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-463, https://doi.org/10.5194/egusphere-egu23-463, 2023.

EGU23-478 | ECS | Orals | GMPV5.1

The Evolution of Paleo-Porosity in Basalts: Reversing Pore-Filling Mechanisms Using X-Ray Computed Tomography 

Alice Macente, Katherine J. Dobson, John MacDonald, Fabian B. Wadsworth, and Jeremie Vasseur

Basaltic rocks are considered excellent candidates for CO2 storage by in situ mineral trapping, due to their large presence on Earth’ surface and their higher reactivity with CO2 to form calcium-rich minerals. Often carrying a high-volume fraction of vesicles, basaltic rocks can be an important reservoir horizon in petroleum systems. When the vesicle network has been filled by earlier mineralization the basalts can act as impermeable seals and traps. Characterizing the spatial and temporal evolution of the porosity and permeability is critical to understand the CO2 storage potential of basalts. We exploited X-ray computed tomography (XCT) to investigate the precipitation history of an amygdaloidal basalt containing a pore-connecting micro-fracture network now partially filled by calcite as an analogue for CO2 mineral trapping in a vesicular basalt. The fracture network likely represents a preferential pathway for CO2-rich fluids during mineralisation. We quantified the evolution of basalt porosity and permeability during pore-filling calcite precipitation by applying novel numerical erosion techniques to “back-strip” the calcite from the amygdales and fracture networks. We found that permeability evolution is dependent on the precipitation mechanism and rates, as well as on the presence of micro-fracture networks, and that once the precipitation is sufficient to close off all pores, permeability reaches values that are controlled by the micro-fracture network. These results prompt further studies to determine CO2 mineral trapping mechanisms in amygdaloidal basalts as analogues for CO2 injections in basalt formations.

How to cite: Macente, A., Dobson, K. J., MacDonald, J., Wadsworth, F. B., and Vasseur, J.: The Evolution of Paleo-Porosity in Basalts: Reversing Pore-Filling Mechanisms Using X-Ray Computed Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-478, https://doi.org/10.5194/egusphere-egu23-478, 2023.

EGU23-626 | ECS | Orals | GMPV5.1

Is secondary mineralization playing a pivotal role in recurring seismicity at Koyna-Warna Seismogenic Region of India: a geochemical perspective? 

Piyal Halder, Anupam Sharma, Matsyendra Kumar Shukla, and Kamlesh Kumar

Since the impoundment of the Shivajisagar Reservoir behind the Koyna Dam in 1962, numerous earthquakes have been felt in the Koyna-Warna Seismogenic Region of Western India. The mesoscopic and microscopic observations on the basement granitoid core samples, recovered under the Continental Deep Drilling Program of the Ministry of Earth sciences, reveal the precipitation of calcite and the formation of clay minerals (illite and chlorite) along the fractures and faults. The presence of these secondary minerals alongside the primary minerals like quartz and feldspar is further supported by X-ray Diffraction, which also points to the fracture scale chemical alteration as a result of fluid-rock interactions. It's interesting to note that the precipitation of these hydrophilic clay minerals along faults and fractures might promote slip by raising fluid pressure and lowering the shear strength of the faults. Thus, secondary mineralization due to fluid-rock interaction may have a contribution to the release of strain in form of seismic tremors. On the other hand, the neoformation of these hydrophilic clay minerals along fault/fracture surfaces may also cause rheological incongruity, which could lower the density as well as P and S wave velocities. Besides, hydrogen atoms in clay-bound water may influence neutron capture, leading to over-optimistic estimations of neutron porosity. Additionally, our study supports past geophysical anomalies found in the KFD1 borehole and infers that the geophysical anomalies correlating to the growing fracture density and fault system of the basement rocks are caused by chemical alteration due to fluid-rock interaction and subsequent secondary mineralization. So, this research offers important new understandings of geochemical activity in the context of geophysics and serves as a bridge between geochemistry and geophysics.

How to cite: Halder, P., Sharma, A., Shukla, M. K., and Kumar, K.: Is secondary mineralization playing a pivotal role in recurring seismicity at Koyna-Warna Seismogenic Region of India: a geochemical perspective?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-626, https://doi.org/10.5194/egusphere-egu23-626, 2023.

EGU23-732 | ECS | Orals | GMPV5.1

Complementing the hydration history of an inverted passive continental margin using epidote U–Pb geochronology and isotope geochemistry 

Veronica Peverelli, Alfons Berger, Martin Wille, Andreas Mulch, Benita Putlitz, Pierre Lanari, Thomas Pettke, and Marco Herwegh

Crustal rocks involved in orogenic processes frequently bear evidence for widespread fluid circulation. The hydration history of the granitic continental crust in inverted passive continental margins is of particular interest, as granitoids experience rheological weakening by fluid-rock interaction processes. Regrettably, it is often unclear if hydration occurs during rifting or during tectonic inversion. Hence, it is difficult to appreciate the interplay of pre- and syn-orogenic fluids inside continental crustal segments of rifted margins. The geochemical fingerprint of ancient hydration events is stored in hydrous minerals that crystallized directly from circulating paleo-fluids. Thus, such minerals can shed light on the nature of these ancient fluids, as well as provide temporal constraints if they can be dated. Hence, advances in geochronological methods applied to hydrous minerals may prove pivotal in untangling the history of fluid circulation in the granitic continental crust in orogens.

We applied U–Pb geochronology of epidote [i.e., Ca2Al2(Al,Fe3+)Si3O12(OH)] in hydrothermal veins hosted by a late Carboniferous/early Permian calc-alkaline granodiorite in the inverted Adriatic passive continental margin (hereafter “Err nappe”), both located in the eastern Swiss Alps. During Jurassic rifting leading to the break-up of Pangea, the continental crust in the Err nappe was hydrated, as seawater-derived fluids percolated along syn-rift faults. However, geochronological data of epidote reveal that the hydration of the granitic continental crust in the Err nappe occurred also later during inversion. Epidote U–Pb geochronology returned two age clusters: (1) 85.2 ± 9.7 Ma, related to Late Cretaceous compression; and (2) 59.9 ± 2.7 Ma, related to subsequent Paleocene extension. These age clusters unveil two distict events of fluid circulation, which are consistent with the timing of tectonic inversion and deformation proposed in the literature. As confirmed by Pb–Sr–O–H isotope geochemistry of epidote, Late Cretaceous fluid circulation was likely mediated by fluids released by underlying units undergoing metamorphism during Eo-Alpine compression. Notably, the Paleocene fluids circulating during extension were most likely surficial in origin (i.e., meteoric water and/or modified/connate seawater), and they percolated into the granitic continental crust by exploiting extensional faults.

In the context of existing data, our results show that the hydration of the granitic continental crust of the Adriatic passive continental margin was mediated by a repeated series of fluid circulation events. Our work advocates that the use of a multi-methodological approach, combining new geochemical and geochronological, tools provides unprecedented insight into complex processes of fluid circulation in the continental crust, and beyond.

How to cite: Peverelli, V., Berger, A., Wille, M., Mulch, A., Putlitz, B., Lanari, P., Pettke, T., and Herwegh, M.: Complementing the hydration history of an inverted passive continental margin using epidote U–Pb geochronology and isotope geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-732, https://doi.org/10.5194/egusphere-egu23-732, 2023.

EGU23-1817 | ECS | Orals | GMPV5.1

Experimental model of cerussite PbCO3 replacement by mimetite Pb5(AsO4)3Cl at pH 2 – 8 

Ewa Stępień and Maciej Manecki

The mobility of arsenic in aquatic environments is controlled by oxidation states of arsenic, stability of solid phases, and chemical composition of water (Meng et al., 2002). Binding of arsenic in the environment may occur through precipitation of low-solubility salts (Magalhães, 2002), like mimetite Pb5(AsO4)3Cl. The aim of this study is to experimentally investigate reactions between cerussite (PbCO3) and solutions containing AsO43- at various conditions favouring mimetite formation. These observations may provide a new recognition for As immobilization, which might be relevant in remediation of contaminated natural waters.

The mechanism of cerussite reaction with arsenate solutions (50 mg As/L) was studied at pH 2 – 8 using synthetic cerussite powder and fragments of natural cerussite crystals (Mibladen, Morocco). The reaction was carried out by direct contact of 500 ml of As-containing solution with PbCO3, in presence of Cl- ions.Cerussite was reacted for up to 4 weeks at in situ and ex situ setups. X–Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS) and Electron Microprobe Analysis (EMPA) were used for analysis of the solid products of the experiments. The solutions were tested for Pb with Atomic Absorption Spectroscopy (AAS) and for AsO43-  using colorimetry.

Precipitation of mimetite on cerussite powder crystals is observed already after 1 day of the reaction with arsenate solutions, at the whole range of pH. Mimetite forms hexagonal rods or needles less than 1 µm in size precipitating in the form of incrustations on PbCO3 crystals. Their size depends on the pH: a fine-grained precipitate forms at higher pH. Observations of natural crystals show replacement of cerussite by polycrystalline mimetite crust. The crust made of columnar and needle crystals is porous allowing for solution penetration and progress of the reaction. The replacement features indicate similarity to pseudomorphic reactions, and the mechanism elucidated as interface coupled dissolution - precipitation. Overall, cerussite replacement by mimetite reduces AsO43- concentration from 50 ppm to below 1 ppm. It also depends on the pH.

This research was funded by AGH University of Science and Technology project No 16.16.140.315.

Magalhães, M. C. F. (2002). Arsenic. An environmental problem limited by solubility. Pure and Applied Chemistry, 74(10), 1843–1850.

Meng, X., Jing, C., & Korfiatis, G. P. (2002). A Review of Redox Transformation of Arsenic in Aquatic Environments. Biogeochemistry of Environmentally Important Trace Elements, 70–83.

 

How to cite: Stępień, E. and Manecki, M.: Experimental model of cerussite PbCO3 replacement by mimetite Pb5(AsO4)3Cl at pH 2 – 8, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1817, https://doi.org/10.5194/egusphere-egu23-1817, 2023.

EGU23-3424 | ECS | Posters on site | GMPV5.1

Heitt Mjolnir: an internally heated triaxial rock deformation apparatus for operando experiments at up to 573 K at Synchrotron imaging beamlines 

Damien Freitas, Ian Butler, Stephen Elphick, James Gilgannon, Roberto Rizzo, Oliver Pluemper, John Wheeler, Christian Schlepuetz, Federica Marone, and Florian Fusseis

The 3rd and 4th generation of synchrotron light sources with their high brilliance, fluxes and beam energies allow the development of innovative X-ray translucent rock deformation apparatus that maximise these capabilities. Following on from the development of the Mjolnir triaxial deformation rig (Butler et al., 2020), we present an upscaled design: Heitt Mjolnir, covering a wider temperature range and larger sample volume while operating at similar pressure, enabling a wide range of time-resolved investigations. This device is designed to characterise coupled hydraulic, chemical and mechanical processes, occurring at various temperatures, from the µm to the centimetre scale in cylindrical samples of 10 mm diameter and 20 mm length. Heitt Mjolnir can simultaneously reach confining pressures of ≤30 MPa (hydraulic), 500 MPa of axial stress while the sample’s pore fluid pressure is controlled in a dedicated fluid channel and can reach 30 MPa. This apparatus has an internal heating system and is able to reach temperatures of 573 K in the sample with a minimal vertical thermal gradient of <0.5 K/mm. This portable and modular device has been successfully deployed in operando studies at TOMCAT (SLS) and I12 JEEP (DLS) beamlines for 4D X-ray microtomography with scan intervals of a few minutes. Heitt Mjolnir allows the 4D characterisation of low-grade metamorphism, fluid-rock interaction and deformation processes. It enables spatially and temporally resolved fluid-rock interaction studies at a wide range of conditions and, by covering most geological reservoirs, will be particularly valuable for geothermal, carbonation or subsurface gas storage research.

How to cite: Freitas, D., Butler, I., Elphick, S., Gilgannon, J., Rizzo, R., Pluemper, O., Wheeler, J., Schlepuetz, C., Marone, F., and Fusseis, F.: Heitt Mjolnir: an internally heated triaxial rock deformation apparatus for operando experiments at up to 573 K at Synchrotron imaging beamlines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3424, https://doi.org/10.5194/egusphere-egu23-3424, 2023.

The equilibration of minerals in the presence of an aqueous fluid phase, with which it is out of equilibrium, has been described in terms of a number of potential mechanisms, specifically mainly either by solid state exchange of elements within the solid phase and the aqueous solution, or by interface-coupled dissolution-precipitation where equilibration is approached by the incremental dissolution of the parent solid and the coupled precipitation of a new product solid (Ruiz-Agudo et al., 2014). The conditions determining the equilibration mechanism can be defined by the specific chemical potential differences at the mineral interface, the kinetics of potential reactions, the solubility of the solid phase in the specific fluid and physical properties such as the mineral: fluid ratio as well as the surface area: fluid ratio, temperature and pressure. We focus on the mechanism of ion exchange in a range of minerals and in most cases ion-exchange in the presence of an aqueous solution occurs by interface-coupled dissolution-precipitation (Putnis and Putnis, 2022).

References

Putnis C.V. and Putnis A. 2022. A mechanism of ion exchange by interface-coupled dissolution-precipitation in the presence of an aqueous fluid. J. Crystal Growth, 600, 126840

Ruiz-Agudo E., Putnis C.V., Putnis A. 2014. Coupled dissolution and precipitation at mineral-fluid interfaces. Chemical Geology 383, 132-146.

How to cite: Putnis, C. V. and Putnis, A.: A mechanism of ion exchange by interface-coupled dissolution-precipitation in the presence of an aqueous fluid, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3792, https://doi.org/10.5194/egusphere-egu23-3792, 2023.

EGU23-3812 | ECS | Posters virtual | GMPV5.1

Fluid-mediated alteration of zircons to fergusonite-(Y) in A-type granites and pegmatite from the Jharsuguda district, India 

Suratha panda, Arkadeep Roy, and Kamal Pruseth

The A-type granites of Jharsuguda at the boundary between the Singhbhum Craton and Rengali Province have rare earth potential. Two populations of zircon are present. One of them represents the unaltered zircons of magmatic origin, as evidenced by the presence of oscillatory zoning and Th/U ratios > 0.7. The other population consists of the altered equivalents of these primary zircons. These zircons have Th/U ratios < 0.1, suggesting their metamorphic origin. Occasionally, single grains of zircon containing both altered and unaltered domains are also encountered. The unaltered zircons comprise a very small proportion. The altered zircons appear dark in CL images and are characterized by low EPMA totals with non-formulae elements like Al, P, Ca, Fe, Y, and REEs. Numerous mineral inclusions, including those of U- Th-bearing ones, are typical of these altered zircons. Xenotime inclusions are typical of altered zircons with xenotime overgrowths in the granites. Rare Nb-rich inclusions are also present in these altered zircons.   In both the granites and pegmatite, fluid-mediated alteration resulted in fergusonite-(Y) and other Nb-Ta-REE oxides in the cracks and fractures. Pseudomorphs of fergusonite-(Y), Nb-Ta-REE oxides, and allanite are also formed by replacing earlier zircon grains. The size of these fergusonite grains ranges from a few micrometers in granite to up to 500 micrometers in pegmatites. The LA-ICPMS U-Pb dating zircons yield a primary age of 2.95 Ga and metamorphism ages of 2.80 Ga and 2.45 Ga. Selected fergusonite-(Y) grains from the pegmatite suggest a 2.1 Ga U-Th-Pb EPMA age for these fergusonites. Rims of some zircon grains in both granites and pegmatite also yield an age of 2.1–2.2 Ga. The age data suggest that the Jharsuguda granites and pegmatite underwent at least three metamorphic/tectonothermal events, during the last of which fergusonites are formed by the remobilization of REEs and HFSEs, probably in the presence of complexing ligands like F and PO4, as confirmed by EPMA X-ray element maps of altered zircons.

How to cite: panda, S., Roy, A., and Pruseth, K.: Fluid-mediated alteration of zircons to fergusonite-(Y) in A-type granites and pegmatite from the Jharsuguda district, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3812, https://doi.org/10.5194/egusphere-egu23-3812, 2023.

EGU23-5330 | ECS | Posters virtual | GMPV5.1

Formation of the zoning parttern in moonstones 

Ke Cao, Fu-Feng Zhao, Zhao-Liang Hou, and Li-Shan Zheng

Moonstones are a gem-quality feldspar with a special exsolution structure and are well-known for the unique moonshine effect of themselves. However, formation of such “moonshine” is still a mystery. One possibility to reveal it, is by understanding, the formation mechanisms of moonstone exsolution fashion, which is constituted by the lamellae inclusions and the associated zoning patterns (banding structures). Here, by combining the mineralogical- and geochemistry techniques, we investigated the chemistry and textures of the chemical patterns in moonstones in detail. Two different color moonstones (orangish and grayish) are the object of study. Although Raman and EPMA analyses indicate that, both moonstones are orthoclase (Or73.65~90.38), the orange moonstone is colored by hematite inclusions while the gray one is by magnetite inclusions. The orange moonstone has two lamellae types, which are An-containing albite phase (An6.53~18.93) and K-high albite phase (≈An6.23). The An-containing albite lamellae demonstrated a µm-size zone with a decrease of An content (18.93 to 6.53) from the zone center to edge. In contrast, the gray moonstone does not show any zoning structure. Those allow for further analyses focusing on the zone structures, in combination of XRD diffraction structure analysis, La-ICP-MS whole-rock principal element analysis and phase diagram simulation, and by which, we proposed a two-stage-growth process for exsolution structure that is formed in the   orange moonstone. The first stage of exsolution results in oligoclase lamellae, and the second stage results in K-high albite lamellae, in which part of Ab-rich phase became to individual K-high albite lamellae, while part of Ab-rich phase continues to dissolve around the oligoclase, forming the zoning structure. We formulated that the gray moonstone has only one formation stage which corresponds to the second stage of the orange moonstone. Our detail descriptions of moonstone might be a valuable contribution to further the study of moonshine effect.

How to cite: Cao, K., Zhao, F.-F., Hou, Z.-L., and Zheng, L.-S.: Formation of the zoning parttern in moonstones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5330, https://doi.org/10.5194/egusphere-egu23-5330, 2023.

EGU23-5460 | ECS | Posters on site | GMPV5.1

Deformation and fluid-infiltration influence in the evolution of the Krossøy dyke-swarm in the northern part of the Bergen Arcs, Norway 

Lorena H. Filiberto, Håkon Austrheim, and Andrew Putnis

The Bergen Arcs, in Norway, consist of several arcuate nappes formed during the Caledonian orogeny 440-420 Ma ago (Bingen et al., 2001; Glodny et al., 2008) when the western margin of Baltica was subducted below Laurentia. This Caledonian orogeny overprinted many of the anorthosites that formed the 930 Ma old (Bingen et al., 2001) granulitic basement. This overprint resulted in both amphibolites and eclogites and have been observed in shear zones within the rocks of the well-studied island of Holsnøy, located on the western margin of the Lindås Nappe. On the adjacent island of Radøy, the Caledonian overprint is associated with amphibolite facies shear zones (Mukai et al., 2014; Moore et al., 2020).

In the northern margin of the Bergen Arcs, near the Bergen Arcs Shear Zone, the much less-studied island of Krossøy also exposes the anorthosites from the old granulitic basement and here the Caledonian overprint also resulted only in amphibolite facies metamorphism. The anorthosites in Krossøy are intruded by a series of subparallel mafic granulitic dykes forming the Krossøy dyke swarm, that has never previously been described elsewhere in the Bergen Arcs. The style of deformation in the granulites and the textural evolution in the amphibolite facies overprint are also markedly different from the rocks on Holsnøy and Radøy. The development of ductile Caledonian shear zones may have been facilitated by initial brittle failure of the basement accompanied by fluid infiltration (Jamtveit et al., 2018). Here we investigate the influence of this deformation and fluid infiltration on different features observed on these rocks such as: the occurrence of plagioclase coronas around the garnets on the dykes; the presence of different types of symplectites; the variability of size, deformation and composition observed on the anorthositic feldspars; or the local changes of fluid composition along cm- long fractures. We will show our first analytical results on some of these key features and discuss their relevance in the context of the previous studies of the Bergen Arcs.

 

Bingen, B., David, W. J., & Austrheim, H. (2001). Zircon U-Pb geochronology in the Bergen Arc eclogites and their Protereyoic protoliths, and implications for the pre-Scandian evolution of the Caledonides in western Norway. In GSA Bulletin (Issue 5). https://doi.org/10.1130/0016-7606(2001)113<0640:ZUPGIT>2.0.CO;2

Glodny, J., Kühn, A., & Austrheim, H. (2008). Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction-collision system, Bergen Arcs, Norway. Contributions to Mineralogy and Petrology, 156(1), 27–48. https://doi.org/10.1007/s00410-007-0272-y

Jamtveit, B., Moulas, E., Andersen, T. B., Austrheim, H., Corfu, F., Petley-Ragan, A., & Schmalholz, S. M. (2018). High Pressure Metamorphism Caused by Fluid Induced Weakening of Deep Continental Crust. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-35200-1

Moore J., Beinlich A., Piazolo S., Austrheim H. & Putnis A.  (2020). Metamorphic differentiation via enhanced dissolution along high permeability zones. Journal of Petrology 61, 10. https://doi.org/10.1093/petrology/egaa096

Mukai H., Austrheim H., Putnis CV. & Putnis A. (2014). Textural evolution of plagioclase feldspar across a shear zone: implications for deformation mechanism and rock strength. Journal of Petrology. 55, 1457-1477. https://doi.org/10.1093/petrology/egu030

How to cite: Filiberto, L. H., Austrheim, H., and Putnis, A.: Deformation and fluid-infiltration influence in the evolution of the Krossøy dyke-swarm in the northern part of the Bergen Arcs, Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5460, https://doi.org/10.5194/egusphere-egu23-5460, 2023.

EGU23-5769 | ECS | Orals | GMPV5.1

Hot when wet: the consequences of exothermic hydration on geochronology 

Simon Schorn, Evangelos Moulas, and Kurt Stüwe

Retrogression and hydration commonly affect large portions of the crust, causing variable degrees of chloritization, sericitization and/or serpentinization depending on the protolith and the conditions of fluid ingression. Retrograde overprint involving hydration is a strongly exothermic process, and leads to a thermal perturbation around the pressure–temperature conditions of hydration, which in the case of chloritization of felsic rocks typically occurs at <500°C. These conditions of retrogression overlap with the closure temperatures of some isotopic systems commonly used for geochronology, for example 40Ar/39Ar in micas and feldspars. The exothermicity of hydration therefore disturbs the recorded apparent ages and cooling histories of reworked terranes. Using an average metapelite composition as case study, we estimate that hydration and retrogression of a high-grade amphibolite facies assemblage to a low-grade greenschist paragenesis involves approximately a twofold increase of the mineral-bound water content and releases about 50 kJ.kg-1 latent heat. Using a simple 1-dimensional numerical model, we solve the heat equation for a steady-state continental geotherm that is advected towards the surface and track the cooling rates for markers that exhume from different depths. Assuming enthalpy production at 380°C to simulate exothermic hydration, the cooling rate is significantly reduced until the markers are exhumed to the temperature/depth of hydration and reaction. The calculated cooling paths feed into KADMOS (Moulas & Brandon, 2022), a set of MATLAB routines designed to calculate apparent 40Ar/39Ar ages as function of customized thermal histories. KADMOS solves the equation of 40Ar production from 40K decay and thermally-activated diffusive loss of 40Ar for time (Fig. 1). Our results reveal that for intermediate exhumation rates, spherical muscovite grains with <100 µm in diameter are affected by a ~10% age error when latent heat is considered (Fig. 1b). Such muscovites in rocks exhuming with a velocity of, for example, 4 mm/year would record an apparent 40Ar/39Ar age of c. 10 Ma (Fig. 1a) and be affected by an absolute age error of ~1 Ma from thermal buffering by hydration, yielding an apparent age of 10 ± 1 Ma (Fig. 1b). Our calculations indicate that latent heat released from exothermic hydration may significantly disturb low-temperature isotopic systems, thereby complicating the cooling histories and obscuring the temporal constraints deduced from state-of-the-art geochronological systems.

Figure 1 – Exhumation velocity vs. grainsize contoured for apparent 40Ar/39Ar age in muscovite (a) and relative error when latent heat is considered (b)

REFERENCES

Evangelos Moulas, & Mark T Brandon. (2022). KADMOS: a Finite Element code for the calculation of apparent K-Ar ages in minerals (Version 1). Zenodo. https://doi.org/10.5281/zenodo.7358138

How to cite: Schorn, S., Moulas, E., and Stüwe, K.: Hot when wet: the consequences of exothermic hydration on geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5769, https://doi.org/10.5194/egusphere-egu23-5769, 2023.

EGU23-5808 | ECS | Posters on site | GMPV5.1

Quartz vein formation in the Agly massif, French Pyrenees: 40Ar/39Ar dating, mineral chemistry, and fluid inclusion study. 

Intan Chalid, Klaudia Kuiper, Leo Kriegsman, Simona Ferrando, Fraukje Brouwer, and Jan Wijbrans

Quartz veins in metamorphic basement rocks document periods of hydrous fluid mobility. Here, we present a study of vein formation in the Agly Massif, eastern French Pyrenees, which was subjected to metamorphism during the Hercynian and Alpine orogenies and during Mesozoic extension between the two (Siron et al., 2020).

In this study, fourteen quartz samples have been selected for 40Ar/39Ar dating of the fluids inside fluid inclusions (FIs) by stepwise crushing. The results are characteristic for this method: all samples show anomalously high ages in the first part of the experiments decreasing to essentially flat plateaus in the final steps. The plateau ages are interpreted as the time of quartz vein formation, ranging from 117 to 62 Ma, i.e., mid-Cretaceous to early Paleocene. The initial values indicate the presence of another trapped argon component, with  40Ar/36Ar intercepts >6000. An additional nine K-feldspar samples from the same veins are dated by incremental heating.

The quartz veins show considerable variation in mineral content, including feldspars, biotite, muscovite, chlorite, and minor amounts of epidote, almandine, apatite, ilmenite, titanite, and scapolite. Mineral assemblages including quartz, chlorites, epidote, muscovite point to crystallization in the greenschist facies around ca 300°C (Palin, 2020).

Preliminary FI data are collected from primary FIs occurring in vein quartz  from the Souanyes and Bélesta areas. FIs from Souanyes are two-phase (liquid + vapor with constant ratio) aqueous inclusions with high salinity (26.0 NaCleq). FIs from Bélesta are aqueo-carbonic multi-phase inclusions (liquid water + gaseous phase, usually supercritical at room temperature ± a cubic salt ± a carbonate, measured using Raman spectroscopy). During microthermometric measurements, these FIs show metastable behavior (e.g., lacking salt re-nucleation after melting) or experienced post-trapping modifications (salt precipitation after cooling) that prevent to obtain an accurate salinity. However, a salinity of ca. 26.3 wt% NaCleq can be deduced. The lack of freezing of the gaseous phase during cooling reveals the presence of contaminant gas (N2, measured using Raman spectroscopy) within CO2.

In summary, most quartz veins in the Agly massif formed during the Cretaceous, which is consistent with recent thermochronology (Odlum & Stockli 2019). The vein mineralogy points to emplacement in the greenschist facies of high-salinity aqueous fluids, locally with CO2 and N2.

  • Odlum, M., Stockli, D.F. (2019) Thermotectonic evolution of the north Pyrenean Agly Massif during early Cretaceous hyperextension using multi-mineral U-Pb thermochronometry. 38: pp. 1509-1531. John Wiley & Sons Ltd.
  • Palin, R.M. (2020) Metamorphism of pelitic (Al-Rich) rocks. In module Earth Systems and Environmental Sciences, 2: pp. 1-12. Elsevier Inc. 
  • Siron G, Goncalves P, Marquer D, Pierre T, Paquette J-L, Vanardois J. (2020) Contribution of magmatism, partial melting buffering and localized crustal thinning on the late Variscan thermal structure of the Agly massif (French Pyrenees). Metamorph Geol. 38: pp. 799-829. John Wiley & Sons Ltd.

How to cite: Chalid, I., Kuiper, K., Kriegsman, L., Ferrando, S., Brouwer, F., and Wijbrans, J.: Quartz vein formation in the Agly massif, French Pyrenees: 40Ar/39Ar dating, mineral chemistry, and fluid inclusion study., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5808, https://doi.org/10.5194/egusphere-egu23-5808, 2023.

Water contamination caused by the overuse of fertilizers has become a concern in many areas throughout the last decades. The intensive use of phosphate fertilizers has led to high concentrations of phosphates in ground waters and effluents, but also to high levels of other toxic elements, especially cadmium. Cadmium can be found in high concentrations in phosphate rocks which are used to synthesize fertilizers, resulting in high concentrations of cadmium in some fertilizers that are then used on fields. Various materials have been studied for cadmium capture in solution and both calcium carbonate and apatite have shown good uptake capacities toward this element. Furthermore, calcium carbonate minerals can be replaced by apatite through a pseudomorphic dissolution-precipitation mechanism when immersed in a solution containing phosphate (Jonas et al., 2014; Klasa et al., 2013; Pedrosa et al., 2016; Wang et al., 2012). Here, we report on the capture of cadmium from solution during the replacement reaction of Carrara marble by hydroxyapatite (Wang et al., 2019). Cubes of Carrara marble have been reacted in sealed hydrothermal reactors at 200°C in solutions containing various concentrations of phosphate and cadmium for times between 4 and 60 days. The samples were then sectioned and analysed by Scanning Electron Microscopy (SEM), BackScattered Electron (BSE) imaging, Electron Dispersive X-ray Spectroscopy (EDS) and Raman Spectroscopy. The nanoscale reaction on the sample surface has been observed with in-situ Atomic Force Microscopy (AFM) in fluid flow and static solutions. The coupled dissolution-precipitation reaction observed and the capture of cadmium by the newly formed phase will be presented.

References:

Jonas, L., John, T., King, H.E., Geisler, T., Putnis, A., 2014. The role of grain boundaries and transient porosity in rocks as fluid pathways for reaction front propagation. Earth and Planetary Science Letters 386, 64–74. https://doi.org/10.1016/j.epsl.2013.10.050

Klasa, J., Ruiz-Agudo, E., Wang, L.J., Putnis, C.V., Valsami-Jones, E., Menneken, M., Putnis, A., 2013. An atomic force microscopy study of the dissolution of calcite in the presence of phosphate ions. Geochimica et Cosmochimica Acta 117, 115–128. https://doi.org/10.1016/j.gca.2013.03.025

Pedrosa, E.T., Putnis, C.V., Putnis, A., 2016. The pseudomorphic replacement of marble by apatite: The role of fluid composition. Chemical Geology 425, 1–11. https://doi.org/10.1016/j.chemgeo.2016.01.022

Wang, L., Ruiz-Agudo, E., Putnis, C.V., Menneken, M., Putnis, A., 2012. Kinetics of Calcium Phosphate Nucleation and Growth on Calcite: Implications for Predicting the Fate of Dissolved Phosphate Species in Alkaline Soils. Environ. Sci. Technol. 46, 834–842. https://doi.org/10.1021/es202924f

Wang, M., Wu, S., Guo, J., Zhang, X., Yang, Y., Chen, F., Zhu, R., 2019. Immobilization of cadmium by hydroxyapatite converted from microbial precipitated calcite. Journal of Hazardous Materials 366, 684–693. https://doi.org/10.1016/j.jhazmat.2018.12.049

How to cite: Julia, M. and Putnis, C. V.: Removal of cadmium from solution during the replacement of calcium carbonate by hydroxyapatite in the presence of phosphate., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6221, https://doi.org/10.5194/egusphere-egu23-6221, 2023.

EGU23-7041 | Orals | GMPV5.1

Emergent permeability in dehydrating rocks is controlled by the stress state and orientation 

Florian Fusseis, James Gilgannon, Arne Jacob, Damien Freitas, Roberto Rizzo, and ian Butler

Fluid-rock interaction relies on the fluid’s ability to migrate through rocks, utilising permeable pore space. While we understand permeability in rocks that interact with fluids to evolve dynamically, e.g. in dehydration or carbonation reactions, we have very little quantitative information on these dynamics, as direct measurements of permeability in reacting rocks are inherently difficult.

Here, we present a series of permeability measurements that capture the evolving fluid transport properties of dehydrating gypsum samples. To derive these measurements, we used an X-ray transparent deformation rig to document gypsum dehydration in 4-dimensional µCT datasets and then modelled the permeability evolution for a segmented sub-volume numerically. In doing so, we were able to characterise the grain-scale porosity and permeability evolution of a dehydration reaction for the first time. We present analyses from two experimental time-series run at a fixed confining pressure, temperature and pore fluid pressure (Pc = 20 MPa; T = ~125 C; Pf = 5 MPa) but contrasting stress states: one with the largest principal stress (Δσ = 16.1 MPa) parallel to the sample cylinder axis and another the largest principal stress (Δσ = 11.3 MPa) being radial. In both cases, as pore space formed due to the negative change in the solid molar volume during the reaction, permeability evolved and increased congruently with porosity in time until ultimately reaching average values of 3.14E-13 m² and 4.55E-13 m², respectively. A clear spatial heterogeneity of fluid flow develops at the grain-scale along with the fabrics in the samples. Importantly,  the calculated permeability tensors are anisotropic from the onset, but  develop over different spatiotemporal trajectories and have different preferred orientations in the two experimental geometries: If the anisotropy is expressed as 1-(min_eigenvalue/max_eigenvalue) of the permeability tensor (where isotropy = 0), then the experiment with the largest principal stress applied radially has a final anisotropy of 0.45, with fluid flow efficiently focussed into a vertical lineation. In the case with an axial largest principal stress, the final anisotropy of permeability is 0.30 with fluid flow being channelled along a foliation that developed orthogonally to σ1.

Our results suggest that the spatial and temporal developments of permeability during a dehydration reaction are controlled by the orientation and relative magnitudes of the principal stresses of a tectonic environment, and that these two parameters exert a strong control on the efficiency of drainage and thus reaction progress. This has consequences for our understanding of fluid movements in thrust tectonics and subduction zones, but also in applications such as the in-situ carbonation of ultramafic rocks.

How to cite: Fusseis, F., Gilgannon, J., Jacob, A., Freitas, D., Rizzo, R., and Butler, I.: Emergent permeability in dehydrating rocks is controlled by the stress state and orientation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7041, https://doi.org/10.5194/egusphere-egu23-7041, 2023.

EGU23-7042 | ECS | Posters virtual | GMPV5.1

Texture formation in Trapiche rubies 

Xinyu Cui, Fufeng Zhao, and Zhaoliang Hou

Abstract:Trapiche describes a gem texture that is characterized by the symmetric six “arms” radiating outward from the cores in gemstone minerals. These is a unique growth pattern, which however is still poorly understood. Here, we document the Trapiche in Trapiche rubies, and discuss formation mechanism of the patterns. The six arms of the Trapiche ruby radiate from a hexagonal core, which separate a single crystal into six growth sectors with internal bandings. Microscopic observations indicate a dendritic growth of the arms. Main branches are dominantly formed by the tube-shaped inclusions, and a part of which exhibit solid minerals, which including graphites, sulfides, calcites. The tube inclusions spatially have a 30° angle to the radiating direction of the arms, and pointing to the direction perpendicular to the hexagonal prism cylindrical {10Ī0}. Our Raman and EPMA analyses suggest that the origin of the ruby may be related to marble. Original source of the inclusions is aluminum-rich fluid with a high amount of CO2, which originated and evolved from magma. Our detail textural and chemistry on Trapiche ruby may suggest that during the ruby formation, a high crystallization driving force is necessary for arms to be a dendritic pattern which can overcome the growth interface of the bandings.   

 

How to cite: Cui, X., Zhao, F., and Hou, Z.: Texture formation in Trapiche rubies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7042, https://doi.org/10.5194/egusphere-egu23-7042, 2023.

EGU23-7599 | ECS | Orals | GMPV5.1

Base metal ore mineralization in the upper crust of the Moldanubian Domain, Bohemian Massif, CZ: generation and source, a question of fluid flow 

Ina Alt, Tobias Fusswinkel, Thomas Wagner, Pieter Z. Vroon, and Fraukje M. Brouwer

Cycling of fluids and their carried metals in the continental crust results in the local enrichment of certain elements, such as Pb, Zn, Cu, at upper crustal levels. Upper crustal ore deposits play a significant role for the advance of our core technologies facilitating communication and transportation. Determining where and how metals are cycled at crustal scale is crucial to infer potential ore deposits.

This study focuses on base metal (Pb, Zn, Cu) quartz vein mineralization in the Moldanubian Domain in central Czech Republic. During the waning stages of the Variscan orogeny, the Moldanubian was affected by MP-HT metamorphism due to underplating of the Saxothuringian Domain and the Brunia microplate [1, 2]. The continuous compressional stress regime led to the collapse and subsequent uplift of the central Moldanubian Domain. This rapid uplift triggered decompressional melting, leading to the formation of a batholith known as the Moldanubian pluton [2]. Collapse occurred along two large scale fault systems perpendicular to the prevailing stress regime [2, 3]. We suggest tectonic movement led to fluid infiltration of the migmatized upper crust preserved as quartz veins with Pb-Zn-Cu mineralization. Once the Moldanubian Domain reached upper crustal levels, rehydration of the rocks and passive enrichment of metals in the fluid occurred.

Petrographic observations show that the composition of fluids changed over time. The first generation of fluids generated translucent quartz with comparable few and small (5 - 30 µm) inclusions whereas the second generation of fluids produced more and bigger (10 - 70 µm) fluid inclusions that incorporate solid phases in 10 % of observed inclusions. The last phases to precipitate in cavities are the base metal sulfides which appear as pyrite, galena, and sphalerite.

Microthermometry data supports a gradual change of fluid composition as first-generation fluid inclusions show NaClequiv values lower than 1 wt.-%, while second-generation fluid inclusions are significantly higher in salinity with 3 - 7 wt.-% NaClequiv. Raman spectroscopy of fluid inclusions of second-generation quartz show enrichment of CH4 and N2 in the gaseous phase, representing a reducing environment. LA-ICPMS data of single fluid inclusions will be used to generate a geochemical fingerprint of the fluids responsible for ore generation.

 

[1] Schulmann, K., et al., An Andean type Palaeozoic convergence in the Bohemian Massif. Comptes Rendus Geoscience, 2009. 341(2-3): p. 266-286.

[2] Verner, K., et al., Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens. Journal of Geodynamics, 2014. 73: p. 100-117.

[3] Žák, J., et al., A plate-kinematic model for the assembly of the Bohemian Massif constrained by structural relationships around granitoid plutons. Geological Society, London, Special Publications, 2014. 405(1): p. 169-196.

How to cite: Alt, I., Fusswinkel, T., Wagner, T., Vroon, P. Z., and Brouwer, F. M.: Base metal ore mineralization in the upper crust of the Moldanubian Domain, Bohemian Massif, CZ: generation and source, a question of fluid flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7599, https://doi.org/10.5194/egusphere-egu23-7599, 2023.

EGU23-7876 | ECS | Orals | GMPV5.1

Apatite as a monitor for sulfur redox reactions during fluid-rock interaction in the subduction channel 

Jesse Walters, Horst Marschall, Tobias Grützner-Handke, Kevin Klimm, Brian Konecke, and Adam Simon

The oxidation state of sulfur in slab fluids is controversial, with both dominantly oxidized and reduced species proposed. Here we use in situ X-ray absorption spectroscopy analysis of sulfur-in-apatite to monitor changes in the oxidation state of sulfur during high-P metasomatism by slab fluids in the subduction channel. Our samples include a 73 cm continuous transect of reaction zones between a metagabbroic eclogite block and serpentinite matrix from a mélange zone on the island of Syros, Greece. The block core consists of garnet, omphacite, phengite, paragonite, epidote-clinozoisite, and rutile. In this region, apatite is only observed as elongate inclusions in omphacite cores. From the core outwards micas are increasingly replaced by epidote-clinozoisite, garnets are smaller and more frequent, pyrite + bornite is observed as inclusions in recrystallized omphacite, and apatite is increasingly abundant in the matrix and inclusions in garnet. A major transition at 48 cm separates an assemblage of Ca-Na amphibole, omphacite, chlorite, pyrite, and apatite from the inner garnet-bearing eclogite assemblages. Omphacite disappears from the assemblage at ~56 cm and amphibole compositions sharply transition to tremolite at 59 cm. Finally, the assemblage tremolite + talc + pyrite is observed after ~70 cm.

Apatites in the eclogite assemblages exclusively display S6+ peaks in their absorption spectra. This includes apatite inclusions in omphacite in the least altered lithology, as well as matrix apatite and isolated apatite inclusions in garnet in the outermost metasomatized eclogite zone. In the intermediate pyrite-rich (~1–5 vol %) amphibole + omphacite + chlorite zone, apatite displays a strong S1- absorption peak in most grains, with rare analyses showing mixed S1- and S6+. Finally, apatite in the outermost tremolite-bearing assemblages only displays a S6+ peak. The pyrite-rich zone at 48 cm occurs at the initial interface between the serpentinite matrix and eclogite block, characterized by a dramatic decrease in Na content and Mg#. Our data suggest that reduction of S6+ in infiltrating fluids to S1- in pyrite became focused as Fe diffused across the steep Mg# gradient, resulting in pyrite precipitation. In contrast, S reduction in the Mg-rich tremolite-dominant portions of the transect was limited by a lack of Fe, resulting in low modes of pyrite and fluid buffered S6+ in apatite. Finally, S6+-bearing apatite is also observed in reaction zone lithologies from elsewhere on Syros, suggesting our observations are not isolated.

Two important conclusions are drawn from these data and observations: (1) In the case of Syros, slab fluids at eclogite-facies conditions carried oxidized S6+, and (2) The interaction of these fluids with eclogites composed of ferrous-Fe silicates resulted in extensive sulfide precipitation.

How to cite: Walters, J., Marschall, H., Grützner-Handke, T., Klimm, K., Konecke, B., and Simon, A.: Apatite as a monitor for sulfur redox reactions during fluid-rock interaction in the subduction channel, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7876, https://doi.org/10.5194/egusphere-egu23-7876, 2023.

EGU23-9162 | Orals | GMPV5.1

What is the cause of lattice rotation in clinopyroxene dendrites? 

Thomas Griffiths, Gerlinde Habler, Olga Ageeva, Christoph Sutter, Ludovic Ferrière, and Rainer Abart

Dendritic crystallisation is a key geological pattern-forming mechanism, typical of, and recording information about, rapid crystallization events. In this contribution we report on clinopyroxene (Cpx) dendrites in a basaltic rock fulgurite, which formed due to electrical discharge impacting a basaltic rock. Unusually, these dendrites exhibit a curved morphology. The curved, tapering main dendrite branches are up to 50 µm long, range from 3 µm to 100 nm thickness, and are surrounded by several higher orders of branches, which are also curved. The morphological curvature corresponds to lattice rotation, so branches have consistent elongation directions in crystal coordinates. Total rotation exceeds 180° for some branches, with the highest curvature found being 7° per µm. Such “bent” Cpx dendrites have been observed in experiments (e.g. Hammer et al. 2010), but the mechanism of bending was not previously understood.

By combining microstructural observations with crystallographic orientation maps from electron backscatter diffraction analyses of multiple Cpx dendrites, their three-dimensional morphological and crystallographic configuration was reconstructed. Dendrites feature a planar latticework of branches parallel to the Cpx (010) plane. Branches in this plane are elongated either parallel to {001}* (i.e. normal to the (001) plane) or <10-1>, and exhibit strong and weak lattice curvature, respectively. Sprouting out of this plane are branches parallel to {021}* (originating from {001}* branches) and <12-1> (originating from <10-1> branches), both types being weakly curved. Regardless of the crystallographic direction parallel to elongation, all branches exhibit a crystallographic rotation axis parallel to [010] of Cpx. Furthermore, the rotation sense is consistent regardless of elongation direction in crystal or sample coordinates.

The crystallographic control on the sense of bending and on the rotation axis indicates that bending is not caused by sample-scale compositional, thermal, or mechanical gradients. Instead, asymmetric compositional and thermal fields around branch tips are responsible for bending, supported by the fact that compositional gradients exist in the glass surrounding dendritic crystals. The specific cause of bending is inferred to be asymmetric distribution of melt supersaturation at branch tips, resulting from unequal growth rates of different facets. Branch-tip morphology alone poorly explains the constant sense of rotation of all branches, as the sense of morphological asymmetry is unlikely to be consistent for all branch types. The [010] rotation axis implies that lattice rotation is accomplished by incorporation of a single sign of [001](100) edge dislocations, with a maximum inferred density of 2*1014 m-2.

This work provides new insights into fundamental processes occurring during rapid crystallization of Cpx and other minerals. Furthermore, microstructural observations suggest that higher degree of undercooling correlates with greater lattice curvature. Bent dendrites may thus encode information about spatial variations in the cooling rate and/or undercooling of samples. Finally, the consistent [010] rotation axis is expected to be preserved during recrystallization, offering a potential way to identify curved dendritic growth stages even after recrystallization.

References:

Hammer et al. (2010), Geology 38:367-370. https://doi.org/10.1130/G30601.1

Griffiths et al. (2022), J Petrol, egac125. https://doi.org/10.1093/petrology/egac125

This contribution was funded by the Austrian Science Fund (FWF): P 33227-N

How to cite: Griffiths, T., Habler, G., Ageeva, O., Sutter, C., Ferrière, L., and Abart, R.: What is the cause of lattice rotation in clinopyroxene dendrites?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9162, https://doi.org/10.5194/egusphere-egu23-9162, 2023.

EGU23-9856 | Posters virtual | GMPV5.1

Stress sensitivity of gypsum dehydration kinetics at constant uniaxial stress under dry conditions 

Christoph Schrank, Tomasz Blach, Yeping Ji, Phung Vu, Xiaodong Wang, Michael Jones, Nigel Kirby, Susanne Seibt, and Klaus Regenauer-Lieb

We recently showed that the dehydration of alabaster, natural gypsum rock with randomly oriented grains, can be accelerated by a factor of two through the application of an elastic differential pre-stress of ~ 5 MPa applied via a uniaxial constant-displacement boundary condition (https://doi.org/10.1038/s43246-021-00156-9). Here, we present a novel series of gypsum dehydration experiments using a new in-situ experimental cell monitored with fast synchrotron transmission small- and wide-angle X-ray scattering (SAXS/WAXS) to investigate if an acceleration of the kinetics also occurs at constant uniaxial stress. Prior to stressing and heating, the loaded sample chamber was flushed with nitrogen to remove atmospheric moisture and finally locked, filled with the nitrogen atmosphere pressurised to 1 bar. Six increasing uniaxial stresses in the interval [0;10] MPa were studied at a dehydration temperature of 142˚C. A strongly nonlinear acceleration of dehydration rate is observed over the studied stress interval. At 10 MPa, the reductions of induction and characteristic time amount to ~60% and ~50%, respectively. 2D SAXS patterns generally evolve from isotropic to highly anisotropic shapes, indicating preferential growth of nano-scatterers. Post-mortem scanning-electron imaging reveals that the phase transformation occurs via pseudomorph replacement. These results are largely consistent with our previous experiments and support the notion that tectonic stresses affect mineral transformation kinetics.

How to cite: Schrank, C., Blach, T., Ji, Y., Vu, P., Wang, X., Jones, M., Kirby, N., Seibt, S., and Regenauer-Lieb, K.: Stress sensitivity of gypsum dehydration kinetics at constant uniaxial stress under dry conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9856, https://doi.org/10.5194/egusphere-egu23-9856, 2023.

We consider a porous medium infiltrated by a reactive fluid which triggers coupled dissolution/precipitation reactions at pore surfaces. To study these processes, we model the porous medium as a system of interconnected pipes with the diameter of each segment increasing in proportion to the local reactant consumption. Moreover, the topology of the network is allowed to change dynamically during the simulation: as the diameters of the eroding pores become comparable with the interpore distances, the pores are joined together thus changing the interconnections within the network. With this model, we investigate different growth regimes in an evolving porous medium, allowing for both erosion and precipitation of the dissolved material.

The interplay of flow, transport and reaction in such a system can give rise to a variety of patterns: from spontaneous channeling to nearly homogeneous transformation of the entire rock matrix into the product phase. Interestingly, even if the product phase has a larger molar volume than the parent phase, clogging in such a system can be avoided, due to the interplay of dissolution and precipitation resulting in the continuous creation of new flow paths. These results can be relevant for the analysis of carbonation reactions, in which an important goal is to avoid clogging of the pore space that can lead to permeability reduction and the overall slowdown of the process.

How to cite: Szymczak, P. and Budek, A.: Channeling, clogging and permeability oscillations: different macroscopic regimes in mineral replacement   , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10432, https://doi.org/10.5194/egusphere-egu23-10432, 2023.

EGU23-10955 | Orals | GMPV5.1

Strontium partitioning in calcite and its controling factors 

Shuo Zhang, Donald DePaolo, and Qicui Jia

Strontium (Sr) is a common trace element in calcite which is incorporated during calcite precipitation through either inorganic or organic pathways. The ratio of Sr to calcium (Ca) in carbonate rocks and minerals has been widely used in studies of paleoceanography, marine sediment diagenesis, and hydrothermal alteration of oceanic crust. The partitioning coefficient of Sr (KSr) describes fundamentally the partitioning of Sr between calcite and aqueous solutions, but is a complicated function of environmental conditions and water composition. It has long been recognized that KSr is strongly dependent on the precipitation rate of calcite (Rp), which has been formulated in a surface kinetic model [1] and a subsequent ion-by-ion model [2]. We re-evaluate available experimental data of Sr partitioning in calcite and find apparent dependence of KSr on calcite oversaturation and solution pH [3]. An ion-by-ion model is developed that successfully reproduces the observed KSr values at given solution chemistry [4]. Our model also reproduces observed KSr-Rp relationships at various temperatures of 5, 25 and 40 oC. This model provides an opportunity to evaluate effects of past seawater composition on Sr partitioning and their possible roles in reconstructing seawater Sr/Ca ratio in the geological history [5], in using pore fluid Sr concentration to extract sediment-fluid exchange rates in deep sea carbonate sediments [5], and in understanding Sr partitioning in biogenic calcite such as foraminifera.

Reference

[1] DePaolo, D.J., Surface kinetic model for isotopic and trace element fractionation during precipitation of calcite from aqueous solutions. Geochimica et Cosmochimica Acta, 2011. 75(4): p. 1039-1056.

[2] Nielsen, L.C., J.J. De Yoreo, and D.J. DePaolo, General model for calcite growth kinetics in the presence of impurity ions. Geochimica et Cosmochimica Acta, 2013. 115: p. 100-114.

[3] Zhang, S. and D.J. DePaolo, Equilibrium calcite-fluid Sr/Ca partition coefficient from marine sediment and pore fluids. Geochimica Et Cosmochimica Acta, 2020. 289: p. 33-46.

[4] Jia, Q., et al., A model for pH dependent strontium partitioning during calcite precipitation from aqueous solutions. Chemical Geology, 2022. 608: p. 121042.

[5] Zhang, S., R.J. Zhou, and D.J. DePaolo, The seawater Sr/Ca ratio in the past 50 Myr from bulk carbonate sediments corrected for diagenesis. Earth and Planetary Science Letters, 2020. 530: p. 115949.

How to cite: Zhang, S., DePaolo, D., and Jia, Q.: Strontium partitioning in calcite and its controling factors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10955, https://doi.org/10.5194/egusphere-egu23-10955, 2023.

EGU23-11542 | ECS | Orals | GMPV5.1

Fault slip in clay-rich rocks due to water-clay interactions 

Markus Rast, Claudio Madonna, Paul A. Selvadurai, Quinn Wenning, Jonas B. Ruh, and Antonio Salazar Vásquez

Clay-rich rocks occur in a wide range of tectonic settings. They are of great interest, for example, for the mechanical properties of shallow subduction zone interfaces, but also for natural barriers in nuclear waste deposits or as subsurface caprocks for CO2 storage. In contact with a polar fluid (e.g., water), the interaction between clay minerals and fluid can lead to swelling or, under confined conditions, build-up of swelling stress. Many studies have focused on the closure of cracks in clay-rich sedimentary rocks by swelling (also referred to as ’self-sealing’). However, less is known about how water-clay interactions affect the stress state of clay-rich rocks and whether they may induce slip along pre-existing faults. We try to address this knowledge gap in the present study by conducting triaxial shear experiments.

The experiments are performed using oblique saw-cut cylindrical samples, where the top half consists of a clay-rich rock (Opalinus claystone) and the bottom half of a permeable sandstone (Berea sandstone). To estimate the frictional properties of the sandstone-claystone interface, dry experiments are performed at 4 to 25 MPa confining pressure and constant axial displacement of 0.1 mm/min. Fluid injection experiments, where fluids are injected through the permeable footwall sandstone, are performed at 10 and 25 MPa confining pressure, constant piston position (no axial displacement), and an initial differential stress of about 70 % of the expected yield stress. The effect of water-clay interactions on the stress state is estimated by comparing the fluid pressures required to initiate slip when a non-polar fluid is injected (no water-clay interactions are expected) and when a polar fluid is injected (water-clay interactions will occur). In some experiments, the sample assemblage is equipped with fiber optics strain sensors glued to the surface of the sample to distinguish between (poro)elastic deformation of the matrix, deformation due to water-clay interaction, and elastic relaxation due to slip along the saw-cut.

For fluid injection experiments with a non-polar fluid (decane), the mechanical data indicate that slip along the saw-cut occurs at fluid pressures close to what is expected based on the friction slip envelope determined for the dry state. For fluid injection experiments with a polar fluid (deionized water), a differential stress drop already occurs when the water initially reaches the sandstone-claystone interface at ambient fluid pressure (0.1 MPa), which is not expected based on the dry friction slip envelope. The fiber optics strain sensor data indicate that swelling of the claystone is followed by a microstructural collapse before slip along the saw-cut likely occurs. In summary, our data suggest that water-clay interactions may initiate slip due to (1) the alteration of the friction slip envelope, (2) build-up of swelling stress, and (3) collapse of the claystone microstructure. However, to what extent these three mechanisms contribute to the according differential stress drop requires further research.

How to cite: Rast, M., Madonna, C., Selvadurai, P. A., Wenning, Q., Ruh, J. B., and Salazar Vásquez, A.: Fault slip in clay-rich rocks due to water-clay interactions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11542, https://doi.org/10.5194/egusphere-egu23-11542, 2023.

EGU23-11811 | ECS | Posters on site | GMPV5.1

Mass transfer between serpentinites and metapelites in a paleo-subduction interface: a case study from the Yuli belt, eastern Taiwan 

Dominikus Deka Dewangga, Chin-Ho Tsai, Hao-Yang Lee, Wen-Han Lo, Yoshiyuki Iizuka, and Chi-Yu Lee

The Yuli belt in eastern Taiwan attests to tectonic evolution involving subduction metamorphism because two metamélange units contain high-pressure (HP) blocks or layers of metaigneous rocks and serpentinites enclosed in metasedimentary schists. Metasomatic reaction zones occur locally along the contact between serpentinite (SP) and pelitic schist (PS). In the Tsunkuanshan area, we recognized five metasomatic zones. From PS to SP, the dominant minerals in each zone are: (I) albite, chlorite, phengite; (II) albite, amphibole, biotite, stilpnomelane; (III) chlorite, phengite, albite, epidote; (IV) epidote, chlorite, albite; and (V) talc, chlorite. Minor garnet and glaucophane are present in zone I and II, respectively. Field and petrographic observations combined with whole-rock major elements data suggest that this rock association was formed by diffusive exchanges between the PS and SP. Zones I - IV and PS samples show identical rare earth element (REE) patterns, indicating that these zones are of PS protolith. Hence, the original boundary between the PS and SP is likely in the zone IV and V. The isocon method was applied to quantify the mass balance among the metasomatic zones. The result shows mass changes in zones: I: +12%; II: -4%; III: +50%; IV: +56%. Enrichment of Ca is present in the entire reaction zones, especially the zone IV (up to 91%), whereas Na is only enriched within the zone I (~80%) and II (~89%). These enrichments are likely due to the involvement of external fluids. The formation of these metasomatic rocks was not only controlled by diffusive exchanges between PS and SP, but also by the Na and Ca rich fluid infiltrations. The existence of glaucophane within the zone II indicates that the metasomatism occurred under HP metamorphic conditions in a paleo-subduction interface.

Keywords: Fluid-rock interactions, isocon method, Na and Ca rich fluids, high-pressure, Yuli belt.

How to cite: Dewangga, D. D., Tsai, C.-H., Lee, H.-Y., Lo, W.-H., Iizuka, Y., and Lee, C.-Y.: Mass transfer between serpentinites and metapelites in a paleo-subduction interface: a case study from the Yuli belt, eastern Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11811, https://doi.org/10.5194/egusphere-egu23-11811, 2023.

EGU23-11886 | ECS | Orals | GMPV5.1

Multiscale solute transfer and porosity evolution during pervasive replacement of serpentine by carbonate and quartz - insights from the Oman ophiolite 

Manuel D. Menzel, Janos L. Urai, Oliver Plümper, Markus Ohl, and Alexander Schwedt

Pervasive carbonation of serpentinized peridotite to carbonate-quartz rock (listvenite) due to infiltration of CO2-bearing fluid is a remarkable process because it can be geologically fast and it increases the rock’s carbon content from initially zero to > 30 wt% CO2. This pervasive conversion is related to an overall solid volume increase while at the same time requiring high time-integrated fluid rock ratios with permeability and diffusivity on all scales. Thus, porosity has to be created dynamically during reaction progress as otherwise fluid pathways become clogged by the reaction products carbonate and quartz, which is one of the major obstacles for artificial carbon storage by peridotite carbonation. Processes that can renew porosity and permeability during carbonation are fracturing and veining – in response to tectonic stress [1] or induced by reaction and crystal growth [2], or a combination of both –, reaction-enhanced ductile deformation [3,4], and spatial decoupling of dissolution and precipitation with solute transfer at different length scales.

Using SEM, EBSD, TEM and FIB nano-tomography, we investigated the microstructural record of local solute transfer and its role for porosity renewal in natural carbonate-bearing serpentinites, transitional serpentine-carbonate-quartz assemblages and listvenites from the Samail Ophiolite, Oman. The clearest indicators of pervasive replacement accommodated by local solute transfer are pseudomorphic replacement structures where carbonate and quartz occur in distinct microstructures corresponding to different inherited peridotite and serpentinite textures. A common pseudomorphic replacement structure in the Samail carbonated peridotite are quartz-fuchsite intergrowths replacing bastite (pseudomorphs after orthopyroxene) in listvenite with harzburgite protoliths. A local strong crystallographic alignment of quartz in each of the bastite/pyroxene pseudomorphs suggests that the anisotropic porosity structure of bastite serpentine favored oriented, epitaxial growth of quartz. Transitional serpentine-carbonate-quartz assemblages show that the first quartz and carbonate generations precipitate coeval but spatially separated, with distinct crystal habits. FIB nano-tomography, STEM analysis and high resolution SEM on ion-polished samples of a transitional serpentine-dolomite-quartz rock from the carbonation reaction front show nano-porous fluid channels in fibrous serpentine at high angle to a highly serrated carbonate-serpentine replacement contact. These nano-scale fluid channels facilitated bidirectional mass exchange of Ca, C, Mg and Si bearing solutes between sites of preferential replacement, such as the cores of serpentine mesh textures, and larger-scale permeability networks along veins and fractures. These observations imply that massive and pervasive solute transfer through the reacting serpentine matrix is possible on a small scale, without clogging of porosity by immediate co-precipitation of quartz or Mg-silicates. Spatial decoupling of dissolution and precipitation was likely caused by the dynamically evolving composition of the reacting fluid and/or due to the influence of differential stress and volumetric strain – a mechanism that can compensate on a local scale for the volume expansion expected of isochemical carbonation reactions.

 

[1] Menzel et al., Solid Earth, 2022; https://doi.org/10.5194/se-2021-152

[2] Kelemen & Hirth, EPSL, 2012; https://doi.org/10.1016/j.epsl.2012.06.018

[3] Menzel et al., Nature Communications, 2022; https://doi.org/10.1038/s41467-022-31049-1

[4] Kelemen et al., JGR, 2022; https://doi.org/10.1029/2021JB022352

 

Funding: Junta de Andalucía (Postdoc_21_00791); DFG grants UR 64/20-1, UR 64/17-1; and EU Horizon 2020 Transnational Access EXCITE _C1_2022_34.

How to cite: Menzel, M. D., Urai, J. L., Plümper, O., Ohl, M., and Schwedt, A.: Multiscale solute transfer and porosity evolution during pervasive replacement of serpentine by carbonate and quartz - insights from the Oman ophiolite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11886, https://doi.org/10.5194/egusphere-egu23-11886, 2023.

EGU23-11946 | ECS | Orals | GMPV5.1

Fluid-rock interaction in sediments subducted to the seismogenic zone: Implication from mineral reactions, fluid-mobile elements and δ7Li isotopes 

Kristijan Rajič, Hugues Raimbourg, Antonin Richard, and Catherine Lerouge

To evaluate fluid-rock interaction in subducted sediments buried down to seismogenic depths (250-330℃), we describe mineral reactions along the prograde path and their influence on the fluid budget, fluid-mobile element concentrations, and δ7Li of fluids. We focused in particular on metapelitic rocks from two paleo-accretionary complexes, the Kodiak accretionary complex, USA, and the Shimanto belt, Japan.

In metapelites from Kodiak and Shimanto, illite-to-chlorite transformation is the main mineral reaction in the temperature range from 250 to 330℃. Such reaction requires additional H2O and the plausible explanation is the consumption of pore water, contributing to the increase in the salinity of the pore fluid from 250 to 330°C, trapped as inclusions in quartz veins. Textural evidences, mineral reactions, and mass-balance calculations suggest that the system behaved as closed in both studied sites in terms of major elements. However, trace elements provide a slightly different picture. Indeed, fluid-mobile elements (FME; Li, B, Rb, Sr, Cs, Ba) indicate opposite trends between the two sites: In Kodiak, FME whole-rock concentrations are preserved from 250 to 330℃, in agreement with FME concentrations in illite and chlorite that suggest redistribution between rock-forming minerals. In contrast, samples from Shimanto show significant loss of all studied FME from 250 to 330℃, reflecting a decrease in the FME content of individual mineral phases.

Further insight into the fluid-rock interactions were provided by the analysis of δ7Li both in quartz and its fluid inclusions (FI) by applying crush-leach technique. In Kodiak, the fluid is characterized by relatively higher δ7Li than Shimanto (+8.1 to +17.07‰ in comparison to +2.53 to +10.39‰, respectively). Such variations can be accounted for by mineral reactions and lithium concentrations in individual phases. Chlorite is the main host of lithium. In the Kodiak complex, lithium concentrations in chlorite remains statistically identical between 250℃ and 330℃ (⁓240 ppm), whereas in the Shimanto belt significant decrease of lithium is observed in chlorite (from ⁓320 ppm in chlorite at 250℃ down to ⁓120 ppm at 330℃). Hence, the higher δ7Li of fluids in Kodiak is explained by the chlorite crystallization as it preferentially consumes 6Li and the fluid remains enriched in 7Li. Conversely, fluids from Shimanto are isotopically lighter than from Kodiak, consistent with lithium loss in chlorite as temperature increases. Therefore, δ7Li of fluids in both Kodiak and Shimanto examples can be accounted for by local redistribution of lithium between reacting phyllosilicates and their isotopic fractionation.

Overall, major elements, FME, and δ7Li of fluids point to a local redistribution of elements in the Kodiak complex, suggesting that the system behave as closed, as the studied units are underplated as a part of thick turbiditic sequence far from any large-scale fault zones. In the Shimanto belt, the loss of FME suggest rather the open system opposite to major elements, as they are more sensitive indicators of transfers between rock and fluid. Such opposite trend between Kodiak and Shimanto is largely controlled by (i) the amount of internal strain within the different units and (ii) the proximity to large-scale fault zones.

How to cite: Rajič, K., Raimbourg, H., Richard, A., and Lerouge, C.: Fluid-rock interaction in sediments subducted to the seismogenic zone: Implication from mineral reactions, fluid-mobile elements and δ7Li isotopes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11946, https://doi.org/10.5194/egusphere-egu23-11946, 2023.

EGU23-12318 | ECS | Posters on site | GMPV5.1

Quartz solubility in low-density aqueous fluids: evaluation and development of thermodynamic models 

Federica Salomone and David Dolejš

Solubility of quartz in aqueous fluids over a wide range of temperatures and pressures is crucial for our understanding of water–rock interaction. Experimental data cover a temperature range of 20 to 1130 °C and pressures from 1 to 20 kbar, and this dataset provides a useful basis for critical comparison and development of thermodynamic models for mineral solubility and aqueous solutes. Thermodynamic models for quartz solubility in pure water (1982-2021) are based on one of the following approaches: (1) successive hydration of solute, (2) correlation with solvent density, (3) virial equation of state for solute-solvent mixtures, or (4) Helgeson-Kirkham-Flowers (HKF) electrostatic equation of state. Predictions from these models generally converge at hydrothermal and supercritical temperatures in the fluid density range of 0.6-1.0 g cm-3. At high temperatures and fluid densities, the models based on successive hydration or virial expansion loose their physical meaning; the electrostatic approaches tend to overestimate the quartz solubility, although the large number of parameters in the HKF equation of state offers remarkably large calibration flexibility. At low pressures and low fluid densities, the individual approaches diverge: the density and virial models correctly approach the limiting case of ideal gas, but the virial equations of state tend to predict consistently higher solubilities. In this study we develop a more physically rigorous density-based model for quartz and test its performance in low-pressure aqueous fluids. Thermodynamic properties of aqueous solute are formulated as a function of hydration number that is typically variable at very low pressures (< 400 bar). At partial hydration, the thermodynamic properties of species are mainly controlled by enthalpy of stepwise hydration reactions and long-range solute-solvent interactions are minimal. At complete inner-sphere hydration the thermodynamic properties of aqueous species become a combined contribution of unhydrated species properties, mechanic interaction in the hydration sphere and standard-state conversion terms. When complete hydration of a species is achieved, Gibbs energy of species becomes linear with log water density at constant temperature, thus mimicking the linear log K – log density relationship for the mineral solubility equilibrium.

How to cite: Salomone, F. and Dolejš, D.: Quartz solubility in low-density aqueous fluids: evaluation and development of thermodynamic models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12318, https://doi.org/10.5194/egusphere-egu23-12318, 2023.

EGU23-15099 | ECS | Posters on site | GMPV5.1

Structurally controlled kaolinite-alunite mineralization in the lithocap of a fossil geothermal system 

Barbara Marchesini, Stefano Tavani, Marco Mercuri, Luca Aldega, Nicola Mondillo, Mattia Pizzati, Fabrizio Balsamo, and Eugenio Carminati

Geothermal heat is a crucial source of renewable energy. Its present and future exploitation can be enhanced by the understanding of the in–situ structural and mineralogical processes and of how these processes may change the reservoir productivity.  Fossil hydrothermal system may thus be used as analogues to study in-situ fluid-rock interaction processes in active geothermal systems.

We present the results of a structural-mineralogical study carried out in the lithocap of the Allumiere high-sulphidation epithermal system (Tolfa Mountains district, northern Latium, Italy). We integrated measurements of attitude of faults and fractures from field analysis with a virtual outcrop model constructed from drone imagery to model the distribution of major faults at the scale of the entire quarry. We then characterized the textures and mineralogical compositions of the alteration facies using optical petrography, Scanning Electron Microscope (SEM), X-ray diffraction analysis and field-based short-wave infrared (SWIR) spectrometer and we mapped their distribution in relation to major faults orientation.

We interpreted that initial argillization was promoted by circulation of highly reactive fluid(s) along a major fluid conduit, probably in the form of a network of fault and fractures. Fluid circulation promotes hydrolytic alteration of the Plio-Quaternary pyroclastic rocks, forming a highly silicified carapace at the immediate vicinity of conduits. Enrichment in alunite and kaolinite increases towards distal areas, which in turn fades out into illite-smectite-bearing zone, where the country rock appears less altered.  Latest fracturing and fluid circulation occurs along two major sets of faults, oriented NE-SW and NW-SE that sharply put in contact different mineralogical facies.

We propose that initial alteration induces a mineralogical-mechanical zonation that control latest reactivations of the system. Strain localization promotes a massive mineralization of alunite and kaolinite by continuous dissolution and precipitation along major faults.

How to cite: Marchesini, B., Tavani, S., Mercuri, M., Aldega, L., Mondillo, N., Pizzati, M., Balsamo, F., and Carminati, E.: Structurally controlled kaolinite-alunite mineralization in the lithocap of a fossil geothermal system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15099, https://doi.org/10.5194/egusphere-egu23-15099, 2023.

EGU23-15834 | ECS | Posters virtual | GMPV5.1

Fault instability and slipping in thermally unstable rock 

Jianhua Huang, Bo Zhang, Junjie Zou, and Honglin He

Faults that cut carbonate rocks are the most important seismogenic sources worldwide, while the fault weakening and recovery mechanism in carbonate fault rock still remains controversial. In this study, the structures of an exposed normal fault zone hosted in dolostones with chert bands from the Yuguang basin southern marginal fault (YBSMF), northeast of the Shanxi graben system, North China, was studied by field-based structural analysis, microstructural and fabric investigations. The microstructural observations show that the fault slip surface exhibits a range of slip-related structures including slickenlines, truncated clasts and nano-scale amorphous materials/fragments. On the fault slip surface, the carbonate fault rock contains a large number of nanoparticles. These nanoparticles were shaped into two forms, single spherulitic nanoparticle and agglomerated nanoparticles. The slip zone, under the slip surface, is characterized by cataclasite, with various foliatization in red injection band. EBSD analysis results show weak CPOs, with the (0001) planes of the dolomite fragments nearly parallel to the slip surface. Our microstructural investigations in the dolomite fault rocks, combined with previous publications, suggest the single spherulitic nanoparticles can be the result of thermal decomposition of dolomite along the major slip surface of the normal fault. Nano powder lubrication caused by the rolling of single spherulitic nanoparticle plays a key role during carbonate fault slipping. The thermal pressurization of pore fluid leads to laminar grain flow along the fracture and finally forms foliations in the red injection layers. The transformation from single spherulitic nanoparticles to agglomerated nanoparticles by superplastic diffusive mass transfer results in the recovery of friction strength at the fault plane. After the coseismic slip (or during afterslip), a relatively thick portion in the principal slip zone suffers a temperature increase, leading to the plastic deformation and formation of CPOs of dolomite in the principal slip zone. We inferred that nanoparticles can be produced by thermal decomposition transformation, which facilitate and inhibit earthquake behavior on fault surfaces. The postseismic strength recovery can be generated partly by agglomerated nanoparticles. We consider that nanoparticles produced by thermal decomposition of dolomite play a key role in carbonate fault instability during coseismic slip.

How to cite: Huang, J., Zhang, B., Zou, J., and He, H.: Fault instability and slipping in thermally unstable rock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15834, https://doi.org/10.5194/egusphere-egu23-15834, 2023.

Melt production and migration are important phenomena in the lower and middle crust. The presence of melt in a volume of rock has a significant impact on its rheology and on the structure of the Earth’s crust in general. Once partial melting starts, the molten portion can either flow towards shallower crustal levels or stay in the area where it originated. A partially molten rock can eventually solidify and be brought to the Earth’s surface, where the distribution of the former melt can provide insight into the conditions in which the rock formed.

Here we present a set of numerical experiments utilising an innovative DEM-continuum model to simulate partial melting and the initial formation of porosity channels. This hybrid model incorporates porous flow to solve for pervasive percolation of melt and a network of springs on a second grid to represent the linear elastic behaviour of the host rock. The latter also includes phenomena such as fracture formation and propagation.

We show under which conditions melt-filled fractures can emerge from local areas of melt production and evolve into larger melt channels. Importantly, our models show that leucosome patterns seen in outcrops can be used to constrain the relative rates of melt diffusion along grain boundaries, syn-migmatisation deformation, and local melt production. Based on the relative rates of these processes, we define regimes with specific melt pattern distributions. The definition of these regimes can be a useful tool for the interpretation of the history of a migmatite.

How to cite: Fedrizzi, G., Piazolo, S., Koehn, D., and Pegler, S.: The Use of Leucosome Patterns in Migmatites to Decipher Rates of Melt Production, Melt Percolation and External Deformation: Insights from Numerical Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16256, https://doi.org/10.5194/egusphere-egu23-16256, 2023.

The Śnieżnik Massif forms the eastern part of the Orlica-Śnieżnik Dome (OSD), located in the north-eastern part of the European Variscan Belt. The OSD, which exposes the root zone of the Variscan Orogen, comprises mostly orthogneisses containing small bodies of ultra-high pressure (UHP) eclogites. Previous studies on the metamorphic conditions recorded by these eclogites yielded inconsistent results. Some authors suggest that they were metamorphosed in conditions of ~1.9-2.2 GPa and ~700-750 °C 1. Others, however, argue that the eclogites experienced nearly-UHP peak metamorphic conditions of ~2.6-3.0 GPa and 800-930 °C.2

This study provides the first evidence of UHP metamorphic episode recorded in eclogites from the OSD, as coesite inclusions were discovered in garnet and omphacite grains. This finding is consistent with our results obtained using Grt-Cpx-Ky-Ph-Coe/Qtz geothermobarometry and phase equilibria modelling, which both indicated conditions of peak metamorphism of ~2.8 – 3.2 GPa and ~830-870 °C, partially overlapping the coesite stability field.

We also applied quartz-in-garnet elastic barometry to provide additional constraints on the pressure conditions of metamorphism. About 60 inclusions of quartz were identified using Raman spectroscopy. The residual pressure calculated from the spectral shifts of 464 cm-1 characteristic quartz Raman band reaches a maximum of ~0.73 GPa. This corresponds to the entrapment pressure of ~2.1 GPa, calculated based on the elastic solution for an isotropic spherical inclusion. This estimation contradicts the results coming from methods based on equilibrium thermodynamics. Moreover, such low peak pressure would not explain the presence of the observed coesite inclusions. We hypothesize that the discrepancy might be related to viscous relaxation of garnet host grains under such high peak metamorphic temperatures.

 

References

[1]     Štípská, P. et al. The juxtaposition of eclogite and mid-crustal rocks in the Orlica-Śnieżnik Dome, Bohemian Massif. J. Metamorph. Geol. 30, 213–234 (2012).

[2]     Majka, J. et al. Integrating X-ray mapping and microtomography of garnet with thermobarometry to define the P-T evolution of the (near) UHP Międzygórze eclogite, Sudetes, SW Poland. J. Metamorph. Geol. 37, 97–112 (2019).

How to cite: Nowak, M., Szczepanski, J., and Dabrowski, M.: Discrepancy between equilibrium thermodynamics-based P-T calculations and quartz-in-garnet elastic barometry in coesite-bearing eclogite (Śnieżnik Massif, NE Bohemian Massif), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-785, https://doi.org/10.5194/egusphere-egu23-785, 2023.

EGU23-3323 | Posters on site | GD7.2

Effective rheology of (de)compacting reactive porous media 

Viktoriya Yarushina, Yury Podladchikov, and Hongliang Wang

Deformation, chemical reactions, fluid flow in geological formations, and many engineering materials, such as cement, are coupled processes. Most existing models of chemical reactions coupled with fluid transport assume the dissolution-precipitation process or mineral growth in rocks. However, dissolution-precipitation models predict a very limited extent of reaction hampered by pore clogging and blocking reactive surfaces, which will stop reaction progress due to limited fluid supply to reactive surfaces. Yet, field observations report that natural rocks can undergo 100% hydration/carbonation. Mineral growth models, on the other hand, preserve solid volume but do not consider its feedback on porosity evolution. In addition, they predict an unrealistically high force of crystallization on the order of several GPa that must be developed in minerals during the reaction. Yet, experiments designed to measure the force of crystallization consistently report values on the order of hundreds of MPa, which is close to the failure limits for most rock types. Recent experimental and observational studies suggest that mineral replacement is a coupled dissolution-precipitation process that preserves porosity and is associated with the change in the solid volume. Volume change associated with chemical reactions has multiple practical implications. It might be hazardous, causing damage to building materials or deterioration of caprock permeability and leakage of waste fluids, at least along the injection wellbore. Or it might be useful. For example, reaction-driven mineral expansion associated with the hydration of some solid additives may be utilized in plugging and abandonment of old petroleum wells to prevent leakage between plug and caprock or between plug and casing. In a geological context, mineral expansion plays an important role in pseudomorphic replacement and vein formation. Here, we propose a new model for reaction-driven mineral expansion, which preserves porosity and limits unrealistically high build-up of the force of crystallization by allowing inelastic failure processes at the pore scale. First, we look at fluid-rock interaction at the pore scale and derive effective rheology of a reacting porous media. We use a two-phase continuum medium approach to investigate the coupling between reaction, deformation, and fluid flow on a larger scale. Our micromechanical model based on observations assumes that rock or cement consists of an assembly of solid reactive grains, initially composed of a single, pure phase. The reaction occurs at the fluid-solid contact and progresses into the solid grain material. We approximate the pores and surrounding solid material as an idealized cylindrical shell to simplify the problem and obtain tractable results. We derive macroscopic poroviscoelastic stress-strain constitute laws that account for chemical alteration and viscoelastoplastic deformation of porous rocks. Our model explains many experimental observations on natural and engineering geomaterials, such as the possibility of achieving a complete reaction, preservation of porosity during chemical reactions, moderate values of the force of crystallization, and dependence of mechanical rock properties on fluid chemistry.

How to cite: Yarushina, V., Podladchikov, Y., and Wang, H.: Effective rheology of (de)compacting reactive porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3323, https://doi.org/10.5194/egusphere-egu23-3323, 2023.

EGU23-3681 | ECS | Posters on site | GD7.2

Fluid-mineral equilibrium under stress: insight from molecular dynamics 

Mattia Luca Mazzucchelli, Evangelos Moulas, Boris Kaus, and Thomas Speck

The interpretation of phase equilibria and reactions in geological materials is underpinned by standard thermodynamics that assumes that the stress in the systems is hydrostatic and homogeneous (i.e., the same for all the phases involved). However, stress gradients and non-hydrostatic stresses are common in rocks, and can be developed even in porous systems with coexisting solid minerals and fluids. In rocks with interconnected porosity, a fluid will always experience a hydrostatic stress gradient. On the contrary, the solid grains will experience different levels of stress due to the changes in the contact area between the grains. Therefore, rocks that are porous or have a granular structure will always experience stress gradients at the small scale, even if their macroscopic stress state is “lithostatic”.

The presence of a heterogeneous-stress distribution at the grain scale casts doubts on the predictive power and accuracy of existing multiphase thermodynamic models. However, currently there is still not an accepted theory which extends thermodynamics to include the effect of non-hydrostatic stress on reactions, and the use of several thermodynamic potentials in stressed geological system is still debated (e.g. [1-3]). Even experiments have not been conclusive, because the direct effect of the applied non-hydrostatic stress on the thermodynamics of the reactions cannot be separated from the indirect effect caused by local stress concentrations [4].

We have investigated the problem of the direct effect of a homogeneous non-hydrostatic stress on the solid-fluid equilibrium with molecular dynamics simulations. With such simulations the energy of the system, the pressure of the fluid and the stress of the solid can be monitored until the stressed system reaches the equilibrium conditions. Our results show that for simple systems at the stress range expected in the lithosphere, the shift of the pressure and temperature of the fluid-solid equilibrium is small for geological applications, consistent with theoretical predictions [5,6]. On the contrary, the mean stress of the solid is largely affected by the applied non-hydrostatic stress and can deviate substantially from the pressure of the fluid. These results suggest that hydro-mechanical-chemical models should not use the pressure of the fluid as a proxy of the mean stress of the solid, and therefore should not equate the thermodynamic pressure of the reaction to the mean stress of the solid. However, our analysis does not take into account the indirect effect of stress heterogeneities at the sample scale. Spatial variations of stress can reach GPa level and can therefore indirectly affect phase equilibria.

MLM is supported by an Alexander von Humboldt research fellowship.

References

[1] Wheeler, J. Geology 42, 647–650 (2014);

[2] Hobbs, B. et al. Geology 43, e372 (2015);

[3] Tajčmanová, L. et al. Lithos 216–217, 338–351 (2015)

[4] Cionoiu, S., et al. J. Geophys. Res. Solid Earth 127, e2022JB024814 (2022)

[5] Sekerka, R. et al. Acta Mater., 52(6), 1663–1668 (2004)

[6] Frolov, T. et al. Phys. Rev. B Condens. Matter Mater. Phys. 82, 1–14 (2010)

How to cite: Mazzucchelli, M. L., Moulas, E., Kaus, B., and Speck, T.: Fluid-mineral equilibrium under stress: insight from molecular dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3681, https://doi.org/10.5194/egusphere-egu23-3681, 2023.

EGU23-3909 | Posters on site | GD7.2

Numerical and analytical solutions for the large-strain elastoplastic Lame problem and its geological applications 

Evangelos Moulas, Anatoly Vershinin, Konstantin Zingerman, Vladimir Levin, and Yuri Podladchikov

Minerals and multiphase rocks in general may have non-trivial material models (constitutive relations) with respect to their volume change as a response of changing pressure and temperature (P-T) conditions. However, natural minerals within rocks do not freely expand/contract. When mineral phases are enclosed by phases that have different thermoelastic properties, a difference in volumetric strain develops upon the loading/unloading of the host-inclusion system. The difference of the volumetric strain between the two phases can lead to the significant stress build up in the vicinity of the host-inclusion interface. This behavior is in fact expected in geological scenarios where mineral reactions and phase transitions are responsible for significant volumetric changes. One of the most classical problems in elasticity theory is the Lame problem of an internally and externally pressurized thick cylinder. When adapted for spherical symmetry, this problem has been extensively used in geological applications in order to evaluate the stress distribution around a pressurized rock or mineral. Using linear elasticity theory and standard mineral properties it can be shown that the level of stresses that can develop around pressurized inclusions may be in the order of ~ 1 GPa. Such stress predictions are well beyond typical values of the yield stress of rocks which leads to large plastic deformations. Therefore, the incorporation of plasticity and finite strains is crucial in such models.

Here we present new analytical and numerical solutions for the classic host-inclusion problem assuming hyperelastic-plastic materials that follow a Drucker-Prager (non-associative) plasticity model under finite strains. Our analytical solution is based on the recently published solution of Levin and others (2021) that reduces to the Murnaghan model for purely hydrostatic loading. Our solutions have been developed to consider the effects of physical and geometrical non-linearities in deforming geomaterials. For stiff mineral hosts that can support GPa-level differential stresses, non-linear formulations provide accurate stress predictions even if the effects of geometrical non-linearities are ignored. For systems that reach the plastic yield, a plastic zone develops that can lead to the reduction of the pressure difference between the host and the inclusion phase. Nevertheless, the development of a plastic zone is occurring simultaneously to the development of pressure variations at the mineral hosts. Therefore, the development of pressure gradients in host-inclusion systems from the mineral to the outcrop scale are to be expected when the host material reaches the yield conditions.

Acknowledgments:

E.M. would like to acknowledge the Johannes Gutenberg University of Mainz for financial support. Y.P., K.Z., A.V. and V.L. were financially supported by Russian Science Foundation (project No. 19-77-10062) in the part related to the geomechanical problem statement and its analysis, and by Ministry of Education and Science of Russian Federation (grant №075-15-2019-1890) in the part related to the development of analytical and numerical algorithms for problem solving.

How to cite: Moulas, E., Vershinin, A., Zingerman, K., Levin, V., and Podladchikov, Y.: Numerical and analytical solutions for the large-strain elastoplastic Lame problem and its geological applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3909, https://doi.org/10.5194/egusphere-egu23-3909, 2023.

Despite the occurrence of high-grade metamorphic rocks next to and along crustal-scale shear zones, the temporal character of their formation and evolution is difficult to extract. We utilize the major-element diffusion in the compositional re-adjustment of garnet from metapelites in two crustal-scale shear zones as a complementary method to extract cooling rates from deforming/reacting rocks. The two thrust zones, the Nestos Thrust Zone (NTZ) in Rhodope, Greece, and the Main Central Thrust (MCT) in Sikkim, Himalaya, exhibit inverted metamorphic zonation. We applied phase equilibria modelling and geothermometry to constrain the peak- and the post-peak-temperature conditions relevant for the cooling-rate estimates. Results are 50–80 ◦C/Myr in the footwalls of both thrust zones, in consistency with published estimates using geochronology methods for MCT. However, results are much less (~0.5–5◦C/Myr) for the base of the MCT hanging wall. The estimated cooling rates are between 300 and 2500 ◦C/Myr for the NTZ hanging wall. The exceedingly fast cooling rates indicate the operation of transient and proximal thermo-mechanical processes consistent with the contribution of thrust related viscous heating during metamorphism. The very slow cooling rate of the MCT hanging wall may reflect a complex thermal history or other overlooked processes.

 

References:

Burg, J.-P., Moulas, E., 2022. Cooling-rate constraints from metapelites across two inverted metamorphic sequences of the Alpine-Himalayan belt; evidence for viscous heating. Journal of Structural Geology 156, 104536. https://doi.org/10.1016/j.jsg.2022.104536

How to cite: Burg, J.-P. and Moulas, E.: Cooling-rate constraints from metapelites across two inverted metamorphic sequences of the Alpine-Himalayan belt; evidence for viscous heating, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4185, https://doi.org/10.5194/egusphere-egu23-4185, 2023.

EGU23-6362 | Posters on site | GD7.2

Alpha-Beta quartz transition in the lower continental crust: perspective from diffraction and acoustic data at high P-T conditions 

Giulia Mingardi, Julien Gasc, Arefeh Moarefvand, Wilson A. Crichton, and Alexandre Schubnel

Quartz is a common constituent of most rocks in the Earth continental crust and it undergoes the α-β transition at depths controlled by the geotherm. Despite the α-β quartz transition representing one of the most well-known and largely studied phase transitions in geological sciences, only few works report the behaviour of this transformation at high pressure (i.e. in the relevant conditions of the deep crust). Hence, it is important to investigate this transformation through an experimental approach at lower-crust pressure and temperature (P-T) conditions.

In this study, we performed deformation experiments at high P-T conditions on novaculite (quartzite) samples using a Griggs apparatus equipped with acoustics and a multi-anvil press at the European Synchrotron Radiation Facility (ESRF, beamline ID06). Experiments were performed at 1-3 GPa and up to 1000°C.

Measurements in the Griggs apparatus indicate that the expected P-wave velocity increase in the β-field is not observed at high pressure. Diffraction data from ESRF show that the transition becomes smoother at high pressure and results in a smaller crystal lattice change than it does at low pressure, consistently with the P-wave velocity measurements in the Griggs apparatus.

In addition, on the temperature-up path we are able to observe the expected negative thermal expansion of β-quartz but, interestingly, this behaviour is not visible on the cooling path. As a possible explanation, we suggest a competing effect of stress and temperature on the crystal lattice parameters. Moreover, at the transition, in a short temperature range, the intensity of quartz diffraction peaks decreases significantly. Acoustic measurements seem to indicate that this could be also related to a transient increase in attenuation. Further experiments will be performed at the ESRF coupling X-ray diffraction and acoustic measurements to assess the relationship between crystal structure and Vp changes.

Our results question the interpretation of seismic contrasts in the deep crust as due to the α-β quartz transition. However the existence of a high attenuation region might reflect the presence of this transformation.

How to cite: Mingardi, G., Gasc, J., Moarefvand, A., Crichton, W. A., and Schubnel, A.: Alpha-Beta quartz transition in the lower continental crust: perspective from diffraction and acoustic data at high P-T conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6362, https://doi.org/10.5194/egusphere-egu23-6362, 2023.

EGU23-7206 | Posters on site | GD7.2

A 3D numerical model for chimney formation in sedimentary basins 

Magnus Wangen, Hongliang Wang, and Viktoriya Yarushina

We propose a 3D model for pipe and chimney formations in tight rocks in sedimentary basins. It is an adaption of a model for hydraulic fracturing in an anisotropic stress field by fluid injection (fracking). The trigger for chimney formation is high overpressure in permeable units, such as reservoirs or aquifers. The permeable units serve as a source of high-pressure fluid that drives the chimney formation. The numerical model is based on cells that “fracture” when the fluid pressure exceeds the least compressive stress and random rock strength. The locally highest points in the reservoir rock become the most likely places for chimney formation. Fracturing implies that cells have their permeability changed from their initial value to a value that represents an average permeability of an open fracture network. Chimney growth appears as chains of cells (branches) emanating from the base of the cap rock. These chains of cells grow towards the surface. The branches have an enhanced permeability during ascension because the fluid pressure in the fracture network is greater than the least compressive stress. The fluid pressure keeps the fracture network open. When the branches reach the hydrostatic surface, the fluid pressure drops below the least compressive stress and the fracture network closes. The model produces pipe structures and chimneys as accumulations of branches that reach the surface. The degree of random rock strength controls how pipe-like the chimneys become. The chimney, which is formed by branches of the fractured cells, drains the reservoir for overpressured fluid. Chimney formation stops when the overpressure in the reservoir is reduced below the least compressive stress at the base of the caprock. The fracture permeability of the chimney branches controls how many branches are produced, and thereby how wide the chimney becomes. A “low” permeability produces wide chimneys with many branches, and a “high” permeability gives narrow chimneys made of just a few branches. The model is demonstrated in a setting similar to the chimneys observed in the cap rock over the Utsira aquifer in the North Sea. By using the proposed model, the permeability of such chimneys is estimated to be of the order of 10 micro-Darcy.

How to cite: Wangen, M., Wang, H., and Yarushina, V.: A 3D numerical model for chimney formation in sedimentary basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7206, https://doi.org/10.5194/egusphere-egu23-7206, 2023.

EGU23-8545 | ECS | Posters on site | GD7.2

Transient rheology of feldspar 

Sagar Masuti and Erik Rybacki

Transient creep of the lower crustal minerals such as feldspar is important to explain postseismic deformation following a large continental earthquake. However, transient creep of feldspar is poorly understood and the flow law parameters are unknown so far. Therefore, we performed constant strain rate deformation experiments on synthetic fine-grained anorthite aggregates under wet conditions using a Paterson-type gas deformation apparatus. We conducted tests at temperatures from 1000 ºC to 1200 ºC and confining pressure of 400 MPa. Typical strain rates in our experiments were 1x10-4 s-1, 2.5x10-4 s-1, 5x10-4 s-1, and 7.5x10-4 s-1, including some strain rate stepping experiments. In general, the transient creep accounted for 6-8% of the total strain (~10-15%), which is high compared to 2-3 % transient deformation observed in previous experiments on anorthite, quartz, and olivine aggregates. Inspection of the microstructures of deformed samples using transmission electron microscopy reveal dislocation activity and antiphase domain boundaries. Analysis of steady-state creep data indicates that the samples were deformed at the boundary between diffusion and dislocation creep with a power law stress exponent of ~1.4 and an activation energy of 272 kJ/mol. Because a constitutive equation for transient creep of feldspar is not well established, we estimated transient creep flow law parameters using inter-granular and intra-granular models. In the intergranular model for a polycrystalline aggregate, where grains are randomly oriented,  it is assumed that low strain (i.e., transient creep) is accommodated by individual grains with soft/easy slip orientation and high strain (steady-state creep) is accommodated by grains with hard/strong slip orientation. In contrast, in the intra-granular model, both transient creep and steady-state deformation are dominated by intragranular processes, such as long-range elastic interactions of dislocations. In the intragranular approach, we find that the full stress vs. strain curve (i.e., including transient and steady-state creep) can be modelled using a stress exponent of ~1.5 and an activation energy of ~200 kJ/mol. Applying the intergranular model, we get a stress exponent of ~3 and an activation energy of ~130 kJ/mol for transient creep of anorthite aggregates. Extrapolated to natural strain rates, these two approaches will have different implications in modelling postseismic deformation.

How to cite: Masuti, S. and Rybacki, E.: Transient rheology of feldspar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8545, https://doi.org/10.5194/egusphere-egu23-8545, 2023.

EGU23-9047 | ECS | Orals | GD7.2

On the sensitivity of inclusion pressures after entrapment: the drastic effect of aqueous fluid on garnet viscous relaxation 

Xin Zhong, David Wallis, Phillip Kingsbery, and Timm John

Elastic geo-thermobarometry has become an important technique in determining the pressure-temperature (P-T) conditions of entrapment during metamorphism. A prerequisite is that the inclusion’s over- or under-pressure is not reset during exhumation. This would be the case if the host-inclusion pair interacts elastically only, which is an oversimplification. It is thus not yet been fully understood how fast the inclusion pressure may become reset. In this study, we performed heating experiment on an almandine-rich (from an eclogite) and a spessartine-rich garnet (gem-stone) under 1) graphite (dry), 2) forming gas (5% H2 and 95% N2) and 3) water vapour (wet) buffered conditions at high T and room P. Raman spectroscopy is used to measure the same quartz and zircon inclusions at room T before and after different heating times. In wet and forming gas conditions, the Raman band wavenumber changes are dependent on time, decreasing for quartz and increasing for zircon inclusions. Under dry condition, the Raman band wavenumber exhibits a small amount of shift and becomes stable shortly. Raman mappings reveal that the stress heterogeneity of the garnet host develops stronger at the early stage of the wet heating experiments and fade away afterward, potentially indicating a diffusion-like behaviour of the dislocation density. A visco-elastic model is performed to fit the measured data. The calculated flow law parameters of garnet around quartz inclusions is comparable to the flow law extracted from deformation experiments, while zircon shows substantially faster relaxation rate. This study highlights that fluid can be an important trigger for fast viscous relaxation together with temperature, time and inclusion mineralogy. The study may have implications for elastic thermobarometry, garnet rheology, and the preservation of coesite inclusions.

How to cite: Zhong, X., Wallis, D., Kingsbery, P., and John, T.: On the sensitivity of inclusion pressures after entrapment: the drastic effect of aqueous fluid on garnet viscous relaxation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9047, https://doi.org/10.5194/egusphere-egu23-9047, 2023.

EGU23-9717 | Posters on site | GD7.2

Mechanisms of pressure buildup in magma reservoir: insights from numerical experiments 

Yury Podladchikov, Ivan Utkin, and Liudmila Khakimova

Understanding mechanisms leading to volcanic eruptions are of fundamental importance in geology and volcanology. A prerequisite to a volcanic eruption is the generation of sufficient overpressure in a magma reservoir, enough to exceed the strength of the rock, potentially triggering the volcanic eruption. In geological models, the pressure buildup in magma reservoir is often linked to magma recharge and volatile exsolution. Another mechanism, that is often overlooked in conventional geological models, is related to the isochoric rise of gas bubbles in almost incompressible magma saturated with volatiles. Predicting volcanic eruptions using numerical models is complicated by the need to solve coupled physical processes spanning multiple temporal and spatial scales.

We present a coupled thermo-chemo-hydromechanical mathematical model for predicting the pressurization of a magmatic reservoir. The model predicts porous and free convection of partially crystallized magma due to thermal and compositional heterogeneities, and compaction of crystals due to density difference between solid and liquid phases. We describe thermodynamic equilibrium and thermo-mechanical properties of phases using the nonlinear equation of state obtained through direct Gibbs energy minimization. We resolve the multi-scale processes within the magma reservoir using high-resolution numerical modeling based on supercomputing.

We demonstrate through numerical experiments that the two mechanisms, volatile exsolution due to retrograde boiling, and rising of gas bubbles in a  nearly isochoric system, could lead to pressure buildup in a magma reservoir, sufficient to exceed rock strength. We study systematically the relative importance of these mechanisms in a simplified problem setup.

How to cite: Podladchikov, Y., Utkin, I., and Khakimova, L.: Mechanisms of pressure buildup in magma reservoir: insights from numerical experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9717, https://doi.org/10.5194/egusphere-egu23-9717, 2023.

EGU23-12140 | ECS | Posters on site | GD7.2

Nonlinear Multi-Component Maxwell-Stefan Diffusion Model In Deforming Rocks: Chemo-Mechanical Coupling 

Lyudmila Khakimova, Evangelos Moulas, Ivan Utkin, and Yury Podladchikov

Widely accepted model of Fickian linear diffusion of inert or trace-like elements is restricted to ideal solution models of components with equal molar mass. Simultaneous diffusion of multiple concentrations without mechanical stresses is well-described by the classical Maxwell-Stefan model, which is limited to the use of concentration gradients. Quantitative predictions of concentrations evolution in real mixtures should be treated instead by modified Maxwell-Stefan closure relations, which result in a correct equilibrium limit due to the use of the chemical potential gradients instead of concentration gradients. There is no linearity and tensorial homogeneity assumptions on flux-force relationships of classical irreversible thermodynamics. Coupling the multicomponent diffusion to mechanics results in pressure gradients that contribute to the Gibbs-Duhem relationship. Note, it was demonstrated that current models used for describing chemical diffusion in presence of stress gradient don’t remain invariance with respect to the choice of units, such as mole and mass, and the thermodynamic admissibility is doubted [1].

We develop a new thermodynamically admissible model for multicomponent diffusion in viscously deformable rocks. Thermodynamical admissibility of this model ensures non-negative entropy production, while maintaining invariance with respect to the choice of units and reference frame. We demonstrate the correct Fickian limit and equilibrium limit with zero gradients of chemical potentials of individual components instead of concentration gradients in classical Maxwell-Stefan model. The model satisfies conventional Gibbs-Duhem and Maxwell relationships under pressure gradients and represents the natural coupling to the viscous multi-phase models featuring spontaneous flow localization.

For numerical purposes, we develop the optimal pseudo-transient scheme for diffusion fluxes coupled to viscoelastic bulk deformation. This new effective damping techniques are compared to analytical solutions. The developed model is applied for radial garnet growth with multicomponent diffusion under pressure gradient, hydration porosity waves and melt transport in the Earth’s crust.

1. Tajčmanová, L., Podladchikov, Y., Moulas, E., & Khakimova, L. (2021). The choice of a thermodynamic formulation dramatically affects modelled chemical zoning in minerals. Scientific reports, 11(1), 1-9.

How to cite: Khakimova, L., Moulas, E., Utkin, I., and Podladchikov, Y.: Nonlinear Multi-Component Maxwell-Stefan Diffusion Model In Deforming Rocks: Chemo-Mechanical Coupling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12140, https://doi.org/10.5194/egusphere-egu23-12140, 2023.

EGU23-12371 | ECS | Posters on site | GD7.2

Deformation of epidote and plagioclase in the semi-brittle regime 

Sarah Incel, Katharina Mohrbach, and Jörg Renner

In the plagioclase-rich lower continental crust, hydrous epidote-group minerals will, among other phases, replace plagioclase in the presence of minor amounts of fluids. It has previously been shown that this reaction has a significant impact on the strength of plagioclase aggregates, with reacting aggregates being much weaker than their unreacted counterparts (Stünitz and Tullis, 2001). Hence, reactions taking place in the lower continental crust may have a strong influence on its deformation behaviour and thus on its strength. Yet, it still remains unclear if the observed weakening is due to the nucleation and growth of inherently weaker product phases, e.g., epidote-group minerals, or due to inhibited grain growth in a polyphase aggregate as a result of Zener pinning. We experimentally investigated the relative strength of pure epidote and pure plagioclase aggregates at a confining pressure of 1 GPa, two different temperatures (550 and 650 °C) and two different strain rates (5·10-5 and 5·10-6 s-1) using a solid-medium Griggs-deformation apparatus. Furthermore, we also investigated potential strength differences due to differences in grain size by deforming aggregates with a grain-size range of either 90-135 μm or <25 μm. After deformation under 650 °C, the epidote aggregates reveal the nucleation and growth of new phases indicating that epidote was no longer stable. The amount of product phases found in the epidote aggregates scales with the duration of deformation. At the explored experimental conditions, the compressive strength of plagioclase and epidote aggregates depends on temperature and strain rate with a decrease in strength with an increase in temperature or a decrease in strain rate. At identical conditions, the epidote aggregates are either significantly stronger or show a similar strength as the plagioclase aggregates. Microstructural analyses of the recovered samples reveal that deformation in both aggregates was almost exclusively accommodated by grain fracturing and occasionally slip along cleavage planes, and remained non-localized except for the epidote aggregate deformed at 650 °C with a strain rate of 5·10-6 s-1, exhibiting kinetically-controlled faulting due to reaction.

 

Stünitz, H. and Tullis, J. (2001). Weakening and strain localization produced by syn-deformational reaction of
plagioclase. International Journal of Earth Sciences, 90(1):136{148.

How to cite: Incel, S., Mohrbach, K., and Renner, J.: Deformation of epidote and plagioclase in the semi-brittle regime, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12371, https://doi.org/10.5194/egusphere-egu23-12371, 2023.

EGU23-12498 | ECS | Orals | GD7.2 | Highlight

How to hydrate almost non-permeable, dry and mafic crust – A mechanistic view on the Kråkenes Gabbro (Western Gneiss Region, Norway) 

Saskia Bläsing, Timm John, and Johannes C. Vrijmoed

Fluid-rock interaction is one of the most important factors regarding the evolution of the Earth’s crust, as it is strongly affecting its petrophysical properties and enabling chemical transport. Therefore, its impact on the Earth’s crustal chemical reservoirs and geodynamic processes can be significant. Fluid-mediated mineral reactions are dependent on the availability of fluids and their capability to percolate through the rock and interact with the minerals, often through pre-existing fluid pathways.

The Kråkenes Gabbro is a mafic enclave, embedded in the felsic gneisses of the Western Gneiss Region in Norway. Although the whole region reached (ultra-)high pressure metamorphic conditions, the gabbro remained in a metastable state and preserved its igneous textures and magmatic minerals. The dry and low permeability gabbro is cut by a N-S-trending fracture network of mode-I cracks, which opened during exhumation. These fractures served as fluid pathways for an aqueous fluid to infiltrate the rock and trigger mineral reactions. Along these fractures the dry gabbro is “hydrated” under amphibolite-facies conditions. The resulting amphibolite reaction front is sharp on outcrop scale and propagates on dm-scale into the gabbro. A complete profile of rock spanning 32 cm in length was taken perpendicular to the vein, including sample material from the vein, the alteration zone, and the mostly pristine gabbroic wall rock.

The gabbro-amphibolite-transition is displayed by the development of a hydrous mineral assemblage, accompanied with a densification and therefore porosity formation. The main cause of this is a drop in the abundance of plagioclase during the amphibolitization. Thermodynamic analysis using Thermolab were done to predict the amphibolite mineral assemblage from the original bulk rock composition of the gabbro. The calculations reveal that mainly H2O is added to the system and minor further element transport is needed. Furthermore, we observe that even the most reacted amphibolite still contains unaffected gabbroic mineral relicts and the main chemical reactions during amphibolitization are limited to a few minerals. The incoming fluid is consumed as soon as the hydrous phases of the amphibolite are formed. As amphibolitization favors porosity formation, a free fluid phase remains in the pore space as soon as the gabbro at the reactive surface of the affected minerals is completely transformed. The fluid progresses through the newly formed pore space and advances as a sharp the amphibolitization front.

In order to test our hypothesis, we formulate a reactive flow model based on local equilibrium thermodynamics, mass balance and Darcy flow, that simulates the hydration of the dry gabbro to amphibolite including the porosity and fluid pressure evolution. Results confirm the formation of a sharp reaction front and the decrease in porosity during the hydration as a potential physical explanation for the observations without the further need for kinetically delayed reactions. We conclude that the metastability of gabbro is mostly controlled by the availability of fluid to the rock.

How to cite: Bläsing, S., John, T., and Vrijmoed, J. C.: How to hydrate almost non-permeable, dry and mafic crust – A mechanistic view on the Kråkenes Gabbro (Western Gneiss Region, Norway), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12498, https://doi.org/10.5194/egusphere-egu23-12498, 2023.

We study the systematics of reaction fronts in multi-component systems using Thermolab. The methodology is based on a finite difference approach for solving the transport problem in combination with lookup tables generated from precomputed thermodynamic equilibria covering the compositional space. The lookup tables generated from Gibbs minimization using linear programming combined with a discrete compound approach are validated against full analytical solutions of the Gibbs minimization problem. We focus on ternary ideal fluid or melt solutions in equilibrium with pure phases as exact solutions are feasible. We show that linear programming techniques yield similar results as a complete analytical solution and that both can be used in stable reactive transport codes.

How to cite: Vrijmoed, J. C. and Podladchikov, Y. Y.: Reaction fronts in multi-component fluid-rock interaction using analytical solutions of the Gibbs minimization problem from Thermolab, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13988, https://doi.org/10.5194/egusphere-egu23-13988, 2023.

EGU23-14012 | Orals | GD7.2

Hydration versus dehydration reactions: increase versus decrease of solid density with pressure rise 

Stefan Markus Schmalholz and Yury Podladchikov

Hydration and dehydration reactions as well as the associated fluid flow are important features of geodynamic processes. For example, hydration of rocks can significantly decrease rock strength and generate shear localization or fluids liberated by dehydration reactions in subducting rocks can flow into the mantle wedge and cause melting and magmatism. However, several aspects of (de)hydration related fluid flow and the propagation of (de)hydration reaction fronts remain unclear.

Here, we study hydration and dehydration reactions with hydro-chemical numerical models based on continuum mechanics and local equilibrium thermodynamics. For simplicity, we mainly consider 1D isothermal models. We focus on the propagation velocity and direction of the (de)hydration reaction front. We define hydration as an increase of chemically, or lattice, bound water in the solid phase. Therefore, hydration requires fluid flow towards the hydration reaction front. Contrary, dehydration is a decrease of chemically bound water in the solid phase. Hence, dehydration requires fluid escape from the dehydration reaction front.

Our models show that hydration requires a negative sign of the solid volume change with pressure increase across the reaction boundary, whereas dehydration requires a positive sign of solid volume change with pressure increase across the reaction boundary. The reason for this difference in sign is due to the fluid flow associated with the (de)hydration reaction which is driven by the fluid pressure gradient following Darcy’s law. Thus, for hydration to happen it must occur on the lower fluid pressure side of the reaction front compared to the side with more porous fluid. Porosity is directly related to the solid density change, so it is larger on the high solid density side of the reaction front. Therefore, the hydration reaction requires that the rock that should be hydrated is on the lower fluid pressure side of the front. Opposite can be reasoned for the dehydration front. We also include in our models the case of zero porosity, and hence zero permeability, on one side of the (de)hydration reaction front. This zero-permeability limit involves a singularity at the reaction front due to the multiplication of zero permeability with an infinite pressure gradient. We resolve this singularity in our numerical algorithm by applying a fully conservative form of the governing equations. Resolving this zero-permeability limit is in agreement with the well-established theory of non-linear degenerate parabolic equations. We apply our model to two natural settings: First, eclogite shear zones in the Bergen Arcs, Norway, where hydration of dry granulite formed eclogite. Second, olivine veins in the Erro-Tobbio unit, Ligurian Alps of Italy, where dehydration of serpentinite during subduction formed olivine.

How to cite: Schmalholz, S. M. and Podladchikov, Y.: Hydration versus dehydration reactions: increase versus decrease of solid density with pressure rise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14012, https://doi.org/10.5194/egusphere-egu23-14012, 2023.

The strength of the lithosphere strongly influences the plate tectonics and mantle convection. The flow behavior of the lithospheric mantle is largely controlled by low-temperature plasticity of olivine, the dominant mineral in the upper mantle. Many experimental studies have explored the low-temperature rheological behaviors of olivine but result in strengths that are highly variable when extrapolated to geological conditions. Kumamoto et al. (2017) performed nanoindentation experiments using Berkovich and spherical indenters on olivine at room temperature and proposed that the strength of olivine depends on the length scale of deformation, with experiments on smaller volumes of material exhibiting larger yield stress, that is, the indentation size effect (ISE). However, their nanoindentation tests were done at room temperature, while traditional creep tests were often done at elevated temperatures of ⩾400°C, the temperature dependence in the ISE must be considered in synthesizing experimental results from different studies. Here, we conducted nanoindentation experiments on a single crystal of Fe-free olivine, eliminating the influence from grain size, using a diamond Berkovich indenter at temperatures of 28, 100, 200, 400 and 600°C. In all tests, the hardness decreases with increasing contact depth that is characteristic of the ISE. Taking our data into the classic hardness-depth relationship of H = H0(1+h*/hc)1/2, where H is hardness, H0 is the so-called “infinite hardness”, corresponding to the hardness at the infinite indentation depth, hc is contact depth, and h is the material length scale parameter. We found hdecreases with increasing temperature, which can be attributed to an increase of the storage volume of geometrically necessary dislocations during nanoindentation test. The decrease of hmeans that the ISE weakens with increasing temperature, suggesting that at lithospheric temperatures the size effect is not strong enough to explain the disagreements between different experiments and between experiments and geophysical observations. Other aspects, such as grain size effect (Hall-Petch effect) and strain-weakening mechanisms may contribute significantly and need to be revisited.

How to cite: Qi, C. and Wang, Q.: Temperature dependence of indentation size effect in olivine and its implications to low-temperature plasticity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17012, https://doi.org/10.5194/egusphere-egu23-17012, 2023.

EGU23-17232 | ECS | Orals | GD7.2

Fluid-pressure induced eclogitisation of a dry granulite: Insights from Hydro-Chemical model 

Erwan Bras, Philippe Yamato, Thibault Duretz, Stefan Schmalholz, and Yury Podladchikov

Eclogitization constitutes one of the most emblematic transformations in continental subduction zones, where conversion of initially dry lower crustal rocks into eclogite facies rocks correlates with the occurrence of seismogenic events. This reaction is generally considered to occur at high pressure conditions during hydration of dry granulite. Several models using « ad hoc » diffusion equation exist to model this hydration process and the consequences of reaction-induced changes in terms of rheology and density. However, to our knowledge, there is no quantitative model allowing to physically explain how fluids propagate inside a dry rock (i.e. with no porosity at all) and how reaction-induced alteration front widens over time. In this study, we therefore propose a new fully coupled hydro-chemical model wherein a two-phase flow model is coupled with the eclogitization reaction. We use a mass conservative approach, solving total mass and solid mass equations, in a closed isothermal system. Fluid and solid densities are calculated with lookup tables from equilibrium thermodynamics. Our model shows that a fluid pressure pulse generates a pressure gradient that can be associated with the densification reaction when the pressure required for the eclogitization is reached. This reaction generates a large increase in porosity (0 to ~16%) and subsequent porous fluid flow inside the initially dry granulite. This process is then sustained as long as the fluid pulse is maintained, and ends shortly after the fluid pressure pulse stops. However, high pressure within the reacted area can persist for a long period of time. A parametric study allowing to constrain both the duration and the widening of the reaction area is proposed as well as an application to the emblematic case study of the eclogitized granulites of Holsnoy (Bergen Arcs, Norway).

How to cite: Bras, E., Yamato, P., Duretz, T., Schmalholz, S., and Podladchikov, Y.: Fluid-pressure induced eclogitisation of a dry granulite: Insights from Hydro-Chemical model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17232, https://doi.org/10.5194/egusphere-egu23-17232, 2023.

EGU23-17238 | Orals | GD7.2

What controls the preservation of hydration interfaces in high grade metamorphic rocks? 

Andrew Putnis, Jo Moore, and Yury Podladchikov

The hydration of initially dry, lower crustal metamorphic rocks during orogenesis is a commonly observed phenomenon and hydration/reaction interfaces are also often preserved, providing a unique insight into the evolution of the lithosphere. Often the interfaces between unreacted and reacted rock are very sharp, even on a thin section scale, and various explanations have been proposed to account for the abrupt changes in mineral assemblage on such a small spatial scale. Common to a wide range of specific examples is the role of an infiltrating aqueous fluid that is generally assumed to be required for the reaction to take place, although other features of such reaction fronts can differ widely in terms of density changes and the apparent difference in metamorphic grade across a sharp interface. 

The examples discussed here all involve the hydration of basement granulite rocks formed during the Caledonian Orogeny and now exposed in the Bergen Arcs in Norway. All stages of hydration can be observed from totally unreacted dry granulites with a wide range of composition to either eclogite facies or amphibolite facies overprints. In these cases the density changes across the interface can either be positive (in the case of eclogite formation from anorthosite granulites), can be negative (in the amphibolitisation of basic rocks) or virtually zero (during the amphibolitisation of garnet bearing anorthosites). The preservation of volume across such interfaces has led to investigations of the coupling between the consequent stress generation and mass transfer, which in turn focusses on the evolution of porosity/permeability in the parent dry rock. The extent of hydration in the Bergen Arcs as a whole ( 90% hydration of ~105 km3 of granulite) suggests a plentiful supply of aqueous solution introduced seismically by fracturing and the consequent generation of shear zones from which hydration fronts spread. The hydration to either eclogite or amphibolite, often observed at the same structural level (i.e. depth in the crust) continues to be an enigma.

Although the details of the reactions and density changes are different, a common feature is the need for an infiltrating aqueous solution and hence the question of what drives the fluid and the hydration reaction and finally why the reaction stops at the sharp interfaces observed in the field. Terminated reactions can be studied by the extent of alteration around fracture planes by modelling the likely fluid pressure gradients that drive Darcy flow from the fluid source towards the reaction interface. Fracture planes represent zones of localised high permeability that facilitate the infiltration of fluid. The difference in fluid saturation between the fracture plane and the alteration halo is thought to be responsible for both the degree of reaction and the difference in assemblage. Additionally, the width of the initial fracture plane is thought to be proportional to the extent of the alteration halo. Examples will be given of hydration fronts associated with amphibolite facies shear zones as well as the observation of eclogite fingers within a partly hydrated granulite host. Combined reaction-fluid flow models attempt to explain these phenomena.

How to cite: Putnis, A., Moore, J., and Podladchikov, Y.: What controls the preservation of hydration interfaces in high grade metamorphic rocks?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17238, https://doi.org/10.5194/egusphere-egu23-17238, 2023.

EGU23-17245 | ECS | Orals | GD7.2

A porous-media model for reactive fluid-rock interaction in a dehydrating rock 

Andrea Zafferi, Konstantin Huber, Dirk Peschka, Johannes Vrijmoed, Timm John, and Marita Thomas

We discuss a model for temperature-induced rock dehydration that features fluid liberation through mineral reactions, diffusion of chemically released species, and flow through porous media. This model can be derived either by considering standard conservation laws and flux definitions (Pl¨umper et al.[2017], Beinlich et al. [2020]) or, alternatively, using the variational framework of GENERIC (General Equations for Non-Equilibrium Reversible Irreversible Coupling)(Zafferi et al. [2021]) introduced by M. Grmela and H.C. ¨ Ottinger. The latter approach is based on the abstract definition of thermodynamical driving potential and operators characterizing the reversible and dissipative contributions of the processes. By doing so we can show that local equilibrium assumptions are recovered as fast limit of irreversible processes. Ultimately, we rigorously prove that the PDE model so derived admits solutions using a discretization strategy that imitates the numerical implementations.

References

Andreas Beinlich, Timm John, Johannes C Vrijmoed, Masako Tominaga, Tomas Magna, and Yuri Y Podladchikov. Instantaneous rock transformations in the deep crust driven by reactive fluid flow. Nature Geoscience, 13(4):307–311, 2020.

Oliver Plümper, Timm John, Yuri Y Podladchikov, Johannes C Vrijmoed, and Marco Scambelluri. Fluid escape from subduction zones controlled by channel-forming reactive porosity. Nature Geoscience, 10(2):150–156, 2017.

Andrea Zafferi, Dirk Peschka, and Marita Thomas. Generic framework for reactive fluid flows. ZAMM-Journal of Applied Mathematics and Mechanics/Zeitschrift für Angewandte Mathematik und Mechanik, page e202100254, 2021.

How to cite: Zafferi, A., Huber, K., Peschka, D., Vrijmoed, J., John, T., and Thomas, M.: A porous-media model for reactive fluid-rock interaction in a dehydrating rock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17245, https://doi.org/10.5194/egusphere-egu23-17245, 2023.

EGU23-17278 | ECS | Posters on site | GD7.2

Oscillatory zoning during the growth of single crystals; a comparison of chemical potential and concentration gradient driven numerical models 

Jo Moore, Liudmila Khakimova, Yury Podladchikov, and Lukas Baumgartner

Oscillatory zoning occurs in a multitude of minerals growing in both magmatic systems (e.g. zircon, plagioclase, clinopyroxene) and in solid rock (e.g. garnet). Despite the ubiquity of oscillatory growth zoning in minerals, the processes responsible for such compositional zoning remain enigmatic. It has been argued that such zones may form in response to fluctuations in intensive properties, such as temperature, pressure, and magma/fluid chemistry, and/or extensive properties such as surface reaction rates and the creation of a compositional boundary layer during diffusion. However, numerical models that simulate the evolution of a growing crystal remain relatively rare. Here we aim to provide insight to the conditions that attribute to oscillatory mineral zoning of major elements during crystal growth by presenting forward models of diffusion-controlled crystal growth, incorporating multicomponent diffusion and local equilibrium thermodynamics. Two methods are presented, one each in chemical potential and concentration space. These models further constrain the conditions that allow for oscillatory growth zoning. Allowing better insight into the processes occurring during crystal growth in the crust.

How to cite: Moore, J., Khakimova, L., Podladchikov, Y., and Baumgartner, L.: Oscillatory zoning during the growth of single crystals; a comparison of chemical potential and concentration gradient driven numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17278, https://doi.org/10.5194/egusphere-egu23-17278, 2023.

EGU23-17302 | Orals | GD7.2 | Highlight

Garnet microstructures suggest ultra-fast decompression of ultrahigh-pressure rocks 

Thibault Duretz, Cindy Luisier, Lucie Tajčmanová, and Philippe Yamato

Radial microcracks surrounding retrogressed SiO2 inclusions in UHP garnets are key microstructural observations allowing to constrain the mechanisms of exhumation of ultra-high-pressure (UHP) rocks. The major challenge lies in identifying whether the microstructures formed during their ascent from mantle depths, or as a consequence of transient variations in the tectonic regime. By combining petrographic observations, petrochronological data and numerical thermo-mechanical modelling, we show that radial cracks around SiO2 inclusions in ultrahigh-pressure garnets from Dora Maira are caused by ultrafast decompression during the early stage of exhumation (< 0.5 Ma). Decompression rates higher than 10-14 s-1 are, for the first time, inferred from natural microstructures independently of current petrochronological estimates1. We demonstrate that the SiO2 phase transition generates shear stresses sufficiently large to trigger plastic yielding, resulting in the generation and propagation of radial and bent shear bands, mimicking the fractures observed in UHP garnet. Our results question the traditional interpretation of the exhumation from great depth of ultrahigh-pressure tectonic. Instead, we propose that such ultrafast decompression rates are related to transient changes in the stress state of the buried continental lithosphere, favoring an exhumation mechanism involving nappe stacking.

 

1 Rubatto, D. & Hermann, J. Exhumation as fast as subduction? Geology 29, 3–6 (2001).

How to cite: Duretz, T., Luisier, C., Tajčmanová, L., and Yamato, P.: Garnet microstructures suggest ultra-fast decompression of ultrahigh-pressure rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17302, https://doi.org/10.5194/egusphere-egu23-17302, 2023.

EGU23-17411 | ECS | Orals | GD7.2 | Highlight

How high can mechanical stresses be within lithospheric materials? 

Thomas P. Ferrand

Thanks to plate tectonics, the Earth lithosphere is composed of very different lithologies, most of which consisting of peridotites, usually covered by either oceanic or continental crust. Depending on several parameters including composition, pressure, temperature, and strain rate, lithospheric materials can deform smoothly and silently or generate seismic ruptures. Collision belts and subduction systems, including subducted materials being heated and sheared in the mantle transition zone, are characterized by intense seismicity; in contrast, the bottom of lithospheric plates, known as lithosphere-asthenosphere boundary (LAB), is not associated with any seismicity, giving the impression that oceanic plates have the intrinsic ability to maintain their basal stress at relatively low values. Comparing results from experimental geophysics, field geology, geodynamics modelling and seismology, I discuss the representativity of experimental findings and potential consequences on our understanding of the rheology of the lithosphere.

The idea that lithospheric materials at intermediate depths or deeper cannot support high deviatoric stresses is still supported by many studies in geosciences or physics. Plenty of authors start by recalling that brittle failure cannot occur at high pressure, and thus conclude that deep earthquakes and their shallow counterparts should consist of totally different events relying on totally different physical processes. Yet, deep seismicity is characterized by double-couple mechanisms and thus is an actual proof of seismic ruptures at great depths. Here I recall achievements from experiments under synchrotron radiation, suggesting that differential stresses can reach several gigapascals within subducting slabs at intermediate depths (30-300 km). In either peridotites or lawsonite blueschists, high-energy X-rays reveal differential stresses above 2 GPa for confining pressures of 1-1.5 GPa, and reaching ≈ 3 GPa for confining pressures of 2.5-3.5 GPa. This is further supported by both field geology studies and numerical modelling.

While mean stresses in seismogenic zones exhibit severe deviations from lithostatic pressure, the base of lithospheric plates deforms in a way that never triggers seismicity. The coupling between lithospheric plates and the underlying asthenosphere is still a matter of debate. According to global dynamics modelling, a basal shear stress as low as only 10-100 MPa would suffice to allow decoupling at the LAB. While partial melting has recently been favoured as an explanation for plate motion, experimental results on an analogue (germanium peridotite) suggest a solid-state lubrication process, involving grain-boundary disordering, and would confirm that mechanical stresses do not exceed 200 MPa at the LAB (60-120 km).

How to cite: Ferrand, T. P.: How high can mechanical stresses be within lithospheric materials?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17411, https://doi.org/10.5194/egusphere-egu23-17411, 2023.

EGU23-608 | ECS | Posters on site | EMRP3.1

Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering 

Sonal Tiwari, Amar Agarwal, Thomas Kenkmann, and Michael H. Poelchau

Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering

Sonal Tiwari1, Amar Agarwal1, Thomas Kenkmann2, Michael H. Poelchau2

1Department of Earth Sciences, Indian Institute of Technology-Kanpur, Kanpur – 208016, India.

2Geology, University of Freiburg, 79104 Freiburg, Germany

Corresponding author´s email: sonaljp20@iitk.ac.in

Abstract

Para- and ferromagnetic fabrics are known to provide essential clues for understanding impact cratering processes. However, research on the effects of shock waves on diamagnetic fabrics is lacking. We, therefore, conducted a hypervelocity impact experiment on a block of diamagnetic Taunus quartzite and studied the changes in diamagnetic fabrics. Taunus quartzite was formed by a low-grade Variscan metamorphism that overprinted a 405 Ma old sandstone. It consists of c. 91 vol % quartz and a fine-grained, greenish phyllosilicate-bearing matrix (c. 8 vol %), along with small amounts of rutile, chromite, zircon, monazite, and iron oxides.

The experiment was carried out on a 20 cm Taunus quartzite cube with a two-stage light-gas gun of the Fraunhofer Ernst-Mach Institute for High-Speed Dynamics (EMI) in Freiburg (EMI), Germany. The gun has a 8.5 mm calibre launch tube. The 0.3690 g basalt sphere projectile was accelerated to 5.457 kms-1, with a target chamber pressure of 1.2 mbar. The projectile diameter (dp) was 6.18 mm. Later, 14 mm-diameter nonmagnetic diamond bits were used to drill oriented cylindrical cores from unshocked and shocked Taunus quartzite blocks.  The AMS of the unshocked and shocked specimens was determined at room temperature in KLY-4S Kappabridge (AGICO). Following the AMS measurements, the cylindrical specimens were cut to make thin sections, which were studied under a Leica DM4 scanning optical microscope.

Hypidiomorphic grain texture, serrated grain boundary, grain boundary migration, ataxial veins, Boehm lamellae, and recrystallized quartz represent the natural microscopic features. Impact-induced microstructures include trans- and intragranular microfractures. Our AMS results demonstrate that in the crater subsurface, the reorientation of the diamagnetic fabrics is concentrated in a zone of ~4 projectile diameters (25 mm) width directly below the point of impact. Higher reorientation in this zone indicates the concentration of damage. The damage is concentrated directly below the point of impact. Another important observation is that weak shock waves have caused an increase in the bulk susceptibility. These results, thus, show that the changes in diamagnetic fabrics can be used as a proxy for plastic deformation caused by shock waves at low peak pressures.

Figure. The images show the specimens' position (black dots), the point source (brown dot), the impact crater (brown arc), and the variation in the orientation of k3.

How to cite: Tiwari, S., Agarwal, A., Kenkmann, T., and Poelchau, M. H.: Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-608, https://doi.org/10.5194/egusphere-egu23-608, 2023.

EGU23-1000 | ECS | Posters virtual | EMRP3.1

Lava-water interaction and formation of associated facies: a multidisciplinary study of the San Bartolo lava flow of Stromboli 

Rasia Shajahan, Elena Zanella, Andrew J L Harris, Lodovico Drovanti, Claudio Robustelli Test, Sonia Calvari, Lucia Gurioli, Sara Mana, and Benjamin van Wyk de Vries

Detailed rock magnetic, facies and textural analyses were carried out across the San Bartolo lava flow (Stromboli) to understand the flow dynamics of lava channel-fed 'a'a entering the water. Having been emplaced 3 ka, San Bartolo is the most recent lava flow field to have been emplaced beyond the Sciara del Fuoco, and underlies the inhabited area on the north-eastern side of the island. One of the remarkable features of the San Bartolo lava flow is the formation of several lobes due to the interaction with seawater. Field analysis shows three facies: 1. Stalling of flow fronts at the coastal interaction to form a littoral barrier to further flow, 2. Ramping of subsequently emplaced units behind this barrier, and creation of a degassed ponded volume, 3. Creation of tubes through the barrier to feed a seaward bench of pahoehoe. Around 12 lobes were identified. All the lobes show similar facies, but each lobe provides a case-type example of the emplacement history and the associated structures. For example, lobe 1 exhibits tube formation associated through the flow front barrier; while lobe 12 shows the formation of inflated pahoehoe lava. Preliminary AMS results show well-confined flow fabrics with a one-to-one relationship to field structures. The samples collected from ramped flow have vertical flow fabrics, while those from tube structures and inflated pahoehoe have horizontal fabrics. Preliminary palaeomagnetic data have characteristic remanent magnetisation (ChRM) directions for all the sampled lobes, with their a95 overlapping, suggesting rapid emplacement. In addition, the average ChRM direction falls in the geocentric axial dipole (GAD) field for Stromboli.

How to cite: Shajahan, R., Zanella, E., Harris, A. J. L., Drovanti, L., Robustelli Test, C., Calvari, S., Gurioli, L., Mana, S., and van Wyk de Vries, B.: Lava-water interaction and formation of associated facies: a multidisciplinary study of the San Bartolo lava flow of Stromboli, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1000, https://doi.org/10.5194/egusphere-egu23-1000, 2023.

To better constrain the drift history of the South Qiangtang block and the closure of the Paleo-Tethys Ocean, we report a paleomagnetic result isolated from 25 sites (199 samples) of Late Triassic volcanic rocks from the Xiaoqiebao Formation. The directions of the characteristic remanent magnetization isolated from these rocks pass both fold- and reversal tests, and are likely primary magnetizations. On base of these data, we estimate that the South Qiangtang block occupied a paleolatitude of 30.1°N±4.6 at 222Ma. When combined with existing paleomagnetic constraints, these new results indicate that the South Qiangtang block moved rapidly northward between the middle Permian and Late Triassic, at an average south‐north speed of ~13.4 cm/yr during middle Permian to Late Triassic. Our new data further suggest that the Paleo-Tethys likely closed by ~222Ma, and the north-south width of the Neo- Tethys Ocean was reached ca. 7000 km at this time.

How to cite: Wei, B., Cheng, X., Domeier, M., and Wu, H.: Paleomagnetism of Late Triassic Volcanic Rocks From the Southern Qiangtang Block, Tibet: Constrains on the Closure of the Paleo-Tethys Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1701, https://doi.org/10.5194/egusphere-egu23-1701, 2023.

The origin and drift history of the Lhasa block in South Tibet is crucial towards unraveling the evolution of the Neo-Tethys Ocean, which has not yet been well constrained by the paucity of paleomagnetic data, especially for the late Paleozoic. Hence, a systematic paleomagnetic investigation of 50 sandstone samples (6 sites), 166 volcanic samples (21 sites) and 76 limestone samples (9 sites) from the middle Permian (267.8 ± 5.0 Ma) Luobadui Formation was conducted in the Lhunzhub area. The results reveal an Eocene re-magnetization component in the sandstone samples, but stable high temperature (field) components obtained from most volcanic and limestone samples can successfully pass the fold, reversal and paleosecular variation tests, which likely represents primary magnetization. On this basis, the middle Permian paleomagnetic pole position (Plat= 40.9°N, Plong=324.5°E, N=27 sites (dp/dm=3.3/6)) and paleolatitude (~15.9°S) of the Lhasa block are presented. Combined with published paleomagnetic data from other Tethyan continental blocks, this new constraint reveals that the Lhasa block was located in the interior of the Neo-Tethys Ocean at about 268 Ma. In further considering the geological records of the Lhasa block, we propose that the block rifted from the northwestern margin of the Gondwana-Australian plate prior to the middle Permian, and the Neo-Tethys Ocean represented by the Bangong Co-Nujiang and Yarlung-Zangbo Suture Zones coexisted during the middle Permian.

How to cite: Xing, L., Cheng, X., and Wu, H.: Locating the Lhasa Block within the Neo-Tethys Ocean at ~268 Ma: Paleomagnetism and Its Paleogeographic Implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1736, https://doi.org/10.5194/egusphere-egu23-1736, 2023.

EGU23-1885 | ECS | Posters on site | EMRP3.1

Paleomagnetic and micromagnetic measurements of Middle Devonian pillow lavas from Germany 

Rosa de Boer, Annique van der Boon, Peter Königshof, and Lennart de Groot

Paleomagnetic data from the Middle Devonian are typically difficult to interpret. Directions and paleointensities often do not fit with dipolar field behavior or expected paleogeography. The reason why the geomagnetic field cannot be reconstructed with traditional methods has been topic of debate, but no consensus has been reached. We would like to understand what happened to the geomagnetic field during the Middle Devonian and why the configuration of the field was potentially unusual.

We aim to expand the existing paleomagnetic record for the Middle Devonian by sampling a site in Braunfels, Germany. This site consists of relatively unaltered pillow lavas. Petrographic and rockmagnetic analyses indicate the presence of magnetite and minor maghemite in the samples. We obtained paleomagnetic directions using alternating field (AF) and thermal demagnetization experiments. The directions are scattered and do not cluster around paleomagnetic directions that are expected for Germany in the Devonian.

Paleointensity data were acquired using the ZIIZP-Thellier method, resulting in a field intensity of approximately 6 µT, which equals a VADM of 8-15 ZAm2. The latter is in line with very low field intensities generally reported for the Devonian.

Various mechanisms have been suggested to explain the typically scattered and ambiguous Devonian paleomagnetic data, such as significant overprinting, tectonic rotations and a non-dipolar field configuration. Our results confirm an extremely weak magnetic field, but this alone does not explain the scattered directions. To exclude the possibility that the scattered directions are related to (partial) overprinting we use Quantum Diamond Microscope imaging to assess the magnetizations of individual magnetic grains instead of the bulk magnetic signal of the sample. With this method, a distinction can be made between e.g., different generations of magnetizations, revealing information on the Middle Devonian geomagnetic field that was previously inaccessible by considering the magnetic moments of bulk samples alone.

How to cite: de Boer, R., van der Boon, A., Königshof, P., and de Groot, L.: Paleomagnetic and micromagnetic measurements of Middle Devonian pillow lavas from Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1885, https://doi.org/10.5194/egusphere-egu23-1885, 2023.

Magnetic susceptibility (both in-phase, ipMS, and out-of-phase, opMS, components) and its anisotropy were investigated in artificial specimens with pure synthetic magnetite and in rocks with titanomagnetite with variable Ti-content reaching XUsp = 0.6 of ulvospinel end member. The opMS of pure magnetite is in its absolute values three orders lower than the ipMS. The phase angle is then lower than 0.2° in absolute values, which is mostly lower than the sensitivity of phase angle determination. Consequently, the opMS can be considered effective zero. In low-Ti titanomagnetite (XUsp~0.2), the intensity of the ipMS variation with field is very low, hardly reaching 1% of the initial value. In high-Ti titanomagnetite (XUsp~0.6), the intensity of ipMS variation is relatively strong reaching 50% of the initial value and that of opMS variation is even much stronger reaching multiples of the initial value.

In artificial specimens with magnetite, the opMS is isotropic from the statistical point of view as indicated by the values of the F-statistics and by confidence angles. In titanomagnetite-bearing rocks, the opAMS ellipsoids resemble the ipAMS ellipsoids, the degree of opAMS being significantly higher than that of ipAMS. The principal directions of ipAMS and opAMS are related closely in specimens with high-Ti titanomagnetites and only poorly in specimens with low-Ti titanomagnetites. In specimens with high-Ti titanomagnetites, there is a linear and very strong (R2 = 0.9433) correlation between the degree of ipAMS and root squared degree of opAMS.

The results of the present research are mainly applicable to the rocks whose magnetism is dominantly carried by titanomagnetite and pure magnetite. The opAMS indicates solely the titanomagnetite fabric unaffected by magnetite whose fabric may often originate in different conditions or in different time.

How to cite: Hrouda, F., Jezek, J., and Chadima, M.: Anisotropy of out-of-phase magnetic susceptibility in titanomagnetite-bearing rocks due to weak field hysteresis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2234, https://doi.org/10.5194/egusphere-egu23-2234, 2023.

EGU23-4479 | ECS | Orals | EMRP3.1

Full vector inversion of magnetic microscopy data using Euler deconvolution as a priori information 

Gelson Ferreira de Souza Junior, Ricardo Ivan Ferreira da Trindade, Leonardo Uieda, Roger Fu, and Janine Araujo do Carmo

Classically, paleomagnetic data is obtained from bulk samples, where the signal is obtained from the sum of all magnetic moments within the sample volume. This typically includes stable and unstable remanence carriers. With the advance of microscope imaging techniques (e.g., SQUID microscopes, Quantum Diamond Microscopes) it is now possible to spatially isolate the contribution of single grains or clusters of grains. Yet, despite recent advances in the inversion techniques to derive full vector information from the magnetic microscopy data, there is still no inversion protocol capable of obtaining the magnetization directions of each magnetic particle without using a priori information or physically separating the spatial position of each anomaly. Here we present an algorithm capable of automatically identifying the position of each magnetic anomaly source by combining signal processing and tridimensional Euler deconvolution. Subsequently, we recover both the direction and the intensity of the magnetic moment of each magnetic source with no need for any kind of additional information. The method presented here is a potential technique that may help increase the statistical accuracy of data obtained in paleomagnetic studies from magnetic microscopy data, especially in the case of complex characteristic remanent magnetization.

How to cite: Ferreira de Souza Junior, G., Ivan Ferreira da Trindade, R., Uieda, L., Fu, R., and Araujo do Carmo, J.: Full vector inversion of magnetic microscopy data using Euler deconvolution as a priori information, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4479, https://doi.org/10.5194/egusphere-egu23-4479, 2023.

EGU23-5045 | ECS | Orals | EMRP3.1

Building Physical Models of the Distribution of Iron-oxides in Basalts: ‘How MMT deals with MicroCT resolution limitations’ 

Frenk Out, Rosa de Boer, John Walmsley, and Lennart de Groot

Micromagnetic tomography (MMT) is a new promising paleomagnetic technique that obtains magnetic moments for individual iron-oxides. These magnetic moments are inferred from surface magnetometry data obtained with quantum diamond microscopy (QDM), and iron-oxide positions determined with micro X-Ray computed tomography (MicroCT). Different to classical techniques, MMT does not depend on bulk measurements of samples. This makes it possible to only select the most reliable magnetic recorders. To make this improvement possible, MMT first has to deal with the presence of undetected magnetic carriers in basaltic rock samples used in previous MMT studies. Although particles smaller than 1 µm are good recorders of the magnetic field and may be visible in surface magnetometry, they are not detected by MicroCT. This violates one of the foundations of MMT and may disturb magnetic moments of other detected grains. However, it is currently unknown how many of these small disturbing particles are present in Hawaiian basaltic samples. We know that the smallest disturbing grains have a diameter of around 40 nm, since particles smaller than this threshold become superparamagnetic and cannot store magnetic signals. For this reason we want to obtain a grain-size distribution for iron-oxides from 20 nm to 10 µm to cover the complete range of grains that are capable of storing Earth’s magnetic field. This requires a combination of FIBSEM slice-and-view and MicroCT techniques; FIBSEM detects single and pseudo-single domain grains with sizes between 20 nm and 1 µm and MicroCT detects multi-domain grains with sizes larger than 1 µm. Subsequently, FIBSEM and MicroCT data are combined to obtain the full spectrum of grain sizes. Unfortunately, grains are not uniformly distributed in the samples, so a scaling by volume would not produce a realistic spectrum. Therefore, based on observations that iron-oxides grains cluster on the interfaces of other minerals, we calculated how many times FIBSEM mineral interfaces from FIBSEM data fit the mineral interfaces from MicroCT data. Then, this factor is used to scale the FIBSEM iron-oxides to MicroCT iron-oxides and to obtain a complete distribution of all grain sizes. Interestingly, this distribution shows a clear peak in grain size at 70-80 nm. Furthermore, the smallest grain fraction is fitted a lognormal trend, but the fraction larger than 0.18 µm are fitted an exponential decay trend. With these trendlines in place we have finally acquired a realistic set of boundary conditions for the distribution of iron-oxide particles in basaltic rocks. This enables us to populate models with a realistic distribution of particles, which ultimately may shed light on the disturbing presence of small iron-oxides in MMT results. If we know the effect of these disturbances, we will understand which grains MMT can solve with highest certainty, ultimately leading to paleomagnetic interpretations on grain scale.

How to cite: Out, F., de Boer, R., Walmsley, J., and de Groot, L.: Building Physical Models of the Distribution of Iron-oxides in Basalts: ‘How MMT deals with MicroCT resolution limitations’, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5045, https://doi.org/10.5194/egusphere-egu23-5045, 2023.

EGU23-6126 | ECS | Posters on site | EMRP3.1

Multi-stage tectonic evolution of the Tatra Mts recorded in the para- and ferromagnetic fabrics 

Dorota Staneczek, Rafał Szaniawski, and Leszek Marynowski

Magnetic fabrics analysis is widely applied in reconstructions of the tectonic evolution of orogenic belts. The main advantage of this method is the ability to trace even weak deformation in rocks. The main goal of this work is to shed new light on the Cretaceous-Neogene tectogenesis of the Tatra Mts by investigating the para- and ferromagnetic fabrics of nappe units and post-thrusting sequences. It is worth mentioning, that this study provides the first magnetic fabric data from the thrust nappe system of the High Tatra Mts (the most elevated part of the Tatra Mts). We focused on Cretaceous marly limestones, the youngest part of the Mesozoic nappe system in the Tatra Mts, and Oligocene post-thrusting shales/siltstones. Petromagnetic methods combined with paleotemperature estimations enabled us to identify the magnetic mineralogy and its origin. The subsequent analysis of para- and ferromagnetic fabrics supported by the previously obtained mineralogical results let us recognize and characterize different stages of the tectonic evolution of the Tatra Mts. Even though the paleotemperatures recorded for Oligocene and Cretaceous rocks are higher in the High Tatra Mts than in the Western Tatra Mts, petromagnetic features of rocks sampled in both areas remain similar. Anisotropy of Magnetic Susceptibility (AMS) fabric of post-thrusting cover is governed by phyllosilicates. A consistent, approximately NE-SW-oriented magnetic lineation of tectonic origin is present in most analyzed sites and documents weak deformation presumably related to the Miocene uplift of Tatra Mts. Mean ferromagnetic mineral in Oligocene clastic sediments is magnetite. Origin of the AARM lineation in this unit is presumably related to the crystallization of the secondary magnetite on a preexisting phyllosilicate matrix and/or the stress field present during magnetite formation. The magnetic fabric of the Cretaceous marly limestones is controlled mainly by the orientation of phyllosilicates and differs significantly among the High and Western Tatra Mts. AMS results from The Western Tatra Mts’ sites document consistently the NW direction of alpine nappe thrusting. On the contrary, the AMS fabric in the High Tatra Mts shows no clear evidence of tectonic deformation. Ferromagnetic mineralogy of the Cretaceous nappe unit is complex and combines magnetite, hematite and maghemite in various proportions, with the usual dominance of magnetite. In the High Tatra Mts, the AARM fabric carried by magnetite is characterized by sub-vertical magnetic lineation, which we interpret as the impact of local transpression-related deformation associated with the Miocene uplift.

How to cite: Staneczek, D., Szaniawski, R., and Marynowski, L.: Multi-stage tectonic evolution of the Tatra Mts recorded in the para- and ferromagnetic fabrics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6126, https://doi.org/10.5194/egusphere-egu23-6126, 2023.

EGU23-6247 | ECS | Posters on site | EMRP3.1

Structural analysis by anisotropy of magnetic susceptibility and U-Pb geochronology of the Gamaye pluton (Kédougou-Kéniéba Inlier, West Africa) 

Aliou Dembele, Olivier Bolle, Marc Poujol, Moussa Dabo, and Mamadou Lamine Bouaré

The Gamaye pluton (Kedougou-Kenieba Inlier, West African Craton) is elongated along a N-S direction, over about 20 km, to the east of the sinistral, transcurrent Senegal-Mali Shear Zone (SMSZ). It is assumed to have been emplaced at around 2045±27 Ma (Rb-Sr whole-rock and feldspar age; Bassot & Caen-Vachette, 1984) and, as other granitoids from the Kedougou-Kenieba Inlier, it displays a spatio-temporal relationship with world-class gold mineralization (Lawrence et al., 2013a, b). The pluton is made of a leucocratic, coarse-grained, locally porphyritic granite, associated with a subordinate, mesocratic, fine-grained facies, mostly found in a small (1.5 x 4 km) body along the western border of the pluton. Preliminary apatite LA-ICP-MS U-Pb dating yield ages with quite large uncertainties, which highlight, however, magmatic pulses with distinct emplacement ages: 2294.6±68.3 Ma (western mesocratic body), 2160±34.8Ma (main leucocratic facies) and 1922.7±53.1 Ma (a tiny mesocratic body in the east of the pluton). The western part, particularly the democratic body, and the southern part of the pluton, close to the SMSZ, are mylonitized, displaying a S-C fabric, whereas the northern, central and eastern parts are almost isotropic. However, a study of the microstructures shows that these parts of the Gamaye pluton have also undergone solid-state deformation and dynamic recrystallization. Measurements of the anisotropy of magnetic susceptibility, conducted on about 50 samples, reveal paramagnetic signatures, with bulk susceptibilities lower than 0.5×10-3 SI. The shape of the magnetic fabric ranges from oblate to prolate, and the degree of anisotropy increases towards the western limit of the pluton and the SMSZ, together with the rock strain intensity. There is also a deflection of the magnetic foliation and lineation in that direction: in particular, when approaching the western border, the magnetic fabric is dominated by NNW-SSE-trending, steeply-dipping foliations (parallel to the C plane of the S-C fabrics) and gently-plunging lineations (concordant with the strike-slip movement of the SMSZ). It is concluded that the Gamaye pluton has been emplaced along the SMSZ and/or has been deformed by this transcurrent regional discontinuity.

Reference

Bassot, J.P., Caen-Vachette, M., 1984. Données géochronologiques et géochimiques nouvelles sur les granitoïdes de l’Est du Sénégal: implications sur l’histoire géologique du Birimien de cette région. In: Klerkx, J., Michot, J. (Eds.), African Geology, Belgium, Tervuren, pp. 196–209.

Lawrence, D.M., Treloar, P.J., Rankin, A.H., Harbidge, P., Holliday, J., 2013a. The geology and mineralogy of the Loulo mining District, Mali, West Africa: evidence for two distinct styles of orogenic gold mineralization. Econ. Geol. 108, 199–227.

Lawrence, D.M., Treloar, P.J., Rankin, A.H., Boyce, A., Harbidge, P., 2013b. A fluid inclusion and stable isotope study at the Loulo mining District, Mali, West Africa: implications for multifluid sources in the generation of orogenic gold deposits. Econ. Geol. 108, 229–257.

 

How to cite: Dembele, A., Bolle, O., Poujol, M., Dabo, M., and Bouaré, M. L.: Structural analysis by anisotropy of magnetic susceptibility and U-Pb geochronology of the Gamaye pluton (Kédougou-Kéniéba Inlier, West Africa), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6247, https://doi.org/10.5194/egusphere-egu23-6247, 2023.

EGU23-6373 | ECS | Posters on site | EMRP3.1

Magnetic analysis of individual iron oxide grains; application of Micromagnetic Tomography to a natural sample. 

Martha Kosters, Rosa de Boer, Frenk Out, David Cortes Ortuno, Michael Volk, and Lennart V. de Groot

The magnetic information stored in volcanic rocks is a valuable archive of the history of the behavior of the Earth’s magnetic field. Micromagnetic Tomography (MMT) allows to determine magnetic moments of individual iron-oxide grains in rocks. Theoretically this enables us to separate contributions from non-ideal recorders and ideal recorders, overcoming the difficulties arising from bulk measurements. Here we present results from two sister specimens from the 1907-flow from Hawaii’s Kilauea volcano to which MMT was applied. One specimen was imaged both by the Quantum Diamond Microscope in Harvard and by the MicroCT scanner Nanoscope–S in Delft, producing magnetic moments of 1,646 individual grains. The sister sample underwent stepwise AF-demagnetization: a step toward classic paleomagnetic analysis, from which we present (preliminary) results. In MMT, individual grains are allocated a magnetization through a least-squares inversion. For the first sample, we produced more than one magnetization for each grain, because each grain was present in multiple unique inversion ‘tiles’ (smaller sub-areas  due to computational constraints). This enabled a statistical analysis of the (robustness of) results, presented here. For the second sample (preliminary) demagnetization results per grain are presented. We also present results of an investigation into a parameter for selecting grains that can be reliably resolved from the statistical analysis. For both samples only relatively large iron-oxide grains (diameter > 1.5 -  2 µm) were resolved, as the resolution of the MicroCT was limited. However, any analysis of magnetism at grain level is a step in understanding how magnetizations are stored in individual grains, and is of importance for those specimens that only contain large iron-oxides.

How to cite: Kosters, M., de Boer, R., Out, F., Cortes Ortuno, D., Volk, M., and de Groot, L. V.: Magnetic analysis of individual iron oxide grains; application of Micromagnetic Tomography to a natural sample., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6373, https://doi.org/10.5194/egusphere-egu23-6373, 2023.

EGU23-10000 | ECS | Orals | EMRP3.1

Toward finer resolution APWPs 

Leandro Gallo, Mat Domeier, Facundo Sapienza, Nicholas Swanson-Hysell, Bram Vaes, Yiming Zang, Maëlis Arnould, Boris Robert, Tobias Rolf, and Annique van der Boon

Our understanding of paleogeography through Earth history relies heavily on apparent polar wander paths (APWPs), which represent the time-dependent position of Earth’s spin axis relative to a given tectonic plate. However, there are a number of limitations associated with conventional approaches to APWP construction. First, the paleomagnetic record contains significant uncertainty in individual pole positions that is not propagated into APWPs. This traditional approach makes it difficult to incorporate age and positional uncertainty into synthesized paths and assigns equal weight to paleomagnetic poles with vastly different numbers of underlying sites. Second, the effective propagation of site-level uncertainties into the APWP requires a transformation that renders traditional parametric assumptions (i.e., Fisher statistics) on the pole level ineffective. Here, we overcome these limitations with a bottom-up Monte Carlo uncertainty propagation scheme that operates on site-level paleomagnetic data. To demonstrate our methodology, we present a large compilation of site-level Cenozoic paleomagnetic data from North America, which we use to generate a high-resolution APWP. We show that even in the presence of significant noise, polar wandering can be assessed with unprecedented temporal and spatial resolution.

How to cite: Gallo, L., Domeier, M., Sapienza, F., Swanson-Hysell, N., Vaes, B., Zang, Y., Arnould, M., Robert, B., Rolf, T., and van der Boon, A.: Toward finer resolution APWPs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10000, https://doi.org/10.5194/egusphere-egu23-10000, 2023.

EGU23-10068 | Orals | EMRP3.1

A (new?) ~50 Kyr geomagnetic event recorded in a stalagmite from the Bat Cave, Portugal 

Eric Font, Elisa M. Sánchez-Moreno, Eduardo Lima, Ana Raquel Brás, Jorge, E. Spangenberg, Larry Edwards, Ricardo Trindade, Luca Dimuccio, Altug Hasözbek, Josep Parés, Fernando Jiménez Barredo, Janine Araujo de Carmo, and Joshua Feinberg

Stalagmites are potential candidates for high-resolution reconstruction of the Earth’s magnetic field and paleoclimatic variations. Here we provided a pristine record of a geomagnetic event recorded in two stalagmites from the Bat Cave, Central Region of Portugal. SQUID microscopy reveals a high concentration of magnetic particles. FORC diagrams and hysteresis parameters point to non-interacting single-domain magnetite as the main magnetic carrier. Carbon and oxygen isotope compositions are interpreted as primary and provide the record of a Greenland interstadial. Paleomagnetic data show a gradual variation of the magnetic declination and inclination from the normal component to an antipodal reverse component. Return to the normal component is abrupt and is not apparently associated with visible hiatus in the precipitation rate of the stalagmite. Preliminary U-Th dating point to an age of ~50-55 Kyr for the geomagnetic event recorded in both stalagmites. However, owing to the speleothem’s high detrital content and low U concentration, alternative techniques are being explored to improve the uncertainty in radiometric dating. This geomagnetic event can possibly correspond to the Laschamp geomagnetic excursion dated at ~41 Kyr or to a newly discovered ~50 kyr short-lived geomagnetic reversal.

 

Acknowledgments: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL, MIT-EXPL/ACC/0023/2021, and PTDC/CTA-GEO/0125/2021).

 

How to cite: Font, E., M. Sánchez-Moreno, E., Lima, E., Brás, A. R., Spangenberg, J. E., Edwards, L., Trindade, R., Dimuccio, L., Hasözbek, A., Parés, J., Jiménez Barredo, F., Araujo de Carmo, J., and Feinberg, J.: A (new?) ~50 Kyr geomagnetic event recorded in a stalagmite from the Bat Cave, Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10068, https://doi.org/10.5194/egusphere-egu23-10068, 2023.

EGU23-10086 | ECS | Orals | EMRP3.1

Micromagnetic Modeling of Thermoremanent Magnetization in Small Natural Pseudo-Single Domain Magnetite Particles 

Annemarieke Beguin, Even Nikolaisen, and Karl Fabian

Earth and planetary rocks record magnetic variations and are crucial recorders to further our understanding of the formation and evolution of the Earth’s magnetic field. The acquisition and stability of remanent magnetization in rocks are controlled by the magnetization state of magnetic particles. Where the thermoremanent magnetization (TRM) of pseudo-single domain (PSD) magnetite particles probably dominates the natural remanence of many igneous rocks. These PSD particles are therefore important carriers of paleomagnetic information. Nevertheless, the extension of Néel's (1955) elegant analytical theory of single domain (SD) particles to larger PSD particles meets with substantial technical challenges. Understanding the unblocking of energy barriers between energetically favorable domain states is important when predicting the TRM behavior of natural particles. While categorizing different magnetization states is manageable for simple SD particles, it will become increasingly difficult with increasing particle size. Mapping the full energy landscape for PSD particles can be challenging and time-consuming. 

Here we present an automated process that can categorize all possible local energy minima (LEM) from micromagnetic modeling results. The automated process determines if magnetic states with approximately equal total energy are in the same reversible region. We incorporate calculations of energy barriers between LEMs for an assemblage of natural magnetite particles obtained by focused-ion-beam (FIB) nano-tomography. The technique was tested for a suite of PSD particles from single-vortex to multi-vortex states, where we systematically studied the energy landscape and relaxation time as a function of temperature. To map the energy landscape, LEM and energy barriers between all possible LEM were calculated for temperatures between room temperature and Curie temperature. Combining these results in a statistical model allows for predicting the TRM acquisition of individual particles and isotropic ensembles of equal particles. The results are discussed in terms of the TRM behavior of natural PSD magnetite, magnetic stability, and the implications for paleomagnetic research.

How to cite: Beguin, A., Nikolaisen, E., and Fabian, K.: Micromagnetic Modeling of Thermoremanent Magnetization in Small Natural Pseudo-Single Domain Magnetite Particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10086, https://doi.org/10.5194/egusphere-egu23-10086, 2023.

The apparent polar wander (APW) path of the Pacific plate during Cenozoic and Late Cretaceous time has important paleogeographic, global tectonic, geodynamic, and paleoclimatic implications. Here we present recent progress on our assessment of Pacific plate APW with a focus on new poles determined from analysis of the skewness of marine magnetic anomalies due to seafloor spreading, which produces high precision paleomagnetic poles.

Our recent and new results include paleomagnetic poles for chron C24r (57–54 Ma; Woodworth et al. 2023), chron 21n (48−46 Ma; Woodworth et al. in preparation), chron 27r (63−62 Ma; Gaastra et al., in preparation), and chron 30n−31n (69−66 Ma; Ritchey et al., in preparation).  The new chron 24r pole extends the northward progression of the 69–58 Ma track in the previously determined Pacific plate apparent polar wander path beyond the southern end of the 46–10 Ma track, which is now extended by our chron 21n pole.  That the two tracks overshoot one another implies either a brief interval during which the Pacific plate moved substantially and rapidly southward relative to a mantle reference frame or to an episode of true polar wander (TPW, the re-orientation of the solid Earth relative to the spin axis).  The reconstructed plate geometry and relative plate motions are inconsistent with ancient plate driving forces having been capable of driving the plate southward.  Considering our results together with drill-core paleomagnetic paleolatitudes, we find that the most likely explanation is a ≈7° episode of TPW between ≈54 Ma and ≈50 Ma.  

The new high precision paleomagnetic poles for the Pacific plate, when compared with continental paleomagnetic results from Torsvik et al. (2012) reconstructed to a common frame of reference, allow an updated test of two plate motion circuits relating the Pacific plate to the circum-Pacific continents. Analysis of the plate-motion circuit through Antarctica (or through Australia) continues to indicate a significant paleomagnetic misfit that increases with age during Cenozoic time up to a maximum of ≈7−8° at ≈50 Ma. Analysis of the fixed hotspot circuit indicates a smaller insignificant misfit of up to ≈5° that also increases with age.

If the plate circuit through Antarctica is flawed, as indicated by the paleomagnetic results, any or all of the following may have contributed to the flaw: (1) intraplate deformation (cf., Kreemer & Gordon, 2014), (2) unrecognized diffuse oceanic plate boundaries (e.g., Gordon & Stein, 1992), (3) motion between East and West Antarctica not localized across mid-ocean ridge segments, and (4) horizontal extension across large expanses of submerged continental area in the south Pacific (e.g., Sutherland et al., 2020).

How to cite: Gordon, R., Woodworth, D., and Gaastra, K.: Cenozoic and Late Cretaceous Apparent Polar Wander of the Pacific Plate: Implications for True Polar Wander and Global Plate Motion Circuits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10221, https://doi.org/10.5194/egusphere-egu23-10221, 2023.

EGU23-12219 | ECS | Posters virtual | EMRP3.1

Deciphering the variation of magnetic fabric intensity across the Main Central Thrust in Garhwal Himalayas 

Asha Borgohain, Pradeep Gairola, Sandeep Bhatt, Virendra Rana, and Sayandeep Banerjee

One of the key aspects of understanding the rapid exhumation of Himalayan core, is to understand the variation of deformation intensity occurring along the major tectonic unit i.e., the Main Central Thrust (MCT). Quantification of magnetic fabrics, derived from analysis of anisotropy of magnetic susceptibility (AMS), defines the strain path in the form of an ellipsoid and provides a rich source of information on the structural evolution of rocks throughout the MCT. The approach of this study is to integrate field and AMS parameters, where field foliation from 73 planes has orientation trending NW-SE with a moderate dip of about 600 (best fit great circle) The magnetic foliation is found to be parallel to the field foliation. Variation in orientation direction of magnetic lineation implies the dominance of superposed folding in the study area. The degree of anisotropy (Pj), which quantifies the intensity of preferred orientation of magnetic minerals show values ranging from 1.1 to 1.8. The AMS study reveals that the shape parameter(T) of susceptibility ellipsoid, in most of the samples are positive representing an oblate ellipsoid. To be more precise, this study reflects the inter-relationship between field structures, superposed folding, magnetic fabric parameters to understand the exhumation of Himalayan core.

How to cite: Borgohain, A., Gairola, P., Bhatt, S., Rana, V., and Banerjee, S.: Deciphering the variation of magnetic fabric intensity across the Main Central Thrust in Garhwal Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12219, https://doi.org/10.5194/egusphere-egu23-12219, 2023.

EGU23-14336 | Orals | EMRP3.1

Temporal constraints on Fe mobility in Jack Hills zircon 

Steven Reddy, Richard Taylor, Richard Harrison, David Saxey, William Rickard, Fengzai Tang, Cauê Borlina, Roger Fu, Benjamin Weiss, Paul Bagot, and Helen Williams

Ancient detrital zircon grains containing magnetite inclusions have the potential to record the Earth’s magnetic field as far back as the Hadean. However, this requires magnetite to be either a primary inclusion or to be a secondary inclusion that forms shortly after zircon crystallization. Microstructural and TEM analysis of Jack Hills zircon show that magnetite, the magnetic recorder in these zircon crystals, is secondary in nature and is associated with the mobility of Fe. However, the timing of Fe mobility within Jack Hills zircon is poorly constrained. Here we undertake nanoscale characterization of highly magnetic zones of zircon, identified by quantum diamond microscopy (QDM), using atom probe tomography (APT). The APT data show the presence of Pb-bearing nanoclusters and these record isotopic compositions consistent with formation during two discrete thermal events at 3.4 Ga and < 2 Ga. The older population of clusters contain no detectable Fe. However, the younger population of clusters are Fe-bearing. This result shows that the Fe required to form secondary magnetite was not present in the zircon prior to 3.4 Ga and that remobilization of Pb and Fe, the latter associated with magnetite formation, took place after 2 Ga, during an annealing event that took place more than one billion years after deposition of the Jack Hills sediment at 3 Ga. This use of APT to date Fe mobility provides a novel approach to temporally constrain the formation of intragranular secondary magnetite inclusions in highly magnetic areas of zircon grains.

How to cite: Reddy, S., Taylor, R., Harrison, R., Saxey, D., Rickard, W., Tang, F., Borlina, C., Fu, R., Weiss, B., Bagot, P., and Williams, H.: Temporal constraints on Fe mobility in Jack Hills zircon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14336, https://doi.org/10.5194/egusphere-egu23-14336, 2023.

EGU23-14498 | ECS | Posters virtual | EMRP3.1

Deformation model of the Cheka pluton of alkaline granitoids: petromagnetic and geochemical data (Southern Urals) 

Petr Shestakov, Alexander Tevelev, Alexey Kazansky, Natalia Pravikova, Egor Koptev, Ekaterina Volodina, and Alexandra Borisenko

Introduction. This study investigates the Cheka block (pluton) of alkaline granitoids (Southern Urals, Chelyabinsk Oblast). The objective of this study was to further investigate its existing deformation model after previous studies though the methods of fracture analysis, petromagnetic studies and geochemical analysis.

The Cheka pluton is composed of the Cheka Mountain and has a meridional strike and dimensions of 6.5 km long and 1-2 km wide. The pluton is composed of alkaline rocks of three intrusion phases: first – monzodiorites, second – alkaline syenites, third – alkaline granites and granosyenites. The pluton is Triassic and intrudes Carboniferous volcanics. The western contact of the Cheka pluton is limited by a dextral fault. The pluton is situated in the Magnitogorsk zone.

During the formation of the pluton, extension changed to compression. This led to formation of a right-lateral transpression setting with a system of meridional strike-slip and near-slip extension zones. These changes were followed by low-grade metamorphism.

This study can be split into two sections: structural analysis and geochemical/isotopes description. The first part was partially conducted previously and presented in 2022.

Materials and methods. To reconstruct structural evolution of the pluton a combination of petromagnetic studies, magnetic mineralogy and fracture analysis were used as well as supporting aerial and satellite imagery. 62 core samples and over 180 fracture measurements from 7 locations were used for each method respectively. Petromagnetic data was collected by drilling procedures, processed using MFK-1 kappabridge at room temperature and after heating to 470 °C and analyzed in Anisoft 5.1.08 software. Magnetic mineralogy lab analyses were performed with interpretation using Max UnMix software. Fracture analysis was conducted in Stereonet v.11.3.0.

As the second part of the study geochemical analyses were conducted – silicate geochemistry and ICP-MS at 6 locations.

Results and discussion. Petromagetic studies showed the magma flow to have an orientation of 036°. Analysis of tectonic fractures points to the Riedel fracture model with main fracture zone orientation (compression) of 039°. Since the magma flow and compression orientation match a deformation model can be constructed. Also based on the magma flow orientation, types of protectonic fractures were identified (S, Q, L).

Geochemical analyses showed that the elemental signature of the pluton matches the upper crust the best and shows signs of subduction. Silicate geochemistry shows a clear trend in Na2O concentration, while K2O concentrations do not. This pattern is interpreted as a sign of low-grade metamorphism (prehnite-pumpellyite facies).

A full deformation model was created based on two methods with additional supporting data providing strong evidence for the Riedel based deformation model, which corresponds to previous structural and geochemical findings. The model suggests that the Cheka pluton was formed in a general right-lateral transpression setting with following tectonic developments and related low-grade metamorphism.

Financial support. The reported study was funded by RFBR and Czech Science Foundation according to the research project № 19-55-26009. Centre of collective usage ‘Geoportal’, Lomonosov Moscow State University (MSU), provided access to remote sensing data.

How to cite: Shestakov, P., Tevelev, A., Kazansky, A., Pravikova, N., Koptev, E., Volodina, E., and Borisenko, A.: Deformation model of the Cheka pluton of alkaline granitoids: petromagnetic and geochemical data (Southern Urals), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14498, https://doi.org/10.5194/egusphere-egu23-14498, 2023.

EGU23-15137 | Posters on site | EMRP3.1

An integrated structural and AMS study to define the emplacement of the Arbus pluton (SW Sardinia, Italy) 

Francesca Cifelli, Francesco Secchi, Leonardo Casini, Stefano Naitza, Enrico Carta, and Giacomo Oggiano

The Arbus igneous complex (SW Sardinia, Italy) represents a good example of a short time lived post-collisional composite pluton emplaced at shallow crustal level in the external zone of the Variscan chain. The pluton almost consists of granodiorite and leucogranite rock-suites emplaced at 304 ± 1 Ma within a main NW trending thrust separating the metamorphic wedge from the fold and thrust belt foreland. The pluton emplaced into a dilatational step over connecting two NW–SE dextral shear zones which belongs to a regional network of post-collisional strike-slip structures marking the transition from col- lision to post-collisional extension. The microstructure observed for quartz and K-feldspar confirms the lack of significant post-emplacement deformation, indicating only limited high-temperature sub-solidus recrystallization. Anisotropy of magnetic susceptivity data and field-structural analysis have been carried out to reconstruct the geometry of the pluton and the trajectories of magmatic flow in relation to regional deformation structures. Overall, the magmatic and the magnetic fabrics are broadly discordant with the metamorphic foliation of the country rocks, defining an EW trending elliptical asymmetric sill rooted in the SW quadrant. The reconstructed architecture combined to petrologic observation indicates that accretion of the pluton involved injection of multiple dykes through a sub-vertical feeder zone, combined to lateral flow of the roof controlled by inherited collisional structure. The duration of magmatic activity and the cooling history of the contact metamorphic aureole have been evaluated through a suite of 2D thermal models. All these observations, together with the available geochronological constraints are suggestive of very rapid construction of the pluton. The proposed emplacement model is fully consistent with the regional phase of strike-slip tectonics and widespread magmatism accommodating the large rotation of the Corsica-Sardinia block during the Carboniferous-Permian transition.

How to cite: Cifelli, F., Secchi, F., Casini, L., Naitza, S., Carta, E., and Oggiano, G.: An integrated structural and AMS study to define the emplacement of the Arbus pluton (SW Sardinia, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15137, https://doi.org/10.5194/egusphere-egu23-15137, 2023.

The interpretation of magnetic fabric (studied mainly by means of anisotropy of magnetic susceptibility) has become one of the well-established, fast, and reliable rock fabric proxies used in many branches of the Earth science. In the usual case, the magnetic fabric ellipsoid reflects the crystallographic or shape preferred orientation of the grains of the main rock-constituent mineral. If two (or more) sets of mineral grains are present, their combined contribution towards the whole-rock magnetic fabric is proportional to their relative content, their value of bulk susceptibility and their degree of anisotropy. This can be the case of, for example, combined contribution of differently oriented paramagnetic and ferromagnetic sub-fabrics, normal and inverse magnetic fabric, or anisotropic fabric and isotropic matrix. In order to overcome some misconception on how various magnetic fabrics can contribute to the overall rock fabric, we present a simple toolbox for visualizing a combined contribution of two pre-defined end-member magnetic sub-fabrics. These end-member fabrics are defined by their bulk susceptibility, degree of anisotropy, shape of anisotropy ellipsoid and the orientations of its principal directions. The toolbox is part of Anisoft software which enables the instant visualization how magnetic fabric changes as a function of the relative content of the end-member sub-fabrics.

How to cite: Chadima, M.: A simple toolbox for evaluating the combined contributions to the whole-rock magnetic fabric, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17170, https://doi.org/10.5194/egusphere-egu23-17170, 2023.

The Reykjanes Ridge is located in the North Atlantic Ocean, southwest of Iceland. Here, the oceanic crust is characterized by a series of V-shaped ridges (VSRs) and V-shaped troughs (VSTs), the formation of which has been linked to three alternative hypotheses: i) thermal pulsing, ii) propagating rifts, and iii) buoyant mantle upwelling. During International Ocean Discovery Program Expeditions 384 and 395C, a transect of five sites were drilled eastwards of the modern Mid-Atlantic Ridge (between 20-30°W) at a latitude of ~60°N, to investigate VSTs/VSRs formation.

In this preliminary study, we analyze basalt samples from four sites, two from VSRs and two from VSTs, using rock magnetic and anisotropy of magnetic susceptibility (AMS) techniques, to investigate the differences between VSRs and VSTs. We analyzed the samples at the CIMaN-ALP (Peveragno) and INGV (Rome) Laboratories of paleomagnetism through bulk susceptibility, AMS, stepwise demagnetization of natural remanent magnetization through alternating field and temperature, hysteresis loops and FORC diagrams, and susceptibility vs temperature curves. Rock magnetism was used to determine the rock magnetic properties of each sample and investigate its correlation with the degree of alteration observed in the basalts. The AMS was measured to determine the magnetic fabric as a proxy of the magmatic fabric, where, for instance, lava flow-like fabric would be typical of an unaltered basalt.

Preliminary results suggest that basalts from VSTs are generally characterized by higher susceptibility values, while the AMS shows a mixed behavior (well defined or dispersed) independently from the structural position. Further rock magnetic data, integrated with petrological, structural and geochemical data will be correlated to the pervasiveness of alteration in each site, the age of basalts and their distance from the Mid-Atlantic Ridge to test the three hypotheses.

How to cite: Satolli, S., Di Chiara, A., and Friedman, S.: Preliminary rock magnetic and anisotropy of magnetic susceptibility results from the Reykjanes Ridge basalts, Atlantic Ocean (IODP Expeditions 384 and 395C), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17243, https://doi.org/10.5194/egusphere-egu23-17243, 2023.

TS2 – Faults: imaging, kinematics and mechanics

EGU23-1208 | ECS | Orals | TS2.1

Characteristics and evolution of strike-slip faults in a stable cratonic block 

Zhao Wang and Lei Huang

The deformation pattern in the interior of cratonic blocks has critical implications for regional structural evolution but still remains an unresolved question. The southwestern Ordos Basin is at the convergence of multiple blocks, leading to intense and complex tectonic stress at this location. However, how the interior of the Ordos block responds to the complex stress field around it is still elusive. This study analyzes the characteristics and evolutionary history of faults in the southwestern part of the inner Ordos Basin using 3D seismic data. Three dominant sets of faults trending NW, NEE, and N–S have developed in the study area. All three sets of faults have subvertical dip angles and straight fault traces and structures that are common in such fault zones, such as flower structures and en-echelon and horsetail arrangements (all indicating strike-slip movement) are present. Structural deformation varies from the center to the periphery of the Ordos block. All three sets of fault systems exhibit small displacements. The polarity of the strike-slip changed in different periods, reflecting the transformation of the stress field in the southwestern Ordos Basin. This illustrates that the formation of cratonic faults is controlled by the regional stress field, while the related strain pattern in the interior of the cratonic block is very different from the deformation around its periphery. These characteristics also demonstrate the special nature of cratonic fault deformation.

How to cite: Wang, Z. and Huang, L.: Characteristics and evolution of strike-slip faults in a stable cratonic block, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1208, https://doi.org/10.5194/egusphere-egu23-1208, 2023.

EGU23-2686 | ECS | Posters on site | TS2.1

Insights on the seismotectonic of Calabria-Lucania border region (Southern Italy): different tectonic styles at different depths 

Ada De Matteo, Paolo Capuano, and Mariarosaria Falanga

The Calabria-Lucania border region represents the transitional area between the Southern Apennines and the Northern sector of the Calabrian arc. Roughly the whole Apennine chain is struck by more or less intense earthquakes. While the northern and central parts of the chain are characterized by foreland contraction and hinterland extension, the Southern Apennine is characterized by a strike-slip kinematics in the eastern sector and by an extensional regime in the western sector. Strike-slip earthquakes have been observed also in the axial part of the Campania-Molise Apennines, rightly beneath the active extensional sector.

The Calabria-Lucania border region is considered a seismic gap in the Apennine chain; few paleo-earthquakes, with magnitude ranging from 5 to 7, have been recorded in the area. During 2010-2014 the region was affected by a low-moderate instrumental seismicity (known as Pollino seismic sequence): thousands of earthquakes occurred. Analysis of that seismicity revealed a shallow hypocentral distribution located into the first few km below the surface, and focal mechanisms of the strongest events of the sequence are consistent with upper crustal extensional deformation. While the shallow seismicity of Calabria-Lucania border region has been deeply studied after the 2010-2013 sequence, the sporadic deep seismicity needs a more detailed analysis.

As highlighted by previous studies, instrumental seismicity recorded from 2013 to 2015 reveals the presence of a sporadic deep (from 9 to more than 20 km) seismicity. The events located between 9 and 17 km deep have transcurrent to transpressional kinematics with NE-SW trending P axes; while deeper events show a strike-slip kinematics with NW-SE trending P axes.

We analyzed deep (> 10 km) seismicity recorded in the area from 2013 to nowadays. Starting from the picking of seismograms of more than 40 events (with M between 2.4 and 3.8), we analyzed the focal mechanisms of events computed using at least six good first motion observations. According to Ferranti et al., 2017, our results highlight the presence of a strike-slip/oblique kinematics at depths of more than 20 km. Between 10 and 20 km depth both dip-slip and strike-slip kinematics are present, with a predominance of the last ones, confirming the presence of a transition zone.  

Finally, we inverted the focal mechanisms dataset to infer about the stress field active in the region.

How to cite: De Matteo, A., Capuano, P., and Falanga, M.: Insights on the seismotectonic of Calabria-Lucania border region (Southern Italy): different tectonic styles at different depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2686, https://doi.org/10.5194/egusphere-egu23-2686, 2023.

The most common method of detecting subsurface structures on continental and marine surfaces is seismic imaging. Although technological advancements have been made, seismic analysis of carbonates remains challenging due to their strong petrophysical heterogeneity, which becomes more challenging when faults are incorporated. This work aims to produce unmigrated forward-seismic models to grasp the deformation behavior of carbonate-bearing fault systems and the related seismic response changes. The porous and faulted carbonates outcropping at the Majella Massif (central Italy) are here used as case study as an analogue of carbonate ramp reservoirs exploited worldwide. Field and laboratory petrophysical data of fault rocks collected at increasing distances from the fault planes show a damage zone/fault core architecture characterized by a decreasing porosity and an increase in shear modulus moving from host rocks towards fault planes. Starting from these observations, unmigrated stacked seismic models have been built simulating fault zones with both increased and decreased porosities with respect to the host rocks. Fault zones with lower porosity than the host rock show slight diffraction hyperbolas, while the diffractive component is pronounced in seismic images of fault rocks with higher porosity than the host rock. Such hyperbolas can be enhanced or weakened by modifying the dip angle of the fault plane or the width of the damage zone but a key role seems to be played by the decreased porosity. The existence of diffraction hyperbolas in unmigrated seismic models is then interpreted as evidence of a damage zone characterized by larger porosity compared to the host rock. Migrated stacked sections would not provide any evidence of increased porosity in the damage zone due to loss of information about the diffractive component resulting from the processing. Consequently, the absence of diffraction hyperbolas in actual unmigrated seismic images is suggested to be related to a decreased porosity in the fault zone. This can be related to cataclasis and solution/cementation of the damage zone rocks as observed in the study area, and related to confining stress acting at depth or fracture filling that counteracts the fracture-related increase in secondary porosity. On the other hand, diffraction hyperbolas in unmigrated seismic images can represent a clue of the presence of large-porosity fault zones.

How to cite: Tomassi, A., Trippetta, F., and de Franco, R.: Seismic signature of carbonate fault rocks changes with changing petrophysical properties: insights from unmigrated seismic forward modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3880, https://doi.org/10.5194/egusphere-egu23-3880, 2023.

EGU23-4803 | ECS | Posters on site | TS2.1

Offshore extension of the Ilan Fault in northeast Taiwan 

Chih-Chia Chang, Shu-Kun Hsu, Lien-Kai Lin, Ching-Hui Tsai, and Hsiao-Shan Lin

The Philippine Sea Plate (PSP) has subducted northwestward beneath the Eurasian Plate (EP) in the northeast Taiwan and has obliquely collided with the EP creating the mountain building. The offshore area of northeastern Taiwan is subject to post-collisional collapse and under extensional regime, forming a series of normal faults. The NE-SW trending Ilan Fault is situated between the Ilan Plain and the Hseushan Range. The Ilan Fault is also call North Ilan Structure (NIS). According to the Taiwan Earthquake Model published by TEC team in 2020, the probability for a Mw 6.9 earthquake happened in NIS in future fifty years is estimated about 13%. However, if the NIS extends to the offshore area, the risk will become greater. This study aims to understand the possible offshore extension of the Ilan Fault and analyze the structural activity. For that, we have collected 24-channel sparker reflection seismic profiles and sub-bottom profilers across the possible fault trace. Based on sparker seismic profiles and sub-bottom profiles, four major normal faults, Fa, Fb, Fc and Fd, trending NE are observed. Faults Fa and Fb are active and have outcropped to the seafloor. A negative flower structure is observed along Fault Fa, which indicates that the regional stress is under transtension. Furthermore, slope failures, slumps and sliding surfaces are found. Overlying on the Last Glacial Maximum (LGM) unconformity, sedimentary layers are tilted in the hanging wall of Fault Fb, indicating Fault Fb is a growth fault. On the other hand, Faults Fc and Fd dip to the NW and SE, respectively. They bound a graben trending NE and only ruptured to the LGM unconformity. It implies that Faults Fc and Fd are no more active.

How to cite: Chang, C.-C., Hsu, S.-K., Lin, L.-K., Tsai, C.-H., and Lin, H.-S.: Offshore extension of the Ilan Fault in northeast Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4803, https://doi.org/10.5194/egusphere-egu23-4803, 2023.

EGU23-4924 | ECS | Posters on site | TS2.1

Post-collisional Geological Structures off Gongliao District in Northern Taiwan 

Yi-Wen Lin, Shu-Kun Hsu, Ching-Hui Tsai, Yen-Yu Cho, and Lien-Kai Lin

The offshore area of northern Taiwan is subject to post-collisional collapse and under an extensional regime. Because of the change from a compressional environment to an extensional environment, a series of normal fault structures has occurred. The reverse faults in the Gongliao area of Taiwan, include the Longdong Fault, Wentzukeng Fault, Aodi Fault, and Fangjiao Faul, are distributed from inland to the coastline. However, their prolongations to the offshore area are unknown. In order to understand the possible fault extension to the offshore area and the possible fault activity, we conducted Sparker reflection seismic surveys in the offshore area of Gongliao. The Sparker seismic system is suitable for shallow water surveys and can provide high-resolution shallow structures. To understand the geological structures in our study area, sequence stratigraphy, seismic facies and faults identification are used to analyze our seismic profiles. According to the sequence stratigraphy, the transgressive surface, the last glacial maximum (LGM) unconformity, and last maximum flooding surface can be identified. In addition, the sand wave base surface, syn-rift unconformity and the acoustic basement are defined. We have identified 5 normal faults (i.e. Fa, Fb, Fc, Fd and Fe) in the prolongation of the onshore faults. All the identified faults cut through the basement and caused large offsets, forming half-graben basins. For the activity of these faults, the strata in the half-graben basin A formed by Fault a, is tilted, which was probably caused by the continuous growth of the fault. The strata in the half-graben basin B formed by Faults b and c, are inclined below the LGM unconformity, but the strata above the LGM unconformity are relatively flat. In contrast, only the sediments in the upper part of the half-graben basin B show the characteristics of sequence stratigraphy, which means the sediments deposit controlled by sea level change. In summary, we infer that the faults b and c were active before the LGM and relatively stable recently. Faults d and are covered by thick sediment layers, indicating early structures not active at all.

How to cite: Lin, Y.-W., Hsu, S.-K., Tsai, C.-H., Cho, Y.-Y., and Lin, L.-K.: Post-collisional Geological Structures off Gongliao District in Northern Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4924, https://doi.org/10.5194/egusphere-egu23-4924, 2023.

EGU23-5141 | Posters on site | TS2.1

The aftershock series of the 2016 Petermann Ranges earthquake in Central Australia 

Christian Sippl, Gregory Brenn, Sharmin Shamsalsadati, and Hrvoje Tkalčić

Although located far from any active plate boundaries, Central Australia features significant seismic activity, with a total of four M>6 events in the last four decades. The most recent such event was the May 25th, 2016 Petermann Ranges earthquake (Mw = 6.1), which occurred close to the border triangle between the Northern Territory, South Australia and Western Australia. The last tectonic reactivation of the region that hosted the earthquake occurred during the intraplate Petermann Orogeny that terminated about 540 Ma ago. It is commonly assumed that although recently inactive, this region still constitutes a lithospheric-scale zone of weakness, so that stresses imposed on the rigid Australian plate at its edges can localize and lead to seismicity here. Previous studies have shown that the Petermann earthquake occurred on a splay fault in the direct vicinity of the Woodroffe Thrust, one of the principal shear zones of the Petermann Orogeny. It occurred at a very shallow depth (<= 5 km) and had a thrust mechanism with a NW-SE oriented rupture plane. Due to its shallow depth, it created a surface rupture that was mapped over a length of about 20 km.

In the present study, we utilized a temporary deployment of 11 seismic stations that was installed in the aftermath of the Petermann earthquake to characterize its aftershock sequence. Since only a single permanent station was operating within a radius of 400 km around the rupture area before the deployments, we do not have much information about the earliest part (first two weeks) of the aftershock series.

We combine two different event catalogs, a handpicked one comprising 1231 events for the first 3.5 months of the aftershock sequence, and a semi-automatically derived one that contains a total of 4918 events. We derived an optimal 1D velocity model and station corrections from the handpicked catalog, and relocate all events with this model. In a second step, we apply a double-difference relocation to the entire dataset. Most of the relocated events occurred at depths between 2 and 4 km, and outline a tight NW-SE striking an NE-dipping plane that aligns well with the mapped trace of the surface rupture. As already indicated in previous studies, we also find scattered aftershock activity within the footwall of the fault.

We further applied a template-matching algorithm in order to further decrease the completeness magnitude of the catalog and to get the best possible estimate for event rate decay over time. Moreover, we present fault plane solutions for a few of the largest aftershocks.

How to cite: Sippl, C., Brenn, G., Shamsalsadati, S., and Tkalčić, H.: The aftershock series of the 2016 Petermann Ranges earthquake in Central Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5141, https://doi.org/10.5194/egusphere-egu23-5141, 2023.

The northern Tyrrhenian Sea separates the northern Apennines of the Tuscany coast (Italy) from the Corsica island (France). 

A comprehensive revision of a vast dataset of vintage public seismic reflection profiles was conducted, re-elaborating via dedicated vectorization codes to improve their resolution and interpretability. 

The bathymetry of this sector shows a very regular and almost flat geometry of the seafloor. Despite this, a close look at seismic profiles reveals an articulated topography of the pre-Neogenic deformed acoustic basement. This is organized in thrust-related structural highs and narrow, N-S and NNW-SSE trending basins, filled by sedimentary successions separated by unconformities.

Nowadays, the sedimentary sequences associated with the most recent evolution of the Tyrrhenian Sea completely sutured the previous morphology.

To date, we found strong evidence regarding the role of structural inheritance in shaping the current architecture of the shallow crust. We identified an intimate relationship between the thrust-related structural highs and the basins' position at the antiforms' forelimb and backlimb. Indeed, the Tuscan Shelf neogenic basins started to develop as intermontane fault-controlled basins along the flanks of the inherited antiforms.

We performed a structural analysis of the faults bounding the basins and a detailed seismic-stratigraphic analysis of the Neogenic succession deposited into such basins to reconstruct the Tyrrhenian Sea extension's initial phases and embed it into the broader evolution of the Mediterranean region.

The evolution of the sedimentary basins from the middle Miocene to the Pleistocene provides a more comprehensive and robust picture of the Tyrrhenian Sea. We were able to track the progressive activation and deactivation of high-angle normal faults controlling the basins deposition and the eastward migration of the extensional front. Such a setting influenced the asymmetrical or symmetrical evolution of the basins. Intriguingly, and partially in contrast with previous works, no evidence of low-angle normal fault was observed.

We also present the first reconstruction of a 3D geological model of the southern Tuscany offshore between Elba Island and Monte Argentario promontory (Italy). 

Such a model poses new questions on the crustal-scale mechanisms responsible for the extensional process, also establishing a unique starting point for fully unraveling the Tuscan Shelf and the Tyrrhenian Sea early stages of evolution.

How to cite: Buttinelli, M., Mazzarini, F., Musumeci, G., Maffucci, R., and Cavirani, I.: Tectonic-Sedimentary evolution of the Tuscan shelf (Italy): seismic-stratigraphic analysis of the Neogenic succession in the northern Tyrrhenian Sea between Elba Island and Monte Argentario promontory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5350, https://doi.org/10.5194/egusphere-egu23-5350, 2023.

Unveiling the geometry and kinematics of subsurface seismic faults is important for earthquake hazard assessment. Earthquake focal mechanisms can provide such fundamental aspects of faulting; however, they often require additional information to distinguish faults and auxiliary planes. We attempt to identify faults using a stress inversion technique, in which fault planes in individual focal mechanisms are selected based on the fault instability parameter. This stress inversion algorithm developed by Vavryčuk (2014) selects a higher instability nodal plane as the fault and finds 70-80% faults correctly to derive reliable stress results. Our tests using synthetic and simulated focal mechanism data with faults known beforehand show that faults are correctly identified especially when the instability of the selected fault plane is significantly higher than that of the auxiliary plane, which can be quantitatively expressed by the instability ratio of the fault plane to that of the auxiliary plane being higher than ~1.3. This constraint can improve further the ability to identify subsurface seismic faults. We apply this technique to the case of geothermal-induced earthquakes that occurred in Pohang, South Korea during 2016-2017. A total of 53 well-constrained and well-located focal mechanism data are inverted to derive a stress condition, during which faults are identified as higher instability nodal planes. These earthquakes occurred in spatially distinct portions of the region associated with water injection through two respective boreholes (PX-1 and PX-2). For the PX-2-related earthquakes, 70% of identified faults are well aligned in their locations and orientations with a large-scale fault, indicating that these earthquakes occurred on the patches of this fault. This fault is responsible for the 2017 Mw 5.5 main earthquake. Fault planes whose instability ratio is higher than ~1.3 are all consistent with this plane. There is more variation in identified fault orientations in PX-1 earthquakes. However, a few fault planes with high instability ratios are generally subparallel to one another. The locations and orientations of these high instability ratio planes are well aligned with a large-scale fault, which is different from, but subparallel to the PX-2 fault. This study demonstrates the possibility of identifying and imaging subsurface seismic faults only using faulting mechanics without other additional information.

How to cite: Chang, C.: Identifying seismic fault geometry from focal mechanisms based on fault instability ratio during a stress inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5622, https://doi.org/10.5194/egusphere-egu23-5622, 2023.

EGU23-5677 | ECS | Orals | TS2.1

The analysis of the Castelsaraceno microearthquake sequence (southern Italy) through a semi-automated template matching and machine-learning approach reveals an anti-apenninic fault 

Serena Panebianco, Vincenzo Serlenga, Claudio Satriano, Francesco Cavalcante, and Tony Alfredo Stabile

The accurate characterization of microearthquake sequences allows seismologists to shed light on the physical processes involved in earthquake nucleation, the deformation processes underlying rupture activation and propagation, and to image faults geometry at depth. The current methodologies used for this purpose first need the event detection and the phase-picking - usually manual-based - and earthquake locations, which require plenty of work even by expert analysts particularly in the case of microearthquake signals, commonly noise contaminated. Thus, improving standard procedures through semi-automatic or fully-automatic workflows would be an essential step forward towards the more efficient analysis of seismic sequences.

Here we show the results of a semi-automated template matching and machine-learning based workflow applied for the characterization of the foreshock-mainshock-aftershock microearthquake sequence occurred close to Castelsaraceno village (High Agri Valley, Southern Apennines, Italy) in August 2020. The analyses were performed on seismic data mainly recorded by a local seismic network belonging to the High Agri Valley geophysical Observatory (HAVO) deployed in the study area and located at a maximum epicentral distance of ~20 km from the seismicity cluster.

The application of the semi-automated single-station template matching technique to the continuous data-streams of the two nearest stations of the HAVO network (from 28th July to 12th October 2020) allowed us to detect more than twice the number of microearthquakes previously identified by standard manual detections. The phase-picking was automatically performed through a deep-learning algorithm (Phasenet) on the 202 ultimate detected microearthquakes. Finally, an automatic multi-step absolute and relative earthquake location procedure was carried out.

A total of 76 events were identified as belonging to the Castelsaraceno sequence, which occurred in a short time span (7-12 August) and in a limited range of depths (10 -12 km). Both the Ml 2.1 foreshock doublet and the Ml 2.9 mainshock occurred on 7 August ruptured the same seismogenic patch, thus suggesting the presence of a persistent asperity. The integrated analysis of the aftershocks distribution, the focal mechanism of the mainshock, and the geological framework of the study area, allowed revealing the seismogenic fault, not currently mapped in literature: a NE-SW striking (225°), high-angle (55°) fault with a left-lateral transtensional (rake -30°) kinematic. We also hypothesize that the seismic sequence occurred at depth in a brittle layer of the crystalline basement confined between two regions with more ductile rheology; futhermore, the estimated b-value (0.73±0.04) indicates the occurrence of the sequence in a relatively low-heterogeneity material and suggests the unimportant effect of pore-fluid pressure in driving its evolution. 

How to cite: Panebianco, S., Serlenga, V., Satriano, C., Cavalcante, F., and Stabile, T. A.: The analysis of the Castelsaraceno microearthquake sequence (southern Italy) through a semi-automated template matching and machine-learning approach reveals an anti-apenninic fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5677, https://doi.org/10.5194/egusphere-egu23-5677, 2023.

EGU23-5756 | ECS | Orals | TS2.1

Characterising faults in geothermal fields using surface waves: a numerical study 

Heather Kennedy, Katrin Löer, Amy Gilligan, and Claudia Finger

Subsurface characterisation of geothermal fields is important for the expansion of geothermal energy as a low-carbon resource. Faults and fractures provide secondary permeability, thus, their characteristics are crucial parameters in deep geothermal fields. Analysis of ambient seismic noise provides a relatively cheap and widely accessible method for constraining faults and fractures in geothermal settings.

 

Three-component (3C) beamforming is an array-based method that extracts the polarizations, azimuths, and phase velocities of coherent waves as a function of frequency from ambient seismic noise, offering a comprehensive understanding of the seismic wavefield. 3C beamforming can be used to determine surface wave velocities as a function of depth and the direction of propagation of waves. It is assumed that anisotropic velocities relate to the presence of faults, giving an indication of the maximum depth of the permeability essential for fluid circulation and heat flow throughout a geothermal field. Previous results suggests that some structures have a stronger effect on surface wave velocities than others. Numerical models are essential to study these relationships in more detail.

 

Here we present a numerical simulation of wave propagation through a model of the subsurface, with anisotropy depicted as faults. This is employed by a rotated staggered grid (RSG) finite-difference (FD) scheme. We model a homogeneous half-space with a fault-like structure (40 m width), changing fault parameters, such as depth, width, velocities and internal conditions of the fault (“fill”). We generate surface waves from a single source as well as multiple sources emulating an ambient noise wavefield.

 

We then use 3C beamforming on the synthetic data to characterise the modelled wavefield and observe the types of waves present. The polarisation and beam power of the synthetic data denote the composition of the synthetic wavefield and what percentage are retro- and prograde Rayleigh waves and Love waves. To investigate the strength of anisotropy introduced by a single fault we propagate surface waves across the fault in different directions, estimating velocities from array recordings using the beamformer. We are further able to assess the sensitivity of Rayleigh waves towards anisotropy at depth by considering Rayleigh waves at different frequencies sampling different depths.

How to cite: Kennedy, H., Löer, K., Gilligan, A., and Finger, C.: Characterising faults in geothermal fields using surface waves: a numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5756, https://doi.org/10.5194/egusphere-egu23-5756, 2023.

EGU23-7651 | ECS | Posters on site | TS2.1

3D scattering and absorption imaging of the Pollino seismic gap (Italy) 

Ferdinando Napolitano, Ortensia Amoroso, Luca De Siena, Simona Gabrielli, and Paolo Capuano

The Pollino area, one of the largest seismic gaps in Italy, has been struck between 2010 and 2014 by a long-lasting seismic sequence. More than 10,000 small-to-medium earthquakes followed a temporal evolution typical of a seismic swarm and, to a lesser extent, of  aftershocks following the two strongest events: a ML 4.3 on 28 May 2012 and a ML 5.0 on 25 October 2012. A delay of almost 4 months separated the two main events, with the first event occurring two years after the beginning of the swarm. A slow slip event began about three months before the strongest earthquake. High VP and high VP/VS values have been found in the swarm area, where clusters of events of similar waveforms have been identified in recent works. The distribution of seismicity has been driven by pore fluid pressure diffusion with relatively low diffusivity value.

The present work aims to provide the first 3D images of scattering and absorption of the Pollino area at different frequency bands, measured through peak delay mapping and coda-attenuation tomography, respectively. We collected 870 earthquakes from the 2010 - 2014 seismic sequence and surrounding area, characterized by ML > 1.7, already applied in a recent tomographic work. We used the manual P-wave pickings of the waveforms to compute the peak delay as the lag between the P-wave onset and the maximum of the envelope. Instead, the coda window has been fixed for the entire dataset at 30 seconds after the origin time of the earthquakes, lasting for 15 seconds. This late lapse time allows us to interpret Qc-1 as a marker of the absorption.

The preliminary results show a high scattering anomaly characterizing the seismogenic volume of the sequence and the newly identified faults surrounding the focal area. A strong scattering contrast has been identified south of the ML 5.0 plane. This contrast is likely related to the presence of a segment of the Pollino Fault that acts as a barrier for the Southern propagation of the sequence. High attenuation anomalies in areas already marked by high VP and high VP/VS confirm the role that fluids played in this complex sequence. These results, together with the recent outcomes, could give more insights about the seismic hazard of this complex area.

This work was supported by the PRIN-2017 MATISSE project (no. 20177EPPN2), funded by the Ministry of Education and Research.

How to cite: Napolitano, F., Amoroso, O., De Siena, L., Gabrielli, S., and Capuano, P.: 3D scattering and absorption imaging of the Pollino seismic gap (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7651, https://doi.org/10.5194/egusphere-egu23-7651, 2023.

EGU23-11176 | Orals | TS2.1 | Highlight

High-resolution 3-D geophysical imaging across a seismogenic fault: the TEst Site IRpinia fAult (TESIRA) project 

Pier Paolo Gennaro Bruno, Giuseppe Ferrara, Luigi Improta, Stefano Maraio, Vincenzo Di Fiore, David Iacopini, Mario Fusco, Michele Punzo, Valeria Paoletti, Giuseppe Cavuoto, and Paolo Marco De Martini

The scientific project TESIRA (TEst Site IRpinia fAult), funded in 2021 by the University of Naples “Federico II”, aims at acquiring multidisciplinary geophysical data above an active fault in an intramontane basin of the Southern Apennines and to achieve, through the integration of this multivariate dataset, an accurate 3D geophysical imaging of the shallow structure of the fault zone in order to understand the link between shallow faulting and petrophysical changes, which affect rock permeability and surface degassing. The target structure is the southern branch of the Irpinia Fault, one of the structures with highest seismogenic potential in the Mediterranean region, causing the 4th Italian earthquake of last century (1980, Ms=6.9, Pantosti & Valensise, 1990) and generating a modest surface throw at Pantano San Gregorio Magno (Salerno).

A microgravimetric survey and a 3D and 2D Electrical Resistivity measurements survey were acquired between September 2021 and January 2022. 3D seismic data were acquired in July 2022, using two overlapping arrays with a dense geophone distribution covering an area of about four hectares, with a detail of 2.5x2.5m. Moreover, four 2D seismic profiles intersect the 3D volume. An aeromagnetic survey, an extension of the gravimetric survey and a sampling of the CO2 surface degassing will be completed within this year. We will show the preliminary results of the individual surveys. Later, the different geophysical and geochemical measurements will be integrated using cooperative inversion and machine learning techniques.  We hope that this multidisciplinary approach will provide a more comprehensive understanding of the interaction between surface faulting and basin development in this key area of the Southern Apennines.

 

References

Pantosti, D.; Valensise, G.; [1990] Faulting Mechanism and Complexity of the November 23, 1980, Campania-Lucania Earthquake, Inferred From Surface Observations, JGR, 95, 319-341

How to cite: Bruno, P. P. G., Ferrara, G., Improta, L., Maraio, S., Di Fiore, V., Iacopini, D., Fusco, M., Punzo, M., Paoletti, V., Cavuoto, G., and De Martini, P. M.: High-resolution 3-D geophysical imaging across a seismogenic fault: the TEst Site IRpinia fAult (TESIRA) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11176, https://doi.org/10.5194/egusphere-egu23-11176, 2023.

EGU23-11539 | ECS | Posters on site | TS2.1 | Highlight

10 years of seismicity on the Reykjanes Peninsula, SW Iceland 

Jana Doubravová, Rögnvaldur Líndal Magnússon, Diana Konrádová, Josef Horálek, Tomáš Fischer, Thorbjörg Águstsdóttir, and Egill Árni Gudnasson

Reykjanes Peninsula (SW Iceland) is an extraordinary place from the geophysical perspective. Lying on the on-shore part of the Mid-Atlantic Ridge, interlaced by volcanic systems and hosting several high temperature geothermal areas, the seismic activity on the Peninsula is generally persistent on a microseismic level, but occasionally reaching up to ML~5-6. Throughout the years, many temporary seismic stations or small to medium size local seismic networks have been deployed there for various purposes, from geothermal prospection monitoring to short time passive seismic experiments. We analyzed 10 years of natural seismicity recorded by the semi-permanent local seismic network REYKJANET (in operation since 2013) together with several permanent stations of the SIL regional seismic network present in the area of interest, in total number of 22 stations covering an area of about 1200 km2. The timespan, 2013-2022, contains times of relative quiescence, several small tectonic earthquake swarms as well as very active periods of volcano-tectonic origin, with dyke intrusions and larger earthquakes of magnitudes up to ML- 5.4. We study the distribution of epicenters of the background seismicity as well as for the several seismically active periods with a consistent set of stations.

We compare several different automatically derived earthquake catalogues using different detection and location algorithms, and their common features such as the upper and lower limit of the epicenter occurrence, seismogenic faults, aseismic zones and void areas. The dataset contains dyke intrusions related events during the the 2021-2022 Fagradalsfjall volcano-tectonic event.

Depending on the exact quality criteria and method used, we deal with over 100,000 events with high quality stable locations imaging the subsurface beneath the Reykjanes Peninsula.

How to cite: Doubravová, J., Magnússon, R. L., Konrádová, D., Horálek, J., Fischer, T., Águstsdóttir, T., and Gudnasson, E. Á.: 10 years of seismicity on the Reykjanes Peninsula, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11539, https://doi.org/10.5194/egusphere-egu23-11539, 2023.

EGU23-13042 | Posters on site | TS2.1

High-resolution local earthquake tomography of seismogenic structures along the Rhone-Simplon fault zone (Swiss Alps) 

Tobias Diehl, Timothy Lee, Edi Kissling, and Stefan Wiemer

In this study, we explore the potential to image the seismic velocity structure of moderate-sized, upper-crustal seismogenic fault zones by means of local earthquake tomography (LET) methods. The study region, located in the transition zone between the Central and Western Alps, represents one of the most seismically active and hazardous areas within the Alpine Arc. Over the past 500 years, several damaging earthquakes with Mw up to 6.2 are documented in historical earthquake catalogs in the vicinity of the Rhone-Simplon Fault (RSF), the dominant tectonic feature of this region. In particular, two major seismogenic structures are imaged by instrumental seismicity on either side of the RSF. To the north, seismicity occurs in the approximately NE-SW striking, 30–40 km long Rawil Fault Zone (RFZ). To the south, diffuse seismicity occurs within the hanging wall of the Pennine Basal Thrust, forming the Penninic Fault Zone (PFZ).

Owing to the dense instrumentation and above-average seismic activity in the study region, the Pg and Sg travel-time data recorded since the year 2000 by the Swiss Seismological Service is of exceptionally high quality and allows for high-quality 3D LET images of the uppermost crust, potentially imaging the damage zones of seismogenic faults. Relative double-difference locations of a recent earthquake sequence within the RFZ, on the other hand, indicate that the width of this fault zone is only on the order of 1 km. Imaging such narrow fault zones with standard LET methods therefore requires model parametrizations with grid spacing of few kilometers and less. Such dense grid spacing, however, poses several challenges in terms of model resolution and the reliability of LET inversion results, especially in less well constrained parts of the model.

To minimize such effects, we therefore tested and applied two different LET inversion strategies to derive 3D Vp and Vs models. The first strategy follows the common approach to compute a minimum 1D model as initial model for the 3D LET. The second strategy uses a coarser 3D regional LET model as initial model for the high-resolution 3D inversion. Synthetic tests suggest that a minimum image resolution of 5x5x3 km can be achieved with the current data, covering a region of about 125x125 km between 0 and 10-15 km depth. The 3D Vp and Vs models derived with the two initial-model strategies are remarkably similar within well resolved parts of the model. This similarity indicates that the anomalies in these parts are well constrained by the data and the solution is stable with respect to differences in the two initial models. On the other hand, the results suggest that results derived with the 3D initial model are more reliable in regions of reduced resolution. Additional synthetic tests were performed to document the potential resolution for hypothetical damage-zone scenarios and to support the interpretation of the derived models presented in this study.

How to cite: Diehl, T., Lee, T., Kissling, E., and Wiemer, S.: High-resolution local earthquake tomography of seismogenic structures along the Rhone-Simplon fault zone (Swiss Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13042, https://doi.org/10.5194/egusphere-egu23-13042, 2023.

EGU23-13872 | Orals | TS2.1

New insights into vintage 3D reflection seismic data in hard-rock environment 

Felix Hlousek and Stefan Buske

The demand for reliable high-resolution reflection seismic exploration campaign in hard-rock environments increases continuously. The target of such surveys varies and covers e.g. mineral exploration, geothermal reservoir characterization or the exploration of potential nuclear waste deposit sites. Although the exploration targets are very different, the expectations on the seismic images and the challenges for data acquisition and processing are similar. The expected structures are often steeply dipping with varying strike directions and conflicting dip situations. Furthermore, the reflection seismic data often has to be acquired on land, possibly in populated areas, or in areas with severe accessibility restrictions. These limitations lead to irregular or sparse datasets in combination with sometimes low signal-to-noise ratio for the target reflections in the recorded data.

 

Therefore, robust imaging methods are needed to generate high resolution reflection seismic images for such kind of data. Focusing prestack depth migration methods have proven to deliver improved image quality compared to standard time- or depth migration approaches. We show the results of our focusing pre-stack depth migration techniques applied to a vintage 3D seismic data set (ISO89) acquired in 1989 around the German deep continental drill site (KTB). We show a comparison to other previously obtained seismic images for the same data set and how the image quality evolved over time.

How to cite: Hlousek, F. and Buske, S.: New insights into vintage 3D reflection seismic data in hard-rock environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13872, https://doi.org/10.5194/egusphere-egu23-13872, 2023.

EGU23-14033 | ECS | Orals | TS2.1 | Highlight

CARS - Catalog of Relative Seismic Locations of 1981-2018 Italian Seismicity 

Maddalena Michele, Raffaele Di Stefano, Lauro Chiaraluce, Diana Latorre, and Barbara Castello

The Istituto Nazionale di Geofisica e Vulcanologia (INGV) monitors the Italian peninsula seismicity by using the data recorded by the Italian National Seismic Network (RSN) together with the ones gathered by other permanent regional networks (PRN). Earthquakes are real-time located by the INGV surveillance system and manually revised by the Italian Seismic Bulletin (BSI) group analysts.

Starting from a catalog composed by homogeneous absolute locations (CLASS; Latorre et al., 2023), obtained by using a 3D regional-scale velocity model, we generated a catalog of relative seismic locations (CARS) of about 310,000 events occurred in Italy during 1981-2018.

We inverted absolute P- and S- waves arrival times derived from data collected by RSN plus PRN for the period 1981-2008 and only by RSN for 2009-2018 to apply the double-difference relocation algorithm (Waldhauser and Ellsworth, 2000).

For the second period, we combined the absolute travel times with relative ones obtained by waveforms cross-correlations analysis performed on pairs of similar events. The time domain cross‐correlation method proposed by Schaff et al., 2004 and Schaff & Waldhauser, 2005 was applied to seismograms of all pairs of events separated by 10 km or less and recorded at common stations. Seismograms were filtered in the 1–15 Hz frequency range using a four pole, zero phase band‐pass Butterworth filter. The correlation measurements were performed on 1.0 s long window for P- and S-waves. We collected a total of ~17 million P- and ~23 million S-wave delay times, retaining all measurements with correlation coefficients greater than 0.7.

1D velocity models characterising 18 different (geologically, seismically and tectonically homogeneous) Italian macroareas (after Pastori et al. B2-2019-2021, Wp1-task4) were used in the location procedure.

To cope with the memory limits (15,000 events with less than 200 readings) of the HypoDD code so to use it in a steady operational mode, we first subdivided the study region in the 18 macroareas related to the velocity models, then we additional discretize each in 100x100km2 cells, overlapped by the 80% in longitude and latitude. We repeatedly produced hypocentral locations of the same events that we merged by computing a final weighted mean location.

We present the double-difference catalog of Italian seismicity, allowing to depict alignments clearer with respect to the starting catalog (CLASS), to be related to seismogenic faults and/or to regional structures along the whole Italian peninsula.

How to cite: Michele, M., Di Stefano, R., Chiaraluce, L., Latorre, D., and Castello, B.: CARS - Catalog of Relative Seismic Locations of 1981-2018 Italian Seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14033, https://doi.org/10.5194/egusphere-egu23-14033, 2023.

EGU23-14206 | Posters on site | TS2.1

A local earthquake tomography model of the Fucino fault-controlled basin (central Apennines, Italy) obtained through a very dense temporary network 

Pasquale De Gori, Luigi Improta, Maurizio Vassallo, Fabrizio Cara, Gaetano De Luca, Alberto Frepoli, Samer Bagh, and Luisa Valoroso

The Fucino basin (central Italy) is the largest Plio-Quaternary tectonic depression of the Apennines extensional belt. The basin is bounded to the north and east by two main normal fault systems striking WSW-ENE and NW-SE, respectively. These fault systems controlled the syntectonic depositions of lacustrine and coarse clastic sequences that reach a total thickness of 1.5 km. The NW-SE fault system is the source of the Mw 7.0, 1915 central Italy earthquake and of previous M6-7 earthquakes recognized through paleoseismic trenching. On the other hand, current activity and seismogenic potential of the WSW-ENE structures are uncertain. The shallow architecture of both fault systems (< 2 km depth) is well defined by surface data and seismic reflection profiles, but the fault’s deep geometry is poorly known. Large uncertainties also regard the crustal structure underneath the basin at seismogenic depths (i.e.; 5-15 km depth) despite a close deep seismic reflection profile (i.e., CROP11 line). The instrumental seismicity occurring beneath the Fucino basin is scarce. On the contrary, an intense activity concentrated to the north (2009, Mw 6.3, L’Aquila sequence) and 25-30 km to the south, where both low-to-moderate sequences and diffuse swarm-like seismicity were recorded in recent years. In 2008-2009, a dense passive seismic survey was carried out in the Fucino area to investigate the basin seismic response and local site effects. The temporary network included 18 stations, with an average spacing of 2-3 km, operating in continuous mode with a sampling rate of 125 Hz and equipped with 5 second seismometers. In this study, we re-processed the data recorded by the Fucino temporary network, integrated by the permanent stations of the Italian seismic network and Abruzzo regional network installed on the surrounding ridges, to construct a new earthquake catalog and perform a local-scale passive tomographic survey. We used a standard (STA/LTA) algorithm to detect very local weak events in addition to those used in the previous site-effects study. P- and S-wave arrival times of the detected seismic events were hand picked and weighted according to a standard scheme. Seismograms for stations deployed in the Fucino basin show strong complexities especially for P-waves onsets that are often masked by background noise. We used the final dataset in terms of P- and S-waves arrival times as input for a Local Earthquake Tomography targeting the upper crustal velocity structure and active faults underneath the Fucino basin and surrounding ridges. The tomographic model, presented in terms of Vp and Vp/Vs, aimed at recovering the crustal heterogeneities with a spatial resolution finer with respect to previous tomographic surveys of central Apennines. The 3D distribution of Vp and Vp/Vs and of relocated events helped us to identify the velocity contrasts related to the main faults and to improve our knowledge on their geometry at depth.

How to cite: De Gori, P., Improta, L., Vassallo, M., Cara, F., De Luca, G., Frepoli, A., Bagh, S., and Valoroso, L.: A local earthquake tomography model of the Fucino fault-controlled basin (central Apennines, Italy) obtained through a very dense temporary network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14206, https://doi.org/10.5194/egusphere-egu23-14206, 2023.

EGU23-14260 | ECS | Posters on site | TS2.1

Comparison of relative locations methods and their accuracy for determining fault structures 

Diana Konrádová, Josef Horálek, and Jana Doubravová

Precise earthquake locations are a prerequisite for determining real fault structures. To improve the precision of the event location, a few relative locations methods are commonly used to refine event locations. Relative relocation methods reduce effects of an imperfect velocity model and errors due to arrival time measurement. We performed comparative tests of tree different relocation methods: HypoDD (HD), GrowClust (GC) and Master event (ME). We tested the efficiency and differences in the event locations using these three methods on dataset from REYKJANET seismic network operating in Iceland on Reykjanes Peninsula. All these methods provide substantially focused shapes of clusters compared to the absolute event locations but the locations of individual events differ evidently depending on the method used.

We also aimed at an effect of the control parameters of HD, GC and ME on final location results and their optimization as well as computational and memory demands.

How to cite: Konrádová, D., Horálek, J., and Doubravová, J.: Comparison of relative locations methods and their accuracy for determining fault structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14260, https://doi.org/10.5194/egusphere-egu23-14260, 2023.

EGU23-15556 | Orals | TS2.1 | Highlight

Rayleigh wave tomography in the north-eastern margin of the Tibetan Plateau by way of training physics-informed neural networks 

Sjoerd de Ridder, Yunpeng Chen, Sebastian Rost, Zhen Guo, and Yongshun Chen

Machine learning is rapidly becoming ubiquitous in the Earth Sciences promising to provide scalable algorithms for data-mining, interpretation, and model building. Initially heralded for its ability to exclude complicated physics from data analysis, recent innovations seek to merge machine learning  solutions with conventional physics-based methods in order to enhance their capability

We present a novel eikonal tomography approach for Rayleigh wave phase velocity and azimuthal anisotropy based on the elliptical-anisotropic eikonal equation, by formulating the tomography problem as the training of a physics informed neural network (PINN). The PINN eikonal tomography (pinnET) neural network utilizes deep neural networks as universal function approximators and extracts traveltimes and medium properties during the optimization process. Whereas classical eikonal tomography uses a generic non-physics-based interpolation and regularization step to reconstruct traveltime surfaces, optimizing the network parameters in pinnET means solving a physics constrained traveltime surface reconstruction inversion, tackling measurement noise and resolving the underlying velocities that govern the physics. The fast and slow velocity and the anisotropic direction information can be directly evaluated from the trained medium property networks. Checkerboard tests indicate that the input velocity model can be well recovered by using this approach and synthetic data.

We demonstrate this approach by applying it to multi-frequency surface wave data from ChinArray phase II sampling the north-eastern Tibetan plateau. We are able to use much less data to achieve similar subsurface images because of the benefit of including the physics constraint while reconstructing the traveltime surfaces. We are able to obtain excellent results using only 10 sources.  Comparing results from pinnET with conventional eikonal tomography, we find good agreement with distinct low velocity structures beneath the Songpang-Ganzi block, Qilian and Western Qinling Orogen. Large phase velocity uncertainties occur in a small part of the southeastern Ordos Block, the western Songpan-Ganzi Block and the eastern Sichuan basin, which correspond to the reduced data coverage dependent on the selection of the 10 sources. We also verify the accuracy and reliability of the pinnET by choosing only one station as virtual source, the retrieved velocities show relatively good resolution which is much better than in conventional eikonal tomography using similar sized datasets. The method is memory efficient because compressing the traveltimes as outputs to a NN is a concept akin to compressed sensing and offers advantages over traditional anisotropic eikonal tomography or neural network approaches.

How to cite: de Ridder, S., Chen, Y., Rost, S., Guo, Z., and Chen, Y.: Rayleigh wave tomography in the north-eastern margin of the Tibetan Plateau by way of training physics-informed neural networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15556, https://doi.org/10.5194/egusphere-egu23-15556, 2023.

EGU23-15881 | Posters on site | TS2.1

Accurate Earthquake Locations of the Adriatic Thrust Fault of the 2021 Seismic Sequence with sP Depth Phases. 

Raffaele Di Stefano, Maria Grazia Ciaccio, Paola Baccheschi, and Dapeng Zhao

We re-located 70 earthquakes belonging to the seismic sequence started on 2021 March 27th, with a mainshock of Mw 5.2 at 13:47 UTC, in the Central Adriatic region (Italy off-shore) by using the on-purpose designed code by Zhao et al. (2007, 2011), modeling the sP converted phases.

The mainshock of the 2021 seismic sequence occurred about 20 km north of the Palagruza island, 80 km from the Gargano promontory and about 40 km from the Croatian island of Lastovo. It was felt in many central-southern Italian regions, from Ancona to Foggia, and in Central Dalmatia. All the epicenters of this seismic sequence lie in the open sea, about 100km to the SE and about 50 km to the NW of the 2003 Jabuka seismic sequence, and the 1988 Palagruza seismic sequence, respectively.

Though the seismicity in the central Adriatic Sea has been recorded by improving seismic networks, especially in recent decades, the precise location of the Adriatic offshore earthquakes was hampered mainly by the large distance of the closest stations, and by the large gap in the distribution of seismic stations.

The possibility to model the sP depth phases enables us to estimate the epicentral parameters and focal depths of these offshore earthquakes more accurately, thanks to the peculiar ray-path that mimics the presence of a receiver approximately on top of the hypocenter. The refined earthquake locations allow us to make inferences on the structure responsible for the seismicity of the 2021 seismic sequence, a thrust fault NW-SE striking and ~35° NE-dipping, and on its seismotectonic context.

The use of depth-phase arrival times to constrain the off-network events' locations is of particular interest to Italy due to both the peculiar shape of the peninsula and the extreme scarcity of seafloor stations, whose cost and management are very expensive and complex.

We present the first attempt to apply this off-network location technique to the Italian offshore seismicity with the aim of improving the hazard estimation of these hard-to-monitor regions.

How to cite: Di Stefano, R., Ciaccio, M. G., Baccheschi, P., and Zhao, D.: Accurate Earthquake Locations of the Adriatic Thrust Fault of the 2021 Seismic Sequence with sP Depth Phases., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15881, https://doi.org/10.5194/egusphere-egu23-15881, 2023.

EGU23-1069 | ECS | Orals | SM2.1

Seismic Anisotropy from 6C Observations 

Le Tang, Heiner Igel, and Jean-Paul Montagner

A new approach is proposed for measuring the local dispersion curves of surface waves in weakly anisotropic media using a single, multi-component station, which consists of translation and rotation or strain. We directly extract the local azimuth-dependent phase velocity of the Rayleigh wave from the 6C amplitude ratio using seismic arrays deployed in Southern California. The extracted dispersion curves match well with the theoretical 2φ azimuthal anisotropy term. And the estimated fast wave direction is also consistent well with results calculated from SKS and beamforming methods which demonstrates the feasibility of studying local seismic anisotropy directly from 6C amplitude observations.

How to cite: Tang, L., Igel, H., and Montagner, J.-P.: Seismic Anisotropy from 6C Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1069, https://doi.org/10.5194/egusphere-egu23-1069, 2023.

Distributed Acoustic Sensing (DAS) in geothermal wells is a particularly attractive technology to implement as part of routine seismic monitoring of geothermal plant operations. It brings a large network of sensors close to the monitoring target – the operated reservoir – increasing the sensitivity towards low magnitude events and allows the application of processing procedures inspired by large network or array processing. However, the technical management of the large flow of produced data and the suitability of the strain-rate acquisitions to monitor locally induced seismicity was yet to be fully assessed.

We present the results of a continuous 6-month monitoring period that aimed at testing an integrated system designed to manage the acquisition, the processing and the saving of DAS data collected from behind casing at the Schäftlarnstraße (SLS) geothermal project (Munich, Germany). The data management system links the existing on-site infrastructure to a cloud Internet-of-Things (IoT) platform integrated into the company’s IT infrastructure. The cloud platform has been designed to deliver both a secure storage environment for the DAS records and optimized computing resources for their continuous processing.

With a special focus on seismic risk mitigation, we investigate the potential of the monitoring concept to provide sensitive detection capabilities, despite operational conditions, while ensuring efficient data processing in order to strive for real-time monitoring. Further analysis of the records confirm additional logging capabilities of borehole DAS. We also evaluate the ability of DAS to provide reliable seismic source description, in particular in terms of location, moment magnitude, and stress drop.

Using two detected local seismic events, we demonstrate the relevance of the system for monitoring the SLS-site in an urban environment, while complementing advantageously the surface seismometer-based monitoring network.

How to cite: Azzola, J. and Gaucher, E.: Continuous seismic monitoring of a geothermal project using Distributed Acoustic Sensing (DAS): a case study in the German Molasse Basin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1292, https://doi.org/10.5194/egusphere-egu23-1292, 2023.

EGU23-2091 | Orals | SM2.1 | Highlight

Using DAS-fibres at ocean floor and lunar surface 

Martin Landrø

We have used two seabed fibre optic cables connecting Ny Ålesund and Longyearbyen at Svalbard, North of Norway, to track several whales for several weeks. Exploiting that we have access to two fibres we demonstrate that it is possible to track several whales in a fairly large region. It is possible to create sound records of whales that can be used for identification and discrimination between various species. The localization method has also been tested by using a small air gun to confirm the localization method used for whales. Examples of earthquake recordings, ship traffic monitoring and distant storms will be shown.

Based on the rapid and promising developments within DAS technology, there is a growing interest for using fibre optic cables at the moon. Some challenges and possibilities related to Lunar DAS applications will be discussed.

How to cite: Landrø, M.: Using DAS-fibres at ocean floor and lunar surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2091, https://doi.org/10.5194/egusphere-egu23-2091, 2023.

EGU23-2814 | Orals | SM2.1

Divergence-based estimation of Rayleigh wave dispersion curves 

Pascal Edme, David Sollberger, Tjeerd Kiers, Cedric Schmelzbach, Felix Bernauer, and Johan Robertsson

We present a novel seismic acquisition and processing technique to efficiently evaluate the local dispersion curves of Rayleigh waves for subsequent inversion of shear velocities and near-surface characterization.

The proposed approach consists of computing the ratio between the (time derivated) horizontal spectra H(f)=(∂tVx(f)2+∂tVy(f)2)1/2  and the pseudo-divergence spectra D(f), with D being the sum of the horizontal gradients of the horizontal components (i.e. D=∂xVx+∂yVy).

The processing method itself is comparable to the commonly used H/V approach, except that the H/D spectral ratio provides a direct estimate of the frequency-dependent phase velocities cR(f)  instead of the site frequency amplification(s). This is demonstrated using synthetic data.

We describe how the D component can be obtained in practice, i.e. by finite-differencing closely spaced horizontal phones or potentially using Distributed-Acoustic-Sensing (DAS) and fibre-optic deployed at the surface. Some limitations about wavelength dependency and impact of Love waves are discussed, as well as potential mitigation measures.

A field test on several hours of ambient noise data collected in Germany with multi-component geophones results in realistic values of Rayleigh wave velocities ranging from ~770 m/s at 10 Hz to ~500 m/ at 30 Hz. Thanks to the local and omni-directional nature of the estimation, the minimal number of required channels and the applicability to ambient noise, we believe that the proposed H/D method can be an attractive alternative to expensive array-based techniques.

How to cite: Edme, P., Sollberger, D., Kiers, T., Schmelzbach, C., Bernauer, F., and Robertsson, J.: Divergence-based estimation of Rayleigh wave dispersion curves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2814, https://doi.org/10.5194/egusphere-egu23-2814, 2023.

EGU23-3061 | Orals | SM2.1

Nano-strain resolution fiber-optic Fabry-Perot sensors based measuring systems 

Simon Pevec and Denis Donlagic

A work describes a deeply etched, long active length, high sensitivity short Fabry-Perot cavity nano-strain resolution sensor. The presented sensors exhibit high spectral sensitivity, low intrinsic temperature sensitivity which is for about 40 times lower than in case of FBG, small size and mounting comparable to conventional Fiber Bragg gratings. The sensor high potential is not only high sensitivity and low temperature intrinsic sensitivity, but also in short cavity length and its tunability, which can be simply accomplished in one production step. This brings versatility in interrogation with different general purpose and cost-efficient VIS-NIR widely available linear detector array-based spectrometers, while still providing strain sensing resolution within the range of few 10 nε. A strain resolution of 20 to 70 nε was demonstrated when using a cost-efficient VIS spectrometer. Furthermore, the sensor structure can be combined with multimode telecom lead-in fibers and low-cost broadband LEDs intended for automotive/lightning applications, which allow production of cost efficient solutions.

How to cite: Pevec, S. and Donlagic, D.: Nano-strain resolution fiber-optic Fabry-Perot sensors based measuring systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3061, https://doi.org/10.5194/egusphere-egu23-3061, 2023.

EGU23-3437 | ECS | Posters on site | SM2.1

Monitoring temperature at the ocean seafloor with fibre optic cables and DAS 

Julián Pelaez Quiñones, Anthony Sladen, Aurelien Ponte, Itzhak Lior, Jean-Paul Ampuero, Diane Rivet, Samuel Meulé, Frédéric Bouchette, Ivane Pairaud, and Paschal Coyle

Ocean water temperature measurements are fundamental to atmospheric and ocean sciences. Obtaining them, however, often comes along with major experimental and logistic challenges. Except for the uppermost ocean surface temperature, which can be measured from satellites, temperature data of the ocean is often poorly sampled or nonexistent, especially in deep-water regions.

Although Distributed Acoustic Sensing (DAS) technology has become popular because its high sensitivity to strains and mechanical vibrations, our work focuses on its usage on tens-of-kilometer-long underwater fibre-optic (FO) telecommunication cables to measure temperature anomalies at the seafloor at millikelvin (mK) sensitivity. This is possible because of the lack of dominant strain signals at frequencies less than about 1 mHz, as well as the poor coupling of the fibre with these signals while remaining highly sensitive to slow ambient temperature variations that locally affect its optical path length. DAS allows us to observe significant temperature anomalies at the continental shelf and slope of the Mediterranean sea, South of Toulon, France over periods of several days, with variability remaining relatively low at the deep ocean. By means of this approach, oceanic processes such as near-inertial internal waves and upwelling can be monitored at unprecedented detail.

Our observations are validated with oceanographic in-situ sensors and alternative Distributed Fibre Optic Sensing (DFOS) technologies established for temperature sensing. We outline key advantages of DAS thermometry over the aforementioned sensors in terms of spatial coverage, sensitivity, versatility and highest attainable frequency. At the current state of the art, DAS can only measure temperature anomalies as opposed to absolute temperature, a drawback that could be compensated via single temperature calibration measurements.

How to cite: Pelaez Quiñones, J., Sladen, A., Ponte, A., Lior, I., Ampuero, J.-P., Rivet, D., Meulé, S., Bouchette, F., Pairaud, I., and Coyle, P.: Monitoring temperature at the ocean seafloor with fibre optic cables and DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3437, https://doi.org/10.5194/egusphere-egu23-3437, 2023.

EGU23-3955 | ECS | Orals | SM2.1

Using Distributed Acoustic Sensing to Monitor and Investigate Eruptive Events at Stromboli Volcano, Italy 

Francesco Biagioli, Jean-Philippe Métaxian, Eléonore Stutzmann, Maurizio Ripepe, Alister Trabattoni, Pascal Bernard, Roberto Longo, Gianluca Diana, Lorenzo Innocenti, Yann Capdeville, Marie-Paul Bouin, and Giorgio Lacanna

Volcano seismology is essential for understanding, monitoring, and forecasting eruptive events. The use of distributed acoustic sensing (DAS) technology can be particularly useful for this purpose because of its high temporal and spatial resolution, which may help to overcome the challenges of deploying and maintaining seismic arrays on volcanoes.

Between 2020 and 2022, we installed 4 km of optical fibre on Stromboli volcano, Italy, whose persistent activity is well-suited for investigating the related dynamic strain rate. The cable was buried at a depth of 30 cm and the layout geometry was designed to provide wide coverage while being constrained by natural obstacles and topographical features. Seismometers were also installed along the fibre. DAS data were collected using a Febus A1-R interrogator, and the acquisition period increased from one week in 2020 to over four months in 2022. We recorded volcanic tremor, ordinary explosions (several per hour), two major explosions in 2021 and 2022, and the entire sequence of a pyroclastic flow in 2022. 

DAS and seismic data show good agreement in both time and frequency domains after converting strain rate to velocity and vice versa using different methodologies. Beamforming of DAS data shows a dominant signal in the 3-5 Hz frequency band coming from the active craters. We will also present preliminary results of major explosions and pyroclastic flow. This experiment demonstrates that DAS can be used for monitoring volcanic activity.

How to cite: Biagioli, F., Métaxian, J.-P., Stutzmann, E., Ripepe, M., Trabattoni, A., Bernard, P., Longo, R., Diana, G., Innocenti, L., Capdeville, Y., Bouin, M.-P., and Lacanna, G.: Using Distributed Acoustic Sensing to Monitor and Investigate Eruptive Events at Stromboli Volcano, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3955, https://doi.org/10.5194/egusphere-egu23-3955, 2023.

EGU23-4256 | ECS | Posters on site | SM2.1

Groundwater monitoring using fibre-optics and DAS: Application to the Lyon water catchment area. 

Destin Nziengui Bâ, Olivier Coutant, and Camille Jestin

Water resource management is a crucial socio-economic issue that requires developing high-resolution monitoring techniques, including non-invasive geophysical methods. Among them, passive seismic interferometry takes advantage of natural ambient seismic noise to recover the slight variations of the seismic wave velocity induced by changes in the groundwater level. In this study, we present the time and space monitoring of groundwater changes artificially generated by infiltration ponds at the exploitation field of Crépieux-Charmy (Lyon, France).  We deployed 3km of optical fibre and a dense array of fifty 3C geophones around infiltration basins. We recorded several cycles of filling-emptying with a DAS using a 2m spatial sampling (i.e., 1500 fibre sensors). The recorded signals are mainly associated with local anthropogenic noise (highways, trains, pumping, etc.). We could track seismic velocity variations with high temporal and spatial resolutions using ambient noise interferometry techniques. These variations are associated with the interaction between the water diffused from the basins and water table variations. This dynamic information helps understand and model water exchanges on the ground. The study confirms the possibility of groundwater monitoring using DAS records of ambient noise for seismic interferometry in a highly urbanized zone.

How to cite: Nziengui Bâ, D., Coutant, O., and Jestin, C.: Groundwater monitoring using fibre-optics and DAS: Application to the Lyon water catchment area., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4256, https://doi.org/10.5194/egusphere-egu23-4256, 2023.

EGU23-4769 | ECS | Orals | SM2.1

Arrival Picking for Distributed Acoustic Sensing seismic based on fractional lower order statistics 

Xiang Wang, Honghui Wang, Yuhang Wang, Shangkun Zeng, and Yiru Wang

In recent years, fiber-optic distributed acoustic sensing (DAS) has been gradually applied to seismology because of its long-distance and dense observation capability. It is a great challenge to effectively process the massive seismic data recorded by DAS. At present, the seismic data processing methods based on deep learning have achieved great success, especially in the tasks of seismic detection and arrival-time picking. However, due to the differences between DAS and geophone, such as sensing principles, spatial and temporal sampling rates, and noise intensity. The seismic arrival time picking model based on deep learning, which is trained by geophone seismic data with low spatial and temporal sampling rates and low noise intensity, severely degrades in performance on DAS seismic data with high spatial and temporal sampling rates and high noise intensity. In addition, a new seismic arrival time picking model is trained by fully supervised learning, which usually requires a large number of seismic data with accurate labels. However, the huge cost of manual picking and the lack of effective automatic picking models make it very difficult to build large-scale DAS seismic data sets with accurate labels. Therefore, it is very difficult to build an arrival time picking model based on fully supervised learning for DAS seismic data.

In this study, we propose a DAS seismic arrival time picking method based on fractional lower order statistics. Based on the difference of probability density function between noise and seismic signal, the proposed method uses alpha-stable distribution modeling noise (generally follow a Gaussian distribution) and seismic signal (generally follow a non-Gaussian distribution), and uses fractional lower order statistics under the assumption of alpha-stable distribution as the characteristic function to pick the arrival time.

Synthetic and actual DAS data tests show that the proposed method has better performance and robustness to random noise than other methods based on characteristic functions, such as STA/LTA, AR-AIC and kurtosis. Since the actual DAS seismic data has no ground truth of arrival time, we have further the performance of the proposed method on the geophone seismic data set. The proposed method provides better results on geophone seismic data and the data after up-sampling them to the typical time sampling rate of DAS.

How to cite: Wang, X., Wang, H., Wang, Y., Zeng, S., and Wang, Y.: Arrival Picking for Distributed Acoustic Sensing seismic based on fractional lower order statistics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4769, https://doi.org/10.5194/egusphere-egu23-4769, 2023.

EGU23-5455 | ECS | Posters on site | SM2.1

Active-source seismic experiments with DAS for monitoring reservoir rock in underground laboratories 

Katinka Tuinstra, Antonio Pio Rinaldi, Federica Lanza, Alba Zappone, Andreas Fichtner, and Stefan Wiemer

Underground laboratories have become indispensable in the understanding of physical processes during e.g., hydraulic stimulation and seismic monitoring of deep geothermal reservoirs or CO2 storage target reservoirs. They provide a test bench and constitute the bridge between small-scale laboratory studies and full-scale pilot sites. Here, we present results from multiple active source seismic campaigns in one of the Swiss underground laboratories: the Mont Terri Rock Laboratory. Here, DAS fibres are cemented behind the casing of multiple monitoring boreholes and active shots are taken with a P-wave sparker. This dense array of active seismic measurements enables us to obtain a baseline characterisation of the P-wave velocity of the rock before any activity (e.g., injection) takes place. During stimulations, dynamic measurements with an active sparker source are recorded, followed by a time-lapse monitoring approach where seismic measurements are collected through active seismic campaigns in set time intervals in the months after stimulations. In this way we can create high-resolution, four-dimensional monitoring and characterisations of the rock body and potential earthquakes during the full monitoring period. We show different configurations and measurements settings with their effect on the DAS recordings of active signals.

How to cite: Tuinstra, K., Rinaldi, A. P., Lanza, F., Zappone, A., Fichtner, A., and Wiemer, S.: Active-source seismic experiments with DAS for monitoring reservoir rock in underground laboratories, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5455, https://doi.org/10.5194/egusphere-egu23-5455, 2023.

EGU23-5701 | ECS | Posters on site | SM2.1

Investigating Vibroseis Sweeps using 6 Rotational Sensors in Fürstenfeldbruck, Germany 

Gizem Izgi, Eva Eibl, Frank Krüger, and Felix Bernauer

Rotational motions can be recorded directly or derived from translational motion recordings. Fairly new rotational sensors allow seismologists to directly record and investigate rotational motions. In order to further investigate and compare recently developed rotational sensors an experiment was made in Fürstenfeldbruck. Within this scope, a vibroseis truck was operated starting from 20 November 2019, 11:00 UTC until 21 November 2019, 14:00 UTC. We recorded 480 Sweep signals at 160 different locations. The truck was operating at 30%, 50%, and 70% relative to a peak force output of 276 kN exciting the ground vertically and each sweep lasted 15 seconds starting with 7 Hz increased up to 120 Hz. We derived back azimuths of each sweep from 6 rotational sensors and calculated root mean squares of each component. We observed that within the first day, the North component of all sensors recorded the largest ground motion energy SV type of energy is dominant. The sweep sources were distributed over two North–South profiles and two East–West profiles.  While the truck moved to the east and its location moved from west to south of the rotational sensors, the signals dominate more and more on the East component.. From our preliminary results, we state that although having different signal to noise ratios all rotational sensor calculated the direction of each sweep. Thus, we can follow the movements of vibroseis truck using all rotational sensors.

How to cite: Izgi, G., Eibl, E., Krüger, F., and Bernauer, F.: Investigating Vibroseis Sweeps using 6 Rotational Sensors in Fürstenfeldbruck, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5701, https://doi.org/10.5194/egusphere-egu23-5701, 2023.

EGU23-5955 | ECS | Orals | SM2.1

Two-dimensional phase unwrapping algorithm aided high-precision source positioning with DAS 

Jianhui Sun, Yuyao Wang, Jialei Zhang, Anchi Wan, Shibo Zhang, Zhenyu Ye, Fulie Liu, Gulan Zhang, and Zinan Wang

Seismic monitoring requires high temporal-spatial resolution and low deployment cost. Distributed acoustic sensing (DAS), as an emerging sensing technology for recording seismic data in recent years, can leverage communication cables for seismic monitoring, providing strong support for more intensive and real-time observation of geological activity. However, the traditional DAS phase unwrapping algorithms (PUAs) derived from Itoh requires the phase difference of adjacent pixels to be less than π, and thus make mistakes in the case of severe noise or large disturbance. In this paper, to the best of our knowledge, two-dimensional (2D) PUA is used to obtain seismograms in DAS for the first time. Satisfactory phase unwrapping is achieved by the 2D PUA method based on the transport of intensity equation (TIE), due to its robustness and noise immunity. Dynamic strain measurements in 80 m straight fiber-optic cable using homemade high-performance DAS, combined with TIE-based 2D PUA produce high-quality seismograms. Time Difference of Arrival (TDOA) Algorithm is applied based on the sensing signal of reliable channels in the seismograms, realizing the high-precision localization of the source. 2D PUAs apply to all phase-demodulation-based sensing techniques and are suitable for recovering spatially correlated objects such as seismic waves, thus having great potential in the field of seismic monitoring.

How to cite: Sun, J., Wang, Y., Zhang, J., Wan, A., Zhang, S., Ye, Z., Liu, F., Zhang, G., and Wang, Z.: Two-dimensional phase unwrapping algorithm aided high-precision source positioning with DAS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5955, https://doi.org/10.5194/egusphere-egu23-5955, 2023.

EGU23-6189 | ECS | Orals | SM2.1

Contribution of spatial features for classifying seismic events from Distributed Acoustic Sensing (DAS) data streams 

Camille Huynh, Clément Hibert, Camille Jestin, Jean-Philippe Malet, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) is an acoustic sensor instrument that turns a single optical fiber into a dense array of thousands of equally spaced seismometers. Geoscientists and companies have an interest in investing in DAS technologies for better understanding the Earth by observing natural and anthropogenic seismic events or assisting in large infrastructure monitoring with low installation and maintenance costs. However, this type of instrument generates a significantly larger amount of data than conventional seismometers, data that can be complex to store, exploit and interpret.

Several strategies for classifying seismic events from fiber-optics DAS data exist in the scientific literature. Conventional approaches rely on the use of features that describe the waveforms and frequency content of signals recorded individually at virtual stations along the fiber; they do not integrate the spatial density of information permitted by DAS. Several studies on dense seismological arrays have introduced similarity measures between the different time series data such as cross-correlations, dynamic time warping (DTW) or compression-based dissimilarity.

This study aims to quantify the contribution of spatial features for DAS data streams classification. We have chosen to explore spatial features related to both standard statistical measures (e.g., spatial mean, median, skewness, kurtosis), and advanced signal processing measures (e.g., auto-correlations, cross-correlations, DTW). This set of measures allows enriching a list of already used time series features which includes waveform, spectrum and spectrogram. A Random Forest (RF) classifier is then trained, and a Random Markov Field (RMF) algorithm is used after classification to account for redundant spatial and temporal information.

The evaluation of the spatial feature contribution is based on the output of the RF-RMF processing chain. Anthropogenically-triggered seismic data were acquired at the FEBUS Optics test bench. We consider five seismic sources: footsteps, impacts, excavators, compactor and fluid leaks. A class of noise is added as the RF-RMF algorithm is developed for processing DAS streams inherently affected by  noise.  Accurate  classification results can be obtained using only time features, and ongoing tests show a 2% increase in the correct classification rate with the use of both time and spatial features. The improvement allowed by the addition of spatial features is tangible but limited on our test dataset, but we think it should have a much greater impact on natural sources and we will discuss this perspective.

How to cite: Huynh, C., Hibert, C., Jestin, C., Malet, J.-P., and Lanticq, V.: Contribution of spatial features for classifying seismic events from Distributed Acoustic Sensing (DAS) data streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6189, https://doi.org/10.5194/egusphere-egu23-6189, 2023.

EGU23-6379 | Posters on site | SM2.1

Rotational ground motion recordings in the West Bohemia / Vogtland region for waveform inversion for seismic moment tensors 

Stefanie Donner, Johanna Lehr, Mathias Hoffmann, Frank Krüger, Sebastian Heimann, Rafel Abreu, and Stephanie Durand

In synthetic tests, rotational ground motion recordings proved to be beneficial for the wavefrom inversion for seismic moment tensors. In a next step, we want to verify these findings using real measurements. To do so, we installed two broadband rotational collocated to translational ground motion sensors in the West Bohemia / Vogtland area in summer 2022.

The area is characterised by regular seismic swarm activity, the last one occurring in December 2021. The seismic swarms are known to be connected with crustal flow of mantle fluids. However, the detailed mechanism of this connection is not well understood yet. Full seismic moment tensors, especially their non-double-couple part, will contribute to investigate the connection between swarm activity and fluid flow. So far, a lacking number of moment tensors and difficulties in the reliability of the non-double-couple part hampered the analysis in the study area. Including rotational ground motion recordings to waveform inversion will help to overcome these difficulties.

In seven months, we have recorded 120 events with magnitudes larger than M ≥ 0 in a distance of up to 35 km, thereof 35 around Nový Kostel, the center of the swarm activity. Considering that rotational sensors are about 2-4 times less sensitive than translational sensors (depending on the local phase velocity of the location) this is already a great success. Here, we show details of the sensor installations, first data analysis, and an estimate on the magnitude of completeness from rotational measurements.

How to cite: Donner, S., Lehr, J., Hoffmann, M., Krüger, F., Heimann, S., Abreu, R., and Durand, S.: Rotational ground motion recordings in the West Bohemia / Vogtland region for waveform inversion for seismic moment tensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6379, https://doi.org/10.5194/egusphere-egu23-6379, 2023.

EGU23-6422 | ECS | Posters on site | SM2.1

Effect of shallow heterogeneities on wavefield gradients measurements 

Mirko Bracale, Romain Brossier, Helle Pedersen, and Michel Campillo

In recent years, the use of rotational sensors and DAS has become a topic of increasing interest within the seismological community because of their increasing sensitivity and affordability. We analyze the sensitivity of wavefield gradients, in the form of normal strain and rotation, to localized shallow velocity changes in a homogeneous medium.
We performed several numerical simulations, using a suitably modified 3D-SEM code, to observe, in addition to wavefield itself, the normal strain and rotation as a direct output.
We analyzed two case studies in which a velocity anomaly is placed in a homogeneous medium. In the first case the velocity change between the anomaly and the surrounding medium is 10%, in the second case 70%. We analyzed the sensitivity of these new observables in terms of phase shift and amplitude change.
We observe a very local effect of the wavefield gradients, which show larger amplitude near the boundary between the medium and the anomaly, while away from it they behave like the displacement wavefield itself.

How to cite: Bracale, M., Brossier, R., Pedersen, H., and Campillo, M.: Effect of shallow heterogeneities on wavefield gradients measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6422, https://doi.org/10.5194/egusphere-egu23-6422, 2023.

EGU23-6915 | ECS | Posters on site | SM2.1

Modeling and analysis of Distributed Acoustic Sensing (DAS) data in Geothermal environments 

Davide Pecci, Juan Porras, Michele De Solda, Francesco Grigoli, Eusebio Stucchi, and Renato Iannelli

DAS technology is particularly suitable for microseismic monitoring application in geothermal environments. This instrumentation can resist to high temperatures (up to about 100°C or more) higher than the operational temperature of standard acquisition instruments (e.g., geophones), allowing the fiber to be located very close to the reservoir. For this reason, DAS is particularly useful for induced seismicity monitoring of Enhanced Geothermal System (EGS). Being of recent development, this acquisition technology still lacks appropriate modeling and analysis tools able to handle such a large amount of data without losing efficiency. Furthermore, open-access DAS datasets are still a rarity, if compared to other geophysical datasets (e.g., seismological data). Therefore, we aim to generate an open-access synthetic (but realistic) DAS dataset that may help the geophysical community to develop “ad hoc” data analysis methods suitable for this kind of data. In the presented work we make use of the spectral element modeling software 'Salvus', developed by Mondaic, which also allows the simulation of DAS data. In particular, it outputs a strain measurement between all points defined as receivers in the simulation. Using the repositories of DAS data collected at the geothermal test site Frontier Observatory for Research in Geothermal Energy (FORGE) located in Utah (USA), we tried to simulate realistic DAS acquisition conditions of seismic events related to low-magnitude natural seismic activity from the nearby Mineral Mountains and microseismic events related to hydraulic stimulation operations for the generation of an EGS.

In order to obtain realistic synthetic data, we first analyze the spectral properties of real noise waveforms by using the Power Spectral Density (PSD) Analysis. Starting from observed PSDs we model the synthetic noise waveforms using a stochastic approach. Then we add it to the synthetic event traces and compare them with the observed ones. We finally test a semblance-based event detector on a 1-hour continuous waveforms of synthetic data to evaluate the performance of the detector in different operational conditions (e.g., different noise levels and inter-event times).

How to cite: Pecci, D., Porras, J., De Solda, M., Grigoli, F., Stucchi, E., and Iannelli, R.: Modeling and analysis of Distributed Acoustic Sensing (DAS) data in Geothermal environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6915, https://doi.org/10.5194/egusphere-egu23-6915, 2023.

EGU23-6998 | ECS | Orals | SM2.1

Exploiting Terrestrial Meshed Optical Data Networks as Environmental Sensing Smart Grids 

Emanuele Virgillito, Stefano Straullu, Rudi Bratovich, Fransisco M. Rodriguez, Hasan Awad, Andrea Castoldi, Roberto Proietti, Andrea D'Amico, Francesco Aquilino, Rosanna Pastorelli, and Vittorio Curri

Optical networks for data transmission have become a pervasive infrastructure in the last years in order to cope with the increasing bandwidth request, thus there is a huge potential to be employed as a wide fiber optic sensing network. In the terrestrial scenario such networks are usually arranged on meshed topologies densely covering large areas of hundreths or thousands of kilometers. On the network's nodes, dedicated hardware is used to routed the data traffic between the connections' endpoints. Such nodes are interconnected by optical fiber links of hundreds of kilometers long, repeated every tenths of kilometers using optical amplifiers.

To fulfill the modern traffic requirements, optical networks are evolving towards multi-service autonomous, flexible, software defined entities based on a centralized intelligence orchestrating the networking functions and communicating with the network elements using standardized interfaces. This trend opens the perspective of using the optical network for evironmental sensing, such as earthquake detection or anthropic activities monitoring. 

Indeed, distributed acoustic sensing (DAS) systems based on Rayleigh scattering have demonstrated that optical fibers are excellent sensors of mechanical stress. However, such systems are expensive and pose some limitations on the maximum reach, so they cannot be deployed extensively. In this context, re-using the already deployed optical data infrastructure to support and integrate dedicated system sensing may be highly beneficial. In this work, we propose an optical data network architecture exposing sensing functionalities with minimum or no additional hardware simply by exploiting the pervasiveness of the telecommunication infrastructure and getting data from the physical quantities already monitored for data transmission purposes. Such architecture on a typical terrestrial optical data network is outlined in figure.

Modern coherent transceivers based on digital signal processing already track the evolution of the transmitted optical signal phase and polarization to recover the transmitted data at the receiver side. As those quantities are strongly affected by external strain, they already contain environmental information. Furthermore, some polarization-based processing can be implemented on cheaper non-coherent transceivers available at each amplifier site as data-service channel, providing several sensing sources.

In addition, further optical devices such as add-drop multiplexer or optical amplifiers typically have several other sensors already embedded (power monitors, temperature sensors) or they can be equipped with some others which can provide environmental data from other physical quantities.

The set of all such environmental data streams produced by the network elements constitutes the streaming telemetry fed to a network controller. A post-process agent may be implemented by exploiting the computational power available in typical network elements to perform local data analysis and reduce the amount of data sent to the sensing controller. By cross-processing the data coming from the network elements, a sensing controller is able to detect and localize events making the network act as a smart grid by continuously monitoring large areas and providing early warning signals.

To support our proposal, in this work we show the results of an experimental activity aimed at detecting and localizing anthropic activities in the city of Turin using a deployed fiber ring.

 

How to cite: Virgillito, E., Straullu, S., Bratovich, R., M. Rodriguez, F., Awad, H., Castoldi, A., Proietti, R., D'Amico, A., Aquilino, F., Pastorelli, R., and Curri, V.: Exploiting Terrestrial Meshed Optical Data Networks as Environmental Sensing Smart Grids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6998, https://doi.org/10.5194/egusphere-egu23-6998, 2023.

EGU23-7309 | ECS | Orals | SM2.1

Effects of cable geometry and specific noise sources on DAS monitoring potential 

Emanuele Bozzi, Nicola Piana Agostinetti, Alan F. Baird, Carlos Becerril, Biondo Biondi, Andreas Fichtner, Sara Klaasen, Nate Lindsey, Takeshi Nishimura, Patrick Paitz, Junzhu Shen, Arantza Ugalde, Fabian Walter, Siyuan Yuan, Tieyuan Zhu, and Gilberto Saccorotti

The Distributed Acoustic Sensing (DAS) method re-purposes fiber optic cables into a very-dense array of strain/strain-rate sensors, capable of detecting different types of seismic events. However, DAS data are characterized by lower SNRs compared with standard seismic sensors, mainly because of a) strong directivity effects, 2) ground coupling inhomogeneities, and 3) site effects. Hence, beyond the array geometry, specific noise sources may reduce the potential of DAS for seismic monitoring. Previous research has already shown successful case-studies for event detection/location. Nevertheless, a coherent test on the performances of various arrays of different sizes and geometries is still lacking.

In this study, an extensive DAS database is organized for such a goal, including 15 DAS arrays that recorded at least one seismic event (located at a range of distances from the arrays). P wave arrival times are exploited to estimate the epicentral parameters with a Markov Chain Monte Carlo method. Then, to analyze the effects of cable geometry and potential sources of noise/ambiguity on the location uncertainties, a series of synthetic tests are performed, where synthetic traveltimes are modified as follows: a) adding noise with equal variance to all the DAS channels (SYNTH-01), b) adding noise characterized by an increasing variance with the distance from the event (SYNTH-02), c) simulating the mis-pick between P and S phases (SYNTH-03) and d) adding noise with a variance influenced by cable coupling inhomogeneities (SYNTH-04). Results show that the epicentral locations with automatic P wave arrival times have different degrees of uncertainty, given the geometrical relation between the event and the DAS arrays. This behavior is confirmed by the SYNTH-01 test, indicating that specific geometries provide a lower constraint on event location. Moreover, SYNTH-04 shows that simulating cable coupling inhomogeneities primarily reproduces the observed location uncertainties. Finally, some cases are not explained by any of the synthetic tests, stressing the possible presence of more complex noise sources contaminating the signals.

How to cite: Bozzi, E., Piana Agostinetti, N., F. Baird, A., Becerril, C., Biondi, B., Fichtner, A., Klaasen, S., Lindsey, N., Nishimura, T., Paitz, P., Shen, J., Ugalde, A., Walter, F., Yuan, S., Zhu, T., and Saccorotti, G.: Effects of cable geometry and specific noise sources on DAS monitoring potential, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7309, https://doi.org/10.5194/egusphere-egu23-7309, 2023.

EGU23-7563 | ECS | Posters on site | SM2.1

TwistPy: An open-source Python toolbox for wavefield inertial sensing techniques 

David Sollberger, Sebastian Heimann, Felix Bernauer, Eva P. S. Eibl, Stefanie Donner, Céline Hadziioannou, Heiner Igel, Shihao Yuan, and Joachim Wassermann

In the past decade, significant progress has been made in the acquisition and processing of seismic wavefield gradient data (e.g., recordings of ground strain and rotation). When combined with conventional multicomponent seismic data, wavefield gradients enable the estimation of local wavefield properties (e.g., the local wave speed, the propagation direction, and the wave type) and the reconstruction of spatially under-sampled seismic wavefields. However, the seismological community has yet to embrace wavefield gradient data as a new observable.

We present TwistPy (Toolbox for Wavefield Inertial Sensing Techniques), an open-source software package for seismic data processing written in Python. It includes routines for single-station polarization analysis and filtering, as well as array processing tools. A special focus lies on innovative techniques to process spatial wavefield gradient data and, in particular, rotational seismic data obtained from dedicated rotational seismometers or small-aperture arrays of three-component sensors. Routines currently included in the package comprise polarization analysis and filtering in both the time domain and the time-frequency domain (for three-component and six-component data), dynamic tilt corrections, and beamforming (Bartlett, Capon, and MUSIC beamformers).  

With TwistPy, we attempt to lower the barrier of entry for the seismological community to use state-of-the art multicomponent and wavefield gradient analysis techniques by providing a user-friendly software interface.

Extensive documentation of the software and examples in the form of Jupyter notebooks can be found at https://twistpy.org.

How to cite: Sollberger, D., Heimann, S., Bernauer, F., Eibl, E. P. S., Donner, S., Hadziioannou, C., Igel, H., Yuan, S., and Wassermann, J.: TwistPy: An open-source Python toolbox for wavefield inertial sensing techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7563, https://doi.org/10.5194/egusphere-egu23-7563, 2023.

EGU23-8327 | Posters on site | SM2.1

Fibre-optic dynamic strain borehole sensing at Etna volcano 

Philippe Jousset, Gilda Currenti, Rosalba Napoli, Mario Pulvirenti, Daniele Pelligrino, Christian Cunow, Graziano Larocca, Alessandro Bonaccorso, Giuseppe Leto, and Charlotte Krawczyk

Volcano monitoring has been experiencing significant improvements in recent years, yet eruption forecasting and scenarios have still lack of understanding, due to the poor observations in low amplitude events and hindered by surface external noise of similar amplitudes. Volcanic events have been shown to be accurately recorded with fiber optic techniques at the surface. In this study, we present preliminary results of fibre optic cable deployed in a new 200 m deep borehole on the southern flank of Etna at about 6 km away from the summit crater. This borehole has been designed primarily for the future deployment of a new strain sensor type. We benefited from the drilling of this new borehole to deploy a single-mode fibre optic cable. We connected an interrogator and recorded dynamic strain rate during several periods: first, in 2020 for several days during the completion of the borehole and the final stage of the drilling; second, in 2021 for several weeks during an active volcanic period; and in December 2022 during a quiet activity period of several months. We present a selection of records of noise while drilling, local volcano-tectonic earthquakes and volcanic events and tremor that occurred during those periods. These examples show the benefit of deploying a fibre in a borehole far from the active area and demonstrate the great variety of signals fibre optic can record is such configuration.

How to cite: Jousset, P., Currenti, G., Napoli, R., Pulvirenti, M., Pelligrino, D., Cunow, C., Larocca, G., Bonaccorso, A., Leto, G., and Krawczyk, C.: Fibre-optic dynamic strain borehole sensing at Etna volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8327, https://doi.org/10.5194/egusphere-egu23-8327, 2023.

EGU23-8569 | Posters on site | SM2.1

Monitoring a commercially operating submarine telecom cable network in the Guadeloupe archipelago (Lesser Antilles) using Brillouin Optical Time Domain Reflectometry (BOTDR) 

Marc-Andre Gutscher, Lionel Quetel, Giuseppe Cappelli, Jean-Gabriel Quillin, Christophe Nativelle, Jean-Frederic Lebrun, and Melody Philippon

Submarine telecom cables criss-cross the oceans, connecting islands to continents and providing internet, financial and media services to consumers all around the world. Laser reflectometry as well as other optical techniques can potentially transform the optical fibers in these cables into sensors which can detect vibrations and ground motion from earthquakes, ocean waves, currents as well as permanent deformation of the seafloor. The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study movements at the seafloor.

 

Within the framework of the FOCUS project, and in collaboration with the “Conseil Regional” of Guadeloupe, in 2022 we began long-term monitoring of a network of submarine telecom cables that link the islands of the Guadeloupe archipelago. These cables connect the larger island of Basse Terre and Grande Terre to the smaller southern islands of Les Saintes, Marie Galante and La Desirade, with segment lengths ranging from 30 to 70 km. This network was deployed recently (in 2019) and is the property of the Conseil Regional of Guadeloupe, operated with the assistance of Orange. All cables contain twelve fiber pairs, of which three pairs are in use by mobile phone operators and thus unused fibers were available for this scientific monitoring project. In June 2022, we established BOTDR baselines on 8 optical fiber segments, in several cases in both directions. In December 2022, we repeated the measurements of the same fiber segments, allowing us to detect any strain along the cable over this period.

 

Here, we report that using the BOTDR technique, we detect significant strain signals  (50 micro-strain and more) in several locations along the cable network. These signals, which can be positive (elongation) or negative (shortening) occur typically in areas of steep seafloor slopes or in submarine valleys/canyons. Our tentative interpretation is that stretching and shortening of the cable (representing about 1 cm over a few hundred meters) is occurring, most likely due to sea-bottom currents. These currents may be related to the late summer/early autumn hurricane season, with the passage of tropical storm Fiona in Sept. 2022 dropping heavy rains, causing torrential floods and debris flows in some of the larger rivers with possible impacts further offshore. A longer time-series and more detailed analysis are necessary to test this preliminary hypothesis.

How to cite: Gutscher, M.-A., Quetel, L., Cappelli, G., Quillin, J.-G., Nativelle, C., Lebrun, J.-F., and Philippon, M.: Monitoring a commercially operating submarine telecom cable network in the Guadeloupe archipelago (Lesser Antilles) using Brillouin Optical Time Domain Reflectometry (BOTDR), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8569, https://doi.org/10.5194/egusphere-egu23-8569, 2023.

EGU23-8851 | ECS | Orals | SM2.1

Using Rotational Motions to understand material damage in Civil Engineering structure 

Anjali Dhabu, Felix Bernauer, Chun-Man Liao, Celine Hadziioannou, Heiner Igel, and Ernst Niederleithinger

The increasing evidence of rotational motions due to earthquakes is now motivating civil engineers to investigate the effects of rotational ground motions on structures. With the advancement in instrumentation techniques, rotational sensors have been developed in the past few years, which can measure three components of rotational waves in addition to the translational waves. Conventionally, buildings are designed to withstand horizontal and vertical translational ground motions to minimize the damage to human life and financial losses during an earthquake. Damage to the structure is identified at two levels; (i) structural and (ii) material. The structural damage in reinforced concrete buildings is visible in the form of cracks and spalling concrete, which reduces the overall load-carrying capacity of the building. The damage at the material level is not visible to the human eye. This damage can be identified using coda wave interferometry techniques. In this method, a high cross-correlation between the coda of two waves passing a point on different days of experiment indicates a negligible change in the shear wave velocity of the material. In comparison, a lower cross-correlation signifies considerable change in the material properties.    

In order to understand how rotational motions affect reinforced concrete structures and how these can be simulated, the present work makes a novel attempt to use the newly developed rotation measuring sensors, BlueSeis 3A and IMU50, to understand the damage in a model concrete bridge structure (BLEIB). We employ advanced sensors in addition to conventional broadband and ultrasonic sensors on the 24m long two-span continuous reinforced concrete bridge equipped with various non-destructive sensing techniques and subjected to a variable pre-tension force of up to 450kN and various static loads. As an initial analysis, we first identify the bridge's first three fundamental frequencies and mode shapes from both recorded translational and rotational data. The analysis shows that the same fundamental frequencies are obtained from the recorded translational and rotational data. However, we expect to see a difference in the mode shapes. Theoretically, rotations are maximum at the bridge support and minimum at the centre of the bridge span. This behaviour is the reverse of what we observe from translational motions, where maximum translations are observed at the centre of the span while minimum at the supports. As the study plans to simulate rotational motions for reinforced concrete structures, a finite element model of the prototype bridge is also developed, and the fundamental frequencies and mode shapes of the model are validated with those obtained from the recorded data. This work shall be extended to applying coda wave interferometry to the rotational data recorded on the bridge to understanding the change observed in material properties when the bridge is subjected to active and passive forces.

How to cite: Dhabu, A., Bernauer, F., Liao, C.-M., Hadziioannou, C., Igel, H., and Niederleithinger, E.: Using Rotational Motions to understand material damage in Civil Engineering structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8851, https://doi.org/10.5194/egusphere-egu23-8851, 2023.

EGU23-9089 | ECS | Orals | SM2.1

Detecting seismo-volcanic events based on inter-channel coherency of a DAS cable 

Julius Grimm, Piero Poli, and Philippe Jousset

Distributed Acoustic Sensing (DAS) has been successfully employed to monitor volcanic seismicity and to infer volcanic subsurface structures. Here, we analyse data recorded in September 2018 at Mount Etna by the 9N seismic network. The multi-instrument network includes a 1.3 km long fibre-optic cable that was buried 2-2.5 km away from the main craters. Additionally, 15 geophones were installed along the trajectory of the DAS cable, allowing for a comparison of strain-rate and ground velocity data.
During the acquisition period, tiny seismic events, likely caused by fluid movement and degassing, are visible with inter-event times in the range of 1 min. Volcanic explosions and volcano-tectonic earthquakes also occur frequently. We detect events over all frequency ranges by calculating the coherence matrix for very short time windows (stacking 15 windows of 5 seconds length). An eigendecomposition of the coherence matrices allows to extract the first eigenvectors, corresponding to the dominant source in the time window. The principal eigenvectors can be clustered to find groups of events with similar source properties. We also use the principal eigenvector of already known events as a matched filter to scan the whole dataset. The results of the DAS cable are compared to the observations of the geophone array. While largely obtaining similar findings, the DAS cable seems to better capture high-frequency features of certain events. We also explore the effects of stacking and downsampling of the DAS data prior to detection, which influences both resolution and computational efficiency of the algorithm.

How to cite: Grimm, J., Poli, P., and Jousset, P.: Detecting seismo-volcanic events based on inter-channel coherency of a DAS cable, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9089, https://doi.org/10.5194/egusphere-egu23-9089, 2023.

EGU23-9312 | Orals | SM2.1

Six-component wave type fingerprinting and filtering 

David Sollberger, Nicholas Bradley, Pascal Edme, and Johan O. A. Robertsson

We present a technique to automatically classify the wave type of seismic phases that are recorded on a single six-component recording station (measuring both three components of translational and rotational ground motion) at the earth's surface. We make use of the fact that each wave type leaves a unique 'fingerprint' in the six-component motion of the sensor. This fingerprint can be extracted by performing an eigenanalysis of the data covariance matrix, similar to conventional three-component polarization analysis. To assign a wave type to the fingerprint extracted from the data, we compare it to analytically derived six-component polarization models that are valid for pure-state plane wave arrivals. For efficient classification, we make use of the supervised machine learning method of support vector machines that is trained using data-independent, analytically-derived six-component polarization models. This enables the rapid classification of seismic phases in a fully automated fashion, even for large data volumes, such as encountered in land-seismic exploration or ambient noise seismology. Once the wave-type is known, additional wave parameters (velocity, directionality, and ellipticity) can be directly extracted from the six-component polarization states without the need to resort to expensive optimization algorithms.

We illustrate the benefits of our approach on various real and synthetic data examples for applications such as automated phase picking, aliased ground-roll suppression in land-seismic exploration, and the rapid close-to real time extraction of surface wave dispersion curves from single-station recordings of ambient noise. Additionally, we argue that an initial step of wave type classification is necessary in order to successfully apply the common technique of extracting phase velocities from combined measurements of rotational and translational motion.

How to cite: Sollberger, D., Bradley, N., Edme, P., and Robertsson, J. O. A.: Six-component wave type fingerprinting and filtering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9312, https://doi.org/10.5194/egusphere-egu23-9312, 2023.

EGU23-9314 | ECS | Orals | SM2.1

Using Distributed Fiber-optic Sensing for Tracking Caprock Fault Activation Processes 

Verónica Rodríguez Tribaldos, Chet Hopp, Florian Soom, Yves Guglielmi, Paul Cook, Tanner Shadoan, Jonathan Ajo-Franklin, Michelle Robertson, Todd Wood, and Jens Birkholzer

Identifying and monitoring the reactivation of faults and opening of fractures affecting low permeability, sealing formations in natural underground storage complexes such as Carbon Capture and Storage projects and Nuclear Waste repositories is essential to ensure storage integrity and containment. Although passive seismic monitoring can be effective for detecting induced failure, stress accumulation and fault reactivation can occur aseismically in clay-rich formations, preventing early failure to be recognized. Here, we investigate the potential of applying strain monitoring with fiber-optics sensing technologies to assess in-situ changing stress conditions at high spatial and temporal resolution.

We present results of fiber-optic sensing monitoring during the FS-B experiment, a controlled activation of a fault zone affecting the Opalinus Clay Formation in the Mont Terri underground Laboratory (Switzerland). Six constant flowrate water injections induced the hydraulic opening of the fault. A hydraulic connection between the injector and a monitoring borehole occurred, developing a flow path sub-parallel to the fault strike. A 2 km long fiber-optic cable looped through 10 monitoring boreholes surrounding and crossing the fault zone was used for distributed acoustic and strain sensing (DAS and DSS) before, during and after injection. Continuous low-frequency (< 1 Hz) DAS data reveals mechanical strain associated with fault reactivation. Increasing extensional strain is recorded near the point of injection and near the newly formed hydraulic flow path, reaching a value of ~150 μɛ. Post-activation residual strain of ~60 μɛ suggests irreversible fault zone deformation. Smaller strain changes are recorded above and below the high pressure flow path, suggesting a mechanically disturbed zone larger than the leakage zone. Low-frequency DAS data are consistent with co-located DSS strain data, local, 3D displacement measurements of fault movements and P-wave velocity anomalies derived from Continuous Active Source Seismic Monitoring (CASSM). Our results are promising and demonstrate the potential of fiber-optic sensing as a powerful tool for monitoring spatio-temporal evolution of fault reactivation processes and leakage in clay formations induced by fluid pressurization.

How to cite: Rodríguez Tribaldos, V., Hopp, C., Soom, F., Guglielmi, Y., Cook, P., Shadoan, T., Ajo-Franklin, J., Robertson, M., Wood, T., and Birkholzer, J.: Using Distributed Fiber-optic Sensing for Tracking Caprock Fault Activation Processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9314, https://doi.org/10.5194/egusphere-egu23-9314, 2023.

EGU23-9629 | ECS | Posters on site | SM2.1

Monitoring material properties of civil engineering structures with 6C point measurements 

Felix Bernauer, Shihao Yuan, Joachim Wassermann, Heiner Igel, Celine Hadziioannou, Frederic Guattari, Chun-Man Liao, Ernst Niederleitinger, and Eva P. S. Eibl

Observing motion within a building in six degrees of freedom (three components of translational motion plus three components of rotational motion) opens completely new approaches to structural health monitoring. Inspired by inertial navigation, we can monitor the absolute motion of a building or parts of it without the need for an external reference. Rotational motion sensors can directly measure harmful torsional modes of a building, which has always been challenging and prone to errors when using translation sensors only. Currently, we are developing methodologies including rotational motion observations for monitoring of material parameters in order to locate and characterize structural damage. Within the framework of the GIOTTO project (funded by the German Federal Ministry for Education and Research, BMBF) we explore these approaches.

Here, we introduce a newly developed 6C sensor network for structural health monitoring. It consists of 14 inertial measurement units (IMU50 from exail, former iXblue, France) that were adapted to the needs of seismology and structural health monitoring. We performed experiments at the BLEIB test structure of the Bundesanstalt für Materialforschung und -prüfung (BAM), a 24 m long concrete beam serving as a large scale bridge model. We present results on detecting changes in material properties (seismic wave speed) of the beam with varying pre-stress and load, as derived from a novel approach by comparing amplitudes of translational to rotational motions at a single measurement point. We compare our findings to results obtained with coda wave interferometry using rotational as well as translational motions.

How to cite: Bernauer, F., Yuan, S., Wassermann, J., Igel, H., Hadziioannou, C., Guattari, F., Liao, C.-M., Niederleitinger, E., and Eibl, E. P. S.: Monitoring material properties of civil engineering structures with 6C point measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9629, https://doi.org/10.5194/egusphere-egu23-9629, 2023.

EGU23-9641 | Posters on site | SM2.1

Loops of slack in dark fiber and their effect on interferometric analysis of ambient noise – symptoms, consequences and remedies 

Christopher Wollin, Leila Ehsaninezhad, Johannes Hart, Martin Lipus, and Charlotte Krawczyk

Seismic microzonation and ambient noise tomography via Distributed Acoustic Sensing (DAS) may contribute to the seismic hazard assessment and the exploration or monitoring of utilizable and utilised subsurface volumes at favorable costs. However, numerous technical aspects remain under investigation to further maturate this innovative seismological approach – particularly when applied to dark telecommunication fibers. For instance unknown coupling of the fiber to the ground or presence of loops of slack fiber may disturb the regular measuring of the stringed virtual sensors.

 

In this study, we investigate how loops of slack fiber affect the results of passive ambient tomography, a particularly appealing exploration approach due to its low footprint. We present results obtained with DAS recordings on purposefully installed as well as dark telecommunication optic fiber. Sledgehammer blows were recorded on an optic fiber laid out in an urban heating tunnel before and after introducing several loops of slack. The loops coiled up fractions and multiples of the utilized gauge length and were spaced in sufficient distance to independently analyze the surrounding wavefield. Discontinuous wavefronts can be observed once the coiled fiber exceeds the gauge length. Similar observations were made on the virtual shot gathers calculated along a 4.5 km long segment of dark fiber along a major road in the city of Berlin, Germany. We show how the loops of slack affect the further processing with respect to ambient noise tomography. On average, the removal of virtual sensors identified to be located in coiled fiber reduces the shear-wave velocities in the resulting model.

 

We conclude that the careful removal of virtual sensors within loops of slack is a mandatory processing step towards ambient noise tomography with linear DAS arrays. However, the calculation of virtual shot gathers can help to reveal the affected fiber segments.

How to cite: Wollin, C., Ehsaninezhad, L., Hart, J., Lipus, M., and Krawczyk, C.: Loops of slack in dark fiber and their effect on interferometric analysis of ambient noise – symptoms, consequences and remedies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9641, https://doi.org/10.5194/egusphere-egu23-9641, 2023.

EGU23-10767 | ECS | Posters on site | SM2.1

Exploring multiscale nonlinear NDTs for damage detection in concrete structures 

Marco Dominguez-Bureos, Celine Hadziioannou, Niklas Epple, Camila Sanchez Trujillo, and Ernst Niederleithinger

It has been shown that non-destructive tests (NDTs) based on nonlinear wave propagation are more sensitive to detecting very small damages in concrete structures than linear techniques. With the aim of exploring the nonlinear effects in civil structures as a damage indicator, we perform a 1-day multiscale vibration monitoring of a test bridge equipped with a pretension system.

We used the pretension system to subject the specimen to eight compression states in its longitudinal direction (400kN at the highest, and 280kN at the lowest). At every compression state, we struck the structure in the vertical direction three times at two locations on the bridge with an impulse source. Throughout the whole experiment, we recorded seismic ambient noise at different frequency bands with a 14-IMU50-sensor array to measure the acceleration and rotation rate, a 14-geophone array with a 4.5 Hz natural frequency, a DAS system, and 4 pairs of ultrasound transducers; the internal temperature of the concrete was also recorded.

At the structural scale (from 1 to 40 Hz) we were able to observe different responses of the structure to pre-tension changes, depending on where the measurement took place in relation to the vertical support pillars by estimating relative velocity changes using the Coda Wave Interferometry stretching processing technique.

At the material scale (ultrasound regime) we can observe temperature-dependent slow dynamics features related to changes in the seismic velocity of the concrete as a consequence of vertical strikes, and its recovery process that returns its physical properties to a steady state after the action of the impulse source.

With this work, we work towards the development of new NDTs that are increasingly sensitive to small cracks and imperfections using conventional and non-conventional seismic instruments to measure linear and nonlinear wave propagation.

How to cite: Dominguez-Bureos, M., Hadziioannou, C., Epple, N., Sanchez Trujillo, C., and Niederleithinger, E.: Exploring multiscale nonlinear NDTs for damage detection in concrete structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10767, https://doi.org/10.5194/egusphere-egu23-10767, 2023.

EGU23-11782 | ECS | Posters on site | SM2.1

A workflow to generate DAS based earthquake catalog, applied to an offshore telecommunication cable in central Chile 

Marie Baillet, Alister Trabattoni, Martijn Van Den Ende, Clara Vernet, and Diane Rivet

Fiber-optic Distributed Acoustic Sensing (DAS) is of critical value for the expansion of seismological networks, particularly in regions that are hard to instrument. The work presented here is part of the 5-year ERC ABYSS project, which aims at building a permanent seafloor observatory to increase our ability to capture low magnitude seismic signals from the subduction fault zone in the DAS data recorded by offshore telecommunication cables along the central coast of Chile.

In preparation for this project, a first experiment named POST was conducted from October to December 2021 on a submarine fiber-optic cable connecting the city of Concón to La Serena. DAS data were recorded continuously for 38 days over a distance of 150 km from Concón, constituting more than 36700 virtual sensors sampling at 125 Hz. This experiment provided an opportunity to anticipate what will be recorded over the next 5 years of the project, and to allow us to develop routines that will be applied later for real-time data processing.

As a first step, we developed an automated routine for generating a preliminary earthquake catalog, comprising various conventional signal processing steps, including data denoising, change-point detection, and separating seismic events from transient instrumental noise making use of the two-dimensional character of the DAS data. Over a span of 38 days (worth 72 TB of data), our pipeline detected more than 900 local, regional, and teleseismic events with local magnitudes down to ML < 2 (based on the Centro Sismológico Nacional (CSN) public catalog). The size of our catalog, enriched with numerous off-shore events, is a significant improvement over the current CSN catalog, which may aid future studies into the Chilean margin subduction zone seismicity.

How to cite: Baillet, M., Trabattoni, A., Van Den Ende, M., Vernet, C., and Rivet, D.: A workflow to generate DAS based earthquake catalog, applied to an offshore telecommunication cable in central Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11782, https://doi.org/10.5194/egusphere-egu23-11782, 2023.

EGU23-11842 | Orals | SM2.1

Using path-integrated strain in Distributed Acoustic Sensing 

Alister Trabattoni, Francesco Biagioli, Claudio Strumia, Gaetano Festa, Martijn van den Ende, Diane Rivet, Anthony Sladen, Jean-Paul Ampuero, Jean-Philippe Metexian, and Éléonore Stutzmann

Distributed Acoustic Sensing (DAS) is becoming a well-established technology in seismology. For historical and practical reasons, DAS manufacturers usually provide instruments that natively record strain (rate) as the principal measurement. While at first glance strain recordings appear similar to particle motion (displacement, velocity, acceleration) waveforms, not all of the seismological tools developed over the past century (e.g., magnitude estimation, seismic beamforming, etc.) can be readily applied to strain data. Notably, the directional sensitivity of DAS differs from conventional particle motion sensors, and DAS experiences an increased sensitivity to slow waves, often composed of highly scattered waves that are challenging to analyze. To address these issues, several strategies have been already proposed to convert strain rate measurements to particle velocity.

Based on a previously proposed mathematical formalism, we stress some fundamental differences between path-integrated strain and conventional displacement measurements. DAS inherently records arc length variation of the cable which is a relative motion measurement along a curvilinear path. We show that if the geometry of the DAS deployment is adapted to the wavefield of interest, path-integrated strain can be used to closely approximate the displacement wavefield without the need of additional instruments. We validate this theoretical result using collocated seismometers, discuss the limitations of this approach, and show two benefits: enhancing direct P-wave arrivals and simplifying the magnitude estimation of seismic events. While using path integrated strain is in some aspects more challenging, it achieves flat (hence lower) noise levels both in frequency and wavenumber. It also provides better sensitivity to high velocity phases, and permits the direct application of conventional seismological tools that are less effective when applied to the original strain data.

How to cite: Trabattoni, A., Biagioli, F., Strumia, C., Festa, G., van den Ende, M., Rivet, D., Sladen, A., Ampuero, J.-P., Metexian, J.-P., and Stutzmann, É.: Using path-integrated strain in Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11842, https://doi.org/10.5194/egusphere-egu23-11842, 2023.

EGU23-12213 | ECS | Posters on site | SM2.1

Near-surface seismic characterisation of a railway embankment slope using fibre-optic distributed acoustic sensing 

Giuseppe Maggio, Andrew Trafford, and Shane Donohue

The behaviour of geological slopes during seasonal weather patterns represents one of the challenges for assessing the geotechnical state of health of the ageing infrastructures. In the presence of man-made soil infrastructure slopes, rainfall and prolonged dry periods can cause cycles of swelling and shrinking of the ground that could potentially compromise their structural integrity. Recent research has found that time-lapse velocity monitoring, has the potential to provide information on climate-related deterioration of geotechnical infrastructure. Variations of the ground conditions could manifest as changes in seismic velocity, detectable through the seasons and after extreme weather events.

In this work, we perform seismic imaging and velocity-monitoring of a critical railway embankment in the United Kingdom using fibre optic distributed sensing (DAS). The study area is a 6 m tall, and 350 m long embankment slope built more than 100 years ago in the outskirts of London (Surrey). The railway is currently utilised mostly by commuter trains. Since August 2022, a passive DAS dataset rich in train signals has been acquired. data acquisition will continue until July 2023. Furthermore, periodic active surveys have been conducted along the slope.

Firstly, to validate the seismic response of the fibre (i.e., maximum usable frequencies based on the gauge length), we calculate and compare surface wave dispersion curves derived from both DAS and geophones using passive ambient noise, train signals and active sledgehammer shots. As a result, we obtain consistent and comparable dispersion curves ranging from ~200 m/s at 10 Hz to ~140m/s at 40 Hz. 

Secondly, we invert, using global search algorithms, DAS-derived dispersion curves for 1D depth-velocity models to identify and clarify the trend of the near-surface (top 10 m) seismic structures. 

Thirdly, we apply seismic interferometry and moving window cross-spectral techniques to measure changes in seismic velocity at the embankment using the 6-month passive DAS data acquired so far. 

The ultimate goal of this project is to develop a geophysical tool diagnostic of geotechnical deterioration of critical infrastructures by linking together DAS-based seismic observations, temporal seismic velocity changes, weather data and laboratory-based soil sample tests.

How to cite: Maggio, G., Trafford, A., and Donohue, S.: Near-surface seismic characterisation of a railway embankment slope using fibre-optic distributed acoustic sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12213, https://doi.org/10.5194/egusphere-egu23-12213, 2023.

EGU23-12740 | ECS | Orals | SM2.1

Coherence-based Amplification of Rayleigh Waves from Urban Anthropogenic Noise recorded with Distributed Acoustic Sensing 

Leila Ehsaninezhad, Christopher Wollin, Benjamin Schwarz, and Charlotte Krawczyk

At a local scale, e.g. in urban settlements, seismic subsurface characterization requires implementing experiments at high spatial resolution. Distributed acoustic sensing (DAS) provides the opportunity of using pre-existing fiber optic cables as dense receiver arrays, thus potentially reducing the effort for active seismic surveying in urban areas. Due to their small footprint, passive experiments appear particularly appealing. However, extracting coherent signals in an urban environment, i.e. in the presence of anthropogenic activity in the receivers' vicinity, remains a challenge.

 

In this study, we present results from combining the well known technique of Multichannel Analysis of Surface Waves (MASW) with the coherency-based enhancement of wavefields. The investigation is based on a DAS dataset acquired along a major road in Berlin, Germany. We analyse a 4.5 km long straight subsegment of a dark fiber that was sampled at 8 m intervals with 1000 Hz over a period of 15 days. After temporal decimation and the interferometric analysis, clear causal and a-causal branches of Rayleigh-surface waves emerge in the virtual shot gathers.

 

In the further processing, we employ coherence-based enhancement of wavefields to amplify the Signal to Noise Ratio of the virtual shot gathers. Compared to the traditional workflow of ambient-noise tomography the modified one yields improved dispersion curves particularly in the low-frequency part of the signal. This leads to an increased investigation depth along with lower uncertainties in the inversion result. The final velocity model reaches depths down to 300 m. We show that the application of coherence-based enhancement of the virtual shot gathers in the MASW-workflow may significantly relax the necessity of collecting long baselines for passive tomography in urban environments.

How to cite: Ehsaninezhad, L., Wollin, C., Schwarz, B., and Krawczyk, C.: Coherence-based Amplification of Rayleigh Waves from Urban Anthropogenic Noise recorded with Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12740, https://doi.org/10.5194/egusphere-egu23-12740, 2023.

EGU23-13600 | Orals | SM2.1

Long-awaited and delayed Transportable Highest grade of Fiber Optic Gyroscope for Seismology 

Frédéric Guattari, Guillaume Lenogue, Kevin Gautier, Arnaud Frenois, and André Couderette

First announced at EGU2021, and said to be “released soon”, the 1C rotation seismometer which complements the blueSeis product line on the high performance segment, will be finally disclosed at EGU2023.

2019 and 2020 results have been shared about large mockup of giant Fiber-Optic Gyroscope from iXblue, having diameter as large as 1.2 meters, and the development road to reach an industrial product had been drawn. But several critical additional issues raised on the track.

Keeping in mind all the requirement of the instrument, the need for a transportable, and easily deployable instrument, the calibration capability, the possibility to push the performance pilling up the sensors, and the need for an optional orthogonal structure, we finally come to an instrumental solution with high versatility at expected performances.

The full development story will be shared, and the tests results of first production units of blueSeis-1C will be disclosed. Explanation about the various way to use it will be offered too.

Perspectives and applications using this long-awaited sensor will be presented, from ocean-bottom system tilt denoising to improved inversion of the seismic source.

How to cite: Guattari, F., Lenogue, G., Gautier, K., Frenois, A., and Couderette, A.: Long-awaited and delayed Transportable Highest grade of Fiber Optic Gyroscope for Seismology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13600, https://doi.org/10.5194/egusphere-egu23-13600, 2023.

EGU23-13803 | ECS | Orals | SM2.1

Magnitude Estimation and Ground Motion Prediction to Harness Fiber Optic Distributed Acoustic Sensing for Earthquake Early Warning 

Itzhak Lior, Diane Rivet, Jean-Paul Ampuero, Anthony Sladen, Sergio Barrientos, Rodrigo Sánchez-Olavarría, German Alberto Villarroel Opazo, and Jose Antonio Bustamante Prado

Earthquake Early Warning (EEW) systems provide seconds to tens of seconds of warning time before potentially-damaging ground motions are felt. For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismological stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work, we harness available optical fiber infrastructure for EEW using the novel approach of Distributed Acoustic Sensing (DAS). DAS strain measurements of earthquakes from different regions are converted to ground motions using a real-time slant-stack approach, magnitudes are estimated using a theoretical earthquake source model, and ground shaking intensities are predicted via ground motion prediction equations. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes.

How to cite: Lior, I., Rivet, D., Ampuero, J.-P., Sladen, A., Barrientos, S., Sánchez-Olavarría, R., Villarroel Opazo, G. A., and Bustamante Prado, J. A.: Magnitude Estimation and Ground Motion Prediction to Harness Fiber Optic Distributed Acoustic Sensing for Earthquake Early Warning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13803, https://doi.org/10.5194/egusphere-egu23-13803, 2023.

EGU23-14093 | Posters on site | SM2.1

Six-component records of local seismicity in the Long Valley Caldera, Californica, US 

Johana Brokesova and Jiri Malek

Long Valley Caldera in the eastern part of California is a depression 32 km long and 18 km width, which was formed during a supervolcano eruption 760 000 years ago.  Weak volcanic activity manifested by hot springs, CO2 emmanations and earthhquake swarms in the caldera and neighboring Mammoth Mountain volcanic complex has been continuing until present. The seismicity in the area is the subject of intensive study. In 2016 - 2017 the monitoring system was supplemented by small-aperture array consisting of three short-period Rotaphone-D seismographs. The instruments were deployed in vaults few hundred meters apart at depts from 3.2 to 2.2 m. They are new short-period seismographs measuring three translational and three rotational components. The array enabled new methods of microearthquakes investigation. The noise from surface sources (mainly traffic along nearby highway) can be suppressed significantly by non-linear summing of redundant translational data from each Rotaphone. This enabled detection of very weak microearthquakes in the vicinity of the array with good signal-to-noise ratio. The true azimuth and phase velocity along surface are determined by two methods:  the zero-crossing point beamforming and rotation-to-translation relations. Based on these quantities, location of microearthquakes was performed and it was compared to the locations from the USGS catalogue of local earthquakes.

The six-component records in the Long Valley Caldera are extremely complex. Strong phases between P- and S-wave onsets and namely within the S-wave group are visible in most seismograms. They probably originated as reflection and refraction waves at distinctive interfaces beneath the sediment filling of the caldera. Six-component records enabled analysis of individual wavetypes in the seismograms. The seismic array was reinstalled in the summer 2021 with new data-acquisition system with bigger dynamic range (32 bits A/D converter). We expect even more sensitive measurements from this new observation. 

How to cite: Brokesova, J. and Malek, J.: Six-component records of local seismicity in the Long Valley Caldera, Californica, US, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14093, https://doi.org/10.5194/egusphere-egu23-14093, 2023.

EGU23-14444 | ECS | Orals | SM2.1

Modelling of DAS cable and ground coupling response using Discrete Particle Schemes 

Nicolas Luca Celli, Christopher J. Bean, Gareth O'Brien, and Nima Nooshiri

Since its first applications in the past decade, the use of fiber optic cables as ground motion sensors has become a central topic for seismologists, with successful applications of Distributed Acoustic Sensing (DAS) in various key fields such as seismic monitoring, structural imaging and source characterisation.

The instrument response of DAS cables however is largely unknown. Instrument response is a combination of instrument design, local site effects and ground coupling, and for DAS, the latter ones are believed to have a strong, spatially variable, but yet largely unquantified effect. This limits the application of a large number of staple seismological techniques (e.g. earthquake magnitude estimation, waveform tomography) that can require accurate knowledge of a signal’s amplitude and frequency content.

Here we present a method for accurately simulating a DAS cable and its response. The scheme is based on molecular dynamic-like particle-based numerical modelling, allowing the investigation of the effect of varying DAS-ground coupling scenarios. At first, we compute the full strain field directly, for each pair of neighbouring particles in the model. We then define a virtual DAS cable, embedded within the model and formed by a single string of interconnected particles. This allows us to control all aspects of the cable-ground coupling and their properties at an effective granular level through changing the bond strengths and bond types (e.g. nonlinearity) for both the cable and the surrounding medium. Arbitrary cable geometries and heterogeneous materials can be accommodated at the desired scale of investigation.

We observe that at the meter scale, realistic DAS materials, cable-ground coupling and the presence of unconsolidated trench materials around it dramatically affect wave propagation, each change affecting the synthetic DAS record, with differences exceeding at times the magnitude of the recorded signal. These differences show that cable coupling and local site effects have to be considered both when designing a DAS deployment and analysing its data when either true or along-cable relative amplitudes are considered.

How to cite: Celli, N. L., Bean, C. J., O'Brien, G., and Nooshiri, N.: Modelling of DAS cable and ground coupling response using Discrete Particle Schemes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14444, https://doi.org/10.5194/egusphere-egu23-14444, 2023.

EGU23-15048 | ECS | Posters on site | SM2.1

On Seismic Wave Equation Gradiometric Inversion for Density 

Marthe Faber and Andrew Curtis

It is of interest for environmental and resource applications to better characterise dynamic processes and properties of the near-surface critical zone of the solid Earth. Seismic wavefield gradiometry refers to a class of imaging techniques that estimate properties of the subsurface by calculating temporal and spatial gradients of incoming wavefields using dense array measurements, usually recorded at the Earth’s surface. One such method called wave equation inversion (WEI) has been shown to require only a few minutes of ambient seismic noise recordings to produce phase velocity maps, and shows promise for rapid field deployment.

Previous applications of WEI are based on the assumption that the 2D scalar Helmholtz wave equation adequately describes the dynamics of recorded wavefields. This approximation is severe for seismic waves because the Helmholtz equation fails to describe elastic wave dynamics. Since ambient noise recordings contain all kinds of interfering elastic wave types, the accuracy of subsurface material property estimates is compromised.

To investigate the potential to enhance the information available from WEI, we test the method synthetically using more sophisticated wave equations that represent wave propagation in the subsurface more accurately. Starting from a 3D seismic array geometry which provides wavefield gradient information both at the surface and at depth, WEI can be formulated in terms of the full elastic wave equation. From there we track approximations in both wave physics and field acquisition geometries that deplete information about the medium, eventually arriving at the conventional 2D scalar wave equation. These experiments highlight approximations that most deteriorate the solution, allowing us to target future effort to remove them.

One approximation made in all previous WEI studies is to assume that density is constant across the local array. In reality, subsurface density varies both laterally and with depth, yet remains poorly constrained in seismic imaging problems. Accurate density estimates would provide important insight into subsurface properties. This prompts us to test wavefield sensitivities to subsurface density contrasts via WEI. Synthetic results for 3D acoustic media suggest that it is possible to estimate relative density structure with WEI by using a full acoustic formulation for wave propagation along the surface. We show that using a constant density assumption for the medium can be detrimental to subsurface images, whereas the full acoustic formulation of gradiometry improves our knowledge of material properties. It allows us to estimate density as an additional material parameter as well as to improve phase velocity estimates by incorporating approximations to the density structure. By expanding this methodology to the elastic case, we will discuss the feasibility of estimating density with gradiometric WEI in the solid Earth.

How to cite: Faber, M. and Curtis, A.: On Seismic Wave Equation Gradiometric Inversion for Density, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15048, https://doi.org/10.5194/egusphere-egu23-15048, 2023.

EGU23-15050 | Orals | SM2.1

Low-frequency seismic wave sensing using coherent optical fiber networks for metrology 

Paul-Eric Pottie, Mads Tonnes, Maxime Mazouth-Laurol, Hendrix Montlavan-Leyva, Etienne Cantin, Benjamin Pointard, Hector Alvarez-Martinez, Rodolphe Le Targat, Olivier Lopez, Christian Chardonnet, and Anne Amy-Klein

Optical fiber networks are being implemented in several countries aiming at dissemination of ultra-stable time and frequency references. This enables the comparison of optical clocks, which is a key part of the roadmap towards the future redefinition of the International System of Units (SI) second. Furthermore, this enables uses in chronometric geodesy, where the sensitivity of the optical clocks to the gravitation field enables measurements of height differences as low as 1 cm [1].
The frequency signals in the optical fibers are sensitive to acoustic vibrations which are present in the ground, which is the main source of noise to the disseminated signals.
In recent years, this has enabled studies in the use of optical fiber links for the detection of earthquakes [2]. In such an approach, the measurement is the integrated noise over the fiber path. This typically allows for one to several orders of magnitudes longer range as compare to DAS techniques, but with the loss of localization along the fiber. Such integrated approaches include measurements of the total polarization change of the light along the fiber [3], or the total phase change of a coherent ultra-stable laser signal, potentially including distributed sensing techniques in submarine fibers [2,4].

Here, we will present the first quantitative studies on the use of coherent optical fiber links for seismic detection. Using a the fiber network REFIMEVE in France (see Fig. 1), we present studies on the sensitivity of coherent optical fiber links to seismic events. We describe the dependence of the sensitivity to a number of parameters like incident angle, magnitude and distance, and compare the sensitivity of a fiber link with that of conventional seismometers. We show, for a first time to our knowledge, the detection of seismic waves by a coherent optical fiber network, and we study the prospects of using such a network for the localization of earthquakes. Lastly, we discuss the principles and results of a machine learning algorithm, which enables automatic detection of earthquakes in a coherent optical fiber link.

Bibliography:
1. M. Takamoto et al., Test of general relativity by a pair of transportable optical lattice clocks, Nat. Phot., 14 (7), 411–415. doi:30210.1038/s41566-020-0619-8
2. G. Marra et al. , Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458. doi: 10.1126/science.aat4458279
3. J.C. Castellanos et al. ,Optical polarization-based sensing and localization of submarine earthquakes. In Optical fiber communication conference (OFC) 2022, doi:26210.1364/OFC.2022.M1H.4
4. G. Marra et al., Optical interferometry–based array of seafloor environmental sensors using a transoceanic submarine cable. Science, doi: 10.1126/science.abo193

Figure 1 : Map of the French REFIMEVE fiber network, shown in red lines. Dotted lines indicates indicate the full scale of the planned network, and continuous red lines indicate links used in these studies. Blue lines indicates the linear approximations of the links. All seismometers of the RESIF network is shown by small green triangles, and seismometers used in theses studies are shown by larger, turquoise triangles.

How to cite: Pottie, P.-E., Tonnes, M., Mazouth-Laurol, M., Montlavan-Leyva, H., Cantin, E., Pointard, B., Alvarez-Martinez, H., Le Targat, R., Lopez, O., Chardonnet, C., and Amy-Klein, A.: Low-frequency seismic wave sensing using coherent optical fiber networks for metrology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15050, https://doi.org/10.5194/egusphere-egu23-15050, 2023.

EGU23-15062 | ECS | Posters on site | SM2.1

Observing and analysing seismicity with a permanet 6C station 

Andreas Brotzer, Heiner Igel, Felix Bernauer, Joachim Wassermann, Robert Mellors, and Frank Vernon

In September 2022, a three-component rotational rate sensor (blueSeis-3A) provided by IRIS has been deployed at the underground vault of the Piñon Flat Observatory (PFO) near San Diego in California. A three-component broadband seismometer (Trillium 240s) is co-located on the granite pier, creating a 6C station for permanent observations of local and regional seismicity and wavefield studies. The permanent record is streamed online via IRIS and freely available with all required metadata (station: BlueSeis at Pinon Flat = BSPF). Additionally, the site offers observations of strain by optical fiber and vacuum laser strainmeters at PFO, allowing to study 7 components of the seismic wavefield in a quiet area with regard to seismic noise, but high seismicity (e.g. San Andreas fault zone, San Jacinto fault zone). Such a setup enables advanced studies of the seismic wavefield. Dense, large-N nodal experiments, temporarily deployed around PFO could provide dense sampling of the seismic wavefield for comparison studies. The seismic array of borehole sensors at PFO is well designed to compute array derived rotations with enables a direct comparison with the rotational record and applied methods. Moreover, the array is employed to compare array analysis with 6C methods (e.g. backazimuth estimation, wavefield separation, source tracking, local subsurface velocity changes). We present characteristics on the 6C station and preliminary analysis results.

How to cite: Brotzer, A., Igel, H., Bernauer, F., Wassermann, J., Mellors, R., and Vernon, F.: Observing and analysing seismicity with a permanet 6C station, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15062, https://doi.org/10.5194/egusphere-egu23-15062, 2023.

EGU23-15265 | ECS | Orals | SM2.1

Towards exploiting the advantages of a Standard telecom multi-fibre cable for volcano monitoring: an example from Mt. Etna 

Sergio Diaz-Meza, Philippe Jousset, Gilda Currenti, Air David, Andy Clarke, Anna Stork, Athena Chalari, and Charlotte Krawzcyk

Distributed Dynamic Strain Sensing (DDSS), also known as Distributed Acoustic Sensing (DAS), is becoming a popular tool for volcano monitoring. The sensing method relies on sending coherent light pulses into an optical fibre and measuring the phase-shift of Rayleigh back-scattered light due to strain on the fibre. This provides distributed strain rate measurements at high temporal and spatial sampling rates. Standard telecom fibres have been conventionally used for this purpose, however engineered fibres are being developed to enhance the back-scattered light, providing up to 100 times improved sensitivity in contrast to the conventional standard fibre. Despite the technical advantages of engineered fibres, standard fibres already have extensive coverage around the Earth surface, and so there is an interest in using the existing telecommunication infrastructure. In this study we compare stack DDSS data from a fibre loops made of several fibres within the same optical fibre cable, with DDSS data measured on an engineered fibre. We analyse how stacking can improve the signal quality of the recorded DDSS data. In an area located 2.5 km NE from the craters of Mt. Etna, we spliced 9 standard fibres together from a 1.5 km long cable to create a single optical path and interrogated using an iDAS unit. At the same time, we interrogated with a Carina unit a 0.5 km engineered fibre installed parallel to the standard multi-fibre cable. Both fibres were interrogated in a common period of 5 days. We use a spatial cross-correlation function to find the channel equivalences between each fibre and then stack them to evaluate the changes in the DDSS data and compare with the engineered fibre data. Our results show that, despite engineered fibres have lower noise, a stack of 5 fibres can achieve a maximum noise reduction of 20% outside of the optical noise band, in comparison to the engineered fibre. We achieved this noise reduction for our specific configuration, and so we show how the stack improvement is dependent on the type of configuration in terms of fibres stacked and length of the fibres. Our findings motivate the exploitation of multi-fibre cables in existing infrastructures, so-called dark fibres, for monitoring volcano and applications to other environments.

How to cite: Diaz-Meza, S., Jousset, P., Currenti, G., David, A., Clarke, A., Stork, A., Chalari, A., and Krawzcyk, C.: Towards exploiting the advantages of a Standard telecom multi-fibre cable for volcano monitoring: an example from Mt. Etna, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15265, https://doi.org/10.5194/egusphere-egu23-15265, 2023.

EGU23-15291 | ECS | Orals | SM2.1

Supporting the completion process of boreholes using combined fiber-optic monitoring technologies 

Johannes Hart, Martin Peter Lipus, Christopher Wollin, and Charlotte Krawzcyk

Efficient, safe and sustainable utilization of geothermal reservoirs depends on reliable well completion and monitoring technologies. Conventional borehole measurement methods can only be used after the completion process and usually show snapshots of the borehole conditions at discrete points in time. Therefore, the successful borehole completion is a risky process and mainly relies on the experience of the driller. By using distributed fiber-optic sensing technologies, it is possible to monitor all along the cable with dense spatial sampling and continuous in real-time.

In this presentation, we give insights into our newest case study in Berlin. A 450 m deep exploration well for an Aquifer Thermal Energy Storage was completed. We installed a fiber optic sensor cable along the whole production tubing, that contained several single-mode and multi-mode fibers in loose tube and tight buffered configuration. This cable allows to simultaneously measure distributed temperature (DTS), distributed acoustics (DAS) and distributed strain (DSS/DTSS) for the entire completion process.

Particularly with a combined analysis and interpretation of the different fiber-optic technologies, conventionally untraceable processes can be visualized. We are able to show changes of subsurface flow paths due to blockages. Processes to be prevented, like caving or bridging can be detected and the proper rise of gravel or cement can be surveyed. Provided to the driller in real time, subsurface uncertainties can be significantly reduced.

Monitoring geothermal wells with a fiber-optic sensing infrastructure is not only a powerful tool to reduce risks during well completion, which can lead to compromised well integrity. The installed equipment and technology can also be used to assess the well integrity over the whole cycle of the well, to ensure a longest possible lifespan.

How to cite: Hart, J., Lipus, M. P., Wollin, C., and Krawzcyk, C.: Supporting the completion process of boreholes using combined fiber-optic monitoring technologies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15291, https://doi.org/10.5194/egusphere-egu23-15291, 2023.

EGU23-15325 | Posters on site | SM2.1

Observation of the microseismic peak from Distributed Acoustic Sensing (DAS) measurements at the LSBB underground Laboratory 

Olivier Sèbe, Camille Jestin, Amaury Vallage, Stéphane Gaffet, Daniel Boyer, Alain Cavaillou, Jean-Baptiste Decitre, Charly Lallemand, Vincent Lanticq, and Olivier Rousseau

Thanks to its ability to provide dense strain rate measurements along Optical Fiber (OF) cable, the Distributed Acoustic Sensing (DAS) technique spreads over different seismic and geophysical domains. They range from exploration geophysics (Mestayer et al. 2011, Daley et al. 2013), to underground structure imaging (e.g. Ajo-Franklin et al. 2019, Cheng et al. 2021) or seismic activity and background noise monitoring (Jousset et al 2018, Nayak et al. 2021). Beyond the advantage of its dense spatial sampling and given a better understanding of its instrument response (e.g. Lindsey et al. 2020), the detection performance of these new DAS measurements also depends on its ability to precisely characterize the amplitude and phase of the seismic background noise in different environments. According to recent offshore seismic noise studies (Ugalde et al. 2021, Lior et al. 2021, Guerin et al 2022), we propose a study based on DAS recordings of the seismic background noise in an on-land quiet environment.

In 2020, a temporary seismic experiment PREMISE (PREliminary MIga Seismic Experiment) was carried out on the site of the underground low noise Laboratory (LSBB, Laboratoire Souterrain Bas Bruit) at Rustrel, France, in order to study the 3D seismic wave field properties in a pretty well-known underground geological structure. During this experiment, we deployed several kilometers of different OF in the LSBB galleries in order to create a multidirectional DAS array with a total fiber length of 10.5km and several ground-coupling conditions. We reprocessed two hours of “raw” DAS data, recorded with a FEBUS A1-R instrument, with different acquisition parameters to find the best configuration for enhancing the DAS measurement Signal to Noise Ratio. The power spectral density (PSD) of these reprocessed strain time-series reveals a peak in the background noise frequency range [0.08-0.25Hz] for gauge lengths of 90m and 150m. Independently, an estimation of the local strain field has been derived by a geodetic analysis (Spudich et al 1995) of the records from the LSBB broadband seismometers antenna. The comparison of the DAS and seismometers array-derived strain PSD shows a very good agreement with the secondary microseism peak in terms of frequency band, amplitude, and the wave field polarization, especially for DAS strain records processed with gauge-length of several tens of meters.

How to cite: Sèbe, O., Jestin, C., Vallage, A., Gaffet, S., Boyer, D., Cavaillou, A., Decitre, J.-B., Lallemand, C., Lanticq, V., and Rousseau, O.: Observation of the microseismic peak from Distributed Acoustic Sensing (DAS) measurements at the LSBB underground Laboratory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15325, https://doi.org/10.5194/egusphere-egu23-15325, 2023.

EGU23-15589 | Posters on site | SM2.1

Variations of the system properties of a high-rise building over 1 year using a single station 6C approach. 

Yara Rossi, Konstantinos Tatsis, Yves Reuland, John Clinton, Eleni Chatzi, and Markus Rothacher

We demonstrate that the dynamic response of an engineered structure, including modeshape identification, can be obtained from just a single measurement at one position - if rotation is recorded in combination with translation. Such a single-station approach can save significant time, effort and cost when compared with traditional structural characterization using horizontal arrays. In our contribution we will focus on the monitoring of a high-rise building by tracking its dynamic properties and their variations due to environmental (e.g. temperature) and operational (e.g. wind) conditions (EOCs) over a 1-year period. We present a real-case structural identification procedure on the Prime Tower in Zurich. This is a 36-story tower of 126 m height, with a poured-in-place-concrete core and floors and precast-concrete columns; this concrete core structure, surrounded by a triple-glazed facade, is the third highest building in Switzerland. 
The building has been continuously monitored, over a 1-year period, by an accelerometer (EpiSensor), a co-located rotational sensor (BlueSeis) and a weather station located near the building center on the roof. Roof and vertical seismic arrays were deployed for short periods. The motion on the tower roof includes significant rotation as well as translation, which can be precisely captured by the monitoring station. More than 20 structural modes, including the first 6 fundamental modes, where translations are coupled with rotations, are tracked between 0.3 – 14 Hz. We will also show the variation of natural frequencies due to seasonal but also more short-term effects, in an effort to understand the effect of environmental and operational variability on structural deformation and response. Additionally, an amplification of the modes, not only during strong winds, but also during a couple of Mw 4.0 - 4.4 earthquakes at regional distance has been observed and analysed. The frequency band between 0.3 and 10 Hz is of key interest for earthquake excitation, making an investigation thereof essential. The work closes with a summary of the main benefits and potential in adopting collocated rotation and acceleration sensing for geo-infrastructure monitoring purposes.

How to cite: Rossi, Y., Tatsis, K., Reuland, Y., Clinton, J., Chatzi, E., and Rothacher, M.: Variations of the system properties of a high-rise building over 1 year using a single station 6C approach., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15589, https://doi.org/10.5194/egusphere-egu23-15589, 2023.

EGU23-15841 | Orals | SM2.1

Monitoring of elastic properties using DAS and DTS in a controlled experiment during road construction 

CharLotte M. Krawczyk, Martin P. Lipus, Johannes Hart, Christopher Wollin, Christian Cunow, and Philippe Jousset

Maintenance of infrastructure is costly and difficult to implement systematically when it spreads over wide areas, such as road or pipeline networks. In the monitoring of road ways, conventional methods to control the road integrity rely on discrete measurements in space and time. There is a large demand for innovative technologies that are able to assess the structural integrity as a whole and in regular intervals or even continuously. Distributed fiber-optic sensing opens the opportunity to measure numerous physical quantities such as temperature and strain with high spatial and temporal resolution over tens of kilometers. In addition, it is easily deployable at reasonable cost.

In order to address the issue of asphalt aging due to exposure to heavy traffic loads, we installed a fiber-optic cable into a reworked road interval and recorded fiber-optic data in a controlled experiment with numerous test vehicles of different sizes and weights. The recorded data suggests that elastic properties of the asphalt can be retrieved from the bypassing traffic. Vehicles can be characterized by the number of axes and load on the asphalt composite. In the next phase, we will monitor the aging of the test field to deduce how varying matrial properties can be better identified for geotechnical and geoscience applications.

How to cite: Krawczyk, C. M., Lipus, M. P., Hart, J., Wollin, C., Cunow, C., and Jousset, P.: Monitoring of elastic properties using DAS and DTS in a controlled experiment during road construction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15841, https://doi.org/10.5194/egusphere-egu23-15841, 2023.

EGU23-16307 | Orals | SM2.1

Local earthquake recordings using Distributed Acoustic Sensing (DAS) at BFO 

Nasim Karamzadeh Toularoud, Ya-Jian Gao, Jérôme Azzola, Thomas Forbriger, Rudolf Widmer-Schnidrig, Emmanuel Gaucher, and Andreas Rietbrock

The application of distributed acoustic sensing (DAS) in seismology is rapidly expanding due to its ability to perform a large number of high-density measurements, i.e., distributed sensing, without using many point sensors, which is cost-effective. DAS application includes vertical seismic profiling, microseismic measurements, and hydraulic fracturing monitoring and mainly focuses on the event detection capability of  DAS data. 

Febus optics DAS interrogator (A1-R) is continuously running at German Black Forest Observatory (BFO) since May 2021, recording RAW data (selectively stored) or strain-rate data (continuously stored). Our study is in the experimental phase and focuses on testing basic concepts of DAS data, i.e., the effect of gauge-length on the amplitude of measurement and comparing the amplitude of DAS with other seismological sensors such as strain-meter array and a STS2 broadband sensor as well as synthetic simulations. Such comparison is performed using background noise characteristics (power spectral density) and examples of local and regional events that are detectable at the BFO site. 

In this study, we show examples of strain rate measurements related to local earthquakes recorded by horizontal fiber optic cables, employing two different DAS interrogators, cable types and coupling of the cables to the ground. We compared simultaneous recordings using Febus A1 DAS interrogator and OptoDAS by Febus optic and Alcatel Submarine Networks (ASN), respectively, and, concluded about the frequency and gauge-length dependent sensitivity of recordings in two cases. In addition, we compare the amplitude of DAS recordings, for example of local earthquakes, with the synthetic strain simulated  at lower frequency bands using the spectral-element method (Salvus) based on 3D media and analytic approach (Qseis) for 1D model. 

 

How to cite: Karamzadeh Toularoud, N., Gao, Y.-J., Azzola, J., Forbriger, T., Widmer-Schnidrig, R., Gaucher, E., and Rietbrock, A.: Local earthquake recordings using Distributed Acoustic Sensing (DAS) at BFO, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16307, https://doi.org/10.5194/egusphere-egu23-16307, 2023.

EGU23-16459 | ECS | Orals | SM2.1

Deep learning approach for detecting low frequency events on DAS data at Vulcano Island, Italy 

Martina Allegra, Gilda Currenti, Flavio Cannavò, Philippe Jousset, Michele Prestifilippo, Rosalba Napoli, Mariangela Sciotto, Giuseppe Di Grazia, Eugenio Privitera, Simone Palazzo, and Charlotte Krawczyk3

Since September 2021, signs of unrest at Vulcano Island have been noticed after four years of quiescence, along with CO2 degassing and the occurrence of long-period and very long-period events. With the intention of improving the monitoring activities, a submarine fiber optic telecommunications cable linking Vulcano Island to Sicily was interrogated from 15 January to 14 February 2022. Of particular interest has been the recording of 1488 events with wide range of waveforms made up of two main frequency bands (from 3 to 5 Hz and from 0.1 to 0.2 Hz).

With the aim of the automatic detection of seismic-volcanic events, different approaches were explored, particularly investigating whether the application of machine learning could provide the same performance as conventional techniques. Unlike many traditional algorithms, deep learning manages to guarantee a generalized approach by automatically and hierarchically extracting the relevant features from the raw data. Due to their spatio-temporal density, the data acquired by the DAS can be assimilated to a sequence of images; this property has been exploited by re-designing deep learning techniques for image processing, specifically employing Convolutional Neural Networks.

The results demonstrate that deep learning not only achives good performance but that it even outperforms classical algorithms. Despite providing a generalized approach, Convolutional Neural Networks have been shown to be more effective than traditional tecniques in expoiting the high spatial and temporal sampling of the acquired data. 

How to cite: Allegra, M., Currenti, G., Cannavò, F., Jousset, P., Prestifilippo, M., Napoli, R., Sciotto, M., Di Grazia, G., Privitera, E., Palazzo, S., and Krawczyk3, C.: Deep learning approach for detecting low frequency events on DAS data at Vulcano Island, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16459, https://doi.org/10.5194/egusphere-egu23-16459, 2023.

In this study we use distributed acoustic sensing (DAS) on a 41-km-long submarine optical fibre (OF) cable located offshore Toulon, France. We record both the amplitude and frequency of seafloor strains induced by ocean surface gravity waves, as well as secondary microseisms. Combining the analysis of the two types of waves, we identify and localize local sources of secondary microseisms that manifest as Scholte waves generated by the reflection of oceanic gravity waves on the coastline. During the experiment, these local sources represent the most energetic contribution to the seismic noise recorded along the OF and by an onshore broad-band station located near the DAS interrogator. As a result, the characteristics of this noise are closely related to local wave conditions. One major challenge in performing seismic imaging using ambient seismic noise correlations using DAS data is that we cannot solve for the true seismic velocity because the noise wave field is dominated by local sources. To address this, we measure the incident angle of the dominant local noise sources, correct the apparent velocity using the incident angle retrieve from beamforming analysis and generate a 2D model. We then quantify the errors that arise from picking the dispersion curves of the most energetic velocities without correcting from the incident angle. Our results show that there are significant differences in velocities, with differences reaching up to several hundred meters per second. This highlights the importance of correcting these velocities before generating a tomography. Finally we evaluate an alternative strategy for a linear DAS fiber that cannot be use to localized the dominant noise source. We measure the dispersion curve of the slowest Scholte waves recorded and compare it to the corrected dispersion curves of the dominant source. Although this strategy suffers from limitation, it minimizes the error in the velocity model.

How to cite: Guerin, G. and Rivet, D.: Using localized microseismic noise sources to perform high-resolution seismic Imaging of seafloor using Distributed Acoustic Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16640, https://doi.org/10.5194/egusphere-egu23-16640, 2023.

EGU23-17585 | Orals | SM2.1 | Highlight

Why high spatial resolution matters: narrow fault zone, but big effects observed by Taiwan Milun-fault Drilling and All-inclusive Sensing (Taiwan MiDAS) project 

Kuo-Fong Ma, Li-Wei Kuo, Hsin-Hua Huang, Sebastian von Specht, Chin-Jen Lin, Jing-Shan Ku, Chen-Ray Lin, En-Shi Wu, Chien-Yin Wang, and Wen-Yen Chang

Understanding fault zone dynamics in multi-scale is important to embrace the complexity of the earthquake behavior and its natural system. However, the opportunity to map and observe the fault zone behavior at depth with high spatial resolution are rare as also the challenge itself on targeting and identifying the fault zone at depth. We placed a 3D cross-fault fiber array with a downhole loop from surface to depth of 700m for Hole-A (Hanging wall site, crossing fault at depth), after drilling and coring to a frequent slip fault, Milun fault in a plate boundary zone, which ruptured during the 6 February 2018 Mw6.4 Hualien earthquake, and resulted in severe damage to several tall buildings with tens of casualties and injuries. Then, the surface segment crosses the surface fault rupture zone using commercial fiber, and to another downhole loop of 500m fiber for Hole-B (Footwall site). The high spatial resolution from distributed acoustic sensing (DAS) allows us to characterize the fault zone feature together with the retrieved core and geophysical logs after drilling through this frequent slip zone. This 3D route includes the experiment of using commercial fiber to the future application of surface rupture zone identification for seismic hazard mitigation. The project successfully retrieved the fault core associated with Milun fault zone, which could be also seen in geophysical logs with low velocity and resistivity, and mapped using Optical Fiber Sensing technique of the downhole fiber. Within the Milun fault zone, while a 20m thick fault core with grey and black gouge was discovered, a distinct seismic feature associated with this 20m fault gouge was found by its amplification of the strain records from DAS. This amplification ratio is about 2.5-3 when compared to the channels at deeper depth related to a consolidated rock material.  This amplification factor was frequency and azimuth independently, as genuinely observed from all events (e.g. local, and teleseismic earthquakes) with similar amplification factor. Our study shows that the amplification from this 20m fault gouge zone is mainly from the nature of the heterogeneous medium in elastic constant while crossing the fault zone, especially the fault core. Similar feature at surface but with wider surface rupture zone (~ 200m) was found in DAS data as well although less evidence using commercial fiber, while could be validated from the densely deployed geophones crossing the surface rupture of the 2018 Hualien earthquake. Through the depth, a high-resolution asymmetric feature of this active fault was evidenced from the downhole optical fiber and cores. This fault zone behavior would be hardly seen or confirmed without continuous viewing of the wavefields to this high spatial resolution to meter scale. Although the narrow fault gouge, the nature of its amplification in strain due to its strong material contrast from fault gouge was intriguing, and requires intensive attention to consider the contribution of the fault zone heterogeneity in the medium. This might give hints on the understanding of the observation of earthquake dynamics triggering reported worldwide after the occurrence of a mega-earthquake.

How to cite: Ma, K.-F., Kuo, L.-W., Huang, H.-H., von Specht, S., Lin, C.-J., Ku, J.-S., Lin, C.-R., Wu, E.-S., Wang, C.-Y., and Chang, W.-Y.: Why high spatial resolution matters: narrow fault zone, but big effects observed by Taiwan Milun-fault Drilling and All-inclusive Sensing (Taiwan MiDAS) project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17585, https://doi.org/10.5194/egusphere-egu23-17585, 2023.

A workflow is presented to estimate the size of a representative elementary volume and 3-D hydraulic conductivity tensor based on the discrete fracture network (DFN) fluid flow analysis through the case study performed for a granitic rock mass near the low and intermediate level radioactive waste disposal site in southeastern Korea. Intensity and size of joints were calibrated using the first invariant of fracture tensor for the 2-D DFN of the study area. Effective hydraulic apertures were obtained by analyzing the results of field packer tests. The representative elementary volume of the 2-D DFN was determined to be 20m square by investigating the variations in the directional hydraulic conductivity for blocks of different sizes. The directional hydraulic conductivities calculated from the 2-D DFN exhibited strong anisotropy related to hydraulic behaviors of the study area. The 3-D hydraulic conductivity tensor for the fractured rock mass of the study area was estimated from the directional block conductivities of the 2-D DFN blocks generated for various directions in 3-D. The orientations of the principal components of the 3-D hydraulic conductivity tensor were found to be identical to those of the delineated joint sets in the study area.

How to cite: Um, J.-G. and Bae, J.: Estimation of 3-D hydraulic conductivity tensor for a granitic rock mass near the low and intermediate level radioactive waste disposal site in Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1696, https://doi.org/10.5194/egusphere-egu23-1696, 2023.

EGU23-4952 | ECS | Orals | ERE5.2

Poroelastic modeling of borehole-based periodic hydraulic tests in non-fractured and fractured porous rocks 

Nicolás Barbosa, Tobias Müller, Marco Favino, and Klaus Holliger

Characterizing fluid transport and pore pressure diffusion is key for understanding and monitoring many natural (e.g., seismically active zones and volcanic systems) and engineered environments (e.g., enhanced geothermal reservoirs and CO2 underground storage). Borehole hydraulic testing allows to infer relevant properties of the probed sub-surface volume, such as, for example, its transmissivity and diffusivity, for assessing the governing flow regime as well as for detecting the presence of hydraulic boundaries. Periodic hydraulic tests (PHT) achieve these objectives using a time-harmonic fluid injection procedure while measuring the fluid pressure response in monitoring boreholes. The relevant information on the pressure diffusion process occurring in the probed formation is retrieved from the phase shifts and amplitude ratios between the injected flow rate and the interval pressure. In general, the interpretation of PHT data relies on the assumption that the pressure diffusion process is uncoupled from the solid deformation of the probed rock volume. We present a poroelastic numerical approach to investigate the role played by hydromechanical coupling (HMC) effects during PHT and to assess whether and to what extent additional mechanical information can be extracted from these tests. We focus on (i) the influence of the borehole wall deformation on the wellbore storage coefficient Sw, which quantifies the difference between the injected flow rates and those actually entering the porous formation; and on (ii) the HMC effects associated with the presence of fractures in the formation. Following the commonly taken approach, we also interpret the synthetic data from the numerical poroelastic approach using the uncoupled diffusion solution. For different rock physical properties, we demonstrate that, in homogeneous formations, the uncoupled diffusion solution reproduces the poroelastic results. In this scenario, neglecting the effect of the deformation of the borehole wall on Sw upon injection can lead to an underestimation of both the transmissivity and diffusivity, which becomes worse for shorter oscillation periods. We also show that the effective values of Sw depend on the shear modulus of the formation and do not change with the oscillatory period. Based on this evidence, we present a methodology to obtain the effective Sw along with the hydraulic properties using observations at various oscillatory periods. Next, we consider formations containing hydraulically open and compliant fractures intersecting the borehole perpendicularly. Here, a single uncoupled diffusion model is not able to fully describe the poroelastic response of the medium at different periods. Furthermore, the presence of fractures significantly affects the effective value of Sw: it increases with respect to the one associated with the intact homogeneous rock, and the HMC effects associated with the compressibility contrast in the formation result in a period dependence of Sw. The characteristic period of the latter is primarily related to the diffusivity and size of the fractures. This result is particularly relevant for the planning and interpretation of monitoring experiments, in which the mechanical properties of the formation are expected to evolve, such as, for example, hydraulic stimulation procedures, seismic and/or volcanic regions, and injection of wastewater and CO2 for subsurface storage.

How to cite: Barbosa, N., Müller, T., Favino, M., and Holliger, K.: Poroelastic modeling of borehole-based periodic hydraulic tests in non-fractured and fractured porous rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4952, https://doi.org/10.5194/egusphere-egu23-4952, 2023.

EGU23-5623 | ECS | Orals | ERE5.2

The evolution of permeability with pressure and temperature in microfractured granite 

Lucille Carbillet, Michael Heap, and Patrick Baud

Measurements of permeability at high-pressure and high-temperature are critical to model and understand the behaviour and evolution of geothermal systems. To perform such measurements and provide constraints on the permeability of crustal rocks, we designed and tested a new apparatus.

Our high-pressure, high-temperature permeameter consists of three independent parts: the permeant gas circuit, the confining fluid circuit, and the heating element. For each measurement, a cylindrical sample is placed between the up- and downstream platens, into an annular Viton jacket which is secured within the pressure vessel. A confining pressure can be applied to the sample by filling the void space between the vessel and jacket through the inlet with kerosene. The confining pressure can be increased up to 50 MPa using a high-pressure hand pump. The temperature of the system can then be increased from room-temperature to up to 150 °C using a heating mantle wrapped around the pressure vessel and connected to a control box. After the confining pressure and temperature have been applied to the system, the permeability measurement is performed by flowing nitrogen (the permeant gas) through the sample while monitoring the pressure differential between the upstream pressure transducer and atmospheric pressure downstream of the sample at different volumetric flow rates (the steady-state method), measured using the downstream flowmeter.

Using this new experimental apparatus, the permeability of Lanhélin granite (from France) samples were measured. Cylindrical samples were prepared and thermally stressed (heated to 700 °C) to ensure that their permeabilities lie in the range that can be measured in our set-up (> 10-18 m2). Permeability measurements were then performed under confining pressures of 2, 5, 10, 15, 20, 30, 40, and 50 MPa at room temperature, 50, and 100 °C. Our results provide the evolution of the permeability of microfractured granite in various pressure and temperature conditions, which will serve to inform numerical modelling designed to explore the influence of in-situ conditions on fluid flow within a fractured geothermal reservoir.

How to cite: Carbillet, L., Heap, M., and Baud, P.: The evolution of permeability with pressure and temperature in microfractured granite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5623, https://doi.org/10.5194/egusphere-egu23-5623, 2023.

EGU23-5675 | ECS | Orals | ERE5.2

Along-strike fault geometry controls damage zone parameters: the case of the Kornos-Aghios Ioannis Extensional Fault (Lemnos Island, NE Greece) 

Luigi Riccardo Berio, Fabrizio Balsamo, Mattia Pizzati, Fabrizio Storti, Manuel Curzi, and Giulio Viola

The study of fault damage zones is key to the understanding of fault-related fluid flow in the upper crust with many applications, including groundwater and hydrocarbon exploration, and underground storage of CO2 and H. Many studies reveal that a relationship exists between fault damage zone width and net fault displacement. Despite this positive relationship, several factors such as the tectonic setting, the depth of deformation, the deformation mechanisms, and the evolving mechanical properties of fault rocks affect damage zone characteristics (e.g., width, asymmetry, fracture attitude, deformation intensity). Furthermore, recent studies show that the overall along-strike fault geometry may play a pivotal role in controlling damage zone characteristics. In particular, areas such as tip regions, linkage sectors, relay ramps and step-overs can be characterised by fault damage zone parameters markedly different from sectors away from these structural complexities. In this contribution, we present new structural data of fault damage zone parameters acquired along the 8 km long extensional Kornos-Aghios Ioannis Fault (KAIF) on Lemnos Island, North Aegean Sea, Greece. The KAIF deforms lower Miocene effusive and hypabyssal magmatic rocks and middle Eocene to lower Miocene turbidites. Deformed rock volumes along the KAIF are locally strongly altered by hydrothermal fluids (e.g., hydrothermal silicification). We provide a detailed characterization of the KAIF in terms of 2D fault geometry (mapped at 1:1000 scale) and kinematics and we present a characterization of fault damage zone parameters, including frequency and attitude of subsidiary fault-related fractures, in different fault sectors. The acquired data allowed us to define the boundaries of fault damage zones in the different sectors and to discuss the differences in terms of fracture attributes in linking- and tip-damage zones compared to damage zones away from these structural complexities. Our results show that fault damage zones in linkage and tip sectors are wider and that fault-related fractures are more clustered around several subsidiary faults with centimetre- to metre-offsets. Also, secondary fractures in linkage and tip sectors are less systematically oriented, thus increasing fracture network connectivity and, consequently, facilitating fluid mobility in structurally complex fault sectors.

How to cite: Berio, L. R., Balsamo, F., Pizzati, M., Storti, F., Curzi, M., and Viola, G.: Along-strike fault geometry controls damage zone parameters: the case of the Kornos-Aghios Ioannis Extensional Fault (Lemnos Island, NE Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5675, https://doi.org/10.5194/egusphere-egu23-5675, 2023.

Fluid flow within low permeable reservoirs such as carbonates is primarily controlled by faults, fractures and other structural networks which can be defined through properties such as intensity, connectivity and aperture. These properties can vary not only among individual fractures but also between scales which can influence uncertainties within permeability calculations and fluid flow simulations. Therefore, understanding the interactions and variations within these networks is fundamental to deriving properties such as permeability and characterising fluid flow through naturally fractured reservoirs.

Determining fracture network properties of reservoirs can be undertaken using several methods across different scales from both surface and subsurface sources. However, where subsurface data is limited (e.g., within the geothermal reservoirs of Northern Bavaria), outcrop analogues become vital for obtaining the important information required for characterising fracture networks. Outcrops such as quarry sections can be imaged and scanned using both 2D and 3D photogrammetry techniques, from which fault and fracture networks can be detected and analysed. Previous work has presented a method to upscale fracture networks to 2D permeability tensors from outcrop sections through independently assigning properties to individual fractures within the networks. However, upscaling the networks to larger scales can lead to uncertainties due to variations within the modelled fracture networks. It its therefore important to understand the how the permeability tensor varies between scales and dimensions to reduce upscaling uncertainties.

Using examples from multiple outcrops within the Franconian Basin, Germany, we present an improved workflow to derive the tensors between dimensions and an investigation of the relationships among fracture networks at different scales. This will show the effect on permeability within geothermal reservoirs in the region and how to reduce the uncertainty in upscaling outcrops to subsurface reservoir scale.

How to cite: Smith, R., Prabhakaran, R., and Koehn, D.: Investigating scale variations in outcrop derived permeability tensors and the effect on geothermal fluid in upscaling naturally fractured reservoirs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6756, https://doi.org/10.5194/egusphere-egu23-6756, 2023.

EGU23-6830 | ECS | Posters on site | ERE5.2

Comparative analysis of analytical and numerical solutions for hydraulic properties upscaling in fractured media 

Erica De Paolo, Andrea Bistacchi, Stefano Casiraghi, and Fabio La Valle

The investigation of hydro-mechanical properties in rock formations is of utmost importance for several geological and engineering applications, e.g. for carbon-dioxide or hydrogen underground storage, exploitation of groundwater, geothermal or oil and gas reservoirs, hydrothermal ore deposits, and the mechanics of earthquakes. In particular, modeling fluid flow into networks of discontinuities (i.e. faults and fractures) is a key task in all these studies. Due to the high complexity of such processes, involving a significant number of feedbacks and occurring at different spatial and time scales, the achievement of a satisfying representation of the physical problem remains a challenge.

In the last decades, a variety of modeling approaches have been proposed in literature, accounting for different orders of complexity and using several computational methods. Analytical solutions are commonly based on simplistic assumptions about the process, allowing for simple fracture geometries and/or implying incompressible Newtonian fluids; as well as about the medium, considered elastic and permeable (or impermeable). Nevertheless, these solutions are still widely employed, as they provide significantly quick, first-order solutions compared to more sophisticated approaches.

On the other hand numerical models, typically accounting for a higher number of parameters and concurrent effects, are expected to return more realistic solutions. Those based on Finite Element Methods (FEMs) or similarly discretized domains, for example, permit to model the fractured rock mass with information that can be inferred from geological surveys and geophysical techniques.

As anticipated, important limitations in the use of more advanced modeling approaches could be the computing time and model size or resolution, not always allowing for cost-efficient solutions. In this study, we aim at a comprehensive review and benchmarking of the main classes of existing methods, comparing their results obtained for an identical dataset. In this way, we are able to highlight the advantages and disadvantages of each technique, defining the differences in accuracy and the ranges of applicability of these methods. 

The outcomes of our work are intended as a cross-benchmarking among available models, as well as a starting point for the future development of novel improved techniques in the field of fluid flows dynamics in networks of discontinuities.

How to cite: De Paolo, E., Bistacchi, A., Casiraghi, S., and La Valle, F.: Comparative analysis of analytical and numerical solutions for hydraulic properties upscaling in fractured media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6830, https://doi.org/10.5194/egusphere-egu23-6830, 2023.

EGU23-7330 | ECS | Orals | ERE5.2 | Highlight

Structural patterns and states of stress at the Hengill Triple Junction, SW Iceland: implications for fluid-injection induced seismic hazard 

Ashley Stanton-Yonge, Thomas Mitchell, Philip Meredith, Sveinborg Gunnarsdóttir, Sandra Ósk Snæbjörnsdóttir, and Vala Hjorleifsdottir

The Hengill region is one of the largest areas of high geothermal gradient and subsurface heat flow in Iceland, and hosts two of its largest geothermal power plants: Hellisheiði and Nesjavellir, which have a combined capacity of 423 MWe and 560 MWth. The Hengill region is located in a unique tectonic setting, characterized by the convergence of three plate boundary segments: the oblique-spreading Reykjanes Peninsula (RP), the orthogonal-spreading rift of the Western Volcanic Zone (WVZ) and the transform, South Iceland Seismic Zone (SISZ). Unlike most tectonic triple junctions, which occur on the ocean floor, the Hengill Triple Junction (HTJ) is exposed above sea level, thus providing a unique opportunity to study the interplay between three plate boundary segments and the local deformation processes occurring at their convergence site. Additionally, the injection of fluids due to on-going geothermal operations enhances the natural tendency of the region for seismic activity, and results in a significant level of induced seismic hazard. Because slip on pre-existing faults is triggered when the applied shear stress surpasses the frictional strength of the fault, regions that are naturally subjected to higher shear stresses are more prone to fault re-activation due to fluid re-injection. Therefore, a spatial variation in tectonic stresses may result in varying induced seismicity potential within a region.

The local interplay of the three converging tectonic regimes, and their effect on the stress fields within the triple junction region, has been examined through a combination of regional structural mapping and a numerical model of the plate boundary interactions using the Boundary Element Method (BEM). Large scale structural mapping and analytical models of oblique rifting were used to estimate the degree of rift obliquity for individual fissure swarms. Our results reveal that the transition from the highly oblique rift system of the RP towards the spreading-orthogonal rift of the WVZ is smooth, and manifests as a rotation of the trend of fissures and eruptive ridges, and the strike of normal faults formed in response to the local stress field developed in the HTJ. These results were then correlated with those from the BEM model, which allows us to predict the orientation, relative magnitude, and distribution of stresses within the study area. Finally, the shear stress distribution determined from the BEM model was plotted against the location of both natural and induced seismic events detected in the region over a time span of 26 months, by the COSEISMIQ project (Grigoli et al., 2022). Our results show that seismic events cluster in either at the triple junction or SW of it, within the highly stressed regions of the RP. Furthermore, the seismicity transitions from scattered to non-existent towards the north of the region, where shear stresses also diffuse. The good correlation between the high shear stress regions predicted by the model and distribution of seismicity suggests that this approach may provide a valuable and cost-effective tool for seismic hazard prediction within regions with complex tectonic settings.

 

How to cite: Stanton-Yonge, A., Mitchell, T., Meredith, P., Gunnarsdóttir, S., Ósk Snæbjörnsdóttir, S., and Hjorleifsdottir, V.: Structural patterns and states of stress at the Hengill Triple Junction, SW Iceland: implications for fluid-injection induced seismic hazard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7330, https://doi.org/10.5194/egusphere-egu23-7330, 2023.

EGU23-7596 | ECS | Posters on site | ERE5.2

Seismic monitoring of laboratory fault reactivation by pore fluid injection 

Aukje Veltmeijer, Milad Naderloo, and Auke Barnhoorn

Rising demand for energy and green energy has led to increasing subsurface activities, such as geothermal energy sites. These increasing human activities in the subsurface have caused substantial induced earthquakes in more densely populated areas, increasing the risks of operating safely. Well-known examples of induced seismicity, due to geothermal sites, are the M5.4 earthquake in Pohang (South Korea) or the M3.4 earthquake in Basel (Switzerland).  

Monitoring and forecasting earthquakes have been a topic of interest for years. Predictions are often made by production scenarios, probabilistic models, or average earthquake size distribution (b-value). Only a few studies focus on predicting fluid-induced seismicity by using seismic monitoring methods. Pore fluid changes play an important role in the reactivation of the fault strength and stability. Variations in pore pressure can cause a drop in the stresses along the fault plane and cause fault instability and movement resulting in induced seismicity.  Monitoring and predicting the stress changes along the fault planes can therefore be essential in forecasting induced seismicity and mitigation, potentially reducing the risks of operating (in denser populated areas). However, monitoring the degree of these changes remains challenging. Most studies using seismic methods to monitor induced seismicity on a field scale or laboratory scale focus on either passive monitoring or active monitoring. This study combines the two methods and shows how they complement each other in monitoring and mitigation of fault reactivation in the laboratory. We have performed pore fluid injection experiments on faulted sandstones to reactivate the faults while monitoring both actively (active seismic) and passively (acoustic emission).

These results show that both acoustic monitoring techniques can be used to detect the different fault reactivation stages: linear strain build-up, early creep (pre-slip), stress drop (main slip), and continuous sliding phase. However, using active monitoring the early creep phase is detected slightly earlier than using passive monitoring. Combining the methods shows that the stress changes along the fault can be detected with more detail in more accuracy. As a result, the combination of passive and active techniques may be useful for monitoring faulted or critically stressed reservoirs that experience pore pressure changes.

How to cite: Veltmeijer, A., Naderloo, M., and Barnhoorn, A.: Seismic monitoring of laboratory fault reactivation by pore fluid injection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7596, https://doi.org/10.5194/egusphere-egu23-7596, 2023.

EGU23-8016 | Posters on site | ERE5.2

Hydrochemical Stimulation in Fractured Carbonate Rocks - Monitoring and Simulation 

Jörn Bartels, Peter Schätzl, and Thomas Baumann

Hydrochemical stimulation by acidification of geothermal wells is a standard procedure to remove drilling mud and to improve hydraulic contact between borehole and reservoir. Several successive stimulations using hydrochloric acid were monitored by both online measurement and conventional analysis. The results show recovery curves with distinct two-step exponential temporal decrease of the chloride concentration. The initial decrease is fast, representing water and acid flow along pathways which are very well connected to the borehole. After the fluid from these flow paths has been recovered, the concentration decreases at a lower rate. This can be attributed to water flowing in less well connected flow paths. With additional stimulations the chloride concentration curve approaches a mono-exponential decrease. This indicates that the flow paths within the reach of the stimulation get more homogeneous.

A numerical model of flow and solute transport in the borehole and the surrounding geothermal reservoir was developed in order to simulate the observed chloride-recovery behaviour in the course of a number of successive hydrochemical stimulations. The finite-element model was adapted to match the observed hydraulic and hydrochemical data range.

Simulation hereby allows to separate time-dependent single contributions from the different flow paths to the total recovery concentration. Based on this information, indications of structural change due to the successive acidification steps can be derived from the chloride-recovery curves of each step. Furthermore, for typical settings the minimum time and volume of solution can be estimated which is required to achieve a significant structural signal

The derived structural information can be useful to predict the long-term behaviour of a geothermal injection well which during operation is exposed to a mild but constant chemical stimulation by the injected cold and, with respect to chloride in the rock matrix, undersaturated water. 

How to cite: Bartels, J., Schätzl, P., and Baumann, T.: Hydrochemical Stimulation in Fractured Carbonate Rocks - Monitoring and Simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8016, https://doi.org/10.5194/egusphere-egu23-8016, 2023.

EGU23-8221 | ECS | Posters on site | ERE5.2

Slip tendency and reactivation pressure prediction of natural fractures at the Bedretto Underground Laboratory, Switzerland 

Kai Bröker, Xiaodong Ma, Deborah Stadler, Nima Gholizadeh Doonechaly, Marian Hertrich, and Domenico Giardini and the Bedretto Team

Hydraulic shearing of natural fractures or fault zones is a key mechanism for enhancing permeability in engineered geothermal systems (EGS) in order to extract geothermal energy from crystalline basement rocks. Shear reactivation is achieved by hydraulic stimulation in an injection borehole, involving a complex hydro-seismo-mechanical response of fractured crystalline rock. A major challenge is to predict which fractures are reactivated at which reactivation pressures, in order to efficiently design the injection protocols and create a large fracture network for sufficient fluid circulation and heat exchange.

The Bedretto Underground Laboratory for Geosciences and Geoenergies (BedrettoLab) in Switzerland serves as an in situ test-bed where meso-scale hydraulic stimulation experiments are conducted to better bridge the knowledge gap between laboratory scale experiments and complex reservoir scale processes (Ma et al. 2022). The BedrettoLab is located in a 100 m long enlarged section of the Bedretto tunnel (Ticino, Switzerland), with an overburden of more than 1000 m of granite. Several characterization, monitoring, and two stimulation boreholes were drilled. One of the stimulation boreholes (referred to as ST1) is 400 m long, 45°-dipping, and was equipped with a multi-packer system that partitions the borehole into 15 intervals. Before conducting two multi-stage hydraulic stimulation phases in borehole ST1, the rock volume was characterized with various geophysical logging tools, hydraulic tests, and mini-frac tests for stress measurements (Bröker and Ma 2022, Ma et al. 2022).

Along the stimulation borehole, we mapped multiple clusters of sub-parallel pre-existing open fractures and fault zones that are preferentially oriented for reactivation in the estimated stress field. In this work, we compare our preceding probabilistic slip tendency and reactivation pressure estimates with the results from hydraulic stimulation experiments. The interval pressure and flowrate data from the stimulations reveal a reactivation of the natural fractures associated with an increase in injectivity. A comparison of the expected stress field around the stimulation interval with the observed reactivation pressure indicates that the fractures were likely reactivated by hydraulic shearing. The observed reactivation pressures are in the range of the preceding estimates, but a precise estimation is challenging due to the large number of input parameters, i.e. stress magnitudes and orientation, fracture orientation, pore pressure, coefficient of friction, and their uncertainties.

References:

Bröker, K., & Ma, X. (2022). Estimating the Least Principal Stress in a Granitic Rock Mass: Systematic Mini-Frac Tests and Elaborated Pressure Transient Analysis. Rock Mechanics and Rock Engineering. https://doi.org/10.1007/s00603-021-02743-1

Ma, X., Hertrich, M., Amann, F., Bröker, K., Gholizadeh Doonechaly, N., Gischig, V., Hochreutener, R., Kästli, P., Krietsch, H., Marti, M., Nägeli, B., Nejati, M., Obermann, A., Plenkers, K., Rinaldi, A. P., Shakas, A., Villiger, L., Wenning, Q., Zappone, A., … Giardini, D. (2022). Multi-disciplinary characterizations of the BedrettoLab -- a new underground geoscience research facility. Solid Earth, 13(2), 301–322. https://doi.org/10.5194/se-13-301-2022

How to cite: Bröker, K., Ma, X., Stadler, D., Doonechaly, N. G., Hertrich, M., and Giardini, D. and the Bedretto Team: Slip tendency and reactivation pressure prediction of natural fractures at the Bedretto Underground Laboratory, Switzerland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8221, https://doi.org/10.5194/egusphere-egu23-8221, 2023.

EGU23-9317 | ECS | Orals | ERE5.2

Effect of stress regime change on fractured carbonate’s permeability: A case of Latemar carbonate buildup (The Dolomites, Northern Italy)  

Onyedika Anthony Igbokwe, Jithender Timothy, Ashwani Kumar, Xiao Yan, Mathias Mueller, Alessandro Verdecchia, Günther Meschke, and Adrian Immenhauser

Changes in stress regimes impact the geometry of fracture networks and affect the porosity and permeability of carbonate reservoirs. This is, predominantly, because of the complexity of the deformation phases, the poor understanding of the mechanical and diagenetic mechanisms that affect apertures, and the difficulty in precisely characterizing aperture distributions in the subsurface. Utilizing outcrop data analysis and displacement-based linear elastic finite element modelling, we study the effect of stress regime change on fracture network permeability. The model is based on fracture networks, specifically fracture sub-structures.

The Latemar, which is primarily affected by subsidence deformation and Alpine compression, is used as an outcrop analogue for isolated (Mesozoic) carbonate formations with fracture-dominated permeability. We apply a novel strategy involving two compressive boundary loading conditions constrained by the study area's NW-SE and N-S stress directions. Stress-dependent heterogeneous apertures and effective permeability were computed by: (i) using the local stress state within the fracture sub-structure and (ii) running a single-phase flow analysis considering the fracture apertures in each fracture sub-structure.

Our results show that the impact of the modelled far-field stresses at: (i) subsidence deformation (first stage loading) from the NW-SE, and (ii) Alpine deformation (second stage loading) from the N-S, increased the overall fracture aperture and permeability. In each case, increasing permeability is associated with open fractures parallel to the orientation of the loading stages and with fracture densities. The anisotropy of permeability is affected by shear dilation and is increased by the density and connectedness of the fracture network. The two far-field stresses simultaneously acting within the selected fracture sub-structure at a different magnitude and orientation do not necessarily cancel out each other in the mechanical deformation modelling. These stresses effect the overall aperture and permeability distributions. These effects, which may be ignored in simpler stress-dependent permeability, can result in significant inaccuracies in permeability estimation, especially in the subsurface carbonate reservoirs.

How to cite: Igbokwe, O. A., Timothy, J., Kumar, A., Yan, X., Mueller, M., Verdecchia, A., Meschke, G., and Immenhauser, A.: Effect of stress regime change on fractured carbonate’s permeability: A case of Latemar carbonate buildup (The Dolomites, Northern Italy) , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9317, https://doi.org/10.5194/egusphere-egu23-9317, 2023.

EGU23-9661 | Orals | ERE5.2

Quantitative structural analysis of fracture networks in outcrop analogues of fractured reservoirs: a review of measurement methodologies and statistical techniques 

Andrea Bistacchi, Sylvain Mayolle, Stefano Casiraghi, Erica De Paolo, Mattia Martinelli, Federico Agliardi, and Fabio La Valle

The characterization and modelling of fractured reservoirs of geofluids are becoming increasingly important in the ongoing energy transition and climate crisis. Fractured reservoirs are fundamental for critical applications such as CO2 sequestration, H2 and natural gas storage, exploitation of geothermal fluids and hydrothermal ore deposits, and management and safeguard of groundwater resources (deep aquifers are considered more resilient in drought scenarios). In addition, the characterization of fracture networks is relevant in earthquake mechanics, slope stability and engineering geology.

Characterization of natural fracture systems and fracture networks is often based on characterization of outcrop analogues, with measurement of large structural datasets with a combination of field and remote sensing techniques (e.g. Digital Outcrop Models - DOMs), leading to statistical and topological analysis. Numerous studies provide significant amounts of data from a broad variety of methodologies and protocols used in the field. These methodologies aim at characterizing fracture systems by a large number of parameters. Individual “fracture” sets are characterized by genetic features (e.g. joint vs. stylolite), relative chronology, spatial distribution (regular, random, clustered...), density and intensity (e.g. P20 and P21), and by statistical distributions of spacing, orientation, length, height, and aperture (the latter being a dynamical property that varies with fluid pressure and confining stress). Fracture networks composed by several sets are also characterized by topology and connectivity (characterized for instance in terms of fracture terminations or with graphs).

Here we propose a thorough review, supported by rich case studies, of quantitative methods for fracture network characterization and analysis on DOMs. This review aims at determining the most relevant and efficient methods for field and remote-sensing measurement, and best-practice statistical analysis techniques, in order to accurately characterize outcrop analogues that can be used to model fractured reservoirs.

How to cite: Bistacchi, A., Mayolle, S., Casiraghi, S., De Paolo, E., Martinelli, M., Agliardi, F., and La Valle, F.: Quantitative structural analysis of fracture networks in outcrop analogues of fractured reservoirs: a review of measurement methodologies and statistical techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9661, https://doi.org/10.5194/egusphere-egu23-9661, 2023.

EGU23-9673 | ECS | Posters on site | ERE5.2

Deformation bands characterization in porous carbonates: a case study from the Matera High (Southern Italy) 

Giovanni Freda, Silvia Mittempergher, Fabrizio Balsamo, Raffaele Di Cuia, and Angelo Ricciato

Faults and fractures have a crucial role in controlling the permeability in carbonate reservoirs, as they can act as a conduit or barrier for fluid flow. Reservoir-scale outcrop analogue studies provide a useful tool to investigate their spatial distribution and connectivity and to establish the relationships between small-scale structures with larger structures that can be identified in the subsurface.

In this contribution, we describe the preliminary results of a structural study carried out in the Matera's High, South Italy, as an analogue for porous carbonate structures that could be used as CO2 storage fields. Matera High is located on the western side of the Murge region, at the boundary between the Apulian foreland and the foredeep of the southern Apennines thrust belt. It consists of an asymmetrical horst structure involving the Cretaceous carbonates of the Apulian platform (Calcare di Altamura). The Calcare di Altamura is unconformably overlain by Plio-Pleistocene shallow-marine coarse-grained carbonates (Calcarenite di Gravina). The Calcare di Altamura is moderately tilted and is characterised by NW-SE striking normal faults with a throw variable from centimetres to tens of meters. The Cretaceous sequence is also characterised by widespread joints, whose intensity increases approaching faults. The Plio-Pleistocene carbonate succession has very few faults. It is dominated by deformation bands organized into 3 main sets dipping at high angles and striking N-S, NW-SE, and NE-SW. This geological setting allows us to conduct a detailed structural study on an area of about 80 km2, investigating how deformation structures affect the secondary porosity in tight limestone and porous calcarenites. The study was conducted at multiple scales in the field and laboratory and includes (1) geological mapping and structural measurements of faults, fractures and deformation bands; (2) use of linear scan-lines to characterise the deformation bands density across faults; (3) use of photogrammetric techniques to obtain Virtual Outcrop Models (VOMs); (4) development of 3D model based on statistical and topological analysis obtained from scan lines and scan areas in the field and VOMs, (5) petrophysical logging (uniaxial strength, in situ permeability, gamma ray) to highlight the factors that control the formation of the deformation bands, (6) image analysis of blue-resin impregnated thin section and optical cathodoluminescence images, and (7) He-density and Hg-intrusion porosimetry to quantify host rock and deformation bands porosity and pore size distribution.

The preliminary results suggest that the combination of fieldwork, VOMs and laboratory measurements allow the characterization of the deformation bands with more confidence to obtain conceptual and quantitative models about its effects on the fluid flow which can be used for reservoirs characterization for CO2 sequestration.

How to cite: Freda, G., Mittempergher, S., Balsamo, F., Di Cuia, R., and Ricciato, A.: Deformation bands characterization in porous carbonates: a case study from the Matera High (Southern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9673, https://doi.org/10.5194/egusphere-egu23-9673, 2023.

EGU23-9694 | ECS | Posters on site | ERE5.2

Modelling fluid flow and water-rock interaction in fractured crust using a Discrete Fracture Network approach 

Ibrahim Harb, Fidel Grandia, Paolo Trinchero, and Jeffrey Hyman

Groundwater accounts for around 25% of the world’s fresh water supply. Due to the increasing anthropogenic pressure on shallow aquifers as well as climate change that is impacting global groundwater recharge, there is an increasing need to access deeper groundwater resources, which are frequently hosted in fractured-rock formations. The migration of groundwater (and other types of fluids, in general) in fractured rocks allows the contact between fluids in geochemical disequilibrium with the host rocks (i.e., large geochemical gradients) promoting water-rock reactions inside the fractures. These reactions may influence the permeability and porosity, as well as they may lead to fracture sealing. So, a thorough understanding of the coupled hydro-chemical processing that occur in fractured media is important for applications such as the sustainable exploitation of the afore-mentioned reserves, the protection and remediations of aquifers used for drinking water production or the safety analyses of deep geological repositories for spent nuclear fuel, energy storage, nuclear waste disposal sites, etc.. In fractured rocks, groundwater flows in specific pathways and interacts with the host rock which may lead to the change in the hydro-geochemical conditions. The prediction of these interactions become critical for a proper management of the different applications. Therefore, the understanding and modelling of fluid-fracture interaction is of high scientific and commercial interest.

Using the software dfnWorks, it is possible to model the fluid transport using a non-reactive Lagrangian method (particle tracking). In this contribution, we intend to implement geochemical reactions in dfnWorks to quantify the impact of these reactions in the fracture network. In fact, flow of water through Discrete Fracture Networks leads to interaction between water and the minerals occurring in the fracture plane and thus alters the underlying groundwater flow patterns. Thus, using these DFN-based reactive transport simulations, we aim at predicting the effect that chemical reactions have on flow and channeling. Besides presenting a proof-of-concept set of calculations, we will also present preliminary results of a real-case application, where fracture filling is produced as a result of a chemical imbalance.

How to cite: Harb, I., Grandia, F., Trinchero, P., and Hyman, J.: Modelling fluid flow and water-rock interaction in fractured crust using a Discrete Fracture Network approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9694, https://doi.org/10.5194/egusphere-egu23-9694, 2023.

EGU23-10311 | Orals | ERE5.2

Use of Mohr diagrams to predict fracturing in rock 

David Peacock, Bernd Leiss, and David Sanderson

Inferences have to be made about likely structures and their effects on fluid flow in a geothermal reservoir at the pre-drilling stage. This is the case for the potential geothermal reservoir in Variscan metasedimentary rocks that are expected to occur in the subsurface at Göttingen. Simple mechanical modelling, using reasonable ranges of values for rock properties, stresses and fluid pressures, is used here to predict the range of possible structures that are likely to exist in the sub-surface and that may be generated during thermal and hydraulic stimulation. Mohr diagrams are a useful way for predicting and illustrating how rocks can go from a stable stress state (i.e., no fracturing occurs) to an unstable stress state (i.e., fracturing occurs). This transition can occur if there are changes in: (1) the failure envelope; (2) the stresses; and/or (3) fluid pressure. Mohr diagrams are used to show under what fluid pressures and tectonic stresses different types and orientations of fractures are likely to be reactivated or generated. The approach enables the effects of parameters to be modelled individually, and for the types and orientations of fractures to be considered. This modelling is useful for helping geoscientists consider, model and predict the ranges of mechanical properties of rock, stresses, fluid pressures and the resultant fractures that are likely to occur in the sub-surface.

The Mesozoic rocks of the Somerset coast, UK, are used to illustrate how Mohr diagrams can help understand the history of fracturing. Such understanding is useful for predicting which fractures are likely to occur in the subsurface, which is important for predicting reservoir behaviour.

How to cite: Peacock, D., Leiss, B., and Sanderson, D.: Use of Mohr diagrams to predict fracturing in rock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10311, https://doi.org/10.5194/egusphere-egu23-10311, 2023.

Pore fluid pressure in the geological formation at depth varies spatially and temporarily. An increase in pore fluid pressure leads to a reduction in effective normal stress and thus affects the rock strength and deformation mode. Extremely high pore fluid pressure induces very low normal stress conditions, where an extension or extension-shear hybrid fractures are formed. To better quantify the stress states and fluid pressure during fracture formation, it is crucial to document mechanical strength and the transition from tensile to shear fracture at low effective stress with elevated pore fluid pressure. However, all previous experimental studies were conducted under dry conditions. Here, we investigate the effects of pore fluid pressure on tensile and hybrid fractures in Berea sandstone by conducting triaxial extension deformation experiments under pore-fluid-pressure controlled conditions at effective maximum principal stress (σ1' = σ1 - Pp, where σ1 is total maximum principal stress and Pp is pore fluid pressure) ranging from 10 to 130 MPa. Fracture strength, inelastic strain, strain at failure, fracture angle to σ1', and the amount of comminution increase with σ1'. The transition of extension to shear fracture occurs at σ1' = ~ 30 MPa, based on the fracture angle and the degree of comminution. All the saturated or pore fluid pressure-controlled test specimens exhibit lower fracture strength than dry samples, and the difference is distinct when the minimum principal stress is tensile (i.e., σ3' < 0). This implies that pore fluid pressure more effectively assists the breakage of the bonds and opening of the microcracks in the extension fracture regime. A series of triaxial extension experiments at σ1' = 20 and 50 MPa with various combinations of σ1 and Pp indicate that the fracture angle to σ1' is independent of σ1 and Pp in the extension fracture regime at σ1' = 20 MPa, and that fracture angle increases with σ1 and Pp in the extension-shear hybrid fracture regime at σ1' = 50 MPa. This implies that the estimation of in-situ stress and pore fluid pressure from natural or human-induced deformation at low effective pressure (such as joints, veins, and drilling-induced tensile fractures) requires careful consideration of the mode of fractures formed.

How to cite: Kitajima, H., Ruplinger, C., and Tilley, C.: Experimental investigations on effects of pore fluid pressure on extension and extension-shear mixed-mode fracture in Berea sandstone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10433, https://doi.org/10.5194/egusphere-egu23-10433, 2023.

EGU23-10795 | ECS | Posters on site | ERE5.2

Phase field method to model mixed-mode fracturing in fluid saturated porous reservoir 

Swapnil Kar and Abhijit Chaudhuri

                                        Hydraulic fracturing is a useful stimulation technique to create cracks in unconventional reservoirs and enhance the effective fluid transmissivity to recover gas from natural gas reservoirs or heat from geothermal reservoirs. However, due to fracturing the overall strength and load bearing capacity of the reservoir is compromised. This may be a serious concern if the reservoir is below a dam or any other massive structures. In such case significant settlement can take place as the result of mixed mode fracturing inside the reservoir which might already have natural fractures. Phase field method based on the formulation of mixed-mode fracturing has been adopted in the present work for modeling fracture propagation in a saturated porous medium when subjected to fluid pressure and increasing overburden load. A numerical method has been developed using Finite element method (FEM) for solving the displacement and damage field, and Finite volume method (FVM) for solving flow field due to its flux conservative nature which is automatically satisfied for each FVM cell. Our FEM code alone has been first validated for modelling mixed mode fracturing considering a single fracture as a notch against the published experimental and numerical results for elastic medium subjected to compressive load. In this method, the notch does not have any material and computational mesh is refined around the notch as commonly done by others. We have later developed an alternative method where the pre-existing crack is modelled as a fully damaged zone. In this method, a structured and uniform grid can be used to obtain same fracturing pattern and load-deflection curve. The alternative method has a few advantages such as it can be easily applied for reservoir with many cracks without any grid refinement around the pre-existing cracks, and it can be easily coupled with FVM code for modeling fluid flow. Our numerical modelling code is capable to simulate fracturing along with the branching and merging effects. We have simulated load-bearing capacity of a fractured reservoir subjected to increasing overburden load. The reservoir is considered to consists of many randomly oriented but poorly connected natural fractures. The load-bearing capacity and load-deflection curves are compared for reservoirs with and without hydraulic fracturing. The simulations have been performed for different set of natural fractures to understand the effect of fracture density and other fracture network properties on the load-deflection curves.

How to cite: Kar, S. and Chaudhuri, A.: Phase field method to model mixed-mode fracturing in fluid saturated porous reservoir, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10795, https://doi.org/10.5194/egusphere-egu23-10795, 2023.

 Deep geothermal reservoirs are often naturally or hydraulically fractured media which consist of a rock matrix and a network of randomly oriented discrete fractures of different sizes. In the present study, a three-dimensional model of coupled flow, heat transfer and deformation of fractured geothermal reservoir is developed. Because of high thermal expansibility and high mobility, supercritical C02 is under consideration as an alternative fluid to water/brine for extracting energy from geothermal reservoir. However, for simulation of CO2 based EGS, two phase flow model should be included and this makes the coupled model far more nonlinear and complex. FEHM which is one of the most robust code developed at LANL is capable to simulate the multi-physics problem of geosciences. We have found that the computational cost for CO2 based EGS a few times higher than that of water based EGS. Due to temperature drawdown and pressure difference between injection and production wells thermo-poro-elastic stresses are induced within the reservoir. This can influence larger shear dislocation, and normal opening /closing of fracture causing changes in the fracture aperture and permeability during the extraction of the geothermal energy from a reservoir. The correlation of the variation of fracture permeability with the variation of the local stress tensor has been taken into account in this study. To study the permeability alteration on geothermal energy extraction for water and CO2  based EGS different fracture networks, different values of injection temperature and injection pressure are considered. Three-dimensional fracture networks of randomly oriented rectangular fractures with different sizes, and dip angles are created using ADFNE Matlab code. A structured computational mesh is created for simulating the multiphase flow, heat transfer and geomechanics. The nodes belonging to the fractures are assigned appropriate permeability, thermal conductivity and mechanical properties depending on the fracture aperture. The values of these properties are subjected to alteration based on local stress values.

How to cite: Adhikary, S. S. and Chaudhuri, A.: Thermo-poro-elastic stress induced aperture alteration of fractured geothermal reservoir and its effect on geothermal energy production, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10797, https://doi.org/10.5194/egusphere-egu23-10797, 2023.

EGU23-12483 | ECS | Orals | ERE5.2

Mineralogical control on fault friction and stability: a systematic study on quartz, calcite and muscovite ternary mixtures. 

Roberta Ruggieri, Giacomo Pozzi, and Cristiano Collettini

During fault evolution different rock types are fractured and sheared within the fault core, producing fault gouges with heterogeneous mineralogical composition. Mineral composition exerts a primary control on fault frictional properties and hence on fault slip behaviour. Understanding the conditions that lead to seismic or aseismic fault slip is of great interest to earthquake hazard assessment both for natural and induced seismicity. Although the effect of single mineral phases is probably the most documented factor in laboratory tests, no clear link has been established to understand how systematic variation of different mineral phases in gouge mixtures influences the macroscopic frictional behaviour.

Here we present an experimental study designed to probe the control of mineral composition on fault friction and stability responses. We selected three representative mineral phases, commonly found in fault zones, that are known to have severely different frictional properties: muscovite (phyllosilicate), quartz (granular silicate) and calcite (granular carbonate). Thirty double direct shear experiments were performed using a biaxial rock deformation apparatus (BRAVA) on powders (with grain sizes < 125 µm) of pure minerals and their mixtures at normal stress of 50 and 100 MPa, at room temperature and water saturation conditions. After an initial sliding of 10 mm at 10 µm/s to develop a steady state shear fabric, slide‐hold‐slide sequences (30-1000 s) and velocity steps (0.3-300 µm/s) were employed to evaluate static healing and frictional stability, respectively.

Our experimental data indicate that the mineralogical composition of fault gouges significantly affects the frictional strength, healing, and stability with a non-trivial pattern. Increasing phyllosilicate (muscovite) content results in a decrease of the frictional strength, from 0.62 for pure calcite and 0.56 for pure quartz down to 0.33 for pure muscovite powders. This effect is more marked in calcite-rich mixtures rather than quartz-rich ones, possibly due to favourable conditions for fluid-assisted pressure-solution at grain contacts. Calcite-muscovite interaction also favours a reduction of frictional healing and a more marked velocity-strengthening behaviour (promoting stable sliding and fault creep) in comparison to quartz-muscovite mixtures.

How to cite: Ruggieri, R., Pozzi, G., and Collettini, C.: Mineralogical control on fault friction and stability: a systematic study on quartz, calcite and muscovite ternary mixtures., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12483, https://doi.org/10.5194/egusphere-egu23-12483, 2023.

EGU23-13820 | ECS | Orals | ERE5.2

Electric self-potential monitoring of hydraulic fracturing experiments in the Äspö Hard Rock Laboratory, Sweden. 

Nadine Haaf, Luis Guarracino, Damien Jougnot, and Eva Schill

A number of six in situ hydraulic fracturing experiments were carried out at the Äspö Hard Rock Laboratory (Sweden) in 2017 in a depth of 410 m. Here we present electric self-potential monitoring during the conventional and the step-wise cyclic injection experiments HF2 and HF3. Electric self-potential data were acquired through a two-sensor array, each including nine measuring probes and one base probe, that were installed at the 410 m and 280 m levels. The experimental borehole F1 is drilled in the direction of Shmin, perpendicular to the expected fracture plane. The self-potential sensors are installed sub-parallel to Shmin at level 410 at a distance of 50-75 m to the borehole F1 and sub-perpendicular to Shmin at level 280 m at a distance of 150-200 m to F1. The self-potential data were measured with a sampling rate of 1 Hz. Here, we propose a 1-D modelling of the streaming potential that approximates the measured self-potential data. These streaming potential gradients ∆V are estimated from the simulated pressure signals and the coupling coefficient.

How to cite: Haaf, N., Guarracino, L., Jougnot, D., and Schill, E.: Electric self-potential monitoring of hydraulic fracturing experiments in the Äspö Hard Rock Laboratory, Sweden., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13820, https://doi.org/10.5194/egusphere-egu23-13820, 2023.

EGU23-13949 | ECS | Posters on site | ERE5.2

Permeability and Compressibility Evolution of Fractured and Intact Reservoir Rocks from the Blue Mountain Geothermal Field, Nevada 

Valerian Schuster, Erik Rybacki, Anja M. Schleicher, Trenton T. Cladohous, Roshan Koirala, and Thomas H.W. Göbel

Many reservoir rocks of productive geothermal energy resources display low porosity and matrix permeability. Therefore, to enhance fluid flow, fault zones and natural fracture networks are increasingly targeted for geothermal energy exploitation that are hydraulically connected to geothermal wells by stimulating the reservoir units. To this end, fluid is injected into the reservoir, which is generally believed to reduce effective stress and induce minor slip along stressed faults. Fluid injection can also lead to induced microseismicity and remotely-triggered earthquakes at great distances from the target reservoirs. The Blue Mountain geothermal field produces the largest seismic activity during maintenance shutdowns of injection and production requiring additional mechanisms such as poroelastic stress effects. In order to improve seismic hazard assessment and the understanding of induced seismicity around injection wells, we explore the coupling between matrix permeability, fault zone hydrology and mechanical behavior.

One main goal of this work is to provide insight into the scale-dependence of permeability by comparing laboratory results with previous permeability measurements using tidal responses in three different idle wells in Blue Mountain. We present a series of laboratory experiments performed on rock samples collected from the DB2 well at the Blue Mountain geothermal site in Humboldt County, Nevada, USA. The geothermal field benefits from the intersection of two W- and NW-directed normal faults resulting in high permeability of the geothermal reservoir production zone controlled by a brittle damage zone. Samples were obtained from two different lithologies, both of Triassic age, that constitute the reservoir. The first set of samples are low-porosity, (0.4 vol%) quartz-dominated (~50 – 60 wt%) phyllites, which exhibit zones with pronounced fracturing and elevated porosity (3.8 vol%). The second set of samples are felsic intrusive rocks with moderate to high porosity (7 – 15 vol%) due to strong hydrothermal alteration and clay mineral formation. Samples from both lithologies were selected from different sections of the damage zone showing varying degrees of faulting, from intact to highly brecciated, containing mineralized veins. We determine flow and poroelastic properties of cylindrical samples with a length of 2 cm and a diameter of 5 cm, subjected to stepwise cyclic variation of pore (<40 MPa) and confining pressure (<45 MPa). At each pressure step, we measure volumetric strain changes to derive the bulk modulus and effective stress coefficient, and use steady-state or pore pressure oscillation to determine permeability.

In addition to the tidal response and laboratory results, we developed a high-resolution seismicity catalog based on more than three years of continuous waveforms records from 2016 to 2019. We performed template-matching and differential travel-time inversions and use the resulting seismic events with magnitudes between 0.7 – 2.7 to search for seismicity migration patterns associated with discrete injection events. Integration of field and laboratory results can improve the characterization of the permeability structure of the fault zone at Blue Mountain and help to understand the mechanisms that trigger seismic events during production shutdown as well as the role of poroelastic stress release.

How to cite: Schuster, V., Rybacki, E., Schleicher, A. M., Cladohous, T. T., Koirala, R., and Göbel, T. H. W.: Permeability and Compressibility Evolution of Fractured and Intact Reservoir Rocks from the Blue Mountain Geothermal Field, Nevada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13949, https://doi.org/10.5194/egusphere-egu23-13949, 2023.

EGU23-14955 | Posters on site | ERE5.2

Equivalent Biot and Skempton coefficients for fractured rocks 

Silvia De Simone, Caroline Darcel, Hossein A. Kasani, Diego Mas Ivars, and Philippe Davy

Biot coefficient and Skempton coefficient are key descriptors of the coupled hydro-mechanical (HM) behavior of fluid-saturated porous materials. Biot coefficient defines a relationship between an applied load, fluid pressure and the stress that effectively acts on the solid skeleton. Skempton coefficient defines the temporary pore pressure variation caused by the application of a load in undrained conditions. The product of the two coefficients establishes the impact of an applied load on the solid skeleton, and thus the material deformation, under undrained conditions. The two coefficients are generally estimated through analytical expressions valid for isotropic homogeneous materials, or they are experimentally estimated at the laboratory sample-scale.

In this work, we define a framework for the evaluation of equivalent Biot coefficient and Skempton coefficient at the scale of a fractured rock mass. We derive theoretical expressions that estimate the two equivalent coefficients from the properties of both the porous intact rock and the discrete fracture network (DFN), including fractures with different orientation, size, and mechanical properties. These formal expressions are validated against results from fully coupled hydro-mechanical simulations on systems with explicit representation of deformable fractures and rock blocks. We show that the coefficients largely vary with the fracture orientation and density, which implies that disregarding the presence of fractures may incur an incorrect evaluation of the HM response. We also discuss the variability of the coefficients under different settings of DFN properties, including realistic scaling conditions of size-dependent and stress-dependent fracture properties.

How to cite: De Simone, S., Darcel, C., Kasani, H. A., Mas Ivars, D., and Davy, P.: Equivalent Biot and Skempton coefficients for fractured rocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14955, https://doi.org/10.5194/egusphere-egu23-14955, 2023.

EGU23-14982 | Orals | ERE5.2

Constraining the impact of cyclic hydraulic stimulation on granites 

Jackie E. Kendrick, Julian Mouli-Castillo, Anthony Lamur, Andrew Fraser-Harris, Alexander Lightbody, Mike Chandler, Katriona Edlmann, Christopher McDermott, and Zoe Shipton

Subsurface engineering, such as geothermal energy extraction, requires knowledge of the rupture of geomaterials. Of particular importance is the time- and rate-dependence of material strength, which impacts fracture architecture and thus hydraulic conductivity and system permeability. Cyclic soft stimulation (CSS) techniques have been developed to maximise the efficiency of resource extraction whilst minimising large amplitude, fluid-injection induced seismicity. Here, we explore the benefits of cyclic stimulation experimentally, utilising novel “pulsed pumping” hydraulic fracture tests in which fluid pressure is cycled within the central borehole of a suite of 20x20cm cylinders of dense granite. The response is monitored at high-resolution by fibre-optic circumferential strain measurements, fluid pressure data and acoustic emission recording. Using cyclic high-low pressure square waves, we found that breakdown pressure was reduced by up to 15% compared to the monotonic case in which pressure was increased by applying a constant flow rate. Whilst peak pressure had the primary control on the number of cycles to failure, increasing the minimum pressure in the borehole (thus increasing mean pressure) further reduced breakdown pressure, suggesting that even small pressure fluctuations during hydraulic stimulation may reduce the largest stress drops, and hence the magnitude of induced seismic events. Strain measurements detected accelerating precursory deformation a few cycles prior to failure, hinting at the opportunity for responsive stimulation practices where activity can be monitored in real-time. These novel large-scale, high-resolution experiments were complemented by indirect tensile measurements at a range of strain rates, and by cyclic fatigue Brazilian disc testing at a range of peak loads and cycle amplitudes. These results further highlight the increasing contribution of time-dependent deformation during slower and cyclic loading, resulting in lower peak loads and reducing large magnitude fracturing events. The generated S-N curves demonstrate that weakening by cyclic hydraulic pressurisation mimics relationships defined by conventional fatigue testing of geomaterials. Such experimental constraints will be of great benefit to the development of cyclic stimulation practices for subsurface engineering.

How to cite: Kendrick, J. E., Mouli-Castillo, J., Lamur, A., Fraser-Harris, A., Lightbody, A., Chandler, M., Edlmann, K., McDermott, C., and Shipton, Z.: Constraining the impact of cyclic hydraulic stimulation on granites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14982, https://doi.org/10.5194/egusphere-egu23-14982, 2023.

EGU23-15424 | ECS | Posters on site | ERE5.2 | Highlight

Structural evolution in the northern Ruhr basin: A case study of urban geothermal exploration in the Münsterland Region 

Vladimir Shipilin and Manfred Dölling

The geothermal potential in the deep subsurface of North Rhine-Westphalia (NRW) has been scarcely explored. Due to the increasing demand for zero-carbon heating applications, there has been a renewed phase of seismic exploration in the region to investigate potential geothermal aquifers. The prime exploration target is the Lower Carboniferous Ruhr Basin and the Devonian substratum of the Variscan foreland, as they host deep carbonate aquifers. Interpretation of the recently-acquired 70-km-long 2D seismic profiles, together with the 2D legacy seismic data in the northern part of the Ruhr basin, the Münsterland region, reveals two carbonate units; the Dinantian platform facies and the Givetian massive facies. These are located at depths that range from c. 4500 m to 6000 m. Considering their great burial depth, the permeability of the carbonate rocks is considered to be primarily facilitated by fault zones with dense fracture swarms. Therefore, understanding the complex deformation history of this fossil foreland basin is crucial to evaluate its geothermal potential. We here reveal the timing and geometric evolution of the fault zones. Using a multiattribute seismic analysis, we delineate three major types of faults; (1) SW–NE-⁠trending, syn-fold thrusts, (2) WNW–ESE-striking normal faults, and (3) E–W and N–S strike-slip faults. Interestingly, we do not observe in the available data flexure-induced faults that are typical for foreland basins and would be expected to strike parallel to the SW–NE-oriented Variscan Orogen. To constrain the relative timing of fault activity, we mapped seven well-constrained and age-calibrated stratigraphic horizons within the Carboniferous molasse sequence and the Cretaceous cover. The preliminary results confirm the observations of previous researchers that the thrust faults formed after the deposition of the Late Carboniferous strata, as evidenced by their concordant folding. Thrusts are crosscut by the normal faults, suggesting that the latter formed at a subsequent stage. Most of the strike-slip faults cut through the Carboniferous–Cretaceous unconformity, with some culminating in the Cretaceous cover as positive flower structures. Notably, one flower structure is co-linear with a thrust fault in the Carboniferous, suggesting that there is some degree of kinematic linkage between the two structural levels. Possibly, some of the optimally-oriented thrusts were reactivated and grew upward as strike-slip faults during Late Cretaceous transpression. Such multiphase evolution of fault zones may enhance permeability structure, since each reactivation event potentially contributes to the widening of the deformation zones, thereby increasing the density of interconnected fractures. In this study, we demonstrate how the integration of new seismic data provides valuable insights into the structural evolution of the Ruhr Basin and its geothermal potential. A 3D seismic acquisition campaign is planned in the investigated region. Using its results, we intend to conduct a high-resolution fault throw analysis to further constrain the kinematic development of the deformation structures.

How to cite: Shipilin, V. and Dölling, M.: Structural evolution in the northern Ruhr basin: A case study of urban geothermal exploration in the Münsterland Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15424, https://doi.org/10.5194/egusphere-egu23-15424, 2023.

Previous hydrocarbon exploration in the Ordos, Tarim, and Sichuan basins of China has indicated that strike-slip faults play an important role in controlling reservoir distribution. High hydrocarbon production within strike-slip fault zones in these basins indicates that the fault zones not only act as conduits or seals for hydrocarbon migration, but also provide space for hydrocarbon accumulation. The productivity of different wells, however, can vary within one strike-slip fault zone, suggesting that variability in fault zone architecture controls hydrocarbon enrichment. To date, very few studies have explored fault zone architecture in the southern Ordos Basin, inhibiting oil exploration and development. We explored faults in the Jinghe Oilfield in the southern Ordos Basin by integrating outcrops, wellbore cores, well logs, and 3D seismic data. We carried out fault segmentation, qualitative characterization of fault zone architecture, and quantitative characterization of the boundary between the damage zone and wall rock. The results showed that fault zone architecture is complicated by fault segmentation, architectural configuration, and damage zone asymmetry. Strike-slip faults can be divided into transtensional, strike-slip, and transpressional segments along the fault strike, with transtensional and strike-slip segments dominant in the Jinghe Oilfield. Each segment is further complicated by different configurations of gouge, breccia, and fracture zones along the fault dip. Compared with the strike-slip segments, transtensional and transpressional segments showed more complexity, with the fracture density and damage zone width of the hanging wall being greater than that of the footwall. Transtensional segments with braided and horsetail structures showed more complexity owing to the presence of multiple fault cores and damage zones around the main fault and its subsidiary faults. Quantitative analysis showed that the fault zone width was the greatest for transtensional segments, intermediate for transpressional segments, and the lowest for strike-slip segments. We determined a positive linear relationship between the relative widths of the fault core and fault zone. The cavities in breccia zones and fractures in damage zones provide conduits and storage space for hydrocarbon migration and accumulation. We conclude that damage zones in transtensional segments, particularly in the hanging wall, are primary potential targets for petroleum exploration and development.

How to cite: Meng, Y., Chen, H., Luo, Y., Zhao, Y., Tang, D., and He, F.: Architecture of intraplate strike-slip fault zones in theYanchang Formation, Southern Ordos Basin, China: Characterizationand implications for their control on hydrocarbon enrichment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17164, https://doi.org/10.5194/egusphere-egu23-17164, 2023.

EGU23-17201 | Orals | ERE5.2

Micro-Continuum Modelling of Coupled Hydro-Bio-Chemical MICP Processes in Fractured Rock 

Guijie Sang, Rebecca Lunn, Grainne El Mountassir, and James Minto

Subsurface storage of CO2 and retrievable green energy (i.e. compressed air and hydrogen) in depleted gas reservoirs, deep saline aquifers and salt caverns, are considered as key transitions within the energy sector to enable many countries to meet their net zero carbon emissions targets. One of the main challenges in underground storage is the presence of potential leakage pathways (such as caprock fractures/faults) which pose a threat to economic feasibility and to the environment. Seeking an efficient technique to remediate leakage pathways is crucial to guarantee sealing efficacy. Microbially induced carbonate precipitation (MICP) is regarded as a promising bio-grouting technique for leakage remediation due to its advantages such as the low water-like viscosity and micron-size microbes, which enables permeation far from the injection point and excellent penetration into fine aperture fractures.

MICP utilizes ureolytic bacteria, commonly Sporosarcina pasteurii (S. pasteurii) to produce highly active urease enzyme, which can catalyze urea hydrolysis and result in the production of carbonate ions. Carbonate precipitation occurs if a calcium source is supplied, which can effectively remediate leakage by filling void space and improve strength by bonding solid grains.

We propose a micro-continuum model which accounts for the coupled hydro-bio-chemical MICP processes in fractured porous rock. In this micro-continuum model, the flow is controlled by the Darcy-Brinkman-Stokes equation over a number of control volumes (i.e. voxels based on X-ray CT scan). The kinetic parameters of urea hydrolysis and calcium carbonate precipitation are calibrated based on batch experiments. The bacteria deposition parameters, which feature the bacteria deposition in fractured rock, are calibrated based on experimentally measured bacteria breakthrough curves in a 1-dimensional column filled with fracture gouge materials. The proposed micro-continuum model can well represent the decreases in porosity and permeability of an artificially-cut anhydrite fracture filled with anhydrite gouges under MICP treatment cycles. Our modelling results also suggest that when the CaCl2 concentration is equal to or higher than the urea concentration in the injected cementing solution, the rate of microbially induced carbonate precipitation is predominantly limited by the kinetics of urea hydrolysis rather than the kinetics of calcium carbonate precipitation. The proposed micro-continuum model serves as a useful tool for evaluating MICP treatment strategies and may be upscaled to predict and optimise field-scale leakage remediation.

How to cite: Sang, G., Lunn, R., El Mountassir, G., and Minto, J.: Micro-Continuum Modelling of Coupled Hydro-Bio-Chemical MICP Processes in Fractured Rock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17201, https://doi.org/10.5194/egusphere-egu23-17201, 2023.

EGU23-431 | ECS | Posters on site | EMRP1.2

New insights into the rheology of a normal fault: the Mw6.1 2009 L’Aquila case study 

Rossella Fonzetti, Luisa Valoroso, Pasquale De Gori, and Claudio Chiarabba

The study of seismogenic faults is one of the most interesting topics in seismology.  Obtaining a more detailed image of the fault zone structure and of its properties (e.g., fluid content, permeability, lithology, rheology) is fundamental to understand how seismic ruptures originate, propagate and arrest and to study the triggering processes.  The 2009 Mw 6.1 L’Aquila seismic sequence is a perfect case study to reach this goal, thanks to the huge amount of multidisciplinary data available. 

In this study, we reprocess the high-precision large earthquake catalog available for the L’Aquila seismic sequence, focusing on the main (Paganica) seismogenic fault (about 20,000 earthquakes occurring between January-December 2009). We used cross-correlation and double-difference tomography methods to compute high-resolution (2.5 x 2.5 x 2 km grid spacing) Vp and Vp/Vs models along the fault plane. High-resolution Vp and Vp/Vs models give insights into the rheology of the Paganica fault, suggesting new ideas on earthquake generation, propagation and arrest.  

How to cite: Fonzetti, R., Valoroso, L., De Gori, P., and Chiarabba, C.: New insights into the rheology of a normal fault: the Mw6.1 2009 L’Aquila case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-431, https://doi.org/10.5194/egusphere-egu23-431, 2023.

EGU23-531 | ECS | Orals | EMRP1.2

Interplay between fluid flow and rock deformation in an exhumed hydrothermal fault-vein network 

Simone Masoch, Michele Fondriest, Rodrigo Gomila, Giorgio Pennacchioni, José Cembrano, and Giulio Di Toro

Faults can act as conduits for the migration of hydrothermal fluids in the crust, affecting its mechanical behaviour and possibly leading to earthquake swarm activity. To date, there are still few constraints from the geological record on how fault-vein networks develop through time in high fluid-flux tectonic settings. Here, we describe small displacement (<1.5 m) epidote-rich fault-vein networks cutting granitoids in the exhumed Bolfin Fault Zone (Atacama Fault System, Chile). The epidote-rich sheared veins show lineated slickensides with scattered orientations and occur at the intersections with subsidiary structures in the fault damage zone. FEG-SEM cathodoluminescence (CL) reveals that magmatic quartz close to the sheared epidote-rich veins is affected by (i) thin (< 10 µm) interlaced deformation lamellae and (ii) a network of CL-dark quartz epitaxial veinlets sharply crosscutting the lamellae. EBSD maps of the deformed quartz indicate minor lattice distortion associated with the lamellae and an orientation nearly orthogonal to the c-axis. These deformation features disappear moving away into the host rock. The epidote-rich sheared veins (i) include clasts of magmatic quartz with both the deformation lamellae and the healed veinlets and (ii) show cyclic events of extensional-to-hybrid veining and localized shearing. We propose that the microstructures preserved in the quartz next to the sheared veins (i.e. deformation lamellae and epitaxial veinlets) record the high-strain rate loading associated with dynamic crack propagation and rapid micro-fracture sealing. On the other hand, the cyclic dilation and shearing within the epidote-rich veins is interpreted as the expression of a highly connected fault-vein network dominated by pore pressure oscillations leading to seismic swarm activity.

How to cite: Masoch, S., Fondriest, M., Gomila, R., Pennacchioni, G., Cembrano, J., and Di Toro, G.: Interplay between fluid flow and rock deformation in an exhumed hydrothermal fault-vein network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-531, https://doi.org/10.5194/egusphere-egu23-531, 2023.

EGU23-1330 | ECS | Orals | EMRP1.2

Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events 

Tatiana Kartseva and Nikolai Shapiro

We propose an approach that is aimed to enrich the catalogs of acoustic emission events recorded in laboratory experiments with such parameters as seismic moment and corner frequency. Because of the difficulty of separation of direct waves in experiments performed on small samples, we use the coda waves that are composed of the reverberation of the acoustic field in the tested sample. After multiple reverberations, the resulting wavefield can be approximated as nearly homogeneously distributed over the sample and with signal amplitudes decaying exponentially in time (linearly in a logarithmic scale).

Within the framework of this model, the frequency-dependent coda amplitude at any moment of time is described as combination of a source spectra, of a decay rate combining internal attenuation with reverberation losses, and of a sensor response. One of the main difficulties with the laboratory experiments is that acoustic sensors are very difficult to calibrate and their absolute response function in most of cases remains unknown. With the simple reverberation model, the logarithms of coda amplitudes at different times and sensors and for multiple events are described by a system of linear equations that we solve in a least-square sense to find frequency-dependent coda-decay rates, relative signal spectra and sensor responses. In a next step, we compute spectral ratios between spectra of different events to eliminate the sensor responses and to estimate main source parameters such as corner frequencies and relative seismic moments.

We provide details of our data analyses technique and present time-dependent corner frequency vs relative moment diagrams for two experiments on granite of the Voronezh massif and Berea sandstone under pseudo-triaxial loading. The dependence close to the cubic that is frequently estimated for tectonic earthquakes observed on the first stages of both experiments when confining pressure steps applied to the intact rock and therefore to the pre-existing inhomogeneties. After applying axial load changes in stress-drop is being observed: with higher stress-drops prevailing in granite and lower stress-drops in sandstone. Also there is a significant difference in Gutenberg-Richter relation in these two experimental conditions observed.

How to cite: Kartseva, T. and Shapiro, N.: Coda-Based Estimation of Source Parameters of Laboratory Acoustic-Emission Events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1330, https://doi.org/10.5194/egusphere-egu23-1330, 2023.

EGU23-2537 * | Posters on site | EMRP1.2 | Highlight

Fault rocks associated with the reservoir-triggered seismicity of the Koyna-Warna area (India) 

Giulio Di Toro, Alessio Chiesurin, Elena Spagnuolo, Rodrigo Gomila, and Sukanta Roy

In 1962, the Kyona Dam was completed in a rural area 250 km southeast of Mumbai (India), primarily for hydropower generation. Since then, the area, which was essentially devoid of natural seismicity, has been affected by a sequence of moderate to large magnitude earthquakes, including the one of December 11th, 1967 (ML6.3, 177 casualties), the largest human-induced earthquake so far. Major earthquakes (ML>4) are modulated by basin-filling and emptying operations, which follow the monsoon regime with peak rainfall between July and September. There are two peaks of seismicity: the first between August and September (“rapid-response”), corresponding to the rainy season, and the second in February (“delayed-response”) corresponding to the dry season. The ML>3 earthquakes have normal to strike-slip focal mechanisms, reactivate steeply-dipping faults/fractures, and are located between 3 and 10 km depth in the granitoid Indian basement (2.7-2.6 Ga) buried beneath the 0.5-2 km thick Deccan basaltic lava flows (68-60 Ma). The temperature at hypocentral depths is estimated to be between 80 and 200°C. Especially the delayed-response seismicity implies poro-elastic effects, also related to the percolation of water from the surface to hypocentral depths. To study the seismicity of the area, a large deep drilling project was completed by the Ministry of Earth Sciences (India) which includes nine wells down to 1.5 km depth and a pilot well down to 3 km depth. Here we describe the fault rocks (mylonites, cataclasites, breccia and faults/fractures filled by epidote, quartz, chlorite and calcite veins) collected in boreholes KBH1, KBH6 and KBH7.

Visual analysis of the cores plus mineralogical, microstructural and geochemical investigations (X-ray powder diffraction; scanning electron microscope equipped with Wavelength-Dispersive X-Ray Spectroscopy) allowed us to reconstruct the sequence of deformation events. Steeply-dipping faults/fractures filled by chlorite and calcite are the last deformation event as they cut through all other structural features. We recognized eight types of chlorites based on optical properties, crosscutting relations and chemical composition. The temperature of formation of the chlorite spans from 350°C (or HT-chlorite found in the shear zones cut by the Deccan basaltic dykes), to 200°C<T<250°C (or LT-chlorite filling fault/fractures cut by calcite veins, but with uncertain crosscutting relations with Deccan basaltic dykes), and 130°C<T<135°C (or Very-LT-chlorite filling fault/fractures, which are also cut by calcite veins, and cut the Deccan basaltic dykes). LT- and Very-LT-chlorite formation temperatures were estimated with the Bourdelle & Cathelineau (2015) chlorite geothermometer. The range of 130°C<T<250°C for chlorite formation, which can be extended to lower temperatures considering that these faults/fractures are cut by calcite veins, overlaps with the one (80°C<T<200°C) estimated at the hypocentral depths of the Koyna-Warna area. Moreover, these fault/fractures found in the boreholes are hosted in steeply-dipping fault/fractures (or sub-parallel to the structures illuminated by the hypocentral distributions), and are filled by minerals precipitated from percolating fluids (i.e., consistent with the evidence of delayed-response seismicity). We conclude that the faults/fractures currently reactivated by reservoir-triggered seismicity most likely correspond to those filled by calcite and LT- to Very-LT chlorites found in the deep boreholes.

How to cite: Di Toro, G., Chiesurin, A., Spagnuolo, E., Gomila, R., and Roy, S.: Fault rocks associated with the reservoir-triggered seismicity of the Koyna-Warna area (India), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2537, https://doi.org/10.5194/egusphere-egu23-2537, 2023.

EGU23-2911 | Orals | EMRP1.2

Microstructural controls on seismicity distribution in simulated fault gouges 

Andre R. Niemeijer, Evangelos Korkolis, Tanmaya Mishra, Rens Elbertsen, Beunen Jop, and Ivan Pires de Vasconselos

In order to make seismic hazard estimates, it is necessary to assume some distribution of the number of earthquakes of a certain magnitude, i.e. a Gutenberg-Richter distribution. This is true for both natural seismicity as well as induced seismicity, but in both cases the number of historical earthquakes at the tail end of the distribution (i.e. the largest ones) is limited and often the maximum possible magnitude is unknown. In contrast, in a laboratory setting the maximum size of an unstable slip event (“stick-slip” or laboratory earthquake) is controlled by the size of the sample and the imposed stress. In our rotary shear apparatus, we can theoretically achieve unlimited fault displacement which allows us to produce earthquake-like distributions with thousands to tens of thousands event.

In this presentation, I will present results from experiments on simulated fault gouges which show unstable frictional behaviour at room temperature conditions. The results show that the event size distribution can change spontaneously, without any changes in the boundary conditions. Observations of fault gouge material after the experiment, suggest that wear of the granular material generates alternative surfaces for slip, which changes the macroscopic behaviour. Interestingly, the change in event size distribution is reversable, presumably because the fine-grained layers become disturbed with ongoing shear.

In an attempt to simulate the macroscopic behaviour, we have, for the first time, measured the rate-and-state frictional (RSF) properties on single grain contacts. Using these values in a numerical model for seismic slip (so-called “seismic cycle simulator”), we obtain maximum stress drops that are comparable to those obtained in the experiments, but with some differences. The differences are most likely due to the fact that the grains in our simulated fault are affected wear in previous slip events, which should change their RSF parameters. In addition, the normal stress at each individual grain contact is unknown in the experiment and could vary significantly from event to event.  This latter difference between model and experiment can be overcome by using a discrete element method with contact-scale RSF properties to simulate slip.

How to cite: Niemeijer, A. R., Korkolis, E., Mishra, T., Elbertsen, R., Jop, B., and Pires de Vasconselos, I.: Microstructural controls on seismicity distribution in simulated fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2911, https://doi.org/10.5194/egusphere-egu23-2911, 2023.

EGU23-3982 | ECS | Orals | EMRP1.2

Energy budget of quasi-dynamic earthquake cycle 

Navid Kheirdast, Michelle Almakari, Carlos Villafuerte, Marion Y. Thomas, and Harsha S. Bhat

The elastic medium that hosts several, multi-scale, faults could be regarded as an energy reservoir that is charged by the far field stress rate and discharged by friction dissipation during earthquake slips on the faults.  In this study, we carefully analyze the energy budget variations that occur throughout a synthetic, 2D plane-strain, earthquake cycle on a fault system comprising of a main fault surrounded by a hierarchy of off-fault slip planes/fractures. We evaluate the rate of kinetic energy variation, stress power across the continuum, far field power supply, and the dissipation due to the rate-and-state friction on the faults given a spectrum of slips ranging from slow-slip to rapid ruptures. We study how the medium's energy budget evolves after these components have been determined.  Additionally, we compute the dissipation rate for a variety of slip rates to determine the contributions of so-called slow-slip events, low-frequency earthquakes (LFEs), and tremors to this budget. We also evaluate the share of off-fault fractures to determine their energetic role during earthquake cycles.

How to cite: Kheirdast, N., Almakari, M., Villafuerte, C., Thomas, M. Y., and Bhat, H. S.: Energy budget of quasi-dynamic earthquake cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3982, https://doi.org/10.5194/egusphere-egu23-3982, 2023.

EGU23-5033 | Orals | EMRP1.2

Modelling seismicity based on fault geometry: maximum magnitudes and magnitude-frequency distributions. 

Vincent Roche, Mirko van der Baan, and John Walsh

Investigating clusters of events and geophysical screening often provides limited constraints on fault geometries. This imaging issue prevents the integration of realistic fault zone geometry into earthquake studies, which can affect our capacity to evaluate the role of pre-existing faults on seismicity. This study describes a modelling strategy accounting for realistic fault zone geometries. Our approach uses stochastic methods underpinned by quantitative fault zone parameterization, followed by an assessment of seismicity from simulations of rupture dynamics controlled by fault geometry. This method is used to investigate the role of fault maturity on seismicity for two case studies, including seismicity associated with the reactivation of a pre-existing fault network due to hydraulic fracturing in Harrison County, Ohio, from 2013 to 2015, as well as the natural seismicity associated with the Yushu-Ganzi left-lateral strike-slip fault system in central-eastern Tibet. In the Harrison County case, we analyze the effect of vertical variability in fault maturity and show how more mature faults in the deeper crystalline basement generate higher magnitude seismicity than shallow, immature faults in younger sedimentary rocks. In the Yushu-Ganzi case study, we show how lateral variability in structural maturity, arising from long-term fault propagation and strain rates, leads to different seismicity on individual fault segments. Our findings indicate that fault geometry determines seismic patterns, with rupture length controlled by fault zone geometry rather than fault lengths, and favour the adoption of a structural geological perspective for the integration of realistic fault geometry into seismicity prediction strategies.

How to cite: Roche, V., van der Baan, M., and Walsh, J.: Modelling seismicity based on fault geometry: maximum magnitudes and magnitude-frequency distributions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5033, https://doi.org/10.5194/egusphere-egu23-5033, 2023.

EGU23-6468 | ECS | Posters on site | EMRP1.2

Evidence for coseismic slip preserved in high-porosity sandstone at very shallow burial conditions (Crotone Basin, Italy) 

Mattia Pizzati, Nicolò Lieta, Anita Torabi, Luca Aldega, Fabrizio Storti, and Fabrizio Balsamo

The seismogenic zone is commonly defined as the portion of the Earth's upper crust where most earthquakes nucleate. According to seismological data, the seismogenic interval is typically located between 5 and 35 km depth. However, shallow seismicity, with earthquake hypocentral depths < 5 km, has been reported in several tectonic settings. Although less studied, such shallow seismic sources represent potential treats and deserve to be thoroughly investigated and included in seismic hazard evaluations.

For this purpose, we present the results of a multidisciplinary study focusing on faults affecting high-porosity fluvio-deltaic, sandstone-dominated deposits belonging to the Pliocene-Pleistocene succession of the Crotone Basin, South Italy. The studied fault zone is well exposed along the Vitravo Creek canyon, has a maximum displacement of ~50 m, and is characterized by an indurated, sharp master slip surface. The fault footwall displays an 8-10 m-wide deformation band-dominated damage zone with deformation bands occurring both as clusters and as single structures. The frequency of deformation bands increases towards the master slip surface. Approaching the master slip surface, a 1.5 m-thick mixing zone occurs, where strong tectonic mixing affected the sandstone strata with different grain size and thickness. The fault core consists of ~1 m-wide, calcite-cemented cataclastic volume and hosts a wealth of fault-parallel deformation bands and subsidiary slip surfaces. Due to its selective cementation, the fault core stems in strong positive relief compared to the host high-porosity sandstone. The hanging wall block is characterized by a dense network of thin deformation bands with diminishing frequency away from the fault surface. Along the master slip surface, at the top of the indurated fault core, a 1-2 cm-thick dark gouge layer is present. The gouge is persistent throughout all the fault exposure, and has been injected in the underlying, fractured cemented fault core. Microstructural analysis of the gouge reveals a strong cataclastic grain size reduction along thin (< 1 mm) slip zones alternated with portions showing lens-shaped (resembling S-C) fabric. XRD analysis of the < 2 µm grain-size fraction of the gouge layer displays short-ordered illite-smectite mixed layers which support deformation temperatures in the 100-120°C range. XRD analysis performed on clay fraction from the fault core, next to the dark gouge layer, indicates temperatures lower than 50-60°C, consistent with the expected shallow burial conditions. Following this, the anomalous temperature rise recorded within the dark gouge layer is suggested to be produced by frictional heating during coseismic deformation. We conclude that the microstructural observations, grain size, and XRD data provide a line of evidence supporting the occurrence of coseismic deformation affecting high-porosity granular materials at near surface conditions and could help in better evaluation and risk assessment of seismically active faults.

How to cite: Pizzati, M., Lieta, N., Torabi, A., Aldega, L., Storti, F., and Balsamo, F.: Evidence for coseismic slip preserved in high-porosity sandstone at very shallow burial conditions (Crotone Basin, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6468, https://doi.org/10.5194/egusphere-egu23-6468, 2023.

EGU23-6517 | Orals | EMRP1.2

On-fault damage evolution in laboratory earthquakes: a numerical perspective on fault complexity 

Guilhem Mollon, Jérôme Aubry, and Alexandre Schubnel

We propose a numerical model of laboratory earthquake cycle inspired by a set of experiments performed on a triaxial apparatus on sawcut Carrara marble samples. The model couples two representations of rock matter: rock is essentially represented as an elastic continuum, except in the vicinity of the sliding interface, where a discrete representation is employed. This allows to simulate in a single framework the storage and release of strain energy in the bulk of the sample and in the loading system, the damage of rock due to sliding, and the progressive production of a granular gouge layer in the interface. After independent calibration, we find that the tribosystem spontaneously evolves towards a stick-slip sliding regime, mimicking in a satisfactory way the behaviour observed in the lab. The model offers insights on complex phenomena which are out of reach in experiments. This includes the variability in space and time of the fields of stress and effective friction along the fault, the progressive thickening of the damaged region of rock around the interface, and the build-up of a granular layer of gouge accommodating shear. We present in detail several typical sliding events, we illustrate the fault heterogeneity, and we analyse quantitatively the damage rate in the numerical samples.

How to cite: Mollon, G., Aubry, J., and Schubnel, A.: On-fault damage evolution in laboratory earthquakes: a numerical perspective on fault complexity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6517, https://doi.org/10.5194/egusphere-egu23-6517, 2023.

EGU23-6974 | ECS | Orals | EMRP1.2

Depth dependence of coseismic off-fault damage 

Roxane Ferry, Marion Thomas, and Louise Jeandet

Faults are complex systems embedded in an evolving medium fractured by seismic ruptures. This off-fault damage zone is shown to be thermo-hydro-mechano-chemically coupled to the main fault plane by a growing number of studies. Yet, off-fault medium is still, for the most part modelled as a purely elastic -- hence passive -- medium. Using a micromechanical  model we investigate the depth variation of dynamically triggered off-fault damage and its counter-impact on earthquake slip dynamics. We show that if the damage zone becomes narrower with depth, it is also denser and thus, unlike what is commonly believed, remains an energy sink even at depth. The results are in agreement with the complementary model by Okubo et al., 2019. In contrast to study cited above, our model accounts for the dynamics changes of elastic moduli related to crack growth. This lead to the dynamic creation of low-velocity zone that can trapped seismic waves and further impact the earthquake dynamics, even at greater depth. We therefore claim that the intertwined dynamics between the main fault plane and its surrounding medium must be including along the all seismogenic.

How to cite: Ferry, R., Thomas, M., and Jeandet, L.: Depth dependence of coseismic off-fault damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6974, https://doi.org/10.5194/egusphere-egu23-6974, 2023.

EGU23-7142 | ECS | Orals | EMRP1.2

Investigating relationships between surface rupture and multiple source parameters of earthquakes 

Suli Yao, Hongfeng Yang, and Ziyue Tang

Surface rupture produced by earthquakes can pose great threat on near-surface infrastructures and elevate damages. Accessing the potential of surface rupture along faults is critical to mitigating such hazards. It is commonly suggested that earthquakes with Mw>6.5 will break the surface. However, there are events with much smaller magnitudes rupturing the ground. To understand the potential controlling mechanisms, we first collect source parameters for earthquakes with  and  surface-breaching events in seismically active regions including west China, North America, Europe, Taiwan, Japan, and Iran. For strike-slip and normal events, almost all earthquakes with magnitudes over 6.7 broke the surface. In contrast, buried and surface-breaching events co-exist with moderate magnitude (6.0-6.7). For reverse events, there is no clear magnitude boundary, as thrust buried events can be quite large due to the downdip size of the seismogenic zone. The relocated hypocenter depths for moderate-to-large events are concentrated at depth of 5 -20 km with no systematic difference between buried and surface-breaching ruptures. Differently, all  surface-breaching events occurred at very shallow depths (<5 km). We also conduct dynamic rupture simulations and propose two conceptual models to explain whether or not ruptures may break the surface. The first model represents a fault with a continuous but heterogeneous seismogenic zone (velocity-weakening) that can hold moderate-to-large earthquakes. In this case, ruptures need to overcome the shallow velocity-strengthening zone (VS) with certain energy sink to reach the surface. Therefore, a thinner shallow RS zone and a higher stress drop of the earthquake can promote surface rupture, consistent with our observations. However, ruptures nucleating from different locations on heterogeneous faults may lead to different surface rupture patterns and final magnitudes, shedding lights on the diverse behaviors among moderate earthquakes. The second model is for small surface-breaching earthquakes. Those events are supposed to occur on shallow isolated velocity-weakening patches, consistent with the fact that usually no large earthquakes have been reported on the same fault zones. Such asperities may be formed on bodies with high-strength materials, leading to energetic ruptures with intense stress release. Our study contributes to the understanding of the surface rupture behaviors references for assessing near-surface damage in future earthquakes.

 

How to cite: Yao, S., Yang, H., and Tang, Z.: Investigating relationships between surface rupture and multiple source parameters of earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7142, https://doi.org/10.5194/egusphere-egu23-7142, 2023.

EGU23-7167 | Posters on site | EMRP1.2

A deep catalogue of 56k focal mechanisms for the 2016 Amatrice, Italy earthquake sequence 

Men-Andrin Meier, Federica Lanza, and Patricia Martinez-Garzon

The 2016 Amatrice, Italy earthquake sequence occurred on a normal fault system in the Central Apennines, and contained over 1,300 M>=3 earthquakes. With ~140 permanent or temporary seismic stations directly above the seismic activity, the sequence has been exceptionally well recorded. Starting from a deep learning-based catalogue of earthquake hypocentres (~900,000 re-located events from ~15 million seismic phases; Tan et al., 2021), we use a convolutional neural network classifier to predict P-wave first motion polarities, from which we compile a deep catalogue of earthquake focal mechanisms. The catalogue consists of >56'000 focal mechanisms, about 8'000 of which have nodal plane uncertainties below 25 degrees.

In contrast to existing, conventional focal mechanism catalogues, the deep catalogue samples almost the entire study region, and almost the entire magnitude range (~M0-M5), although nodal plane uncertainties generally tend to increase with decreasing magnitude. We use the focal mechanism catalogue to study the kinematics of the Amatrice earthquake sequence, to test the hypothesis of a coseismic rotation of the static stress field by large and small events, and to analyse the complexity of the stress field before, during and after the earthquake sequence.

How to cite: Meier, M.-A., Lanza, F., and Martinez-Garzon, P.: A deep catalogue of 56k focal mechanisms for the 2016 Amatrice, Italy earthquake sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7167, https://doi.org/10.5194/egusphere-egu23-7167, 2023.

EGU23-7327 | Posters on site | EMRP1.2

The impact of fault surface 3D geometry on risking fault reactivation 

Janis Aleksans, Conrad Childs, and Martin Schöpfer

The reactivation of faults can occur when the effective stresses acting on them are perturbed. In some cases man-made changes in effective stress can result in fault reactivation that can have enormous impacts including loss of integrity of underground storage facilities. Current practical methods for making this assessment are generally based on shear stresses calculated over fault surfaces. Depending on the absolute or relative magnitudes of these resolved shear stresses, which depend primarily on the local orientation of the fault surface relative to the regional stress field, different faults or parts of faults are said to be closer or further from the Coulomb failure envelope and are therefore more likely to slip due to changes in effective stress. This proximity to failure/slip is referred to as the slip tendency or reactivation tendency.

Although the slip/reactivation tendency approach is firmly grounded in Coulomb theory and laboratory experiments, there may be issues applying it to the reactivation of irregular fault surfaces. A key assumption of the approach is that an area of a fault surface can be treated in isolation so that the slip tendency can be evaluated once its orientation and frictional properties are known. However, it is well established that fault surfaces are not planar but often have highly irregular geometries and fault rock distributions so that the likelihood that a particular part of a fault will reactivate must also depend, not only on the properties at that point but also on adjacent areas of the fault surface.

To investigate the significance of fault surface irregularity for the evaluation of fault slip/reactivation tendency, we conduct numerical modelling of fault reactivation resulting from an increase in pore pressure within a normal faulting stress regime. The modelling employs a form of the Discrete Element method that uses rigid blocks. This approach provides for both accurate representation of the geometry and frictional properties of the irregular slip surfaces and also failure in the surrounding wall-rock and is capable of modelling the variety of ways in which slip may initiate on, or adjacent to an irregular fault.

How to cite: Aleksans, J., Childs, C., and Schöpfer, M.: The impact of fault surface 3D geometry on risking fault reactivation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7327, https://doi.org/10.5194/egusphere-egu23-7327, 2023.

EGU23-7594 | ECS | Posters on site | EMRP1.2

Frictional behavior and rheology of bi-disperse quartz gouge mixtures 

Nathalie Casas, Carolina Giorgetti, Cristiano Collettini, and Marco Maria Scuderi

Earthquake nucleation has been understood as controlled by the frictional properties of fault zones. Mature fault zones host abrasive wear products, such as gouges, which result from the frictional sliding occurring in successive slip events. Shear localization in fault gouges is strongly dependent on, among others, fault mineralogical composition and grain size distribution, originating a wide variety of microstructural textures that may be related to different types of fault motion from aseismic creep, slow earthquakes to fast slip events. Additionally, within a fault, one can encounter different stages of maturity, ranging from an incipient and poorly-developed fault zone (i.e. discontinuous and thin gouge layer) to a mature fault zone that has experienced a lot of wear from previous sliding events (i.e. well-developed gouge layer). The localization of deformation within a mature gouge layer has been identified as possibly responsible for mechanical weakening and as an indicator of a change in stability within the fault.

To gain insights on the role of grain size distribution, and thus fault maturity, in slip behavior and fault rheology, we performed friction experiments on quartz fault gouge in a double direct shear configuration using a biaxial apparatus (BRAVA at INGV in Rome, Italy). The experiments were performed at a constant normal stress of 40 MPa and under 100% humidity.  We investigated different sliding velocities, from 10 µm/s to 1 mm/s, to assess time-dependent physical processes. Different bi-disperse mixtures of quartz were sheared to reproduce different initial grain size distributions within the fault (F110, average grain size  and Min-u-sil, average grain size ). Samples were carefully collected at the end of the experiments to prepare thin sections for microstructural analyses.

A first set of experiments was performed increasing the proportion between smaller and larger particles within a homogeneous blend. The friction evolves from a strain-hardening behavior for a sample with only F110 to a slip-weakening one for the one with only Min-u-sil. The difference in rheology is observable in the analyzed microstructures. Particularly, the two end members clearly show comminution and localization along boundary shear planes, whereas mixtures of the two sizes of particles only present a more diffused deformation. In the second set of experiments, we sheared gouges with a horizontal layering of the two grain sizes and observed different behaviors in terms of friction and rheology. These layered gouges present strain hardening behavior, with a strengthening part corresponding to the material of the layer in contact with the sliding block and a steady-state part with slightly higher friction than for the homogeneous mixtures.

These results give important information on the connection between grain size distribution, shear localization, and the resulting fault slip behavior. In this context, the proportion between small/large particles and their distribution and percentages within the fault plays an important role in controlling fault rheology. We also complete our knowledge by using Discrete Element Method, simulating gouge sliding with different grain scale properties (size, distribution, cementation…), and observing a detailed evolution of shear localizations.

How to cite: Casas, N., Giorgetti, C., Collettini, C., and Scuderi, M. M.: Frictional behavior and rheology of bi-disperse quartz gouge mixtures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7594, https://doi.org/10.5194/egusphere-egu23-7594, 2023.

EGU23-7849 | ECS | Orals | EMRP1.2

Dynamics and radiation of thrust earthquakes with coseismic off-fault damage 

Carlos Villafuerte, Kurama Okubo, Esteban Rougier, Raul Madariaga, and Harsha S. Bhat

Major earthquake ruptures occur predominantly in thrust faults producing devastating events and tsunamis such as the 2011 Mw 9.0 Tohoku earthquake, the 2004 Mw 9.2 Sumatra earthquake and the 1999 Mw 7.7 Chi-Chi earthquake. Understanding the mechanics of earthquakes in thrust faults and the effect of the free surface is thus crucial to explain their large shallow slip, their asymmetric ground motion and their damage patterns surrounding the fault and the free surface. In this work, we carry out 2D dynamic rupture simulations on thrust faults to accurately characterize a possible unclamping effect, its responsible physical mechanism, and to produce dynamically activated off-fault fracture networks. To conduct the simulations, we use the software tool based on the Combined Finite-Discrete Element Method (FDEM), HOSSedu, developed by Los Alamos National Laboratory. Our dynamic rupture models in an elastic medium confirm that unclamping occurs in thrust faults and increases significantly as the rupture reaches the free surface and for the fault models with lower dip-angles. We show that this is a consequence of the torque mechanism induced in the hanging wall, and the release of this torque when the rupture reaches the free surface produces a “flapping” in the toe of the wedge where the most significant unclamping (possibly leading to fault opening) is taking place. Our results indicate that the free surface produces a considerable reduction of the compressive normal stress when the rupture is propagating up-dip that facilitates the extension and the amount of slip close to the trench as observed for large thrust earthquakes.This significant normal stress change is reflected in the orientation of the principal stresses before and after the rupture, where under certain conditions, the greatest principal stress changes from subhorizontal to almost vertical leading to a post-rupture tensional stress state in the hanging wall that has been confirmed by observations of recent in-situ, seismological and geodetic studies. Finally, we investigate whether this dramatic normal stress reduction stands when we allow for the activation of coseismic off-fault damage and explore its role in the rupture dynamics, the near-field deformation and radiation patterns.

How to cite: Villafuerte, C., Okubo, K., Rougier, E., Madariaga, R., and Bhat, H. S.: Dynamics and radiation of thrust earthquakes with coseismic off-fault damage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7849, https://doi.org/10.5194/egusphere-egu23-7849, 2023.

EGU23-7933 | Orals | EMRP1.2

Micromechanics of damage localisation and shear failure of a porous rock: sound and vision 

Alexis Cartwright-Taylor, Maria-Daphne Mangriotis, Ian G. Main, Ian B. Butler, Florian Fusseis, Martin Ling, Edward Andò, Andrew Curtis, Andrew F. Bell, Alyssa Crippen, Roberto E. Rizzo, Sina Marti, Derek D. V. Leung, and Oxana V. Magdysyuk

Catastrophic failure in brittle, porous materials initiates when structural damage, in the form of smaller-scale fractures, localises along an emergent failure plane or 'fault' in a transition from stable crack growth to dynamic rupture. Due to the extremely rapid nature of this critical transition, the precise micro-mechanisms involved are poorly understood and difficult to capture. However, these mechanisms are crucial drivers for devastating phenomena such as earthquakes, including induced seismicity, landslides and volcanic eruptions, as well as large-scale infrastructure collapse. Here we observe these micro-mechanisms directly by controlling the rate of micro-fracturing events to slow down the transition in a unique triaxial deformation experiment that combines acoustic monitoring with contemporaneous in-situ x-ray imaging of the microstructure. The results [1] provide the first integrated picture of how damage and associated micro-seismic events emerge and evolve together during localisation and failure and allow us to ground truth some previous inferences from mechanical and seismic monitoring alone. They also highlight where such inferences miss important kinematically-governed grain-scale mechanisms prior to and during shear failure.

The evolving damage imaged in the 3D x-ray volumes and local strain fields undergoes a breakdown sequence involving several stages: (i) self-organised exploration of candidate shear zones close to peak stress, (ii) spontaneous tensile failure of individual grains due to point loading and pore-emanating fractures within an emergent and localised shear zone, validating many inferences from acoustic emissions monitoring, (iii) formation of a proto-cataclasite due to grain rotation and fragmentation, highlighting both the control of grain size on failure and the relative importance of aseismic mechanisms such as crack rotation in accommodating bulk shear deformation. Dilation and shear strain remain strongly correlated both spatially and temporally throughout sample weakening, confirming the existence of a cohesive zone, but with crack damage distributed throughout the shear zone rather than concentrated solely in a breakdown zone at the propagating front of a pre-existing discontinuity.

Contrary to common assumption, we find seismic amplitude is not correlated with local imaged strain; large local strain often occurs with small acoustic emissions, and vice versa. The seismic strain partition coefficient is very low overall and locally highly variable. Local strain is therefore predominantly aseismic, explained in part by grain/crack rotation along the emergent shear zone. The shear fracture energy calculated from local dilation and shear strain on the fault is half of that inferred from the bulk deformation, with a smaller critical slip distance, indicating that less energy is required for local breakdown in the shear zone compared with models of uniform slip.

This improvement in process-based understanding holds out the prospect of reducing systematic errors in forecasting system-sized catastrophic failure in a variety of applications.

[1] Cartwright-Taylor et al. 2022, Nature Communications 13, 6169, https://doi.org/10.1038/s41467-022-33855-z

How to cite: Cartwright-Taylor, A., Mangriotis, M.-D., Main, I. G., Butler, I. B., Fusseis, F., Ling, M., Andò, E., Curtis, A., Bell, A. F., Crippen, A., Rizzo, R. E., Marti, S., Leung, D. D. V., and Magdysyuk, O. V.: Micromechanics of damage localisation and shear failure of a porous rock: sound and vision, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7933, https://doi.org/10.5194/egusphere-egu23-7933, 2023.

EGU23-8163 | ECS | Posters on site | EMRP1.2

Mechanical and microstructural characterization of spatially heterogenous simulated fault gouges, derived from the Groningen gas field stratigraphy 

Job Arts, André Niemeijer, Martyn Drury, Ernst Willingshofer, and Liviu Matenco

Gas production from the Groningen gas field in the northeast of the Netherlands causes compaction and induced seismicity within the reservoir and overlying/underlying lithologies. Recent earthquake localization studies show that seismicity dominantly occurs on complex normal fault systems that juxtapose lithologies of contrasting mechanical properties. However, little is known about the effects of along-fault heterogeneity on the frictional behaviour of these faults. This study aims at understanding how material mixing and clay-smearing in fault gouges affects the mechanical strength and stability of faults that juxtapose contrasting lithologies (e.g. clay-rich and quartz-rich) by performing friction experiments.

Velocity stepping tests are performed on homogeneously mixed and spatially segmented simulated fault gouges, within a rotary shear configuration. Experiments are performed under normal stresses ranging between 2.5 and 10 MPa and imposed velocities ranging between 10 and 1000 µm/s. The rotary shear configuration allows for the large shear-displacements (>145 mm in our experiments) required to study the effects of lithology mixing. Simulated gouges are saturated with DI-water and subsequently sheared under drained conditions. Because low-permeability clay-rich materials promote the build-up of local pressure transients, a specially designed piston with four installed pressure transducers is used to monitor fluid pressures in the vicinity of the simulated fault gouges.

The mechanical data on segmented gouges show an evolution in frictional strength, characterized by a phase of strong displacement-weakening followed by displacement-strengthening. The frictional stability strongly increases with shear-displacement, comprising a transition from velocity-weakening to velocity-strengthening. Microstructural analysis of the sheared gouges provides evidence for the development of clay-smears and strain-localization within localized shear bands, explaining the evolution in frictional stability and the initial phase of shear-weakening. However, the dilatation observed at large displacements suggests that the quartz-rich gouge is incorporated within the clay smear. This incorporation is confirmed by microstructural analysis of the clay smear and provides a mechanism responsible for the observed strengthening at large shear-displacements. Monitoring of local pore fluid pressures shows that segmented gouges are more susceptible to pressure transients, depending on the initial distribution of high porosity sandstone gouges and low permeability claystone gouges.

This study shows that the frictional strength and stability of spatially heterogeneous gouges highly depends on the amount of shear-displacement. The frictional strength is characterized by subsequent phases of displacement-weakening and strengthening, whereas the frictional stability only increases with shear-displacement. This eventually leads to relatively strong but also frictionally stable faults at large displacements. The results have important implications for modelling earthquake nucleation,  propagation, and arrest and apply to faults in geological settings that exhibit induced seismicity, like the Groningen gas field, but are also relevant for tectonically active faults located elsewhere.

How to cite: Arts, J., Niemeijer, A., Drury, M., Willingshofer, E., and Matenco, L.: Mechanical and microstructural characterization of spatially heterogenous simulated fault gouges, derived from the Groningen gas field stratigraphy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8163, https://doi.org/10.5194/egusphere-egu23-8163, 2023.

EGU23-8389 | Posters on site | EMRP1.2

Frictional melting and thermal pressurization during seismic slip controlled by drainage 

Wen-Jie Wu, Li-Wei Kuo, Chia-Wei Kuo, Wei-Hsin Wu, and Hwo‐Shuenn Sheu

frictional melting and thermal pressurization are commonly proposed to reduce dynamic shear resistance along a fault during earthquake propagation. The key factor on triggering either thermal pressurization or frictional melting may be the hydraulic properties of surrounding rock. Observations in Taiwan Chelungpu-fault drilling project (TCDP) Hole-A and Hole-B suggest that frictional melting and thermal pressurization occurred along the fault during the Mw 7.6 Chi-Chi earthquake, but the underlying process is still unclear. Here, we present the microstructural observation in experimental and natural fault gouge, the mechanical data at seismic rate and mineralogical characteristics. Results show that amorphous material only occurred at drained condition. Taken together, these results imply that the difference between Hole-A and Hole-B is attributed to the drainage.

How to cite: Wu, W.-J., Kuo, L.-W., Kuo, C.-W., Wu, W.-H., and Sheu, H.: Frictional melting and thermal pressurization during seismic slip controlled by drainage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8389, https://doi.org/10.5194/egusphere-egu23-8389, 2023.

EGU23-8634 | ECS | Orals | EMRP1.2

Laboratory Observations linking Fault Surface Characteristics to Preparatory Earthquake Processes and Fault Stability 

Sofia Michail, Paul Antony Selvadurai, Sara Beth Leach Cebry, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Markus Rast, Claudio Madonna, and Stefan Wiemer

Preparatory earthquake processes such as slow preparatory slip (preslip) are connected to variations in frictional strength linked to frictional instabilities and appear in various scales across the Earth’s crust. For dry and bare surfaces, the fault surface characteristics affect the contact conditions. These conditions are established through asperities, which are topographical heights where the normal stress concentrates, imposing variations in fault strength. The effect of surface conditions on preslip can be studied in the laboratory where fault surface characteristics can be identified. Developing a more refined understanding of features controlling preslip (e.g., roughness) will lead to more realistic models describing frictional stability. In this study, we performed a triaxial test at sequentially increasing confining pressure steps (P= 60, 80, 100 MPa) on a saw-cut sample of Carrara Marble in dry and unlubricated conditions. Two types of technologies were used to study this frictional response in space and time: (1) an array of acoustic emission sensors monitored localized precursory seismicity and (2) quasi-static deformation in the fault-parallel strain was monitored using distributed strain sensing (DSS) with fiber optics. The differential stress was also measured throughout and allowed us to study the onset of frictional weakening/strengthening. In the first confining pressure step (Pc = 60 MPa), a single stick-slip event was observed with an associated 43 MPa static stress drop. In the subsequent confining pressure steps of P= 80 and 100 MPa, even though the normal stress on the fault was increased, no stick-slip events were observed, and the fault smoothly transitioned to sliding with smaller magnitude stress drops of 3 and 4 MPa, respectively. That suggests that a change in the frictional nature of the interface was incurred during the first rupture at P= 60 MPa. The high-density DSS array displayed a significant heterogeneous distribution of fault-parallel strain in time and space and experienced sudden reorganization at various phases of the experiment. Due to the high spatial resolution, DSS allowed us to investigate local deviations from an elastic response attributed to inelastic processes. A larger amount of local strain accumulation was needed to produce a stick-slip instability. At higher normal stress on the pre-ruptured fault, this level of locking was not possible in the subsequent confining pressure steps. Dissipative inelastic deformation was attributed to local frictional weakening that resulted in non-uniform preslip. Furthermore, priori measurements of contact pressure heterogeneities were obtained using a pressure sensitive film. These results showed regions of lower normal stress along the fault that correlated with regions that incurred more anelastic response on the DSS array. Post-mortem contact pressure measurements showed clear changes in the normal stress distribution that correlated to visual damage and wear. We believe that this contributed to the fault's inability to lock as before and mitigate dynamic rupture. Our results provide more insight into potential mechanisms controlling preslip distribution leading to dynamic and quasi-static frictional weakening.

How to cite: Michail, S., Selvadurai, P. A., Cebry, S. B. L., Salazar Vásquez, A. F., Bianchi, P., Rast, M., Madonna, C., and Wiemer, S.: Laboratory Observations linking Fault Surface Characteristics to Preparatory Earthquake Processes and Fault Stability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8634, https://doi.org/10.5194/egusphere-egu23-8634, 2023.

EGU23-8778 | Orals | EMRP1.2

Dynamic damage in dry and wet rocks monitored by ultra-fast synchrotron imaging 

Francois Renard, Benoit Cordonnier, Mai-Linh Doan, Michele Fondriest, Bratislav Lukic, and Erina Prastyani

During earthquake propagation, a shock wave damages rocks at the rupture tip, creating numerous microfractures and altering the mechanical properties of fault zone rocks. This damage, which occurs dynamically at the millisecond time scale, controls rock strength during earthquake slip that occurs in the wake of rupture propagation. How the presence of water and the initial porosity of the rock control damage during high strain rate deformation remains an open question. We have performed a series of shock experiments using a split Hopkinson pressure bar apparatus installed at the European Synchrotron Radiation Facility. Using two ultra-fast cameras synchronized with the X-ray bunches of the synchrotron; we imaged deformation with microsecond time resolution on centimetre-scale core samples during shock wave damage. We deformed dry and water saturated low porosity Westerly granite and porous Berea sandstone samples. Several samples were surrounded by a thin aluminium jacket allowing recovering them after deformation and image them using X-ray microtomography with micrometre spatial resolution. Results confirm previous studies that have shown that rock pulverization occurs above a threshold strain rate produced by the shock wave. Water saturated samples are consistently weaker than dry samples as they pulverize under lower peak stress. Analyses of rock microstructure acquired using the ultrafast cameras and X-ray microtomography data shed light on the micro-mechanisms of damage production. Either the entire sample pulverized (Westerly granite) or a compaction of the sample occurred before shear zones were dynamically produced (Berea sandstone). These results demonstrate fundamental differences in dynamic damage production in crystalline and porous dry and wet rocks. Our data unravel mechanisms of gouge production before any significant slip has occurred on a fault, which control the shear strength during earthquake slip.

How to cite: Renard, F., Cordonnier, B., Doan, M.-L., Fondriest, M., Lukic, B., and Prastyani, E.: Dynamic damage in dry and wet rocks monitored by ultra-fast synchrotron imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8778, https://doi.org/10.5194/egusphere-egu23-8778, 2023.

EGU23-9600 | ECS | Posters on site | EMRP1.2

Fault-healing and tribochemical processes in granodiorite under hydrothermal conditions 

Rodrigo Gomila, Wei Feng, and Giulio Di Toro

Understanding the mechanical and geochemical processes of fault rock development is a key clue into the understanding of fault healing rates. Fault healing rate β – the change of the static friction coefficient (Δμ) with log time (β = μ0 + Δμ/log(1+thold /tcutoff)) – is a significant parameter in the seismic cycle, controlling the storage of the elastic strain energy in the fault wall rocks and allowing earthquakes to repeatedly occur in pre-existing faults.

Fault healing is investigated with slide-hold-slide (SHS) experiments aimed at reproducing the seismic cycle. However, most of these experiments have been conducted under room conditions, while natural earthquakes nucleate at temperatures T > 150°C and in presence of pressurized fluids. Under these conditions, fluid-rock interaction (reaction kinetics, pressure-solution transfer, sub-critical crack growth, etc.) may impact severely on β and on the magnitude of Δμ.

In this study, motivated by the evidence of intense fluid-rock interaction in exhumed seismogenic faults hosted in the continental crust (Gomila et al., 2021, G3), we performed SHS experiments in a rotary shear apparatus equipped with a dedicated hydrothermal vessel. The goal is to investigate (1) the tribochemical processes and healing behavior of gouge-bearing faults made of granodiorite and, (2) explore how the mechanical properties and healing rates evolve with fault maturity (e.g., fault displacement, duration of fluid-rock interaction).

For the simulated gouge samples (grain size < 75 µm), three set of experiment of SHS were conducted, the first with run-in duration of 500s, whereas the 2nd and 3rd with 5000s, and geochemically contrasted against a non-sheared sample. The fluid (deionized water) saturated gouges were kept under an effective normal stress (σneff) of 10 MPa, a fixed temperature T of 300°C and a constant pore fluid pressure Pf of 25 MPa, and they were slid for ca. 15 mm and 60 mm at a slip rate of 10 µm/s. Hold periods between slip events ranged from 3s to 10000s (1st and 2nd experiments) and from 3s to 300000s (3rd), to investigate the dependence of β and the underlying tribochemical processes with both cumulative slip and duration of the experiment.

Under these hydrothermal conditions, Δμ first increased with holding time (β value of ca. 2.0x10-2 , independently of run-in duration) and then decreased (β = -3.6x10-2, β = -3.0x10-2 and β = -2.6x10-2, for the 1st, 2nd and 3rd experiment, respectively). Bulk XRF analyses on sheared samples show an enrichment of TiO2, MgO and P2O5, while a loss of MnO and CaO oxides with respect to the non-sheared sample. Detailed SEM-EDS analyses show a main mineral loss of biotite and quartz within the main slip zone.

This suggest that under hydrothermal conditions, total shear displacement and duration of the fluid-rock interaction enhance mineral reactions that promote negative healing rates (β < 0) in faults during the seismic cycle. This would imply that during the life-span of an evolving fault, as it matures, it would be possible to (1) lower the fault yield strength due to and increasing fluid-rock interaction, henceforth (2) increase the recurrence but decrease the intensity of the seismic activity.

How to cite: Gomila, R., Feng, W., and Di Toro, G.: Fault-healing and tribochemical processes in granodiorite under hydrothermal conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9600, https://doi.org/10.5194/egusphere-egu23-9600, 2023.

EGU23-9616 | ECS | Orals | EMRP1.2

Healing of gabbro-built faults under hydrothermal conditions 

Wei Feng, Lu Yao, Rodrigo Gomila, Shengli Ma, and Giulio Di Toro

Fault frictional healing Δμ controls the storage of the elastic strain energy in the fault wall rocks and the re-occurrence of earthquakes in pre-existing faults. In the last 40 years, fault healing has been investigated with laboratory slide-hold-slide (SHS) experiments aimed at reproducing the seismic cycle. Experiments performed with different rocks types (e.g., granite, limestone, basalt) revealed that (1) Δμ increases with hold time th and, (2) the frictional healing rate βμ/log th >0. This increase in fault frictional strength with th is interpreted as due to the increase (1) in the real area of contact or (2) of chemical bond strength. However, most of these experiments were conducted under room conditions, whereas natural earthquakes generally nucleate at ambient temperatures T  >150℃ and in the presence of pressurized fluids. Under these ambient conditions, fluid-assisted and thermally-activated processes (pressure-solution transfer, stress corrosion, etc.) may impact on the magnitude of Δμ and on β.

In this study, SHS experiments were performed on gabbro-built gouges (grain size <88 mm) in a rotary shear machine equipped with a pressurized vessel to explore frictional healing under hydrothermal conditions. All experiments were conducted at a constant effective normal stress (σeff =50MPa), and temperature (T) ranging from 25 to 400 ℃  under dry or pore fluid (deionized H2O) pressure (Pf=30 MPa) conditions. In the SHS sequence, the imposed slip velocity was V=10 μm/s, and hold time th varied from 3 to 10000 s. For each experiment, two SHS sequences separated by a slip displacement interval of 40 mm were conducted.

Under dry conditions at all tested temperatures and under hydrothermal conditions but at T  <100℃, Δμ increases with th, consistent with previous experiments. Moreover, the Δμ and β values in the 2nd SHS sequence are slightly higher than those in the 1st sequence, possibly due to the smaller grain size at the larger displacement that promotes fault healing. By contrast, in the experiments performed under hydrothermal conditions but T >200℃, Δμ decreases and β switches to negative values (<0) when the hold is longer than a threshold hold time. In detail, at T=300℃: β= 0.0161±0.0017 for holds <300s and -0.0074±0.0043 for holds >300s, and at T=400℃: β= 0.0057±0.0020 for holds <100s and -0.0227±0.0042 for holds >100s.

The underlying mechanism responsible for the decrease in Δμ and the transition from β > 0 to β < 0 with the hold time, which could result in the transition from seismic to aseismic fault behavior in nature, is still poorly understood. However, high-resolution microstructural analyses conducted by scanning electron microscopy on experimental fault products rule out the formation of weak minerals (e.g., clays) in the gouge layer.  Consequently, the weakening of the fault is probably related to the decrease in bond strength at the asperity contacts.

The experimental data presented here suggest that fault healing of natural faults is controlled by the feedback of multiple physico-chemical processes associated with the slip history and type of fluid-rock interaction under hydrothermal conditions.

How to cite: Feng, W., Yao, L., Gomila, R., Ma, S., and Di Toro, G.: Healing of gabbro-built faults under hydrothermal conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9616, https://doi.org/10.5194/egusphere-egu23-9616, 2023.

EGU23-10016 | ECS | Orals | EMRP1.2

The role of loading path on fault reactivation: a laboratory perspective 

Carolina Giorgetti, Marie Violay, and Cristiano Collettini

Slip along pre-existing faults in the Earth’s crust occurs whenever the shear stress resolved on the fault plane overcomes fault frictional strength, potentially generating catastrophic earthquakes. The coupling between shear stress and normal stress during fault loading depends on 1) the orientation of the fault within the stress field and 2) the tectonic setting. In compressional settings, a load-strengthening path occurs because along thrust faults the increase in shear stress is coupled with an increase in effective normal stress. On the contrary, in extensional settings, the increase in shear stress is coupled with a decrease in effective normal stress, resulting in load-weakening paths for normal faults.

Analytical approaches to evaluate the potential for fault reactivation are generally based on the assumption that faults are ideal planes, characterized by zero thickness and constant friction, embedded in homogeneous isotropic elastic media. However, natural faults typically host thick fault cores and highly fractured damage zones, which can compact or dilate under different loading paths (i.e., different coupling between normal and shear stress). In addition, in most laboratory friction experiments, the fault is loaded under constant or increasing normal stress and at optimal orientation for reactivation. Here, we present laboratory experiments simulating reactivation of thick gouge-bearing faults that experienced different loading paths.

Our results show that the differential stress required for reactivation strongly differs from theoretical predictions, and unfavourably oriented faults appear systematically weaker, especially when a thick gouge layer is present. Before reactivation fault zone compacts in load-strengthening paths whereas dilation is observed in load-weakening path. Upon fault reactivation at comparable normal stress, load-strengthening promotes stable creep  whereas load-weakening results in accelerated slip. Our study highlights the importance of fault thickness and loading path in fault hydromechanical coupling and stability with significant implications for fluid circulation within fault zones and earthquake mechanics.

How to cite: Giorgetti, C., Violay, M., and Collettini, C.: The role of loading path on fault reactivation: a laboratory perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10016, https://doi.org/10.5194/egusphere-egu23-10016, 2023.

EGU23-10314 | ECS | Orals | EMRP1.2

Foreshocks preceding moderate earthquakes in Western Yunnan, China 

Gaohua Zhu and Hongfeng Yang

Although the physical mechanism of earthquake nucleation processes and the link with foreshocks are under debate, foreshocks are still considered as the most reliable earthquake precursors. Investigating the temporal and spatial evolution of foreshock sequences with high resolution and monitoring b-values in real time may shed light on these key issues. Many foreshock and aftershock sequences accompanying moderate mainshocks have been reported in the west of Yunnan Province, China, such as the 2016 Yunlong M 5.1 and 2021 Yangbi Ms 6.4 earthquake sequences. The recently improved coverage of seismic network in western Yunnan provides the opportunity to investigate how the foreshock sequence evolved and establish the temporal transient in b values. To find missing earthquakes and built more comprehensive earthquake catalogs, we carried out earthquake detection using the matched-filter detector. We used events in the standard catalog of China Earthquake Networks Center as templates to scan through continuous waveforms 3-6 months before and after the main shock. We then estimated the b-value and its temporal changes based on the newly developed catalogs. An obvious reduction in b-values before the major earthquake is observed in both the 2016 Yunlong and 2021 Yangbi sequences. We also found that the scattered spatial pattern of foreshocks exhibits a cascading manner and does not support the hypothesis of slow slip driving nucleation of mainshocks.

How to cite: Zhu, G. and Yang, H.: Foreshocks preceding moderate earthquakes in Western Yunnan, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10314, https://doi.org/10.5194/egusphere-egu23-10314, 2023.

The constitutive behavior of faults is central to many interconnected aspects of earthquake science, from fault dynamics to induced seismicity, to seismic hazards characterization. Yet, a friction law applicable to the range of temperatures found in the brittle crust and upper mantle is still missing. In particular, rocks often exhibit a transition from steady-state velocity-strengthening at room temperature to velocity-weakening in warmer conditions that is poorly understood. Here, we investigate the effect of competing healing mechanisms on the evolution of frictional resistance in a physical model of rate-, state-, and temperature-dependent friction. The yield strength for fault slip depends on the real area of contact, which is modulated by the competition between the growth and erosion of interfacial micro-asperities. Incorporating multiple healing mechanisms and rock-forming minerals with different thermodynamic properties allows a transition of the velocity- and temperature-dependence of friction at steady-state with varying temperatures. We explain the mechanical data for granite, pyroxene, amphibole, shale, and natural fault gouges with activation energies and stress power exponent for weakening of 10-50 kJ/mol and 55-150, respectively, compatible with subcritical crack growth and inter-granular flow in the active slip zone. Activation energies for the time-dependent healing process in the range 90-130 kJ/mol in dry conditions and 20-65 kJ/mol in wet conditions indicate the prominence of viscoelastic collapse of micro-asperities in the absence of water and of pressure-solution creep, crack healing, and cementation when assisted by pore fluids. 

How to cite: Barbot, S.: A rate-, state-, and temperature-dependent friction law with competing healing mechanisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10779, https://doi.org/10.5194/egusphere-egu23-10779, 2023.

EGU23-11776 | Orals | EMRP1.2

Dynamic weakening and rupture re-nucleation in rock gouge 

Vito Rubino, Ares Rosakis, and Nadia Lapusta

Many large and damaging earthquakes on mature faults in the Earth’s crust propagate along layers of rock gouge, the fine granular material produced by comminution during sliding. Characterizing gouge rheology is of paramount importance to improve our understanding of earthquake physics, as friction controls key processes of earthquakes, including nucleation, propagation and arrest and how damaging they can be.  In this work, we characterize friction evolution in rock gouge layers during the propagation of dynamic ruptures in a laboratory setting. The experimental setup features a hybrid configuration with a specimen made of an analog material and a rock gouge layer embedded along the interface. This configuration allows us to trigger dynamic ruptures due to the lower shear modulus of the analogue material while at the same time study the gouge frictional behavior during spontaneously evolving dynamic events. Ruptures are captured by the use of digital image correlation coupled with ultrahigh-speed photography. Our measurements reveal dramatic friction variations, with the gouge layer initially displaying strengthening behavior and inhibiting earthquake rupture propagation. However, the gouge layer later features dramatic frictional strength losses, and hosts rupture re-nucleation enabled by dynamic stressing and marked friction weakening at higher slip velocities. Our measurements of the weakening and strengthening behavior of friction in fine rock gouge illustrate the strong dependence of their rheology on slip velocity and related processes, including shear heating, localization/delocalization of shear, and dilation/compaction of the granular shear layer.

How to cite: Rubino, V., Rosakis, A., and Lapusta, N.: Dynamic weakening and rupture re-nucleation in rock gouge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11776, https://doi.org/10.5194/egusphere-egu23-11776, 2023.

EGU23-14284 | Posters on site | EMRP1.2

Frictional evolution of gouge-bearing faults during multiple seismic slip velocity pulses 

Chiara Cornelio, Stefano Aretusini, Elena Spagnuolo, Giulio Di Toro, and Massimo Cocco

Fault zones consist of one or more fault cores sandwiched by a damage zone surrounded by less deformed wall rocks. Most of the deformation is accommodated in the fault core through slip along one or more principal slipping zones. The thickness of fault cores (mm to m) and individual slipping zones (µm to dm) increases with fault slip displacement. In particular, small-displacement or immature faults have such thin slip zones that resemble bare rock surfaces. When exhumed from <5-6 km depth, slip zones are made by poorly cohesive fault gouges.

Several laboratory experimental configurations aim to reproduce the deformation processes activated during seismic slip episodes. In the laboratory, the slip zone is represented as the interaction volume of two bare rock surfaces (i.e., immature faults) or as a mm-thick gouge layer (i.e., more mature faults). Most studies have focused on the frictional behavior of gouge layers or bare rocks during single seismic events, and only a few on the mechanical and microstructural evolution of a gouge layer subjected to multiple events of seismic slip (e.g., Smith et al., 2015). Here, we present rotary-shear friction experiments that reproduce seismic slip on both gouge layers and bare rocks derived from calcite-rich marble. The aim of this study is to analyze the frictional evolution of a gouge layer undergoing multiple seismic slip pulses: four trapezoidal slip pulses at 1 m/s for 1 m of slip, with hold time of 120 s between each pulse. Moreover, we compare this evolution with one of bare rocks of the same material but slid only once at 1 m/s for a total slip higher than 1 m. Experiments were performed at normal stress of 10, 20, and 30 MPa under room humidity conditions.

Our experimental results show that despite the static and dynamic friction coefficients are higher in the gouge layer than in the bare rock experiments, the frictional work to achieve the dynamic friction decreases at each seismic slip pulse in the gouge experiments and is comparable with the bare rock one after the second pulse. High-resolution scanning electron microscope investigations of the sheared gouge layers show that in the first two slip pulses most of the frictional work is spent on (1) strain localization into newly-formed slip zones bounded by continuous ultra-smooth surfaces and, (2) grain size reduction, sintering and compaction (i.e., porosity reduction) within the bulk gouge layer. However, after the second pulse, the slip is localized in one or more well-developed slip zones bounded by ultra-smooth surfaces, that cut through the compacted gouge layer, and the mechanical behavior is similar to that of bare rocks.

Carbonate-bearing fault zones are common seismogenic sources in the Mediterranean area (e.g. 2009 L'Aquila Mw6.3 and 1981 Corinth M6.6 earthquakes). In a series of subsequent seismic slip events, it is shown that the evolution of a gouge layer in carbonate-bearing fault rocks tends to produce a similar mechanical behaviour of bare rocks although the volumetric distribution of strain is significantly different. Importantly, the energy spent by apparently different mechanical processes is eventually similar.

How to cite: Cornelio, C., Aretusini, S., Spagnuolo, E., Di Toro, G., and Cocco, M.: Frictional evolution of gouge-bearing faults during multiple seismic slip velocity pulses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14284, https://doi.org/10.5194/egusphere-egu23-14284, 2023.

In this paper, based on the model of thermal pressurization, we present a new way for the emergence of rate and state phenomenology (RSF, friction law) during the earthquake cycle. In the framework of fault mechanics, the common physical mechanism for the RSF phenomenology is slip and plastic deformation at the asperity contacts. We show that the fundamental physical mechanism of thermal pressurization together with viscosity inside the fault can also reproduce rate and state phenomenology.


More specifically, in our numerical analyses we model frictional weakening during large seismic slip due to thermal pressurization inside the fault. We introduce thermo-hydro-mechanical couplings to model thermal pressurization and a first order micromorphic Cosserat continuum, in order to avoid mesh dependence of the numerical results. Moreover, we introduce viscosity in the form of strain rate hardening. When we perform velocity stepping analyses, our numerical findings show that friction presents, initial peak over-strength and frictional oscillations around a residual value (see Figure). Our results, deriving from fundamental modeling assumptions, exhibit rate and state phenomenology, without the need to introduce the physical mechanism of slip at the asperity contacts.


Keywords: THM couplings; Viscosity; Cosserat continuum; Tribology; Earthquakes

How to cite: Stathas, A. and Stefanou, I.: Viscosity and thermal pressurization during large seismic slip lead to rateand state phenomenology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14607, https://doi.org/10.5194/egusphere-egu23-14607, 2023.

EGU23-15563 | ECS | Posters on site | EMRP1.2

A novel automated procedure for determining steady-state friction conditions in the context of rate- and state- friction analysis 

Piercarlo Giacomel, Daniel Faulkner, Valère Lambert, and Michael Allen

In the framework of empirically-derived rate- and state- friction (RSF) laws, friction constitutive parameters a, b, and Dc  (and further sets of state parameters) are obtained from inverse modelling of laboratory data on the assumption that steady-state conditions are reached following the velocity steps. This method also includes removing any slip-dependent linear trends in friction by linear regression when steady-state conditions are considered to be achieved. The choice of where linear detrending, thereby where to assume the attainment of steady-state friction conditions is therefore key for a correct retrieval of the modelled RSF parameters and their consequent use in modelling of earthquake nucleation. Nonetheless, to date this procedure is still user-dependent and as such, RSF outputs may differ ceteris paribus.

To better elucidate the detrimental consequences of an incorrect assumption of steady-state friction conditions in RSF analysis, in this study synthetic velocity steps were generated with superimposed random Gaussian noise, characterized by increasing characteristic slip distances in the second set of state variables, Dc2,from 0 to 500 µm. In each velocity step, steady-state conditions were assumed starting at progressively larger displacements with respect to the occurrence of the velocity jump. This means that the arbitrarily chosen “steady-state” may or may not correspond to the true steady-state conditions. To retrieve RSF parameters, a slip window of constant size (i.e., 100 µm) was applied from the selected “steady-state” point onwards to remove any linear trend in friction, implying that the remainder of the velocity step beyond the slip window is also at steady-state. During each RSF analysis, the slope calculated from linear regression within the 100 µm long slip window after the velocity steps is systematically compared with the slope computed from linear regression prior to the velocity steps.

Our results show that:

  • while a, b1 and Dc1 are essentially constant regardless of the choices of steady-state and equal to the true values used to generate the synthetic velocity steps, b2 and Dc2 may significantly differ if Dc2 is commensurate with the whole displacement window that contains the velocity step;
  • all modelled RSF parameters coincide with the true ones when the ratio of the slopes before and after the velocity steps approach unity; this observation can be regarded as a proxy for the achievement of the steady-state conditions and becomes increasingly relevant with larger Dc2.

Based on such evidence, we developed a routine that automates the above described work flow, providing a systematic and reproducible technique to determine steady-state friction and thus return the correct RSF parameters. Furthermore, this novel procedure determines the optimal minimum slip window size to remove slip-dependent linear trends in friction and alerts the user when steady-state is not reached within a given step length and hence when Dc2 and b2 cannot be properly determined with experimental data.

How to cite: Giacomel, P., Faulkner, D., Lambert, V., and Allen, M.: A novel automated procedure for determining steady-state friction conditions in the context of rate- and state- friction analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15563, https://doi.org/10.5194/egusphere-egu23-15563, 2023.

EGU23-16290 | Orals | EMRP1.2

Fault zone complexity naturally produces the full slip spectrum: Insights from numerical models 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In addition to regular earthquakes, observations of spatiotemporally complex slip events have multiplied over the last decades. These slip events range along different time scales: from creep , slow slip events to LFEs and tremors. At present, these events are generally interpreted by imposed frictional heterogeneities along the fault plane. However, fault systems are geometrically complex in nature over different scales. We aim in this work to investigate the role of “realistic” fault geometry on the dynamics of slip events. We consider a fault system in a 2D quasi-dynamic setting. The fault system consists of a main self-similar rough fault, surrounded by a dense network of off-fault fractures. All fractures are frictionally homogeneous (rate weakening) and can potentially undergo dynamic slip. We aim to understand how the deformation in the volume is accomodated by the off-fault damage zone and the main fault. What fraction of the “supplied” moment rate is hosted by the off-fault fractures during an earthquake cycle?

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: Fault zone complexity naturally produces the full slip spectrum: Insights from numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16290, https://doi.org/10.5194/egusphere-egu23-16290, 2023.

EGU23-16320 | Orals | EMRP1.2

How do earthquakes stop? Insights from a minimal model of frictional rupture 

Fabian Barras, Kjetil Thøgersen, Einat Aharonov, and François Renard

The question "what arrests an earthquake rupture?" sits at the heart of any potential prediction of earthquake magnitude. Here, we present a one-dimensional, thin-elastic-strip, minimal model, to illuminate the basic physical parameters that control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables, valid for both in-plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge-Knopoff model, with an added characteristic length scale, that corresponds to either the thickness of the damage zone for strike-slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and present closed-form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack- and pulse-like rupture propagation and arrest. Despite its simplicity, this minimal model is able to reproduce several salient features of natural earthquakes that are still debated (e.g. various arrest scenarios, stable pulse-like rupture, back-propagating front, asymmetric slip profiles).

How to cite: Barras, F., Thøgersen, K., Aharonov, E., and Renard, F.: How do earthquakes stop? Insights from a minimal model of frictional rupture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16320, https://doi.org/10.5194/egusphere-egu23-16320, 2023.

EGU23-16777 | ECS | Orals | EMRP1.2

The Stability Transition from Stable to Unstable Frictional Slip with Finite Pore Pressure 

Raphael Affinito, Derek Elsworth, and Chris Marone

Pore fluids are ubiquitous throughout the lithosphere and are commonly cited as a major factor producing slow slip and complex modes of tectonic faulting. Here, we investigate the role of pore pressure on slow slip and the frictional stability transition and find that the mode of fault slip is largely unaffected by pore pressure once we account for effective stress. Ambient temperature experiments are done on synthetic fault gouge composed of quartz powder with a median grain size of 10μm with an average permeability of  8E-17m2 – 6E-18m2 from shear strains 0 - 26. We conduct constant velocity experiments at 20MPa σn’, with Ppnratios of λ from 0.05 to 0.28. Under these conditions, dilatancy strengthening is minimal and we find that slip rate dependent changes in the critical rate of frictional weakening are sufficient to explain slow slip.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: The Stability Transition from Stable to Unstable Frictional Slip with Finite Pore Pressure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16777, https://doi.org/10.5194/egusphere-egu23-16777, 2023.

EGU23-4009 | ECS | Posters on site | NP7.1

Size distributions reveal regime transition of dominant driving force in lake systems 

Shengjie Hu, Zhenlei Yang, Sergio Torres, Zipeng Wang, and Ling Li

Power law size distribution, associated with important system behaviors including scale-invariance, critical tipping and self-organization, has been observed in many complex systems. Such distribution also emerges from natural lakes, with potentially important links to the dynamics of lake systems. But the driving mechanism that generates and shapes this feature in lake systems remains unclear. Moreover, the power law itself was found inadequate for fully describing the size distribution of lakes, due to deviations at the two ends of size range. Based on observed and simulated lakes in China’s 11 hydro-climatic zones, we established a conceptual model for lake systems, which covers the whole size range of lake size distribution and reveals the underlying driving mechanism. The full lake size distribution is composed of three components featured by exponential, stretched-exponential and power law distribution. These three distributions are referred to as three phases which represent system (size) states with successively increasing degrees of heterogeneity and orderliness, and more importantly, indicate the dominance of exogenic and endogenic forces in lake systems, respectively. As the dominant driving force changes from endogenic to exogenic, a phase transition occurs with lake size distribution shifted from power law to stretched-exponential and further to exponential distribution. Apart from compressing the power law phase, exogenic force also increases its scaling exponent, driving the corresponding lake size power spectrum into the regime of “blue noise” with reduced system resilience. Besides, the change may also lead to a rising proportion of small lakes in the whole size distribution, which would increase the overall greenhouse gas emissions from natural lakes.

How to cite: Hu, S., Yang, Z., Torres, S., Wang, Z., and Li, L.: Size distributions reveal regime transition of dominant driving force in lake systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4009, https://doi.org/10.5194/egusphere-egu23-4009, 2023.

EGU23-4271 | ECS | Orals | NP7.1

Study on the rotation of blocks in two-dimensional block-rock mass 

Kuan Jiang and Cheng-zhi Qi

Rock mass has complex block-hierarchical structure involving various scale levels, which should be considered both in dynamic and static conditions. Because the interlayer has weak mechanical properties compared with rock blocks, the deformation of rock mass mainly concentrates at the interlayers both in dynamic and static conditions, which provides the possibility of translation and rotation for rock blocks. The basic carriers of pendulum-type wave in rock mass are geoblocks with translational and rotational degrees of freedom involving various hierarchical levels. The major part of the energy of a blast is spent to fragmentation of rocks and is transferred to rock blocks of the stressed geomedium in the form of kinetic energy (including translational kinetic energy and rotational kinetic energy). The in-situ experimental data has shown that the block-rock mass has significant angular deformation under dynamic impact, and the rotation of blocks can deeply affect the wave propagation and dynamic behavior of rock mass. Previous research on 1D dynamic model of block-rock mass cannot reflect the rotation effect of blocks, and the new 2D dynamic model should take into account the rotation of blocks and energy transfer. Consequently, aiming at the investigation of rotation of blocks, the 2D dynamic model of block-rock mass is established based on the accurate consideration of rotation effect. The research based on this model reveals the mechanism of the rotation of blocks, and determines the characteristics of energy transfer and the influence of the rotation of blocks on the inhomogeneous deformation of interlayers. Research shows that the rotation of blocks is not directly related to whether the structure of rock mass is symmetrical, or whether the interlayer is deformed or not, or the form of external loads, but is caused by the non-equilibrium shear between interfaces in the absence of the external torque. The rotation of blocks results in the inhomogeneous deformation of interlayers, and has a significant influence on the shear deformation of interlayers. At some local positions, in addition to the deformation of the interlayer caused by translation, the block-rock mass also produces additional tension and compression deformation caused by the rotation of blocks, which may lead to the phenomenon of rock crushing. This study theoretically solves the problems of wave propagation in block medium under arbitrary loads and torque, and is helpful for the research of seismic wave propagation in block medium with inhomogeneous complex structures.

How to cite: Jiang, K. and Qi, C.: Study on the rotation of blocks in two-dimensional block-rock mass, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4271, https://doi.org/10.5194/egusphere-egu23-4271, 2023.

EGU23-6080 | ECS | Posters virtual | NP7.1

Rocks with rotating blocks: 1D displacement, rotation and wave propagation 

Maoqian Zhang, Elena Pasternak, and Arcady Dyskin

Fragmentation of rocks, e.g. splitting into blocks, is a common occurrence at a range of scales from rock fragmentation caused by rockbursts or blasting to blocky rock mass produced by systems of fractures to rubble-pile asteroids. Common in these diverse objects is the ability of blocks (fragments) to assume relatively independent displacement and/or rotation.

 

Modelling deformation of blocky/fragmented rocks is complicated by the phenomenon of elbowing [1] whereby the rotating block pushes away the neighbouring blocks. The direction of the push can be independent of the direction of block rotation making the problem strongly non-linear (the “absolute value” type non-linearity). In order to investigate elbowing we constructed a simple 1D physical model of a chain of blocks with one translational and one rotational degrees of freedom. It is found that when one block (the initial block) is rotated, the neighbouring blocks may not rotate, only displace, depending on the magnitude of friction and the number of blocks in the chain. A discrete element (3DEC) model of the chain is developed. It shows the conditions of rotation of the blocks and the rotational wave propagation following a pulse rotation of the initial block.

 

  • Pasternak, E., Dyskin, A.V., Estrin, Y. (2006) Deformations in transform Faults with rotating crustal blocks. Pure Appl. Geophys. 163 2011–2030.

 

Acknowledgement. The authors are grateful to Dr I. Shufrin and School of Engineering workshop for help with designing and manufacturing of the physical model. EP and AVD acknowledge support from the Australian Research Council through project DP210102224.

How to cite: Zhang, M., Pasternak, E., and Dyskin, A.: Rocks with rotating blocks: 1D displacement, rotation and wave propagation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6080, https://doi.org/10.5194/egusphere-egu23-6080, 2023.

EGU23-6358 | ECS | Posters virtual | NP7.1

Thermal spallation and fracturing of rocks produced by surface heating 

Yide Guo, Elena Pasternak, and Arcady Dyskin

Heating of rock surface (e.g., flame heating) induces compressive stresses in the surface layer and tensile stresses of lower magnitude in the layer beneath. If the heating temperature is large enough (around 900 deg for shales), the compressive stresses initiate spallation produced by pre-existing cracks that and extensively grow parallel to the surface under compression. The extensive cracks separate thin layers from different parts of the heated surface which eventually buckle opening a new surface which starts being subjected to flame heating. Then the spallation process repeats itself producing a cavity of approximately cylindrical shape growing into the rock normal to the surface.

 

The presentation reports the results of tests on flame heating of shales, which demonstrate that the spallation process is accompanied by emergence of a large tensile fracture normal to the surface. In order to check whether the fracture can be produced by tensile thermal stresses induced in the layer situated under the compressed layer we conducted a series of finite element simulations of thermal stresses for different spallation depths (depths of the cavity). The modelling shows that: (1) as the spallation cavity deepens the magnitudes of maximum compressive and tensile stresses remain approximately the same except of two peaks at the spallation depths of about 6% and 30% of the diameter of the heating flame; (2) the magnitude of the maximum tensile stresses is about half of the compressive stress. Given that the spallation strength is about half of the UCS (e.g., [1]) and that the tensile strength is often up to an order of magnitude lower than the UCS, the induced tensile thermal stresses can be considered as sufficient to produce the tensile fracture.

 

The experiment and computer modelling suggest that the production of tensile fractures is an intrinsic feature of the spallation process. These results can assist in understanding large scale spallation-like processes in the Earth’s crust and design rock cutting based on thermal spallation.

 

  • Wang, H., A.V. Dyskin, Pasternak, P. Dight and B. Jeffcoat-Sacco, 2021. Fracture mechanics of in-situ spallation. Engineering Fracture Mechanics, 260, 108186.

How to cite: Guo, Y., Pasternak, E., and Dyskin, A.: Thermal spallation and fracturing of rocks produced by surface heating, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6358, https://doi.org/10.5194/egusphere-egu23-6358, 2023.

Spallation is a type of surface rock failure under uniaxial and biaxial compression manifested by successive production and ejection of spalls/fragments. This type of failure is observed in laboratory experiments on uniaxial/biaxial compression of rocks and mortar as well as in rock masses. In the latter case spallation is seen in slopes and in the walls of underground openings. In its unstable phase the spallation can lead to such a dangerous phenomenon as strain rockburst.

Spallation is caused by formation and extensive growth of wing cracks parallel to a free surface (e.g., excavation wall) under the applied compressive load. Their growth amplified by the strong interaction with the surface leads to separation of thin layers whose subsequent buckling produces the spalls and opens a new surface. This produces new wing cracks extensively growing parallel to the new surface, thus enabling the process that repeats itself, e.g. [1].

A critical role in this mechanism is played by the interaction of the wing crack with the free surface. The interaction is the stronger the closer the wing crack to the free surface. The closeness to the free surface is limited by the sizes of the largest pre-existing defects seeding the wing cracks. Therefore, the wing cracks inducing each step of spallation are approximately coplanar. Subsequently, the layer separated from the bulk of the rock can be considered as a plate connected to the main part of the rock by bridges formed by intact rock sections remaining between the wing cracks. In the first approximation the effect of bridges can be modelled by Winkler layer [2]. The cracks are assumed to be disc-like; the interaction with the free surface is computed using the beam asymptotics [3].

The velocity of flexural wave propagation depends upon the Winkler layer stiffness and the frequency of oscillations. There exists a minimum frequency, below which the wave does not propagate.  Both parameters depend upon the average crack radius and the number of wing cracks. If the monitoring of the wave velocities and the minimum frequency is complemented by monitoring of the average surface deformation (for instance using non-contact methods such as the digital image correlation) the parameters of the spallation process can be determined, and the approaching buckling phase identified. Results of this research will be instrumental in developing methods of monitoring and predicting strain rockbursts.

1. Wang H, A.V. Dyskin, E. Pasternak, P. Dight and B. Jeffcoat-Sacco, 2022. Fracture mechanics of spallation. Engineering Fracture Mechanics, 260:108186.

2. He, J., Pasternak, E. and A.V. Dyskin, 2020. Bridges outside fracture process zone: Their existence and effect. Engineering Fracture Mechanics, 225, 106453.

3. Dyskin, A.V., L.N. Germanovich and K.B. Ustinov, 2000. Asymptotic analysis of crack interaction with free boundary. J. Solids Structures, 37, 857-886.

4. Lloyd J.R. and Miklowitz, 1962. Wave Propagation in an Elastic Beam or Plate on an Elastic Foundation. J. Applied Mechanics, 459-464.

Acknowledgement. The authors acknowledge support from the Australian Research Council through project DP210102224.

How to cite: Dyskin, A. and Pasternak, E.: Monitoring of spallation processes in rocks by continuous measurements of surface deformation and wave parameters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6427, https://doi.org/10.5194/egusphere-egu23-6427, 2023.

EGU23-6464 | Orals | NP7.1

Cracking properties of shale influenced by bedding layers and a pre-existing slot 

Yuxin Ban, Jun Duan, Qiang Xie, Xiang Fu, and Weichen Sun

The key to increasing shale gas production is to construct fracture networks in shale reservoir to provide channels for shale gas. Understanding the cracking characteristics of shale is necessary for oil and gas exploitation engineering. Given this, uniaxial compression tests were conducted on Longmaxi shale in China to study the mechanical properties and cracking behaviors affected by bedding layers and pre-existing slot. Sandstone specimens with different pre-existing slot angles were also tested as a comparison. A mechanical-optical-acoustical comprehensive data acquisition system consisting of a rigid hydraulic machine, high-speed industrial camera and acoustic emission acquisition instrument was established to monitor the cracking behaviors in real time. The results show that the cracking behaviors of shale specimens are quite different from sandstone specimens in the uniaxial compression tests. Crack initiation is predominantly controlled by the pre-existing slot and is also affected by bedding layers. Crack propagation is mainly controlled by bedding layers and stress field distribution. When the bedding layers are vertical, the cracks are most likely to propagate along the direction of the bedding and tensile cracks are observed. When the bedding is 30°, the shale specimens are most likely to be controlled by the bedding layers, resulting in shear slip failure along the bedding layers. The experimental results contribute to the understanding of cracking properties in layered anisotropic materials.

How to cite: Ban, Y., Duan, J., Xie, Q., Fu, X., and Sun, W.: Cracking properties of shale influenced by bedding layers and a pre-existing slot, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6464, https://doi.org/10.5194/egusphere-egu23-6464, 2023.

EGU23-6515 | Posters virtual | NP7.1

Harmonics multiple to the driving frequency of damped bilinear oscillators 

Elena Pasternak, Arcady Dyskin, Roman Pevzner, and Boris Gurevich

Field observations show that power spectra of the response to high amplitude harmonic excitation contain peaks at frequencies multiple to the driving frequency, e.g. [1]. This phenomenon is conventionally attributed to the effect of mechanical non-linearity of the Earth’s crust. Given that there exist various types of non-linearity it is important to identify the types of non-linearities that can produce multiple harmonics in response to high power excitation and thus ensure the correct interpretation of the monitoring data.

One type of non-linearity capable of producing multiple resonances is bilinearity of stiffness, the simplest representation of which is a bilinear oscillator – the oscillator with different stiffnesses for compression and tension. In the Earth’s crust the role of bilinear oscillators can be played by pre-existing fractures initially closed by the in-situ compression but capable of being opened by the tensile phase of the applied high amplitude harmonic excitation.

Bilinear oscillators possess multiple resonances, e.g. [2], however these are multiples of the natural frequency. We note that extreme damping effected by the presence of fluids in fractures and porous rocks can quickly eliminate the effect of the natural frequency leaving only the stationary oscillations with the driving frequency in each linear (tensile or compressive) stage of oscillations. The transition from one stage to another is characterised by short transients, which gives rise to multiple spectral peaks. This mechanism is investigated in asymptotics of high damping ratio. It is shown the existence of the following spectral peaks: if f0 is the driving frequency, the peaks will be observed at 2f0, 3f0, 5f0 and further at all odd multiples of f0.

The theory developed is essential for identifying the prevailing mechanisms of non-linearity in the Earth’s crust and determining their parameters.

1. Yurikov, A., B. Gurevich, K. Tertyshnikov, M. Lebedev, R. Isaenkov, E. Sidenko, S. Yavuz, S. Glubokovskikh, V. Shulakova, B. Freifeld, J. Correa, T.J. Wood, I.A. Beresnev and R. Pevzner, 2022. Evidence of nonlinear seismic effects in the earth from downhole distributed acoustic sensors. Sensors 2022, 22, 9382.

2. Dyskin, A.V., E. Pasternak and E. Pelinovsky, 2012. Periodic motions and resonances of impact oscillators. Journal of Sound and Vibration 331(12) 2856-2873.

Acknowledgement. EP, AVD and BG acknowledge support from the Australian Research Council through project DP190103260. RP and BG acknowledge financial support from the Australian Department of Industry, Science and Resources for the 2021 Global Innovation Linkage (GILIII000114) grant and the Sponsors of the Curtin Reservoir Geophysics Consortium.

How to cite: Pasternak, E., Dyskin, A., Pevzner, R., and Gurevich, B.: Harmonics multiple to the driving frequency of damped bilinear oscillators, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6515, https://doi.org/10.5194/egusphere-egu23-6515, 2023.

EGU23-6565 | Posters virtual | NP7.1

Study of deformation and fracture behavior of shale by a novel anisotropic regular lattice spring model 

Qiang Xie, Weichen Sun, Kai Wu, Zhilin Cao, Xiang Fu, Alessio Fumagalli, and Yuxin Ban

This research aims to study the deformation and fracture behavior of shale by a novel anisotropic regular lattice spring model (ARLSM). The novel ARLSM applies the normal and tangential coupling spring to release the Poisson's ratio limitation in the traditional regular lattice spring model. Meanwhile, a nonlinear strength criterion is introduced into ARLSM to simulate the fracture failure of shale. Two benchmark problems are tested to implement the research. The study shows that ARLSM has larger range of Poisson's ratio and better effects comparing with the existing anisotropic lattice spring model. Moreover, ARLSM can accurately predict the deformation and fracture behavior of shale under different conditions.

How to cite: Xie, Q., Sun, W., Wu, K., Cao, Z., Fu, X., Fumagalli, A., and Ban, Y.: Study of deformation and fracture behavior of shale by a novel anisotropic regular lattice spring model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6565, https://doi.org/10.5194/egusphere-egu23-6565, 2023.

After the impoundment of a high dam reservoir, the water pressure environment of the rock masses in dam base and reservoir bank changes, which may easily induce engineering problems such as bank slope instability and dam collapse. In order to investigate the differences and mechanisms of different constant water pressures on the rock mass of dam base, triaxial loading tests were conducted on sandstone with initial damage under different high constant porewater pressures, and the multidirectional fracture mechanism was analyzed by combining CT and electron scans. The test results show that:(1) Under the confining pressure of 80 MPa, the greater the pore water pressure, the more brittle the sandstone is, the lower the peak strength, the smaller the volume expansion stress, the pore water pressure increases from 10 MPa to 50 MPa, and the peak strength decreases by 33%.  (2) For different pore water pressure, there are significant differences in sandstone internal deterioration range and deterioration effect  as the fracture surfaces of sandstone specimens have various forms and directions. Due to CT scaning results, with the pore water pressure increases, the deterioration effect spreads from specimen middle to both ends. When the water pressure-confining pressure ratio is less than 25.0%, the deterioration of pore water pressure is mainly concentrated in the middle 1/3 of the specimen. When the water pressure-confining pressure ratio is bigger than 62.5%, the pore water pressure has obvious deterioration effect on the whole specimen. (3) Electron microscopy scanning reveals that with the increase of pore water pressure: the microgranular structure of sandstone changes from shear slip failure to shear fracture failure, and the microcrystalline structure of sandstone changes from cauliflower to rice granular. The macroscopic failure mode changes from plastic failure to brittle failure, and multidirectional fracture plane is formed, which is related to the migration of fine particles and the fracture of large particles in the meso-particle structure under pore water pressure. The formation of the multidirectional fracture plane is directly related to the shear strength of the microscopic crystal structure.

How to cite: Fu, X., Ban, Y., Xie, Q., and Sun, W.: Triaxial compression mechanical properties and multidirectional fracture mechanism of sandstone under different pore pressure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6852, https://doi.org/10.5194/egusphere-egu23-6852, 2023.

EGU23-7495 | ECS | Orals | NP7.1

Joint multifratcal analysis of available wind power and rain intensity from an operational wind farm 

Jerry Jose, Auguste Gires, Ernani Schnorenberger, Ioulia Tchiguirinskaia, and Daniel Schertzer

Wind power production plays an important role in achieving UN’s (United nations) Sustainable development goal (SDG) 7 - affordable and clean energy for all; and in the increasing global transition towards renewable and carbon neutral energy, understanding the uncertainties associated with wind and turbulence is extremely important. Characterization of wind is not straightforward due to its intrinsic intermittency: activity of the field becomes increasingly concentrated at smaller and smaller supports as the scale decreases. When it comes to power production by wind turbines, another complexity arises from the influence of rainfall, which only a limited number of studies have addressed so far suggesting short term as well as long term effects. To understand this, the project RW-Turb (https://hmco.enpc.fr/portfolio-archive/rw-turb/; supported by the French National Research Agency, ANR-19-CE05-0022) employs multiple 3D sonic anemometers (manufactured by Thies), mini meteorological stations (manufactured by Thies), and disdrometers (Parsivel2, manufactured by OTT) on a meteorological mast in the wind farm of Pays d’Othe (110 km south-east of Paris, France; operated by Boralex). With this simultaneously measured data, it is possible to study wind power and associated atmospheric fields under various rain conditions.

Variations of wind velocity, power available at the wind farm, power produced by wind turbines and air density are examined here during rain and dry conditions using the framework of Universal Multifractals (UM). UM is a widely used, physically based, scale invariant framework for characterizing and simulating geophysical fields over wide range of scales which accounts for the intermittency in the field. While statistically analysing the power produced by turbine, rated power acts like an upper threshold resulting in biased estimators. This is identified and quantified here using the theoretical framework of UM along with the actual sampling resolution of instruments under study. Further, from event based analysis, differences in UM parameters were observed between rain and dry conditions for the fields illustrating the influence of rain. This is further explored using joint multifractal analysis and an increase in correlation exponent was observed between various fields with increase in rain rate.

How to cite: Jose, J., Gires, A., Schnorenberger, E., Tchiguirinskaia, I., and Schertzer, D.: Joint multifratcal analysis of available wind power and rain intensity from an operational wind farm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7495, https://doi.org/10.5194/egusphere-egu23-7495, 2023.

EGU23-7726 | Orals | NP7.1

Dynamic response of an elliptic cylinder inclusion with imperfect interfaces subjected to plane SH wave 

Tao Ming, Luo Hao, Zhao Rui, and Xiang Gongliang

Underground chambers or tunnels often contain inclusions, the interface between the inclusion and the surrounding rock is not always perfect, which influences stress wave propagation. In this study, the spring model and Ricker wavelet were adopted to represent the imperfect interface and transient seismic wave. Based on the wave function expansion method and Fourier transform, an analytical formula for the dynamic stress concentration factor (DSCF) for an elliptical inclusion with imperfect interfaces in infinite space subjected to a plane SH-wave was determined. The theoretical solution was verified via numerical simulations using the LS-DYNA software, and the results were analyzed. The effects of the wave number (k), radial coordinate (ξ), stiffness parameter (β), and differences in material properties on the dynamic response were evaluated. The numerical results revealed that the maximum DSCF always occurred at both ends of the elliptical minor axis, and the transient DSCF was generally a factor of 2-3 greater than the steady-state DSCF. Changes in k and ξ led to variations in the DSCF value and spatial distribution, changes in β resulted only in variations in the DSCF value, and lower values of ωp and β led to a greater DSCF under the same parameter conditions. In addition, the differences in material properties between the medium and inclusion significantly affected the variation characteristics of the DSCF with k and ξ.

How to cite: Ming, T., Hao, L., Rui, Z., and Gongliang, X.: Dynamic response of an elliptic cylinder inclusion with imperfect interfaces subjected to plane SH wave, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7726, https://doi.org/10.5194/egusphere-egu23-7726, 2023.

EGU23-7767 | ECS | Orals | NP7.1

Simulating Evapotranspiration in Green roofs using a Multifractal approach 

Arun Ramanathan S, Pierre-Antoine Versini, Daniel Schertzer, Ioulia Tchiguirinskaia, Remi Perrin, and Lionel Sindt

Abstract

Several equations and their simplified versions already exist for estimating evapotranspiration. Still, the practical difficulty in using them is that they contain too many variables and empirical parameters including some non-atmospheric vegetation-based ones which may not be appropriate for all plant types. Therefore, a simple empirical equation is suggested here to approximately estimate evapotranspiration loss in a deterministic manner as a function of the green roof’s water content, ambient air temperature, wind speed, relative humidity, and total net radiation flux. For nonlinear processes such as evapotranspiration clearly, such deterministic estimates are not representative of the extreme values observed in evapotranspiration losses. Therefore, a universal multifractal-based simulation procedure is proposed here to improve such deterministic estimates, so that the simulated evapotranspiration loss has realistic intermittency and temporal scaling behaviour, while preserving its diurnal variability.

 

Keywords

Multifractals, Non-linear geophysical systems, Cascade dynamics, Scaling, Hydrology, Meteorology.

 

How to cite: Ramanathan S, A., Versini, P.-A., Schertzer, D., Tchiguirinskaia, I., Perrin, R., and Sindt, L.: Simulating Evapotranspiration in Green roofs using a Multifractal approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7767, https://doi.org/10.5194/egusphere-egu23-7767, 2023.

EGU23-8426 | ECS | Posters on site | NP7.1

Effect of Rainfall Fractal Behaviour on that of Recharge and Groundwater Levels 

Abrar Habib, Athanasios Paschalis, Adrian P. Butler, Christian Onof, John P. Bloomfield, and James P. R. Sorensen

Using a physically based recharge-groundwater flow model, a multiplicative random cascade rainfall model and robust detrended fluctuation analysis (r-DFA), the effect of the fractal behaviour of rainfall on recharge and groundwater levels is investigated. The study site selected for this work is in Wallingford, United Kingdom, where groundwater levels in a shallow riparian aquifer and meteorological data of high temporal resolution are monitored.

The rainfall model is calibrated to the observed rainfall and used to simulate 40 synthetic rainfall series exhibiting different scaling behaviour (with r-DFA scaling exponents between 0.6 and 1.05). The scaling behaviour of the rainfall series are then objectively quantified using r-DFA. The synthetic rainfall is used as forcing to run the recharge-groundwater flow model which is calibrated to the observed groundwater levels.

It is found that small changes in the fractal behaviour of rainfall has a significant effect on the fractal behaviour of recharge and this in turn results in a small change in the fractal behaviour of groundwater levels. The significant effect on the fractal behaviour of drainage is attributed to the extended recharge periods which correspond to more frequent rain events in rainfall with higher scaling exponents. This effect is more subdued in groundwater level fluctuations due to attenuation of the recharge signal as it percolates through the unsaturated zone.

How to cite: Habib, A., Paschalis, A., Butler, A. P., Onof, C., Bloomfield, J. P., and Sorensen, J. P. R.: Effect of Rainfall Fractal Behaviour on that of Recharge and Groundwater Levels, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8426, https://doi.org/10.5194/egusphere-egu23-8426, 2023.

Rainfall fields exhibit extreme variability over wide range of space-time scales which make them complex to characterize, model and even measure. Furthermore, rainfall, as most geophysical fields, is strongly anisotropic. Fortunately, scaling anisotropy has been developed for a few decades to generalise scaling in an anisotropic framework, e.g., in the simplest case iso-surfaces become self-affines ellipsoids instead of self-similar spheres. This is particularly straightforward for continuous in scale cascades. For them, as well as for discrete in scale cascades, Universal Multifractals (UM) have been widely used to analyse and simulate such geophysical fields with the help of a very limited number of physically meaningful parameters. Recently blunt cascades have been introduced. They enable to remain in the simple framework of discrete cascades while partly overcoming their well known strong limitations such as non-stationnarity. It basically consists in geometrically interpolating over moving windows the multiplicative increments at each cascade steps.

Here we suggest to incorporate observed features in blunt 2D and 3D (space-time) blunt discrete cascade simulations. The data analysis corresponds to a 1D analysis along various directions ,considering each lof them as a different “sample” of the process. Analysing how the UM parameters change with the angle of the chosen direction enables to unveil underlying rainfall anisotropy features. Impacts, and notably potential biases, of these features on standard spatial analysis in 2D are also explored and discussed. For this purpose high resolution space-time rainfall data collected with help of a dual polarisation X-band radar operated by HM&Co-ENPC is used .

To simulate anisotropy features with the help of blunt extension of discrete UM cascades, we tentatively suggest to use moving window shaped as ellipses instead of squares. Tuning the eccentricity and orientation of the ellipses enables to introduce various levels of anisotropy within the simulated fields. First, multifractal expected behaviour is theoretically established and then it is numerically confirmed with the help of ensembles of stochastic simulations and the previously developed analysis approach.

Authors acknowledge the RW-Turb project (supported by the French National Research Agency - ANR-19-CE05-0022), for partial financial support.

How to cite: Gires, A., Tchiguirinskaia, I., and Schertzer, D.: Characterizing and simulating with blunt extension of discrete cascades rainfall anisotropy in a Universal Multifractals framework, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9020, https://doi.org/10.5194/egusphere-egu23-9020, 2023.

Over the past years in the development of oil and gas fields, there has been a trend towards an increase in the development of unconventional low-permeability reservoirs. In this regard, it is becoming increasingly important to study the problems associated with the use of hydraulic fracturing technology (HF) in rocks with a complex internal structure. To achieve the maximum oil and gas production rate and increase the drainage zone in the near-wellbore space, it is necessary to carry out hydraulic fracturing with the most extensive system of fractures.

In this work the authors investigate the propagation of a hydraulically driven fracture in a fully saturated, permeable, and porous medium at the pore scale. To achieve a goal, at the first stage, we set a system of determining ratios and a crack propagation criterion. At the next stage, a three-dimensional numerical poroelastic model of a rock sample is prepared based on a three-dimensional image of the pore space of rock samples. Then numerical poroelastic modeling of the processes of one- and two-phase filtration and rock destruction using the extended finite element method is performed. For a more accurate description of filtration processes, the authors have prepared a physico-mathematical model that takes into account the flow rate and leakage of fluid into the rock during fracture growth at the pore scale. The obtained numerical results are compared with the previously conducted results of laboratory studies.

As a result of the numerical simulation, the authors prepared a digital rock model (DRM) based on microCT data, performed numerical simulation of the filtration process in the DRM and numerical simulation of fracture propagation in a fully saturated, permeable, and porous medium at the pore scale. Then, the dependences of filtration, initiation and fracture propagation were investigated depending on various conditions of HF fluid injection.

How to cite: Taurenis, D. and Nachev, V.: Three-dimensional numerical simulation of multiphase filtration and fracture propagation at the pore scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9483, https://doi.org/10.5194/egusphere-egu23-9483, 2023.

EGU23-10989 | ECS | Posters virtual | NP7.1

Using Equivalent Horton-Strahler Ratios to Predict Extreme Events in Colombian Andes Catchments 

Juan Mauricio Bedoya-Soto and Heli Steven Ocampo-Zapata

The frequency and severity of extreme hydrometeorological events in the Colombian Andes have increased due to the combined effects of climate change and climate variability, with the El Niño-Southern Oscillation (ENSO) being the main contributor. To address this issue and improve hydrologic and hydraulic infrastructure designs, it is necessary to develop better tools for accurately predicting the impact of these events. Hydrological scaling and similarity, based on relatively simple mathematical laws, can synthetically translate the high heterogeneity of hydrological processes into equations that are particularly useful in ungauged catchments, a widespread problem in the Colombian Andes. This research proposes the use of specific hydrological scaling tools, including the Geomorphological Instantaneous Unit Hydrograph (GIUH) and the equivalent Horton-Strahler (H-S) ratios, to calculate peak flows. These ratios express the self-similarity of channels and basins, independent of the threshold area for channel initiation, which the classical bifurcation ratio (RB), length ratio (RL), and area ratio (RA) depend on. Using digital elevation model (DEM) data from NASA's ALOS-PALSAR mission, which provides terrain elevation at a resolution of 12.5m x 12.5m, we analyzed regional patterns of extreme event scaling on various slopes of the Andes Mountains (Colombia) using the GIUH/equivalent H-S theory. With this DEM data, we developed a methodology for automatically extracting the equivalent H-S (RBe, RLe, RAe) in several catchments of the Western, Central, and Eastern ranges that compose the Colombian Andes, while simultaneously validating the self-similarity assumption of their channel networks. Our results highlight the importance of the equivalent H-S ratios as self-similarity indices and regional indicators of the intrinsic relationship between geomorphology and hydrology in the Colombian Andes and their usefulness for hydrological design engineering purposes.

How to cite: Bedoya-Soto, J. M. and Ocampo-Zapata, H. S.: Using Equivalent Horton-Strahler Ratios to Predict Extreme Events in Colombian Andes Catchments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10989, https://doi.org/10.5194/egusphere-egu23-10989, 2023.

EGU23-11210 | ECS | Posters on site | NP7.1

Power law Scaling in Drainage Basin Areas of Independent landscapes 

Dnyanesh Borse and Basudev Biswal

Power-law distributions occur in a diverse range of phenomena. Natural drainage networks also exhibit distinctive fractal properties and certain power-law scaling relationships irrespective of the underlined controls, such as geology, topography, and climate. Here we study the distribution of basin areas of continents as well as some islands. We used area-fraction vs. rank distribution, where the area fraction represents the area of a basin with respect to the total landscape area. To obtain the basin area distribution, we used HydroRivers data for the nine continent regions and performed DEM analysis for 12 islands. The results show that basin area distribution follows a power law in the case of all continents with scaling exponent ranging from -1.15 to -1.4. In the case of islands, the majority of them followed power law scaling with exponent ranging from -1.2 to around -2.5; however, distributions of some islands deviated from the power laws.

We also looked at the basin area distribution with the optimal channel network model with all boundary pixels modelled as outlets. We got the scaling exponent around -1.8. Our recently proposed probabilistic model for drainage network evolution (Borse & Biswal, 2023) shows the capability to produce networks with different distributions. This model can capture the varying range of exponents with its flexible parameters. Further studies would be needed to understand the significance of this basin area distribution scaling exponent and whether it could be used as a metric to characterize landscapes.

How to cite: Borse, D. and Biswal, B.: Power law Scaling in Drainage Basin Areas of Independent landscapes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11210, https://doi.org/10.5194/egusphere-egu23-11210, 2023.

EGU23-11767 | ECS | Orals | NP7.1

Small Scales Space-Time Variability of Wind Fields: Simulations with Vector Fields and Transfer to Turbine Torque Computation 

Ángel García Gago, Auguste Gires, Paul Veers, Ioulia Tchiguirinskaia, and Daniel Schertzer

Wind fields are extremely variable in space and time over a wide range of scales. This extreme variability is transferred to the wind turbine torque and ultimately to wind energy production. The Universal Multifractal (UM) framework is a powerful tool that allows to characterise and simulate the extreme variability of geophysical fields across scales with the help of only three parameters (α, C1 and H) with physical interpretation; while the 4th, the power a of a conservative flux, is absorbed by the empirical estimation of the mean singularity over a non-conservative field.

The main challenge is to simulate over 2D space plus time vector fields which realistically reproduce observed spatial and temporal variability of wind fields. The outer scale of the simulated fields should basically correspond to the size of the wind turbine in space and ten minutes in time. To achieve that, we combine two broad classes of stochastic processes: stable Levy processes and Clifford algebra. We use as input characteristic parameters obtained from the multifractal analysis of the data collected by two high-resolution 3D anemometers with approx. 33 m vertical distance on a meteorological mast. The data is collected as part of the RW-Turb measurement campaign (https://hmco.enpc.fr/portfolio-archive/rw-turb/), supported by the French National Research Agency (ANR-19-CE05-0022). The expected behaviour of the simulated field is confirmed by multifractal analysis. 

In the second step, we investigate the effect of small-scale wind variability on the wind turbine torque computation by imputing the simulated vector fields to three modelling chains with increasing complexity. The first one only considers the temporal variability, averaging the wind field and considering it at hub height. The second one is based on the angular moment definition and allows us to consider both spatial and temporal variability by computing the torque at each blade point and integrating it along the radius for each time step. Finally, the third one uses the realistic software OpenFAST developed by the US National Renewable Energy Laboratory (NREL). To analyse and physically interpret wind variability's effect, we compared the torque obtained by the three modelling chains focused on the small scales. As we expected, we found pronounced differences on small scales with stronger fluctuations exhibited in the second modelling chain, followed by OpenFAST and the first one. 

How to cite: García Gago, Á., Gires, A., Veers, P., Tchiguirinskaia, I., and Schertzer, D.: Small Scales Space-Time Variability of Wind Fields: Simulations with Vector Fields and Transfer to Turbine Torque Computation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11767, https://doi.org/10.5194/egusphere-egu23-11767, 2023.

We propose a theory for preventing instabilities in frictionally unstable systems such as earthquakes are. We exploit the dependence of friction on fluid pressure and use it as a backdoor for provoking controlled, slow-slip over a single mature seismic fault. We use the mathematical Theory of Control and notions from passivity in order to (a) stabilize and restricting chaos, (b) impose slow frictional dissipation and (c) tune the system toward desirable global asymptotic equilibria of lower energy. Our control approach is robust and does not require exact knowledge of the frictional behavior of the system and its fluid diffusion properties (e.g. permeability, viscosity, compressibility) or of other parameters related to complex physical processes that are hard to determine in practice. We expect our methodology to inspire earthquake mitigation strategies regarding anthropogenic and/or natural seismicity.

References

[1] Stefanou, I. (2019). Controlling Anthropogenic and Natural Seismicity: Insights From Active Stabilization of the Spring‐Slider Model. Journal of Geophysical Research: Solid Earth, 124(8), 8786–8802. https://doi.org/10.1029/2019JB017847
[2] Tzortzopoulos G., Braun P., Stefanou I. (2021), Absorbent Porous Paper Reveals How Earthquakes Could be Mitigated, Geophysical Research Letters 48. https://doi.org/10.1029/2020GL090792.
[3] Stefanou, I., Tzortzopoulos, G. (2022). Preventing instabilities and inducing controlled, slow-slip in frictionally unstable systems. Journal of Geophysical Research: Solid Earth. https://doi.org/10.1029/2021JB023410
[4] Gutiérrez-Oribio D., Tzortzopoulos G., Stefanou I., Plestan F. (2022). Earthquake Control: An Emerging Application for Robust Control. Theory and Experimental Tests. http://arxiv.org/abs/2203.00296
[5] Papachristos, E., Stefanou, I. (2022), Controlling earthquake-like instabilities using artificial intelligence. http://arxiv.org/abs/2104.13180.
[6] Gutiérrez-Oribio D., Stefanou I., Plestan F. (2022). Passivity-based Control of a Frictional Underactuated Mechanical System: Application to Earthquake Prevention. https://arxiv.org/abs/2207.0718

How to cite: Stefanou, I., Tzortzopoulos, G., and Gutierrez-Oribio, D.: Preventing earthquake instabilities and inducing controlled, slow-slip by active fluid pressure control in the vicinity of a single seismic fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14939, https://doi.org/10.5194/egusphere-egu23-14939, 2023.

EGU23-16812 | Posters virtual | NP7.1

Study of tectonic fault transition from aseismic to seismic slip due to fluid injection 

Sergey Turuntaev and Vasily Riga

The conditions for the transition from slow slip to seismic generation motion along a tectonic fault as a result of fluid injection through a well located near the fault are studied.

Movements along the fault caused by fluid injection can occur in the form of slow slips or lead to earthquakes. The implementation of a particular type of movement is dependent on the injection parameters and the fault friction and stress conditions. Numerical calculations were performed in which the consequences of fluid injection lasting from 1.5 months to 6 years were modeled. The calculations varied the total volume of the injected fluid, the flow rate during injection, the rate-state friction law properties of the fault, tangential stresses on the fault. It was found that under certain combinations of fault parameters and fluid flow, seismic generations occur. The transition to such a mode within the framework of the considered model occurs abruptly, a further increase in the injection rate does not lead to an increase in the rate of seismic movement, reaching values of 0.1-1 m/sec, depending on tectonic tangential stresses.

With fixed parameters of the rate-state friction law, the magnitude of the maximum displacement velocity depends on the rate of the pressure perturbation on the fault. Until the sliding velocity reaches a value of the order of 10-6 m/sec, the dependence of the logarithm of the sliding velocity on the rate of the pressure perturbation is linear or close to it, then there is a significant more dramatic increase in sliding velocity depending on the rate of the perturbation growth. The influence of the rate-state friction law parameters on the movements along the fault is not so unambiguous. However, it can be said that the sliding is determined by a combination of the following parameters: the critical length at which the stiffness of the fault section reaches the value of critical stiffness, and the characteristic response time determined by the parameters of the friction law.

How to cite: Turuntaev, S. and Riga, V.: Study of tectonic fault transition from aseismic to seismic slip due to fluid injection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16812, https://doi.org/10.5194/egusphere-egu23-16812, 2023.

TS3 – Active tectonics, seismicity, and deformation

EGU23-680 | ECS | Posters on site | TS3.3

3D crustal structure of the Irpinia region (Southern Apennines): constraints from the integration of subsurface data and local earthquake tomography 

Fabio Feriozzi, Luigi Improta, Francesco Emanuele Maesano, Pasquale De Gori, and Roberto Basili

The Irpinia region in the Southern Apennines is one of the areas with the highest seismic hazard in Italy, as also testified by several recent and historical earthquakes ranging between Mw 6.6-6.9 (1694, 1732, 1930, 1980). The shallow crust structural setting of this area is characterized by multiple deformational stages, which caused the tectonic stacking of Meso-Cenozoic sedimentary sequences deposited in different paleogeographic domains. The overall structure of the chain still contends between the thin-skinned and thick-skinned models.
We present a 3D geological model of key stratigraphic and tectonic elements based on the analysis of 2D seismic reflection profiles, integrated with well data and surface geology information. We also computed a 3D velocity model of the upper crust (Vp and Vp/Vs) through a local earthquake tomography (LET) to provide inferences on the structure and rock properties of the deep Apulian tectonic stack, especially where this is poorly imaged by seismic reflection imaging. We propose an integrated interpretation of the deep structure based on the analysis of the CROP-04 deep seismic profile and Vp and Vp/Vs patterns.
Our results highlight the presence of a regional thrust separating a shallow domain, characterized by relatively low-angle thrust surfaces (Allochthonous domain), from a deeper domain characterized by high-angle buried thrusts that affect the Apulian carbonate platform. The Plio-Pleistocene Apulian compressional architecture seems to control the rock physical properties in the upper crust and the seismotectonic of the area related to NE-SW regional extension active since the Middle Pleistocene. We observed that background seismicity concentrates in high-V, high-Vp/Vs regions that follow the Apulian structural trends and strictly correlate with the main crustal ramp anticlines. Furthermore, our structural model provides new geological insight regarding the destructive 1980 Irpinia earthquake (Mw=6.9), which ruptured three main fault segments.
From a methodological point of view, the integration of 3D geological model and LET is suitable for future earthquake relocations based on a data-driven velocity model reconstruction that considers the 3D geological complexities.

How to cite: Feriozzi, F., Improta, L., Maesano, F. E., De Gori, P., and Basili, R.: 3D crustal structure of the Irpinia region (Southern Apennines): constraints from the integration of subsurface data and local earthquake tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-680, https://doi.org/10.5194/egusphere-egu23-680, 2023.

EGU23-1228 | Posters on site | TS3.3

On the several shearing evidences developed in the Yangsan Fault, Korea 

Chung-Ryul Ryoo

In large fault zone, various contractional and extensional structures accommodate horizontal shortening and extension in response to differential plate movements related to the Earth’s rotation. In this study, it was conducted a structural analysis of the Yangsan Fault, developed in the southeast Korea. The fault is about 200 Km long in land and has a general NNE-trend, cutting not only the Cretaceous rocks but also the Quaternary layers. We studied several main fault zones along Yangsan Fault. Here, we discuss some kinematic evidences and characteristics developed in the main fault zones of the Yangsan Fault, Korea. In the core of the Yangsan Fault Zone, fault-bounded sheets or blocks are horizontally rotated, duplexed and folded. From the kinematics of the sheet-bounding faults and intra-sheet minor folds, we suggest some evolutionary models of the Yangsan Fault Zone in which repeated fault-related rotation, dragging and folding are occurred.

How to cite: Ryoo, C.-R.: On the several shearing evidences developed in the Yangsan Fault, Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1228, https://doi.org/10.5194/egusphere-egu23-1228, 2023.

EGU23-1465 | Posters on site | TS3.3

Morphostructural and geophysical surveys of the late Pleistocene-Holocene Broni-Sarmato Fault (Emilia Arc, northern Italy) 

Alessandro Tibaldi, Rita De Nardis, Patrizio Torrese, Sofia Bressan, Martina Pedicini, Donato Talone, Fabio Luca Bonali, Noemi Corti, Elena Russo, and Giusy Lavecchia

We present new morphostructural and geophysical data to discuss the recent activity of the Broni-Sarmato structure, an 18 km-long outcropping section of the north-verging Stradella thrust, located 50 km south of Milan, along the pede-Apennine compressional front in the rear of the Emilia Arc. An accurate seismic hazard assessment of this structure is necessary due to the presence in the area of widespread housing settlements, industries, lifeline infrastructures and large towns. Along the fault scarp we quantified the offset of recent river deposits by GPS, DTM and drone surveys; the scarp height values range from 6 to 23 m. Respect to previous works, we also better defined the geometry in plan view of the scarp; it is not continuous along the area, being characterized by several left- and right-stepping segments. We also performed new geoelectrical surveys across the scarp that suggest the presence of a wide zone of shallow deformation along the Broni-Sarmato fault trace. These deformations could correspond to fractures that act as preferential flow path for deep saline waters and facilitate the flow towards the surface. Horizontal interruption and vertical dislocation of a shallow, high resistivity layer also revealed by geoelectrical surveys, suggest that the Broni-Sarmato fault possibly produced shallow deformation along vertical and inclined zones. These data, supported by seismic activity, although quite sparse,  can be interpreted as evidence of late Pleistocene-Holocene tectonic activity of this section of the Stradella thrust.

How to cite: Tibaldi, A., De Nardis, R., Torrese, P., Bressan, S., Pedicini, M., Talone, D., Bonali, F. L., Corti, N., Russo, E., and Lavecchia, G.: Morphostructural and geophysical surveys of the late Pleistocene-Holocene Broni-Sarmato Fault (Emilia Arc, northern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1465, https://doi.org/10.5194/egusphere-egu23-1465, 2023.

EGU23-2420 | Posters on site | TS3.3

Exploration and recognition of active basement thrust sheet and crustal-scale duplex in the central Lesser Caucasus orogen using seismic reflection profile, Georgia 

Victor Alania, Tamar Beridze, Onise Enukidze, Thomas Gusmeo, Demur Merkviladze, Tamar Shikhashvili, and Niko Tevzadze

The Lesser Caucasus (LC) double-wedge orogen accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the LC. Herein we introduce the active deformation structural style of the Georgian part of the LC orogen based on seismic reflection profile, several oil-well, and surface geology data. Seismic reflection data reveals the presence of a Khrami basement thrust sheet, fault-related folds, triangle zone, and duplexes. The rocks involved in the deformation range from Paleozoic basement rocks to Pliocene-Quaternary basaltic lava flows.

Pliocene-Quaternary lava flows are involved in compressional deformation and are related to an out-of-thrust sequence of the Khrami basement thrust sheet. Based on the interpreted seismic reflection profile, the crustal-scale duplex was recognized under the basement thrust sheet which propagates northward along the Early Jurassic shale layers.

The structural architecture and tectonic evolution will be briefly presented and discussed in the new regional balanced and reconstructed cross-section across the axial zone and retro-wedge of the LC and published fission-track data (Gusmeo et al., 2021, 2022), as well as detailed examples of active tectonics, and seismicity (e.g., Tsereteli et al., 2016).

Reference

Gusmeo, T., et al. (2022). Tectono-thermal evolution of central Transcaucasia: Thermal modelling, seismic interpretation, and low-temperature thermochronology of the eastern Adjara-Trialeti and western Kura sedimentary basins (Georgia). J. As. Earth Sci. 238, 105355.

Gusmeo, T., et al. (2021). Structural inversion of back-arc basins-The Neogene Adjara-Trialeti fold-and-thrust belt (SW Georgia) as a far-field effect of the Arabia-Eurasia collision. Tectonophysics 803, 228702.

Tsereteli, N. et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328-344.

 

 

 

How to cite: Alania, V., Beridze, T., Enukidze, O., Gusmeo, T., Merkviladze, D., Shikhashvili, T., and Tevzadze, N.: Exploration and recognition of active basement thrust sheet and crustal-scale duplex in the central Lesser Caucasus orogen using seismic reflection profile, Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2420, https://doi.org/10.5194/egusphere-egu23-2420, 2023.

EGU23-3365 | Posters on site | TS3.3

New high-resolution relocation of the seismicity in the Southwestern Alps (France, Italy) to improve active faults imaging: Preliminary results 

Maxime Godano, Laeticia Jacquemond, Frederic Cappa, and Christophe Larroque

The geodynamic complexity of the Southwestern Alps (France, Italy) comes from its strong tectonic inheritage due to the European-African plates convergence. The motion being currently mainly accommodated along the Maghrebides, this region of the Alps only registers small to moderate seismicity linked to low-deformation rates (convergence rates of 0.3-0.9 mm/yr). Hence until now, the geometry of the active faults in the Southwestern Alps remains unclear and imprecise. Yet, a better knowledge of these faults is a prerequisite for the establishment of a regional deformation model and the improvement of the seismic hazard assessment.
Taking advantages of a nine-year seismicity catalog (7659 earthquakes of local magnitudes ranging between -0.73 and 5.03), recorded by the French and Italian permanent national networks presenting no major evolution since 2014, a high-resolution relocation is currently ongoing. The purposes are to (1) understand how the seismic events are linked to the mapped faults, (2) highlight unknown deep seismogenic structures and (3) finally improve the overall picture of the 3D geometry of active faults in the Southwestern Alps.
We present here the preliminary analysis of the relocated catalog. The seismicity is relocated using the double-difference relative method HYPODD with both cross-correlation and catalog times. As a result, the relocation is achieved for 5828 earthquakes. The uncertainties are reduced to less than 120m in horizontal and less than 600m in vertical compared to the initial average uncertainties of less than 2 kilometers for both values, referred by previous papers.
We assess the reliability of our results by comparing, at regional scale, our new relocations with those obtained by similar methods in Ubaye region. We illustrate how the double-difference relocation refines active zones imaging at multiple scales, particularly in the swarms. In Isola region located around 60 kilometers from Nice, a swarm, active since summer 2021, initially detected by the national network as a 3-kilometerlong/1-kilometer-large shape, has been precised into a 1-kilometer-long/100-meterlarge spatial activity. This relocation improvement enabled us to detect progressive activation of fault segments. On larger scale, relation between faults that may play a key role in the present-day general dynamics of the Alpine chain and deep seismogenic structures is clarified. It is the case for the High-Durance valley (France), where the precise geometry at depth of the Crustal penninic Front and High-Durance fault is determined.

How to cite: Godano, M., Jacquemond, L., Cappa, F., and Larroque, C.: New high-resolution relocation of the seismicity in the Southwestern Alps (France, Italy) to improve active faults imaging: Preliminary results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3365, https://doi.org/10.5194/egusphere-egu23-3365, 2023.

Abstract

 The megacity of Tehran, the capital of Iran, is located on the southern slope of the central part of the Alborz Mountain range. The earthquake risk assessment studies in the Tehran metropolis have been focused mainly on earthquake data and technical aspects of buildings and structures. In the meantime, the data on the fault that can cause earthquakes and the related triggered fracture system, like the potential of direct surface rupture that can be developed or occur as the result of an earthquake faulting, have not been significantly updated during the last two decades for mountain front foothills. The land use changes and the growth of the metropolis of Tehran during the last two decades, especially in the city's northern half, with the lack of any regulatory action on the fault zone, are escalating the risk of surface rupture. In this regard, the need to update the fault map and establish a fault zone regulatory act is paramount to importance. By reviewing the existing information and combining it with new satellite data, an updated map of the faults in the northern zone of Tehran city has been presented. The vital point in this map is to recognize the continuation of the fault trends that were introduced before, but their end was unknown. Also, a vast network of fractures or subsidiary faults belonging to the North Tehran fault system has been mapped, especially in its hanging wall part, which has not been published before. The result of the overlapping faults with urban structures and building areas shows that in the lack of regulation, the fault zone's ignoring continues in the new constructions of the Tehran metropolis. It is estimated that more than twenty hospitals, many of which are newly built, along with other strategic and sensitive structures, are in danger of surface rupture, and it is indispensable to think of a solution for them.

Additionally, many important buildings are in danger of fault rupture. We recently found that large ancient mega-landslides exist in the northern foothills of Tehran that are under more investigation. In the end, this research emphasizes the special attention to the lateral investigation of thrusts located in the north of Tehran between the North Tehran fault and the Masha fault, especially the Imamzadeh Dawood, Kigah and Pourkan faults.

Keywords: fault surface rupture, fault setback, earthquake, seismic hazard, Tehran, North Tehran Fault

How to cite: Ehteshami-Moinabadi, M. and Nasiri, S.: A critique review and update of the earthquake surface fault rupture hazard in the northern zone of Tehran metropolis, Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3749, https://doi.org/10.5194/egusphere-egu23-3749, 2023.

EGU23-4282 | ECS | Orals | TS3.3

Application of photogrammetry to reconstruct the architecture of the Fremrinamar rift, Northern Volcanic Zone, Iceland 

Martina Pedicini, Fabio Luca Bonali, Alessandro Tibaldi, Noemi Corti, Federico Pasquaré Mariotto, and Kyriaki Drymoni

The Northern Volcanic Zone is a tectonically and volcanically active area, of approximately 220 x 97 km, that accommodates the plate spreading in Northern Iceland. Given its extension, it is clear the need to enhance remote-sensing methodologies that give the possibility to obtain a reliable depiction of the main structures that characterize the area. 

Here we present the study of the Fremrinamar rift, which has a length of 13 km and a width between 8 to 9 km. To cover its entire extension we used a set of  983 historical aerial photos, freely available through the National Land Survey of Iceland. These images were acquired in 3 different years (1983, 1990, 1991), at the same flight elevation (5486 m a.s.l.), and are characterized by 60% of overlap.  Using Agisoft Metashape (v. 1.7.1) we obtain 3 Digital Elevation Models (DEMs) and 3 orthomosaics with a maximum resolution of 2.14 and 0.52 m/pixel respectively. We tested different quality combinations for both photo alignment and dense cloud processing, identifying a medium one as the best compromise between good-quality results (similar resolution levels as the one obtained with high-quality parameters) and relatively short-processing times (4-79 min. to reconstruct orthomosaics, 2-5 min. for DEMs). 

We then outline the geometry of the rift zone through mapping in a GIS environment at a 1:2500 scale. We identified 2528 extension fractures, 1785 normal fault scarps, and 207 eruptive fissures and distinguished between W- and E-dipping normal faults. The recognised structures show an overall strike of N-S to NNE-SSW, with minor values between NE-SW, and length values ranging from 4 to 7000 m. The highest length values are associated with normal faults, while extension fractures are characterized by shorter segments. Both normal faults and extension fractures show the highest length values in association with N-S strikes. E-dipping normal fault scarps show predominant dip-direction towards E-ESE, with minor ENE; W-dipping normal fault scarps dip mostly towards W-WNW, with minor WSW values. The Fremrinamar rift is characterised by a higher frequency of structures, especially eruptive fissures, in its southern and central portions (where volcanic centres are mainly located), while the northern one is defined by a decreased number of structures which also show a rotation in their strike values toward NNW-SSE. These results were finally integrated with field surveys over key areas, allowing us to evaluate and confirm the integrity and consistency of the data collected on the models.

This methodology gave us the possibility to reconstruct the geometry of an entire rift in high detail, without going to the field and with few costs (since the images are freely accessible the only costs derive from the selected software). Moreover, the presence of different sets of aerial photos, taken during different years, provides the opportunity to evaluate the temporal evolution of some key areas of the rift.

How to cite: Pedicini, M., Bonali, F. L., Tibaldi, A., Corti, N., Pasquaré Mariotto, F., and Drymoni, K.: Application of photogrammetry to reconstruct the architecture of the Fremrinamar rift, Northern Volcanic Zone, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4282, https://doi.org/10.5194/egusphere-egu23-4282, 2023.

EGU23-4966 | ECS | Orals | TS3.3

Coseismic slip of the 2020 Mw 6.4 Petrinja earthquake (Croatia) from dense geodetic benchmarks, optical image correlation and InSAR data 

Maxime Henriquet, Branko Kordić, Marianne Métois, James Hollingsworth, Cécile Lasserre, Olivier Cavalié, Lucilla Benedetti, Stéphane Baize, Marko Špelić, Matija Vukovski, and Ryan Gold

The Mw 6.4 Petrinja earthquake (2020, Croatia) is among the strongest continental earthquakes that occurred in Eastern Europe for decades. In such low-strain contexts, the sparse terrestrial-monitoring (few seismic and geodetic stations) of rare but strong earthquakes often prevents a detailed analysis of their seismic source. Here, we take advantage of > 160 geodetic benchmarks and optical image correlation to obtain a dense near-field coverage of the coseismic surface displacements. The geodetic dataset is obtained by repeated measurements of benchmark networks designed for civilian purposes and constitutes a unique dataset of coseismic displacements in the near-field of the fault. The optical image correlation is based on pre-earthquake (December 2017) WorldView and post-earthquake (February 2021) Pleiades satellite images with a 50 cm resolution. We also complete these displacement fields with unwrapped coseismic interferograms based on Sentinel-1 products, except in the near field affected by decorrelation. These displacement fields are consistent and thus suitable for modeling the slip distribution of the Petrinja earthquake. The elastic inversion of the geodetic benchmarks revealed interesting characteristics of this event: the rupture occurred on a near-vertical strike-slip fault, at a shallow depth (< 10 km), with significant slip reaching the surface. It also suggests that the deformation was partly accommodated by a subparallel strand 2.5 km from the main source northward. The aim of this research is to improve the source model of Petrinja 2020earthquake sequence, with a joint inversion of the geodetic benchmarks, optical image correlation, and InSAR data. Nevertheless, the comparison of the geodetic and coseismic offsets measurement on the field, shows that > 70% of the slip is likely distributed at the surface. Moreover, the coseismic strain maps derived from the unique benchmark data set helped us to identify zones where deformation appears distributed. Finally, the new data raises questions about whether such moderate earthquakes are accompanied by subsurface off-fault deformation or residual elastic strain.

How to cite: Henriquet, M., Kordić, B., Métois, M., Hollingsworth, J., Lasserre, C., Cavalié, O., Benedetti, L., Baize, S., Špelić, M., Vukovski, M., and Gold, R.: Coseismic slip of the 2020 Mw 6.4 Petrinja earthquake (Croatia) from dense geodetic benchmarks, optical image correlation and InSAR data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4966, https://doi.org/10.5194/egusphere-egu23-4966, 2023.

EGU23-5012 | ECS | Orals | TS3.3

Seismic Hazard Assessment along the Northern Apennines front (Italy): Deterministic inputs from the mapping of active and capable faults 

Thomas Gusmeo, Giacomo Carloni, Gianluca Vignaroli, Luca Martelli, and Giulio Viola

Understanding how the brittle deformation pattern at the surface relates to active seismogenic sources at depth is one key element for accurate Seismic Hazard Assessment procedures based on deterministic inputs. Establishing a relationship between surface faulting and deep sources can, however, be very challenging, especially in areas where seismogenic structures lack obvious and readily interpretable geological evidence at the surface. Here, we present results of detailed structural and geological investigations from a field-based study of active and capable faults along the Northern Apennines front (Pedeapenninic margin) between Reggio Emilia and Bologna, in northern Italy. Those results are then implemented into a Probabilistic Seismic Hazard Assessment model (PSHA) that also relies on an accurate surface acceleration model computed by considering site effects from the local stratigraphic amplification factors.

In the study area, the geological framework is characterized by two lithotectonic units: the Eocene-to-Miocene Epiligurian Units and the Pliocene-to-Present successions cropping out along the frontal Pedeapenninic margin. A compressive tectonic regime is currently dominant, with a regional-scale, NE-verging thrust system shaping the first-order architecture of the Pedeappenninic front. This thrust system is complex and is dissected by transverse normal and transpressive/transtensive faults. The architecture of the studied margin reflects exposed NE-verging thrusts within the Epiligurian Units in the more internal domains, and mostly blind thrusts below the Pliocene-to-Present units in the external domains. The Pliocene-to-Present units are also faulted and folded, indicating that tectonic activity is still in full swing, hence with significant seismogenic potential (as also documented by seismic archives). Top-to-NE and -SW normal faults are common in the area and deform the Pliocene-to-Present successions together with mostly NE-SW striking strike-slip and transpressional/transtensional faults.

Based on these structural/stratigraphical constraints we produced a geological model that represents the deterministic input to improve our current knowledge of seismogenic sources in the study area.

Regarding the seismic response at the surface in terms of the maximum expected acceleration, we computed the mean equivalent value of shear wave velocities in the uppermost 30 m of subsoil (VSeq) by using the available geognostic database of the area. The VSeq value allowed to calculate a specific stratigraphic amplification factor at each measurement point. In the study area, amplification varies, on average, from a 1.2 factor within the more rigid substrate to a 2 factor within the less consolidated, Pleistocene-Holocene in age, intra-valley deposits and in the Apennines foothills. This classification will be used as input to the Ground Motion Prediction Equations (GMPEs), as well as the Earthquake Source Model built through the combination of geological information about the sources (width, depth, slip rate, kinematics...) and historical/instrumental seismicity.

How to cite: Gusmeo, T., Carloni, G., Vignaroli, G., Martelli, L., and Viola, G.: Seismic Hazard Assessment along the Northern Apennines front (Italy): Deterministic inputs from the mapping of active and capable faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5012, https://doi.org/10.5194/egusphere-egu23-5012, 2023.

EGU23-5098 | Orals | TS3.3

Structural model of the two orogens convergence zone: A case study from western Kura foreland fold-and-thrust belt, Georgia 

Onise Enukidze, Victor Alania, Tamar Beridze, Paolo Pace, Alexandre Razmadze, Demur Merkviladze, and Tamar Shikhashvili

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region. Inversion of back-arc basins, exhumation and crustal thickening took place in the far-field zone, forming two orogens, and leading to a convergence between the Lesser Caucasus (LC) and Greater Caucasus (GC). Continuous convergence between the LC and GC caused incremental deformation of the Rioni and Kura foreland basins. Recent GPS, earthquakes, and paleoseismic data indicate that the Kura foreland fold-and-thrust belt (KFFTB) is tectonically fairly active (e.g., Sokhadze et al., 2018; Tibaldi et al., 2020; Tsereteli et al., 2016; Stahl et al., 2022).

In this study, we have integrated the post-stack depth-migrated 2D seismic profiles, borehole, and outcrop data to explore the structural geometry and kinematic features of the western KFFTB. Here we show the structural style of deformation of the convergence zone between the frontal part of the LC retro-wedge and the GC pro-wedge based on seismic reflection profiles. The seismic reflection profiles reveal the presence of a triangle zone and south-and north-vergent fault-related fold and south-vergent thrusts.

In combination with surface geology and borehole data, we have analyzed along-strike variations of the south-vergent passive-back thrust and transition from the fault-propagation fold to wedge structure by using 2D seismic profiles in the western KFFTB.

Based on the 2D seismic profiles and field data interpretations as well as our sequential kinematic modeling results, we have established the geometry and structural evolution of the LC-GC convergence zone in the western KFFTB since the Late Miocene.

Acknowledgement: This research was supported by Shota Rustaveli National Science Foundation of Georgia (SRNSFG) [grant # YS-21-612. Geometry and kinematic evolution of frontal part of the Eastern Achara-Trialeti fold-and-thrust belt]

How to cite: Enukidze, O., Alania, V., Beridze, T., Pace, P., Razmadze, A., Merkviladze, D., and Shikhashvili, T.: Structural model of the two orogens convergence zone: A case study from western Kura foreland fold-and-thrust belt, Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5098, https://doi.org/10.5194/egusphere-egu23-5098, 2023.

EGU23-5102 | ECS | Orals | TS3.3

Active tectonics and Fault behavior analysis based on deformation of mud layer on Wuhe Tableland, Eastern Taiwan 

Suman Panday, Jia-Jyun Dong, Jiun-Yee Yen, Chih-Heng Lu, and Che-Ming Yang

The fragile geology, tectonically and active seismic mountain belt like Taiwan are exposed to numerous geological controls on development of landforms. Especially North-South elongated suture zone between Eurasian and Philippine sea plate formed a Longitudinal valley remarks very active seismic behaviors and bounded by west dipping Central Range Fault (CRF) and east dipping Longitudinal Valley Fault (LVF). Wuhe table land lies on the western side of central part of valley and approximately 200 meters elevated from Xiuguluan River bed. The unconsolidated Mud layers (>50 ka) with few carbonaceous materials of about ten meters’ thicknesses lies in thick conglomerates of tableland could be the lacustrine deposits based on sedimentary environment, which suggest that there was a short-term damming event which is inclined approximate 30 degrees towards northwest. Deformation of mud layer is further studied to analysis the active tectonics and structural controls on tableland. Numerous boreholes, geophysical prospecting, InSAR data, GPS data and past earthquake information are processed on this study as preparation of 3- dimensional geological model and deformation characteristics. Past earthquake behavior shows that CRF acts as blind strike slip movement and very less surface deformation or ruptures but small-scale fissuring on south along Yuli ruptures (Yuli fault trace from 1951 earthquake) from the tableland and the upliftment rate of tableland is slow approximately about   >1mm/year.  While there are debatable issues regarding to CRF mechanism but this research tries to correlate the active deformation behavior and preservation of Wuhe Tableland on the basis of fault characteristics in this region.

How to cite: Panday, S., Dong, J.-J., Yen, J.-Y., Lu, C.-H., and Yang, C.-M.: Active tectonics and Fault behavior analysis based on deformation of mud layer on Wuhe Tableland, Eastern Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5102, https://doi.org/10.5194/egusphere-egu23-5102, 2023.

EGU23-5530 | Posters on site | TS3.3

A multidisciplinary approach gives new insights into the shallow structural setting of the Val d’Agri oilfield (Basilicata, southern Apennines, Italy) 

Roberta Maffucci, Marco Caciagli, Thomas Braun, Mauro Buttinelli, Francesca Cinti, Stefania Danesi, Paolo Marco De Martini, Maddalena Errico, Daniela Famiani, Valerio Materni, Daniela Pantosti, Stefano Pucci, Simone Salimbeni, and Vincenzo Sapia

The Val d’Agri (VA) oilfield in the Lucanian Apennines (southern Italy), represents the largest onshore in Europe. Since the 1990's, hydrocarbons are produced from a fractured carbonate reservoir with an average extraction rate of 7*104 barrels/day of oil and 3*106 Smc/day of gas. Part of the wastewater has been re-injected since 2006 into a marginal portion of the reservoir by a high-rate well (Costa Molina 2, CM2). Charged by the Italian oil and gas safety authority, the National Institute of Geophysics and Volcanology (INGV) monitors the VA industrial hydrocarbon operations through the research activity of a dedicated working group (CMS, Centro di Monitoraggio del Sottosuolo) and according to the governmental monitoring guidelines. The CMS operates the real-time acquisition and offline analyses of seismic data recorded at 56 seismic stations associated with public and private local seismic networks. The principal aim of the CMS is to investigate the risk associated with industrial activities that can induce or trigger seismic events by producing stress changes within the upper crustal volume. Previous works have highlighted a spatio-temporal relationship between micro-seismicity (ML ≤ 2.2) and wastewater injection, delineating a NE-dipping back-thrust near the CM2. Part of the microseismicity recorded in the southwestern portion of the VA has also been associated with the water level changes of the Pertusillo lake. One of the main challenges is to define an accurate structural setting of the VA to understand the potential of earthquakes in the area and investigate the presence of active faults. The VA consists of a Quaternary extensional tectonic basin and it is one of the areas of highest seismic hazard in Italy (Basilicata, 1857, M7 earthquake). The basin is bounded by two parallel and oppositely dipping normal fault systems: the Monti della Maddalena Fault System (MMFS) on its western side and the Eastern Agri Fault System (EAFS) on the eastern one. The characterization of the ongoing tectonic activity of the MMFS and EAFS, and their hierarchical relationship is still generating debate among the scientific community. We adopt a multidisciplinary approach based on detailed geological-structural, geophysical and seismic analyses, and electrical resistivity tomography, aimed at reconstructing the subsurface geology of the area and recognizing and characterizing the active and capable faults, and the associated potential for local seismic hazard. We present and discuss the results of this work, focusing on the relative location of seismic events that occurred between March and June 2022. The outcomes allow inferring interesting geologic constraints, highlighting the relationships between the distribution of local seismicity and the structural setting of the area in the uppermost crust (depth < 6 km).

How to cite: Maffucci, R., Caciagli, M., Braun, T., Buttinelli, M., Cinti, F., Danesi, S., De Martini, P. M., Errico, M., Famiani, D., Materni, V., Pantosti, D., Pucci, S., Salimbeni, S., and Sapia, V.: A multidisciplinary approach gives new insights into the shallow structural setting of the Val d’Agri oilfield (Basilicata, southern Apennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5530, https://doi.org/10.5194/egusphere-egu23-5530, 2023.

EGU23-5836 | Posters on site | TS3.3

Reviewing the 1997 Umbria-Marche seismic sequence: a fresh look from the integration of new seismological and subsurface data 

Mario Anselmi, Mauro Buttinelli, and Francesco Emanuele Maesano

The central-northern Apennines represent a high seismic hazard area characterized in the last decades by multiple seismic sequences (1997 Umbria-Marche, 2009 L’Aquila, 2016-2017 Amatrice-Visso-Norcia) related to the post-orogenic extension.

After the recent Amatrice-Visso-Norcia seismic sequence, the large availability of subsurface geological data and the dense seismological and geodetic networks allowed for better imaging of the shallow crust structural setting and the relationship with the occurred seismic sequences. 

Recent advances in those areas focused on comprehending the role of inherited structures (namely the large thrust faults related to the building up of the Apennines orogen) in compartmentalizing both horizontally and vertically the seismic sequences. Also, they suggested that major compressive structures may play an active role in seismogenesis through their kinematic inversion into the current extensional regime.

Such behavior was already debated after the 1997 Umbria-Marche seismic sequence, characterized by six main shocks with 5 < Mw < 6. All the large shocks originated on adjacent and parallel NW trending normal faults whose extent varies between 5 and 10 km at a hypocentral depth of 5 –6 km.

Our work presents a review of the data available for the 1997 Umbria-Marche seismic sequence. Using a combined dataset of seismic reflection profiles and deep boreholes, as well as detailed data from geological surveys, we present a new 3D geological and velocity model of the area. We also re-analyzed the passive seismic data recorded by both the temporary and permanent seismic networks. As a result, we computed a new 1-D relocation catalog based on the 3-D geological and geophysical imaging of the shallow portion of the crust in the target area.

The comparison of the geological model and the relocated seismicity shows a substantially vertical and horizontal compartmentation of the shallow crust due to the action of the thrusts. The seismicity distribution is strictly conditioned by the organization of crustal volumes separated by major thrusts and is concentrated within the same structural and stratigraphic levels, both on normal faults and pre-existing thrusts, possibly reactivated during the sequences.

The integrated analysis of seismological and geological subsurface data shed light on the open questions related to the interference between Quaternary normal faults and Tertiary thrusts and on the geometry of the causative faults of the 1997 seismic sequence. In addition, they help to define a more robust seismotectonic behavior and to assess the seismic hazard of those areas.

How to cite: Anselmi, M., Buttinelli, M., and Maesano, F. E.: Reviewing the 1997 Umbria-Marche seismic sequence: a fresh look from the integration of new seismological and subsurface data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5836, https://doi.org/10.5194/egusphere-egu23-5836, 2023.

EGU23-6140 | Posters on site | TS3.3

Data from depth to surface to define the 3D anatomy of an active fault-propagation fold: a key example from the western Caucasus (Georgia) 

Fabio Luca Bonali, Alessandro Tibaldi, Elena Russo, Victor Alania, Aleksandre Chabukiani, Onise Enukidze, and Nino Tsereteli

In the present work we showcase a multidisciplinary study aimed at defining the ongoing deformation processes due to fault propagation and folding at the Tsaishi fold, western Caucasus (Georgia).

Our approach consists in the integration of geomorphological observations, field geological-structural data and seismic reflection sections, allowing us to reconstruct a 3D model of this active fold, from depth to surface.

The Tsaishi fold is an anticline located at the southwestern tip of the Rioni Basin uplifted area, at the foothill of the Greater Caucasus. The folding process that has been recognized started at the beginning of the Middle Miocene, although preliminary data suggest the possibility of an initial local uplift in the Oligocene. Considering field observations, we suggest that the folding process continues nowadays, giving rise to a south-verging anticline, as shown by upwarped late Quaternary river deposits.

Integrating seismic reflection sections and field observations, we show that the fold backlimb is affected by three main back-thrusts, whereas, based on seismic sections, at the foot of the forelimb a main north-dipping thrust is very close to the surface. Where the thrust reaches the surface, we recognized the presence of a 13-km-long fault scarp (or fold scarp), where historical seismological data locate the epicenter of the strongest earthquake of the area, with Ms 6.0, the so-called Tsaishi earthquake of 1614 CE.

How to cite: Bonali, F. L., Tibaldi, A., Russo, E., Alania, V., Chabukiani, A., Enukidze, O., and Tsereteli, N.: Data from depth to surface to define the 3D anatomy of an active fault-propagation fold: a key example from the western Caucasus (Georgia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6140, https://doi.org/10.5194/egusphere-egu23-6140, 2023.

EGU23-7228 | ECS | Orals | TS3.3

Evidence of Late Cenozoic transpressive reactivation of an inherited strike-slip fault system and its influence in drainage reorganization in the Longitudinal Valley of Northernmost Chile 

Ambrosio Vega Ruiz, Pia Victor, Sara Pena-Castellnou, Klaus Reicherter, Ariane Binnie, and Steven Binnie

The Longitudinal Valley in Northernmost Chile was the main depocenter of widespread fluvial-alluvial systems active through the Neogene. These formed extensive lacustrine systems located at the eastern slope of the Coastal Cordillera until exorheic drainages developed between Arica and Pisagua (~18°30’S – 19°30’S) ca. 3 Ma ago. The top surfaces of the continental deposits form a regional scale pediplain (Pacific Paleosurface), where run-off is focused in present-day perennial streams draining to the Pacific Ocean through deeply incised quebradas. Some geomorphic and climatic constraints and suggestions exist regarding how the uplift of the Coastal Cordillera and the western Andes influence the shift in drainage regimes. However, little is known about how tectonic activity across this region affected landscape evolution since the structural architecture is difficult to unravel in this area of high sedimentation but low displacement rates.

We performed an exhaustive regional mapping of structural and geomorphic evidences of fault activity and drainage patterns based on high-resolution DEMs, satellite, and UAV imagery data, as the long-term hyperaridity of this area leads to well-preserved landforms and lack of vegetation cover. Our investigations reveal evidence of a reactivated complex inherited strike-slip system across the Longitudinal Valley, deforming Miocene to Quaternary surfaces. Local growth strata, angular unconformities, and flower structures within the Late Miocene to Early Pliocene lacustrine deposits suggest syn-sedimentary and dextral transpressional faulting near the boundary between the Longitudinal Valley and Coastal Cordillera. Importantly, we observe that large drainage reorganization patterns can be triggered by only little displacement along often blind fault structures, creating sufficient topography that cannot be surpassed by drainage incision in this hyperarid setting.

The interpretation of a reprocessed ENAP seismic section at ~19°20’S, suggests that this fault system consists of inherited Mesozoic inverted structures deforming Oligocene to Late Miocene strata. Furthermore, progressive abandonment and deformed terraces of low-incised rivers crossing compressive structures suggest that these were active during the Quaternary, most probably ongoing until the recent past. New dating of deformed marker horizons will bring further insights regarding key parameters of fault activity for the Late Cenozoic and Quaternary.

How to cite: Vega Ruiz, A., Victor, P., Pena-Castellnou, S., Reicherter, K., Binnie, A., and Binnie, S.: Evidence of Late Cenozoic transpressive reactivation of an inherited strike-slip fault system and its influence in drainage reorganization in the Longitudinal Valley of Northernmost Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7228, https://doi.org/10.5194/egusphere-egu23-7228, 2023.

EGU23-7386 | ECS | Posters on site | TS3.3

A multidisciplinary workflow to assess seismic hazard by active and capable faults when planning railway lines 

Selina Bonini, Giulio Viola, Giulia Tartaglia, Stefano Rodani, Massimo Comedini, and Gianluca Vignaroli

The planning phase of a railway line has to carefully consider the potential impact of several geohazards, including the seismic hazard associated with active faults capable to cause significant offset (dm to m) of the ground surface. Italian authorities are investing large resources in the construction of new railway lines in Italy, which is a territory that stands out as high-risk due to the presence of active faults, including those accommodating extension within the Apennines belt. Numerous seismogenic sources have been recognized therein by the geophysical and geological community over the last few years. Their identification and characterization represent the foundation of the seismic hazard map of Italy, which is regularly used to assess the seismic hazard of any given area of the country. Active and Capable Faults (ACFs) may contribute to increasing the seismic hazard of an area, though, and may interfere with railway lines. Following the Italian guidelines for the seismic microzonation procedures, an ACF is capable of producing, within a time interval of concern the society, macro-earthquakes and deformation/displacement at or near the ground surface and should have done so during the last 40 ka (upper Late Pleistocene – Holocene).

We propose a multidisciplinary workflow for improving and standardizing the use of the existing Italian geohazard databases. As the area covered by a railway line may extend for tens or hundreds of kilometers, it is crucial to define systematic criteria that make it possible for the intersected ACFs to be sorted into classes of varying hazard, each requiring different approaches and study levels. The seismicity associated with the ACF’s, the fault geometric and kinematic compatibility with the current regional tectonic setting and stress field, the involvement of < 40 ka old rocks and sediments, the proximity to the ground surface of the historical hypocenters, the geometrical relationships between the ACF’s and the orientation of the railway line are just a few of the aspects to be considered by such an approach.

We aim to define and constrain all the input parameters necessary to perform site-specific fault displacement and seismic hazard analysis, since the currently available Italian seismic hazard map is still too coarse in its resolution (with PGA values every 10 km). Our new approach will allow us to include the detection of near-field effects (e.g., the increasing of the vertical component due to seismic acceleration, forward-directivity phenomena, co-seismic rotation) if the trailway line runs within a 15 km zone from the main fault plane.

Knowing ACFs behavior will make it possible, during the planning, to choose the best railroad options, in order to reduce the vulnerability of the planned infrastructure.

How to cite: Bonini, S., Viola, G., Tartaglia, G., Rodani, S., Comedini, M., and Vignaroli, G.: A multidisciplinary workflow to assess seismic hazard by active and capable faults when planning railway lines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7386, https://doi.org/10.5194/egusphere-egu23-7386, 2023.

EGU23-7834 | ECS | Orals | TS3.3

Distributed right-lateral faults accommodating strain at the northern boundary of the Quito-Latacunga microblock of the Northern Andean Sliver 

Nicolas Harrichhausen, Léo Marconato, Laurence Audin, Stephane Baize, Hervé Jomard, Pierre Lacan, Diana Saqui, Alexandra Alvarado, Patricia Mothes, Frédérique Rolandone, Iván Ortiz, and Mónica Arcila

We present initial remote sensing and field data that suggest active distributed right-lateral faulting at the northern edge of the Quito-Latacunga tectonic block in northern Ecuador and southern Colombia. In this region, oblique subduction of the Nazca Plate beneath the South America plate induces northward migration of the Northern Andean Sliver (NAS), with respect to stable South America. Recent geodetic studies now suggest that this sliver is composed of several independent tectonic blocks, and the boundaries of these blocks are locations where we hypothesize crustal strain is accommodated. One of these blocks, the Quito-Latacunga block, is located in the densely populated Interandean valley of northern Ecuador and southern Colombia, and geodetic modelling predicts approximately 3 mm/yr of right-lateral strain at its northern boundary. A shallow July 25, 2022, MW 5.6 earthquake and damaging historical earthquakes along the northern boundary have illustrated the importance of understanding where this strain is being accommodated. We use available digital surface models (DSMs), local DSMs derived from Pleiades and SPOT satellite stereo-imagery, Interferometric Synthetic Aperture Radar (InSAR), Google Earth imagery, and a field survey to show that this boundary is distributed across several parallel northeast striking right-lateral faults. InSAR shows the July 25 event resulted in right-lateral surface displacement of > 20 cm along an east-northeast striking, steeply dipping fault. Offset volcanic soils and glacial moraines indicate recent earthquakes on two faults north of and subparallel with this rupture. Both faults overlap with the proposed area for the August 15, 1868, M 6.4–6.8 El Angel earthquake, suggesting either fault could be associated with this event. As the DSMs reveal a number of parallel strike-slip faults to the north in Colombia, further paleoseismic studies are needed in this region to delineate active faults and help define regional seismic hazard.

How to cite: Harrichhausen, N., Marconato, L., Audin, L., Baize, S., Jomard, H., Lacan, P., Saqui, D., Alvarado, A., Mothes, P., Rolandone, F., Ortiz, I., and Arcila, M.: Distributed right-lateral faults accommodating strain at the northern boundary of the Quito-Latacunga microblock of the Northern Andean Sliver, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7834, https://doi.org/10.5194/egusphere-egu23-7834, 2023.

EGU23-8823 | Posters on site | TS3.3

Geometry and stress interaction of a complex lithospheric-scale thrust system as unveiled by background seismicity and moderate seismic sequences - the Marche-Adriatic case (eastern Central Italy) 

Rita De Nardis, Federico Pietrolungo, Claudia Pandolfi, Simone Bello, Donato Talone, and Giusy Lavecchia

A recent paper showed the evidence of two well-distinct low-angle and SW-dipping individual reverse shear zones of the Italian Outer Thrust System in Central Italy (de Nardis et al., 2022). One, referred to as Thrust 1 (T1),  corresponds to the down-dip prosecution of the Adriatic Basal Thrust with its major splay; the other, referred to as Thrust 2 (T2), corresponds to a hidden independent structure, illuminated at a depth between 25 and 60 km, for an along-strike extent of ~150 km. Combining geological information with high-quality hypocentral locations and focal mechanisms, a detailed 3D geometric and kinematic fault model of the compressional system, active at upper crust to upper mantle depths, is built. In addition, evidence of coexisting deformation volumes undergoing a co-axial stress field at different lithospheric depths is reported.

November 9, 2022, seismic sequence principally activated T1  at upper crustal depth with pure compressional kinematics. Two significant events (Mw 5.5 and 5.2) enucleated within 1 minute, at depths of about 5 km and 7.5 km, respectively, and ~8 km away in map view. The sequence also released a cluster of microseismic events at mid-crust depths along the up-dip prolongation of the T2, thus opening the questions on the possible stress interaction during an ongoing seismic sequence.

In this paper, we further constrain and detail the T1 upper-crust geometry and investigate the likelihood of static stress interactions between T1 and T2. Considering that in historical and instrumental times, T1 has been responsible for earthquakes with Mw 6-6.5  at upper- and lower-crust depths, we create possible Coulomb stress transfer scenarios using the Coulomb code 3.4 (Lin and Stein, 2004; Toda et al., 2005).

We build three seismic sources (C1, C2, C3) assuming an Mw 6.2 thrust event enucleated on T1 at variable depths (8 km, 15 km, 22 km). The section-view and map-view distribution of the positive lobes of the modeled Coulomb stress scenarios show that a hypothetical T1 earthquake of the above magnitude may well determine, although marginally, stress increase along the underlying T2 segment.

 

 

 

How to cite: De Nardis, R., Pietrolungo, F., Pandolfi, C., Bello, S., Talone, D., and Lavecchia, G.: Geometry and stress interaction of a complex lithospheric-scale thrust system as unveiled by background seismicity and moderate seismic sequences - the Marche-Adriatic case (eastern Central Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8823, https://doi.org/10.5194/egusphere-egu23-8823, 2023.

The left-lateral Altyn Tagh Fault (ATF) is one of the longest active strike-slip faults in the world. Investigating the present-day state of the ATF is critical for our broader understanding of the India-Asia collision zone and the current motion of the Tibetan Plateau. Previous geodetic studies of the ATF using InSAR focused on relatively small areas, which is insufficient for a whole-fault understanding, but with the launch of the Sentinel-1 SAR constellation and the development of InSAR techniques, we can measure the crustal deformation and stress fields associated with interseismic motion along the fault more systematically as Sentinel-1 has provided high spatial coverage, better spatial resolution compared to GNSS, and shorter repeat times compared to previous SAR satellites. The large spatial coverage from such research could not only allow a better understanding of along-strike variations of fault slip rate and locking depth, but provide an opportunity to see how fault bends influence the deformation and strain fields, both of which are important for synthetic evaluation of future seismic risk along the fault. In this research, we use interferograms, which are produced by LiCSAR processing system, on 7 ascending tracks and 6 descending tracks to map surface velocities for a total area of ~ 600,000 km2 (~ 1,300 km × 450 km) around the central and eastern segment of ATF. Each track uses nearly 180 epochs between October 2014 and July 2022. To reduce the impact of phase biases and nontectonic seasonal signals, we combine both short temporal (< 4 months) and 1-year to 7-year long summer-to-summer baseline interferograms in the network, which generates an average of nearly 2000 interferograms in each LiCSAR frame (a track includes 1 or 2 frames). We use the Generic Atmospheric Correction Online Service (GACOS) to reduce the tropospheric delay in the unwrapped phase. Time-series analysis was applied using LiCSBAS. We estimate 83 3D GPS velocities using the data measured during 1998-2021 from the Crustal Movement Observation Network of China-I/II and then solve for the best-fit model of surface velocities and strain rates for the central-eastern Altyn Tagh fault zone based on both InSAR and GNSS velocities. Our results suggests that deformation and strain in the study area is concentrated along the ATF and show an along-strike variation from west to east. Using a screw dislocation model, we constrain best fit values for the slip-rate, locking depth, creep rate, and fault dip, for 12 fault-perpendicular velocity profiles along the length of the ATF using a Bayesian inversion and the Markov chain Monte Carlo (MCMC) sampler. Our results provide an important constraint on the present-day motion and structure of the Eastern and Central ATF. Additionally, by comparing with previous geodetic and geological investigation results, our study could bring some new thoughts and directions for future research about the ATF and other active faults.

How to cite: Wang, D., Elliott, J., Zheng, G., Wright, T., and Watson, A.: Large-scale crustal deformation and strain rate distribution along the central-eastern Altyn Tagh fault (NW Tibet) from Sentinel-1 InSAR and GNSS data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10516, https://doi.org/10.5194/egusphere-egu23-10516, 2023.

EGU23-10577 | ECS | Orals | TS3.3

The scaling properties of fault networks and their relationship with the size distribution of orogen-internal seismicity 

Sandro Truttmann, Marco Herwegh, Tobias Diehl, and Stefan Wiemer

Understanding orogen-internal seismic deformation in regions with diffuse spatial earthquake occurrence is challenging. To gain deeper insights into the processes driving seismic fault reactivation, it is crucial to obtain information on the ubiquitous pre-existing fracture patterns. In orogens with long tectonic histories – such as the Alps – such patterns can be complex, and information on their appearance is mainly limited to observations of faults at the surface, while the detailed patterns at depth remain mostly unknown. Moreover, the link between such surface-based fault observations and active seismicity is often ambiguous. However, it has been shown that both earthquake magnitudes (Gutenberg-Richter law) and various fault properties (e.g., length, displacement) follow power-law distributions.

In this work, we aim to investigate the potential relationship between the scaling properties of faults and earthquakes, which has been little explored. To this end, we use statistical tools based on field data collected with remote sensing techniques at different scales to quantitatively characterize the length distributions of exposed fault networks at different study sites in the southwestern Swiss Alps. Due to the good outcrop conditions at high elevations, the dense seismic monitoring network, and the enhanced earthquake activity, this region provides an ideal natural laboratory for the study of orogen-internal seismicity. By combining fault trace maps from three different scales, we are able to derive power law parameters and decipher similarities in scaling exponents for the different sites studied. Assuming that the fault networks exist in a similar form at depth and form the pre-existing discontinuities along which recent earthquakes develop, we compare the derived scaling laws with the frequency-magnitude distribution of local seismicity over the past 15 years. Here we find similar scaling properties between the seismicity and fracture networks only at depths below 3 km. However, in shallower regions, the large discrepancy between the scaling laws suggests that partial seismic ruptures of individual fault segments are more common than at greater depths. Such a statistical comparison of fault and earthquake scaling laws provides interesting insights into orogen-internal seismic deformation and fault reactivation processes that also have implications for regional seismic hazard.

How to cite: Truttmann, S., Herwegh, M., Diehl, T., and Wiemer, S.: The scaling properties of fault networks and their relationship with the size distribution of orogen-internal seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10577, https://doi.org/10.5194/egusphere-egu23-10577, 2023.

EGU23-10900 | ECS | Posters on site | TS3.3

The geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula 

Dabeen Heo, Tae-Seob Kang, Jin-Han Ree, Kwang-Hee Kim, Junkee Rhie, and YoungHee Kim

The southeastern part of the Korean Peninsula is known to have high seismic activity and many Quaternary faults. Nonetheless, there have been uncertainties in estimating seismic hazards due to insufficient information on potential seismic sources. We investigated the geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula by detecting microearthquakes and determining their source parameters. We used the seismic data recorded at the Gyeongju hi-density broadband seismic network, the temporary seismic networks operated to monitor the aftershocks of two moderate earthquakes (the 2016 ML 5.8 Gyeongju and 2017 ML 5.4 Pohang earthquakes), and the national seismic network of South Korea. An earthquake catalog for the southeastern Korean Peninsula was built using automatic earthquake detection methods based on measurements of energy ratio. We identified the five clustered earthquake regions via the microearthquake distribution: the 2016 Gyeongju earthquake region (GJ), the 2017 Pohang earthquake region (PH), the eastern part of the Ulsan Fault (UF), eastern offshore Gyeongju (EG), and the western part along the Miryang Fault (MF). We determined the relative location and focal mechanisms of the earthquakes occurring in those regions using the double-difference location method and the P-wave first motion polarity method, respectively. Finally, the geometry of the earthquake causative faults was inferred using the spatial distribution of the relative locations and the focal mechanisms. It was found that there are at least two NNE-SSW trending fault segments and multiple NE-SW trending fault segments in the GJ and PH, respectively. In the case of MF, UF, and EG, it is difficult to relate directly to the surface faults, but the strikes of the causative faults, which are confirmed by the spatial distribution of earthquakes, are similar to those of the surface faults.

How to cite: Heo, D., Kang, T.-S., Ree, J.-H., Kim, K.-H., Rhie, J., and Kim, Y.: The geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10900, https://doi.org/10.5194/egusphere-egu23-10900, 2023.

EGU23-11644 | Orals | TS3.3

The influence of lithology on the Magnitude–Frequency-Distribution of earthquakes 

Cristiano Collettini and Elisa Tinti

The earthquake Magnitude-Frequency-Distribution, FMD, is usually modelled with the Gutenberg-Richter relation law, where the b-value controls the relative rate of small and large earthquakes. b-value has been documented to show an inverse dependence on differential stress, it increases with the fault roughness or during fluid-induced earthquakes. For some seismic sequences a near real-time characterization of the b-value has been used to discriminate between foreshocks and aftershocks. Here we examine the influence on b-values of different lithologies hosting earthquakes.

In general, seismicity not only localizes along the major structures where mainshocks nucleate, but it can be also distributed within volumes of the seismogenic layer characterized by different lithologies. For the Mw 6.5 2016–2017 Central Italy seismic sequence, the lithology can be properly defined by seismic reflection profiles. Here the fractured carbonate of the Apennines, located at almost 1-2 km and 4-6 km of depth, are characterized by b-values ranging between 1.3 and 1.4 that can be diagnostic of brittle dominated deformation. At 2-4 km and 6-10 km of depth, the Triassic Evaporites showing a bimodal brittle-ductile deformation and compartmentalized fluid overpressure (documented in deep boreholes) are linked to high b-values, in the range of 1.5-1.65 reaching 1.80 for clustered swarms. Between 10-12 km of depth the phyllosilicate rich basement, with its predominant velocity strengthening behaviour, is hosting small magnitude earthquakes with b-values around 1.4. Our results indicate that away from the large earthquake faults, characterized by a stress dependent elasto-frictional rheology, FMD are strongly controlled by rock lithology and style of deformation.

How to cite: Collettini, C. and Tinti, E.: The influence of lithology on the Magnitude–Frequency-Distribution of earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11644, https://doi.org/10.5194/egusphere-egu23-11644, 2023.

EGU23-11810 | ECS | Orals | TS3.3

A conceptual 3D fold-and-thrust database for seismic hazard, seismotectonic and geodynamic purposes - a first release from eastern Central Italy 

Claudia Pandolfi, Rita de Nardis, Andrea Carducci, Aybige Akinci, and Giusy Lavecchia

We present SEISC-3D, an ArcGIS geodatabase for 3D SEIsmic Source Characterization. It integrates multi-scale and multi-depth geological and seismological information in a compressional environment to build a detailed regional-scale, geometric and kinematic, 3D curvilinear fault model suitable for seismic hazard modelers and seismotectonic purposes and geodynamic modeling. This first release focuses on the late Pliocene-to-Quaternary arcuate and eastward convex fold-and-thrust belt still active along the Outer front of the Italian Apennines in eastern Central Italy. The near-surfaces, onshore, and offshore thrust faults represent the hanging-wall structures of a potentially seismogenic regional shear zone, known as Adriatic Basal Thrust, which develops from near-surface to MOHO depths (about 35 km).

Three hierarchic levels of structural maps are provided with decreasing details moving from fold-and-thrusts traces, enveloping thrust, and regional thrust alignments.

Different datasets (points, lines, surfaces) are unified, compiled, and held in a common ArcGIS file system folder and linked on the basis of relational models.

SEISC is composed of:

  • one dataset consisting of fold hinges traces (syncline and anticlines)
  • one dataset consisting of individual fold-related thrust
  • one dataset consisting of enveloping thrusts organized in hierarchic orders
  • one dataset consisting of interconnected curvilinear fault surfaces built along the down-dip projection of the enveloping thrusts, segmented along-strike and along-dip
  • one structural data set containing geometric and kinematic point data (attitude, dip-angle, slip-vector, rake, sense of movement) for the node of each triangulated mesh of each fault surface.

A crucial point when dealing with compressional structures is the difficulty in adopting segmentation criteria suitable for a realistic earthquake-fault association. In our methodological approach, the along-strike segmentation is strongly driven by the en-echelon distribution of the fold-related thrusts and by sharp variation in strikes and bending of the enveloping thrusts. On the other hand, the down-dip segmentation is controlled by the mechanical crustal layering derived from earthquake distributions and the rheological investigation.

How to cite: Pandolfi, C., de Nardis, R., Carducci, A., Akinci, A., and Lavecchia, G.: A conceptual 3D fold-and-thrust database for seismic hazard, seismotectonic and geodynamic purposes - a first release from eastern Central Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11810, https://doi.org/10.5194/egusphere-egu23-11810, 2023.

EGU23-13060 | ECS | Posters on site | TS3.3

Application of photogrammetric approaches to studying the 1971 dike-induced surface structures on Mt Etna, Italy 

Sofia Bressan, Fabio Luca Bonali, Noemi Corti, Federico Pasquaré Mariotto, Emanuela De Beni, Massimo Cantarero, Marco Neri, Elena Russo, Kyriaki Drymoni, and Alessandro Tibaldi

Mt Etna, located on the east coast of Sicily, Italy, is a basaltic stratovolcano with a volcanotectonic evolution of 500 ka, characterized by a wide horse-shoe-shaped depression on its eastern flank, called Valle del Bove. The study area is located near the northern escarpment of this depression, where it is possible to recognize the 1971 eruptive fissure system, generated by the lateral propagation of a feeder dike. The purpose of this research is to thoroughly examine the area affected by dike-induced surface deformation, which is marked by a textbook example of a graben structure produced by dike propagation. Due to the presence of meters-thick, recent pyroclastic deposits covering the study area and the difficult logistics, the main outcrops are inaccessible for classical field data collection. To overcome this limitation, we used the following methodology based on the analysis of photogrammetry-derived models.

We first designed a structural map related to the development of the 1971 dike-induced structures, using two sets of historical aerial photos characterized by a 2400 DPI resolution. Particularly, the 20 selected images, equally divided between 1954 and 1983, have been processed using the software Agisoft Metashape to produce two referenced orthomosaics with a resolution of 29 and 19.5 cm/pixel, respectively. By comparing the obtained orthomosaics, we identified and mapped all the normal faults associated with the 1971 dike intrusion. This structural map has been used to organize the subsequent drone surveys, performed by a DJI Phantom 4 Pro equipped with RTK high-precision technology, which allowed us to collect 656 pictures with an overlap and a side lap of 85% and 80% respectively. Afterward, we processed the drone-collected photos by using Structure-from-Motion photogrammetry techniques, so as to obtain a Digital Surface Model (DSM) and a 3D Tiled Model, with a resolution of 11 and 5.48 cm/pixel, respectively. Such models have been used to analyze in detail the graben faults, especially the ones along the Valle del Bove steep wall.

The analysis of photogrammetry-derived models over different time windows enabled us to individuate 14 lineaments within the study area, 2 eruptive fissures with a NE-SW strike, and 13 fault scarps associated with the dip-slip faults of the graben. Finally, thanks to the 3D Tiled Model obtained from drone-captured pictures, we were able to quantify the dip direction and dip angles of the graben faults, their vertical offsets, and the graben width related to the elevation.

How to cite: Bressan, S., Bonali, F. L., Corti, N., Pasquaré Mariotto, F., De Beni, E., Cantarero, M., Neri, M., Russo, E., Drymoni, K., and Tibaldi, A.: Application of photogrammetric approaches to studying the 1971 dike-induced surface structures on Mt Etna, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13060, https://doi.org/10.5194/egusphere-egu23-13060, 2023.

EGU23-13989 | Posters on site | TS3.3

Reconstruction of the evolution of the Osning Lineament in northern Germany using 2-D retrodeformation 

David C. Tanner and Sonja H. Wadas

Neotectonic movements can cause severe geohazards and thus require examination for seismic hazard assessment, and utilisation of the subsurface for e.g. nuclear-waste disposal sites and geothermal exploitation. In northern Germany, very little is known about these processes and the associated structures, despite proven neotectonic activity, because many faults are hidden beneath sediments.

The Osning Lineament (OL) in North Rhine-Westphalia is a recently-active fault zones. Three major earthquakes and seven other macro-seismic earthquakes occurred at the OL during the last 400 years. The strongest earthquakes occurred in 1612, 1767, and 1770, with an estimated intensity of VI to VII on the MSK scale. The OL is a unique fault system compared to other faults in northern Germany. The faults of the OL reach the basement, whereas in the north of the Lower Saxony Basin, most faults are decoupled from the basement by salt. Furthermore, the OL dips to the northeast and therefore the vector of the fault plane points towards the former iceload from Scandinavia, enabling glacial isostatic adjustment to occur on the faults. Additionally, the OL has had a history of multiphase reactivation in the geological past.

To better understand the neotectonic evolution of the OL on a regional scale, we carried out a 2D retrodeformation using already existing large-scale cross sections along the lineament, which are based on surface geological maps and sparse drilling information. Balancing of these cross-sections verifies whether the fault geometry and kinematics derived from surface data are justified or need to be revised. Retrodeformation is also used to suggest the path of the fault(s) at greater (seismogenic) depth. Later on, retrodeformation will also be performed including new, highly-detailed seismic profiles and a joint interpretation will be carried out to improve the understanding of the past evolution of the Osning Lineament.

How to cite: Tanner, D. C. and Wadas, S. H.: Reconstruction of the evolution of the Osning Lineament in northern Germany using 2-D retrodeformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13989, https://doi.org/10.5194/egusphere-egu23-13989, 2023.

EGU23-15747 | ECS | Posters on site | TS3.3

A multidisciplinary approach for 3D modelling of the Serre and Cittanova Faults, the responsible of the 1783 seismic sequence in Southern Calabria, Italy. 

Salvatore Giuffrida, Fabio Brighenti, Francesco Carnemolla, Salvatore Gambino, Giorgio De Guidi, Giovanni Barreca, Flavio Cannavò, Luciano Scarfì, and Carmelo Monaco

Since the Late Pliocene - Early Pleistocene, the Calabrian Arc (southern Italy) is affected by extensional and transcurrent tectonic superimposed on the previous collisional context. Various seismogenic sources have been proposed over time to explain such a complex structural framework, but the topic is still matter of debate. 

In this work we apply a multidisciplinary approach, concerning Geology, Geomorphology, Seismology and Geodesy, to develop a reliable 3D model of the Cittanova and Serre faults. These faults are considered the causative faults for the 1783 seismic sequence (M 6.5-7) as proposed by Jacques et alii (2001). We used CROP data to investigate the crustal architecture of the area and to constrain the geometry at depth of the major structures. through two schematic geological sections orthogonal to these two faults. The shallow geometric patterns of the Cittanova and Serre faults, were verified trough geological, geomorphological and structural field data. Earthquakes hypocentres were analysed and relocated in order to recognize possible cluster alignments useful to constrain the faults geometry at depth. The high-density level of crustal seismicity attests that this domain is seismically active, between 0 km and 23 km and it concentrates along the main faults. To compute the strain and velocity field of the area (time span of the last 20 years) we measured the IGM95  (Instituto Geografico Militare) benchmarks and processed several GNSS permanent stations belonging to the RING Network (http://ring.gm.ingv.it) and TopNETlive Italy Network (https://rtk.topnetlive.com/italy/networks/topnet-live-italy) using GipsyX 1.5 Strain inversion (performed through grid_strain 2D software) allowed us to define a predominant WNW-ESE extensional deformation, in agreement with previous studies). Combining all previous data, we built for the first time a reliable 3D model of the Cittanova and Serre fault planes, that are consistent with:  i) fault magnitude/size empirical relations (Magnitude vs rupture Area, Magnitude vs fault length; ii) geological and geomorphological field observation (fault attitude and kinematic), iii) seismological and geodetic data. Results show that our model is compatible with the seismogenic sources of the 1783 seismic sequence.

How to cite: Giuffrida, S., Brighenti, F., Carnemolla, F., Gambino, S., De Guidi, G., Barreca, G., Cannavò, F., Scarfì, L., and Monaco, C.: A multidisciplinary approach for 3D modelling of the Serre and Cittanova Faults, the responsible of the 1783 seismic sequence in Southern Calabria, Italy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15747, https://doi.org/10.5194/egusphere-egu23-15747, 2023.

EGU23-15827 | Orals | TS3.3

Pre-conditioned seismic attributes applied to deep vintage seismic reflection line: enhancing fault patterns on the Italian CROP-04 . 

Maurizio Ercoli, Filippo Carboni, Assel Akimbekova A, Ramon B. Carbonell, and Massimiliano R. Barchi

Reflection seismic is the best active geophysical method to constrain the geometry and kinematics of faults at depth. In some specific areas, seismic profiles derived from industry or from past research programs can be nowadays still used in seismotectonic studies to link the surface faults traces with hypocentral earthquake sources. Deep reflection seismic profiles such as the ones recorded in the framework of  the Italian “CROP” aimed shed light on the deep subsurface structures, despite the high levels of random noise hampering the seismic interpretation. Also the CROP-04 “Agropoli-Barletta”, seismic transect acquired from the Tyrrhenian to the Adriatic Sea across the Southern Apennines fold-and-thrust belt and the foreland system, is strongly affected by random noise. Various geological interpretations based on this data are available in literature, as this seismic profile crosses important active faults such as the Irpinia fault, which produced the destructive 1980 Mw 6.9 earthquake. Aiming to improve the data quality, by reducing the noise, to perform a structural interpretation of its shallower sector, we applied a dedicated workflow encompassing pre-conditioning filters, selected seismic attributes and co-rendered views. Following this workflow we have considerably enhanced the reflection patterns and the overall data interpretability, unveil a dense and complex sets of normal faults, thus imaging tectonic structures which were invisible in the original CROP-04. In addition, the master faults mapped at surface well matches the seismic signature. The reprocessed profile displays also clear low-angle W-dipping thrusts and deep regional features, contributing to better understanding the complex subsurface geology of the Southern Apennines. Our advances interpretation strategy is able to efficiently revive deep legacy data like the CROP, which are unique and nowadays hardly to repeat. New important insights across seismically active areas worldwide can be obtained reproposing this workflow in other contexts, extending to depth the surface evidences of outcropping faults as well as revealing unknown structures to survey with targeted fieldwork mapping.

How to cite: Ercoli, M., Carboni, F., Akimbekova A, A., Carbonell, R. B., and Barchi, M. R.: Pre-conditioned seismic attributes applied to deep vintage seismic reflection line: enhancing fault patterns on the Italian CROP-04 ., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15827, https://doi.org/10.5194/egusphere-egu23-15827, 2023.

EGU23-16336 | Posters on site | TS3.3

Integrated structural-seismological constraints for a 3D multi-depth fault model of the Stradella and  Emilia Arcs (northern Italy) 

Giusy Lavecchia, Rita de Nardis, Donato Talone, Sofia Bressan, Martina Pedicini, Fabio Luca Bonali, Noemi Corti, Elena Russo, Patrizio Torrese, and Alessandro Tibaldi

Investigating active tectonics and the structural style of potentially-seismogenic structures at the outer front of active orogenic belts is particularly challenging when the frontal structures are buried and slowly deforming. This is the case of the blind fold-and-thrust belts surrounding the Padanian foreland of Northern Italy and developing across one of the most populated and industrialized Italian territories. In this paper, we focus on the seismogenic role of the Stradella thrust and its possible involvement in the activity of the buried Emilia arc, through a 3D geometric, kinematic, and seismotectonic reconstruction of the overall system. The integrated multi-scale analysis of structural and seismological data, inclusive of new focal mechanisms, highlights two seismological thrust volumes dipping at low-angle southwest-ward, at upper (<12 km) and lower crustal depths (~20-30 km). However, the shallow seismicity only partially illuminates the down-dip prosecution of the Stradella structure. In contrast, the deeper earthquake volume, at the hanging wall of the along-strike southeastward prosecution of the Stradella fault, well highlights the lower crust portion of the Emilia Arc basal thrust.

We interpret the above multi-scale data as evidence of ongoing tectonic activity of the outer fronts of the Emilia arc under a regional NNE-directed compressional stress field, with some minor evidence of involvement of the Stradella thrust along the pede-Apennine front. In our 3D reconstruction, both thrust systems are expressions of a thick-skinned deformation that controls earthquake release at different structural depths.

How to cite: Lavecchia, G., de Nardis, R., Talone, D., Bressan, S., Pedicini, M., Bonali, F. L., Corti, N., Russo, E., Torrese, P., and Tibaldi, A.: Integrated structural-seismological constraints for a 3D multi-depth fault model of the Stradella and  Emilia Arcs (northern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16336, https://doi.org/10.5194/egusphere-egu23-16336, 2023.

Recent seismic hazard models are increasingly relying on fault slip rates as the fundamental quantity for translating the activity of a fault source model into earthquake rates. In this conversion, modelers are often tasked with selecting different estimates and alternative methods to assess the fault slip rates and related uncertainties and incorporate them into the seismic hazard analysis. In the central Apennines, several techniques, such as paleoseismic trenching, mapping of offset geomorphic markers, and dating of scarp profiles have been used to determine slip rates of normal faults. Recently geodetic data have also been used to determine the first estimates of the slip rate (loading) rate on active faults.

Combining measurements obtained with different methods remains challenging because non tectonic processes can introduce noise or spurious signals that are elusive to quantify, and these influence slip rate estimates. After careful and planned data collection, we argue that a rigorous meta-analysis is required to quantify erratic fluctuations and method-related variances. In this case, throw rates are overdispersed with respect to nominal uncertainties in throw and age; therefore, they are commonly affected by unmodeled noise processes to be rigorously quantified for seismic hazard assessment.

Geodetic data can provide slip-rate estimates with a model of elastically unloading seismogenic faults within a viscously deforming lithosphere. However, short-term transients can also infect geodetic data in the central Apennines. Such transients can be isolated and subtracted by time series or included as noise in the long-term covariance matrix; otherwise, the resulting spatial distribution of deformation rates locally fits short-term transients. In some cases, strain rate peaks represent the currently unclear signal of tectonic processes like crustal visco-elasto-plastic deformation and aseismic slip or indicate missing faults in the adopted database. In the central Apennines, we have proved that reasonable estimates of long-term fault slip rates can be extracted even at signal-to-noise ratios of order unity using a more sophisticated modeling approach, including the stress orientations. For well-sampled faults, the slip rate estimates fit the corresponding geological estimates, leading us to conclude that they can be considered for seismic hazard models in regions such as the Apennines.

We remark that geodetic and geological data can be used together to highlight (and possibly model) both the likely occurrence of short-term transients in GPS time series and the existence of non-tectonic processes contributing to the progressive surface exposure of active faults. Given the current understanding of temporal and spatial fault throw rate variability in the central Apennines, producing complex input models for seismic hazard assessment is still not feasible. A base model with a uniform throw rate along the trace (tapering to zero at unconnected fault tips) and merging information from offset features of different ages to constrain a single time-independent rate is still the most reasonable.

How to cite: Carafa, M.: Meta-analysis of fault slip rates across the central Apennines for seismic hazard assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17153, https://doi.org/10.5194/egusphere-egu23-17153, 2023.

EGU23-159 | Orals | TS3.4

Neotectonic characterization of potential seismogenic structures in NW Argentina 

Victor Hugo Garcia, Fernando Hongn, Carolina Montero, Ahmad Arnous, Leonardo Elías, Emilio Criado Sutti, Martin Zeckra, Sara Figueroa Villegas, Rodolfo Germán Aranda Viana, Leonardo Escalante, William Peyerl, Eduardo Salamuni, Gustavo Ortíz, Eugenia Monteros, Fabiano Pupim, Frank Krüger, Bodo Bookhagen, and Manfred R. Strecker

Historical and instrumental seismicity records from the Central Andes of north-western Argentina spanning the last ca. 350 years have been the primary data source to characterize this region’s exposure to seismic hazard as “moderate” to “high” (0.18-0.25 PGA). Despite the relevance of the existing dataset in seismic hazard assessments (SHA), we propose that the lack of detailed neotectonic and paleoseismological studies regarding widespread evidence of Quaternary seismogenic deformation has prevented a more accurate SHA in the vicinity of densely populated areas, such as the metropolitan regions of San Salvador de Jujuy, Salta, and San Miguel de Tucumán, which together total almost 2 million inhabitants and host important infrastructure.

In order to improve the neotectonic characterization of potential seismogenic sources in this region our research efforts we have employed a multidisciplinary and multimethodological research approach to develop an improved register of active Quaternary structures. This approach includes remote sensing analysis, detailed structural and geomorphic mapping and topographic surveying, interpretation of seismic reflection lines and near-surface geophysical surveys, structural modeling, the deployment of temporary local seismic networks, as well as geochronology. The geochronological methods include terrestrial cosmogenic nuclide dating (TCN) and U-Pb dating of volcanic ashes to establish the age of abandoned fluvial terraces (104 to 105 yrs) and optically stimulated luminescence (OSL) and AMS14C dating to constrain the depositional ages of sedimentary sequences on centennial to multi-millennial timescales.

These efforts have shed light on important parameters for SHA (i.e. fault geometry and kinematics, Late Pleistocene-Holocene slip rates) of at least a dozen of potentially seismogenic faults that were not very well known before. Our results show that besides the expected N-S-striking structures related to shortening, oblique, transpressive fault systems also exist that are probably related to the highly diachronous compressional reactivation of Cretaceous normal faults. Mean fault lengths are of around 15-20 km with extremes between 10 and 50 km, while mean slip rates typically reach 1 mm/a, with some structures reaching 2 mm/a.

Among the analyzed structures in the transition between the Eastern Cordillera and its foreland, two affect directly urban areas (Medeiros fault, Salta; Los Alisos fault, Jujuy) or they occur in the vicinity of critical infrastructure (Medina fault, El Tunal hydroelectric power plant). Further detailed studies are being carried out on these structures in order to better constrain their paleoseismological behavior and seismogenic capability.

How to cite: Garcia, V. H., Hongn, F., Montero, C., Arnous, A., Elías, L., Criado Sutti, E., Zeckra, M., Figueroa Villegas, S., Aranda Viana, R. G., Escalante, L., Peyerl, W., Salamuni, E., Ortíz, G., Monteros, E., Pupim, F., Krüger, F., Bookhagen, B., and Strecker, M. R.: Neotectonic characterization of potential seismogenic structures in NW Argentina, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-159, https://doi.org/10.5194/egusphere-egu23-159, 2023.

EGU23-794 | ECS | Posters on site | TS3.4

Characterisation of Quaternary scarps in the Baix Ebre Basin (NE Spain) and analysis of their potential seismogenic origin 

Marc Ollé-López, Julián García-Mayordomo, and Eulàlia Masana

The Baix Ebre Basin (BEB), located in the NE of Spain, is a passive margin where different systems of normal faults exist, oriented NNE-SSW, oblique-to-parallel to the coast. Those intraplate faults are considered slow faults, with slip rates around 0,2 mm/yr. However, their active status has been proved by different studies during last years. Close to this area, the main fault in which paleoseismic studies have demonstrated a seismogenic behaviour is the El Camp Fault (ECF), located towards the NE of the BEB. It has been studied in detail due to its remarkably geomorphological expression and due to its proximity to the Vandellós nuclear power plant. Recently, thanks to higher resolution Digital Elevation Models (DEM) of the terrain, some morphological scarps affecting Quaternary alluvial fans have also been detected along the BEB, from Pla de Sant Jordi Basin (NE of the BEB) until La Sènia (SW of the BEB). Those scarps are oriented in the same direction as the ECF, suggesting a possibly tectonic origin related to the same stress field. In this case, they would have to be considered as the ECF propagation to the south, which could imply a big impact on the seismic hazard of the entire region. Nevertheless, other possible origins for these topographic scarps should be explored, as a possible paleo-coast line or some kind of karstic or gravitational processes. With this aim, it has been planned a detailed geomorphological analysis to identify and characterise all the possible scarps along the BEB and to locate the suitable places for field detailed studies and a geophysical survey. In this geophysical study, it is planned to use different techniques (GPR, electric tomography and magnetotellurics) in order to explore its combined use and to analyse the subsoil structure from shallow to depth. In case of demonstrating its tectonic origin, firstly, it is planned to carry out a paleoseismological study (to determine their seismological history) and, secondly, to analyse their contribution into the seismic hazard models of the region. In this work, we present the first preliminary results of our ongoing research.

How to cite: Ollé-López, M., García-Mayordomo, J., and Masana, E.: Characterisation of Quaternary scarps in the Baix Ebre Basin (NE Spain) and analysis of their potential seismogenic origin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-794, https://doi.org/10.5194/egusphere-egu23-794, 2023.

EGU23-805 | ECS | Posters on site | TS3.4

Earthquake geology for fault displacement hazard analysis of normal faults, a case study from the Upper Tiber Valley (Northern Apennines, Italy). 

alessio testa, Paolo Boncio, Stephane Baize, Francesco Mirabella, Stefano Pucci, Cristina Pauselli, Maurizio Ercoli, Bruno Pace, and Lucilla Benedetti

Fault displacement can be a source of hazard for critical infrastructures located in the nearby of a capable fault.  This issue is usually addressed with zonation and avoidance strategies, but sometime the facilities have not this option. An alternative approach to assess likelihood of exceeding a certain level of displacement for pre-existing infrastructures is the Probabilistic Fault Displacement Hazard Analysis. Different empirical approaches have been proposed since the early 2000s to assess the probability of occurrence and the probability of exceedance of certain values of displacement, for both Primary and Distributed faulting, starting from the fault parameters.            
We propose the methodological approach used to gain the needed parameters and the results of the PFDHA applied to the Anghiari Fault, a poorly constrained NE-dipping segmented normal fault located in the Upper Tiber Valley (Italy) and belonging to the well-known Altotiberina low-angle normal fault system.

In order to constrain the fault geometry and to select sites suitable for paleoseismologic trenching we performed geological survey, morphotectonic analysis and geophysical investigations. To assess the capability of the fault and its rate of activity we carried out a paleoseimic campaign, investigating several segments of the Anghiari fault. To obtain a multiscale evaluation of the fault slip rate, we collected samples to date paleosurfaces displaced by the fault with the cosmogenic nuclides methodology.           
At the end we performed the PFDHA obtaining curves and maps of hazard for both primary and distributed faulting, managing the uncertainties through various rupture scenario involving different fault segment.

How to cite: testa, A., Boncio, P., Baize, S., Mirabella, F., Pucci, S., Pauselli, C., Ercoli, M., Pace, B., and Benedetti, L.: Earthquake geology for fault displacement hazard analysis of normal faults, a case study from the Upper Tiber Valley (Northern Apennines, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-805, https://doi.org/10.5194/egusphere-egu23-805, 2023.

EGU23-815 | ECS | Posters on site | TS3.4

Challenges of fault characterization in areas of high anthropization. Surface variation along the Palomares Fault zone (SE Iberian Peninsula). 

Júlia Molins-Vigatà, María Ortuño, Juan Miguel Insua-Arévalo, and Raquel Martín-Banda

The study of seismogenic faults in low deformation rate regions is a challenging task, and their correct characterization is often limited due to the action of other external processes not related to the faults. Due to their lower rates, the expression of these structures is minor and more difficult to identify compared to regions with higher tectonic rates. Furthermore, in some areas, the erosion rates can be higher than the tectonic rates and the expression of the fault can be eroded easily. Another challenge is the exponential increase of surface modification due to anthropogenic processes, related e.g. to the placement of new infrastructures or agricultural activity. Anthropic modification of the landscape due to agriculture, farming, and greenhouses land covering is extremely high in the regions of Murcia and Almeria, where the major part of the main faults of the Eastern Betics Shear Zone (EBSZ) are located. The EBSZ is a low-to-moderate strain region situated in the SE of the Iberian Peninsula, a crustal-scale transpressive fault system that absorbs a significant part of the shortening between the Eurasian and the Nubian plates. Despite its low rates, it is the most active fault system on the Peninsula. The Palomares Fault (PF) is one of the principal structures of the EBSZ, bounding to the East the main Neogene-Quaternary basins of the area. At the foot of the bounding ranges, a high level of agricultural activity has taken place on top of the alluvial deposits. Therefore, in some areas where this activity is affecting the fault expression, it is required to work with historical aerial images in order to detect erased landforms. To overcome this limitation, some digital elevation models (DEMs) have been obtained with historical aerial photos through photogrammetry, as the current DEMs are not sufficiently useful. By this methodology, it is possible to detect some vertical fault slips now affected by agricultural activity, and the variation of the surface trough time. With GIS, the two models can be compared, subtracting the photogrammetric model from the current model. The result is a map showing the areas where the surface topography has increased or decreased. This analysis has been applied in zones where fault traces have been detected by historical images, but are currently unidentifiable due to anthropogenic activity.

How to cite: Molins-Vigatà, J., Ortuño, M., Insua-Arévalo, J. M., and Martín-Banda, R.: Challenges of fault characterization in areas of high anthropization. Surface variation along the Palomares Fault zone (SE Iberian Peninsula)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-815, https://doi.org/10.5194/egusphere-egu23-815, 2023.

EGU23-1100 | Orals | TS3.4

The Børglum fault, Sorgenfrei-Tornquist Zone, northern Denmark: a natural laboratory to investigate a hidden active intra-plate fault 

Christian Brandes, Ulrich Polom, Jutta Winsemann, Peter Sandersen, Patrick Wu, and Holger Steffen

Intra-plate faults are a special challenge in seismology, because of the long intervals between individual seismic events and the fact that such faults are often hidden below young sediments. This makes such faults difficult to detect and thus they can be the source of unexpected and fatal earthquakes. The Børglum fault is located in a slowly deforming area in northern Denmark and represents one of the northern boundary faults of the Sorgenfrei-Tornquist Zone. With a length of at least 250 km, it is capable to produce significant seismic events. Previous studies indicated that the Børglum fault is seismically active and this fuelled the demand for further analysis of the fault structure and its seismic hazard potential. Due to excellent coastal outcrops and available high-resolution DEMs, the Børglum fault is a perfect natural laboratory to analyse a hidden active fault. We present a multi-method approach based on outcrop analyses, shear-wave seismic reflection surveys, DEM analysis and numerical simulations of deglaciation-induced Coulomb failure stress change. The 2D seismic surveys show that the analysed segment of the Børglum fault is a complex fault system with a strike-slip component. This interpretation is based on positive flower structures on the seismic surveys, the presence of elongated mini-basins and the geometry of the drainage pattern in the study area. On the basis of soft-sediment deformation structures and disaggregation bands developed in Late Pleniglacial to Lateglacial marine and lacustrine deposits, we derive repeated phases of fault activity with earthquake magnitudes of up to M=7. The geometry of the drainage pattern in the study area indicates a close relationship between fault activity and topography. Based on the timing of fault activity and results from numerical simulations of deglaciation-related lithospheric stress build-up, it is likely that the Børglum fault is a glacially triggered fault and that the analysed part of the Sorgenfrei-Tornquist Zone is susceptible to glacially triggered fault reactivation.

How to cite: Brandes, C., Polom, U., Winsemann, J., Sandersen, P., Wu, P., and Steffen, H.: The Børglum fault, Sorgenfrei-Tornquist Zone, northern Denmark: a natural laboratory to investigate a hidden active intra-plate fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1100, https://doi.org/10.5194/egusphere-egu23-1100, 2023.

EGU23-2419 | Orals | TS3.4

Coulomb stress transfer as an explanation for a XVI-century earthquake cascade in the Eastern Betics Cordillera, Spain; Insights from viscoelastic relaxation of the lithosphere and postseismic stress triggering. 

Pouye Yazdi, Julián García-Mayordomo, José Antonio Álvarez-Gómez, Jorge Miguel Gaspar-Escribano, and Eulàlia Masana

The Eastern Betics Cordillera embraces a zone of low-to-moderate seismic activity located at the SE of the Iberian Peninsula. However, a major active fault system which crosses the area, ca. 500 km long, known as the Eastern Betics Shear Zone (EBSZ), has been responsible for the occurrence of several large historical earthquakes (Mw> 6.0) since the beginning of the historical record. Finding physics-based evidence for relations between significant historical events in such a moderate-slipping fault system would help us narrate them as long-term cascades. Such a perspective provides valuable insights into faults interactions over time and, thus, until the contemporary periods.

Some authors have examined static Coulomb failure stress changes (ΔCFS) to explain the triggering influence of moderate instrumental earthquakes in this region. However, the applied approach in this study, which implies the estimation of postseismic ΔCFS, is the first attempt of this kind to identify triggering connections between historical earthquakes in EBSZ.

This study addresses a sixteenth-century cascade of three large earthquakes that occurred in less than 13 years within a radius of 100 km in the southern section of the EBSZ. It includes the 1518 Vera (Mw~6.2), the 1522 Alhama de Almería (Mw~6.5 -7.1) and the 1531 Baza (Mw~6.5) earthquakes, each one associated with a different causative fault, namely the N-S strike-slip Palomares fault, the NE-SW strike-slip Carboneras fault and the N-S to NW-SE normal Baza fault, respectively. We aim to explore the Coulomb stress transfer along the occurrence of this cascade and the plausible rupture scenarios that could favour or not a triggering connection between the causative faults.

First, a simple smoothed slip model is performed to simulate the earthquake ruptures. The applied slip models respect existing information on the attributes and hypotheses based on seismological and paleoseismic studies. Then, the multilayered viscoelastic relaxation modelling by Wang et al. (2006) is used to calculate the time-dependent deformation fields (since the 1518 Vera earthquake) across the crust and the lithospheric mantle. Finally, the cumulative co+postseismic ΔCFS are solved for the kinematics of the Carboneras and Baza fault planes in 1522 and 1531, respectively.

Our results strongly suggest a sequential stress-triggering connection between these three large events. According to our models, the 1531 Baza earthquake occurred along with an increase in the ΔCFS due to the viscoelastic relation over time. We further explore the implication of the characteristic curved-shape of the Baza fault when considering different rupture scenarios of the 1522 event at the Carboneras fault. We found that the northern NS-oriented section of the Baza fault remains more exposed to positive cumulative co+postseismic ΔCFS and, indeed, was more prone to rupture in 1531 rather than the southern NW-SE section. We believe our results would pave the way for understanding the relationship between many other major historical earthquakes in the Betics Cordillera.

How to cite: Yazdi, P., García-Mayordomo, J., Álvarez-Gómez, J. A., Gaspar-Escribano, J. M., and Masana, E.: Coulomb stress transfer as an explanation for a XVI-century earthquake cascade in the Eastern Betics Cordillera, Spain; Insights from viscoelastic relaxation of the lithosphere and postseismic stress triggering., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2419, https://doi.org/10.5194/egusphere-egu23-2419, 2023.

EGU23-2730 | ECS | Orals | TS3.4

Update of the Seismogenic Potential of the Upper Rhine Graben Southern Region 

Sylvain Michel, Clara Duverger, Laurent Bollinger, Romain Jolivet, and Jorge Jara

The Upper Rhine Graben (URG), located in France and Germany, is bordered by north-south trending faults, some of them considered active, posing a potential threat to dense population and infrastructures from the Alsace plain. The largest historical earthquake in the region is the 1356 Basel earthquake associated to a magnitude M6.5+/-0.5. Current seismicity (M>2.5 since 1960) is mostly diffuse and located within the graben. The seismic hazard of the URG southern region was recently assessed by Chartier et al. (2017). In this study, we build upon their evaluation by exploring uncertainties in greater detail, revisiting a number of assumptions. Based on a complex fault network from Nivière et al. (2008), we evaluate scenarios that have not been taken into account previously, exploring uncertainties on Mmax, its recurrence time, the b-value, and the moment released aseismically or through aftershocks. Uncertainties on faults’ moment deficit rates, on the observed seismic events’ magnitude-frequency distribution, and on the moment-area scaling law of earthquakes are also explored. Given the four faults considered, and the scenario in which the Black Forest fault is not active anymore but where the other faults can still rupture simultaneously, and assuming only a dip-slip mechanism, the Mmax maximum probability is estimated at Mw5.95. Considering this scenario, there would be a 99% probability that Mmax is below 7.15. In contrast, considering instead strike-slip, as suggested by paleo-seismological work from Castellnou et al. (2022), and taking the Black Forest Fault into account, Mmax maximum probability is estimated at Mw6.85. Based on this scenario, there would be a 99% probability that Mmax is less than 7.65.

How to cite: Michel, S., Duverger, C., Bollinger, L., Jolivet, R., and Jara, J.: Update of the Seismogenic Potential of the Upper Rhine Graben Southern Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2730, https://doi.org/10.5194/egusphere-egu23-2730, 2023.

EGU23-3842 | Posters on site | TS3.4 | Highlight

TREAD daTa and pRocesses in sEismic hAzarD: a MSCA-Doctoral Networks project 2023-2027 

Bruno Pace, Lucilla Benedetti, Ylona Van Dinther, Marco Pagani, David Marsan, Alice Gabriel, Maria Ortuno, Giulio Di Toro, and Men-Andrin Meier and the TREAD working group

TREAD is a new project funded by the European Commission in the framework of Marie Sklodowska-Curie actions, Horizon Europe Doctoral Networks.

The aim of TREAD is to train a new generation of researchers to tackle the challenges of earthquake forecasting in complex tectonic settings using integrated observations and physics. The TREAD objectives are: (i) to develop a novel integrative approach to seismic hazard analysis in Europe and the Mediterranean from small-scale laboratory experiments to large-scale observations. (ii) to establish physics-based earthquake modelling bridging time scales from millions of years to fractions of a second in complex tectonic settings. (iii) to improve the link between earthquake geology, computational modelling and hazard and risk assessment with a focus on the needs of governments, industry and scientific stakeholders.

To reach these objectives the TREAD consortium comprises 14 academic and 8 non-academic institutions, of which 8 private partners, of high scientific level, from 7 European countries, covering cutting-edge knowledge and expertise in observational, experimental and modelling fields. 11 PhD positions will be available soon.

How to cite: Pace, B., Benedetti, L., Van Dinther, Y., Pagani, M., Marsan, D., Gabriel, A., Ortuno, M., Di Toro, G., and Meier, M.-A. and the TREAD working group: TREAD daTa and pRocesses in sEismic hAzarD: a MSCA-Doctoral Networks project 2023-2027, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3842, https://doi.org/10.5194/egusphere-egu23-3842, 2023.

EGU23-5039 | Orals | TS3.4

Investigating seismotectonic activity in northern France from LiDAR, palaeosismological trench and OSL/C-14 dating : new results along the Artois and Mélantois structures 

Fabien Graveleau, Frank Chanier, Laurent Deschodt, Hervé Jomard, Louise Watremez, Patrick Dusautoy, and Cécile Durin

Northern France presents mostly a low level of seismic hazard according to the French national seismic hazard map. Despite low instrumental seismicity rates, strong and unfrequent historical earthquakes occurred, with for instance the M~6, 1580 Strait of Dover earthquake, or the M~5, 1896 Lens-Arras earthquake, whose seismogenic sources are presumably the Sangatte and the Marqueffles Faults, respectively. Both belong to the NW-SE-directed Weald-Boulonnais-Artois structure. Moreover, the Haubourdin Fault (also named Lille-Hazebrouck Fault), at the hinge of the Mélantois anticline, and bordering the southern edge of the Lille Metropolis (1.2 millions inhabitants), is considered as potentially active during Quaternary times. All these above-mentioned faults are linked to deep Paleozoic structures in the basement that formed along the northern front of the Variscan orogeny, and that were regularly reactivated during the Mesozoic and Cenozoic. To investigate and document the possible neotectonic activity of the Artois structure and the Haubourdin Fault, and therefore improve seismic hazard assessment in northern France, we used a pluridisciplinary approach based on the analysis of 1) LiDAR dataset, 2) paleoseismological trenching, 3) OSL/14C dating, and 4) sub-surface geophysical survey.

Along the Artois structure, we focused on the locality of Harnes within Lens city suburbs. A preventive archeological work unraveled a clear sub-surface deformation feature that we analyzed through several ~2m-deep trenches. Field investigations indicated that the fault presents a regular N130° strike, which is consistent with surface and subsurface regional structures, and a 25-30° southwestward dip. Reverse throw along the fault were measured to about 15-20 cm thanks to a clearly displaced coal-rich horizon, sampled for C-14 dating. Interpretation of the data is complex since the site is located in a region where glacio-tectonic processes, severe First World War bombing and subsidence due to underground mining are documented.

Along the Haubourdin Fault, our analysis of high resolution LiDAR data highlighted two topographic scarps aligned along a N110°E trend, but that do not match with the fault trace extracted from the geological map. This new fault trace is confirmed by subsurface geophysical survey (electric resistivity tomography and mapping). Both scarps present contrasted uplifted blocks since the southern block is uplifted (by several meters) for the western branch, whereas the northern block is uplifted (by 1-2 m) for the eastern branch. All these new field mapping results call for a substantial revision of the fault trace in the region together with a consideration of its segmentation. Finally, two new OSL datings has been obtained from a sandy-clay layer unconformably sealing some Late Paleocene deformation in the southern Lille suburb (i.e., Villeneuve d’Ascq). It gives the first minimum age in the literature for the deformation of the Mélantois northern limb.

How to cite: Graveleau, F., Chanier, F., Deschodt, L., Jomard, H., Watremez, L., Dusautoy, P., and Durin, C.: Investigating seismotectonic activity in northern France from LiDAR, palaeosismological trench and OSL/C-14 dating : new results along the Artois and Mélantois structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5039, https://doi.org/10.5194/egusphere-egu23-5039, 2023.

EGU23-5228 | Orals | TS3.4

Identification of faulted geomorphic markers and slip-rate estimation along the source of the 2020 Mw6.4 Petrinja earthquake (Croatia), the Petrinja-Pokupsko Fault. 

Lucilla Benedetti, Maxime Henriquet, Stéphane Baize, Branko Kordic, Adrien Moulin, Josipa Maslač, Nikola Belić, Francesca Cinti, Daniela Pantosti, Stefano Pucci, Riccardo Civico, Alessio Testa, Paolo Boncio, Bruno Pace, Petra Jamšek Rupnik, Cecile Lasserre, and Marianne Metois

Europe has experienced over the last years earthquakes of moderate magnitude (Mw 5-6), yet destructive, reminding us of the seismogenic potential of slowly deforming regions. Among them, the 2020 Mw 6.4 Petrinja earthquake ruptured the Petrinja-Pokupsko Fault (PPKF) in Central Croatia, about 50-km southeast of Zagreb, a region in which the caracterisation of seismogenic faults had been insufficiently studied before that event. Understanding the strain accommodation through time and space is critical for accurate assessment of the regional seismic hazard.

Using field observations and high-resolution topographical data derived from airborne LiDAR (~10 cm resolution) and tri-stereo satellite images (Pléiades, resolution 50 cm), we accurately mapped the fault trace, underlined at several sites by geomorphic markers such as valleys, terrace risers, and alluvial fans that have recorded cumulative displacements ranging from 5 to > 50 m and potentially up to ~180 m. Along the studied section, our fault mapping is composed of a clear NW-SE-trending 10-km-long strand between Donja and Cepelis, and of 1-4-km-long right-stepping segments marked by a non-negligible vertical component. The southern strand is composed of 2-3 sub-parallel segments that accommodate the deformation within a < 500 m wide fault zone.

We have identified several sites on the main southern strand where offsets have been accurately measured and where displaced markers have been sampled for cosmogenic nuclide exposure dating and radiocarbon datings. This will allow to estimate the slip-rate for this fault at different sites and over several time spans.

The mapped fault appears very discontinuous with the deformation absorbed by a series of small fault sections rather than on a single fault strand. This likely reflects a recent transpressive deformation, with immature faults,  in agreement with the source parameter of the 2020 Petrinja earthquake derived from seismology.

Finaly, the 2020 coseismic surface ruptures affected the northern section of the PPKF, while the mapped cumulative displacements appears more prominent along the southern section. A better knowledge of the seismic history of this entire fault system is thus crucial for seismic hazard assessment of this area.

How to cite: Benedetti, L., Henriquet, M., Baize, S., Kordic, B., Moulin, A., Maslač, J., Belić, N., Cinti, F., Pantosti, D., Pucci, S., Civico, R., Testa, A., Boncio, P., Pace, B., Jamšek Rupnik, P., Lasserre, C., and Metois, M.: Identification of faulted geomorphic markers and slip-rate estimation along the source of the 2020 Mw6.4 Petrinja earthquake (Croatia), the Petrinja-Pokupsko Fault., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5228, https://doi.org/10.5194/egusphere-egu23-5228, 2023.

EGU23-5686 | ECS | Posters on site | TS3.4

Can we observe North Andean Sliver motion using long InSAR time-series analysis? 

Léo Marconato, Marie-Pierre Doin, Laurence Audin, Nicolas Harrichhausen, Jean-Mathieu Nocquet, Paul Jarrin, and Frédérique Rolandone

In Northern Andes, oblique subduction of the Nazca plate below the South America Plate induces a northward motion of the North Andean Sliver, at a rate of ~10 mm/yr with respect to Stable South America. In Ecuador in particular, the associated strain is mainly accomodated along the large Chingual-Cosanga-Puna-Pallatanga (CCPP) fault system, which hosted several 7+ magnitude earthquakes in the historical period. Recent studies using block-modeling of GNSS data raise important questions about the partitioning and the localization of the deformation both inside and at the limits of the North-Andean sliver. Therefore, time-series analysis of InSAR data, allowing a large spatial resolution, would complement the existing geodetic dataset of observation of low-rate crustal motions in this region. Taking advantage of 7 to 8 years of Sentinel-1 archive, we compute long time-series of InSAR data for the whole Interandean region of Ecuador (~100 by 400 km), using the NSBAS processing chain. Because processing of InSAR data in this ecuatorial region raises several challenges, such as low-coherence due to vegetation, ionospheric and troposheric noise, and fading signals,we develop strategies to mitigate the noise terms. By using an optimized interferogram network, improvedweighting during multilooking, and a temporal decomposition of the time-series, we produce the first InSAR velocity maps of the Ecuadorian Cordilleras. We then compare these results to the existing block-model derived from GNSS horizontal data in order to evaluate the possibility of characterizing the motion of North Andean Sliver with an increased spatial resolution.

How to cite: Marconato, L., Doin, M.-P., Audin, L., Harrichhausen, N., Nocquet, J.-M., Jarrin, P., and Rolandone, F.: Can we observe North Andean Sliver motion using long InSAR time-series analysis?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5686, https://doi.org/10.5194/egusphere-egu23-5686, 2023.

EGU23-6872 | ECS | Posters on site | TS3.4

Geological, geophysical and geotechnical highlights of the southern part of the Al Idrissi strike-slip fault system from the Alboran sea 

Léa Vidil, Elia d'Acremont, Sylvie Leroy, Sara Lafuerza, Laurent Emmanuel, and Alain Rabaute and the ALBACORE and ALBANEO teams

In the Alboran Sea, oblique convergence between the African and Eurasian plates led to the establishment of the Al Idrissi sinistral strike-slip fault system, initiating a new plate boundary, 1 Ma ago. Several moderate magnitude earthquakes (Mw > 6) have been recorded on different segments of this fault system. The objective of this study is to analyse the dynamics of this plate boundary by studying the tectonic activity and physical properties of the sedimentary series along a key transect of the fault system. To do so, we used a panel of geological, geophysical and geotechnical tools, some of which were acquired during the ALBACORE oceanographic campaign (R/V Pourquoi Pas? 2021).

The data analysed are derived from (i) sediment cores of the ALBACORE oceanographic cruise (with multi-sensor core logger - MSCL), (ii) heat flux measurements, (iii) penetration tests with the Ifremer Penfeld piezocone (CPTU) as well as (iv) multibeam bathymetry data and (v) seismic reflection/depth data. These data were acquired along a transect of the Bokkoya fault system, south of the Al Idrissi fault system. The length of the sedimentary series investigated allows the dating of major sedimentary events that occurred during the late Pleistocene and Holocene. Along this segment, isotope analysis of the carbonate biogenic components provided a 𝛿18O evolution curve that was converted into time series. Thus, a chronostratigraphic framework up to 80 ky could be constrained as well as variations in sedimentation rate between compartments on either side of the fault. The analysis of physical properties using heat flow, CPTU and MSCL data allows a detailed lithological and geophysical stratigraphy to be established along the transect and highlights the variability of geological, geotechnical and geophysical signatures on either side of the fault system.  This work is part of the ANR ALBANEO project, which aims to understand the dynamics of this new plate boundary and, in the longer term, to assess the hazards in this area of the western Mediterranean Sea.

How to cite: Vidil, L., d'Acremont, E., Leroy, S., Lafuerza, S., Emmanuel, L., and Rabaute, A. and the ALBACORE and ALBANEO teams: Geological, geophysical and geotechnical highlights of the southern part of the Al Idrissi strike-slip fault system from the Alboran sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6872, https://doi.org/10.5194/egusphere-egu23-6872, 2023.

EGU23-7376 | ECS | Orals | TS3.4 | Highlight

Convolutional neural network for normal fault scarp characterization :  application to the Trans-Mexican Volcanic Belt 

Léa Pousse-Beltran, Sophie Giffard-Roisin, Laurence Audin, Pierre Lacan, Theo Lallemand, and Andres Núñez Meneses

Normal fault markers in the landscape such as scarp are records of fault activity. The scarp morphology is used for exemple to estimate slip rates or rupture behaviors. The scarp morphology varies along strike, and needs to be estimated to assess this variation. Currently this is often a time-consuming step with expert-dependent results, often qualitative and with uncertainties that are difficult to estimate. To overcome those issues, we are developing a bayesian supervised machine learning method using convolutional neural networks (CNN) trained on a database of simulated profiles, called ScarpLearn. We train the CNN to use high resolution data (< 5m). From a 2D topographic profile across normal fault scarps, ScarpLearn is able to automatically give the scarp height with an uncertainty and to illuminate the area of the profile containing the scarp. We apply ScarpLearn for the characterization of normal active faults in the Trans-Mexican Volcanic Belt. This region is a slow deforming area (~0.2±0.05 mm/yr), which extends over more than 800km, crossed  by more than 600 potentially active faults but less than 5% of those have been correctly characterized by paleoseismological studies. In this context an automatic method to characterize the escarpments in a global, reproductible, robust (not expert-dependent) quantitative way will be highly valuable and a great step towards a better characterization of the seismic hazard of the region. In particular we tested our approach across the Ameca-Ahuisculco fault system, and by comparing ScarpLearn with with other methods based on profile analisis (not based on deep learning), we explore the advantages (computation time, accuracy, uncertainties) that deep learning methods bring, as well as the current limits (such as bias and dependance of the resolution).

How to cite: Pousse-Beltran, L., Giffard-Roisin, S., Audin, L., Lacan, P., Lallemand, T., and Núñez Meneses, A.: Convolutional neural network for normal fault scarp characterization :  application to the Trans-Mexican Volcanic Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7376, https://doi.org/10.5194/egusphere-egu23-7376, 2023.

EGU23-8282 | ECS | Posters on site | TS3.4

Physics-based modeling of earthquakes in slow deforming areas: a case study from the Eastern Betic Fault System (SE Spain) 

Paula Herrero-Barbero, José A. Álvarez-Gómez, Charles Williams, Pilar Villamor, Meaza Tsige, Juan M. Insua-Arévalo, Jorge Alonso-Henar, and José J. Martínez-Díaz

The challenges in the characterization of slow-moving faults and the temporal limitations of the earthquake records in these regions complicate the seismic hazard assessment. The instrumental and historical seismic catalogs cover a short time period compared with the long recurrences between large destructive events in some faults. Paleoseismic evidence allows us to increase the time frame, but when field data is scarce, scattered or difficult to collect, numerical modeling provides us with an excellent tool to support the characterization of a fault system and its associated threat. Physics-based earthquake simulators overcome the limitations of actual earthquake catalogs and generate long-term synthetic seismicity. Recent numerical codes based on rate- and state-dependent friction allow the modeling of both the long-term seismic cycle deformation and the short-term rupture based on quasi-dynamic physical approximations. We use the RSQSim earthquake simulator to reproduce a 100 kyr synthetic catalog of earthquake ruptures based on a 3D fault model that contains the long-term slip rates, rakes and frictional properties of the main active sources of the Eastern Betic Fault System, a slow deforming area (< 1.5 mm/yr) at southeastern Spain with only one instrumental event greater than MW 5.0: the 2011 Lorca earthquake (MW 5.1). The resulting long-term earthquake statistics (more than 77.000 events) show that only about 10% of the simulated events have a magnitude greater than MW 5.0, but all faults in the system are capable of generating MW ≥ 6.0 earthquakes, supporting paleoseismic observations of surface ruptures and some historical events (I > VIII) that likely reached magnitudes greater than MW 6.0 (e.g., 1522 Alhama de Almeria and 1829 Torrevieja earthquakes). Complex ruptures involving several fault segments and spatial-temporal clustering of events are physically compatible in this system, according to our simulations. The largest MW > 6.5 events are as a result of complex ruptures between the major faults, with recurrence times of 1 kyr. The occurrence of larger earthquakes, even MW ≥ 7.0 in the Alhama de Murcia and Carboneras faults, cannot be ruled out, contrasting with the low magnitudes of the instrumental earthquake catalog. Knowing the characteristics and behavior of these large seismic ruptures, with no instrumental data available, is crucial for the estimation of the maximum ground motion that could be reached in this region. With this contribution, we intend to discuss how physics-based models could contribute to this task for deterministic and probabilistic seismic hazard assessments (DSHA and PSHA). Funded by Project DT-GEO: A Digital Twin for GEOphysical extremes, project ID 101058129.

How to cite: Herrero-Barbero, P., Álvarez-Gómez, J. A., Williams, C., Villamor, P., Tsige, M., Insua-Arévalo, J. M., Alonso-Henar, J., and Martínez-Díaz, J. J.: Physics-based modeling of earthquakes in slow deforming areas: a case study from the Eastern Betic Fault System (SE Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8282, https://doi.org/10.5194/egusphere-egu23-8282, 2023.

EGU23-9511 | Orals | TS3.4

Fragmentation of the Victoria microplate: geomorphological evidence for active faulting along the Isuria-Utimbara fault system, Kenya-Tanzania transboundary region 

Beth Kahle, Alina Ludat, Simon Kübler, Mjahid Zebari, Stefanie Rieger, Mugabo Wilson Dusingizimana, Sara Carena, and Anke Friedrich

The Victoria microplate is generally assumed to be internally rigid, i.e. non-deforming.  Here, we describe geomorphological evidence for active fragmentation of the microplate along the E-W to NE-SW striking Isuria-Utimbara fault system, Lake Victoria, in the Kenya-Tanzania transboundary region.

The Isuria-Utimbara fault system has received little previous attention and is not recognised as seismically active. The fault system marks the northern boundary of the Mara River Basin and lies within the mapped extent of the Victoria microplate, an apparently relatively rigid block situated on the Tanzanian craton. The area is defined by low seismicity within the temporal limits of the instrumental record: seismicity is concentrated along the western arm (as well as, to a lesser extent, the southernmost part of the eastern arm) of the East African Rift (EAR). Here, we describe geomorphological evidence for geologically recent earthquake activity, which has produced scarps and alluvial fans in the hanging walls of the major escarpments. The scarps appear to be segmented, with typical segment lengths of approximately 15 km, and together sum to an along-strike length of approximately 100 km. The height of the scarps exceeds 8 m with a maximum height of 25 m (measured using TanDEM-X Digital Elevation Model (DEM) Global data which has a horizontal resolution of 12 m and an ~2 m height error). Considering the length of a typical segment, scaling relationships suggest the possibility for multiple >Mw 6 earthquakes. If the segments slipped together, this would result in a maximum earthquake magnitude of >7. Although dating has not yet been carried out, a constraint on slip rate comes from displaced Neogene volcanics found above and below the main escarpment, which give a long-term vertical displacement rate of approximately 0.1mm/yr, comparable with stable continental intraplate settings. Our findings have implications for the seismic hazard of the region: although parts of the Mara River Basin are protected areas of great ecological importance, population density is increasing along the shores of Lake Victoria and a major gold mine lies directly to the south of the fault system. This fault appears to be fragmenting the Tanzanian craton, albeit at relatively slow rates, and cratonic settings are in general capable of producing large and damaging earthquakes due to the possibility for a large seismogenic thickness.

How to cite: Kahle, B., Ludat, A., Kübler, S., Zebari, M., Rieger, S., Dusingizimana, M. W., Carena, S., and Friedrich, A.: Fragmentation of the Victoria microplate: geomorphological evidence for active faulting along the Isuria-Utimbara fault system, Kenya-Tanzania transboundary region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9511, https://doi.org/10.5194/egusphere-egu23-9511, 2023.

EGU23-9718 | Posters on site | TS3.4

Which fault was it? - Late Pleistocene, glacially triggered earthquakes in NE Germany 

Holger Steffen, Małgorzata Pisarska-Jamrozy, Szymon Belzyt, Andreas Börner, Gösta Hoffmann, Michael Kenzler, Henrik Rother, and Rebekka Steffen

A sedimentological, geochronological, and geodynamic investigation of detailed micro- and meso-scale soft-sediment deformation structures (SSDS) within internally deformed layers on Gnitz Peninsula, Usedom Island, Germany, was performed in the last years. Five layers with SSDS were described of which four were possibly caused by glacial isostatic adjustment (GIA)-triggered earthquakes mirrored in liquefaction and reliquefaction phenomena (Pisarska-Jamroży et al., 2022). Hence, in line with earlier investigations and suggestions by Hoffmann and Reicherter (2012), the SSDS generation is related to oscillation of the Scandinavian Ice Sheet whose loading cycle caused stress changes likely releasing local earthquakes along pre-existing faults.

Optically stimulated luminescence dating indicates a most probable time span of corresponding earthquake occurrence between 23.2 and 14.6 ka (including uncertainty). For the first time, glacially induced Coulomb failure stress changes were modelled for this area with a set of commonly accepted GIA models. They strongly support the interpretation of SSDS trapped in layers as seismites during that time. Using reliable fault parameters of faults in near vicinity of Gnitz Peninsula and suggested stress regimes and directions for northern Germany, the modelling can help indicate the most probable reactivated pre-Quaternary fault(s). If they can be confirmed after detailed palaeoseismological, geomorphological, geophysical, and structural investigations as so-called glacially induced fault(s), this would add another puzzle piece to a geodynamic scenario of glacially triggered faulting having affected an area from northern central Europe to northern Fennoscandia in the Late Pleistocene and Early Holocene.

Our presentation will focus on the geodynamic setting of NE Germany, how it was changed during the last glaciation and how potentially reactivated faults can be determined.

References

Hoffmann, G., Reicherter, K., 2012. Soft-sediment deformation of late Pleistocene sediments along the southwestern coast of the Baltic Sea (NE Germany). Int. J. Earth Sci. 101, 351-363, doi:10.1007/s00531-010-0633-z.

Pisarska-Jamroży, M., Belzyt, S., Börner, A., Hoffmann, G., Kenzler, M., Rother, H., Steffen, R., Steffen, H., 2022. Late Pleistocene earthquakes imprinted on glaciolacustrine sediments at Gnitz Peninsula (Usedom Island, NE Germany). Quat. Sci. Rev. 296C, 107807, doi:10.1016/j.quascirev.2022.107807.

How to cite: Steffen, H., Pisarska-Jamrozy, M., Belzyt, S., Börner, A., Hoffmann, G., Kenzler, M., Rother, H., and Steffen, R.: Which fault was it? - Late Pleistocene, glacially triggered earthquakes in NE Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9718, https://doi.org/10.5194/egusphere-egu23-9718, 2023.

EGU23-11719 | Posters on site | TS3.4

Exceptionally preserved neotectonic fault scarps in SW Namibia record large-magnitude structurally-controlled SCR paleoseismicity 

R. Alastair Sloan, Robert Muir, Benjamin Whitehead, Thomas New, Victoria Stevens, Paul Macey, Conrad Groenewald, Guy Salomon, Beth Kahle, and James Hollingsworth

Namibia is situated within a stable continental region (SCR), far away from plate boundary zones, and is therefore not expected to be at risk of significant earthquakes; the largest events in the instrumental record have a moment magnitude of 5.5.  Despite this, a paleoseismic fault scarp on the Hebron Fault has been interpreted as indicating much larger events have occurred in the past.  In this study, we demonstrate that a relatively small area of SW Namibia contains four more major neotectonic fault scarps.  These 16-80 km long structures have vertical separations between 0.7-10.2 m and could produce earthquakes of Mw 6.4 or greater.  Some of these scarps are interpreted to have formed through repeated failure of the same segment and they highlight the potential for further seismicity that far exceeds the maximum observed magnitude in the national catalogue. We identify strong structural controls on the location and orientation of these fault ruptures which reactivate N-S and NW-SE trending zones of crustal weakness.  These structures may be driven by E-W extension associated with the distribution of gravitational energy caused by the anomalously high elevation of the Namibian Escarpment.  If this explanation of the driving stresses is correct, these and similarly oriented faults represent a previously unrecognised source of continuing seismic hazard.  The discovery of these major fault scarps suggests that fault studies should be incorporated into seismic hazard analyses of stable Southern Africa as has been done in Australia and other SCR regions. Their apparent spatial clustering also merits further study.  At this point it is not clear if this clustering indicates a region of elevated strain rate (relative the surrounding SCR) or alternatively, an area of exceptional preservation due to a semi-arid climate and extensive calcrete-cemented surficial deposits.

How to cite: Sloan, R. A., Muir, R., Whitehead, B., New, T., Stevens, V., Macey, P., Groenewald, C., Salomon, G., Kahle, B., and Hollingsworth, J.: Exceptionally preserved neotectonic fault scarps in SW Namibia record large-magnitude structurally-controlled SCR paleoseismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11719, https://doi.org/10.5194/egusphere-egu23-11719, 2023.

EGU23-13396 | Orals | TS3.4

Geologic records of moderate-to-large pre-historical earthquakes in South Korea 

Jin-Hyuck Choi, Chung-Ryul Ryoo, Tae-Ho Lee, Youngbeom Cheon, Hoil Lee, Taehyung Kim, Yire Choi, and Chang-Min Kim

South Korea, one of the most densely populated areas, has been considered a tectonically safe region as there were no destructive earthquakes in modern society. Indeed, there is no report of any earthquake event with surface ruptures in a historical period. After the 2016 Mw 5.5 Gyeongju earthquake, the largest instrumentally recorded event in South Korea, the need for research on large-earthquakes has highlighted and multidisciplinary research projects were conducted for paleoseismological investigations. Here we introduce the newly discovered geologic records of pre-historical large-earthquakes. Firstly, paleoearthquake surface ruptures were newly identified along the entire section of the Yangsan Fault, one of the most major strike-slip structures in the Korean Peninsula. For a 50-km-long fault section, a fault theme map with a scale of 1:25,000 was produced and paleo-earthquake records were found at multiple sites mainly based on excavation surveys. The results provide an opportunity to interpret the temporal and spatial scenarios of the paleo-earthquakes along the fault. Secondly, stratigraphic records of paleo-earthquake surface rupture were found at a few localities near another major strike-slip fault system; the Gongju Fault System, and we obtained paleoseismic data. These records imply that moderate-sized earthquakes often occurred on minor faults, not on the main trace of the major faults. Our results indicate that the crustal deformation of the Korean Peninsula, which belongs to the very slow-deforming regions, is accommodated by moderate-to-large earthquakes with a recurrence time ranging from thousands to tens of thousands of years. Considering that it is not easy to detect any crustal deformations using micro seismicity and/or geodetic data due to too slow deformation, we note that it is necessary to obtain more paleoseismological data to well understand tectonic deformations as well as to assess hazards associated with future earthquakes.

How to cite: Choi, J.-H., Ryoo, C.-R., Lee, T.-H., Cheon, Y., Lee, H., Kim, T., Choi, Y., and Kim, C.-M.: Geologic records of moderate-to-large pre-historical earthquakes in South Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13396, https://doi.org/10.5194/egusphere-egu23-13396, 2023.

EGU23-13443 | Posters on site | TS3.4

Geodetic vs. geologic measures of fault slip rates of the Carboneras fault in the Betics 

Giorgi Khazaradze, Octavi Gómez-Novell, Maria Ortuño, Eulàlia Masana, and Raimon Pallàs

As part of the recently initiated research project, we are in the process of studying in detail the geodynamic behavior of the Carboneras fault (CF) in the SE Betics in Spain. Specifically, we plan to quantify the geodetic and geologic slip rates for the on-land section of the fault, as well as getting some insight on the state of locking of the fault. As a result of our previous GPS observations, we have been able to illustrate the continuing tectonic activity of the Carboneras fault, expressed mainly as a left-lateral strike slip motion of 1.3±0.2 mm/yr, with a less significant compression of 0.4±0.2 mm/yr (Echeverria et al., 2015). To reveal how the deformation is partitioned between different structures, in the last years 2 new continuous GPS points were established along the fault-perpendicular profile. In addition, we have conducted several surveys of the nearby CuaTeNeo and IGN Regente points and established and measured several new geodetic points in the vicinity of the Carboneras fault. The updated horizontal geodetic slip rates for the CF are 1.1±0.2 and 0.4±0.3 mm/yr in fault parallel and perpendicular directions, respectively. These estimates are somewhat smaller than previously published results, although considering the uncertainties, are statistically equivalent.

The above-mentioned geodetic, short-term, slip rates deduced from GNSS observations, are in good agreement with the estimates of geologic slip rates based on paleoseismic and geomorphologic studies, which indicate a minimum strike-slip rate of 1.3 mm/yr and dip-slip rate of 0.05 mm/yr since 110.3 ka (Moreno et al. 2015). In the coming years we plan to conduct further geodetic surveys and paleoseismic trenching surveys. These new data, should significantly improve the reliability of the existent deformation data and therefore, contribute to better understanding of the seismic hazard posed by the Carboneras fault in the SE Betics.

Project NSOURCES (PID2020-119772RB-I00) financed by MCIN/AEI/10.13039/501100011033

How to cite: Khazaradze, G., Gómez-Novell, O., Ortuño, M., Masana, E., and Pallàs, R.: Geodetic vs. geologic measures of fault slip rates of the Carboneras fault in the Betics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13443, https://doi.org/10.5194/egusphere-egu23-13443, 2023.

EGU23-13509 | ECS | Posters on site | TS3.4

Unsupervised clustering to jointly interpret geophysical datasets across the Alhama de Murcia active fault, Spain. 

Adrià Hernandez i Pineda, Tural Feyzullayev, Ignacio Marzan, Juan Alcalde, David Martí, and Ramon Carbonell

Joint interpretation of multidisciplinary geophysical data is the best way to reduce ambiguity in subsurface exploration. The combination of seismic velocity and electrical
resistivity has proven to be an excellent geological characterization strategy, however, the integration of these geophysical parameters is a complex process. In this work, we use unsupervised clustering to jointly interpret three geophysical datasets (P wave velocity, S wave velocity, and electrical resistivity). The target is a cross-section across the Alhama de Murcia Fault (FAM), which is one of the main active faults in the Iberian Peninsula. In our approach, we first join the three datasets into a common multiparametric grid. Then, in order to find data clusters that can be correlated with known lithologies in the area, we investigated the performance of three unsupervised machine learning algorithms: one hierarchical, one centroid-based, and one model-based. The latter proved to be the most efficient for clustering our highly mixed data and providing geological meaning. The three classes obtained correlated well with the lithological units present in the area and, from their relationship, it was possible to deduce structural elements not yet well understood, providing new perspectives in the characterization of the Alhama de Murcia fault zone. Research supported by grants: VECTOR EU project ID 101058483, and SIT4ME -EITRawMaterials.

How to cite: Hernandez i Pineda, A., Feyzullayev, T., Marzan, I., Alcalde, J., Martí, D., and Carbonell, R.: Unsupervised clustering to jointly interpret geophysical datasets across the Alhama de Murcia active fault, Spain., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13509, https://doi.org/10.5194/egusphere-egu23-13509, 2023.

EGU23-14350 | ECS | Posters on site | TS3.4

200 000 years of glacially induced faulting in the Tornquist Fan area, SW Baltic Sea. 

Elisabeth Seidel, Holger Steffen, Rebekka Steffen, Niklas Ahlrichs, and Christian Hübscher

We present a comparative study of the glacially induced fault reactivation within the Southern Baltic Sea since the Upper Saalian. A complex tectonic pattern characterizes the Tornquist Fan, which spans between the Tornquist Zone in the North and the Trans European Suture Zone in the South. Multiple fault zones result from the varying transpressional and transtensional stress activities since the Paleozoic. The current tectonic pattern of this unique natural laboratory is composed of several faults with varying strike and dip directions, depths and characters (normal, reverse, strike slip). Moreover, some shallow faults are associated with Zechstein salt pillows, and others are related to anticlines formed during the Cretaceous to Paleogene compression.

Using finite-element simulations of different glacial isostatic adjustment models (varying the material parameters in the Earth and the ice history), we obtained glaciation induced Coulomb failure stress changes (∆CFS) at the faults over time, covering the past 200 ka. Comparing the activation potential of several faults of different tectonic background reveals the impact of the varying crustal and fault properties, as well as the influence of salt structures below. Besides lateral differences in the ∆CFS due to the changing geology, we see temporal differences, by comparing the occurrence of glacially induced faulting with different ice advances.

How to cite: Seidel, E., Steffen, H., Steffen, R., Ahlrichs, N., and Hübscher, C.: 200 000 years of glacially induced faulting in the Tornquist Fan area, SW Baltic Sea., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14350, https://doi.org/10.5194/egusphere-egu23-14350, 2023.

EGU23-14783 | ECS | Posters on site | TS3.4

A segment model for surface rupture scenarios in the eastern Rhine Graben Boundary fault (Upper Rhine Graben, Germany) 

Sara Pena-Castellnou, Stéphane Baize, Jochen Hürtgen, and Klaus Reicherter

The eastern Rhine Graben Boundary fault (eastern RGBF) constitutes the eastern margin of the Upper Rhine Graben (URG), the most seismically active area in the plate interiors of Europe. Our recent paleoseismic studies have revealed Late Pleistocene-Holocene surface-rupturing paleoearthquakes with magnitudes M 6–6.5 and cumulative surface displacements in the order of 1–1.2 m vertically and 4–6 m horizontally. Based on the empirical relationships of Wells and Coppersmith, these parameters suggest that the plausible rupture scenarios of those paleoearthquakes are linked to shorter fault segments within the 300 km long eastern RGBF rather than an entire rupture of the fault. Up to date, segmentation on faults of the URG has yet to be evaluated. We aim to define fault segments within the eastern RGBF and their relative tectonic activity to understand how deformation is distributed along the marginal faults and within the graben. To achieve this, we integrate seismicity data, morphotectonic observations (from SRTM, TanDEM-X and LiDAR-based DEMs), geology (Plio-Pleistocene sediment thickness), and interpretation of commercial seismic lines.

We define up to seven segments of varying lengths based on geometric and structural fault trace discontinuities (bend, gaps, and changes in strike and dip) and the occurrence and degradation state of tectonic landforms (triangular facets, beheaded channels, hanging valleys and offset alluvial fans), which we also take into account to define the relative level of tectonic activity at each segment. The most active segments are the South-Kraichgau and Freiburg segments, with potential magnitudes of M 7–7.5 (including the historical M 6.7 Basel eq of 1356). The northern area, comprising the Frankfurt-Darmstadt and Odenwald segments, constitute presently a seismic gap with quiescence in historical and instrumental seismicity but with tectonic expression in the landscape and thickest Late Tertiary-Pleistocene deposits, suggesting a potential hazard. Our results provide a basis to propose plausible rupture scenarios for the eastern RGBF for future PSHA studies.

How to cite: Pena-Castellnou, S., Baize, S., Hürtgen, J., and Reicherter, K.: A segment model for surface rupture scenarios in the eastern Rhine Graben Boundary fault (Upper Rhine Graben, Germany), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14783, https://doi.org/10.5194/egusphere-egu23-14783, 2023.

EGU23-14995 | ECS | Posters on site | TS3.4

The 1804 Dalías earthquake: ranking seismic sources with the Boxer and seismic scenario methods in SE Iberia 

Yolanda de Pro-Díaz, José Jesús Martínez-Díaz, and Carolina Canora Catalán

SE Iberia is a tectonically active area with an important history of destructive earthquakes. Some of these earthquakes have been associated with known active faults, but the seismic source of most of them remains unclear. The majority of these earthquakes happened long before instrumental record began, so we can only study them through paleoseismology and/or historical records. In some cases, due to current soil usage, paleoseismic studies are extremely difficult to perform and researchers can only rely on historical records. Such is the case of the 1804 Dalías earthquake.

In this communication our objective is double. First, we present a methodology which can be useful to constrain the seismic source of historical earthquakes for which only intensity data are available. And second, we apply this methodology to the 1804 Dalías earthquake in order to constrain its seismic source, which remains unclear up to this day. Our proposed methodology is a combination of Gasperini et al. (1999, 2010)’s and de Pro-Díaz et al. (2022)’s methods. Our methodology searches for the faults that are most plausible candidates for the earthquake rupture, then builds seismic scenarios for each candidate rupture and finally compares these scenarios with the observed intensity field in order to find the candidate with the best fit. Seismic scenarios are built using OpenQuake and ArcGIS software (although QGIS can be used as well). The candidate that generates the simulation which better resembles the observed intensity field is considered the best candidate and the one closest to the actual earthquake source.

For the 1804 Dalías earthquake, we consider different ruptures along the Loma del Viento Fault (LVF) and Llano del Águila Fault (LLAF) traces as candidate ruptures, including some combined ruptures along the two faults. Our results show that there are two almost equally best candidates: a full rupture of the whole inland extension of the LVF, and a combined rupture of this fault and the LLAF.

How to cite: de Pro-Díaz, Y., Martínez-Díaz, J. J., and Canora Catalán, C.: The 1804 Dalías earthquake: ranking seismic sources with the Boxer and seismic scenario methods in SE Iberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14995, https://doi.org/10.5194/egusphere-egu23-14995, 2023.

EGU23-16439 | ECS | Posters virtual | TS3.4

Review of methods for characterization of active faults for seismic hazard purposes. 

Adriana Fatima Ornelas Agrela, María Belén Benito, and Conrad Lindholm

This work presents a review of some methods for seismic hazard assessments based on hybrid source models, composed of active faults and seismic zones. These approaches are applied in a slow deformation area, defined as areas where the slip rate of the active faults is slower than 5 mm/yr.

The introduction of active faults as independent seismic sources in seismic hazard assessment has a great impact on the results that can be obtained in urban areas close to active faults, with respect with those obtained with classical zoning methods (CZM). 

Currently, there are no widely contrasted methodological developments to include zones and the characterized active faults in the source models, especially in slow deforming areas. Even though, some approaches that have used hybrid models (HM) composed of zone-type sources and fault-type sources, revealed that expected ground motion values around main faults may double (on average) those obtained by zoned models, in agreement with observations in recent earthquakes (Rivas-Medina, A., 2018; Gómez-Novell O., 2020).

This presentation compares some methods that address two key aspects: how to quantify the geological information and transfer it to recurrence models, and how to distribute the seismic potential between the two types of sources. Some of these methods are: 1) Moment-rate based method proposed by Bungum (2007), 2) Slip-rate based method also proposed by Bungum (2007), 3) Hybrid method developed by Rivas-Medina et al. (2019).

This study is centered in the Eastern Betics Shear Zone (EBSZ) in southeast Spain, which is a low to moderate seismicity region. These methods were applied in the seismic zones 37 and 55 defined by Garcia-Mayordomo (2015) due to the seismological and geological data availability of the present faults in each zone.

How to cite: Ornelas Agrela, A. F., Benito, M. B., and Lindholm, C.: Review of methods for characterization of active faults for seismic hazard purposes., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16439, https://doi.org/10.5194/egusphere-egu23-16439, 2023.

EGU23-17273 | Posters on site | TS3.4

Slowly deforming metropolitan France: what can GNSS tell about physical processes ? 

Marianne Metois, Axel Periollat, Stéphane Mazzotti, Frédéric Masson, Mathilde Vergnolle, Anne Socquet, Philippe Vernant, Alexis Rigo, Stéphane Baize, Jesús Piña-Valdés, and Juliette Grosset

Analysis of lithospheric deformation is key to understanding current tectonics and other active deformation processes. The Alceste project, conducted in the framework of the Résif Seismicity Transverse Action, aims at proposing an updated seismic hazard model in metropolitan France built from the most recent data and academic consensus. One of the contributions will come from geodetic observations through strain rate integration in seismotectonic zoning and seismic hazard models.

Most of Western Europe in general, and metropolitan France in particular, is located within the Eurasian Plate, which has very low deformation and seismicity rates. These GNSS-derived secular velocity field could be related to the combination of different deformation processes, with a minor contribution from plate tectonics (relative plate motions, mantle convection, etc), while most of the measured velocities could be explained by non-tectonic long-term or transient processes (gravitational motions, Glacial Isostatic Adjustment, erosion, anthropogenic deformation, etc). Some of these physical processes causing surface deformation also reflect stress changes at depth that may be associated with loading on active faults and seismicity. Properly mapping this deformation is therefore a key to better assess seismic hazard in slow straining areas.

In order (i) to assess the variability due to the diversity of the strain-rate calculation methods used in the scientific community and (ii) to test their capacity to resolve low-amplitude consistent surface deformation, we conduct a benchmark exercise. We build sets of synthetic velocity fields sampled at the existing GNSS permanent stations from the RENAG (REseau NAtional GNSS Permanent), RGP (Réseau GPS Permanent) and other permanent and non-permanent benchmarks. Our synthetic velocity fields have the same characteristics (noise, uncertainties) as the observed velocities in metropolitan France but they contain surface deformation signals from known physical processes (block rotations, fault elastic loading, large scale flexure, etc). We compare the strain rate invariants derived independently by nine different RENAG research teams (using different software) to the expected strain rate patterns and discuss drawbacks and advantages of each approach. In a second step, we analyzed the strain rate tensors derived from the synthetic velocity fields to discuss potential regional style of the deformation in metropolitan France. Previous studies have shown that the computation of strain rate tensors is impacted by the user-defined parameters and the algorithm specificity used. Exploring these different biases in the strain rate solutions represent the opportunity to improve the understanding of the conventional problem of the standard interpolation.

How to cite: Metois, M., Periollat, A., Mazzotti, S., Masson, F., Vergnolle, M., Socquet, A., Vernant, P., Rigo, A., Baize, S., Piña-Valdés, J., and Grosset, J.: Slowly deforming metropolitan France: what can GNSS tell about physical processes ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17273, https://doi.org/10.5194/egusphere-egu23-17273, 2023.

EGU23-1315 | ECS | Posters on site | TS3.6

Earthquake relocation at intermediate depths using automatically detected teleseismic depth phases 

Alice Blackwell, Timothy Craig, and Sebastian Rost

Intermediate-depth earthquakes, accommodating intra-slab deformation, typically occur within subduction zone settings at depths between 40-350 km. High magnitude events can pose a significant hazard to populations, and increase the risk of damaged infrastructure, injury and fatality. Despite improvements in recorded seismic data density and quality, the distribution and controls of these events remain poorly understood. Here, we demonstrate an automatic method for the detection of depth phases from these intermediate-depth earthquakes using seismic array data, with the aim of determining their hypocentral depths and locations to a greater level of accuracy. These will allow new comparisons and insights into the governing controls on the distribution of earthquakes in subducted slabs.

Depth phases (near-source surface reflections, e.g. pP and sP) are crucial for the accurate determination of earthquake source depth using global seismic data, however, they suffer from poor signal-to-noise ratios in the P-wave coda. This reduces the ability to systematically measure differential travel times to the corresponding direct arrival, particularly for the frequent lower-magnitude seismicity which highlights considerable seismogenic regions of the subducted slabs. To address this limitation, we have developed an automated approach to group globally distributed stations at teleseismic distances into sub-arrays, before optimising and applying phase-weighted beamforming techniques to each sub-array. Resultant vespagrams allow automated picking algorithms to determine differential arrival times between the depth phases (pP, sP) and their corresponding direct P arrival. These are subsequently used to invert for a new hypocentre location. We demonstrate this method by relocating intermediate-depth events associated with the Peruvian flat slab region of the subducting Nazca plate.

How to cite: Blackwell, A., Craig, T., and Rost, S.: Earthquake relocation at intermediate depths using automatically detected teleseismic depth phases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1315, https://doi.org/10.5194/egusphere-egu23-1315, 2023.

EGU23-2034 | ECS | Orals | TS3.6

A Re-examination of Temporal Variations in Intermediate-Depth Seismicity 

Sam Wimpenny, Tim Craig, and Savvas Marcou

Changes in the frequency of intermediate-depth (60–300 km) earthquakes in response to static stress transfer can provide insights into the mechanisms of earthquake generation within subducting slabs. In this presentation, we will demonstrate that global and regional earthquake catalogues from Japan and northern Chile show that both aftershock productivity, and the changes in the frequency of intermediate-depth earthquakes around the timing of major megathrust slip, support the view that faults within the slab are relatively insensitive to static stress transfer on the order of earthquake stress drops. We interpret these results to suggest the population of faults within the slab are much further from their failure stress than is typical for shallow faults, and that the mechanism that enables faults to rupture at the high confining pressures within slabs is likely to be spatially heterogeneous over length-scales of a few tens of kilometres. We suggest dehydration-related weakening mechanisms can best account for this heterogeneity.

How to cite: Wimpenny, S., Craig, T., and Marcou, S.: A Re-examination of Temporal Variations in Intermediate-Depth Seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2034, https://doi.org/10.5194/egusphere-egu23-2034, 2023.

Postseismic deformation following large megathrust earthquakes is widely observed with geodetic measurements and coastal geological investigations and contains important information on subduction zone rheology and megathrust slip behaviour. Short-term (a few years) horizontal deformation exhibits a consistent pattern common to almost all large megathrust earthquakes. For example, the coastal area moves consistently in the seaward direction, but the trench area moves in the landward direction. The horizontal deformation is readily explained by the effects of viscoelastic relaxation (VER) of earthquake-induced stress and afterslip. However, the vertical deformation exhibits greater complexity. For example, the sense of coastal deformation varies not only between different earthquakes but also along strike for the same earthquake. In this work, by separately modelling the VER and afterslip processes of synthetic and real subduction earthquakes, we show that the vertical motion can be explained in a simple manner in the same conceptual framework as for the horizontal motion, although the vertical motion is more sensitive to details of the rheological structure and afterslip. VER results in a long-wavelength, tri-segment deformation pattern consisting of near-trench uplift, midway subsidence, and near-arc uplift. The near-trench uplift and midway subsidence follow coseismic uplift and subsidence, respectively, and are both controlled by the viscosity of the sub-slab oceanic mantle. The near-arc uplift results from viscoelastic relaxation in the presence of a cold and elastic forearc mantle wedge corner (the cold nose) and is controlled by the viscosity of the hot part of the mantle wedge beneath the arc and back arc (Luo & Wang, 2021). In contrast to VER, each afterslip patch results in a local bi-modal pattern of uplift and subsidence dominated by elastic deformation, with variable wavelengths depending on the location and size of the afterslip. The complexity in postseismic vertical motion arises mainly from the heterogeneity and site-specific nature of afterslip (Luo & Wang, 2022). If observations are made near the rupture area, the observed vertical postseismic motion can be very complex, because the effects of heterogeneous afterslip around or within the rupture zone can obscure or conceal the pattern of near-trench uplift and midway subsidence due to VER. Farther away from the rupture area, the observed postseismic deformation mainly reflects the contribution of VER, and near-arc uplift appears to be ubiquitous. Separating the common VER process and the site-specific afterslip effect helps to constrain mantle rheology and illuminate fault slip behaviour. Our work also has strong implications for deciphering paleoseismic estimates of coastal motion associated with ancient earthquakes to understand coseismic vs. postseismic contribution.

References:

Luo, H., & Wang, K. (2021). Postseismic geodetic signature of cold forearc mantle in subduction zones. Nature Geoscience, 14(2), 104-109. https://doi.org/10.1038/s41561-020-00679-9

Luo, H., & Wang, K. (2022). Finding simplicity in the complexity of postseismic coastal uplift and subsidence following great subduction earthquakes. Journal of Geophysical Research: Solid Earth, 127(10), e2022JB024471. https://doi.org/10.1029/2022JB024471

How to cite: Luo, H. and Wang, K.: Complex postseismic vertical motion following megathrust earthquakes explained by simple mechanisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3007, https://doi.org/10.5194/egusphere-egu23-3007, 2023.

Slip observed within subduction zones falls within a broad range, with non-volcanic tremor (NVT), slow slip, repeating small earthquakes, to great earthquakes all contained within this spectrum.  The diversity of observed slip suggests diversity in fault zone conditions, which can be affected by a variety of factors, such as fluids, sediment inputs, upper plate structure, and topography on the subducting plate.  The role of subducting topography on seismicity appears to be regionally variable, with some bathymetric features leading to high slip during earthquakes, and others leading to plate creep and small earthquakes associated with upper plate deformation.  Seismicity characteristics in regions of subducting topography can be difficult to assess in many areas however, because traditional land-based seismic networks can easily miss offshore smaller earthquakes associated with this process. We use data from an amphibious seismic network deployed along the Cascadia subduction zone to examine seismic characteristics of thousands of newly detected and located earthquakes along the margin.  Over 5000 earthquakes in the catalog generally agree with asperity locations modeled from geodetic data and the 1700 M9 rupture, along with several clusters of upper plate earthquakes in areas of subducting topography.  Stress drop estimates, based on a spectral ratio technique, vary depending on earthquake location, with higher stress drop earthquakes occurring on the upper plate faults relative to the lower stress drop earthquakes occurring along the megathrust.  These variations may reflect important changes in fault conditions between upper plate splay faults and the megathrust.

How to cite: Bilek, S. and Morton, E.: Heterogeneous earthquake distributions and stress drop estimates along the Cascadia subduction megathrust and upper plate faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3600, https://doi.org/10.5194/egusphere-egu23-3600, 2023.

While intraslab events in subducting oceanic slabs have been widely studied, intraslab earthquakes in slabs of continent-oceanic transition zones, where lithospheric rheology differs, remain little understood. Here, we investigate the 2006 Pingtung (southwestern Taiwan) offshore intraslab earthquake doublet (Mw 7.0 and Mw 6.9), striking around the northern Manila subduction zone, where the highly thinned continental crust subducts. The two main shocks were at the depth of ~40 – 60 km, below the local MOHO, and ~8 minutes apart. The several source models that have been proposed vary, and do not consider all available observations. In this study, we incorporate comprehensive datasets, including teleseismic body waves, regional broadband, near-field strong motion waveforms, and high-rate GNSS, to propose a new source model, and further discuss source characteristics in the regional tectonic context. We first determine a reliable near-field velocity model and the frequency ranges for waveform inversions by path calibration based on inverting a nearby Mw 5.6 aftershock. We then constrain the multiple point sources (MPS) solutions for both events. The location and fault planes from MPS are used to resolve slip distributions by finite fault inversions. We finally validate this slip model by the static coseismic displacement observed by the dense, near-field campaign GNSS and precise leveling. Our results show that the Mw 7.0 normal event ruptured a west-dipping fault at the depth of ~40 km, characterized by at least two major asperities. This rupture was followed by the deeper Mw 6.9 strike-slip event, located ~40 km to the north. The earthquake sequence was located around a failed rift indicated by seismic tomography and likely represented a reactivation of the faults formed in the mantle lithosphere during the continental rifting in the northern South China Sea margin. The doublet’s complex mechanisms could be explained by stress fields imposed by the subducting transitional crust.

How to cite: Hu, W.-L., Wei, S., Feng, L., Hsiao, S.-H., Ching, K.-E., and Hu, J.-C.: The 2006 Pingtung intraslab earthquake doublet offshore southwestern Taiwan: Complex normal and strike-slip faulting in the northern Manila subduction zone where the continent-oceanic transitional slab subducts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4603, https://doi.org/10.5194/egusphere-egu23-4603, 2023.

EGU23-4944 | Orals | TS3.6

Earthquakes illuminate the incipient collision and subduction of Loyalty Ridge at Vanuatu subduction zone 

Luigi Passarelli, Simone Cesca, Nima Nooshiri, and Sigurjón Jónsson

Bathymetric highs resist subduction producing large- to small-scale change in the morphology of the subduction zone: Increase of the outer-rise curvature, trench indentation and large-scale slides and slumps in the fore-arc region. At the plate interface, bathymetric highs induce geometrical and frictional changes that can produce increase or decrease of the local coupling, and thus having an effect on the likelihood of occurrence of large megathrust earthquakes. Numerical models predict complex strain and stress patterns arising from subduction of such relief mainly driven by the size and relative geometry of trench and subducted high. However, the collision and subduction of bathymetric highs is investigated mainly via geophysical and geological surveys since seismic sequences have rarely illuminated the subduction of seafloor relief. Here, we report of a year-long and very energetic earthquake activity (10 Mw 6.5-7.5) at the Loyalty Ridge – Vanuatu trench at both the plate interface and in the outer-rise region. The spatio-temporal and magnitude of the earthquakes revealed complex release of the accrued flexural strain along the outer-rise and a pronounced segmentation of the interface with repeating M7 earthquakes, low aftershock activity and a large “aseismic” zone. The collision and subduction of the Loyalty Ridge along the Vanuatu trench seem to indicate a frictionally segmented interface where large megathrust earthquakes are unlikely to occur.

How to cite: Passarelli, L., Cesca, S., Nooshiri, N., and Jónsson, S.: Earthquakes illuminate the incipient collision and subduction of Loyalty Ridge at Vanuatu subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4944, https://doi.org/10.5194/egusphere-egu23-4944, 2023.

EGU23-4981 | ECS | Orals | TS3.6

Seamount subduction and megathrust seismicity: the interplay between geometry and friction. 

Irene Menichelli, Fabio Corbi, Silvia Brizzi, Elenora van Rijsingen, Francesca Funiciello, and Serge Lallemand

It has been widely recognized that the presence of seamounts can profoundly affect megathrust seismicity. With their outstanding topography, seamounts can tune interplate stress and favor the development of a fracture network in the overriding plate. Subducting seamounts can also control fluid accumulation and sediment porosity. However, their role as barriers or triggers for rupture propagation remains a matter of debate.

In this work, we used analog models to study how geometric and frictional heterogeneities associated with a single subducting seamount influence the seismogenic behavior of the megathrust. We used four different model configurations (i.e., a flat interface, a high-friction and low-friction seamount, and a low-friction patch) to investigate both the combined and individual effect of geometry and friction.

Our results show that low friction areas, either flat or with a seamount relief, reduce interplate coupling. Also the presence of a geometric feature tends to decrease seismic coupling and segment ruptures promoting earthquakes enucleation on the flat region. The maximum barrier efficiency is achieved with the low-friction patch model, where the accumulated stress is preferentially released by the occurrence of small earthquakes. This behavior is well suited to natural cases where seamounts are supposed to lower interplate friction due to fluid release or by the development of fracture systems development, causing microseismicity and slow slip events.

How to cite: Menichelli, I., Corbi, F., Brizzi, S., van Rijsingen, E., Funiciello, F., and Lallemand, S.: Seamount subduction and megathrust seismicity: the interplay between geometry and friction., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4981, https://doi.org/10.5194/egusphere-egu23-4981, 2023.

EGU23-5748 | ECS | Orals | TS3.6

Evidence of water transport in the Earth’s mantle from an Undetected Seismic Phase in Waveforms from Southern Tyrrhenian (Italy) intermediate-depth and Deep Earthquakes 

Teresa Ninivaggi, Giulio Selvaggi, Salvatore Mazza, Marilena Filippucci, Fabrizio Tursi, and Wojciech Czuba

We found a previously unreported later seismic phase from intermediate-depth and deep earthquakes of the Southern Tyrrhenian subduction zone recorded by European seismic stations. Later phases are useful to constrain local-scale discontinuities, especially in subduction zones, but their observation is infrequent, since it depends on seismic stations distribution and slab geometry. Their detection, therefore, is a great opportunity to improve our knowledge of subduction systems and Earth’s interior. They also represent a powerful mean to retrieve the chemical composition of such deep structures. 

We analysed thousands of waveforms of the strongest earthquakes occurred in the Southern Tyrrhenian subduction system and recorded by European seismic stations from 1990 to 2020. 

The unknown seismic phase is visible at stations from 6 to 9 degrees from the epicentre, towards the north. Only earthquakes located in a well-defined region of the slab, in the depth range of 215–320 km, generate this secondary phase. We built a direct 2D P-velocity model of the Tyrrhenian slab to reproduce observed travel times and ray paths of direct and later phases. We interpret the later phase as a compressional (P) wave that propagates downward in a narrow, high P-wave velocity layer within the deepest part of the subducting slab. We proprose that the high P-wave velocity layer in the subducting slab could be related to the presence of the dense hydrous magnesium silicate phase A, which is probably the main (meta) stable hydrous phase in the upper-mantle deep slab. Our findings provide further insights on the Southern Tyrrhenian slab structure and have also relevant implications on water transport in the Earth’s mantle and slab petrology.

How to cite: Ninivaggi, T., Selvaggi, G., Mazza, S., Filippucci, M., Tursi, F., and Czuba, W.: Evidence of water transport in the Earth’s mantle from an Undetected Seismic Phase in Waveforms from Southern Tyrrhenian (Italy) intermediate-depth and Deep Earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5748, https://doi.org/10.5194/egusphere-egu23-5748, 2023.

EGU23-6214 | Posters on site | TS3.6

The role of sediments in the mechanics of the subduction plate interface – Chugach accretionary prism Alaska 

Ismay Vénice Akker, Whitney M. Behr, Luiz F.G. Morales, and Zoe Braden

The subduction interface is a shear zone that defines the boundary between two convergent tectonic plates, the subducting slab and its overriding upper plate. The rheological and seismic behavior of the plate interface is a function of interacting physicochemical processes such as metamorphic grade and mineral dehydration reactions. Here we study the role of initial oceanic crustal composition in controlling these low-grade (prehnite-pumpellyite facies) conditions, and investigating the potential links between composition, deformational styles and modes of fault slip along subduction megathrusts. Our study area is located on the Kenai Peninsula in southern Alaska where the Jurassic-Cretaceous Chugach accretionary complex is preserved. This complex comprises underplated slices of basaltic oceanic crust and sedimentary material. We compare two field sites at similar metamorphic temperatures that each represent an interface shear zone: a basalt dominated section and a sediment-rich section. Raman spectroscopy to determine graphite crystallinity and deformation temperatures, combined with detrital zircon dating (U-Pb) are examined as function of structural depth and provide constraints on the metamorphic conditions and timing of underplating, and the peak temperature reached in underplated slices. Observations from field work and drone imaging shows that the sediment-rich interface shear zone includes a chert-argillite mélange zone of up to 15-m thick. Within this mélange, greywacke blocks occur and are surrounded by brittle-deformed and heavily veined basalt and/or greywacke slabs. The basalt dominated section includes several localized duplex faults. The fault planes are much narrower fault surfaces (< 5 cm thicknesses) and are decorated by highly orientated laths of chlorite. Microstructural observations will allow us to decipher the microphysical deformation mechanisms. Comparing the deformation structures and mechanisms at these two sites provides new insights into the compositional control on the rheology of the subduction interface.

How to cite: Akker, I. V., Behr, W. M., Morales, L. F. G., and Braden, Z.: The role of sediments in the mechanics of the subduction plate interface – Chugach accretionary prism Alaska, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6214, https://doi.org/10.5194/egusphere-egu23-6214, 2023.

EGU23-6754 | Posters on site | TS3.6

Historical activity of an onshore subduction thrust and related geomorphic changes, northeastern Nankai subduction zone 

Tatsuya Ishiyama, Toshimichi Nakanishi, Daisuke Hirouchi, Nobuhisa Matsuta, Naoko Kato, and Hiroshi Sato

We show new geomorphic and geologic evidence for historical activity of the onshore deformation front of the Nankai subduction zone, constrained by Holocene tectonic geomorphology, high-resolution borehole stratigraphy, and seismic reflection profile.  Borehole transect across a newly recognized late Holocene fold scarp contains middle to late Holocene fluvial sedimentary units. Structures of these units correlated based on sedimentary facies, diatom assemblages and radiocarbon dating illuminates that around 12-15th century to middle Holocene units are repeatedly folded and cut by a shallowly dipping thrust fault, suggesting multiple seismic events.  In addition, a new high-resolution seismic reflection profile suggests that these structures are associated with west-dipping imbricate thrust faults comprising a deformation front of the onshore subduction zone. This historical fault activity is also consistent with land use changes linked with pre- and post-earthquake flood events revealed by geographic analysis on early-modern maps drawn in early to middle 19th century and contemporaneous documents.  These multidisciplinary observations suggest that the onshore deformation front activated during the AD 1854 Ansei Tokai megathrust earthquake (M8.4),  the most recent historical event,  comprising the northern end of the ruptured area. 

How to cite: Ishiyama, T., Nakanishi, T., Hirouchi, D., Matsuta, N., Kato, N., and Sato, H.: Historical activity of an onshore subduction thrust and related geomorphic changes, northeastern Nankai subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6754, https://doi.org/10.5194/egusphere-egu23-6754, 2023.

EGU23-7253 | ECS | Posters on site | TS3.6

Probabilistic estimation of postseismic relaxation parameters and processes following the 2011 Tohoku earthquake 

Celine Marsman, Femke Vossepoel, Ylona van Dinther, Mario D'Acquisto, and Rob Govers

Geodetic observations of 3-component surface motions following a megathrust earthquake are key to a better understanding of features and processes controlling the dynamics at subduction margins. The relative contributions of dominant drivers during the postseismic phase, such as viscoelastic relaxation, afterslip, and relocking, remain difficult to estimate individually and are often derived at the end of an observation period, without showing the temporal evolution of the processes. Data assimilation combines physical models with observations, and can be a way to constrain these contributions by estimation of model parameters, the associated uncertainties, and identifying parameter tradeoffs. We use Bayesian inference in the form of an ensemble smoother to estimate geodynamic parameters during the postseismic phase of the megathrust earthquake cycle. The ensemble smoother uses a Monte Carlo approach to represent the probability density distribution (pdf) of model states with a finite number of realizations. Prior estimates of the imperfect physical model are combined with the likelihood of noisy observations to estimate the posterior pdf of model parameters. We first discuss a synthetic data experiment where observations are sampled from a 3D earthquake cycle model and where we added variable levels of noise. We assimilate 3-component surface displacements into a 2D finite element viscoelastic earthquake cycle model. We incorporate an a priori heterogeneous temperature field to estimate the asthenospheric viscosity distribution through power-law parameters (e.g., stress power). Preliminary results show that model parameters, such as the extent of the cold nose, maximum depth of afterslip, and power-law parameters can be recovered remarkably well by assimilating synthetic on- and offshore surface observations. We show preliminary results of data assimilation of postseismic surface displacements following the 2011 Tohoku earthquake.

How to cite: Marsman, C., Vossepoel, F., van Dinther, Y., D'Acquisto, M., and Govers, R.: Probabilistic estimation of postseismic relaxation parameters and processes following the 2011 Tohoku earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7253, https://doi.org/10.5194/egusphere-egu23-7253, 2023.

EGU23-8028 | ECS | Orals | TS3.6

Megathrust stress drop as trigger of aftershock seismicity in subduction zone forearcs: Insights from the 2011 Mw 9.0 Tohoku earthquake, Japan 

Armin DIelforder, Gian Maria Bocchini, Kilian Kemna, Andrea Hampel, Rebecca Harrington, and Onno Oncken

Large megathrust earthquakes like the 2011 Mw 9.0 Tohoku earthquake (Japan) are followed by numerous aftershocks in the subduction zone forearc overlying the seismogenic fault. The aftershocks in the forearc can include normal-faulting events despite the thrust mechanism of the main shock. Postseismic normal faulting has been explained by stress changes induced by the coseismic stress drop along the megathrust. However, details of stress changes in the forearc and aftershock triggering mechanisms remain poorly constrained. Here we use numerical force-balance models combined with Coulomb failure analysis to show that the megathrust stress drop indeed supports normal faulting, but that forearc-wide triggering of aftershocks is feasible within a narrow range of megathrust stress-drop values and forearc stress states only. We determine this range for the Tohoku earthquake and show that the associated stress changes explain the aftershock seismicity in unprecedented detail. In particular, our analysis reveals that ~78% of the aftershocks and ~92% of the seismic moment release occurred in areas where the Tohoku earthquake caused a stress increase, and that the detailed aftershock distribution was also governed by spatial variability in fault strength and forearc topography. Our findings provide new insights into aftershock triggering and help to understand where aftershocks occur after great earthquakes at subduction zones.

How to cite: DIelforder, A., Bocchini, G. M., Kemna, K., Hampel, A., Harrington, R., and Oncken, O.: Megathrust stress drop as trigger of aftershock seismicity in subduction zone forearcs: Insights from the 2011 Mw 9.0 Tohoku earthquake, Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8028, https://doi.org/10.5194/egusphere-egu23-8028, 2023.

EGU23-8201 | ECS | Orals | TS3.6

Does transient pore-pressure diffusion drive upper-plate aftershocks following megathrust earthquakes? 

Carlos Peña, Oliver Heidbach, Bernd Schurr, Sabrina Metzger, Marcos Moreno, Onno Oncken, and Claudio Faccenna

Aftershocks are a time-dependent (exponential decay) phenomenon in the aftermath of large earthquakes. In subduction zones, those occurring in the upper plate are of special concern given their potential seismic hazard, as they may produce substantial surface shaking close to highly populated cities. Therefore, the understanding of the mechanisms that drive upper-plate aftershocks is of utmost importance to improving seismic hazard assessment. Transfer of static coseismic stresses has been commonly proposed to explain this; however, they fail to explain their exponential decay over time. This time-dependency is observed in postseismic geodetic measurements, suggesting that the processes that control the postseismic surface deformation also govern or at least are involved in the generation of upper-plate aftershocks. Here, the postseismic surface deformation is dominated by aseismic slip along the fault interface (afterslip), non-linear viscoelastic relaxation in the lower crust and upper mantle, and pore-pressure diffusion in the crust. Despite great research efforts, however, the key driver remains elusive.

In this study, we investigate which postseismic mechanism mainly controls the occurrence of aftershocks in the upper plate in subduction zones using the 2014 Mw=8.1 Iquique earthquake, northern Chile, as a study case. We employ a 4D numerical forward model to simulate the transient poroelastic and non-linear viscoelastic relaxation, whose contributions are subtracted from the cumulative Global Navigation Satellite System (GNSS) measurements to then invert for afterslip. Using realistic rock material properties, we first show that this approach explains the surface displacements during the first nine months of postseismic deformation recorded by continuous GNSS. For the same period, we then compute the spatiotemporal Coulomb Failure Stress changes (ΔCFS) that result from individual postseismic processes and compare them with the upper-plate aftershocks using a high-resolution seismicity catalog and focal mechanisms. We show for the first time that the ΔCFS produced by pore-pressure diffusion induced by the mainshock are unambiguously better correlated in space and time with the increase in upper-plate aftershocks than those from afterslip or non-linear viscous relaxation. In addition, pore-pressure diffusion lowers the effective normal stress of the stress tensor more effectively, while its resulting ΔCFS are relatively independent of the fault orientation. The latter would also explain the diversity of faulting styles in the upper plate exhibited by focal mechanisms following the 2014 Iquique earthquake and other subduction zone earthquakes. Our findings provide new insights into the link between pore-pressure diffusion and upper-plate deformation in subduction zones with implications for time-dependent seismic hazard.

How to cite: Peña, C., Heidbach, O., Schurr, B., Metzger, S., Moreno, M., Oncken, O., and Faccenna, C.: Does transient pore-pressure diffusion drive upper-plate aftershocks following megathrust earthquakes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8201, https://doi.org/10.5194/egusphere-egu23-8201, 2023.

EGU23-9869 | ECS | Orals | TS3.6

Slab segmentation of the Nazca plate across the Juan Fernández Ridge 

Nipaporn Nakrong, Marnie Forster, Hielke Jelsma, Wim Spakman, and Gordon Lister

We report preliminary results based on the construction of a new 3D model for the geometry of the subducted lithosphere of the Nazca Plate. This new 3D model differs from Slab2 in that it enables capture of the slab geometry in greater detail and allows the identification of previously unrecognised potential slab tears, both down-dip and along strike, as well as slab gaping as tears open. These differences in the inferred 3D structure emerge because previous models were excessively smoothed. Here we use the interpolation of line strings derived from the interpretation of individual cross-sections: a method that has the capacity to capture detail, and to accurately drape and thus derive a 3D geometry consistent with the observed hypocenter patterns, by using Delaunay triangulation alongside with 3D grid interpolation. The 3D slab morphology obtained provides insight into the interplay between subduction earthquakes at different depths. The variation in slab morphology reinforces the concept that the megathrust comprises distinct rupture segments that behave differently in terms of their overall seismotectonic behaviour. The slab morphology also links to changes in the broad geodynamics of the subduction zone, with links between shallow, intermediate, and deep seismicity that are consistent with variation in 3D slab morphology. It is also possible to explain the variation in surficial crustal tectonic processes in the context of geodynamic processes inferred to be taking place at depth in specific segments of the descending slab.

Surficial structures in the form of megathrust ruptures can be seen to be both a consequence of the highly segmented nature of the overriding plate, particularly in the Peruvian Andes, as well as the deeper variation in 3D slab morphology. For example, the inferred slab tears at the northern (Puna) edge and the southern (Payenia) edge of the Pampean segment may be explained as due to significant variation of the slab morphology and are reflected in changes in the characteristics of earthquake ruptures, and different tectonic modes in the supra-subduction zone lithosphere. Lineaments that separate the segments of the frontal megathrust also coincide with inherited surface fault systems on the South American plate. Clusters of intermediate extensional earthquakes weaken the lithosphere south of the Taltal Ridge (TR) and north of the Juan Fernandez Ridge (JFR). These structures mark the edge of the magmatically inactive plate interface due to the termination of magmatism in shallow dipping slab segments associated with the JFR, or in the flat slab of the Pampean segment.

How to cite: Nakrong, N., Forster, M., Jelsma, H., Spakman, W., and Lister, G.: Slab segmentation of the Nazca plate across the Juan Fernández Ridge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9869, https://doi.org/10.5194/egusphere-egu23-9869, 2023.

Postseismic deformation following subduction earthquakes includes the combined effects of afterslip surrounding the coseismic rupture areas and viscoelastic relaxation in the asthenosphere and provides unique and valuable information for understanding the rheological structure. Because the two postseismic mechanisms are usually spatiotemporally intertwined, we developed an integrated model combining their contributions, based on 5 years of observations following the 2016 Pedernales (Ecuador) earthquake. The results show that the early, near-field postseismic deformation is dominated by afterslip, both updip and downdip of the coseismic rupture, and requires heterogeneous interface frictional properties. Viscoelastic relaxation contributes more to far-field displacements at later time periods. The best-fit integrated model favors a 45-km thick lithosphere overlying a Burgers body viscoelastic asthenosphere with a Maxwell viscosity of 3 × 1019 Pa s (0.9 - 5 × 1019 Pa s at 95% confidence), assuming the Kelvin viscosity equal to 10% of that value. In addition to the postseismic afterslip, the coastal displacements of sites north and south of the rupture clearly require extra slip in the plate motion direction due to slow slip events that may be triggered by the coseismic stress changes (CSC), but are not purely driven by the CSC. Spatially variable afterslip following the Pedernales event, combined with the SSEs during the interseismic period, demonstrate that spatial frictional variability persists throughout the whole earthquake cycle. The interaction of adjacent fault patches with heterogeneous properties may contribute to the clustered large earthquakes in this area.

How to cite: tian, Z., Freymueller, J., Yang, Z., Li, Z., and Sun, H.: Frictional properties and rheological structure at the Ecuadorian subduction zone revealed by the postseismic deformation due to the 2016 Mw 7.8 Pedernales (Ecuador) earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10957, https://doi.org/10.5194/egusphere-egu23-10957, 2023.

EGU23-11030 | Posters on site | TS3.6

A near-vertical slab tear in southeastern Solomon Islands 

Ching-Yu Cheng, Chin-Shang Ku, Yu-Ting Kuo, Hao Kuo-Chen, Bor-Shouh Huang, and Yue-Gau Chen

Mw 6.3 and 6.0 earthquakes occurred on January 27 and 29 in 2020 in the southeastern Solomon Islands which is one of the most seismically active areas in the southern Pacific. To investigate the seismogenic mechanism and structure of the southeastern Solomon Islands, we locate the foreshocks-main-shock-aftershocks sequence of two moderate earthquakes recorded by the regional seismic network. In this study, we establish the new database and locate earthquakes for analyzing the seismogenic structures and deriving the new regional 1D velocity model. Based on the special distribution of the foreshock-aftershock sequence, the interaction of subduction and transform zones between the Pacific and the Australia Plates leads to the near-vertical dip-slip tear structure in the southeastern Solomon Islands. Confirmed with PREM and the new 1D velocity model for testing the robustness of the earthquake locations, the seismic gap at depths from 25 to 35 km is observed as the “jelly sandwich” rheology. In addition, seismic events with large-amplitude, high-frequency signals could be observed in the fore-arc area is due to waves that guided by the subducted Australia plate. In order to improve the capability of earthquake detection, we generate templates from foreshocks-aftershocks sequence to detect repeating or near-repeating seismicity. Our study provides unprecedented seismic data and velocity model for the study area that could benefit understanding detailed structure beneath the region and promoting the initial reference model for locating earthquakes and seismic tomography.

How to cite: Cheng, C.-Y., Ku, C.-S., Kuo, Y.-T., Kuo-Chen, H., Huang, B.-S., and Chen, Y.-G.: A near-vertical slab tear in southeastern Solomon Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11030, https://doi.org/10.5194/egusphere-egu23-11030, 2023.

EGU23-174 | ECS | Posters on site | TS3.7

A new velocity field for El Salvador derived from combined InSAR and GNSS data 

Juan Portela, Ian J. Hamling, Alejandra Staller, Marta Béjar-Pizarro, Douglas Hernández, Cecilia Polío López, and Manuel Díaz

The country of El Salvador lies on an active tectonic margin, where the Cocos plate is subducting under the Caribbean plate. A crustal fault system, the El Salvador Fault Zone (ESFZ), crosses the country from East to West through the Central American Volcanic Arc, accommodating more than 1 cm/yr of differential deformation between the Chortís block and the volcanic forearc sliver. 

Here we use GNSS and interferometric synthetic aperture radar (InSAR) data to measure interseismic ground deformation across ESFZ. We have processed and updated GNSS data in more than 110 continuous and episodic stations in the region. GNSS results have been useful for determining the broad pattern of the tectonic signal in the area. However, they are scarce and unable to characterise complex behaviour in the intra-fault basins.

SAR data acquired by the ALOS PALSAR L-band satellite (2006-2011), for both the ascending and descending tracks covering El Salvador, were used to form interferograms with a Small Baseline (SBAS) approach. The time series and average velocity were computed. The average coherence obtained for the area is overall good, and the results are coherent with the regional tectonics. 

How to cite: Portela, J., Hamling, I. J., Staller, A., Béjar-Pizarro, M., Hernández, D., Polío López, C., and Díaz, M.: A new velocity field for El Salvador derived from combined InSAR and GNSS data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-174, https://doi.org/10.5194/egusphere-egu23-174, 2023.

EGU23-552 | ECS | Posters on site | TS3.7

Long-term Earthquake Cycle along the eastern Altyn Tagh Fault, China 

Nicolás Pinzon Matapi, Yann Klinger, Xiwei Xu, Jing Liu, and Paul Tapponnier

Identifying earthquake recurrence times and slip distributions over the span of many seismic cycles is key to understand fault-rupture processes and to better assess the seismic hazard. In this study, we used three paleoseismological excavations along the Aksai segment of the Altyn Tagh Fault (ATF) to document preserved evidence of past earthquakes in the sedimentological record such as vertical offset, fault cracks, and folding. We integrated these findings with previous studies on the Annanba and Xorxoli segments in order to build a larger-scale rupture history of the ATF. We reported nine large paleo-earthquakes and three of these with ground rupture expression along the whole three segments (∼ 400 km). Based on a Bayesian approach we present 95-percentile range ages of 6149 – 5285 BC, 5296 – 4563 BC, 3026 – 2677, 2469 - 2254 BC, 2069 - 1964 BC, 1184 – 709 BC, 270 – 635 AD, 875 – 1325 AD and 1491 - 1741. Furthermore, we used high-resolution satellite imagery to measure horizontal offsets recorded in the morphology, which are associated with potential co-seismic deformation. We find that the mean recurrence time is 1171±425yr with a COV of ∼0.31 suggesting a quasi-periodic behavior with a characteristic slip motion based on the similar distribution of fault offsets. The last event seems to be strongly expressed in Xorxoli segment and also found along the Aksai segment, although we could not identify it along the Annanba bend. Whereas, the penultimate event and the two before this appear to well correlate across the Aksai, Annanba and Xorxoli segments. Thus, being strong candidates for the three largest and successive earthquakes along the ATF (roughly rupture longitude ≥ 350 km). Variations in the COVs along the eastern Altyn Tagh Fault accounts for the important control of local structural complexity and/or slip rate variations on the rupture behavior of major fault systems.

How to cite: Pinzon Matapi, N., Klinger, Y., Xu, X., Liu, J., and Tapponnier, P.: Long-term Earthquake Cycle along the eastern Altyn Tagh Fault, China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-552, https://doi.org/10.5194/egusphere-egu23-552, 2023.

EGU23-1195 | Posters virtual | TS3.7

Irregular recurrence of surface-faulting paleoearthquakes along the Gowk fault, southeast Iran 

Mohammad Foroutan, Bertrand Meyer, Michel Sébrier, Andrew Murray, Mohammad-Ali Shokri, Shahryar Solaymani Azad, Hamid Nazari, Faezeh Azhandeh, Ailar Sajedi Far, and Mojtaba Bassiri

While long-averaged recurrence times of large earthquakes are documented on many slow-slipping fault zones in intracontinental settings, the variability of the return periods through multiple seismic cycles remains poorly known. Paleoseismic investigations across fault zones with the well-documented instrumental sequence of surface-breaking earthquakes are a way to tackle the problem. In this context, the Gowk fault, a 160-km-long dextral fault in central Iran, that experienced four surface-rupturing earthquakes with magnitudes ranging from Mw 5.8 to 7.0 during a 1981-1998 earthquake sequence offers a case study. The four earthquakes have ruptured a 90-km-stretch of the fault. The most recent one, the 14 March 1998 Fandoqa earthquake of Mw 6.6, produced a 23-km-long surface rupture along the northern part of the Gowk fault with a maximum right-lateral displacement of 3 m. With a Holocene slip-rate between 3.8-5.7 mm yr-1 and several recent seismic events testifying to its high level of seismicity, the Gowk fault is an appropriate target to conduct paleoseismic investigations and address the earthquake behavior of slow-slipping faults activated by a sequence of well-documented instrumental earthquakes. We excavated two neighboring trenches across the 1998 fault breaks and identified at least four Holocene event horizons that preceded the 1981-1998 earthquake sequence. The age of the faulted stratigraphic sequence is constrained by eighteen optically stimulated luminescence samples and one radiocarbon age on charcoal. The ages of the event horizons suggest an irregular seismic behavior of the Gowk fault characterized by significant variability in the return period of surface rupturing earthquakes.

How to cite: Foroutan, M., Meyer, B., Sébrier, M., Murray, A., Shokri, M.-A., Solaymani Azad, S., Nazari, H., Azhandeh, F., Sajedi Far, A., and Bassiri, M.: Irregular recurrence of surface-faulting paleoearthquakes along the Gowk fault, southeast Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1195, https://doi.org/10.5194/egusphere-egu23-1195, 2023.

EGU23-2262 | Orals | TS3.7

Deformation-dependent aftershocks in laboratory earthquakes sequences 

Axelle Amon, Ambroise Mathey, David Marsan, Jerome Weiss, and Jerome Crassous

We study an experimental model of a fault consisting in a stationary shear band in a compressed granular sample. To obtain those bands, we perform a biaxial compression of a granular sample constituted of glass beads during which we observe the spontaneous formation of shear planes along the Mohr-Coulomb directions in the sample. We study the post-failure regime during which all the deformation occurs along the stationary shear bands. Using an interferometric method of measurement of micro-deformations based on multiple scattering, we obtain full-field measurements of the local incremental deformation in the sample. The deformation measured are typically of $10^{-5}$ with a resolution of about 300 microns (3 bead diameters). Our technics gives access to the strain fluctuations inside the shear band and we show that the macroscopic mean deformation in the bands is the result of the accumulation of local, intermittent, shear events. The size distribution of those shear events follows the Gutenberg-Richter law. We observe clustering of those events following Omori's law and we apply a declustering method to reveal the causal structure underlying our sequences of events (Houdoux et al. 2021). 

In my talk, I will focus on recent experimental results regarding the dependence of the series statistics on the driving velocity. We have studied sequences of aftershocks for different compression velocities and we have shown that surprinsingly the aftershock sequences we observe are deformation-dependent and not time-dependent. We discuss such a deformation memory effect in the framework of an Olami-Feder-Christensen model.

Houdoux et al. Commun Earth Environ 2, 90 (2021)

How to cite: Amon, A., Mathey, A., Marsan, D., Weiss, J., and Crassous, J.: Deformation-dependent aftershocks in laboratory earthquakes sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2262, https://doi.org/10.5194/egusphere-egu23-2262, 2023.

EGU23-3813 | ECS | Orals | TS3.7

Automated workflow to compute earthquake chronologies on faults from paleoseismic datasets 

Octavi Gómez-Novell, Bruno Pace, and Francesco Visini

A major challenge in seismic hazard research is to quantify the frequency of large earthquakes along active faults, more so when the observational time windows of seismic catalogs are much shorter than the average fault recurrence intervals. In this respect, paleoseismology continues to prove to be an excellent tool to extend the seismic catalogs of faults into prehistorical times. The combination of the ever more advanced trenching surveys and accurate numerical dating techniques allows constraining the timing of paleoearthquakes and, for some datasets, approximating their recurrence models. Despite this, paleoseismic data carries along large uncertainties frequently related to dating technique limitations, poor stratigraphic preservation, and along-strike slip variability that hinder the identification of a complete paleoearthquake record. Subsequently, these issues, among others, challenge the constraint of reliable earthquake chronologies along faults and of the parameters defining their earthquake cycle.

We present an automatic workflow capable to compute and constrain earthquake chronologies along a fault based on the correlation of its available paleoseismic records, including multi-site and poorly constrained datasets. Our inherent premise is that the correlation of paleoseismic data from multiple along-fault locations can help to improve the time constraints and completeness of its paleoearthquake record. Given that paleoseismic records are, by definition, underpopulated, event correlation is not restricted to single occurrences. Instead, an event in a site might be simultaneously correlated with more than one in another if time compatible. Furthermore, to avoid subjectivity biases in event timing estimates and correlation, we exclusively rely on the trench numerical dates limiting each event horizon as the inputs. All earthquake chronologies are modelled probabilistically with a four-step algorithm as we detail. First, all earthquake times in each site are computed as probability density functions (PDFs) using the input numerical dates. The event PDFs from all sites are then integrated to derive a mean curve representing the overall event probabilities for the studied fault in the time span investigated. The probability peaks in this curve, which are assumed as indicative of the event timing at the fault scale, are automatically detected based on peak prominence analysis. A final PDF is then computed for each peak by multiplying all site event PDFs intersecting the peak position. The set of product PDFs constitutes the earthquake chronology of the fault, provided to the user in simple output files that can be externally used to calculate fault parameters for the seismic hazard assessment, and to visualize the modelling.

Preliminary tests on several paleoseismic datasets of the Central Apennines (Italy), the Eastern Betics (Spain), the Dead Sea Fault and the Wasatch Fault (US), have provided good outcomes. The approach significantly reduces the uncertainties in event timing of paleoearthquakes and provides an objective and reliable interpretation of the datasets, especially when these are complex or have wide uncertainties. By extension, the workflow has the potential to reduce the uncertainties in earthquake recurrence estimates and can give insight on the recurrence models that better describe the earthquake cycle in the studied faults.

How to cite: Gómez-Novell, O., Pace, B., and Visini, F.: Automated workflow to compute earthquake chronologies on faults from paleoseismic datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3813, https://doi.org/10.5194/egusphere-egu23-3813, 2023.

High-resolution geodetic measurements of the accumulated strains along active faults are important for faulting dynamics studies and seismic hazard evaluation. InSAR has been widely applied to measure the interseismic strain along active strike-slip faults. However, phase unwrapping errors, tropospheric delays, along with over-smooth effects in calculating the strain from velocity limit its capability of mapping the highly localized strain along faults. Phase-gradient stacking that sums up the wrapped phase differences of adjacent pixels has been successfully applied to reveal localized deformation across coseismic fractures and slow-moving landslides, yet lacks application to reveal interseismic strain along faults. Here, we conduct phase-gradient stacking on Sentinel-1 SAR interferograms, for the first time, to map the interseismic strain along the North Anatolian Fault with unprecedented resolution. We reveal several segments with extremely high strain rates attributed to shallow creep of the fault. By comparing with historical earthquake ruptures, we find that the creeps are either related to afterslip of recent earthquakes, or related to slip deficits of earthquakes occurred decades ago, challenging the opinion that the NAF has a uniform surface strain rate, particularly along its eastern portion. Our results show that the phase-gradient stacking can not only reduce the computation burden from phase unwrapping and tropospheric correction, but also achieve a much higher spatial resolution strain map than the traditional InSAR method. The proposed method can be applied to other large strikes-slip faults for distinguishing segments with surface creep and strong coupling and therefore better quantify the shallow strain budget and its associated hazards.

How to cite: Liu, Z. and Wang, T.: High-resolution Interseismic Strain Mapping from InSAR Phase-Gradient Stacking: Application to the North Anatolian Fault with Implications to the Non-uniform Strain Distribution Related to Historical Earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3915, https://doi.org/10.5194/egusphere-egu23-3915, 2023.

The propagation of the 2021 Mw7.4 Madoi earthquake rupture from the central Jiangcuo fault (JCF) onto the eastern portion exhibits the most complex geometry with a series of conjugate faults, bends, and stepovers. At the east ~50 km of the 2021 epicenter, the surface rupture along the Jiangcuo eastern branch (JCEB) deviating ~12° anticlockwise from the general strike provides a valuable chance for understanding the particularly complex surface ruptures propagation and the branching behavior of the poorly known JCEB. Using sub-metric orthophotos collected by UAV with a ground resolution of 6 cm, complemented by multiple field investigations, we implemented the surface rupture mapping and coseismic slip distribution of the JCEB in detail associated with this earthquake sequence. Our mapping illuminated the sporadic breaks of the tectonic region in the dune area immediately near the branching point and eastward propagated linear rupture trace. The measurements of the high-resolution coseismic slip along the JCEB show that the slip distribution reveals an approximate dogtail shape to the eastern termination with the maximum left-lateral strike-slip offset of 2.9 m. These data might support the perspective that the rupture propagated with a supershear velocity toward the east. Combined with the accrued displacements along the JCEB, these results indicate that the poorly known divergent branch could accumulate pre-2021 surface breaks as an immature fault and bifurcated in the Madoi quake due to the matched regional stress field. We found linear surface breaks along the NW-strike geologic faults indicating triggered coseismic slip on conjugate faults. In the meantime, the intersections with conjugate faults mark discontinuities in rupture geometry and surface slip on the main fault, suggesting strong fault interaction in the eastern tip zone of the Madoi rupture.

How to cite: Yao, W., Liu-Zeng, J., and Wang, Z.: Rupture Branching and Propagation at the Eastern End of the 2021 Mw 7.4 Madoi Earthquake, North Tibet Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4233, https://doi.org/10.5194/egusphere-egu23-4233, 2023.

EGU23-5124 | ECS | Orals | TS3.7

Quantifying the slip over various time scales on active normal faults in the Apennines (Italy):  the Liri fault from paleoearthquakes to long-term slip rate 

Magali Riesner, Lucilla Benedetti, Stéphane Baize, Stefano Pucci, Matthieu Ferry, Stéphanie Gautier, Régis Braucher, Jules Fleury, Hervé Jomard, Stéphane Mazzotti, and Fabio Villani

Long-term fault escarpments are built by the accumulation of individual earthquakes producing incremental surface displacements on the fault releasing crustal tectonic loading. Cumulative escarpment studies have revealed a spatial slip variability along active faults as well as a temporal variability with the alternation of phases of intense seismic activity over a short period of time followed by long periods of quiescence. Understanding this spatial and temporal slip variability on individual faults and over a complex fault system provide a better knowledge of co-seismic rupture extents, essential for estimating past earthquakes magnitude and for seismic hazard assessment.

Up to now, most studies have focused on a timeframe over few seismic cycles, making it difficult to apprehend the rupture barriers persistence and cumulative slip distribution.  Here, we aim at quantifying the slip variability over several timescales ranging from a few months to a few million years on the same fault.

Our study focusses on the ~50 km-long Liri fault, SW of the Fucino basin. The fault is located at the contact between Cretaceous limestone and patches of Quaternary deposits locally convering Mio-Pliocene flysch sediments. Detailed mapping of the fault trace on high-resolution Digital Elevation Model (DEM) from UAV-acquired images, Pleiades images and Lidar together with field observations revealed changes in the morphological expression of the fault north and south of an important wind gap located at Capistrello. To the north, the faut trace is ~16 km-long located on the eastern side of ~2km-wide limestone ridge, reaching ~1300m asl elevation. Two bends in the fault trace, made of ~5km long segments, can be observed with the fault strike varying between N115° and N140°. In this northern section, the fault scarp appears subtle and we did not observe Quaternary deposits on the hanging wall. In the 30 km-long section, south of Capistrello, the cumulative scarp composed of numerous splays is evidenced by a sharp trace, offsetting several morphological surfaces and associated Quaternary sediment packages. Three major bends are observed in this section of the fault, separating 10 to 30 km-long segments striking between N110° and N160°. An alluvial surface offset by ~14 m of cumulative displacement was dated at ~35kyr using 36Cl cosmogenic exposure dating suggesting a minimum slip rate of 0.4 mm/yr.  Other morphological markers that have accumulated displacement between ~10 and 70 m-high have also been sampled for 36Cl cosmogenic exposure dating. Moreover, we excavated two small trenches at the base of the fault scarp within the Quaternary deposits affected by the fault revealing 3 rupture-surfacing earthquakes over the last 2500 yr, the last one occurring after 1226 CE. 

We will present those results and will discuss how the displacement varies along the fault both in time and space.

How to cite: Riesner, M., Benedetti, L., Baize, S., Pucci, S., Ferry, M., Gautier, S., Braucher, R., Fleury, J., Jomard, H., Mazzotti, S., and Villani, F.: Quantifying the slip over various time scales on active normal faults in the Apennines (Italy):  the Liri fault from paleoearthquakes to long-term slip rate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5124, https://doi.org/10.5194/egusphere-egu23-5124, 2023.

Earthquakes on faults in the brittle upper crust cause sudden changes in pore fluid pressure as well as postseismic viscoelastic flow in the lower crust. Such transient processes change the velocity field in the crust and cause significant Coulomb stress changes on receiver faults in the vicinity of the source fault, which may trigger or delay next earthquakes. As previous studies focused on natural earthquakes and/or considered poroelastic and viscoelastic processes separately, the combined influence of poroelastic effects and viscoelastic relaxation on postseismic velocity and stress fields has not been systematically studied so far. In a previous study with 2D finite-element models, we showed that postseismic velocity fields contain signals from overlapping poroelastic and viscoelastic effects (Peikert et al., Tectonophysics, 2022). Here, we use 3D finite-element models with arrays of normal and thrust faults, respectively, to analyze the Coulomb stress changes resulting from the interaction between poroelastic effects and viscoelastic relaxation. In different experiments, we vary the permeability of the crust and the viscosity of the lower crust or lithospheric mantle, while keeping the other parameters constant. We also performed experiments with and without pore fluid flow and viscoelastic relaxation, to isolate the effects of fluid flow and viscoelastic relaxation from each other. Our results show that the coseismic (= static) Coulomb stress changes are immediately altered by the signal from poroelastic effects during the first month after the earthquake. In the first postseismic year, Coulomb stress changes arising from poroelastic effects are one order of magnitude stronger than Coulomb stress changes arising from viscoelastic relaxation. In models considering fluid flow, poroelastic effects dominate the stress field in the first two years. Viscoelastic relaxation already occurs in the early postseismic phase, but is overlapped by the strong signal from poroelastic effects and dominates the Coulomb stress change pattern from about the fifth postseismic year onward for several decades.  The Coulomb stress change patterns show a combined signal from poroelastic and viscoelastic effects already during the first postseismic year, if the viscosity is sufficiently low. For sufficiently low permeabilities, Coulomb stress changes induced by poroelastic effects overlap with the signals from viscoelastic relaxation and interseismic stress accumulation for decades. Finally, poroelastic and viscoelastic effects have a strong impact on the magnitudes and patterns of Coulomb stress changes and should therefore be considered together when analyzing Coulomb stress transfer between faults.

How to cite: Peikert, J., Hampel, A., and Bagge, M.: Relative Importance of Poroelastic Effects and Viscoelastic Relaxation for Co- and Postseismic Coulomb Stress Changes on Normal and Thrust faults: Insights from 3D Finite-Element Modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5555, https://doi.org/10.5194/egusphere-egu23-5555, 2023.

EGU23-5953 | ECS | Posters on site | TS3.7

Paleoseismic Investigation along the straight section of the central Altyn Tagh fault and its constrain on the rupture history 

Longfei Han, Jing Liu-Zeng, Guiming Hu, Yann Klinger, Wenxin Wang, Heng Wang, Jing Xu, Bo Zhang, Yunpeng Gao, Zijun Wang, Xianyang Zeng, and Xiaoli Liu

Paleoseismic records are essential for constraining the earthquake recurrence behavior of active faults and evaluating the rupture history. However, paleoseismic studies on the central Altyn Tagh fault (ATF) are still scarce, and previous studies indicate that this fault section with simple geometry is not periodic. In addition, paleoseismic data from two sites along central ATF reveal different amounts of paleoearthquakes and present discordant in time. Therefore, we conducted paleoseismic studies and documented six reliable paleoseismic events at the LaPeiQuan site along the straight section of the central ATF. The results indicate that the most recent event is a small earthquake with a tiny vertical offset. The data A.D. (1752–1880) yr (event A) is significantly later than the last event along the Xorkoli section. The penultimate event at the LaPeiQuan site is a large earthquake for the ages of this event B is A.D. (667–764) yr (event B), which is consistent with the Xorkoli site and Aksay double bend site, producing at least 140 km rupture. In addition, the large vertical offset measurement from the deformed sediment of event B also supports its large one. The ages of Event D are discordant with the adjacent paleoseismic sites. The ages of Event C, Event E and Event F are still in process. The reason earthquake histories are inconsistent may be that small-scale geometrical complexities can prevent earthquake rupture propagation.

How to cite: Han, L., Liu-Zeng, J., Hu, G., Klinger, Y., Wang, W., Wang, H., Xu, J., Zhang, B., Gao, Y., Wang, Z., Zeng, X., and Liu, X.: Paleoseismic Investigation along the straight section of the central Altyn Tagh fault and its constrain on the rupture history, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5953, https://doi.org/10.5194/egusphere-egu23-5953, 2023.

EGU23-6332 | ECS | Posters on site | TS3.7

Realistic interseismic strain rate uncertainties from inherently sparse GNSS-networks 

Taco Broerse, Mario D'Acquisto, Rob Govers, Celine Marsman, and Alireza Amiri-Simkooei

Before geodetically derived strain and rotation rates can be robustly compared to geological or seismological observations, we need reliable strain rate uncertainties. Various methods exist to compute strain rates from GNSS-derived interseismic velocities, but a realistic representation of interpolation uncertainties has remained a challenge. The main problem is that commonly used deterministic interpolation methods do not account for uncertainty resulting from the absence of information in between observation sites. We apply stochastic interpolation by means of ordinary kriging to propagate errors both from discontinuous data coverage as well as from observation uncertainties to our strain rate estimates. However, interseismic horizontal surface velocities in tectonically active regions are spatially highly non-stationary, with high spatial variability around active faults and lower velocity variability in tectonically more stable regions. This requires an extension of traditional ordinary kriging approaches. For interpolation uncertainties that reflect the local variability and spatial correlation of the observed surface velocities, we apply a novel method that incorporates the spatially variable statistics of the underlying data. We estimate realistic uncertainties and covariances of the interpolated velocity field. For regions with a high spatial velocity variability, we find a large increase in uncertainty with increasing distance from observation sites, while in areas with little spatial variability, we estimate a small increase in uncertainty with distance. Subsequently, we propagate interpolated velocity covariance to strain rate uncertainties, such that we can assess the statistical significance of the interpolated strain rate field. Applied to a number of actively deforming regions, including the Pacific coast of North America and Japan, we show to what degree we can robustly determine strain rates based on available GNSS-derived velocities. Realistic uncertainties assist the community to better discriminate continuous or localized deformation on active faults from the available geodetic data. 

 
 

How to cite: Broerse, T., D'Acquisto, M., Govers, R., Marsman, C., and Amiri-Simkooei, A.: Realistic interseismic strain rate uncertainties from inherently sparse GNSS-networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6332, https://doi.org/10.5194/egusphere-egu23-6332, 2023.

EGU23-6567 | ECS | Orals | TS3.7

Holocene deformation on a transform fault: Insights from paleoseismology on the Húsavík-Flatey Fault in North Iceland 

Rémi Matrau, Yann Klinger, Jonathan Harrington, Thorvaldur Thórdarson, Ármann Höskuldsson, Esther Gudmundsdöttir, Laura Parisi, Margherita Fittipaldi, Ulas Avsar, and Sigurjón Jónsson

Studies of Oceanic Transform Faults (OTFs) usually rely on geophysical data because of the OTF inaccessibility on the seafloor. The Húsavík-Flatey Fault (HFF) in northern Iceland is an OTF connecting the onshore rift in Iceland to an offshore rift segment of the Mid-Atlantic Ridge, accommodating 30% to 50% of the relative plate motion at this latitude between North America and Eurasia. The HFF is unique because its easternmost 25 km-long segment is exposed on land, allowing to study the long-term deformation of the fault. Two historical earthquakes of estimated magnitudes M6.5 - M7 have been reported on the eastern HFF in the last 270 years. However, almost no information exists from prior to the 18th century.

To study the Holocene deformation of the HFF and to build a catalogue of past earthquakes, we excavated 11 paleoseismology trenches at two locations, six on an alluvial fan and five in a pull-apart basin. We also excavated and tracked buried river channels to estimate long-term slip rates and to assess the coseismic displacement of single events. We used radiocarbon dating of birch wood samples together with major element compositions of volcanic ashes (tephras) to constrain the timing of events on the fault.

Trenches at both locations show clear evidence of deformation and surface rupturing events. From offset measurements of glacial morphologies and buried river channels, we calculate a Holocene slip rate of 4 - 6 mm/yr, slightly lower than the estimated present-day geodetic slip rate, suggesting that some of the deformation may be distributed. Based on upward terminations of cracks and faults, we identified eight events in the last ~6000 years, yielding fewer major earthquakes than expected from the 270-year record. We thus suggest that large earthquakes of magnitude ~M7 on the HFF, producing significant surface ruptures, are rare, with a return time of 500 to 600 years. We also propose that the short recurrence times often observed on OTFs may therefore not be representative of the full seismic cycle.

How to cite: Matrau, R., Klinger, Y., Harrington, J., Thórdarson, T., Höskuldsson, Á., Gudmundsdöttir, E., Parisi, L., Fittipaldi, M., Avsar, U., and Jónsson, S.: Holocene deformation on a transform fault: Insights from paleoseismology on the Húsavík-Flatey Fault in North Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6567, https://doi.org/10.5194/egusphere-egu23-6567, 2023.

EGU23-7209 | ECS | Orals | TS3.7

Impact of rupture complexity on seismic hazard: Case of the 2018 Mw7.5 Palu earthquake 

Liqing Jiao, Teng Wang, Guangcai Feng, Paul Tapponnier, Andrean V. H. Simanjuntak, and Chung-Han Chan

Rupture complexity results in difficulty in quantifying seismic hazards, such as the probability of an earthquake on multiple fault segments and spatial distribution of fault displacement on the surface. Here we tried to propose a dynamic model to fit the rupture behavior of the 2018 Mw7.5 Palu earthquake, which splays along several sub-fault plans on the surface. The Palu event was initiated on an unknown fault and propagated on a curved plane on the Palu-Koro and Matano faults. According to the Interferometric Synthetic Aperture Radar (InSAR) data, both principal (on-fault) and distributed (off-fault) faulting were identified and spatial displacement on the surface could be evaluated. To model the complex geometry of the coseismic rupture plane and corresponding deformation, we proposed a dynamic model through the Discrete Element Method (DEM). Our model demonstrated rupture along a planar fault at depth and several splay faulting with various deformations on the surface, corresponding to the observations. The simulations represented temporal rupture behavior that covers several earthquake cycles and the probability of superficial fault displacement, which shed light on subsequent seismic hazard assessment and probabilistic fault displacement hazard analysis, respectively.

How to cite: Jiao, L., Wang, T., Feng, G., Tapponnier, P., Simanjuntak, A. V. H., and Chan, C.-H.: Impact of rupture complexity on seismic hazard: Case of the 2018 Mw7.5 Palu earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7209, https://doi.org/10.5194/egusphere-egu23-7209, 2023.

EGU23-7301 | Posters on site | TS3.7

Is the Pampean flat-slab responsible for the differences in post-seismic motions between Maule and Illapel earthquakes? 

Emilie Klein, Hugo Boulze, Christophe Vigny, Luce Fleitout, and Jean-Didier Garaud

Ever since the Maule earthquake (Mw8.8, 2010), a quick vertical uplift is measured thanks to GNSS in the Andes, facing the rupture zone (~250 km to the trench). Models built for the Maule earthquake [Klein et al. 2016] have highlighted that a low-viscosity channel is required to explain the post-seismic uplift. This channel is located along the slab between 50 km and 130 km depth and has a viscosity of a few 1017 Pa.s - lower than in the asthenosphere, 1018 Pa.s. 

After the Illapel earthquake (Mw8.3, 2015), simple observations on GNSS time-series show that no uplift occurred in the Andes at an equivalent distance to the trench than in the case of the Maule earthquake. The subduction in the Illapel region is characterized by a flat-slab (called the Pampean flat-slab) in contrast with the normal-dipping subduction in the region of Maule.

Here, we investigate what is the impact of the Pampean flat-slab on the post-seismic deformations of the Illapel earthquake. In particular, we try to understand  whether the presence of the flat-slab inhibits the effect of the low-viscosity channel. For that purpose we compare GNSS vertical displacements with predictions in both regions of Maule and Illapel from a 3D spherical finite-element model that accounts for the slab geometry of the Chilean subduction zone.

How to cite: Klein, E., Boulze, H., Vigny, C., Fleitout, L., and Garaud, J.-D.: Is the Pampean flat-slab responsible for the differences in post-seismic motions between Maule and Illapel earthquakes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7301, https://doi.org/10.5194/egusphere-egu23-7301, 2023.

EGU23-7909 | Orals | TS3.7

The time-dependent stress changes within the seismic gap of the Eastern Marmara Sea (NW Türkiye) through multiple earthquake cycles since 715 AD. 

Murat utkucu, Hatice durmuş, Fatih uzunca, Süleyman nalbant, and Serap kIZILBUĞA

The M7.4 1999 İzmit earthquake apparently advanced the occurrence of possible future event or events along the segments of North Anatolian Fault Zone (NAFZ) beneath the Eastern Marmara Sea due to the positive stress load. This part of the NAFZ did not produce any large earthquake since the May 1766 earthquake, constituting a seismic gap close to the city of Istanbul. In the present study we constructed a Coulomb stress evolution model for the seismic gap that includes the effect of coseismic, time-dependent postseismic viscoelastic relaxation of the substrate beneath the elastic crust and secular stress loadings through the multiple earthquake cycles since 715 AD. The snapshots of stress changes before and after the large and destructive earthquakes of 740, 989, 1343, 1509, May 1766 and 1999 İzmit have been carefully examined. It has been estimated that the total stress changes before 989, 1343, 1509 and May 1766 earthquakes were in the range from 26 to131 bars. Present stress values at the eastern, middle and western sampling points on the faults within the gap are computed as 115, 131 and 85 bars respectively. Considering that the global mean of stress drops for continental strike-slip faults is about 35 bars, it is suggested that the earthquake hazard for the seismic gap critically high.

How to cite: utkucu, M., durmuş, H., uzunca, F., nalbant, S., and kIZILBUĞA, S.: The time-dependent stress changes within the seismic gap of the Eastern Marmara Sea (NW Türkiye) through multiple earthquake cycles since 715 AD., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7909, https://doi.org/10.5194/egusphere-egu23-7909, 2023.

EGU23-8011 | ECS | Orals | TS3.7

Crustal deformation of southwestern Tianshan orogenic belt based on InSAR and GPS observations 

Xiaohang Wang, Mahdi Motagh, and Caijun Xu

The Tianshan range, one of the most active mountain building belts in central Asia, has complex geological structures and frequent strong earthquakes since the Cenozoic. Due to lack of sufficient high-resolution geodetic survey measurments, little is known about detailed fault slip rates and seismic hazards related to main active faults in Tianshan. However, in recent years, the improvements in space-based geodetic technologies (Global Navigation Satellite System (GNSS) and interferometric synthetic aperture radar (InSAR)) with growing coverage and accuracy provide us an opportunity to image more subtle features in this area. In this study, we assesses inter-seismic deformation for the period 2014-2022 over the southwestern Tianshan based on ascending and descending Sentinel-1 SAR data.  Combined with GNSS data, we then constructed the 3D crustal deformation with high precision and high spatial resolution to study the active structures in southwestern Tianshan. The results indicate that: (1) The Tianshan orogenic belt (TSOB) has intense crustal deformation and the shortening rate is approximately 20 mm/yr. The Keping fold-thrust belt (KFB) is the most intensely deformed areas in TSOB, it’s convergence rate accounts for 1/3 of the entire southwestern Tianshan. (2) The South Tianshan fault (STF) and the Piqiang fault (PQF) have obvious left-lateral strike-slip components and the South Tianshan fault also has thrust characteristic. (3) The folds in both western and eastern KFB play an important role in accommodating regional strain, the shortening rate in KFB is accommodated by the thrust-anticlinal zone at the KFB front.

How to cite: Wang, X., Motagh, M., and Xu, C.: Crustal deformation of southwestern Tianshan orogenic belt based on InSAR and GPS observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8011, https://doi.org/10.5194/egusphere-egu23-8011, 2023.

Constraining the effective rheology of major faults is crucial to improve our understanding of the physics of plate boundary deformation. Laboratory studies have used analog experiments to propose rheological models based on viscoelasticity or friction that match laboratory-observed behavior under stress-controlled conditions. Such models have since been used to fit real-world observations of deformation near plate interfaces (both for co- and postseismic displacement timeseries), yielding a variety of estimates of key rheological parameters.
However, confidently differentiating between models using purely observations of a single earthquake (coseismic and postseismic deformation) is difficult — especially in the presence of coarse spatiotemporal sampling, inherent observational noise, and the simplifications of our forward models. In this study, we present a framework built on numerical probabilistic simulations aimed at using displacement timeseries across multiple earthquake cycles in a subduction zone, which successfully distinguishes between endmember constitutive models and recovers key rheological properties. Using synthetic Global Navigation Satellite System network datasets, we furthermore investigate the sensitivity of (hyper-)parameters to the recovery of the true underlying rheological models, and present progress made towards using real 3D observations of a megathrust.

How to cite: Köhne, T., Mallick, R., and Simons, M.: Description Of A Framework And Associated Sensitivity Analysis For Recovery Of Rheological Models And Their Key Parameters Using Multi-Cycle Fault Slip Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8837, https://doi.org/10.5194/egusphere-egu23-8837, 2023.

EGU23-9213 | Orals | TS3.7

An Adjoint-based Method for Inverting for Heterogeneous Material Properties and Fault Slip From Earthquake Surface Deformation Data 

Thorsten Becker, Simone Puel, Umberto Villa, Omar Ghattas, and Dunyu Liu

Analysis of geodetic and seismological data helps constrain earthquake dynamics and the physics of lithospheric deformation. Here, we discuss a new modeling approach based on an open-source finite-element framework to invert surface deformation data for constitutive laws and their parameters, such as the Poisson’s ratio or shear modulus in the crust and mantle wedge.

These inversions can be realized by using adjoint-based optimization methods which efficiently reduce the misfit between the calculated and observed displacements. To quantify the associated model uncertainties, we extend the inverse approach to a Bayesian inference problem. Since the data are usually informative only in a few directions in parameter space, we use a low-rank Laplace approximation of the posterior distribution to make the inverse problem computationally tractable. The mean and the posterior covariance are approximated by the solution of the inverse problem (MAP point) and the inverse of the Hessian of the negative log posterior evaluated at the MAP point, respectively. We show how smoothly varying parameter fields can be reconstructed satisfactorily from noisy data.

To improve the spatial resolution of the inverse solution we solve a Bayesian optimal experimental design problem to find the best station configuration by maximizing the expected information gain, defined as the Kullback-Leibler divergence between posterior and prior distributions. We show how and why the optimal network improves the material property inference more than evenly spaced stations. Based on our previous work on inverting for fault slip without Green’s function computations, we combine the two inversion schemes to jointly infer both model parameters, the coseismic slip, and material properties distribution. Lastly, we test this numerical forward/inverse framework with an application, the 2011 Tohoku-oki M9 earthquake. Both continuous land-based and six offshore acoustic GNSS stations located around the earthquake epicenter are inverted to jointly estimate the shear modulus and the fault slip during the megathrust event.

Our results demonstrates the potential of our computational framework and the general approach for inferring constitutive laws to evaluate sensitivity to parameters, and define strategies to improve our understanding of relevant parameters for earthquake dynamics. 

 

How to cite: Becker, T., Puel, S., Villa, U., Ghattas, O., and Liu, D.: An Adjoint-based Method for Inverting for Heterogeneous Material Properties and Fault Slip From Earthquake Surface Deformation Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9213, https://doi.org/10.5194/egusphere-egu23-9213, 2023.

EGU23-9752 | ECS | Posters on site | TS3.7

Interseismic deformation in the Tjörnes Fracture Zone, North Iceland from GNSS measurements 

Alejandra Barreto, Renier Viltres, Rémi Matrau, Benedikt G Ófeigsson, and Sigurjón Jónsson

The Tjörnes Fracture Zone poses significant seismic hazard to the town of Húsavík and other nearby coastal communities in North Iceland as it is capable of generating earthquakes of magnitude ~7. The 120 km long offset connects the offshore Kolbeinsey Ridge to the onshore Northern Volcanic Zone and accommodates approximately 18 mm/yr of transform motion between the North American and Eurasian plates. Most of the deformation is taken up by the two main structures of the fracture zone. The Grímsey Oblique Rift exhibits bookshelf faulting and consists of steeply dipping faults, arranged en-echelon and striking roughly N-S, bounding a series of left-stepping basins. The Húsavík-Flatey Fault is a ~100 km-long right-lateral strike-slip fault. It is mostly offshore, except for its easternmost ~25 km that comes onshore just north of Húsavík. To assess how the deformation is partitioned within the Tjörnes Fracture Zone and to calculate the rate of seismic moment accumulation on the Húsavík-Flatey Fault we use geodetic data from our North Iceland GNSS network. The network covers an area of roughly 200 km by 130 km in size and includes 21 continuous and 92 campaign-style GNSS stations. The continuous data now span up to ~21 years from 2001 to 2022. The first campaign measurements that focused on the HFF were carried out in 1995 and since then we have expanded the campaign-station network to the West towards Tröllaskagi and Skagafjörður and remeasured the network on several occasions. Data from the 2002, 2007, 2009, 2010, 2011, 2013, 2016, 2019, and 2022 campaigns are included in our study. In addition, several stations from the nationwide ISNET reference station network within our study area also included. The GNSS data is used to produce the most up to date velocity field from North Iceland. Relative to the North American plate, our results show a gradual increase of East velocities towards the Northeast across the two main transform structures that reach roughly 18 mm/yr on the Eurasian plate. At the northern tip of the Tjörnes peninsula, between the two transform structures, the velocities are roughly at half the total rate seen at the easternmost stations on the Eurasian plate. Limited deformation is found Southwest of the Húsavík-Flatey Fault in Tröllaskagi, within the so-called Dalvík zone, located on the North American plate.  These results are used to study the present day-kinematics of the Tjörnes Fracture Zone and to further improve the locking depth and slip-rate estimates of the main lineaments.

How to cite: Barreto, A., Viltres, R., Matrau, R., Ófeigsson, B. G., and Jónsson, S.: Interseismic deformation in the Tjörnes Fracture Zone, North Iceland from GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9752, https://doi.org/10.5194/egusphere-egu23-9752, 2023.

EGU23-10710 | ECS | Posters on site | TS3.7

The deep subduction earthquake machine: A synoptic view of the Chile Subduction Zone. 

Joaquín Julve, Marcos Moreno, Sylvain Barbot, Andrés Tassara, Rodolfo Araya, and Nicole Catalán

In the last 20 years, the Chile Subduction Zone (CSZ) has hosted two deep-located subduction events, the 2007 Mw 7.7 Tocopilla earthquake at the Mejillones Peninsula, and the 2016 Mw 7.6 Melinka earthquake at the south of the Chiloé Island. Interseismic seismicity at the Northern and Southern segments of the CSZ, show that in both cases, the ruptures initiated at the down-dip limit of the seismogenic zone. Locking degree models suggest that hypocenter location of this kind of megathrust earthquakes is spatially related with the transition from strongly to weakly locked areas. There are major differences in fault geometry, temperature-pressure regime, petrology at the plate interface and forearc structure between the North and South of the CSZ, raising the question about how such different tectonic settings allow a similar style of rupture. By constructing geologically and geophysically constrained dynamic numerical simulations, here we show that moderate-to-large deep nucleated earthquakes are controlled by petrology and pressure-temperature conditions at the plate interface, along with the structure of the forearc wedge. Our results explain the occurrence, recurrence times and coseismic upper crust deformation of both earthquakes, suggesting that blind ruptures are not only generated at specific conditions, but a suitable combination of the aforementioned parameters is needed. Since the Northern Chile subduction zone has no sediments at the megathrust, the frictional behavior is controlled by altered basalt at the seismogenic depth, and seismicity shows a strong temperature-dependence. Once altered basalt no longer behaves as a velocity weakening material, blueschist rocks allow slow-slip events to develop. The Southern Chile subduction zone is filled with Pliocene-to-present sediments feeding a quartz-dominated subduction channel that defines the seismogenic limit. Within this framework, basal accretion structures are overlapped with a fluid concentration zone at the Moho depth, where the Melinka earthquake initiated. These synoptic views of the CSZ manifest a strong interaction between fluid-rock and forearc structures, which explains the occurrence of blind ruptures at the subduction seismic cycle.

How to cite: Julve, J., Moreno, M., Barbot, S., Tassara, A., Araya, R., and Catalán, N.: The deep subduction earthquake machine: A synoptic view of the Chile Subduction Zone., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10710, https://doi.org/10.5194/egusphere-egu23-10710, 2023.

This study aims to forecast the magnitude of future strong (6.0≤M<7.0) and major (7.0≤M<8.0) earthquakes along the East Anatolian Fault Zone (EAFZ), a major fault zone of Turkey and an active plate boundary that lies between Arabian and Anatolian plates. We first investigated the segmentation of the EAFZ in this context after compiling the earlier research on its structural setting and historical earthquakes. In order to determine the distribution of slip deficit rates, we analyzed GPS slip rates to obtain back-slips. The current slip budgets on each fault segment are calculated using the resulting slip deficit estimates. To elaborate on whether b-values might be used to distinguish between locked and creeping fault segments, we also examined the distribution of b-values along the fault. As a result, we found a reverse correlation between slip deficit rates and b-values. According to our findings, the EAFZ has currently a slip deficit of 1.51 m. While there is a segment such as Hacılar with no slip deficit, there is enough slip deficit accumulation to generate three strong and three major earthquakes on the other fault segments. Presently, these fault segments have the potential to re-generate previous earthquakes, within the magnitude range of 6.8-7.4. The latest strong earthquake on January 24, 2020, the Elazığ earthquake (M 6.8) verified our magnitude forecasts for the Sivrice-Pütürge segment.

How to cite: Uçan, K. A. and Bulut, F.: Forecasting Earthquake Magnitudes along the East Anatolian Fault Zone using Fault Zone Segmentation, Historical Earthquakes, and GPS Slip Rates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11401, https://doi.org/10.5194/egusphere-egu23-11401, 2023.

EGU23-11616 | Orals | TS3.7

InSAR observations of syn-seismic slip on faults due to M~6 earthquakes 

Henriette Sudhaus, John Begg, Vasiliki Mouslopoulou, Julia Knüppel, and Tilman May

As well as slip on a primary fault plane, earthquakes can produce slip on neighbouring faults which are not directly linked to the main source. This slip is called syn-seismic. With modern space-borne observation techniques, we observe syn-seismic slip down to a few centimeters on active faults nearby the source. An excellent example is the mapped slip on secondary faults during the 2019 Ridgecrest earthquake sequence in California. The overall spatial pattern of syn-seismic slip with respect to the main fault suggest that these faults respond to local stress changes caused by the main shock.

Data that enable the detection of surface fault slip on such small scale are provided by optical and radar satellites which allow a very high precision with high spatial resolution. In particular, short revisit times of these satellite observations lead to high coherence between images matched in pixel-offset and radar interferometric techniques.

We present further examples of syn-seismic fault slip during ~M6 earthquakes from different regions, such as those recorded in Greece in 2021 (Tyrnavos and Arkalochori) and 2020 in Tibet (W Xizang and near Xegar). We use Sentinel-1 interferometric wide-swath SAR acquisitions, which we process on the highest spatial resolution and apply weak filtering only. Our examples have in common that their syn-seismic fault activation reveals slip of a few centimeters only, persistently along a section of the fault’s length. The slip directions commonly appear to follow the coseismic surface displacement gradients which, in some cases, results in reverse slip on long-term normal faults. The activated faults were either faults previously mapped or concealed faults which were identified due to InSAR.

It is difficult to estimate the depth of syn-seismic fault slip and therefore how much strain has been released due to localized stress changes. We are also uncertain of the extent to which this small slip release contributes to the long-term displacement and displacement rate on faults and whether its contribution should be included in dislocation fault slip models. Our compilation suggests that syn-seismic slip is rather common, despite the rarity of previous observations, and is now detectable only because of improved resolution provided by InSAR data.

How to cite: Sudhaus, H., Begg, J., Mouslopoulou, V., Knüppel, J., and May, T.: InSAR observations of syn-seismic slip on faults due to M~6 earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11616, https://doi.org/10.5194/egusphere-egu23-11616, 2023.

Using GPS measurements, historical earthquake records, and instrumental earthquake data, we investigated GPS slip rates along the rupture zone of the 1668 Great Anatolian Earthquake (M8.1). We found three complete and one incomplete earthquake cycles since 1254 compiling all available historical and paleo-earthquake records in the literature. These records verified that a ~750-kilometer section of the North Anatolian Fault Zone was ruptured in 1668.  To simultaneously estimate segment-based slip rates and locking depths, we combined all available GPS measurements and modeled them using an arctangent approach. Slip rates are used to estimate preliminary inter-seismic slip storages assuming fault segments are fully locked after a mainshock. Large residuals between preliminary slip estimates and co-seismic slips indicate that the fault segments do not store slip for some time after a major earthquake. The creeping and locked stages vary in time and space, as our investigation revealed. Our results show that the slip rates along the NAFZ systematically increase from east to west suggesting that the Aegean extensional regime is the main driving force for the westward movement of the Anatolian Plate. Additionally, the locking depths show an east-to-west decreasing pattern verifying east-to-west thinning of crustal thickness along the Anatolian Plate. The earthquakes over the past three complete cycles and the current incomplete cycle indicate that the failure of the NAFZ begins in the east and moves westward reflecting a decelerating pattern. The failure is typically completed within a time period of 239±3 years.

How to cite: Yıldırım, S. C., Bulut, F., and Garagon, A.: East to West Acceleration of the Slip Rates Along the North Anatolian Fault and Its Implıcations Regarding Plate Tectonics and Earthquake Cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11854, https://doi.org/10.5194/egusphere-egu23-11854, 2023.

EGU23-12158 | ECS | Orals | TS3.7

Modeling surface deformations during the seismic cycle along the Chilean subduction zone 

Hugo Boulze, Luce Fleitout, Emilie Klein, Christophe Vigny, and Jean-Didier Garaud

Thanks to space geodesy we know with a millimetric precision how the lithosphere deforms at each stage of the seismic cycle. In particular, during the post-seismic phase, it can deform over thousands of kilometers and for decades. These deformations are partly due to viscoelastic relaxation of the asthenosphere.

In a previous work, we have shown that at the temporal and spatial scale of the seismic cycle, the viscoelastic relaxation can be modeled by a linear creep law [Boulze et al. 2022]. Therefore, because of the linearity of the creep law, the superposition principle applies and the present day deformation is simply the sum of the post-seismic deformations induced by past earthquakes. Based on this result, the objective of our work is to determine what slip history is needed on the Chilean subduction interface to reproduce the current deformation of South America, which is well measured by GNSS.

To investigate this challenging problem, we first develop a 3D spherical finite-element model of the Chilean subduction zone. This model covers the entire South American continent and incorporates a slab with a geometry described by Slab2.0 model [Hayes et al. 2018]. Then, we compare different ways to model the seismic cycle using the backslip theory [Savage 1983]. Finally, by comparing GPS time-series with our seismic cycle model prediction, we discuss many ingredients of the model: e.g. the viscosity of the asthenosphere (Maxwell, Burgers), the impact of a flat slab and low viscosity zones, the magnitude and extent of historical earthquakes.

How to cite: Boulze, H., Fleitout, L., Klein, E., Vigny, C., and Garaud, J.-D.: Modeling surface deformations during the seismic cycle along the Chilean subduction zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12158, https://doi.org/10.5194/egusphere-egu23-12158, 2023.

Measuring 36Cl cosmogenic nuclides on exposed bedrock fault scarps has now been used in several places in the Mediterranean to retrieve ages of the fault seismic history (e.g. Mechernich et al. 2022, Iezzi et al. 2021 and Cowie et al. 2017).

In Central Apennines, around the Fucino basin, at least 15 36Cl sampling sites were analyzed in previous studies to interpret the 36Cl data as seismic history or slip-rates. Several codes (e.g., Beck et al. 2018, Shlagenhauf et al. 2010) were used as a basis for solving 36Cl production equations to calculate the 36Cl concentration resulting from bedrock scarp exhumation history. Some codes included an MCMC routine to retrieve the seismic histories the closest to the dataset. The main differences between the various codes lie in: 1-the fault history prior to exhumation, 2-the parameters previous authors decided to inverse (as an example, mean density of the colluvium is inversed in Beck et al. 2018 but not in Tesson et al. 2019) and 3-the a priori distribution of those parameters (for instance, the time between two earthquakes follows an inverse gaussian distribution for Beck et al. 2018 but a uniform distribution for Tesson et al. 2019). I have compared the various codes and run them on the same dataset (one site at Campo Felice, one site at Roccapreturo and one site at Magnola) and found that retrieved seismic histories are similar, although the estimation of uncertainties differs.

Moreover, all previous cited codes run under Matlab or Fortran. Fortran codes have the advantage of fast computing time but could be cumbersomeI here propose a new code, adapted from Tesson et al. 2019, in the more accessible and widely used Python language. The inferred pre-exposure is also inversed and is a function of the height of the fault cumulative escarpment. The parameters considered are the number of events, ages of event, the associated slips, the long term slip rate, the quiescence and the pre-exposure and their optimal evaluation is done with a MCMC algorithm provided by Numpyro (Du Phan et al. 2019).

Using this new code, we have reanalyzed the 15 36Cl sites around the Fucino and, through a gaussian mixture algorithm, checked the hypothesis of common periods of activity throughout all the Fucino basin.

 

How to cite: Llinares, M., Benedetti, L., Gassier, G., and Viseur, S.: A new python code to invert 36Cl cosmogenic nuclide dataset on normal fault bedrock scarps: comparison with previous published codes and results on the accuracy of the retrieved seismic history of two normal fault systems in Central Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12874, https://doi.org/10.5194/egusphere-egu23-12874, 2023.

EGU23-13616 | ECS | Posters on site | TS3.7

Evolution of the Off-Fault Deformation during experimental strike-slip earthquakes 

Sarah Visage, Pauline Souloumiac, Nadaya Cubas, Bertrand Maillot, and Yann Klinger

Large continental strike-slip earthquakes produce spectacular surface deformations. However, ground displacements are only partially measured in comparison with the amount of slip inferred at depth. Relatively few estimates of the proportion of surface deformation accumulated on faults and deformation distributed regionally around faults are available. However, new technological advances such as state-of-the-art space imaging techniques now greatly improve the quality of surface rupture measurements. Their application has revealed that a significant amount of deformation is accommodated as diffuse deformation in an area of several hundred meters around the fault. This distribution is suggested to depend on the fault complexity. It is therefore essential to understand this distribution and its relation with fault segmentation to study the impact of fault complexities in a seismic context, we recently developed an innovative experimental prototype using some granular materials in layers similar to the earth's crust. They consist of a basal layer of rubber powder that stores elastic energy provided by the displacement of a basal plate sliding parallel to a second, fixed plate. The second layer is made of raw, twice broken rice that brings the stick-slip behaviour required for locking the slip between ruptures, and a third layer of sand with the frictional behaviour of cold shallow sediments at the surface. The surface sand layer allows following the evolution of the fault surface trace from the R-shears stage to the anastomosed fault zone composed of a succession of segments separated by zones of complexities. Using image correlation, we analyse the surface displacements. Since the rice layer causes a stick-slip behaviour, the analysis of the surface displacement is done on several seismic cycles: if the surface displacement is lower than the displacement imposed by the motor, it is an inter-seismic period, if the surface displacement is faster than the displacement imposed by the motor then it is a seismic event.

Once this catalog of events is established, the analysis of the gradient of the displacement Ux parallel to the basal enables us to quantify the deformation: localized (On-Fault Deformation) or distributed (Off-Fault Deformation).

At the R-shear stage, we measure [50~80] % of Off-Fault Deformation. Once the strike-slip fault is formed, the percentage of OFD drops between 20 to 30 %. These results are comparable to measurements made by experiments devoid of a stick-slip behaviours (with only of sand). Moreover, if we compare these values to the proportions of OFD estimated for natural earthquakes, we find the same distribution.

These experiments show that the more mature the fault, the more it will rupture seismically, in time as in space.

How to cite: Visage, S., Souloumiac, P., Cubas, N., Maillot, B., and Klinger, Y.: Evolution of the Off-Fault Deformation during experimental strike-slip earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13616, https://doi.org/10.5194/egusphere-egu23-13616, 2023.

EGU23-14568 | Posters on site | TS3.7

Active Tectonics in Southern Haiti and Surface Rupture of the 14 August 2021 Earthquake 

Newdeskarl Saint Fleur, Yann Klinger, Joseph Emmanuel Dessable, Germain Saint-Preux, Nathalie Feuillet, Dominique Boisson, Eric Calais, and Jean-Bernard de Chabalier

The 14 August 2021 earthquake occurred along the southern peninsula of Haiti only 11 years after the 12 January 2010 devastating earthquake. According to seismological and geodetic data, the events are both complex involving more than one fault. The 2021 rupture mainly portrayed reverse motion to the east near L’Asile town and left-lateral strike-slip motion to the west near Camp-Perrin town and Macaya mountain. A few days after the 2021 event, we conducted the first post-seismic field reconnaissance along the left-lateral Enriquillo-Plantain Garden Fault (EPGF) zone from L’Asile to Macaya mountain. We found numerous fresh cracks and landslides along that fault zone. The 111 cracks are mainly E-W-striking, some are oriented WNW-ESE, consistent with fault orientation in the area. In addition, the biggest cracks are mostly located to the west of the rupture zone, some of them may be potential fault surface rupture as revealed by seismological data. Furthermore, our observations along the northern coast of the southern peninsula revealed no significant coseismic coastal uplift as also suggested by InSAR data. Besides that field reconnaissance, we revisited the fault map around the epicentral area using high-resolution LiDAR data, Pléiades imagery and aerial photographs. We identified several left-lateral offsets of tens of meters corresponding to successive slips along the EPGF from L’Asile to Macaya mountain. In addition to the strike-slip deformation, we identified numerous geomorphic features related to long-term tectonic uplift to the north of the EPGF surface trace near the eastern part of the 2021 rupture. Those features are strikingly rare to the south. Such a pattern may indicate that the EPGF is north-dipping in the area. The 14 August 2021 rupture offers a new opportunity to constrain the kinematics and geometry of the EPGF system in southern Haiti.

How to cite: Saint Fleur, N., Klinger, Y., Dessable, J. E., Saint-Preux, G., Feuillet, N., Boisson, D., Calais, E., and de Chabalier, J.-B.: Active Tectonics in Southern Haiti and Surface Rupture of the 14 August 2021 Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14568, https://doi.org/10.5194/egusphere-egu23-14568, 2023.

Foreshocks are commonly observed before the happening of earthquakes in seismic catalogs. They provide critical precursors to reveal the process for the nucleation and rupture of earthquakes. Two mechanisms, pre-slip and cascade triggering, are thought to be the main physical process to explain the foreshock sequences and the mainshock. However, different from the regular micro-magnitude foreshock sequences (e.g. M1.0-3.0), some moderate-size (e.g. ~M6) foreshocks are also found before the mainshock (e.g. the M6.4 foreshock before the 2017 M7.1 Ridgecrest earthquake). How these moderate-size foreshocks affect the happen of mainshocks as well as their possible triggering mechanisms are still ambiguous and less studied.

In this study, fortunately, we obtain geodetic observations of moderate-size (M5.8 and M6.5) foreshocks for the 2020 M6.0 Turkey and 2022 M6.9 Taiwan earthquakes using Sentinel-1 Synthetic Aperture Radar (SAR) images. It is very rare for the geodetic observations of such foreshocks as they are very temporally close to the mainshocks within one day (i.e. ~10 hours and ~17 hours). We then invert for the fault geometries and slip distributions for these two earthquakes together with their moderate foreshocks constrained by these geodetic observations. Coulomb stresses on the fault planes of mainshocks produced by the moderate-size foreshocks are also calculated as well as the static stress drops of the mainshocks. Our study provides a unique opportunity to explore the possible triggering mechanism between moderate-size foreshocks and mainshocks as well as the conditions for the happening of earthquakes.

How to cite: Luo, H. and Wang, T.: Geodetic modeling of moderate-size foreshocks with mainshocks and the implication to earthquake trigger mechanisms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15420, https://doi.org/10.5194/egusphere-egu23-15420, 2023.

EGU23-16199 | ECS | Orals | TS3.7

Assessing distribution and pattern of the earthquake-related deformation caused by large continental normal earthquakes using optical image correlation 

Lucia Andreuttiova, James Hollingsworth, Pieter Vermeesch, and Tom Mitchell

Earthquakes on normal faults in the continental setting are relatively uncommon. The scarcity of surface-rupturing events underpins an absence of surface displacement measurements. It is a common practice to use surface offset as a proxy to understand the fault structure at depth. Hence, the lack of comprehensive surface data impedes the subsurface reconstruction of seismogenic normal faults and prohibits the thorough assessment of earthquake hazards. To supplement the available surface displacement measurements and to make statistically significant inferences, we apply optical image correlation (OIC) methods to historical images from three large continental normal earthquakes in the western United States (1954 Dixie Valley (Mw 6.8) - Fairview Peak (Mw 7.1) earthquake sequence, the 1959 Mw 7.2 Hebgen Lake earthquake and the 1983 Mw 6.9 Borah Peak earthquake). The results of this study are displacement maps with three components of deformation from which we extract high-resolution 3-d measurements everywhere along the surface rupture. 

 

The high-resolution 3-d data are used to quantify the magnitude and direction of the earthquake-related offset, the percentage of off-fault damage as well as the width of the fault zone. These parameters represent the fault maturity, geometric complexity and subsurface structure of the fault. Our observations confirm behaviours previously observed along strike-slip faults (e.g. magnitude of off-fault deformation is proportional to the rupture complexity). In addition, a comparative assessment of the results from the three study areas demonstrates that features such as excess slip detected close to the fault scarp are not unique and can be found along multiple dip-slip faults. Consequently, this study documents the variation of the quantifiable parameters along the normal faults. It suggests that while some parameters are a universal reflection of the fault characteristics, others vary according to the geology or topography in the area and should not be accepted without further investigation.

How to cite: Andreuttiova, L., Hollingsworth, J., Vermeesch, P., and Mitchell, T.: Assessing distribution and pattern of the earthquake-related deformation caused by large continental normal earthquakes using optical image correlation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16199, https://doi.org/10.5194/egusphere-egu23-16199, 2023.

EGU23-16845 | ECS | Posters on site | TS3.7

Characterizing the transition from diffuse to localized deformation using optical image correlation: the 2021 Mw7.4 Maduo, Tibet, earthquake 

Solene L Antoine, Zhen Liu, Yann Klinger, Arthur Delorme, and Jing Liu-Zeng

The 2021 Mw7.4 Maduo earthquake generated a ~160 km-long fault rupture within the Eastern Tibetan plateau, at about 100-150 km to the south-west of the Eastern Kunlun fault. Fault slip measured on the field represents only 20% of the displacements from satellite Interferometric Synthetic Aperture Radar (InSAR) measurements, highlighting the primarily diffuse nature of the surface deformation for this earthquake. Most surface deformation associated with this event corresponds to diffuse shear, occurring over widths of a few hundreds of meters to a few kilometers, and sometimes associated with shearing and tensional cracks mapped in the field. In this study, we use sub-pixel correlation of Pleiades (0.5 m) and SPOT-6/7 (1.6 m) optical images to characterize the near-fault displacement patterns associated with the 2021 Maduo event. We also use other optical data to assess the impact of sensor resolution on the measurements. Our results cover three kilometers on both sides of the rupture area with a resolution of 0.5 m. These results show that, despite the large rupture gaps observed in the field, the shear deformation zone at the surface is continuous along the entire length of the 2021 rupture. Even though, we observe variations in the surface deformation patterns, with regions that present more localized deformation whereas others are primarily characterized by diffuse shear. Using the high-resolution displacement maps, we characterize the transitions from the localized to the diffuse shear along the rupture strike, and investigate the relations with the bulk rock properties, and coseismic slip distribution. We also determine the limit at which deformation starts to localize on fractures that are large enough to be visible in the field.

How to cite: Antoine, S. L., Liu, Z., Klinger, Y., Delorme, A., and Liu-Zeng, J.: Characterizing the transition from diffuse to localized deformation using optical image correlation: the 2021 Mw7.4 Maduo, Tibet, earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16845, https://doi.org/10.5194/egusphere-egu23-16845, 2023.

EGU23-17189 | ECS | Posters on site | TS3.7

Testing a novel cave-based proxy for palaeo-earthquake shaking on the Alpine Fault, Aotearoa/New Zealand. 

Jeffrey Lang, Joel Baker, Julie Rowland, Adam Hartland, Paul Williams, John Hellstrom, Jamie Howarth, Ingrid Ukstins, Travis Cross, and Christopher Wood

Speleoseismology aims to reconstruct palaeoseismic records by dating pre- and post-damage speleothem calcite. A common approach is to infer palaeo-earthquakes from evidence of coinciding damage features (e.g., rockfall and broken speleothems) at multiple locations, which can be challenging in regions of high tectonic strain where short recurrence intervals of large earthquakes require dating of an impractically large number of damage features. Alternative approaches concerned with dating successive growth changes in individual speleothems (e.g., axis changes and growth hiatuses) are better suited to high-seismicity settings, as closely spaced events are more readily resolved. However, the origins of these growth changes can be ambiguous.

This study tested a novel geochemical proxy for quantifying ground shaking that is amenable to high-resolution speleothem studies, and potentially more diagnostic of earthquake damage. We evaluated the hypothesis that past large earthquakes temporarily elevate Mg/Ca in cave drip waters via incongruent carbonate dissolution following host rock fracturing (ICDC), leading to corresponding Mg enrichments in speleothem calcite. To do this, we examined a well-dated Holocene stalagmite (GT1) from a cave near the Alpine Fault, which is Aotearoa/New Zealand’s longest (>500 km) active onshore fault and a major source of seismic hazard. The locality is 4 km from the Alpine Fault’s northern section, which typically ruptures every 414–470 yr in a major (MW >7) to great (MW >8) earthquake, resulting in shaking intensities of MMI >VIII at the study site (MMI: Modified Mercalli Intensity).

We present a record of Mg/Ca variability in GT1 since ~5 ka, obtained by laser ablation inductively coupled plasma mass spectrometry along the stalagmite growth axis, and constrained temporally by >40 U–Th ages. Preliminary data show high baseline Mg concentrations in GT1 that cannot be explained solely by other mechanisms of drip water Mg/Ca enrichment (i.e., prior calcite precipitation), suggesting an ongoing contribution of Mg to drip waters by ICDC. Anomalous Mg peaks are therefore interpreted as high-intensity shaking events that temporarily elevated drip water Mg/Ca above baseline values. Post-2.5 ka Mg peaks are generally more subtle (30–50% enrichment) than pre-2.5 ka peaks (40–100%). Magnesium peaks are also strongly associated with brown-stained laminae inferred to reflect soil-derived organics. We propose that the high-Mg/high-organics horizons represent large earthquakes that both fractured the host rock and enhanced the mobilisation of organics from overlying soil.

We compared the GT1 record with a proximal and independent 1.4-kyr record of well-dated seismically triggered lacustrine turbidites. Given the subtle nature of Mg peaks in this interval, we consider those associated with physical growth changes (i.e., growth onset/cessation and/or axis change) as more likely to represent earthquakes. Of nine Mg peaks identified, five are associated with major physical growth changes. Of the four largest (MMI >VIII) shaking events in the lake turbidite record, which correspond to northern Alpine Fault surface-rupturing earthquakes, three overlap in age with a GT1 Mg peak and physical growth change. Further, two of the three historic earthquakes that generated MMI ≥VII shaking at the study site also overlap in age with a Mg peak.

How to cite: Lang, J., Baker, J., Rowland, J., Hartland, A., Williams, P., Hellstrom, J., Howarth, J., Ukstins, I., Cross, T., and Wood, C.: Testing a novel cave-based proxy for palaeo-earthquake shaking on the Alpine Fault, Aotearoa/New Zealand., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17189, https://doi.org/10.5194/egusphere-egu23-17189, 2023.

EGU23-1250 | Orals | TS3.8

Active segments along the North Anatolian Fault system in the Sea of Marmara 

Luca Gasperini and Alina Polonia

High-resolution multibeam and seismic reflection data collected during several oceanographic expeditions allowed us to compile an updated morphotectonic map of the North Anatolian Fault below the Sea of Marmara. We reconstructed kinematics and geometries of active fault segments at 10 ka time-scale, an interval that includes several earthquake cycles, taking the base of the latest marine transgression as a stratigraphic marker. Given the high deformation rates relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor, even in the presence of composite fault geometries and/or overprinting due to mass-wasting or turbidite deposits. In the frame of the right-lateral strike-slip domain characterizing the North Anatolian fault system, three types of deformation are observed: almost pure strike-slip faults, mainly oriented E-W; NE/SW-aligned axes of transpressive structures; NW/SE-oriented trans-tensional depressions. Fault segmentation occurs at different scales, but main segments develop along three major right-lateral oversteps, which delimit main fault branches, from east to west: i) the transtensive Cinarcik segment; ii) the Central (East and West) segments; iii) the westernmost Tekirdag segment. We performed a quantitative morphometric analysis of the shallow deformation patterns observed by seafloor morphology maps and high-resolution seismic reflection profiles along the entire basin, to determine the nature and cumulative lengths of individual fault segments. These data were used as inputs for empirical relationships, to estimate maximum expected Moment Magnitudes, obtaining values in the range of 6.8 to 7.4 for the Central, and 6.8 to 7.1 for the Cinarcik and Tekirdag segments, respectively. We discuss such findings considering analyses of inherited geological structures, historical catalogs, and available paleoseismological studies for the Sea of ​​Marmara region, to formulate reliable seismic hazard scenarios.

 

How to cite: Gasperini, L. and Polonia, A.: Active segments along the North Anatolian Fault system in the Sea of Marmara, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1250, https://doi.org/10.5194/egusphere-egu23-1250, 2023.

EGU23-2295 | ECS | Posters on site | TS3.8

Brittle tectonics and paleostress analysis of the Strzegom – Sobótka granite massif 

Mariusz Fiałkiewicz, Bartłomiej Grochmal, Marcin Olkowicz, Kamil Bulcewicz, and Marcin Dąbrowski

The Strzegom – Sobótka Massif has been subject of brittle tectonics studies for more than a century. Due to an ongoing extensive mining activity, numerous good exposures occur in a relatively small area, especially in the western part of the massif. A pioneering tectonic model of jointing in granite was established by Cloos (1922) for the study area, in which the NW-SE striking joint set is the dominant one (Q) and the perpendicular set (S), striking NE-SW, is longitudinal to mineral fabric. Also, there are two sets of the so-called diagonal joints, which are supposedly younger and strike N-S and W-E.


The effects of field work conducted in 20 quarries in the Strzegom – Sobótka Massiff are presented in the form of a tectonic map. In addition to direct measurements in the field, photogrammetric models were produced using aerial photographs to allow structural analysis within hardly accessible walls. For inaccessible quarries joint orientations were extracted using orthophoto maps. Several examples of fault related structures were identified and documented during field work in the studied granite quarries. Faults with slickensides and kinematic indicators were scarce but paleostress analyses were conducted whenever possible.


We discuss our field measurements of joint and fault orientations in relation to different petrographic types of granites and their lateral extent to address the effects of petrographic differentiation on the evolution of brittle tectonic structures in granites. We compare our new measurements to the results of previous tectonic studies of the Strzegom – Sobótka Massiff and paleostress analyses conducted for several other parts of the Sudetes. We also discuss our new results in terms of the Alpine reactivation of the Sudetes Mountains.

How to cite: Fiałkiewicz, M., Grochmal, B., Olkowicz, M., Bulcewicz, K., and Dąbrowski, M.: Brittle tectonics and paleostress analysis of the Strzegom – Sobótka granite massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2295, https://doi.org/10.5194/egusphere-egu23-2295, 2023.

EGU23-4713 | Posters on site | TS3.8

Structure and evolution of the active Ulsan Fault Zone, SE Korea: New insights from geophysical studies 

Youngbeom Cheon, Young Hong Shin, Samgyu Park, Jin-Hyuck Choi, Dong-Eun Kim, Kyungtae Ko, Chung-Ryeol Ryoo, and Moon Son

Integration of geophysical and geological data is essential to illuminate the configuration and geometry of surface and subsurface structures as well as their long-term evolution history. The NNW–SSE-striking incised valley and parallel mountain range in southeastern margin of the Korean peninsula, extended from Gyeongju to Ulsan cities (~50-km-long on land), have been regarded as the most active geographical feature in Korea, which was named as the Ulsan Fault zone (or system). This study presents a new insight of the structural architecture and its deformation history during the Cenozoic based on a combined data of gravity and electronic survey results with previous field observations. Our major results based on integrated data are as follows. First, the incised fault valley is divided into (1) the northern part of several distributed, buried and exposed fault strands and (2) the southern part of a concentrated deformation zone. Different deformation features between the two parts are controlled by the distribution pattern of the pre-existing Miocene structures (i.e., Yeonil Tectonic Line, YTL). Second, the Ulsan Fault is only constrained as a NNW–SSE-striking Quaternary fault zone within the incised valley-mountain range. The fault zone is composed of several interconnected and disconnected strands forming an imbricate thrust zone located along the western front of the mountain range (or eastern margin of the >2-km-wide incised valley). The constituent fault strands mainly exhibit an east-side-up geometry with moderate to low dip angles and reverse-dominant kinematics in near-surface. These strands are interpreted as reactivated ones of the pre-existing subvertical structures, such as the YTL. In here, we newly designate ‘the Ulsan–Yeonil Fault system’, composed of all NNW–SSE to N–S-striking buried and exposed faults on the incised valley-mountain range, regardless of tectonically controlled sequence of movement stages. Third, movements of the NNW–SSE-striking fault system during the Miocene to Quaternary were arrested by the NNE–SSW-striking Yangsan Fault, which is pre-formed prominent mature structure. Our results highlight the spatiotemporal structural characteristics in SE Korea, emphasizing that the configuration of pre-formed structures have strongly controlled the distribution and characteristics (i.e., geometry and kinematics) of the subsequent deformation during the Cenozoic crustal deformation.

How to cite: Cheon, Y., Shin, Y. H., Park, S., Choi, J.-H., Kim, D.-E., Ko, K., Ryoo, C.-R., and Son, M.: Structure and evolution of the active Ulsan Fault Zone, SE Korea: New insights from geophysical studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4713, https://doi.org/10.5194/egusphere-egu23-4713, 2023.

EGU23-4753 | Orals | TS3.8

Combining faulting and ductile deformation in long-term models of continental deformation 

Gregory Houseman, Philip England, and Lynn Evans

The spatial variation of strain rate in broad regions of continental collision, extension, or shear can often be well represented by the deformation of a thin viscous shell representing the lithosphere. The simplest explanation of this observation is that the deformation of the lithosphere is to first order a ductile process, even though shallow focus earthquakes imply slip on faults and release of elastic strain. In the thin-viscous-shell concept the strain of the upper brittle layer is assumed to simply follow the ductile strain of the stronger layers beneath, at least in the inter-seismic period. If the faults extend only to depths of 10 or 20 km, the brittle upper layer is not sufficiently thick or strong to do otherwise, and the concept of the brittle upper layer controlled by the ductile substrate is consistent with ductile models of the displacement-rate field constrained by GNSS observations. However, some large-scale faults do not comply with this concept and, rather than following the deformation of the ductile layer beneath, the strain localization on these structures appears to constrain the ductile deformation field of the adjoining regions. There are multiple lines of evidence from seismology and geodesy that great continental strike-slip faults, such as the San Andreas fault of California, the Alpine Fault of New Zealand, or the Altyn Tagh fault of China, extend through the crust and at least the upper part of the mantle lithosphere, even though earthquakes on these structures occur only in the upper 20 km. Taken together, the strain-localization and the lack of deep earthquakes suggest that these fault systems might be represented for the purpose of long-term continental deformation models as narrow ductile shear zones. A simple mechanical representation of localized strain on a ductile shear zone is defined by assuming traction is proportional to slip rate, with the proportionality constant described as a fault resistance coefficient. At the cost of ignoring the complexity of the earthquake cycle in such a model, we obtain a simple mechanical representation which we suggest is valid in the representation of long-term (and inter-seismic) continental deformation. In conceptual terms the fault resistance coefficient would be proportional to the effective viscosity of a ductile shear zone and inversely proportional to its width. However, an effective numerical implementation in a two-dimensional finite-element model is obtained by collapsing the narrow ductile shear zone to a one-dimensional structure characterised locally by the fault resistance coefficient. We illustrate the application of this conceptual model to the deformation field around the Alpine Fault in New Zealand, as constrained by an extensive array of GNSS displacement rates. The region as a whole is represented by a thin viscous shell that obeys a non-Newtonian viscous constitutive law, but we enable slip on model faults where there are steep local gradients in the geodetic displacement rates. The magnitude of the fault resistance coefficient is constrained by the requirement to fit the displacement rates and balance the stress.

How to cite: Houseman, G., England, P., and Evans, L.: Combining faulting and ductile deformation in long-term models of continental deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4753, https://doi.org/10.5194/egusphere-egu23-4753, 2023.

EGU23-6973 | Posters on site | TS3.8 | Highlight

3D geological modeling of the blind thrust system activated during the November 2022 Pesaro offshore seismic sequence (Adriatic sea, Italy). 

Francesco Emanuele Maesano, Mauro Buttinelli, Roberta Maffucci, Giovanni Toscani, Roberto Basili, Lorenzo Bonini, Pierfrancesco Burrato, Jakub Fedorik, Umberto Fracassi, Yuri Panara, Gabriele Tarabusi, Mara Monica Tiberti, Gianluca Valensise, Roberto Vallone, and Paola Vannoli

The undersea portion of the Northern Apennines is characterized by blind thrust faults running parallel to the Adriatic Sea coastline in northeastern peninsular Italy. These thrusts are buried below a thick cover of syntectonic Quaternary deposits. Their elusive geological signature at shallow depths and the low seismicity associated with them gave rise to diverging interpretations and views concerning the current activity of these thrusts and their earthquake potential.

On 9 November 2022, a seismic sequence started with an Mw 5.5 earthquake in the Pesaro Offshore. Hypocentral depth, focal mechanism, and aftershocks location all suggest that the earthquake was generated by one of the outermost thrusts of the Northern Apennines front that was already mapped as a potential seismogenic source in the DISS database (https://diss.ingv.it/diss330/sources.php?ITCS106).

We present a 3D reconstruction of the thrust system that caused the Pesaro Offshore seismic sequence obtained through the reinterpretation of publicly available seismic reflection profiles and well logs. The 3D geometry and size of the thrust activated during the seismic sequence suggest that it can also host larger earthquakes. We also present the application of a well-established workflow for calculating the slip rates of this buried thrust already tested in nearby structures. The outcomes of this study represent a step forward for earthquake and tsunami hazard models, the study of the seismic source, the enhancement of earthquake location by mix and match of seismological and geological independent data, and the expected kinematics of future potential earthquake ruptures.

These results are particularly relevant in offshore areas, where neither surface co-seismic ruptures nor GPS/InSAR deformation data are available in the aftermath of a significant earthquake. In these cases, multichannel seismic reflection profiles represent the only tool to appraise the subsurface structural setting. 

How to cite: Maesano, F. E., Buttinelli, M., Maffucci, R., Toscani, G., Basili, R., Bonini, L., Burrato, P., Fedorik, J., Fracassi, U., Panara, Y., Tarabusi, G., Tiberti, M. M., Valensise, G., Vallone, R., and Vannoli, P.: 3D geological modeling of the blind thrust system activated during the November 2022 Pesaro offshore seismic sequence (Adriatic sea, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6973, https://doi.org/10.5194/egusphere-egu23-6973, 2023.

EGU23-8291 | Orals | TS3.8 | Highlight

A Tsunami Generated by a Strike-Slip Event: Constraints From GPS and SAR Data on the 2018 Palu Earthquake 

Wim Simons, Taco Broerse, Lin Shen, Nicolai Nijholt, Olga Kleptsova, Andrew Hooper, Julie Pietrzak, Yu Morishita, Marc Naeije, Stef Lhermitte, Rob Govers, Christophe Vigny, Pieter Visser, and Riccardo Riva

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 Mw = 7.5 Palu earthquake (Sulawesi, Indonesia). With a predominantly strike-slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake-induced landslides. In this study we examine the tsunami potential of the co-seismic deformation. To this end, we present a novel geodetic data set of Global Positioning System and multiple Synthetic Aperture Radar-derived displacement fields to estimate a 3D co-seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co-seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co-seismic uplift (>2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co-seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video-derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co-seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic data set constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike-slip faults in transtensional basins.

How to cite: Simons, W., Broerse, T., Shen, L., Nijholt, N., Kleptsova, O., Hooper, A., Pietrzak, J., Morishita, Y., Naeije, M., Lhermitte, S., Govers, R., Vigny, C., Visser, P., and Riva, R.: A Tsunami Generated by a Strike-Slip Event: Constraints From GPS and SAR Data on the 2018 Palu Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8291, https://doi.org/10.5194/egusphere-egu23-8291, 2023.

The Coefficient of Complexity (CoCo) is a metric that quantifies the relative structural complexity of the fault system surrounding a specific study site on a primary fault extending through the system. Specifically, the CoCo metric has been used successfully to correlate the relative constancy or non-constancy of incremental slip rates on major strike-slip faults with the proximity, number, and slip rates of other neighboring active faults within a given radius of observation. Interestingly, our analysis shows that faults that extend through more structurally complex plate-boundary fault systems are characterized by more temporally variable slip behavior than faults that are embedded within simpler settings. Complex stress interactions within structurally complicated tectonic networks, as well as possible temporal changes in fault strength and kinematic interactions amongst mechanically complementary faults, likely explain these different behaviors. The CoCo metric thus not only provides a potential means for better evaluating the future behavior of large plate-boundary faults in the absence of well-documented incremental slip-rate behavior, but also can be used to differentiate faults that typically slip at a constant rate from the ones which do not. Using these results, we explore the relationship between incremental fault slip rates averaged over both short and large displacements on major strike-slip faults and geodetic estimates of strain accumulation rate on faults with different CoCo values. As might be anticipated, our analysis shows that the relatively constant slip rates on faults embedded within structurally simple strike-slip tectonic networks (i.e., low-CoCo faults) generally match rates of elastic strain accumulation of the faults’ shear zones, as measured by geodetic slip-deficit rates. In marked contrast, geodetic slip-deficit rates for faults embedded within structurally complex fault systems (high-CoCo faults) are less consistent with geological rates, whether averaged over short or large displacement scales, indicating significant variations in strain-accumulation rate on high-CoCo faults. We use these data to suggest possible patterns of geodetic-to-geologic rate ratios that may be indicative of the likely near-future behavior of the fault in question.

How to cite: Gauriau, J. and Dolan, J.: Using the CoCo metric of relative structural complexity of major plate-boundary fault networks to explore potentially time-variable fault loading rates on major strike-slip faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8544, https://doi.org/10.5194/egusphere-egu23-8544, 2023.

EGU23-9009 | ECS | Orals | TS3.8

The long-term evolution of Monte Marine and Monte Pettino seismogenic faults: tectono-stratigraphic, isotopic, and chronological constraints 

Giorgio Arriga, Marta Marchegiano, Valentina Argante, Junjie Zhang, Paola Cipollari, Domenico Cosentino, Michele Soligo, Marion Peral, Hsun-Ming Hu, Chuan-Chou Shen, Mauro Brilli, Philippe Claeys, and Federico Rossetti

The central Apennines are a Cenozoic fold-and-thrust belt that has been affected by post-orogenic extension in its axial region since the end of the early Pliocene (ca. 4 Ma). Post-orogenic extension generated several intermontane basins bounded by high-angle normal faults, striking NW-SE, subparallel to the backbone of the chain. The Monte Pettino and the Monte Marine seismogenic faults (MPF, MMF) are the boundary faults of the western portion of the late Pliocene-Quaternary L’Aquila intermontane basin. Their long-term activity is typified by exhumed fault cores that coexist with active fault strands localised at the fault hanging walls, providing evidence of a polyphase tectonic activity. The fault cores are decorated by diffuse dolomitization, which indicates structurally controlled fluid-flow and metasomatism. To constrain the long-term (space-time) evolution of the MPF-MMF faults, we integrated fieldwork, stable isotope systematics (δ18O, δ13C and Δ47), carbonate thermoluminescence and U-Th dating. Our results highlight two main tectonic phases, with different structural evolution and fluid-rock interaction. The first phase corresponds to the development of a major cataclastic zone, defined by meter-thick, SW-dipping (65-70°), fault cores exposed at the piedmont of the MPF-MMF ridges. The C-O systematics of the cataclasite and of the associated calcite slickenfibers, which are in the range of the carbonate bedrock, indicate a "closed" system behaviour during fault nucleation and development. Preliminary results from Δ47 thermometry of syn-kinematic carbonate structures indicate temperatures of 34 ± 2 °C. Thermoluminescence dating of dolomite clasts in the fault zone indicates age in the range of 3.0 – 3.4 Ma, whilst the cataclastic fault core is younger (< 800 ka). The second phase is mainly recorded in upper Pleistocene sedimentary Breccias (ca. 350 ka) which unconformably cover the bedrock and the exhumed fault cores at the SE termination of the MPF. It consists of anastomosed, high-angle WNW-ESE striking fault strands, spaced meters apart and with cm-m displacements, associated with carbonate veining and travertines. Stable isotopes measured from the fault slickenfibers, carbonate veins and travertines show negative δ13C and δ18O values, suggesting a depositional system dominated by meteoric fluid ("open" system) with an important contribution of organic carbon. Travertines and veins precipitated at colder temperatures (12 ± 4 °C), in the range of the average local air temperatures, thus excluding precipitation from a hydrothermal circuit. Moreover, their U-Th ages range between 182 and 331 ka, compatible with the temporal constraints from stratigraphic data. Structural and isotopic results do not support tectonic reactivation of the cataclastic core of the MPF during the middle-late Pleistocene, confirming the stratigraphic evidence. Our results provide the first absolute age constraint on the post-orogenic extensional faulting in the L’Aquila basin, demonstrating a two-stage fault activity, characterised by a change from localised (from ca. 3 to ca. 0.8 Ma) to delocalised faulting (200-300 ka to present). We infer that this change in the style of extensional faulting was consequence of the evolving rheological structure of the fault zones, primarily regulated by the feedback and interactions involving structurally-controlled fluid flow, rock metasomatism and cataclastic processes in space and time.

How to cite: Arriga, G., Marchegiano, M., Argante, V., Zhang, J., Cipollari, P., Cosentino, D., Soligo, M., Peral, M., Hu, H.-M., Shen, C.-C., Brilli, M., Claeys, P., and Rossetti, F.: The long-term evolution of Monte Marine and Monte Pettino seismogenic faults: tectono-stratigraphic, isotopic, and chronological constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9009, https://doi.org/10.5194/egusphere-egu23-9009, 2023.

EGU23-9272 | Posters on site | TS3.8

Ultra-high resolution (micro-bathymetric mapping and sub-bottom profiling) imaging of an active strike-slip fault, the North Alfeo Fault, offshore Catania, Eastern Sicily (Ionian Sea, Central Mediterranean) 

Barreca Giovanni, Gaillot Arnaud, Klingelhoefer Frauke, Dupont Pauline, Lenhof Edgar, Coussin Vincent, Dominguez Stèphane, and Gutscher Marc-Andrè

The goal of the ERC funded FOCUS project is to study an active fault offshore Catania using fiber optics, sea-floor geodesy, seismological stations (onshore and OBS on the seafloor) and detailed in-situ observations using an ROV and an AUV. Here, we report on the latter. In October 2020 using the ROV Victor6000 and in January 2022 using the AUV IdefX, we performed micro-bathymetric mapping (at an altitude of 50 m above the seafloor) of a 15-km-long segment of the North Alfeo Fault, covering water depths of about 1600 m to 2300 m. A prominent lozenge-shaped transpressive ridge or “pop-up” type structure is one of the primary features of this portion of the fault zone. It forms a flat-topped plateau culminating at about 1700 m water depth. It is cross-cut by a network of N-S striking faults resembling domino blocks or books in a book-shelf.

Sub-bottom profiling (using a chirp system on the AUV IdefX at an altitude of 70 m above the seafloor) crossed the transpressive ridge and imaged the network of narrowly spaced (typically 100 - 200 m spacing) N-S striking faults, which are steeply W dipping normal faults. This suggests the transpressive ridge is currently collapsing. Indeed, the eastern part of the plateau is marked by a small (600 m long from headscarp to toe) submarine landslide. The overall pattern in the northern portion of the mapped area (west of the plateau) is a series of oblique secondary faults, crossing the primary fault at an angle of about 30°. Using a very simple analog model of a thin layer of cohesive granular material above two rigid plates, with a slightly curved fault track, it was possible to produce a primary strike-slip fault directly above the cut between the two plates, and several distinct transpressional ridges (pop-ups) as well as transtensional fissures or gashes. Secondary faults form obliquely to the primary fault and are oriented at about a 30° angle clockwise from the trend of the primary fault. This pattern reproduces the large-scale features observed in the micro-bathymetry from the NW prolongation of the North Alfeo fault. A series of analog experiments using different rheologies in the sediment layer is planned in the future to test the likely detachment (nucleation) depth for the strike-slip fault in the basement.

 

How to cite: Giovanni, B., Arnaud, G., Frauke, K., Pauline, D., Edgar, L., Vincent, C., Stèphane, D., and Marc-Andrè, G.: Ultra-high resolution (micro-bathymetric mapping and sub-bottom profiling) imaging of an active strike-slip fault, the North Alfeo Fault, offshore Catania, Eastern Sicily (Ionian Sea, Central Mediterranean), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9272, https://doi.org/10.5194/egusphere-egu23-9272, 2023.

The northward migration of the Mendocino Triple Junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike-slip faults, that become the San Andreas plate boundary. How and why these faults develop where they do is enigmatic. We find that the 3-D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. Recently developed, high-resolution seismic-tomographic imagery of northern California indicates that (1) the Pioneer Fragment, and extension of the Pacific plate beneath the western margin of North America occupies the western half of the slab window, immediately south of the MTJ; (2) the eastern edge of the Pioneer Fragment lies beneath the newly forming Maacama Fault system, which develops to become the locus for the primary plate boundary structure after approximately 6-10 Ma (eg. the present-day East Bay faults in the SF Bay region); and (3) the placement of the translating Pioneer Fragment adjacent to the asthenosphere of the slab window, and its coupling to the overlying North American crust generate a shear zone within and below the crust that develops into the  plate boundary faults. This plate boundary configuration has been operable since the initial formation of the transform plate boundary. As a result, the San Andreas plate boundary forms within the western margin of North America, approximately 100 km inboard of the western edge of North America, rather than at its western edge. One additional result of this is that blocks of North America lithosphere are detached and become terranes (such as the Salinian and Nacimiento (Franciscan) blocks) that are captured by and translate with the Pacific plate, producing the complex crustal architecture of coastal California.

How to cite: Furlong, K. P.: The Development of the Northern San Andreas Plate Boundary Fault System - Importance of Lower-crustal Ductile Shear in Producing Primary Plate Boundary Structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10059, https://doi.org/10.5194/egusphere-egu23-10059, 2023.

EGU23-10111 | Orals | TS3.8

Frictional-viscous flow and the aseismic-seismic transition at shallow depths 

Carolyn Boulton, André Niemeijer, Marcel Mizera, Timothy Little, Inigo Müller, Martin Ziegler, and Maartje Hamers

During the interseismic period of an earthquake cycle, creeping patches and locked asperities on crustal faults control the distribution of accumulated elastic strain and thus their seismic potential. Yet the frictional and frictional-viscous processes that facilitate creep on shallow crustal faults, such as near-trench subduction zone décollements, remain poorly understood. At mid-to-low latitudes, calcareous sediments are important subduction zone input materials. Compared with siliciclastic lithologies, calcareous rocks more readily accommodate strain aseismically via crystal plasticity and diffusive mass transfer processes at low temperatures and pressures in the upper crust. Along the Hikurangi Subduction Margin of New Zealand, accretionary prism uplift has exposed the Hungaroa fault zone, an inactive thrust fault developed within fine-grained, calcareous sedimentary rocks.

In this research, we present observational and theoretical evidence that the Hungaroa fault zone accommodated deformation primarily by distributed aseismic creep within a ~33 m-wide fault core.  Syntectonic calcite vein clumped isotope thermometry and maximum differential stress estimates indicate that deformation took place at 2 to 4 km depth. We model the fault zone rheology assuming diffusion-controlled frictional-viscous flow, with deformation at strain rates ≤10-9 s-1 able to have taken place at low shear stresses (τ <10 MPa) given sufficiently short diffusion distances (d <0.1 mm), even in the absence of pore fluid overpressures. Critically, fault zones with diffusion-controlled frictional-viscous flow rheology can exhibit spatially and temporally variable strain rates if grain-scale and fracture-scale processes change the diffusion distance. Thus, the shallow (up-dip) limit of the seismogenic zone is not a simple function of temperature in fault zones governed by a frictional-viscous flow rheology.

How to cite: Boulton, C., Niemeijer, A., Mizera, M., Little, T., Müller, I., Ziegler, M., and Hamers, M.: Frictional-viscous flow and the aseismic-seismic transition at shallow depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10111, https://doi.org/10.5194/egusphere-egu23-10111, 2023.

EGU23-11050 | Orals | TS3.8 | Highlight

Normal fault network evolution in 3D numerical models 

Sascha Brune, Thilo Wrona, Derek Neuharth, Anne Glerum, John Naliboff, and Esther Heckenbach

Understanding how normal fault networks initiate and evolve is important for quantifying plate boundary deformation, assessing seismic hazard and finding natural resources. In recent years, 3D numerical models have been developed that can simulate the entire process of normal fault formation, from the start of rifting to the creation of new ocean floor. However, state-of-the-art methods treat faults as finite-width shear zones not as discrete entities, so additional work is needed to isolate individual faults and their characteristics in order to better understand fault system dynamics over geological scales.

We present 3D numerical rift models of moderately oblique extension using the ASPECT software. These models reproduce the thermo-mechanical behavior of Earth's lithosphere and simulate fault system dynamics from inception to breakup accounting for visco-plastic rheology, strain softening and surface processes. We use a method that extracts surficial fault systems as 2D networks of nodes and edges to study the evolution of normal faulting. By applying data analysis techniques, we group nodes and edges into components that represent individual faults and track their geometry and movement over time.

We find that the initial fault network forms through rapid fault growth and linkage, followed by competition between neighboring faults that leads to their coalescence into a stable network. At this point, modelled normal faults continue to accumulate displacement but do not grow any longer. As deformation localizes towards the center of the rift, the initial border faults shrink and disintegrate, being replaced by new faults in the center of the rift. During that transition, we document strain partitioning between predominantly dip-slip border faults and oblique-slip or strike-slip intra-basin faults. The longevity of faulting is thereby controlled by crustal rheology and surface process efficiency. Quantitative analysis of fault evolution allows us to deduce fault growth and linkage as well as fault tip retreat and disintegration in unprecedented detail.

How to cite: Brune, S., Wrona, T., Neuharth, D., Glerum, A., Naliboff, J., and Heckenbach, E.: Normal fault network evolution in 3D numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11050, https://doi.org/10.5194/egusphere-egu23-11050, 2023.

EGU23-11843 | ECS | Posters on site | TS3.8

Multidisciplinary approach to the study of a crustal tectonic discontinuity: an example from the Central Mediterranean offshore (Sicily channel) 

Simona Bongiovanni, Mariagiada Maiorana, Antonino D'Alessandro, Raffaele Martorana, and Attilio Sulli

The central Mediterranean is a geodynamically very complex area included in the convergence zone between the European plate and the African plate. We investigated the western sector of the Sicily Channel , which shows, according to literature data, different deep and shallow tectonic structures than the eastern sector.  Structural data show the presence of a crustal-scale discontinuity that has generated major seismic events such as the Belice earthquake of 1968. This structure has been identified as a wideband roughly oriented N-S from the San Vito Lo Capo to the Sciacca area (SVCS band, San Vito Lo Capo - Sciacca band) (Di Stefano et al., 2015) and continuing offshore to the Pantelleria area. In this work, through multidisciplinary data analysis, we aim to investigate the correlation between the surface structures highlighted onshore and the offshore continuation. For this purpose, we considered offshore data from the Sicily Channel including: gravimetric data, which show negative anomalies in the Pantelleria graben (Palano et al., 2020) and in the Sciacca offshore and velocity models showing the lateral variation of the Moho with values ranging from 30 to 33 km depth and values ranging from 20 to 23 km depth respectively west and est of the Pantelleria graben (Finetti, 2005). These data were compared with our interpretation of crustal reflection seismic profiles and seismic events (since 2005 with M≥2). The results show an alignment of seismic events with roughly N-S direction from offshore Sciacca to Lampedusa. Moreover, the seismic profiles show a lateral variation of the Moho depth deepening estward. From the joint analysis of these data we obtained a geological model of the investigated sector defining the offshore prosecution of the SVCS band present onshore. The present work may be useful for understanding the geodynamic evolution and for studying the seismic hazard of this area.

 

References

Di Stefano P., Favara R., Luzio D., Renda P., Cacciatore M. S., Calò M., Napoli G., Parisi L., Todaro S., Zarcone G. (2015). A regional-scale discontinuity in western Sicily revealed by a multidisciplinary approach: A new piece for understanding the geodynamic puzzle of the southern Mediterranean, Tectonics, 34, 2067–2085, doi:10.1002/2014TC003759.

Finetti I. R. (Ed.). (2005). CROP project: deep seismic exploration of the central Mediterranean and Italy. Elsevier.

Palano M., Ursino A., Spampinato S., Sparacino F., Polonia A., Gasperini L. (2020). Crustal deformation, active tectonics and seismic potential in the Sicily Channel (Central Mediterranean), along the Nubia–Eurasia plate boundary. Scientific reports, 10(1), 1-14.

How to cite: Bongiovanni, S., Maiorana, M., D'Alessandro, A., Martorana, R., and Sulli, A.: Multidisciplinary approach to the study of a crustal tectonic discontinuity: an example from the Central Mediterranean offshore (Sicily channel), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11843, https://doi.org/10.5194/egusphere-egu23-11843, 2023.

EGU23-12583 | ECS | Posters on site | TS3.8

Influence of mechanical stratigraphy and structural inheritance on the geometrical evolution of normal faults in the German Molasse Basin 

Vladimir Shipilin, David Tanner, Jennifer Ziesch, and Hermann Buness

Lithospheric flexure is the primary mechanism for the development of normal faults in foreland basins. While the tectonic regime defines the overall fabric of such flexure-induced faults, mechanical heterogeneity of the sedimentary sequence and pre-existing faults exert a major control on the geometry of the individual faults. Interpretation of 3-D seismic reflection data in the central part of the German Molasse Basin, a northern Alpine foreland basin, reveals a normal fault network that exhibits varying degrees of vertical segmentation. Two major faults oriented parallel to the strike of the Alpine orogen are characterised by geometrically coherent displacement of deeper Mesozoic strata and shallower Cenozoic strata. In contrast, another major fault system, oriented obliquely to the orogenic strike, shows an along-strike variation in geometric coupling between deeper and shallower structural levels. Although a thoroughgoing fault in the northeast, it bifurcates laterally to the southwest, with the deep and shallow segments decoupling across a southeastwardly-thickening, mechanically-weak layer. To establish the geometric evolution of these faults and understand to what extent it was governed by mechanical stratigraphy and structural inheritance, we here analyse throw distribution on the faults and variations in stratal thicknesses across the faults. High-resolution throw mapping indicates a general updip decrease in throw for the orogen-parallel faults, whereas the obliquely-oriented fault, in its coupled portion, has two throw maxima separated by a throw minimum at the mechanically incompetent interval. These results, together with syn-kinematic strata observations, show that the former faults initiated with the onset of the Cenozoic foreland flexure and grew upward by radial propagation, whereas the latter fault formed by an oblique reactivation of precursory Mesozoic faults and developed in the Cenozoic as a segmented structure. We hypothesise that the coupling of its deep and shallow segments to the northeast was established by a dip-linkage mechanism, which was inhibited further to the southeast as the mechanical barrier thickens. The reactivation of the pre-existing structures explains the non-optimal orientation of the younger fault segments at a shallower level, with the former acting as kinematic attractors for the latter faults. This study demonstrates how a detailed fault kinematic analysis can help to decipher the effect of multi-layered mechanical stratigraphy and structural inheritance on the spatial evolution of individual flexure-induced faults.

How to cite: Shipilin, V., Tanner, D., Ziesch, J., and Buness, H.: Influence of mechanical stratigraphy and structural inheritance on the geometrical evolution of normal faults in the German Molasse Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12583, https://doi.org/10.5194/egusphere-egu23-12583, 2023.

EGU23-13053 | ECS | Posters on site | TS3.8

Mirror-like fault surfaces in bituminous dolostones (Central Apennines, Italy) 

Miriana Chinello, Michele Fondriest, Telemaco Tesei, Elena Spagnuolo, Andrea Schito, Stephen A. Bowden, Luigi Germinario, Claudio Mazzoli, Chiara Cornelio, and Giulio Di Toro

Mirror-like surfaces (MSs) are ultra-polished fault surfaces that reflect visible light thanks to their low surface roughness (nm-scale). These ultra-polished surfaces are often found in seismogenic fault zones cutting limestones and dolostones (e.g., Siman-Tov et al., 2013; Fondriest et al., 2013; Ohl et al., 2020). Both natural and experimentally-produced fault-related MSs were described in spatial association with ultrafine matrix (grain size <10µm), nanograins (<100nm in size), amorphous carbon, decomposition products of calcite/dolomite (i.e., portlandite, periclase) and larger in size but “truncated” clasts (Verberne et al., 2019). However, the mechanism of formation of MSs is still a matter of debate. Indeed, experimental evidence shows that MSs can develop both under seismic (slip rate ≈1 m/s; Fondriest et al., 2013; Siman-Tov et al., 2013; Pozzi et al., 2018; Ohl et al., 2020), and aseismic (slip rate ≈0.1-10 µm/s; Verberne et al., 2013; Tesei et al., 2017) deformation conditions, involving various physical-chemical processes operating over a broad range of P-T conditions, strain and strain rates.

To understand how MSs form and their role in the seismic cycle, 10 samples were collected and analysed from normal faults cutting bituminous dolostones (Central Apennines, Italy). The MSs samples were from faults with increasing cumulated slip (from < 1 mm to few meters) and different resolved stress.

Ultra-high resolution scanning electron microstructural investigations of the MSs and the associated slip zones, show that the mirrors consist of exposed surfaces of ultra-flat dolostone grains and dolomite nanoparticles cemented by a <1-2 μm thick matrix of smeared bitumen. Cataclastic flow and pressure solution aided by the presence of bitumen are the main deformation mechanisms, probably associated with aseismic creep and fault healing/sealing during the seismic cycle.

Surface microroughness measurements (White Light Profilometry) reveal that (1) the RMS microroughness is < 500 nm over a lateral distance < 1 mm and (2) both the profile and the areal RMS show a weak inverse correlation with increasing displacement. Power Spectral Density (PSD) analysis shows that only in the sample with a displacement less than 1 mm is there a dependence of roughness on slip direction (that is, striae are observed).

Finally, Gas Chromatography-Mass Spectrometry analysis of bitumen from a fault MS which accommodated 86 cm of slip displacement has less quantities of larger molecular weight biomarkers and enrichment in lower molecular weight homologues relative to unfaulted rock. A difference that can be explained by frictional heating during seismic slip causing the destruction of higher molecular weight homologues.

This multidisciplinary study, by investigating the mechanism of formation of MSs, show that these ultra-polished features record the main phases of the seismic cycle, including coseismic slip (changes in the biomarkers structure), aseismic creep (viscous flow of bitumen) and inter-seismic fault sealing/healing (pressure-solution and cold sintering).

How to cite: Chinello, M., Fondriest, M., Tesei, T., Spagnuolo, E., Schito, A., Bowden, S. A., Germinario, L., Mazzoli, C., Cornelio, C., and Di Toro, G.: Mirror-like fault surfaces in bituminous dolostones (Central Apennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13053, https://doi.org/10.5194/egusphere-egu23-13053, 2023.

EGU23-13787 | Orals | TS3.8

Postglacial strike-slip faulting within the Skjálfandi Bay, N-Iceland 

Bryndís Brandsdóttir, Robert Detrick, Neal Driscoll, Jeffrey Karson, and Gunnar Guðmundsson

The Tjörnes Fracture Zone (TFZ) is a complex transform fault zone linking the Northern Volcanic Zone (NVZ) on land Iceland, with the offshore Kolbeinsey Ridge. The TFZ is roughly 150 km long (E-W) by 50-75 km wide (N-S) incorporating three major N-S trending pull-apart basins bounded by a complex array of normal and oblique-slip faults. The Skjálfandi Bay is the southern extension of the central basin. Seismicity within the Skjálfandi Bay is mostly confined to its western margin and the Húsavík-Flatey fault system (HFFS) across the southern part of the bay, extending eastwards into the NVZ and westwards into the westernmost basin. The main strands of the HFFS can be traced offshore across the Skjálfandi Bay in both CHIRP and multibeam data, as two WNW-trending, south-facing fault scarps. Several smaller WNW-trending faults are located sub-parallel of the main HFFS, many of which are delineated by pockmarks on the seafloor. Pockmark lineaments in northeastern Skjálfandi are elongated NE-SW, and WNW-ESE in the western part of the bay. The NE-SW pockmarks appear to be aligned along sediment covered marginal faults of the Skjálfandi basin whereas the northwestern pockmark field seems to be linked to WNW-ESE –trending strike-slip faults with little or no vertical displacement. The inferred pattern of WNW-ESE strike-slip faults and NE-SW basin-bounding faults matches results from adjacent areas of the Tjörnes Peninsula and Flateyjarskagi. Paleoearthquake records can be derived from highresolution seismic reflection profiles of active fault-growth sequences where long-term rate of sedimentation exceeds the rate of vertical fault displacement. Dense profiles across strike-slip faults within Skjálfandi exhibit vertical slip of up to 15 m during several earthquake sequences during the last ~12000 years.

How to cite: Brandsdóttir, B., Detrick, R., Driscoll, N., Karson, J., and Guðmundsson, G.: Postglacial strike-slip faulting within the Skjálfandi Bay, N-Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13787, https://doi.org/10.5194/egusphere-egu23-13787, 2023.

EGU23-13935 | ECS | Posters on site | TS3.8

From Lake Iznik to the Marmara Sea (NW Turkey): new insights in marine and lacustrine paleoseismology. 

Renaldo Gastineau, Pierre Sabatier, Stefano C. Fabbri, Flavio S. Anselmetti, Patricia Roeser, Mustafa Şahin, Serkan Gündüz, A. Catalina Gebhardt, Sven O. Franz, Frank Niessen, and Julia De Sigoyer

The North Anatolian Fault (NAF), located in Turkey, is one of the world's most active faults and accommodates Anatolia's westward motion relative to Eurasia. Over the last century, several earthquakes (M>6.8) have migrated from east to west. It is in the Marmara region, south of Istanbul, that the subsequent rupture is expected. However, this is where the geometry of the fault becomes more complex. It divides into three branches, one of which borders Lake Iznik and the southern Marmara Sea. As there is now very little seismic activity along this portion of the NAF (MNAF), and GPS only detects small displacements (Reilinger et al., 2006), it is thought to be inactive. However, the city of Iznik, the cradle of Christianity, has preserved valuable historical evidence in contrast to its observations. Therefore, to better understand the seismic hazard in this area, it is necessary to catalogue the seismic activity and locate past ruptures.

Two active faults were discovered in Lake Iznik thanks to our geophysical and coring campaigns (Gastineau et al., 2021). The study of short (<4m) sediment cores sampled on both sides of the E-W fault running close to Iznik city reveals that the previous rupture (1065 CE) coincides with a highly destructive historical earthquake recorded in the city's archaeological structures (Benjelloun et al., 2020). In addition to this localised rupture, numerous other event deposits are present in the sediments (laterally and temporally). We demonstrated that the same earthquake in 1065 CE is associated with various deposit types. One type of deposition is only observed for the 1065 CE earthquake, which takes place in the lake, unlike the others, suggesting that this type of deposition may depend on ground motion parameters besides the source-core distance.

A compilation of marine and lacustrine palaeoseismological studies was carried out at the scale of the western part of the NAF. We show that the relationship between sedimentation rate and the presence of earthquake-induced slope destabilisation doesn't work in the marine environment, unlike in the lacustrine environment. We also show that Lake Iznik records earthquakes from the NNAF and the MNAF, whereas the Sea of Marmara records only NNAF earthquakes. These observations open new perspectives and demonstrate the need to consider seismology and site effects in marine and lacustrine paleoseismology.

References:

Benjelloun, Y., De Sigoyer, J., Dessales, H., Baillet, L., Guéguen, P., Şahin, M., 2020. Historical earthquake scenarios for the middle strand of the North Anatolian Fault deduced from archeo-damage inventory and building deformation modeling. Seismol. Res. Lett. https://doi.org/10.1785/0220200278

Gastineau, R., De Sigoyer, J., Sabatier, P., Fabbri, S.C., Anselmetti, F.S., Develle, A.L., Şahin, M., Gündüz, S., Niessen, F., Gebhardt, A.C., 2021. Active Subaquatic Fault Segments in Lake Iznik Along the Middle Strand of the North Anatolian Fault, NW Turkey. Tectonics 40, e2020TC006404. https://doi.org/10.1029/2020tc006404

Reilinger, R., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Cakmak, R., Ozener, H., Kadirov, F., Guliev, I., Stepanyan, R., others, 2006. GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions. J. Geophys. Res. Solid Earth 111. https://doi.org/10.1029/2005JB004051

How to cite: Gastineau, R., Sabatier, P., Fabbri, S. C., Anselmetti, F. S., Roeser, P., Şahin, M., Gündüz, S., Gebhardt, A. C., Franz, S. O., Niessen, F., and De Sigoyer, J.: From Lake Iznik to the Marmara Sea (NW Turkey): new insights in marine and lacustrine paleoseismology., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13935, https://doi.org/10.5194/egusphere-egu23-13935, 2023.

EGU23-14121 | ECS | Posters on site | TS3.8

The impact of human factors and measurement obliquity when extracting geological slip-rate from seismically imaged normal faults. 

Billy Andrews, Zoë Mildon, and Christopher Jackson

Seismic reflection datasets can help unpick the long term (i.e., 100 kyr to Ma) slip history of active normal faults (e.g., Nicol et al., 2005). To constrain slip-rate from seismically imaged normal faults you measure the across-fault offset of stratigraphic markers of known age.  Ideally, this is undertaken parallel to the slip-vector, i.e., orthogonal to fault-strike. In many active systems this is not possible with only non-optimally orientated 2D surveys available. Here we assess how obliquity effects continuous and discontinuous fault properties (throw, heave, dip, displacement) extracted from normal faults imaged in a 3D seismic cube. We targeted ‘straight’ faults and extracted cut off data from sequentially oblique sample lines ranging from ±50˚, comparing oblique data to that extracted from optimally orientated lines. Additionally, repeat picks were undertaken on two horizons to investigate the relative importance of measurement obliquity and human error.

Oblique measurements showed different along-fault profiles compared to orientated sample lines. This causes some datasets to be statistically different, with >100 % difference occasionally observed. Continuous deformation is more prone to obliquity errors, with the measurement of an apparent dip causing heave, and therefore displacement and dip, to display large differences at high obliquity. The dip of horizons close to the fault and localised complexity at the sample location (e.g., nearby faults) are also important factors. Differences regularly exceed 20% at high obliquity and we therefore suggest obliquity should not exceed 15˚ and were this is not possible measurements are corrected using fault cut offs and local fault strike.

For repeats picks, the shape of along-fault profiles is similar; however, subtle differences exist. Variability depends on the fault and fault parameter, with greater differences observed for faults with low displacement. Several locations along the fault exceeded the population difference. This was locally associated with a particular dataset; however, trends rarely persisted along the whole fault. Factors influencing this include a) shallow folding close to the fault, b) localised complexity at the sample location, and/or c) poor imaging near the fault plane. Unexpectedly, no correlation between variability and obliquity was found. Overall, we suggest errors due to human factors could be ~10-15% for throw and 20-25% for heave, with higher errors possible.

If we consider the fault data extracted using 2D seismic lines across the Cape Egmont Fault by Nicol et al., 2005, >50% of the measurement points exceed our recommended maximum obliquity. Nicol et al. (2005) report that the maximum throw between the 3.2 and 3.7 Ma horizons as 1364 m, giving a throw rate of 0.0028 mm/yr. However, the 2D survey at this location has a measurement obliquity of 21˚. Considering our findings throw rate could range from 0.0022 to 0.0033 mm/yr due to obliquity and human factors. It is therefore important users are aware that spatio-temporal variations in slip-rate may be caused by geological controls, human errors, and measurement obliquity.

Nicol et al., 2005. Growth of a normal fault by the accumulation of slip over millions of years. J. Struct. Geol. 27 (2), 327-342.

How to cite: Andrews, B., Mildon, Z., and Jackson, C.: The impact of human factors and measurement obliquity when extracting geological slip-rate from seismically imaged normal faults., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14121, https://doi.org/10.5194/egusphere-egu23-14121, 2023.

EGU23-14659 | ECS | Orals | TS3.8

New insights into the deformation history of the Brenner Fault by the application of ESR thermochronometry 

Valentina Argante, Sumiko Tsukamoto, David Colin Tanner, Christoph von Hagke, and Christian Brandes

The Brenner Fault (BF) is an extensional low-angle fault in the eastern Alps that borders the western edge of the Tauern Window. The BF was instrumental in the exhumation of the latter, allowing the formation of the tectonic window by the uplift of the footwall. It consists of a wide shear zone, dipping to the west by an angle of 25-30°, overprinted by a brittle and steeper fault zone with a few metres thickness.  Exhumation and cooling history of its footwall has been investigated by several low temperature thermochronometry approaches, which have defined the Neogenic deformation history, using the zircon and apatite U-Th/He dating methods (Wolff et al. 2021). Because of the lack of thermochronological methods able to date the thermal history of the rocks during Quaternary, the most-recent knowledge of this fault activity has not yet been defined. New studies have shown the possible application of ESR dating on quartz as an ultralow-temperature thermochronometer, characterized by a closure temperature of 30°-90°C, and dating range of 103-107 years that is therefore a useful tool to reconstruct the tectonic deformation of the upper crust during the Quaternary. In this work, we show new structural data and the first results of ESR thermochronometry on quartz applied to rocks of BF collected across both the shear and fault zones. An en-echelon system of normal faults can be distinguished within the continuous N-S striking main fault, suggesting the probable start of brittle deformation or a following deformation phase overprinted the previous one. Moreover, ESR measurements of ten samples collected across the BF show that the ESR ages of quartz get younger toward the Tauern Window, in accordance with fission track and (U-Th)/He ages. The ESR ages indicate the Quaternary exhumation of the BF, i.e. the youngest activity of the BF. Our results promise the successful application of ESR thermochronometry in defining the youngest deformation histories of Neogenic faults in the Alpine chain.

How to cite: Argante, V., Tsukamoto, S., Tanner, D. C., von Hagke, C., and Brandes, C.: New insights into the deformation history of the Brenner Fault by the application of ESR thermochronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14659, https://doi.org/10.5194/egusphere-egu23-14659, 2023.

EGU23-15260 | ECS | Orals | TS3.8

Linking surface deformation with lower crustal shear zones: insights into drivers of millennial-scale earthquake clustering and time-dependent seismic hazard 

Zoe Mildon, Gerald Roberts, Joanna Faure Walker, Joakim Beck, Ioannis Papanikolaou, Alessandro Michetti, Shinji Toda, Francesco Iezzi, Lucy Campbell, Ken McCaffrey, Richard Shanks, Claudia Sgambato, Jenni Robertson, Marco Meschis, and Eutizio Vittori

Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies in multiple active tectonic settings, including central Greece, southern California and central Italy. However, the mechanism(s) responsible for clustering, such as fault interaction, strain-storage, and evolving dynamic topography, are poorly quantified and hence not well understood. We combine surface dating of active normal fault scarps in central Italy with stress modelling and quartz flow laws, to produce a quantified replication of observed earthquake clustering.

We study six active normal faults (including the Mt Vettore fault which ruptured during the 2016 central Italy earthquake sequence) using 36Cl cosmogenic dating. This reveals periods of high and low slip rate, which we interpret to be earthquake clusters/anti-clusters. Interestingly, these changes in slip rate (or clustering) are out-of-phase between neighbouring faults, i.e. when one fault slows down, nearby faults speed up at the same time. To explore the underlying processes driving this out-of-phase clustering behaviour, we link stress transfer caused by slip over clusters/anti-clusters on coupled fault/shear-zone structures with viscous quartz flow laws derived from laboratory experiments.

We show that differential stress fluctuates due to fault/shear-zone interactions, and that the magnitude of these fluctuations are sufficient to induce changes in strain-rate and associated slip-rate on neighbouring faults and shear zones. Our results suggest that fault/shear-zone interactions are a plausible and quantifiable explanation for earthquake clustering, thus opening possibilities for process-led and time-dependent seismic hazard assessments.

How to cite: Mildon, Z., Roberts, G., Faure Walker, J., Beck, J., Papanikolaou, I., Michetti, A., Toda, S., Iezzi, F., Campbell, L., McCaffrey, K., Shanks, R., Sgambato, C., Robertson, J., Meschis, M., and Vittori, E.: Linking surface deformation with lower crustal shear zones: insights into drivers of millennial-scale earthquake clustering and time-dependent seismic hazard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15260, https://doi.org/10.5194/egusphere-egu23-15260, 2023.

EGU23-833 | ECS | Posters on site | TS3.9

Spatio-temporal monitoring of surface deformation of the North Anatolian Fault Zone in Düzce Region by InSAR technique 

Çağkan Serhun Zoroğlu, Tülay Kaya Eken, Emre Havazlı, and Haluk Özener

The North Anatolian Fault Zone (NAFZ), that represents a transform plate boundary between the Anatolian and Eurasian plates, generated several devastating earthquakes in the 20th century. The well-known seismic sequence along the NAFZ has begun with the 1939 M7.9 Erzincan Earthquake and followed a westward migrating pattern until the 1999 M>7 Izmit-Düzce ruptures. Although there have been extensive efforts on modeling co-seismic slip properties of the recent large events along the NAFZ, possible interplay of crustal properties with fault mechanics and inter-seismic loading parameters characterized by surface deformation behavior is less known. This study aims to determine the spatio-temporal behavior of long-term surface deformation along the Düzce Fault segment of the NAFZ. We examine the effect of physical properties of the crustal structure on the inter-seismic loading and surface creep parameters in this actively deforming area. For this purpose, we adopted the well-known InSAR timeseries method using publicly available Sentinel-1 data. Sentinel-1 observations covering our study area has a time span of 8 years between 2014 and 2022. We exploit geoelectrical properties and other available seismological observations/models of the crust to be evaluated with the velocity fields inferred from InSAR time series analysis. We further compare variations in the surface deformation prior to and after the most recent November 23rd, 2022, Mw6.0 Gölyaka-Düzce earthquake by using data obtained from the analysis of both ascending and descending InSAR datasets. Our preliminary results show the slip rate of ~25 mm/yr on the Duzce Fault.

This project is funded by the Bogazici University with the BAP Project No SUP-18161.

How to cite: Zoroğlu, Ç. S., Kaya Eken, T., Havazlı, E., and Özener, H.: Spatio-temporal monitoring of surface deformation of the North Anatolian Fault Zone in Düzce Region by InSAR technique, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-833, https://doi.org/10.5194/egusphere-egu23-833, 2023.

We used 70 campaign-mode, 12 continuous and 6 high-rate GNSS and InSAR data to examine the coseismic off-fault antithetic shear triggered by the 2016 Mw 6.4 Meinong oblique thrust earthquake at the Hsinhua fault area, ~30 km northwest of the epicenter. The GNSS and InSAR data were inverted to estimate the 3D coseismic displacement field at the Tainan frontal fold-thrust belt, where the deformation is mostly affected by the directivity along the rupture front direction of the Meinong earthquake. The coseismic deformation pattern shows dominantly synthetic shear along the rupture direction, on the contrary, a nearly N-S striking, 7-km-long and 5-km-wide area indicating antithetic motion appeared at northeast of the Tainan tableland and cross-cutting the ENE-WSW-striking Hsinhua fault at a high angle. The N-S striking structure at the Hsinhua fault area reveals coseismic horizontal displacements of 3.0-7.0 cm to the southeast and vertical displacements of 0.4 to 4.4 cm, and although in the opposite direction, the magnitude of horizontal displacements of the antithetic shear are comparable to those of the synthetic motion in the adjacent areas. We calculated the static Coulomb stress change on the possible west-dipping shallow structure at the Hsinhua area due to slip on the source fault of the 2016 Meinong earthquake. The calculated static stress change is about 0.05 bar, which is negligible and very unlikely to promote the structure or bedding to slip at 30-km away for such a moderate earthquake. We also processed 6 high-rate, two 50-Hz and four 1-Hz, GNSS data for the PPP displacement and SNIVEL GPS-derived velocities, in that two stations, one 50-Hz and one 1-Hz, are located inside the block with antithetic motion. The high-rate GNSS solutions indicate that the displacements occurred at the same time when the P and S waves arrived, and velocity pulses up to 90.0 cm/s appeared at all six stations. We suggest that, as evidenced by large velocity pulses resulted from the strong directivity effect, the dynamic stress change caused by the rupture of the 2016 Meinong earthquake triggered the structure 30-km away.

How to cite: Rau, R.-J., Lai, L.-C., and Ching, K.-E.: Coseismic off-fault antithetic shear deformation in southwestern Taiwan triggered by the 2016 Mw 6.4 Meinong earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1803, https://doi.org/10.5194/egusphere-egu23-1803, 2023.

EGU23-2188 | ECS | Posters on site | TS3.9

Seismic and aseismic slip on the Central Range fault associated with the 2013 Mw 6.3 Ruisui earthquake (Taiwan) 

Hsiao-Fan Lin, Alexandre Canitano, Yu-Fang Hsu, Adriano Gualandi, Ya-Ju Hsu, Hsin-Hua Huang, and Hsin-Ming Lee

The 2013 Ruisui earthquake is the first unequivocal evidence of the seismicity activity of the Central Range Fault (CRF) in the central Longitudinal Valley in Taiwan, and hence reveals the existence of aseismic slip on the CRF. The finite-fault coseismic model obtained from the Bayesian joint inversion of GNSS and strainmeter data suggests that the rupture area is mainly distributed on a 26 km × 22 km fault plane located at the depth of 3 to 19 km with a maximum slip of about 0.5 m. A variational Bayesian independent component analysis (vbICA) technique is applied to the detrended GNSS time series to extract postseismic deformations in the near-source region. Although the afterslip distribution was not able to be well inverted due to the lack of observation on the western side of the fault plane, using rate-and-state friction rheology to simulate the surface displacements generated by the stress-driven afterslip model, we infer for the first time the existence of a shallow velocity-strengthening region on the CRF, which is capable of hosting and sustaining aseismic transient deformations over months.

How to cite: Lin, H.-F., Canitano, A., Hsu, Y.-F., Gualandi, A., Hsu, Y.-J., Huang, H.-H., and Lee, H.-M.: Seismic and aseismic slip on the Central Range fault associated with the 2013 Mw 6.3 Ruisui earthquake (Taiwan), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2188, https://doi.org/10.5194/egusphere-egu23-2188, 2023.

EGU23-2484 | ECS | Posters on site | TS3.9

The Seismogenic Potential of the Southernmost Ryukyu Subduction Zone as Revealed by Historical Earthquakes and Slow Slip events 

Sean Kuanhsiang Chen, Yih-Min Wu, and Yu-Chang Chan

The southernmost Ryukyu subduction zone may have a geodetically inferred Mw 7.5 to 8.7 megathrust earthquake in a shallow locked region, the Ryukyu fault. Paleoseismological evidence of historical earthquakes available from the last 417 years indicates that only a 1920 Mw 7.7 earthquake occurred within this magnitude range, near the downdip end of the Ryukyu fault. As slow slip events downdip the locked seismogenic zone may trigger a large subduction earthquake, we investigate how the first observed slow slip events in 2005, 2009, and 2015 initiated downdip in the Ryukyu fault interface affect the occurrence of a megathrust. We establish possible megathrust earthquake cycles from Mw 7.5 to 8.7 on the Ryukyu fault using constraints from the magnitude-frequency relation based on local historical earthquakes. This analysis shows a b value of 1.2 for magnitudes greater than Mw 7.0, which is higher than the empirical 1.0 value. This indicates that the recurrence of an event up to Mw 8.7 is longer than previously thought if the megathrust events follow the observed magnitude-frequency relation. Then, we quantify the influence of slow slip events on the triggering of a potential megathrust earthquake by calculating the static stress increase. We find that stress perturbations caused by the three slow slip events are generally consistent with the values that have triggered the large interplate earthquakes in several subduction zones. However, a large earthquake has not yet been triggered on the Ryukyu fault after a sequence of slow slip events. If the 1920 Mw 7.7 earthquake is the last rupture of the Ryukyu fault, the earthquake cycle on the Ryukyu fault is very likely in an early stage. However, this is not true if the slow slip events occur toward the end of the earthquake cycle and there has been no megathrust earthquake at the fault interface in the last 417 years, as the 2011 Mw 9.0 Tohoku earthquake. Thus, higher potential for a megathrust earthquake may occur in the southernmost Ryukyu subduction zone.

How to cite: Chen, S. K., Wu, Y.-M., and Chan, Y.-C.: The Seismogenic Potential of the Southernmost Ryukyu Subduction Zone as Revealed by Historical Earthquakes and Slow Slip events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2484, https://doi.org/10.5194/egusphere-egu23-2484, 2023.

Since the relatively recent discovery of slow slip events (SSEs), the nature of the relationship between SSEs and ordinary earthquakes has become one of the most important questions in earthquake science.  Specifically, questions as to whether SSEs decrease or increase the likelihood of large-magnitude earthquakes, whether or how slow and fast earthquakes can occur on the same fault patch, and whether SSEs are potential earthquake precursors have important implications for earthquake hazards.

Here, laboratory friction experiments on simulated fault gouges are used to gain insight into the relationship between SSEs and ordinary earthquakes.  The experiments are conducted water-saturated, at room temperature and at low pressure (10 MPa effective normal stress) to simulate the shallow, near-surface portions of major fault zones.  A key feature of these experiments is employing driving velocities as low as 5 cm/yr (1.6 nm/s) to simulate natural far-field tectonic driving rates.  From a larger dataset which includes a wide range of simulated fault gouges, four gouge types exhibited consistent stick-slip and these are analyzed further.  These materials are pyrite, hematite, gypsum, and Carrara marble powders.

Preliminary results show that the pyrite and hematite gouges exhibit small stress drops and increases in sample sliding velocity, interpreted to be SSEs, prior to stick-slips.  The SSEs occur near the peak in friction before the large stick-slip stress drop, suggesting that they are precursors.  In hematite at 5 cm/yr, the precursory SSEs exhibit stress drops on the order of 10’s of kPa and peak slip velocities within an order of magnitude of the driving rate, whereas the stick-slips exhibit stress drops of about 1 MPa and peak slip velocities of up to ~1 mm/s.  The peak stress at which the SSEs occur is within 1% of the peak stress prior to the stick-slip events.  Gypsum and Carrara marble, however, did not exhibit SSEs prior to stick-slips.  The results suggest that both slow and fast slip can occur on the same fault patch under the same conditions, and indicate the possibility that SSEs can be used as earthquake precursors in some cases.  However, the lack of precursory SSEs in the gypsum and marble gouges suggests that precursory SSE behavior is not universal and requires further investigation.

How to cite: Ikari, M.: Slow slip events as stick-slip precursors in laboratory friction experiments on simulated fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2602, https://doi.org/10.5194/egusphere-egu23-2602, 2023.

EGU23-2745 | ECS | Posters on site | TS3.9

Largest aftershock nucleation driven by afterslip during the 2014 Iquique sequence 

Yuji Itoh, Anne Socquet, and Mathilde Radiguet

Megathrust faults are known to host both seismic and aseismic slip. Laboratory experiments and numerical simulations have demonstrated that seismic-aseismic interaction can be involved in the earthquake source process such as nucleation and termination. However, models of seismic-aseismic interaction regarding the source process are still controversial because their observational evidence is limited to the small number of events among instrumentally recorded earthquakes. This is likely due to the low signal-to-noise ratio of observations and/or short duration of the nucleation and termination processes. In this study, we newly report aseismic slip accompanying intriguing seismicity during the 2014 Iquique earthquake sequence by analysing seismicity and high-rate GPS crustal deformation data.

We document early postseismic deformation during the 3 days following the M 8.1 mainshock and demonstrate that afterslip started immediately after the mainshock and led 27 hours later to the M 7.6 largest aftershock which located ~120 km further south. The interevent afterslip peaks down-dip of the mainshock with decaying moderate aftershock rate, exhibiting typical postseismic megathrust response. A local peak of the afterslip is inferred between the mainshock and the largest aftershock epicentres. This local peak suggests that this area acted as an aseismic barrier to the southward mainshock rupture propagation so that the two big quakes did not occur simultaneously.

The geodetic moment everywhere decreased with time during the 27h interevent stage with different decaying rate. The decay was slower in the afterslip area between the two epicentres than the main down-dip peak. Interestingly, the seismicity rate and associated moment release in this area increased with time during the interevent 27 hours. We propose that the largest aftershock nucleation was driven by the afterslip. Contrary to predictions of some numerical simulation models, our result implies that aseismic slip during the nucleation process does not necessarily accelerate. Our new observational discovery illuminates the mechanical connection between sequential great earthquakes mediated by aseismic slip.

How to cite: Itoh, Y., Socquet, A., and Radiguet, M.: Largest aftershock nucleation driven by afterslip during the 2014 Iquique sequence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2745, https://doi.org/10.5194/egusphere-egu23-2745, 2023.

EGU23-4151 | ECS | Orals | TS3.9

Collective behavior of asperities before large stick-slip events 

Weiwei Shu, Olivier Lengliné, and Jean Schmittbuhl

The multi-scale roughness of a fault interface is responsible for multiple asperities that establish a complex and discrete set of real contacts. Since asperities control the initiation and evolution of the fault slip, it is important to explore the intrinsic relationships between the collective behavior of local asperities and the frictional stability of the global fault system. However, such a mechanism is still elusive due to the difficulty of imaging an exhaustive spatiotemporal variability of a fault interface at depth, and the limited computational efficiency of the numerical models with heterogeneity over a large time and space domain. Here we propose a novel analog experimental approach, which allows us to capture the temporal evolution of the slip of each asperity on a faulting interface. We link the collective behavior of asperities with the mechanical response of the whole fault interface. We find that many destabilizing events at the local asperity scale occurred in the frictional strengthening stage which is conventionally considered as the stable regime of a fault. We compute the interseismic coupling to evaluate the slipping behaviors of asperities during the fault strengthening stage. Based on a high-resolution topographical map of the fault surface, we evidence that the interseismic coupling is not only dependent on the normal load and the peak height of asperity but also can be affected by the interactions between asperities through the embedding soft matrix. Furthermore, we quantify the spatiotemporal interactions of asperities as slip episodes. The significant characteristics and scaling-laws observed in natural earthquakes, such as the magnitude-frequency distribution and the moment-duration scaling, are reproduced through the catalog of slip episodes to demonstrate the effective upscaling. We give geophysical implications for the physics and mechanics of natural faults and discuss some limitations of our experimental setup.

How to cite: Shu, W., Lengliné, O., and Schmittbuhl, J.: Collective behavior of asperities before large stick-slip events, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4151, https://doi.org/10.5194/egusphere-egu23-4151, 2023.

Transient aseismic deformation is observed using dense geodetic measurements across the northern Jordan Valley Fault segment of the Dead Sea Fault. The fault was creeping until 2013 at a rate of 2.7±0.4 mm/yr. It stopped creeping between 2013 and 2018 and then started creeping again at a similar rate. These transitions between the creep and locked modes of deformation correlate well with the 2013 and 2018 seismic sequences that occurred near the tip of the northern Jordan Valley creeping segment. The creep caused the accumulation of Coulomb stresses near the fault tip, which promoted earthquake nucleation in this region. The 2013 seismic sequence was probably too small to release these stresses, and they were released during the 2018 seismic sequence, which allowed the fault to creep again. We suggest that seismic activity will continue to occur near the tip of this creeping segment.

How to cite: Hamiel, Y. and Piatibratova, O.: Interplay between seismic and aseismic deformation near the tip of a creeping segment: Insights from the northern Jordan Valley segment of the Dead Sea Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4225, https://doi.org/10.5194/egusphere-egu23-4225, 2023.

EGU23-4259 | Posters on site | TS3.9

A unified geodetic data-based earthquake catalog of Taiwan from 2006 to 2018 

Kuo-En Ching, Po-I Li, Wu-Lung Chang, Shih-Han Hsiao, Chien-Liang Chen, and Kwo-Hwa Chen

A unified geodetic data-based earthquake catalog may provide the asperity information to improve the seismic hazard assessment. Therefore, we propose a unified geodetic data-based earthquake catalog in Taiwan from 2006-2018 using the geodetic data from 333 campaign-mode GNSS stations and 19 precise leveling routes and the published continuous GNSS data to improve the spatial resolution and reliability of vertical component in coseismic displacement fields. The coordinate time series analysis was used to derive the coseismic displacements of each earthquake from the sGNSS and precise leveling data by using the least square method. This earthquake catalog involves 2006 ML 7.0 Pingtung offshore earthquake, 2010 ML 6.4 Jiashian earthquake, March 2013 ML 6.2 Nantou earthquake, June 2013 ML 6.5 Nantou earthquake, 2013 ML 6.4 Ruisui earthquake, 2016 ML 6.6 Meinong earthquake, and 2018 ML 6.2 Hualien earthquake. Then the coseismic source models of these events were evaluated by inverting the coseismic displacement fields. Based on this earthquake catalog, we provided high spatial resolution and precision in the vertical deformation and the resolution of the modeled fault dip angle is also improved. In addition, unknown coseismically reactivated anticlinal structures in SW Taiwan were discovered in this study, which may be associated with the active mud diapirs. Finally, because of abundant coseismic geodetic data adopted in this study, the spatial resolution of coseismic slip distribution is also increased in those earthquake events.

How to cite: Ching, K.-E., Li, P.-I., Chang, W.-L., Hsiao, S.-H., Chen, C.-L., and Chen, K.-H.: A unified geodetic data-based earthquake catalog of Taiwan from 2006 to 2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4259, https://doi.org/10.5194/egusphere-egu23-4259, 2023.

EGU23-4292 | ECS | Orals | TS3.9

Interactions between the dual-verging thrust faults in eastern Taiwan revealed by the 2022 Chihshang earthquake sequence and centennial historical seismicity 

Chi-Hsien Tang, Yunung Nina Lin, Hsin Tung, Yu Wang, Shiann-Jong Lee, Ya-Ju Hsu, J. Bruce H. Shyu, Yu-Ting Kuo, and Horng-Yue Chen

Nearby faults interact with each other through stress fluctuation incurred by seismic rupture, aseismic slip, and viscoelastic flow in the lithosphere. Understanding fault interactions and their temporal variation under different geometry are critical to regional seismic hazard and risk assessments. However, the complex interplay between adjacent faults is often unclear due to insufficient observations of large earthquakes with prolonged recurrence intervals. The 2022 Chihshang earthquake sequence in eastern Taiwan provides unprecedented insights into the interaction between two head-to-head thrust faults during and after a major earthquake. The Chihshang sequence was initiated by an Mw 6.5 foreshock on 17 September, followed by an Mw 7.0 mainshock 7 km to the north and 17 hours later. Based on the coseismic displacements constrained by field survey, optical satellite images, interferometric synthetic aperture radar (InSAR) data, and a dense network of Global Navigation Satellite System (GNSS) measurements, we map the major coseismic rupture on the east-verging Central Range fault (CRF), and the secondary induced slip on the west-verging Longitudinal Valley fault (LVF). The induced slip on the LVF accounts for 9-15% of the total moment release (Mw 7.1). Before the Chihshang earthquake sequence, the seismic hazard along the CRF was much overlooked due to the high seismic activity of the LVF. The 2022 Chihshang earthquake sequence demonstrates for the first time that the CRF is capable of generating earthquakes of Mw 7. The early afterslip primarily took place on the downdip extension of the CRF at great depth, indicating a contribution of ductile deformation there. Incorporating historical earthquake records over the past 120 years, we demonstrate that a rupture on the CRF or LVF reduces the stress level on the other, causing periods of seismic quiescence and an out-of-phase moment release pattern over time between the two faults. These results not only illuminate the fault geometry at the plate suture zone of eastern Taiwan, but also revise the conventional view of the nearby fault interaction. Integrating geometric complexity and fault slip history among adjacent faults in future modeling is essential for assessing realistic seismic hazards in similar structural settings.

How to cite: Tang, C.-H., Lin, Y. N., Tung, H., Wang, Y., Lee, S.-J., Hsu, Y.-J., Shyu, J. B. H., Kuo, Y.-T., and Chen, H.-Y.: Interactions between the dual-verging thrust faults in eastern Taiwan revealed by the 2022 Chihshang earthquake sequence and centennial historical seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4292, https://doi.org/10.5194/egusphere-egu23-4292, 2023.

EGU23-4704 | Orals | TS3.9

Creep and seismic rupture of a serpentinite-rich Sumatran fault segment 

Shengji Wei, Zheng-Yang Choong, Chenyu Li, Yukuan Chen, Muksin Umar, Karen Lythgoe, Arifullah Arifullah, and Andrean Simanjuntak

Earthquake is produced by shear dislocation of rocks across the fault, the frictional status and the area of locked/creeping patches on the fault thus govern the size and occurrence of damaging earthquakes. To better understand these fundamental earthquake physics issues, we deployed over 130 short period seismic nodal stations along the plate boundary type Sumatran fault in Aceh region to cover a segment that was reported to be creeping at various depths. We maintained the nodal array deployment from Jan 2020 to July 2021 by recharging the nodes every 35 days. A machine learning based earthquake detection algorithm was applied to the acquired dataset, which results in a high-resolution seismic catalog that has more than 8000 micro-seismic events. These events clearly delineate the subvertical creeping segment of the Sumatran fault and its Seulimeum branch to the northwest. The seismicity on the creeping segment is almost uniformly distributed from 3 to 12 km in depth, confirming the creeping nature of the fault segment as revealed by geodetic observations, but providing a much more accurate depth constraint. In contrast, the Seulimeum fault branch shows a much deeper seismicity at the depth range of 18 to 25 km, indicating the entire upper crust is fully locked. Sharp stepovers are observed along both strike (~10km) and strike-normal (~4km) directions between the seismicity on these fault segments. The creeping segment of the Sumatran fault, as defined by similar earthquake families, agrees well with the lenses of serpentinite, which has much smaller frictional coefficient that facilitates fault creep. Similar earthquake families show ~ km scale lineation along strike of the fault, where repeating earthquake pairs are identified. However, two shallow Mw6 earthquakes occurred on the creeping segment in the last 25 years. In particular, finite fault inversion of the 2013 Mw6.1 earthquake shows the rupture from 12 km to the surface. These observations suggest a partially creeping/locking or conditionally stable frictional status on the serpentinite-rich segment of the Sumatran fault, that should be considered in both single event and earthquake cycle simulations, as well as seismic hazard assessment.

How to cite: Wei, S., Choong, Z.-Y., Li, C., Chen, Y., Umar, M., Lythgoe, K., Arifullah, A., and Simanjuntak, A.: Creep and seismic rupture of a serpentinite-rich Sumatran fault segment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4704, https://doi.org/10.5194/egusphere-egu23-4704, 2023.

EGU23-5485 | ECS | Orals | TS3.9

Acoustic signatures of slow and fast earthquake: insights from laboratory experiments on simulated fault gouge 

Federico Pignalberi, Carolina Giorgetti, Elisa Tinti, Nathalie Casas, Chris Marone, Cristiano Collettini, and Marco Maria Scuderi

In the last decades, it has been observed that faults can slip both by slow aseismic creep and seismic events (i.e., earthquakes). Between these two slip modes, a wide variety of fault slip behavior can be observed, including low-frequency earthquakes, slow slip events and tremors. This wide variety of slip modes can radiate seismic energy at different frequencies whose content may be linked to the physical mechanisms at play. 

In the laboratory, it is possible to reproduce the entire spectrum of fault slip modes by modulating the loading stiffness of the apparatus depending on the critical fault rheologic stiffness (i.e. k/kc). This technique allows us to study, under controlled laboratory conditions, the acoustic signature of different fault slip modes to infer the physical mechanisms at their origin. To shed light on the nucleation mechanisms and seek for reliable precursors to failure of different slip modes, we performed friction experiments on powders that differ for granulometry and grain shape (i.e., glass beads with a grainsize < 150 µm; and quartz powders MinUSil with an average grain size of 10.5 µm),  to simulate fault gouge.  The experiments were conducted in a double direct shear configuration, instrumented with an array of piezoelectric sensors to record continuously Acoustic Emissions (AEs) at high recording rate (~10MHz). The experiments are performed at a constant displacement rate of 10 µm/s and using a spring to reduce the apparatus stiffness k, to match the critical fault rheological stiffness (kc). Following this procedure we  obtain slow slip events (i.e., k = kc) and fast events (i.e. k<kc). The continuous recording of the AE (a proxy for seismicity) during the seismic cycle shows an increase in the acoustic energy release while approaching failure, which is related to changes in fault physical properties associated with grain sliding/fracturing. This behavior is reflected in a systematic variation of the b-value approaching failure.

Through this work, we focus on the frequency content of AEs during the laboratory earthquakes to understand how different slip modes radiate acoustic energy. Indeed, we observe two orders of magnitude differences in frequencies associated with AEs in MinUSil and AEs in Glass Beads. The analysis of this frequency content can add important information on the deformation mechanism of fault gouge at the microscale and the size of the slip patch during laboratory earthquakes.

How to cite: Pignalberi, F., Giorgetti, C., Tinti, E., Casas, N., Marone, C., Collettini, C., and Scuderi, M. M.: Acoustic signatures of slow and fast earthquake: insights from laboratory experiments on simulated fault gouge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5485, https://doi.org/10.5194/egusphere-egu23-5485, 2023.

EGU23-6896 | ECS | Orals | TS3.9

Synchronous Slow Slip Event and Seismic Swarm in Central Ecuadorian forearc, 2013 

Alexander Wickham-Piotrowski, Yvonne Font, Marc Regnier, Quentin Bletery, Monica Segovia, Jean-Mathieu Nocquet, and Bertrand Delouis

In Ecuador, on some areas of the subduction interface, accumulated stress is released aseismically through slow slip events (SSE) synchronous to seismic swarms (S5). In the La Plata island region in the Central Ecuadorian forearc, recurrent and shallow S5 occur near a portion of the plate interface highly coupled by the subduction of a massive oceanic relief. This study shows a sequence of seismicity and SSE organization propitious to investigate the cause and effect relation-ship between both phenomena.

GPS data show that an SSE (Mw 6.3) initiated at the end of November 2012 and ruptured 2 shallow aseismic patches 25 km apart (~10 km along the vertical direction). The first patch (P1), located southeastward of the island on a moderately coupled portion of the plate interface at the leading edge of the subducting oceanic mount, has a rupture area of about 80 km2 and a maximum cumulated slip of 15 cm. Its slipping behavior is pulse-like for about a month and a half. Mid-January, the slip of the SSE suddenly accelerates. A day later, a second aseismic patch (P2), updip from P1, ruptured a highly coupled area of about 250 km2 with a maximum slip of 35 cm. This second rupture lasted 8 days and accounted for 80% of total aseismic moment. Both SSE patches stopped slipping by the end of January 2013.

The spatial-temporal distribution of 2,000 micro-earthquakes between November 2012 and February 2013 provides clues about the interface processes and highlights that faulting occurred on secondary faults during an S5. An outer rise seismic cluster with an ML 4.8 earthquake occurred on a bending fault of the Nazca Plate, 10 days before P1 started. The cluster is collinear with P1 with respect to the relative plate convergence direction, suggesting a possible causal relationship. Almost no seismicity affects the plate interface during the pulse-like development of P1 until mid-January. As the P1-SSE’s slip accelerates, an intense seismic swarm developed updip of P1 along a narrow NNE-SSW trending direction, organized in sub-vertically active structures within the subducting plate. The Coulomb stress variation computed from the cumulative slip of P1 as well as the velocity migration of the cluster (about 10 km/day) suggests that the intraplate swarm is triggered and developed at the P1-SSE’s rupture front. Synchronously to P2, seismicity developed at the Northern edge of the oceanic relief.

The seismicity swarm witnesses the reactivation of oceanic bending faults within the Nazca plate. We hypothesize that this reactivation is likely responsible of a fluid release on the plate interface, that contributed to overpressuring the highly coupled area near P2, priory saturated with fluids, which ruptures aseismically afterwards. 

How to cite: Wickham-Piotrowski, A., Font, Y., Regnier, M., Bletery, Q., Segovia, M., Nocquet, J.-M., and Delouis, B.: Synchronous Slow Slip Event and Seismic Swarm in Central Ecuadorian forearc, 2013, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6896, https://doi.org/10.5194/egusphere-egu23-6896, 2023.

EGU23-7118 | Orals | TS3.9

Fault stability transition with slip and wear production: laboratory constraints 

Corentin Noël, Carolina Giorgetti, Marco M. Scuderi, Cristiano Collettini, and Chris Marone

Large earthquakes take place on mature faults with hundreds of meters to kilometres of cumulative slip. At shallow depths, the fault zone is generally composed of non-cohesive rock wear products, often referred to as gouge. Seismic and aseismic slip occur in this fault gouge and fracture/brecciation of the wall rock and damage zone can add to the fault gouge as part of the wear process. Gouge thickness generally increases linearly with the cumulative fault shear displacement and laboratory work shows that gouge tends to stabilize fault frictional stability. Previous works show that frictional stability of simulated fault gouge varies as a function of shear displacement. The stability evolution is interpreted as a consequence of the degree of shear localisation within the simulated fault gouge: the more the deformation is localized, the more the fault slip is unstable. This implies that for bare rock surfaces, unstable behaviour is expected as the deformations are forced to be localized at the interface between the two sheared surfaces.

On natural faults at large shear displacement (or for faults having a high gouge production rate), a competition must take place between 1) the localization of the deformation at rock-on-rock surfaces, 2) the delocalization of deformation due to gouge production and wall rock brecciation, 3) fault zone lithification and frictional healing and 4) shear localization within the gouge and wear material. The competition and interaction between these phenomena are modulated by cumulative fault slip, temperature and fluid chemistry. In turn, this competition may influence the frictional stability of faults with increasing shear displacement, and thus, their potential seismic activity.

To characterise the influence of shear displacement on fault stability, constant velocity and velocity step experiments were performed to large displacement. Two initially intact rocks were chosen as starting material: a high porosity Fontainebleau sandstone and a low porosity quartzite. These samples represent very different resistances to abrasion (i.e., wear production with slip) for the same initial mineral composition (< 95% quartz), which allows us to investigate wear and wear rate on fault stability. Additionally, simulated quartz gouge was tested for comparison. Mechanical data are analysed within the rate-and-state framework, and post-mortem microscopic analyses of the sample were performed. For initially bare surface experiments a threshold shear displacement is required to transition from stable to unstable sliding. Stick-slip events (laboratory earthquakes) evolve systematically as a function of fault zone shear displacement. The inversion of the rate-and-state parameters shows that shear displacement has a dominant influence on both (a-b) and Dc. For all the faults tested, (a-b) decreases with increasing shear displacement. For high wear rates and simulated gouge, Dc decreases with increasing shear displacement. However, for low wear rate faults, Dc is constant within the tested shear displacement. These results demonstrate that, under the tested boundary conditions, fault stability varies systematically with fault maturity and in particular that shear displacement and strain localization are the dominant parameters controlling fault slip stability.

How to cite: Noël, C., Giorgetti, C., Scuderi, M. M., Collettini, C., and Marone, C.: Fault stability transition with slip and wear production: laboratory constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7118, https://doi.org/10.5194/egusphere-egu23-7118, 2023.

Western Slovenia belongs to actively deforming north-eastern Adriatic region. Active tectonic deformations of the region are a response to the anti-clockwise rotation of Adria and still ongoing collision with Eurasia. Active deformations are generally accommodated by right-lateral strike-slip and thrust faulting at rates of 2–4 mm/yr.

Monitoring of active tectonics at the junction of seismically active NW External Dinarides and Southern Alps (Slovenia) through quantification of micro-displacements of faults began in 2004, with a TM 71 extensometer situated in Postojna cave (NW External Dinarides). At present there are 12 monitoring sites with TM 71 and 72 extensometers throughout Slovenia, 9 of the instruments are stationed in natural and artificial cave environments. Cave climates are considered to be stable and thus provide a reliable environment for micro-displacement monitoring, minimizing or nullifying the effect of fluctuating temperatures on the TM instrument. The instruments were preferably installed in major regional Dinaric fault zones (NW-SE direction). Where the latter wasn’t possible, suitable locations on their ancillary faults was chosen as an indirect substitute. All the monitored TM extensometer sites display tectonic displacements, that on average range from a few microns to several tens of microns in time scales from days to years. Postojna cave is one of the most intriguing micro-displacement monitoring sites. The site exhibited large tectonic transient signals that coincided with the local swarm-like earthquake activity in the years, 2009-2010 and 2014-2015. Monitoring site of Pološka cave in Julian Alps (Southern Alps) in addition to recording tectonic displacements, inadvertently records some displacements that are not tectonic in origin, but rather exhibits slope instability, likely deep-seated gravitational slope deformation. TM extensometer micro-displacement monitoring in Slovenia is still an ongoing project.

Of late, creepmeters were installed on major active western Dinaric regional faults, in 2022. In an effort to advance the understanding of characteristics and relationships between earthquake activity and potential fault creep. A fault creep monitoring campaign, with some instruments already installed, on two major active western Dinaric faults, Idrija and Raša fault, has begun and more are pending to be installed on the Dinaric fault system.

How to cite: Novak, U.: Monitoring active tectonics via fault micro-displacements in western Slovenia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7388, https://doi.org/10.5194/egusphere-egu23-7388, 2023.

The Xianshuihe Fault Zone (XSHF) is one of the most active strike-slip faults on the eastern Tibetan Plateau. Along the NW-striking, left-lateral XSHF, as many as 8 M >7 and 29 M >6.5 earthquakes have occurred since 1700 CE. The Kangding segment is a special part of the XSHF that has four active faults and can exhibit large earthquakes. From north to south, they are the Yalahe Fault, Selaha Fault, Mugecuo South Fault, and Zheduotang Fault. However, the activity and paleoearthquake sequence of branch faults in Kangding segment remain controversial. Our detailed research is focus on the Yalahe Fault and Zheduotang Fault in Kangding segment. We mapped accurate fault traces and deformed landforms based on detailed interpretations of high-resolution imagery and aerial photographs combined with field observations. Geological and geomorphological evidence was obtained for the Holocene activities. Paleoearthquake sequence was built based on the trench work. We discussed the recurrence characteristics and slip behavior.

The Yalahe Fault follows a quasiperiodic recurrence model and Zheduotang Fault displays uniform slip behavior. From the result of paleoearthquake, the Yalahe Fault, Selaha Fault, and Zheduotang Fault experienced cascading ruptures. Therefore, the branch faults in Kangding segment have ability to generate large earthquakes in the future.

How to cite: Ma, J., Zhou, B., and Wang, M.: Latest quaternary active faulting and paleoearthquakes on the Kangding segment of the Xianshuihe Fault Zone, Eastern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7491, https://doi.org/10.5194/egusphere-egu23-7491, 2023.

EGU23-7807 | ECS | Orals | TS3.9

3D Quasidynamic cycles accelerated using Hierarchical Matrices: Role of complex fault geometry 

Jinhui Cheng, Michelle Almakari, Carlo Peruzzo, Brice Lecampion, and Harsha Bhat

Fault systems have geometrically complex structures in nature, such as stepovers, branches, and roughness. Both geological and geophysical studies indicate that the fault geometry complexities can have a first order effect on spatio-temporally complex slip dynamics. However, a vast majority of models of slip dynamics are conducted on planar faults due to algorithmic limitations. We develop a 3D quasi-dynamic slip dynamics model with Hierarchical matrices to overcome this restriction. The calculation of elastic response due to slip is a matrix-vector multiplication, which can be accelerated by using hierarchical matrices and easily multi-threaded. The computational complexity is reduced from the order of O(N2) to O(NlogN). We cross-validate our code with the SCEC run SEAS benchmark/validation exercise. With this approach, we then explore the role of fundamental geometry complexities and realistic fault geometry on slip dynamics. We also plan to analyse synthetic signals and compare with seismological and geodetic observations.

How to cite: Cheng, J., Almakari, M., Peruzzo, C., Lecampion, B., and Bhat, H.: 3D Quasidynamic cycles accelerated using Hierarchical Matrices: Role of complex fault geometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7807, https://doi.org/10.5194/egusphere-egu23-7807, 2023.

EGU23-8512 | ECS | Orals | TS3.9

Quantifying stress fields to better understand shallow tectonics of the Hikurangi Subduction Margin, NZ 

Effat Behboudi, David McNamara, and Ivan Lokmer

Quantitative stress data is crucial to understanding the mechanical behaviour of faults and the variation of  interface slip behaviours at subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variations in subduction interface and fault slip behaviour, changing from shallow slow slip events (SSEs) and creep to interseismic locking and stress accumulation moving south. We quantify the shallow (<3km) HSM stress magnitudes and orientations and utilise this new data to determine tectonic variation along the HSM and discuss how this may relate to the large-scale observation in HSM subduction dynamics. For depths below ~650 mTVD results show σ3: Sv ratios of 0.92-1 along the entire HSM, and SHmax: Sv ratios of 0.95-1.81 in the central HSM, and 0.95-2.15 in the southern HSM. Such ratios infer that below ~650 mTVD a prevalent thrust to strike-slip (σ1=SHmax) faulting regime exists along the entire HSM. Our results also reveal a NE-SW (margin-parallel) SHmax orientation in the shallow central HSM, which rotates to a WNW- ESE/NW-SE (margin-perpendicular) SHmax orientation in the shallow southern HSM.

In the central HSM, we determine the  NE-SW orientation of SHmax= σ1, which is inconsistent with  NNE/NE striking reverse faults (inferring a NW-SE oriented SHmax= σ1) in the region. This suggests that the stress state evolved over time from a contractional to a strike/oblique-slip state. This temporal change in stress state in the central HSM is likely driven by development of clockwise rotation of the Hikurangi forearc and upper plate overpressures. A contemporary NW-SE oriented SHmax in the southern HSM, associated with NNE/NE striking faults, suggests the stress regime here remains contractional over time, and is less effected by forearc rotation. The variation in stress state along the HSM spatially correlates with reported along-strike variation in subduction interface slip behaviour. This spatial correlation suggests that contemporary stresses in the overriding plate above the subduction interface may reflect contemporary elastic strain accumulation processes related to subduction megathrust locking.

 

How to cite: Behboudi, E., McNamara, D., and Lokmer, I.: Quantifying stress fields to better understand shallow tectonics of the Hikurangi Subduction Margin, NZ, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8512, https://doi.org/10.5194/egusphere-egu23-8512, 2023.

EGU23-10525 | ECS | Posters on site | TS3.9

On the use of resolution test in calculating strain rate using GNSS velocity 

Zhengfeng Zhang, Huai Zhang, and Yaolin Shi

We proposed a method to simultaneously calculate the strain rate from GNSS (Global Navigation Satellite System) velocity data and present a set of inspection standards to assess the validity and resolution of this kind of method calculating strain rate using GNSS velocity in this study. We first explain the mathematical principle of the spherical spline method. And then, we introduce the spherical spline method to fit artificial GNSS velocity data of mainland China to illustrate inspection standards. In realization, we first calculate the artificial linear velocity value of the station with a rigid rotation model, then obtain the strain rate of the Chinese mainland by the spherical spline method. In this case, the theoretical rotational strain should be zero to illustrate the generality of the spherical coordinate method. Furthermore, we construct a spherical harmony model for the resolution test. By the test criteria, the spherical spline method can reproduce the velocity and strain rate field at quite a high level, suggesting that our method has high applicability and resolution in estimating strain rate. Finally, we used measured GNSS velocity data to calculate the strain rate field in mainland China using the spherical spline method. We also analyze the correlation between the seismic mechanism and the strain rate field of earthquakes since 1960 and consider the seismic rate of mainland China.

How to cite: Zhang, Z., Zhang, H., and Shi, Y.: On the use of resolution test in calculating strain rate using GNSS velocity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10525, https://doi.org/10.5194/egusphere-egu23-10525, 2023.

EGU23-10664 | ECS | Orals | TS3.9 | Highlight

Complex laboratory earthquake sequences show asperity interactions through creep fronts and illuminate the mechanics of delayed earthquake triggering 

Sara Beth Cebry, Chun-Yu Ke, Srisharan Shreedharan, Chris Marone, David Kammer, and Gregory McLaskey

Natural earthquakes occur in clusters or sequences that arise from complex triggering mechanisms, but direct measurement of the mechanisms responsible for complex temporal sequences and delayed triggering is rarely possible. A central question involved whether delayed triggering is due to slow slip and stress transfer or local weakening/fatigue processes such as stress corrosion. We investigate the origins of this complexity and its relationship to fault heterogeneity using a biaxial loading apparatus with an experimental fault that has two dominant seismic asperities. The fault is composed of a 5 mm layer of quartz powder, a velocity weakening material common to natural faults, sandwiched between 760 mm long polymer blocks that deform similar to the way 10 meters of rock would behave. Due to the higher local normal stress and the free surface boundary condition on the sample ends, the sample behaves like two asperities, one at each end, that can fail independently. As the quartz powder was continuously sheared, the friction properties changed, and we observed a transition from steady sliding to periodic repeating earthquakes that transitioned into aperiodic and complex sequences of fast and slow events. There is also reason to believe that friction properties evolved differently on the higher normal stress asperities and made them more unstable than the center part of the laboratory sample. Sequential ruptures on the two different asperities were linked via migrating slow slip which resembles creep fronts observed in numerical simulations and on tectonic faults. The propagation velocity of the creep fronts ranged from 0.1 to 10 m/s, which is broadly consistent with the velocity of slow slip fronts inferred from migrating tectonic tremor sources. Utilizing both local stress measurements and numerical simulations, we observe that the speed and strength of creep fronts are highly sensitive to fault stress levels left behind by previous earthquakes and may serve as on-fault stress meters.

How to cite: Cebry, S. B., Ke, C.-Y., Shreedharan, S., Marone, C., Kammer, D., and McLaskey, G.: Complex laboratory earthquake sequences show asperity interactions through creep fronts and illuminate the mechanics of delayed earthquake triggering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10664, https://doi.org/10.5194/egusphere-egu23-10664, 2023.

EGU23-11133 | Posters virtual | TS3.9

Seismotectonics of the northeast Indian region based on GPS velocities, stress and strain rate  field characterization 

Raj kumar, Sanjay Kumar Prajapati, Sanjit Kumar Pal, and Om Prakash Mishra

The North-Eastern (NE) area of India is bounded by the confluence of three major tectonic plates constituting two convergent plate boundaries that essentially govern the complex seismotectonic of this Himalayan region that renders it seismically most active.  The area studied in the present work is confined to the hyperactive zone contained in the grid 20o - 30o N latitude and 88o -100o E longitude.  We analyze five years of GPS data obtained from sixteen Global Positioning System (GPS) campaign mode stations and two permanent ones deployed in the NE region. These velocities are used in estimating dilatational and shear strain rates along with the principal axes of strains. The estimated dilatational strain rate ranges from -0.13 to 0.1 microstrain/yr. In general, the velocity and strain rate fields are consistent with ongoing India-Eurasia collision and Indo-Burma subduction processes. Superposed on this pattern, we find that the intense dilatational field corresponds to the vicinage of the region between the main boundary and central Himalayan thrusts (viz. MBT, MCT), and while it is moderate in some regions of Indo Burmese Arc (IBA). Three distinct regions with high compressive strain rate distribution are delineated along the thrust zones. Two of these regions corresponds to the regions where the Kopili fault and  Tista lineament transversely converge MCT and transgresses into the MBT/MCT in Sikkim Himalaya and Bhutan Himalaya respectively and other with northern syntax region,  posing a high seismic hazard. , Some pockets of moderate strain rate near to the intersection areas of Kopili, Dauki faults and IBA, positionally relate to the high seismic zones and are consistent well with the statistical seismology, seismic topography and potential field anomalies.  Our study focuses on velocity and strain rate distribution vis-à-vis seismicity and crustal heterogeneity in the region facilitating the estimation of earthquake hazard potential.

How to cite: kumar, R., Prajapati, S. K., Pal, S. K., and Mishra, O. P.: Seismotectonics of the northeast Indian region based on GPS velocities, stress and strain rate  field characterization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11133, https://doi.org/10.5194/egusphere-egu23-11133, 2023.

EGU23-12162 | ECS | Orals | TS3.9

Earthquake Cycle of the East Anatolian Fault Between Palu-Erkenek (Eastern Türkiye): Insights of Tectonic Geodesy 

Seda Özarpacı, Uğur Doğan, Semih Ergintav, Ziyadin Çakır, Cengiz Zabcı, Alpay Özdemir, Efe Turan Ayruk, İlay Farımaz, and Mehmet Köküm

The East Anatolian Fault (EAF) is one of the continental transform systems in the Eastern Mediterranean, with a length of about 420 km between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş). The 24 January 2020 Sivrice earthquake with Mw 6.8 once again demonstrated the seismic potential of this sinistral strike-slip fault.

The recent earthquakes and discoveries creeping along the Palu Segment (~100km far to the NE of epicenter of Mw6.8 earthquake) by geodesy- and seismology-based studies increase scientific attention. The spatio-temporal characteristics of the creep observed along the Palu Segment were investigated using nearfield GPS, InSAR, and creepmeter data. After Mw6.8 earthquake, we expanded our study area towards the Pütürge Segment in the south to determine the postseismic effects of the 24 January 2020 earthquake and the kinematics of the Pütürge Segment using multidisciplinary methods (GNSS, creepmeter, InSAR, seismology, paeloseismology) and to investigate the effects on the surrounding faults.

During the first year of the project work, a new GNSS network was established in the region and these networks will be regularly measured every six months. In addition, two permanent GNSS stations were installed. Additionally, using Sentinel-1 data sets, surface deformations mapped by PSINSAR analysis. Generally, post-earthquake effects continue and deformations moved to the SW part of unbroken part of Pütürge segment and based on the creepmeter data, surface deformations still continue at the epicenter locations, following the logarithmic afterslip responce.

This work is supported by TUBITAK project number 121Y400.

 

Keywords: East Anatolian Fault, Earthquake, GNSS, InSAR

How to cite: Özarpacı, S., Doğan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özdemir, A., Ayruk, E. T., Farımaz, İ., and Köküm, M.: Earthquake Cycle of the East Anatolian Fault Between Palu-Erkenek (Eastern Türkiye): Insights of Tectonic Geodesy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12162, https://doi.org/10.5194/egusphere-egu23-12162, 2023.

EGU23-13002 | Orals | TS3.9

Rupture dynamics driven by strain localisation within fault gouges 

Nicolas Brantut and Fabian Barras

During fast slip, fault strength may decrease due to weakening mechanisms linked to constitutive properties of the deformed material (e.g., flash heating, thermal pressurisation), but also due to structural effects driven by changes in strain distribution within the shear zone. Extensive theoretical work on thermally activated weakening mechanisms, such as thermal pressurisation of pore fluids, has shown that strain can spontaneously localise in very narrow zones during rapid shear, which promotes further macroscopic weakening of faults. Here, we develop a multiscale fault model which combines a detailed description of thermal pressurisation of fault gouges within large scale elastodynamic rupture simulations. We show that spontaneous strain localisation inside the fault gouge dramatically changes the dynamics of ruptures, and makes the faults more brittle, i.e., decreases the fracture energy and thus produces faster ruptures. We provide closed-form approximations for the resulting localised width and fracture energy as functions of rupture speed. Our work provides a link between structural observations and earthquake dynamics.

How to cite: Brantut, N. and Barras, F.: Rupture dynamics driven by strain localisation within fault gouges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13002, https://doi.org/10.5194/egusphere-egu23-13002, 2023.

EGU23-13207 | Orals | TS3.9 | Highlight

Improving active faults monitoring leveraging submarine telecom fiber optic cables : first results from central Chile 

Diane Rivet, Marie Baillet, Alister Trabattoni, Martijn van den Ende, Clara Vernet, Itzhak Lior, Sergio Barrientos, Anthony Sladen, and Jean-Paul Ampuero

Subduction zones host some of the greatest diversity in seismic and aseismic fault slip behaviors, such as recurrent slow slip, non-volcanic tremors and repeating earthquakes, that are large enough to be measurable at the surface. Our understanding of the mechanisms leading to fault rupture, especially the role of aseismic slip is limited by the sparsity of instrumentation near the nucleation zone, which is predominantly located offshore away from permanent onland seismic networks.

Fiber-optic Distributed Acoustic Sensing (DAS) offers a new opportunity for long-term seismic observation of off-shore active faults by turning existing fiber-optic seafloor telecom cables into dense arrays of seismic and acoustic sensors. We conducted a one-month long DAS experiment on the northern leg of the Concón landing site of the Prat cable belonging to the GTD company. The longitudinal strain rate was recorded every 4m over a 150km-long fiber section at a temporal sampling rate of 125 Hz, which enabled us to measure low magnitude earthquakes and to locate them precisely. The earthquake catalog generated from the DAS data comprises more than 900 seismic events, which greatly extends the existing regional catalog. A preliminary analysis indicates that several seismic sequences are clustered in time and space, which include numerous events that cannot be detected by the onland seismological network. The ABYSS project will deploy this new observation tool continuously over several years, which will offer a new opportunity to better characterize the distribution of the seismicity in time and space, and will provide new constraints to the models of fault behavior during the seismic cycle. Combined with other types of analysis, such as seismic wave velocity changes monitoring at depth, these data will also provide additional constraints on the aseismic deformation of the fault zone.

How to cite: Rivet, D., Baillet, M., Trabattoni, A., van den Ende, M., Vernet, C., Lior, I., Barrientos, S., Sladen, A., and Ampuero, J.-P.: Improving active faults monitoring leveraging submarine telecom fiber optic cables : first results from central Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13207, https://doi.org/10.5194/egusphere-egu23-13207, 2023.

EGU23-13761 | Posters on site | TS3.9

The early postseismic phase of Tohoku-Oki earthquake (2011) from kinematics solutions: implication for subduction interface dynamics 

Axel Periollat, Mathilde Radiguet, Jérôme Weiss, Cédric Twardzik, Nathalie Cotte, Lou Marill, and Anne Socquet

Earthquakes are usually followed by a postseismic phase where the stresses induced by the earthquakes are relaxed. It is a combination of different processes among which aseismic slip on the fault zone (called afterslip), viscoelastic deformation of the surrounding material, poroelastic relaxation and aftershocks. However, little work has been done at the transition from the co- to the postseismic phase, and the physical processes involved.

 

We study the 2011 Mw 9.0 Tohoku-Oki earthquake, one of the largest and most instrumented recent earthquakes, using GEONET GPS data. We focus on the few minutes to the first month following the mainshock, a period dominated by afterslip. 

Based on the method developed by Twardzik et al. (2019), we process 30-s kinematic position time series and we use it to characterize the fast displacements rates that typically occur during the early stages of the postseismic phase. We quantify precisely the co-seismic offset of the mainshock, without including early afterslip, and we also characterize the co-seismic offset of the Mw 7.9 Ibaraki-Oki aftershock, which occurred 30 minutes after the mainshock. We analyze the spatial distribution of the co-seismic offsets for both earthquakes. We also use signal induced by the postseismic phase over different time windows to investigate the spatio-temporal evolution of the postseismic slip. We determine the redistribution of stresses to estimate the regional influence of the mainshock and aftershock on postseismic slip.

 

From a detailed characterization of the first month of postseismic kinematic time series, we find that the best-fitting law is given by an Omori-like decay. The displacement rate is of the type v0/(t+c)p with spatial variation for the initial velocity v0 and for the time constant c. We find a consistent estimate of the p-value close to 0.7 over most of the studied area, apart from a small region close to the aftershock location where higher p values (p~1) are observed. This p value of 0.7 shows that the evolution of the Tohoku-Oki early afterslip is not logarithmic. We discuss about the implications of these observations in terms of subduction interface dynamics and rheology. We also discuss about the different time-scales involved in the relaxation, and how this model, established for the early postseismic phase over one month, performs over longer time scales (by comparison with daily time series lasting several years).

Twardzik Cedric, Mathilde Vergnolle, Anthony Sladen and Antonio Avallone (2019), doi.org/10.1038/s41598-019-39038-z 

Keywords: Early Postseismic, Afterslip, GPS, Kinematic, Omori Law

How to cite: Periollat, A., Radiguet, M., Weiss, J., Twardzik, C., Cotte, N., Marill, L., and Socquet, A.: The early postseismic phase of Tohoku-Oki earthquake (2011) from kinematics solutions: implication for subduction interface dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13761, https://doi.org/10.5194/egusphere-egu23-13761, 2023.

EGU23-14610 | ECS | Orals | TS3.9

Slip velocity and fault stability in serpentine-rich experimental faults 

Giacomo Pozzi, Cristiano Collettini, Marco Scuderi, Elisa Tinti, Telemaco Tesei, Cecilia Viti, Chris Marone, Alessia Amodio, and Massimo Cocco

Serpentinites are poly-mineralic rocks distributed almost ubiquitously in active tectonic regions worldwide. They are composed of rheologically weak (lizardite and crysotile) and strong (e.g., magnetite and pyroxene) phases. In particular, lizardite typically shows low friction coefficients and is supposed to localise deformation along weak shear zones characterized by aseismic behaviour. Major faults hosting serpentinite lithologies are characterised by seismic activity, tremors, and other slip modes. We advance the hypothesis that low strain domains, which are enriched in rheologically strong phases, can act as potential site of nucleation of unstable slip as the result of the velocity-dependent rheology of magnetite-rich serpentinites. Through an experimental and microstructural approach, we explore the different mechanisms whose interplay controls the complex behaviour of these lithologies.

For this study we collected natural samples of lizardite-magnetite rich serpentinites within the low strain domains of the Elba Island ophiolites (Italy). Rocks were characterised, powdered, and deformed in a set of shear experiments at four different normal stresses (25, 50, 75 and 100 MPa) in the biaxial apparatus BRAVA. The experiments consist of an initial phase of sliding at 10 μm/s, a slide-hold-slide test, and two series of velocity stepping (sliding velocity from 0.1 to 300 μm/s). Fundamental parameters to quantify the frictional properties of serpentinites are individuated in the (a-b) value, the critical slip distance Dc, and the critical stiffness kc, which is derived by their combination.

The material shows friction values of ~0.4 with velocity weakening behaviour and negative frictional healing. The module of the negative (a-b) parameter increases neatly with decreasing sliding velocity while Dc decreases, causing kc to rise. At low velocities (< 3 μm/s) sliding is unstable and the fault undergoes stick-slip behaviour. This is explained by the increase of the critical stiffness to values higher than the loading system stiffness. This systematic change of mechanical properties and fault slip behaviours with sliding velocity is interpreted to be the result of the time-dependent arrangement of grains in a heterogeneous experimental fault architecture.

Back-scattered SEM images of the principal slip zones of recovered samples support this hypothesis. Elasto-frictional behaviour is controlled by the build-up of a partial (granular) load-bearing framework of strong magnetite grains, while visco-frictional rheology is controlled by the (phyllosilicatic) anastomosing and foliated lizardite matrix. At low sliding velocities, the granular phase interacts creating force chains thus promoting frictional instabilities. At higher velocities, dilation promotes the activity of throughgoing weaker phyllosilicate planes thus favouring stable slip.

Our experiments shed light on the role of fault rock heterogeneity in nucleating dynamic slip in nature as well as in controlling the slip mode during earthquakes or slow-slip events in serpentinite terrains.

How to cite: Pozzi, G., Collettini, C., Scuderi, M., Tinti, E., Tesei, T., Viti, C., Marone, C., Amodio, A., and Cocco, M.: Slip velocity and fault stability in serpentine-rich experimental faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14610, https://doi.org/10.5194/egusphere-egu23-14610, 2023.

EGU23-15559 | Orals | TS3.9

Aseismic rupture on rate-weakening faults before slip instability 

Sohom Ray and Dmitry I. Garagash

The nucleation of earthquakes relies on an interfacial instability that facilitates the transition of a slow fault slip to a faster dynamic rupture. Here, we highlight the scenarios when (rate-weakening) interfaces exhibit a phase of slow aseismic rupture—before slip instability—that propagate large distances compared to the usual nucleation sizes. This aseismic rupture propagation results from rate-weakening interfaces' response to reach a state of steady sliding when forced to slip below steady-state frictional conditions. We numerically simulate the slip cycle—aseismic rupture, instability, and dynamic rupture—driven by prototype loading configurations:

  • Slip dislocation accrues at a constant rate at one end of a finite fault with the other end (a) at the free surface of an elastic half-space and (b) completely locked (buried) in an elastic full-space.
  • Imposed slip dislocation accruing at a constant rate on both ends of a finite fault
  • A localized distribution of shear traction that increases at a constant rate.

All the above loading conditions can permit a slow aseismic rupture along the fault when the fault is initially locked: a state of interfacial slip for which the frictional strength, at the current slip rate, is significantly less than the steady-state frictional strength at the same slip rate. The slow rupture occurs in all the above loading configurations when the fault is initially locked; the subsequent transition to instability, or not, shows a fault-size dependence for configurations 1a and 1b, even when the fault exceeds the usual nucleation sizes. The cut-off fault size that permits instability after aseismic rupture also depends on the friction parameters, the extent of initial contrast from steady-state sliding, and slip conditions towards which aseismic rupture progresses. The remaining loading configurations exhibit instability whenever the fault size exceeds the usual nucleation sizes. Further, we find that slow rupture’s transition to early-stage instability happens through an intermediate breathing (spatiotemporal oscillation) type evolution of slip rate.

How to cite: Ray, S. and Garagash, D. I.: Aseismic rupture on rate-weakening faults before slip instability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15559, https://doi.org/10.5194/egusphere-egu23-15559, 2023.

EGU23-16840 | ECS | Orals | TS3.9

Interplay between aseismic and seismic slip in an earthquake swarm in Western India 

Pathikrit Bhattacharya, Kattumadam Sreejith, Vineet Gahalaut, Adhaina Susan James, Subhasish Mukherjee, Ratna Bhagat, and Ritesh Agrawal

The Palghar Swarm in Western India is unique given its occurrence within the stable continental interior, its unusually long duration (having started in November 2018 it continues unabated), and extremely high seismicity rate (up to a few hundreds of earthquakes a day). Given the small spatial extent (around 100 km2) of the swarm and the dense seismic network deployed by Indian agencies to monitor it, the swarm offers a unique opportunity to understand the processes driving swarms within the stable interior of the Indian plate which, compared to continental interiors elsewhere in the world, is unusually seismically active. The swarm clusters along two lineaments not expressed on the earth surface. Our InSAR analysis, assuming the lineaments to be subsurface faults, reveals predominantly normal dip-slip motion along both faults during several time windows between March 2019 and January 2020. We find the geodetically inferred moment to be an order-of-magnitude larger than the cumulative seismic moment throughout this time window indicating the presence of substantial aseismic slip. The aseismically slipping patches on the two faults migrate spatially and seem well correlated with the migration of seismicity. We explore the interaction between aseismic slip and the swarm seismicity by calculating resolved Coulomb Stress changes due to migrating aseismic slip on each fault and at the hypocentres of earthquakes large enough for a reliable moment tensor to be inferred. Preliminary results suggest a complex relationship between aseismic and seismic slip and a possible involvement of fluids. These results raise the question whether aseismic slip is commonly associated with earthquake swarms within the Indian continental interior and if these might be associated with deep fluid sources within the Indian continental crust.

How to cite: Bhattacharya, P., Sreejith, K., Gahalaut, V., James, A. S., Mukherjee, S., Bhagat, R., and Agrawal, R.: Interplay between aseismic and seismic slip in an earthquake swarm in Western India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16840, https://doi.org/10.5194/egusphere-egu23-16840, 2023.

EGU23-96 | ECS | Orals | TS3.10

Subduction, uplift and serpentinite in Cyprus: insights from seismicity 

Thomas Merry, Ian Bastow, David Green, Stuart Nippress, Charlie Peach, Rebecca Bell, Sylvana Pilidou, Iordanis Dimitriadis, and Freddie Ugo

Cyprus sits at the plate boundary between Anatolia in the north and Africa in the south, at a transition from oceanic subduction in the west to continental strike-slip and collision tectonics in the east. The nature of the plate boundary at Cyprus has been historically controversial and poorly understood, in part due to a lack of constraints on local seismicity. Ongoing subduction of either oceanic or continental African lithosphere is argued, with some invoking subduction of the Eratosthenes Seamount, a continental fragment to the south of Cyprus rising 2km above the sea floor, as a driver of uplift in Cyprus. At the centre and highest point of the Troodos ophiolite, which dominates the island, is the Mt Olympus mantle sequence, an outcrop of heavily serpentinised peridotite that is associated with a localised gravity low and proposed to be the top of a rising serpentinite diapir. Geophysical constraints to test these hypotheses at depth are lacking. 

 

We analyse data from a two-year deployment of five broadband seismometers along with the existing permanent network to create a new earthquake catalogue for Cyprus. We use our catalogue to constrain the first formalised 1-D velocity model for the island, improving earthquake locations. Earthquake hypocentres clearly delineate a northward-dipping African slab beneath Cyprus at 20-60 km depth. The most seismically active part of the island is at 15-20 km depth beneath the southern edge of the ophiolite, approximately the expected depth to the plate interface; thrust faulting focal mechanisms here are consistent with ongoing subduction. Hypocentral depths suggest a topography of the slab top, with the shallowest depths in the centre of the island, coincident with the greatest uplift in the overlying plate, supporting hypotheses of uplift driven by subduction of the Eratosthenes Seamount. A lack of seismicity in a 20km-wide zone at this ‘peak’ coincides with the outcropping Mt Olympus mantle sequence, and may be associated with the deep root of the proposed serpentinite diapir. 

How to cite: Merry, T., Bastow, I., Green, D., Nippress, S., Peach, C., Bell, R., Pilidou, S., Dimitriadis, I., and Ugo, F.: Subduction, uplift and serpentinite in Cyprus: insights from seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-96, https://doi.org/10.5194/egusphere-egu23-96, 2023.

EGU23-3431 | ECS | Posters on site | TS3.10

Investigation the performance of ensemble clustering techniques in latest GPS velocity field of Turkey 

Batuhan Kilic, Seda Özarpacı, and Yalçın Yılmaz

The primary active strike-slip faults in Turkey are the North and East Anatolian Faults (NAF and EAF), as well as the Ölüdeniz Fault. These transform boundaries are the result of various tectonic regimes, including the collapse of the oceanic lithosphere in the Hellenic and Cyprus arcs, continental collisions in the Zagros/Caucasus and Black Sea; Anatolia's related continental escape and expansion in western Turkey; and the Nubian, Arabian, and Eurasian plate interactions, which are Turkey's main tectonic domains. Block modeling may be useful for establishing slip rates for major faults or calculating block movements in order to better understand these regimes and deformations. Previous to block modeling, clustering analysis may be used to identify Global Positioning System (GPS) velocities in the absence of prior data.

Clustering analysis, as an unsupervised learning, is an essential technique to discover the natural groupings of a set of multivariate data. Its aim is to explore the underlying structure of a data set based on certain criteria, specific characteristics in the data, and different ways of comparing data. There have been many studies conducted in the last ten years that determine and investigate cluster/block boundaries without any a priori information by considering the similarity of GPS-derived velocities. With the rapid progress of clustering technology, various partitioning, hierarchical, and distribution-based techniques such as k-means, k-medoids, Balanced Iterative Reducing and Clustering using Hierarchies (BIRCH), Gaussian Mixture Model (GMM), and Hierarchical Agglomerative Clustering (HAC) have been utilized to find appropriate solutions that are acceptable and to determine boundaries before block modeling in geodetic studies.

Although clustering techniques are diverse and span in clustering GPS velocities, there are several common problems associated with clustering, including the inability of a single clustering algorithm to accurately determine the underlying structure of all data sets and the lack of consensus on a universal standard for selecting any clustering algorithm for a specific problem. To overcome this problem, ensemble clustering (consensus clustering) techniques that can employ from gathering the strengths of many individual clustering algorithms has been introduced (Kılıç and Özarpacı, 2022). Therefore, the objective of this study is to explore the performance of ensemble clustering techniques for clustering GPS-derived horizontal velocities. In the direction of this research, we used newly published horizontal velocities inferred from a combination of a dense network of long term GNSS observations in Turkey (Kurt et al., 2022). After that, we tested the number of clusters that best represents the data set using the GAP statistic algorithm, and we clustered GPS velocities using five different clustering techniques, including BIRCH, k-means, mini batch k-means, HAC, and spectral clustering. Then, we investigated the performance of three ensemble clustering techniques such as Cluster-based Similarity Partitioning Algorithm (CSPA), Hybrid Bipartite Graph Formulation (HBGF), and Meta-CLustering Algorithm (MCLA) by combining the strengths of five individual clustering algorithms. The outcome of this study revealed that the MCLA ensemble clustering algorithm can be utilized to determine cluster/block boundaries for this region and give enhanced results compared to single clustering techniques.

Keywords: Clustering analysis, GPS velocities, Ensemble clustering

 

How to cite: Kilic, B., Özarpacı, S., and Yılmaz, Y.: Investigation the performance of ensemble clustering techniques in latest GPS velocity field of Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3431, https://doi.org/10.5194/egusphere-egu23-3431, 2023.

EGU23-4723 | ECS | Orals | TS3.10

New 3D models for the subducted lithosphere of the Eastern Mediterranean Basin 

Sonia Yeung, Marnie Forster, Hielke Jelsma, Adam Simmons, Wim Spakman, and Gordon Lister

We present a new regional three-dimensional (3D) slab reconstruction of the Eastern Mediterranean Basin utilising the UU-P07 global tomography model and two earthquake data packages (GCMT and ISC) to produce 3D slab models to a depth of 2900 km. The model data are permissive of the presence of a south-eastward-propagating horizontal tear in the Aegean slab beneath the Rhodope Massif in the Balkanides extending towards the Thermaic Gulf. Alternatively: i) the local pattern of reduced amplitudes at ~ 200km depth could also reflect a different type of lithosphere; and/ or ii) tearing might have been preceded by down-dip stretching, resulting in abrupt thinning of the lithosphere in the extended zone.

Further to the southeast, beneath the Peloponnese and Crete, the model data support the existence of multiple subduction-transform (or STEP) faults. The subduction–transforms have since themselves begun to founder, and to roll back towards the southeast.  Even further east, beneath Cyprus, the model data appears to support the existence of yet another STEP fault, linking the slab to the east flank of the Arabia indenter.  

The 3D geometry of the subducted slabs demonstrates ‘lithological steps’ that formed as the lithosphere tore and bent while descending. Previous 3D reconstructions of the region’s deep lithospheric geometry confirmed the presence of fragmented segments but details on: i) the vertical extent of the descended slabs; and ii) the correlation between surface deformation structure and geometry at depth had yet to be established. In order to allow such a correlation, the 3D model was floated [or returned to the planet surface] utilizing a wire mesh with a Delaunay tessellation, using the program Pplates. This enabled area-balancing and therefore a more accurate approximation to the areal extent of the slabs prior to their subduction. The floated slab(s) can be incorporated in a 2D+time tectonic reconstruction to provide additional constraints not available using surface geology. The inferred tears correlate with surface structures such as the Strabo and Pliny trenches between the Hellenic Arc (Aegean Trench) and the Cyprian Trench near the Cyprus Arc, as well as with the seaward extent of the East Anatolian Fault separating the Cyprus Arc and the Arabian indenter. Such correlations between surface and deep lithospheric structures have four-dimensional (4D) implications for episodic closure of the West Tethys suture from its Mesozoic onset, through the tectonically active Tertiary to the present-day.

How to cite: Yeung, S., Forster, M., Jelsma, H., Simmons, A., Spakman, W., and Lister, G.: New 3D models for the subducted lithosphere of the Eastern Mediterranean Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4723, https://doi.org/10.5194/egusphere-egu23-4723, 2023.

EGU23-5380 | ECS | Posters on site | TS3.10

Strike-slip faulting in the western prolongation of the North Anatolian Fault: the Lichades – Oreoi Channel – Skiathos Basin lineament 

Fabien Caroir, Frank Chanier, Dimitris Sakellariou, Fabien Paquet, Julien bailleul, Louise Watremez, Virginie Gaullier, and Agnes Maillard

          The North Anatolian Fault (NAF) is one of the major active structures in the Eastern Mediterranean. Its right-lateral strike-slip fault initiated in eastern Turkey 13 Ma ago. The NAF westward propagation during Neogene and Quaternary times delineates the plate boundary between Eurasia and Anatolia-Aegean. The western termination of NAF is currently located in the North Aegean Trough (NAT) where NAF displays a NE-SW direction. In the NAT, the NAF termination is located near to the Sporades Islands. In the western prolongation of this termination, there is a wide domain characterised by distributed deformation. This major extensional area is mainly constituted by the Corinth rift and the North Evia domain, our study area. The whole zone experience a relative high seismicity with strike-slip focal mechanisms, especially right-lateral displacements along NE-SW-striking faults, which are mainly located between the North Evia domain and the Southern Thessaly.

          Our study is mostly based on new very-high-resolution seismic reflection profiles (Sparker) acquired during the WATER surveys (Western Aegean Tectonic Evolution and Reactivations) in July-August 2017 and 2021, onboard the R/V “Téthys II”. We also analysed several seismicity catalogues in order to connect the recent structures from seismic lines to active tectonics over the region. The interpretations from these datasets emphasize the evolution of the deformation of the North Evia domain, in particular, along the NE-SW striking lineament “Lichades Area – Oreoi Channel – Skiathos Basin” (L-O-S).

          The deformation in the Lichades Area is dominated by numerous active normal faults striking W-E or WNW-ESE and showing metric-scale offsets (up to 5 m.) within the Holocene sequence. One of the largest sub-active to active fault is striking NE-SW, parallel to the Oreoi Channel, and thus strongly oblique to the main rift deformation. The Oreoi Channel is a marine straight linking the Lichades Area and the Skiathos Basin. The seismic profiles highlight normal faults of different ages with a NE-SW direction. In the south-east, the Oreoi Channel is delineated by the Oreoi Fault, a mainly onshore normal fault which is dipping towards north-west. The Skiathos Basin is a newly discovered structure from our seismic dataset that is separated from the Skopelos Basin by a NE-SW striking acoustic ridge. The Skiathos Basin presents two main depocenters individualized by areas of rising acoustic basement. Some normal faults, oriented NE-SW and W-E, have been identified in the basin. Finally, many earthquakes focal mechanisms located in the Skiathos Basin and the Oreoi Channel indicate strike-slip faulting, with a right-lateral motion along the NE-SW direction.

          This detailed structural analysis together with the synthesis of seismic activity allow to propose a tectonic map with new insights on the recent deformation of the key-area “L-O-S” in the south-western prolongation of NAF. The Skiathos basin development shows indications of transtensive deformation. The Oreoi Channel is controlled by NE-SW-striking faults with a right-lateral component and the Lichades Area displays several fault with oblique direction and pure extension. We propose that the L-O-S tectonic system prolongs the NAF system and may progressively evolve as the future plate boundary.

How to cite: Caroir, F., Chanier, F., Sakellariou, D., Paquet, F., bailleul, J., Watremez, L., Gaullier, V., and Maillard, A.: Strike-slip faulting in the western prolongation of the North Anatolian Fault: the Lichades – Oreoi Channel – Skiathos Basin lineament, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5380, https://doi.org/10.5194/egusphere-egu23-5380, 2023.

Understanding the crustal structure of the Anatolian Plate has important implications for its formation and evolution, including the extent to which its high elevation is maintained isostatically. However, the numerous teleseismic receiver function studies from which Anatolian Moho depths have been obtained return results that differ by <21km at some seismograph stations. Thus, we determine Moho depth and bulk crustal Vp/Vs ratio (K) at 582 broadband seismograph stations across Anatolia, including ~100 for which H-K results have not been reported previously. We use a modified H-K stacking method in which a final solution is selected from a suite of up to 1000 repeat H-K measurements, each calculated using randomly-selected receiver functions and H-K input parameters, with the result quality assessed by ten quality control criteria. By refining Moho depth constraints, including identifying 182 stations, analysed previously, where H-K stacking yields unreliable results (particularly in Eastern Anatolia and the rapidly-uplifting Taurides), our new crustal model (ANATOLIA-HK21) provides fresh insight into Anatolian crustal structure and topography. Changes in Moho depth within the Anatolian Plate occur on a shorter length-scale than has sometimes previously been assumed. For example, crustal thickness decreases abruptly from >40km in the northern Kirsehir block to <32km beneath the Central Anatolian Volcanic Province and Tuz Golu basin. Moho depth increases from 30-35km on the Arabian Plate to 35-40km across the East Anatolian Fault into Anatolia, in support of structural geological observations that Arabia-Anatolia crustal shortening was accommodated primarily on the Anatolian, not Arabian, Plate. However, there are no consistent changes in Moho depth across the North Anatolian Fault, whose development along the Intra-Pontide and Izmir-Ankara-Erzincan suture zones was more likely the result of contrasts in mantle lithospheric, not crustal, structure. While the crust thins from ~45km below the uplifted Eastern Anatolian Plateau to ~25km below lower-lying western Anatolia, Moho depth is generally correlated poorly with elevation. Residual topography calculations confirm the requirement for a mantle contribution to Anatolian Plateau uplift, with localised asthenospheric upwellings in response to slab break-off and/or lithospheric dripping/delamination example candidate driving mechanisms.

How to cite: Ogden, C. and Bastow, I.: The Crustal Structure of the Anatolian Plate: Evidence from Modified H-K Stacking of Teleseismic Receiver Functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5855, https://doi.org/10.5194/egusphere-egu23-5855, 2023.

EGU23-6274 | Posters virtual | TS3.10

InSAR constraints on coseismic and postseismic deformation of the 2021 Ganaveh earthquake along the Zagros Foredeep fault 

Zahra Mousavi, Mahin Jafari, Mahtab Aflaki, Andrea Walpersdorf, and Khalil Motaghi

The moderate magnitude (Mw 5.8) Ganaveh earthquake, as a compressive event. occurred on 2021 April 18 in the southwest of the Dezful embayment of the Zagros Mountain belt, Iran. We process Sentinel-1 SAR images in ascending and descending geometries to investigate the coseismic deformation and its source parameters. The resultant displacement maps indicate a maximum of 17 cm of surface displacement in the satellite line of sight direction with no evidence of surface rupture. The NW-oriented elliptical fringes in coseismic ascending and descending displacement maps are in agreement with the strike of the major Zagros structures. The InSAR displacement map is inverted to evaluate the earthquake source parameters and the inversion results reveal a low-angle NE-dipping fault plane characterized by a maximum dip slip of 95 cm at ~6 km depth and a slight sinistral slip component (2.9 cm). Inversion of 39 earthquake focal mechanism (from 1968 to 2021), including the Ganaveh mainshock and its five larger aftershocks indicate a regional compressional stress regime and applying this stress on the retrieved Ganaveh fault plane leads to a minor sinistral movement confirming the geodetic results. InSAR coseismic displacement and relocated mainshock and aftershocks situate on the hanging wall of the Zagros Foredeep fault. This underlines the ZFF as the causative fault of the Ganaveh earthquake. The occurrence of Ganaveh moderate magnitude earthquake on the Zagros Foredeep fault highlights its role as the western structural boundary for recurrent Mb>5 events in the Dezful embayment.

To examine the possibility of postseismic deformation after such a moderate magnitude earthquake in Zagros, we processed and created the interferograms using the Sentinel-1 SAR images based on the SBAS timeseries analysis approach after the mainshock until the end of 2021. The time series analysis of the constructed interferograms indicates a maximum of 7 cm of postseismic deformation with a similar strike and shape as the coseismic displacement. The short-term postseismic displacement of the Ganaveh earthquake is released seismically by aftershocks. The agreement between the cumulative displacement, cumulative number of aftershocks, and their related moment release through time and the similar pattern and direction of postseismic and coseismic deformation suggest that an afterslip mechanism can be the causative mechanism of the Ganaveh postseismic motion. We estimate a maximum of 30 cm slip at a depth of ~5 km along the coseismic causative fault plane by inverting the postseismic cumulative deformation map.

How to cite: Mousavi, Z., Jafari, M., Aflaki, M., Walpersdorf, A., and Motaghi, K.: InSAR constraints on coseismic and postseismic deformation of the 2021 Ganaveh earthquake along the Zagros Foredeep fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6274, https://doi.org/10.5194/egusphere-egu23-6274, 2023.

EGU23-6612 | ECS | Posters virtual | TS3.10

Seven years of postseismic deformation following Mw 7.7 2013 Saravan intra-slab earthquake from InSAR time series 

Meysam Amiri, Andrea Walpersdorf, Erwan Pathier, and Zahra Mousavi

The 2013 April 16 Mw 7.7 Saravan earthquake, an intra-slab earthquake with a normal faulting mechanism, occurred in the Makran subduction zone, where the Arabian oceanic lithosphere subducts northward under Iran and Pakistan. To examine the postseismic displacement of the Saravan earthquake, we processed one ascending (A13) and one descending track (D122) from 2014 to 2022. We construct 1000 and 504 interferograms for ascending and descending tracks, respectively. We remove the topographic and flatten-earth phase contributions using the 30 m Shuttle Radar Topography Mission Digital Elevation Model and precise orbital parameters. We correct the turbulent component of the tropospheric delay using atmospheric parameters of the global atmospheric model ERA-Interim provided by the European Center for Medium‐range Weather Forecast. Then, we filter the generated interferograms using Goldstein’s filter and unwrapped them with a branch-cut algorithm. Once all interferograms are corrected and unwrapped, we employ an SBAS time-series analysis based on the phase evolution through time for each pixel, to retrieve the mean velocity map and displacement through time. The mean velocity map in the LOS direction indicates a sharp signal close to the Saravan earthquake suggesting that the observed signal belongs to the postseismic phase of this event. The postseismic spatial profile derived from high-quality time series analysis of Sentinel 1-A images has the opposite pattern of displacement with respect to the coseismic profile derived from Radarsat-2 interferograms. Due to the 50-80 km depth of the earthquake, observing such a deformation approximately seven years after the earthquake is interesting and consequently, we decided to study it in detail.

Large earthquakes are usually followed by transient surface deformation which reflects the rheology of the lithosphere and sub-lithospheric mantle following three mechanisms: afterslip, viscoelastic relaxation, and poroelastic rebound. In this study, we investigate the responsible mechanism of Saravan 2013 postseismic deformation through the before mentioned mechanisms. Due to the opposite sense of deformation during co and postseismic periods, we first try to assess the viscoelastic relaxation mechanism using the PSGRN/PSCMP code. We calculate the time-dependent green functions of a given layered viscoelastic-gravitational half-space for our dislocation sources at different depths using the PSGRN code. Then, we use the result as a database for PSCMP, which discretizes the earthquake's extended rupture area into several discrete point dislocations and calculates the co- and post-seismic deformation by linear superposition. For the viscoelastic mechanism modeling, it is important to consider a proper layering and velocity structure of the earth. We use the velocity structure of the GOSH seismic station implemented by the Institute for Advanced Studies in Basic Sciences to define Green’s functions. Finally, we use the distributed fault slip resulting from coseismic linear modeling as a source for viscoelastic relaxation and modeled the surface displacement for different periods after the earthquake. In the next step, we will compare the observed postseismic deformation using InSAR analysis and modeled displacement to examine whether the viscoelastic rules the postseismic movement. ‌Besides, exploring other mechanisms like afterslip and poroelastic rebound is required to fully assess the possible mechanisms.

How to cite: Amiri, M., Walpersdorf, A., Pathier, E., and Mousavi, Z.: Seven years of postseismic deformation following Mw 7.7 2013 Saravan intra-slab earthquake from InSAR time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6612, https://doi.org/10.5194/egusphere-egu23-6612, 2023.

EGU23-7674 | Posters on site | TS3.10

Geometry and kinematics of the active structures along the Latakia Ridge (Cyprus Arc) 

Michelle Vattovaz, Nicolò Bertone, Claudia Bertoni, Lorenzo Bonini, Angelo Camerlenghi, Anna Del Ben, and Richard Walker
 

The eastern Mediterranean has been the locus of catastrophic earthquakes and related tsunamis (e.g., the 365 Crete and 1222 Cyprus earthquakes). The primary sources of these seismic events are structures related to the subduction of the Nubian Plate along the Hellenic and Cyprus arcs.  A detailed identification and description of the potential tsunamigenic sources are required as part of an assessment of earthquake and tsunami hazards. Here we focus on the Cyprus Arc region, in which the oceanic crust is still subducting beneath the Anatolian Plate in the west, whereas in the eastern sector, the oceanic crust has been completely subducted, and the lower plate consists of thinned continental crust. The rates of shortening are higher in the western sector than in the east. During recent decades, new data from extensive hydrocarbon exploration have allowed us to image structures that deform the seafloor and influence the shape of the recent basins in the eastern sector. The Latakia Ridge is the most prominent tectonic structure in the area. The present-day architecture of this ridge is the result of Meso-Cenozoic convergence followed by a transpressive phase related to the northward migration of the Arabian Plate. Therefore, the present geometry of the tectonic structure results from a complex interplay between reverse and strike-slip faults. Our reinterpretation of previously published seismic reflection profiles crossing the Latakia Ridge allows us to reconstruct the geometry of the main active faults and suggests their recent kinematics. Our findings could be crucial for the reassessment of seismic and tsunami hazards in the eastern sector of the Cyprus Arc. 

How to cite: Vattovaz, M., Bertone, N., Bertoni, C., Bonini, L., Camerlenghi, A., Del Ben, A., and Walker, R.: Geometry and kinematics of the active structures along the Latakia Ridge (Cyprus Arc), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7674, https://doi.org/10.5194/egusphere-egu23-7674, 2023.

EGU23-8525 | ECS | Orals | TS3.10

Geodetic evidence for compressional interseismic deformation onshore Paliki Peninsula, Cephalonia, Greece 

Varvara Tsironi, Athanassios Ganas, Sotiris Valkaniotis, Vassiliki Kouskouna, Ioannis Kassaras, Efthimios Sokos, and Ioannis Koukouvelas

We present new geodetic (InSAR) data (ground velocities) combined with GNSS data over the Paliki Peninsula, western Cephalonia, Greece. Paliki Peninsula suffers from strong, frequent earthquakes due to its proximity to the Cephalonia Transform Fault (CTF). The CTF, a 140 km long, east-dipping dextral strike-slip fault, accommodates the relative motion between the Apulian (Africa) and Aegean (Eurasia) lithospheric plates. The most recent earthquakes of Paliki include two events during early 2014 (Ganas et al. 2015); which occurred on 26 January 2014 13:55 UTC (Mw=6.0) and 3 February 2014 03:08 UTC (Mw=5.9), respectively. Long-term monitoring of active faults through InSAR has been successfully applied in many studies so far, not only towards identifying locked or creeping sections, but also to monitor the spatial and temporal patterns of deformation of the surrounding rocks. The processing of InSAR time series analysis was held by the LiCSBAS, an open-source package. To perform an estimate of the velocity of a surface pixel through time based upon a series of displacement data, we apply an SB (small baseline) inversion on the network of interferograms, in particular we applied the N-SBAS method. Then, we transformed the ground velocities of InSAR into Eurasia-fixed reference frame using the available GNSS station velocities. The time series analysis covers the period 2016-2022. The InSAR results demonstrate that active faults onshore Paliki are oriented approximately N-S and slip with rates between 2-5 mm/yr in line-of-sight (LOS) direction. The InSAR results also show that the horizontal component of movement is dominant, therefore supporting initial evidence of the existence of right-lateral strike slip faulting onshore the peninsula. The velocity pattern of the NW part of the peninsula also reveals a possible post-seismic motion along the ruptured plane of the 3 February 2014 earthquake. In addition, the time series analysis has identified other possible active structures (both strike-slip and thrust) onshore the Paliki peninsula and across the gulf of Argostoli that are confirmed by field geological data. The coastal town of Lixouri undergoes uplift (a few mm/yr) as it observed with positive LOS values in both satellite imaging geometries. Through the East-West velocity cross-sections, we determine several velocity discontinuities (block boundaries?) which are possibly bounded by active faults and/or crustal flexure. Overall, our results indicate a complex deformation pattern onshore the Paliki peninsula.

How to cite: Tsironi, V., Ganas, A., Valkaniotis, S., Kouskouna, V., Kassaras, I., Sokos, E., and Koukouvelas, I.: Geodetic evidence for compressional interseismic deformation onshore Paliki Peninsula, Cephalonia, Greece, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8525, https://doi.org/10.5194/egusphere-egu23-8525, 2023.

Plate boundary deformation zones represent a challenge in terms of understanding their underlying geodynamic drivers. Active deformation is well constrained by GNSS observations in the SW Balkans, Greece and W Turkey, and is characterized by variable extension and strike slip in an overall context of slow convergence of the Nubia plate relative to stable Eurasia. Diverse, and all potentially viable, forces and models have been proposed as the cause of the observed surface deformation, e.g., asthenospheric flow, horizontal gravitational stresses (HGSs) from lateral variations in gravitational potential energy, and rollback of regional slab fragments. We use Bayesian inference to constrain the relative contribution of the proposed driving and resistive regional forces.

 

Our models are spherical 2D finite element models representing vertical lithospheric averages. In addition to regional plate boundaries, the models include well-constrained fault zones like north and south branches of the North Anatolian Fault, Gulf of Corinth and faults bounding the Menderes Massif. Boundary conditions represent geodynamic processes: (1) far-field relative plate motions; (2) resistive fault tractions; (3) HGSs mainly from lateral variations in topography and Moho topology; (4) slab pull and trench suction at subduction zones; and (5) active asthenospheric convection. The magnitude of each of these is a parameter in a Bayesian analysis of ~100,000 models and horizontal GNSS velocities. The search yields a probability distribution of all parameter values including model error, allowing us to determine mean/median parameter values, robustly estimate parameter uncertainties, and identify tradeoffs (i.e., parameter covariances).

 

The average viscosity of the overriding plate is well resolved 4x10^22 Pa.s, which is higher than published models without faults. Westward velocities of Anatolia and significant trench suction forces from the Hellenic slab, including along the Pliny-Strabo STEP Fault, are required to reproduce the observations. Slab pull and convective tractions have a small imprint on the observed deformation of the overriding plate. HGSs are less important for fitting the regional pattern of velocities. Resistive tractions on most plate boundaries and faults are low.

How to cite: Govers, R., Herman, M. W., van de Wiel, L., and Nijholt, N.: Probabilistic Assessment of the Causes of Active Deformation in Greece, western Anatolia, and the Balkans Using Spherical Finite Element Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8603, https://doi.org/10.5194/egusphere-egu23-8603, 2023.

EGU23-8915 | Orals | TS3.10 | Highlight

Aseismic slip behavior along the central section of the North Anatolian Fault: insights from geodetic observations. 

Jorge Jara, Romain Jolivet, Alpay Ozdemir, Ugur Dogan, Ziyadin Çakir, and Semih Ergintav

Recent observations suggest seismogenic faults release elastic energy through a wide variety of slip modes covering a spectrum from sudden rapid earthquakes to slow aseismic slip. Aseismic slip releases energy very slowly without radiating seismic waves and plays an important role in the initiation, propagation, and arrest of large earthquakes. Aseismic slip is thought to be influenced by the presence/migration of fluids, stress interactions through fault geometrical complexities, and/or fault material heterogeneities. Descriptions of occurrences of aseismic slip at the surface and depth are hence required to feed into models and eventually characterize the factors controlling the occurrence of slow, aseismic versus rapid, seismic fault slip.

We focus on the central segment of the North Anatolian Fault, which has been creeping since at least the 1950s. This region was struck by the Mw 7.3 Bolu/Gerede earthquake in 1944, and since then, no earthquake of magnitude greater than 6 has been recorded. During the 1960s, aseismic slip was discovered as a wall built across the fault in 1957 was being slowly offset. Geodetic studies (InSAR, GNSS, and creepmeters) focused on capturing and analyzing aseismic slip around the village of Ismetpasa. Creepmeter measurements during the 1980s and 2010s, along with InSAR time series analysis, suggest that aseismic slip occurs episodically rather than persistently.

We use Sentinel-1 time series and GNSS data to provide a spatio-temporal description of the kinematics of fault slip. We show that aseismic slip observed at the surface is coincident with a shallow locking depth and that slow slip events with a return period of 2.5 years are restricted to a specific section of the fault. We contrast such results with GNSS time series analysis of a local network, confirming our findings. In addition, we discuss the potential rheological implications of our results, proposing a simple alternative model to explain the local occurrence of shallow aseismic slip at this location.

How to cite: Jara, J., Jolivet, R., Ozdemir, A., Dogan, U., Çakir, Z., and Ergintav, S.: Aseismic slip behavior along the central section of the North Anatolian Fault: insights from geodetic observations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8915, https://doi.org/10.5194/egusphere-egu23-8915, 2023.

EGU23-9062 | Posters on site | TS3.10

Source Model of the 2022 Mw6.0 Gölyaka, Düzce (Western Turkey) Earthquake 

Ali Ozgun Konca, Sezim Ezgi Guvercin, and Figen Eskikoy

On November 23, 2022 an Mw6.0 earthquake struck northwest Turkey. The location of this earthquake is along the boundary of the northeast striking Karadere and east striking Düzce segments of the North Anatolian Fault. Remarkably the area had already ruptured twice during the 1999 Mw7.4 Izmit and Mw7.1 Düzce earthquakes. In this study we analyzed the seismicity, aftershocks and the co-seismic rupture of the 2022 earthquake. Relocated aftershocks reveal a north dipping rupture plane consistent with the previously known fault segments. We modeled the co-seismic slip using InSAR data from Sentinel-1 satellite and near-source seismic waveforms. The kinematic model shows an up-dip bilateral rupture with majority of the slip to the west of the hypocenter.  While the slip is primarily right-lateral there is significant normal component. The fact that the rupture occurred at the junction of two segments, its depth extent and oblique rake angle implies that the 2012 earthquake ruptured along a geometrical complexity that sustained a remanent slip deficit after the 1999 earthquakes.

How to cite: Konca, A. O., Guvercin, S. E., and Eskikoy, F.: Source Model of the 2022 Mw6.0 Gölyaka, Düzce (Western Turkey) Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9062, https://doi.org/10.5194/egusphere-egu23-9062, 2023.

EGU23-9268 | ECS | Orals | TS3.10

The sprawl of the External Hellenides: from post-Alpine collapse to present-day kinematics 

Simon Bufféral, Pierre Briole, Nicolas Chamot-Rooke, and Manuel Pubellier

During the Neogene, the Aegean domain underwent intense deformation, leading to a thinning by a factor of two or more of the Alpine orogenic prism. Today, tectonic velocity gradients are still among the fastest in Europe due to the Anatolian extrusion induced by the Arabian indentation and by the Hellenic slab retreat. The present-day deformation essentially localizes in the subduction backstop. With respect to the central Aegean, which is almost stable today, this still-thick buttress has remained at a much earlier and brittle deformation stage. This is particularly the case in the ~east–west-extending External Hellenides (Southern Greece), shaped by a series of major NNW–SSE-oriented normal faults.

  • How has the crustal deformation been accommodated by the various fault systems present in the Peloponnese since the Paleogene?
  • Which of those fault systems are still active today?
  • To what extent can boundary forces such as the Hellenic slab pull be sufficient to explain this extension?

Thanks to a significant increase in the GNSS network density in the Peloponnese, we present an updated local strain field. The resulting strain confirms the ~east–west sprawl of the External Hellenides, with extension also, to a lesser extent, in the other directions. Through identifying low-angle detachments by field and satellite morpho-structural analysis, we show that this spreading has been occurring since the Pliocene, mostly by reusing décollement layers of the Alpine nappes as extensional structures. We suggest that the main high-angle normal faults existing in the Peloponnese correspond to a localization of the extension in the weakest azimuth dictated by the Alpine backbone. We propose that this surface sprawl results not only from the Hellenic slab retreat but also from the exhumation of the deep Peloponnesian stacked units, and the subsequent crustal gravity collapse.

How to cite: Bufféral, S., Briole, P., Chamot-Rooke, N., and Pubellier, M.: The sprawl of the External Hellenides: from post-Alpine collapse to present-day kinematics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9268, https://doi.org/10.5194/egusphere-egu23-9268, 2023.

EGU23-9851 | ECS | Posters on site | TS3.10

Preliminary Results from Comprehensive Seismic and Geodetic Observations Around the Caucasus Region 

Sezim Ezgi Güvercin, Mironov Alexey Pavlovich, Seda Özarpacı, Hayrullah Karabulut, Vadim Milyukov, Semih Ergintav, Cengiz Zabcı, Ali Özgün Konca, Uğur Dogan, Ruslan Dyagilev, Steblov Grigory Mikhailovich, and Eda Yıldıran

The active deformation and shortening in the Caucasus region are predominantly driven by the collision of Arabian and Eurasian plates where significant differences in the surface uplift, large basins, variations on the plate motion rates along the convergence are observed. To the west of the region the lack of sub-crustal seismic activity, low velocity anomalies in tomographic images and the decreased rate of shortening imply that western Caucasus has different kinematics compared to its east. Previous studies suggested that either slab detachment or lithospheric delamination is responsible for the complex deformation beneath the Caucasus. Large uncertainties due to sparse and non-uniform data coverage for local and regional tomography studies, diffuse seismicity, significant crustal thickness variations and strain field lead to poor understanding on the formation and active deformation of this fold and thrust belt. In this study, we aim to obtain a joint database collected from Turkey and Russia between 2007 and 2020. A waveform data base is created from 37 stations in Russia and more than 60 stations in Turkey. An improved seismicity catalog is built including relocated earthquakes with more than 100 stations. The crustal thickness map of the study region is updated by receiver function analysis using stations both from Turkey and Russia covering the Greater Caucasus. A high resolution Pn tomographic model is computed to determine velocity perturbations in uppermost mantle. The data from GNSS (Global Navigation Satellite System) stations both in Turkey and Russia are processed together for the first time and used to map the updated strain field. The new strain field is correlated with the crustal stress orientations from earthquake source mechanisms. New block models are determined for the Caucasus region in order to better estimate the block boundaries and related slip rates. By the improved azimuthal coverage of the seismic and geodetic stations the uncertainties of vertical and horizontal earthquake locations and the velocity field are reduced, thus; a reliable source for the geometry and kinematics of the faults in the Caucasus region is obtained. With the improved seismological and geodetic observations, reliable inferences on the seismic hazard and earthquake potential is expected for the region.

 

 

How to cite: Güvercin, S. E., Pavlovich, M. A., Özarpacı, S., Karabulut, H., Milyukov, V., Ergintav, S., Zabcı, C., Konca, A. Ö., Dogan, U., Dyagilev, R., Mikhailovich, S. G., and Yıldıran, E.: Preliminary Results from Comprehensive Seismic and Geodetic Observations Around the Caucasus Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9851, https://doi.org/10.5194/egusphere-egu23-9851, 2023.

EGU23-9911 | ECS | Posters virtual | TS3.10

Shallow deformation of the Mw 4.9 Khonj earthquake (6 January 2017) in the Zagros Simply Folded Belt, Iran 

Aram Fathian, Cristiano Tolomei, Dan H. Shugar, Stefano Salvi, and Klaus Reicherter

On 6 January 2017, an Mw 4.9 earthquake occurred c. 40 km northeast of the city of Khonj, in the Simply Folded Belt (SFB) of the Zagros, southwestern Iran. Using the JAXA ALOS-2 PALSAR as well as the Copernicus Sentinel-1 SAR images, we applied two-pass Interferometric Synthetic Aperture Radar (InSAR) to acquire the corresponding surface deformation of the Khonj earthquake. The fault plane solutions confirm the thrust mechanism for the earthquake that has a shallow depth of 5 km resulting in a subtle, permanent surface deformation visible through InSAR displacement maps. Concentric fringes on the interferograms in both ascending and descending geometries indicate the rupture has not reached the surface; nonetheless, they indicate shallow seismic deformation within the Zagros SFB. The Khonj earthquake is one of the smallest events with a discernible InSAR deformation field of c. 5–10 cm in the satellite line-of-sight (LOS). The epicenter of the earthquake is located in a plain between the northwestern and southeastern hinges of the Qul Qul and Nahreh anticlines. The source modeling from the InSAR data quantifies an NW-SE-striking fault either dipping to the northeast or the southwest. This shallow event is aligned with a zone in which the only documented surface ruptures in the Zagros—i.e., the Furg and Qir-Karzin earthquakes—are located.

How to cite: Fathian, A., Tolomei, C., H. Shugar, D., Salvi, S., and Reicherter, K.: Shallow deformation of the Mw 4.9 Khonj earthquake (6 January 2017) in the Zagros Simply Folded Belt, Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9911, https://doi.org/10.5194/egusphere-egu23-9911, 2023.

EGU23-10222 | Posters on site | TS3.10

Broadband seismological analyses in the Eastern Mediterranean: implications for late-stage subduction, plateau uplift and the development of the North Anatolian Fault 

Ian Bastow, Christopher Ogden, Thomas Merry, Rita Kounoudis, Rebecca Bell, Saskia Goes, and Pengzhe Zhou

The eastern Mediterranean hosts extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this region using broadband seismology: mantle tomographic imaging (Kounoudis et al., 2020), SKS splitting analysis of seismic anisotropy (Merry et al., 2021), and receiver function study of crustal structure (Ogden & Bastow, 2021). Anisotropy and crustal structure are more spatially variable than recognised previously, but variations correspond well with tomographically-imaged mantle structure. Moho depth correlates poorly with elevation, suggesting crustal thickness variations alone do not explain Anatolian topography: a mantle contribution, particularly in central and eastern Anatolia, is needed too. Lithospheric anisotropy beneath the North Anatolian Fault reveals a mantle shear zone deforming coherently with the surface, while backazimuthal variations in splitting parameters indicate fault-related lithospheric deformation. Anisotropic fast directions are either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone.

How to cite: Bastow, I., Ogden, C., Merry, T., Kounoudis, R., Bell, R., Goes, S., and Zhou, P.: Broadband seismological analyses in the Eastern Mediterranean: implications for late-stage subduction, plateau uplift and the development of the North Anatolian Fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10222, https://doi.org/10.5194/egusphere-egu23-10222, 2023.

EGU23-10733 | ECS | Orals | TS3.10

Asymptomatic lithospheric drip driving subsidence of Konya Basin, Central Anatolia 

Julia Andersen, Ebru Şengül Uluocak, Oguz Göğüş, Russell Pysklywec, and Tasca Santimano

Geological and geophysical observations show instances of surface subsidence, uplift, shortening, and missing mantle lithosphere inferred as manifestations of the large-scale removal of the lower lithosphere. This process—specifically by viscous instability or lithospheric “drips” —is thought to be responsible for the removal or thinning of the lithosphere in plate hinterland settings such as: Anatolia, Tibet, Colorado Plateau and the Andes. In this study, we conduct a series of scaled, 3D analogue/laboratory experiments of modeled lithospheric instability with quantitative analyses using the high-resolution Particle Image Velocimetry (PIV) and digital photogrammetry techniques. Experimental outcomes reveal that a lithospheric drip may be either ‘symptomatic’ or ‘asymptomatic’ depending on the magnitude and style of recorded surface strain. Notably, this is controlled by the degree of coupling between the downwelling lithosphere and the overlying upper mantle lithosphere. A symptomatic drip will produce subsidence followed by uplift and thickening/shortening creating distinct ‘wrinkle-like’ structures in the upper crust. However, the ‘symptoms’ of an asymptomatic drip are subdued as it only yields subsidence or uplift, with no evidence of shortening in the upper crust. Here, we combine analogue modelling results with geological and geophysical data to demonstrate that the Konya Basin in Central Anatolia (Turkey) is one such example of an asymptomatic drip. Global Navigation Satellite System (GNSS) measurements reveal elevated vertical subsidence rates (up to 50 mm/yr) but no well-documented crustal strain or structural features such as fold-and-thrust belts. This work demonstrates that different types of lithospheric drips may exist since the Archean, and there may be instances where the mantle lithosphere is dripping with no distinct manifestations of such a process in the upper crust.

How to cite: Andersen, J., Şengül Uluocak, E., Göğüş, O., Pysklywec, R., and Santimano, T.: Asymptomatic lithospheric drip driving subsidence of Konya Basin, Central Anatolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10733, https://doi.org/10.5194/egusphere-egu23-10733, 2023.

EGU23-11399 | Orals | TS3.10 | Highlight

Geometry and kinematics of active normal faulting on Crete; implications for Hellenic subduction slab retreat 

Andy Nicol, Vasiliki Mouslopoulou, John Begg, Vasso Saltogianni, and Onno Oncken

The eastern Mediterranean island of Crete is located on the overriding plate of the Hellenic subduction thrust which is curved and changes strike from ~170° to ~50° in a west to east direction. Crete is located in the zone of maximum curvature of the subduction thrust. Basin and range topography together with prominent limestone scarps indicate that Quaternary deformation at the ground surface on Crete is dominated by normal faults with slip rates of up to ~1 mm/yr. These active faults comprise two primary sets that strike N-NNE (0-30°) and E-ESE (90-120°), with the more easterly faults dominating in southern Crete. Each fault set is characterised by dip slip and together they accommodate coeval W-WNW and N-NNE crustal extension. The E-ESE normal faults are approximately parallel to the strike of the subducting North African plate and form part of a regional fault system that swings in strike in sympathy with depth contours on the top of the concave northwards plate. By contrast, N-NNE normal faults are sub-parallel to the line of maximum curvature on the subduction thrust. These geometric relationships support the view that normal faulting on Crete formed, at least partly, in response to Cenozoic slab retreat (e.g., Jolivet et al., 2013), which continued into the Quaternary. In this model contemporaneous multi-directional crustal extension on Crete is driven by geologically simultaneous westward and southward retreat of the slab.

 Jolivet, L., Faccenna, C., Huet, B., Labrousse, L., Le Pourhiet, L., Lacombe, O., et al. (2013). Aegean tectonics: Strain localisation, slab tearing and trenchretreat. Tectonophysics, 597–598, 1–33. https://doi.org/10.1016/j.tecto.2012.06.011

How to cite: Nicol, A., Mouslopoulou, V., Begg, J., Saltogianni, V., and Oncken, O.: Geometry and kinematics of active normal faulting on Crete; implications for Hellenic subduction slab retreat, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11399, https://doi.org/10.5194/egusphere-egu23-11399, 2023.

EGU23-11592 | ECS | Posters on site | TS3.10

High-resolution N-S deformation of active normal faults in SW Turkey derived from Sentinel-1 InSAR time series 

Manuel-L. Diercks, Ekbal Hussain, Zoë K. Mildon, and Sarah J. Boulton

Active tectonics in south-western Turkey is dominated by rapid N-S extension at a rate of 22 mm/a (e.g. Aktug et al., 2009), which is mostly accommodated by several large E-W trending, graben-forming normal fault zones. Seismic activity of these fault zones appears to vary both spatially and temporally (e.g. Leptokaropoulos et al., 2013). Generally, Synthetic Aperture Radar interferometry (InSAR) is a useful technique to assess the recent deformation of fault zones and locate potentially creeping segments. However, as Sentinel-1 satellites orbit the Earth on approximately N-S directed tracks, line-of-sight (LOS) velocities are relatively insensitive to N-S deformation and therefore it can be a challenge to resolve deformation in this direction. With its rapid N-S extension, the SW-Anatolian graben system is a suitable study area to develop an approach to derive a tectonic N-S deformation signal from Sentinel-1 InSAR.

We compute InSAR LOS velocities from Sentinel-1 data for all ascending and descending frames covering the study area. A least-squares inversion is used to decompose the LOS velocities into north, east and up components. To reduce the number of unknowns, we constrain the E-W component with interpolated GNSS velocities, so we effectively only invert for N-S and up components. Mathematically, the inversion requires at least two time series products to be solved, but given the low sensitivity of InSAR to N-S deformation, we use three Sentinel-1 scenes, with at least one from ascending and descending tracks to increase the accuracy. As a result, this approach is limited to regions where either two ascending or two descending tracks are overlapping, which fortunately covers most of the large grabens in Western Turkey. Using our new technique, we compute a smooth velocity field for all three components of motion (N-S, E-W and up-down) on a N-S swath crossing all major E-W-trending normal fault systems in the region, at a pixel resolution of about 100x100 m. With some improvements to come, we are able to calculate swath profiles displaying surface deformation across all fault zones. Our approach resolves both the broad scale velocity field and localised deformation differences across individual fault zones.

Compared to GNSS velocities, InSAR has a much higher resolution, allowing us to infer localised information on surface deformation in the vicinity of major fault zones instead of just quantifying a broad, regional trend. This can be used to assess individual fault zones, quantify changes in N-S surface deformation across faults and compare these results with recorded seismicity to reveal detailed insights into the active deformation of the largest fault zones in the region. Once the technique is established, we aim to expand the studied region. This study shows that overlapping tracks of Sentinel-1 data are a valuable resource, enabling detailed analysis of fault zones that are otherwise hard to assess by InSAR data from N-S orbiting satellite systems.

References:

Aktug et al. (2009). Journal of Geophysical Research, 114(B10), B10404. https://doi.org/10.1029/2008JB006000

Leptokaropoulos et al. (2013) Bulletin of the Seismological Society of America, 103(5), 2739–2751. https://doi.org/10.1785/0120120174

How to cite: Diercks, M.-L., Hussain, E., Mildon, Z. K., and Boulton, S. J.: High-resolution N-S deformation of active normal faults in SW Turkey derived from Sentinel-1 InSAR time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11592, https://doi.org/10.5194/egusphere-egu23-11592, 2023.

EGU23-12210 | Orals | TS3.10

Active extensional tectonics along the Mirabello Gulf – Ierapetra Basin depression (Eastern Crete, Greece) 

Konstantinos Soukis, Stelios Lozios, Emmanuel Vasilakis, Varvara Antoniou, and Sofia Laskari

The present-day geotectonic regime of Crete Island is mainly controlled by the processes occurring along the seismically active Hellenic subduction zone, e.g., the fast convergence between Africa - Eurasian plates (at a rate of 36 mm/yr) and the simultaneous SSW-ward retreat of the subducting slab. The result is a large south-facing orogenic wedge extending from the southern coast of Crete up to the Hellenic subduction trench to the South. Contractional structures (thrusts, folds, and duplexes) have formed in the deeper parts of the wedge and caused the thickening of the crust. This has led to substantial regional uplift and extension of the upper part of the wedge. Hence, two significant arc-parallel and arc-normal sets of active normal faults crosscut the Cretan mainland, affecting the entire alpine nappe pile. These faults have created a characteristic basin and range topography expressed through impressive E-ESE and N-NNE horst and graben structures bounded by fault zones with segments ranging from 5 to more than 20 km.

 

Detailed fault mapping of the Mirabello Gulf – Ierapetra Basin depression revealed a dominant NNE-SSW fault system, occupying the central and northern part, and a subordinate E-W to ESE-WNW system, observed mainly along the southern coastal zone. In the ESE margin, the deformation is localized mainly along the 30 km long NNE-SSW Kavousi – Ieraptera fault zone. On the other hand, in the WNW margin, the deformation is distributed in a larger population of relatively minor faults, organizing in more complex second-order horst and graben structures. In the southern part of the Ierapetra Basin, the E-W to ESE-WSW faults are significantly less and concern 2-3 specific zones. Specific morphological structures such as the remarkable range high, the deep V-shaped gorges, the large scree thickness, and the prominent post-glacial fault scarps produced along the basin margins indicate the intensive activity of these faults during the Quaternary. The NNE-SSW fault system seems to be younger and more active, given that i) intersects the E-W or ESE-WNW faults of the southern part, ii) produces significant fault scarps and polished fault surfaces in the cemented scree along the fault zone, and iii) kinematically is compatible with the recent and present-day focal mechanisms (e.g., the 2021 Arkalochori earthquakes). In conclusion, the Ierapetra Basin has formed and developed through an overall E-W extension parallel to the present-day geometry of the arc.

How to cite: Soukis, K., Lozios, S., Vasilakis, E., Antoniou, V., and Laskari, S.: Active extensional tectonics along the Mirabello Gulf – Ierapetra Basin depression (Eastern Crete, Greece), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12210, https://doi.org/10.5194/egusphere-egu23-12210, 2023.

EGU23-12258 | ECS | Orals | TS3.10

A new and uniformly processed GNSS-velocity field for Turkey 

Ali Değer Özbakır, Ali Ihsan Kurt, Ayhan Cingöz, Semih Ergintav, Uğur Doğan, and Seda Özarpacı

The Anatolia–Aegean domain represents a broad plate boundary zone, with the deformation accommodated by major faults bounding quasi-low deforming units. The main characteristics of the Anatolia-Aegean deformation were identified using a GNSS-derived velocity field. Recent advancements in GNSS measurements and networks have improved the spatial resolution of the Anatolia-Aegean deformation field, however, for a better understanding of the deformation, interstation distances that are smaller than fault-locking depth and consistent data processing using a single reference system are needed. Our goal is to address this gap and produce a uniform velocity solution.

In this study, we processed the time series of 836 stations, of which 178 are published for the first time with sub-millimeter accuracy. With a period of up to 28 years, we present the most accurate velocity field with increased spatial and temporal resolution and homogeneity. We used the improved coverage of the velocity field to calculate strain accumulation on the North and East Anatolian Faults.  Modeled slip rates vary between 20 and 26 mm/yr and 9.7 and 11 mm/yr for the North and East Anatolian faults, respectively. Further analysis of the data can help better understand the kinematics of continental deformation in general, and test outstanding hypotheses about the kinematics and dynamics of the Anatolia - Aegean domain in particular.

How to cite: Özbakır, A. D., Kurt, A. I., Cingöz, A., Ergintav, S., Doğan, U., and Özarpacı, S.: A new and uniformly processed GNSS-velocity field for Turkey, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12258, https://doi.org/10.5194/egusphere-egu23-12258, 2023.

EGU23-12408 | Posters on site | TS3.10

Evaluating the seismic activity of the Adriatic Sea region 

Orecchio Barbara, Debora Presti, Silvia Scolaro, and Cristina Totaro

The seismic activity occurred in the last decades in the Adriatic Sea region has been investigated by means of new hypocenter locations, waveform inversion focal mechanisms and seismogenic stress fields. After a preliminary evaluation of seismic distribution, the Bayloc non-linear probabilistic algorithm has been used to compute hypocenter locations for the most relevant seismic sequences and to carefully evaluate location quality and seismolineaments reliability. We also provided an updated database of waveform inversion focal mechanisms integrating data available from official catalogs with original solutions we properly estimated by applying the waveform inversion method Cut And Paste. This database has been used to compute seismogenic stress fields through different inversion algorithms. The seismic activity, mainly concentrated in the Central Adriatic region, indicates high fragmentation and different patterns of deformation. In particular, our results highlighted the presence of two NW-SE oriented, adjacent volumes: (i) the northeastern one, characterized by pure compressive domain with NNE-trending axis of maximum compression, and mainly W-to-NW oriented seismic sources; (ii) the southwestern one, characterized by a transpressive domain with NW-trending axis of maximum compression, where thrust faulting preferentially occurs on ENE-to-NE oriented planes and strike-slip faulting on E-W ones. We jointly evaluated seismic findings of the present study and kinematic models proposed in the literature for the Central Adriatic region. The present analysis, furnishing new seismological results provide additional constraints useful for better understanding and modeling the seismotectonic processes occurring in the Adriatic Sea region.

How to cite: Barbara, O., Presti, D., Scolaro, S., and Totaro, C.: Evaluating the seismic activity of the Adriatic Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12408, https://doi.org/10.5194/egusphere-egu23-12408, 2023.

EGU23-12937 | Posters on site | TS3.10 | Highlight

The North Anatolian Fault: an example to regularity of ‘irregular’ seismic behaviour of continental strike-slip faults 

Cengiz Zabcı, Erhan Altunel, and H. Serdar Akyüz

In the complex puzzling of the lithospheric plates, the transform boundaries and related strike-slip faults are under focus of earth scientists for more than a hundred years not only for their important role in the lithospheric-scale deformation, but also for being sources of destructive earthquakes. Particularly, spatial and temporal seismic behaviour of these faults has been a subject of great curiosity for several decades with a special emphasis on the relationship between their geometry and earthquake recurrence. The North Anatolian Shear Zone (NASZ) is one of these tectonic structures, which makes the northern boundary of the Anatolian Scholle connecting the Hellenic Subduction in the west and the Arabia-Eurasia Collision in the east. This dextral system has a remarkable seismic history, especially in the 20th century, when the westward migrating earthquake sequence generated surface ruptures of about 1100 km with addition of ~140 km from two out of sequence events, 1912 Mürefte and 1949 Elmalı earthquakes, leaving unbroken only Marmara in the west and Yedisu in the east along its most prominent structure, the North Anatolian Fault (NAF).

In this study, we aim to review palaeoseismic studies of more than three decades that provide invaluable information on the earthquake history all along the NAF with an attempt to understand which fault pieces have been involved in any of these palaeoevents. Thus, we decided to use their geometric properties, with an assumption that certain geometric discontinuities play an important role as end-points of an earthquake rupture. Palaeoseismological studies are grouped together according to the NAF’s geometric segments, on which they are located. In this classification, we excluded the ones with incomplete dating records or providing indirect evidence (i.e., cores). Then, we used a Bayesian approach to calculate the probability distributions of each palaeoevent, but applied it not to the individual sites but to the tectonostratigraphic data of merged trenches along the same fault segments. Our analyses suggest an ‘irregular’ seismic behaviour of the NAF although there are still gaps in data especially for the central parts. Large geometric complexities (e.g., Niksar step-over, Çınarcık Basin) significantly control the heterogenous stress conditions, but the ‘irregular’ behaviour is not only restricted to the segments close to these structures, but observed almost along the entire fault. In spite of the compiled 118 trench sites with more than 275 trenches, there is still necessity of further studies in order to increase the spatial and temporal resolution of palaeoseismic data along the NAF, especially for its central segments.

How to cite: Zabcı, C., Altunel, E., and Akyüz, H. S.: The North Anatolian Fault: an example to regularity of ‘irregular’ seismic behaviour of continental strike-slip faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12937, https://doi.org/10.5194/egusphere-egu23-12937, 2023.

EGU23-13568 | ECS | Posters on site | TS3.10

Coseismic and Early Postseismic of 23 November 2022 Mw = 5.9 Düzce Earthquake with InSAR and GNSS Measurements 

İlay Farımaz, Uğur Doğan, Semih Ergintav, Ziyadin Çakır, Cengiz Zabcı, Seda Özarpacı, Alpay Özdemir, Efe Turan Ayruk, Figen Eskiköy, Alpay Belgen, and Rahşan Çakmak

The North Anatolian Fault (NAF) was broken over the last century by a series of Mw > 7 earthquakes, most of which migrated westward, starting from the 1939 Erzincan Earthquake and ending with the 1999 Izmit and Düzce Earthquakes.  For 23 years the area remained silent for destructive earthquakes but also produced relatively small seismic activities until November 23, 2022 Düzce Earthquake, Mw 5.9.

In this study, we aim to investigate the source mechanism for the 23rd November 2022 Düzce Earthquake and associate it to the ruptures of 1999 Izmit and Düzce Earthquakes. For this purpose, in the same day that the earthquake occurred, our team established 8 new continuous GNSS sites covering the area to monitor the postseismic deformation and surveyed the historical sites to estimate coseismic field. Additionally, a stack of interferograms has been interpreted from Sentinel-1 data to densify the deformation fields.

Based on our first order analysis, the earthquake occurred at the overlap of the rupture zones of 1999 Izmit and Düzce Earthquakes (west of Eftani Lake on Düzce segment). Our GNSS and InSAR monitoring showed that the coseismic deformation is around <6 cm in the near field and ~33% of the InSAR coseismic deformation field is related with postseismic deformations.  

 

Keywords: Düzce earthquake, Coseismic and early postseismic deformation, InSAR, GNSS

How to cite: Farımaz, İ., Doğan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özarpacı, S., Özdemir, A., Ayruk, E. T., Eskiköy, F., Belgen, A., and Çakmak, R.: Coseismic and Early Postseismic of 23 November 2022 Mw = 5.9 Düzce Earthquake with InSAR and GNSS Measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13568, https://doi.org/10.5194/egusphere-egu23-13568, 2023.

EGU23-13724 | ECS | Posters on site | TS3.10

Kinematics of North Anatolian Fault Under the Constrain of New GNSS Velocity Field 

Efe T. Ayruk, Seda Özarpacı, Alpay Özdemir, İlay Farımaz, Volkan Özbey, Semih Ergintav, and Uğur Doğan

North Anatolian Fault (NAF) is one of the most important transform faults over in World. NAF produced an important earthquake sequence Mw ≥ 7 in the 20th century, that migrates westward between 1939 and 1999. The earthquake sequence has broke the great part of the NAF which is approximately 1000 km. Due to this seismic activity of NAF, it is important to keep strain accumulation up to date and use the recent data. Many precious works have been studied to clarify the kinematics of NAF using the data that collected with geodetic methods (terrestrial and space geodetic).

In this study, we compiled published GNSS data and analyzed it to understand the present strain accumulation of NAF, with TDEFNODE block modelling code using a simple block geometry. The study area extends between Sapanca Lake at the west (Sakarya) to Yedisu at the east (Bingöl) and it stretches out in the north-south direction from the north coast of Blacksea to 130 kilometers south.

The 90% of GNSS velocity field have RMS values less than 2 mm and the accuracy of estimated slip rates is increased. Additionally, with the dense station distributions in the near field, spatial resolution improved, dramatically.

According to the first order results, fault slip rates are estimated as 20.5 mm/yr at the east and 21.6 mm/yr at the west. Locking depth is also estimated as 15 km at the east while the middle and the west part of the study area has shallower locking depth values.

In the presentation, we will demonstrate the power of our new GNSS velocity field and discuss its contribution to the understanding of the NAF kinematics in detail.

keywords: North Anatolian Fault, Block Modelling, Velocity Field

How to cite: Ayruk, E. T., Özarpacı, S., Özdemir, A., Farımaz, İ., Özbey, V., Ergintav, S., and Doğan, U.: Kinematics of North Anatolian Fault Under the Constrain of New GNSS Velocity Field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13724, https://doi.org/10.5194/egusphere-egu23-13724, 2023.

EGU23-13785 | Posters on site | TS3.10

Recent kinematics of Crete, observed by InSAR, reveal complex, curved-forearc deformation and aquifers changes 

Sabrina Metzger, Md Aftab Uddin, Vasiliki Mouslopoulou, John Begg, Andy Nicol, Vasso Saltogianni, and Onno Oncken

Located on the overriding plate of the Hellenic subduction margin, the 250 km-long island of Crete offers a unique opportunity to study curved-forearc deformation. The African-Eurasian plate-convergence of ~40 mm/yr (~80 %) is primarily accommodated aseismically, but intense seismicity is recorded at the plate-interface and a reverse splay faults along the Hellenic trough; frequent M6+ earthquakes and (at least one) tsunami-genic event, causing up to 10 m of paleoshoreline uplift in western Crete, are reported. Global Navigation Satellite System (GNSS) data revealed N-S shortening of ~2 mm/yr within western Crete due to pure plate convergence. Further east, the curved subduction trench accommodates increased oblique slip, causing E-W extension of ~2 mm/yr in eastern Crete.

Recently, the European Ground Motion Service published dense InSAR surface deformation data in East and Up direction of whole Europe. The InSAR time-series comprise positioning samples every six days, respectively, every ~50 m, and, in Crete, exhibit long-wavelength deformation signals caused by deep-rooted, tectonic sources that are overlaid by (often seasonally-modulated) signals originating in shallow aquifers. We analyze these time-series in space and time and validate the results using available GNSS rates, a seismic catalog and an active fault data base. Preliminary results suggest a slight eastward tilt of Crete, which is not confirmed by published GNSS rates, and has to be investigated further. Spatially-confined uplift of up to ~5 mm/yr are observed at the karstic Omalos plateau, and up to ~30 mm/yr subsidence in the Messara basin, both probably related to groundwater replenishment/abstraction. Relative eastward motion increases towards eastern Crete, particularly in the fault zones embracing Mirabello bay and east of it, thus confirming the aforementioned E-W extension, and towards the southern coast.

How to cite: Metzger, S., Uddin, M. A., Mouslopoulou, V., Begg, J., Nicol, A., Saltogianni, V., and Oncken, O.: Recent kinematics of Crete, observed by InSAR, reveal complex, curved-forearc deformation and aquifers changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13785, https://doi.org/10.5194/egusphere-egu23-13785, 2023.

EGU23-14310 | ECS | Posters on site | TS3.10

Influence of fault rocks’ mineralogy on fault behaviour: implications from the Palu-Hazar Lake section of the East Anatolian Fault (Elazığ, Türkiye) 

İrem Çakır, Cengiz Zabcı, Mehmet Köküm, Hatice Ünal Ercan, Havva Neslihan Kıray, Müge Yazıcı, Mehran Basmenji, Özlem Yağcı, N. Beste Şahinoğlu, Uğur Doğan, and Semih Ergintav

The multi-disciplinary studies yield a more complicated picture on seismic cycles, especially with the increasing evidence on creeping, slow slip events, tremors and repeating earthquakes. Recent observations support triggering of large earthquakes even by small or slow earthquakes and creeping of different portions of the fault. The Palu-Hazar Lake section of the East Anatolian Fault (EAF) is an example place of such kind of behaviour, where the 24 January Mw 6.8 Sivrice Earthquake was nucleated along the neighbouring segments. This sinistral strike-slip fault forms the eastern boundary of the Anatolian Scholle between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş) in the southwest within the complex tectonic frame of the Eastern Mediterranean.

In this study, we aim to correlate any potential influence of bedrock lithology on this creeping section of the EAF. First, we revised the active fault and geological maps by using the multi spectral satellite images (e.g., Landsat 8 OLI) and high-resolution digital surface models (~0.65 m ground pixel resolution). Then, we determined potential exposures along the EAF and made systematic sampling both from cohesive and incohesive fault rock exposures within our study region. Collected samples are prepared for X-ray diffraction (XRD) measurements, especially for the determination of the fault clay types. Fault rock samples from ophiolitic (mafic and ultramafic) rocks and accretionary complexes (shale, sandstone, volcanics, ophiolite fragments) are mostly made of vermiculite and include minor amounts of smectite and chlorite according to our XRD measurements. Although the low shear strength of vermiculate may trigger aseismic slip at shallow depths with change in pore water pressure, it is possible that there may be no correlation between bedrock lithology and creeping, considering the poorly known seismic history of the EAF.

This study is supported by TÜBİTAK Project no. 118Y435.

Keywords: earthquake, East Anatolian Fault, creep, fault rocks

How to cite: Çakır, İ., Zabcı, C., Köküm, M., Ünal Ercan, H., Kıray, H. N., Yazıcı, M., Basmenji, M., Yağcı, Ö., Şahinoğlu, N. B., Doğan, U., and Ergintav, S.: Influence of fault rocks’ mineralogy on fault behaviour: implications from the Palu-Hazar Lake section of the East Anatolian Fault (Elazığ, Türkiye), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14310, https://doi.org/10.5194/egusphere-egu23-14310, 2023.

EGU23-14343 | Orals | TS3.10

Paleoseismicity of Northern Cyprus, implications from coastal geomorphology and geochronology 

Cengiz Yildirim, Daniel Melnick, Okan Tüysüz, Cevza Damla Altınbaş, Julius Jara-Munoz, Konstantinos Tsanakas, Orkan Özcan, and Manfred Strecker

The Cyprus Arc is one of the major sources of earthquakes in the Eastern Mediterranean Region. There is limited large-magnitude earthquake activity during the instrumental period. Still, archeoseismological data imply the occurrence of large-magnitude earthquakes that hit the island and gave rise to casualties and destructions. Nevertheless, these data are insufficient to give information about the source of the earthquakes. In this study, we focussed on coastal geomorphology to unravel paleoseismic activity, at least generated by near offshore faults, that released sufficient seismic energy to deform the shoreline in Holocene.

We mapped coseismically uplifted abrasion platforms, tidal notches, fish tanks and a surface rupture implying active near offshore faults in Holocene. The elevation of paleo shorelines varies between 0.4 m to 3 m above sea level, indicating multiple occurrences of paleo earthquakes. Our radiocarbon 14C ages from biological markers (algal rims, etc) indicate that the coseismic uplift of the shoreline starts from 4,5 ka to 1.2 ka BP.

The ages of the paleoearthquakes display non-uniform spatial distribution and show migration of paleoearthquakes from west to east, especially along the island's northern coast. This study is supported by Istanbul Technical University Research Fund (Project No: 37548) and Alexander von Humboldt Foundation, Germany.

How to cite: Yildirim, C., Melnick, D., Tüysüz, O., Altınbaş, C. D., Jara-Munoz, J., Tsanakas, K., Özcan, O., and Strecker, M.: Paleoseismicity of Northern Cyprus, implications from coastal geomorphology and geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14343, https://doi.org/10.5194/egusphere-egu23-14343, 2023.

EGU23-15463 | ECS | Orals | TS3.10

Structure and evolution of the Dead Sea Transform 

Jakub Fedorik and Abdulkader M. Afifi

The Dead Sea Transform (DST) extends from the Red Sea to the East Anatolian Fault, displaying various structural styles along its ~1100 km length. In this study, we combine previous work with new mapping of fault patterns and displacements, geochronological data, and analogue and numerical modeling to provide new insights on the temporal evolution of the DST.

In the southern DST, we mapped a 30 km wide distributed shear belt along the eastern margin of the Gulf of Aqaba (GOA), consisting of a distributed shear faulting, similarly to the western belt in Sinai. Total left lateral offset across the eastern distributed shear belt is ~ 15 km, with offset across individual faults ranging from a few meters up to 5.7 kilometers. Ar-Ar dating of sheared basalt dikes and U-Pb dating of calcite cements in faults indicate that the distributed shear system was activate between 22-16 Ma, overlapping with the rifting of the proto Red Sea and Gulf of Suez. This distributed shear is observed along the GOA and the deformed area narrowed along the Arava Valley. Distributed shearing marks the initial stage of continental break-up along the DST, which was abandoned by faulting concentration within the GOA and propagation of the DST towards the north.

The structural analysis of bathymetry data from the GOA and fault mapping along the entire DST highlight various structural styles: rotational transtension within the GOA, narrowing to simple strike-slip faulting of the Wadi Araba and Jordan Valley, and pull-apart basins along the Dead Sea, Sea of Galilee and Hula Basin. These structures are linked at depth to the principal displacement zone, nowadays-active plate boundary. Our analogue model produces similar structural styles and with the seismicity data it confirms that deformed area narrowed in the more recent stage of deformation. We also present an approach based on the boundary element method at the regional scale to test the structural interpretation of a complex transpressional mountain range of Lebanon Restraining Bend. These results are validated by structural evidences and highlight that various structural styles lead to formation of Mt. Lebanon, Anti-Lebanon and Palmyrides structures.

This review study of the DST emphasizes the role of structural styles, inherited structures and relative movement between tectonic plates in the transform continental break-up evolution.

How to cite: Fedorik, J. and Afifi, A. M.: Structure and evolution of the Dead Sea Transform, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15463, https://doi.org/10.5194/egusphere-egu23-15463, 2023.

EGU23-16089 | ECS | Orals | TS3.10

Monitoring spatio-temporal evolution of aseismic slip along the Ismetpasa segment between 2016-2023 with GNSS measurements 

Alpay Özdemir, Uğur Doğan, Jorge Jara, Semih Ergintav, Romain Jolivet, and Ziyadin Çakır

Aseismic slip (creep) is critical above the onset, propagation, and time of occurrence of large earthquakes on active faults. Also elastic strain in the crust between large earthquakes is controlled by the aseismic slip along the active faults. Key characteristics of aseismic slip behavior is that it is typically very slow and gradual, with the faults moving only a few millimeters or centimeters per year. This type of movement is often difficult to detect and measure, and may not be immediately apparent to observers.

Although it has been determined that the İsmetpaşa segment of the North Anatolian Fault has been slipped aseismically since 1970, without producing an earthquake, there is no reliable and detailed information about the spatial and temporal changes of this movement. After it was first recognized by Ambraseys in 1970, the creep movement is monitored by the researchers with terrestrial and campaign type GNSS measurements in the 6-point geodetic network established in Hamamlı. InSAR observations has made it possible to derive maps of ground velocities over the past 20 years that indicate aseismic slip is present along a ~100 km portion of the fault. Additionally, the aseismic slip rate changes spatially along the strike, peaking at 15–24 km to the east of Ismetpasa. Furthermore, InSAR time series and creepmeter measurements shows that aseismic slip in the Ismetpasa region behaves episodically rather than continuously, with stationary periods alternated with transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault, which has important implications for hazard along the seismogenic zone.

To answer these questions, it is necessary to expand terrestrial observation capacity along the creeping segment and to conduct a detailed examination of the change in creep accelerations by associating it with seismological activity. We established ISMENET -Ismetpasa Continuous GNSS Network- in July 2016 to monitor spatial and temporal variations in the aseismic slip rate and to detect slow slip events along the fault. ISMENET stations are located approximately 120 kilometers along strike. Stations are located within 200m to 10 km of the fault to investigate the shallow, fine spatiotemporal behavior of aseismic slip. In addition to this network, 19 GNSS stations belonging to the TUSAGA-Aktif network located in the vicinity of the İsmetpaşa segment have been added to this network. To reduce the influence of non-tectonic noises, we analyze the GNSS time series to extract the signature of creep movement using Multivariate Singular Spectrum Analysis (M-SSA). Initial estimations shows that creep rates change along the fault between 6-8 mm/yr at a 4-5 km depth 10 km east side of the Ismetpaşa town. On the western edge of the Ismetpaşa segment between Bayramören and Ilgaz towns creep rate decreases ~3-4 mm/yr.

In this study, we examine the results of the temporal and spatial variation of the aseismic slip between 2016-2023 from the GNSS stations located in the immediate vicinity of the İsmetpaşa segment.

Ismetpasa, Aseismic slip, GNSS, M-SSA, NAFZ

How to cite: Özdemir, A., Doğan, U., Jara, J., Ergintav, S., Jolivet, R., and Çakır, Z.: Monitoring spatio-temporal evolution of aseismic slip along the Ismetpasa segment between 2016-2023 with GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16089, https://doi.org/10.5194/egusphere-egu23-16089, 2023.

EGU23-17079 | Orals | TS3.10 | Highlight

Sequential development of shear zones in a Metamorphic Core Complex: cause and consequences in the Menderes Massif (Western Turkey) 

Vincent Roche, Laurent Jolivet, Stéphane Scaillet, Johann Tuduri, Vincent Bouchot, Laurent Guillou-Frottier, and Erdin Bozkurt

During the Cenozoic, the Menderes Massif (western Turkey) records several tectonic and thermal events from subduction to collision, then back-arc extension. But the detailed timing of the succession of different P-T regimes and deformation until today remains debated. To address this, we targeted the main shear zones, providing for the first time a full picture of the 40Ar/39Ar system across the massif. This approach is combined with Tmax, and P-T estimates tied to kinematic-structural data. Extensive sampling along the large top-S Selimiye shear zone allows constraining the deformation at least between 44 and 33 Ma. This shear zone acted as a thrust and was active under HT-MP (530 - 590 °C and 8.5 - 10 kbar). Conversely, the top-S South Menderes Detachment System is associated with a younging of 40Ar/39Ar ages related to exhumation and strain localization during the Late Oligo-Miocene in the Central Menderes Massif. The Bozdağ top-S shear zone then allowed the exhumation of the Bayındır nappe at ~ 21 Ma from high-temperature metamorphic conditions (590 °C). Based on these new elements, we propose for the first time a detailed scenario of the Menderes Massif evolution from the Late Cretaceous to the Present. We finally discuss why the Menderes Massif belongs currently to the regions with the highest geothermal potential in the world. We propose that geothermal activity here is not of magmatic origin but rather associated with active extensional tectonics (detachments) related to the Aegean slab dynamics (i.e., slab retreat and tearing).

How to cite: Roche, V., Jolivet, L., Scaillet, S., Tuduri, J., Bouchot, V., Guillou-Frottier, L., and Bozkurt, E.: Sequential development of shear zones in a Metamorphic Core Complex: cause and consequences in the Menderes Massif (Western Turkey), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17079, https://doi.org/10.5194/egusphere-egu23-17079, 2023.

EGU23-1837 | ECS | Posters on site | TS3.11

Rheology of host-inclusion mineral systems by in situ Raman spectroscopy 

Nicola Campomenosi, Ross John Angel, Matteo Alvaro, and Boriana Mihailova

Earthquakes and stress distribution inside the earth depend on the rheology of rocks and their constituent crystals at variable conditions of temperature (T) and pressure (P). The contrast in the thermoelastic properties between a mineral inclusion and its surrounding host often leads to a positive inclusion residual pressure (Pinc) at ambient conditions, which can be used to retrieve the P and T of entrapment (e.g. Angel et al. 2015). In addition, the evolution of the inclusion residual strain and Pinc as function of P and T also provides the opportunity to explore the rheology of the crystals involved.

In this study, we explored the rheology of zircon inclusions within pyrope-rich garnet by in situ Raman spectroscopy at high T.

Because garnet has a larger thermal expansion than zircon, inclusions showing a positive Pinc at ambient conditions experience continuous relaxation upon heating until the P gradient disappears. Available equations of state (EoS) can predict the experimental results within uncertainties, implying that the system behaves purely elastically up to a certain temperature. At higher T, zircon inclusions have a negative Pinc, which increases in magnitude according to the EoS predictions. However, at T corresponding to Pinc of about -0.2(5) GPa, the residual strains deviate from those predicted by EoS and the inclusion approaches the strain of a free zircon crystal at the same T. We interpret such a deviation as the result of plastic relaxation of the system.  On cooling, a new stress gradient in the host and a positive Pinc in the inclusion developed within the same T range where a negative Pinc was observed upon heating. Importantly, the new residual strains can be predicted by the EoS only if the entrapment conditions correspond to the first T where Pinc = 0 after plastic deformation occurred. Thus, the system underwent resetting within the time-scale of laboratory experiments. In addition, multiple heating-cooling cycles carried out on the same inclusions show that the maximum negative Pinc attainable does not change within a T range of about 200 K. These results suggest that the resistance to plastic deformation (i.e. yield strength) of garnet decreases under tensile stress. Therefore, we conclude that the sign of the stress field affects the yield strength of crystals and may have important consequences on the overall rock rheology and related processes.

Financial support by the Alexander von Humboldt Foundation and the ERC grant agreement 714936 (ERC-STG TRUE DEPTHS) to M. Alvaro

Angel, R. J., Nimis, P., Mazzucchelli, M. L., Alvaro, M. & Nestola, F. (2015). Journal of Metamorphic Geology, 33(8), 801-813.

How to cite: Campomenosi, N., Angel, R. J., Alvaro, M., and Mihailova, B.: Rheology of host-inclusion mineral systems by in situ Raman spectroscopy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1837, https://doi.org/10.5194/egusphere-egu23-1837, 2023.

EGU23-3360 | ECS | Posters on site | TS3.11

Experimental observation of antigorite dehydration triggered by shear stress at subduction zone pressure and temperature conditions 

Lisa Eberhard, Oliver Plümper, and Holger Stünitz

The trigger mechanism of intermediate depth earthquakes (30 - 300 km) is a long-standing debate. Many studies showed that these seismic events nucleate along a double-seismic zone within the subducting slab. The seismic events of the lower plane coincide with the depth of major dehydration reactions in the lithospheric mantle. Consequently, it is thought that these events are related to the release of fluids. Several scenarios are currently discussed that might lead to brittle deformation. Among these are dehydration embrittlement and dehydration-driven stress transfer.

Antigorite is one of the most important candidates for fluid release due to its high H2O content and stability limits within the lower Wadati-Benioff zone. The release of water through antigorite dehydration can be calculated by equilibrium thermodynamics and is mainly a function of temperature. This does, however, not account for deformation (e.g., stored internal strain energy) leading to local variations in the free energy of minerals. In this study we aim to explore the effect of shear stress on the stability of antigorite.

We performed high-pressure and high-temperature experiments in a Griggs rig. We used intact drill cores of two different starting materials for our experiments: a foliated and an isotropic antigorite-serpentinite. Both starting materials did not contain relict olivine and/or orthopyroxene. We run our experiments at 620 to 650 °C with a confining pressure of 1.5 GPa and a strain rate of 10-6 s-2. Subsequent analyses of the experimental runs revealed no dehydration products within the bulk sample. However, we observed the formation of ultra-fine grained (< 100 nm) olivine and orthopyroxene along narrow zones, which are orientated 30 to 40 ° with respect to the compression axis. These zones are similar in all runs and independent of the starting material microstructure. We thus propose that shear stress localization within our cylindrical sample triggered the dehydration. Within subduction zones local variations in stress field due to mineralogical or textural heterogeneities could promote dehydration, eventually leading to seismic events through stress transfer.

How to cite: Eberhard, L., Plümper, O., and Stünitz, H.: Experimental observation of antigorite dehydration triggered by shear stress at subduction zone pressure and temperature conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3360, https://doi.org/10.5194/egusphere-egu23-3360, 2023.

EGU23-3414 | ECS | Posters on site | TS3.11

Deformation and healing processes in the damage zone of a lower-crustal seismogenic fault 

Stephen Paul Michalchuk, Kristina Dunkel, Markus Ohl, and Luca Menegon

Coseismic fracturing of the lower crust is an effective mechanism for creating permeable pathways for fluids to infiltrate and interact with the host rock, thus effectively altering the rheology of otherwise anhydrous and strong lower-crustal rocks. Most of the fracturing and fragmentation that facilitate fluid infiltration occurs in the damage zone of seismogenic faults. In this study, we have focused on characterizing the damage zone adjacent to a lower-crustal pseudotachylyte (solidified frictional melt produced during seismic slip) to understand the fracture generating and healing processes during a seismic event.

The Nusfjord East shear zone network (Lofoten, Norway) contains coeval pseudotachylytes and mylonitized pseudotachylytes that formed at lower-crustal conditions within anhydrous anorthosites. We present a micro- and nanostructural analysis of plagioclase grains in the damage zone of a natural pseudotachylyte using focused ion beam (FIB) prepared scanning transmission electron microscopy (S/TEM), electron backscatter diffraction (EBSD) analysis, electron microprobe analysis (EMPA), and SEM-cathodoluminescence (CL) imaging.

The damage zone of the host anorthosite is characterized by a network of fractures with minimal offset, consistent with a pulverization-style fragmentation process. CL intensities differentiate primary plagioclase (plagioclase1), from secondary plagioclase neoblasts (plagioclase2) filling some of the fractures. Plagioclase1 grains often exhibit a diffuse CL intensity zonation from bright grain cores to a dark grey in healed cracks, while plagioclase2 have a uniform mid-tone grey CL intensity with dark grain boundaries. CL zonation in the plagioclase1 does not correlate with EMPA major element maps nor EBSD misorientation maps. TEM foils targeted key microstructure domains characterized by CL: (1) bright CL plagioclase1 core, (2) dark CL plagioclase1 in healed cracks, (3) transitional CL from bright to dark across a healed crack, and (4) plagioclase2 neoblast. Results from S/TEM show that the dark CL spanning the healed cracks is associated with a high concentration of crystalline nanoparticles. In contrast, bright CL is associated with a few scattered dislocations, no nanoparticles, and numerous dispersed Ba-Ti-oxide nanograins. The mid-tone grey CL plagioclase2 neoblast have the lowest dislocation density. Follow-up Transmission Kikuchi Diffraction (TKD) and NanoSIMS analyses on the nanoparticles in the healed cracks and the plagioclase1 grains immediately next to these cracks will help further elucidate the origins of the nanoparticles and the CL intensity zonation.

How to cite: Michalchuk, S. P., Dunkel, K., Ohl, M., and Menegon, L.: Deformation and healing processes in the damage zone of a lower-crustal seismogenic fault, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3414, https://doi.org/10.5194/egusphere-egu23-3414, 2023.

EGU23-5052 | ECS | Orals | TS3.11

Stress amplification around weak inclusions can trigger earthquakes in a dry subducting oceanic slab 

Giovanni Toffol, Jianfeng Yang, Giorgio Pennacchioni, Manuele Faccenda, and Marco Scambelluri

The origin of intermediate-depth seismicity in subducting oceanic lithosphere is still debated. A key for interpretation is provided by deep-seated pseudotachylytes (quenched frictional melts produced during seismic slip along a fault), exhumed counterparts of the actual deep seismicity, that can record relevant information on the seismic processes at hypocenter depths. Pseudotachylytes crosscutting the dry ophiolitic peridotite/gabbros of Moncuni (Lanzo ultramafic Massif, W. Alps)[1] have been interpreted to have formed at intermediate-depth (ca. 70 km) conditions under high differential stress and proposed as an analogue for the lower plane of the double seismic layer of subducting plates.

Moved by these observations, we investigated by numerical simulations the potential of a subducting dry slab to achieve the high differential stress required for brittle failure in absence of fluid-mediated embrittlement during the plate bending and unbending. We performed pseudo-2D thermo-mechanical simulations of free subduction of a dry slab considering a visco-elasto-plastic rheology. We tested a homogeneous dry plate and a dry plate with weak circular inclusions representing partially hydrated volumes in the first 40 Km of the slab. The effect of low temperature plasticity (LTP) in olivine was also tested. In the unbending portion of the subducting slab the stress field describes two arcs - the outer one in compression and the inner one in extension - matching the two planes of seismicity. However, the homogeneous slab can only reach a differential stress of around 1 GPa, that is not high enough for triggering earthquakes. The presence of weak inclusions, with degraded elastic properties, but still high viscosity, induces a local amplification of the stress field. Differential stresses in excess of 4 GPa are obtained considering inclusions with a shear modulus decreased by 60-70% relative to the surrounding material but similar viscosity. Increase of the spatial density of inclusions determines a general increase of stress due to local interactions of the stress fields. The LTP of olivine, when considered in the simulations, introduces a stress cut off hampering the differential stress around weak inclusions to rise above 1.5 GPa. However, if the effect of pressure and strain hardening are considered, differential stresses above 3 GPa are achieved, that are high enough for brittle failure at intermediate-depth conditions. The modeled slab with scattered weak inclusions is compatible with a dry and strong peridotitic mantle with partially serpentinized domains, most likely related to faulting during slab bending.

Our results show that brittle failure can occur at intermediate depths during subduction in relatively dry rocks, confirming the hypothesis developed from field interpretations. Further advanced microstructural investigations (e.g. TEM, HR-EBSD) on selected mantle pseudotachylytes, as well as on experimental analogues, can help to better understand the behavior of intermediate-depth earthquakes, hopefully providing new insights into the processes of stress accumulation and release during the seismic cycle.

 

[1]: Pennacchioni et al., 2020, Record of intermediate-depth subduction seismicity in a dry slab from an exhumed ophiolite, Earth Planet. Sc. Lett. 548, 116490

How to cite: Toffol, G., Yang, J., Pennacchioni, G., Faccenda, M., and Scambelluri, M.: Stress amplification around weak inclusions can trigger earthquakes in a dry subducting oceanic slab, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5052, https://doi.org/10.5194/egusphere-egu23-5052, 2023.

EGU23-5200 | ECS | Posters on site | TS3.11

High coseismic differential stress preserved in the lattice of seismically shocked garnets 

Giovanni Toffol, Giorgio Pennacchioni, Luca Menegon, Alfredo Camacho, Manuele Faccenda, David Wallis, and Michel Bestmann

The seismogenic environments build up the highest differential stresses on Earth. Differential stress of as much as hundreds of MPa to few GPa is accumulated during the interseismic loading stage and it is abruptly released in a sequence of fast, high-stress events (earthquake rupture tip propagation, frictional fault slip, thermomechanical interactions) determining large-magnitude, local stress changes on and near the fault plane. A major challenge to obtain a quantification of these stresses is represented by their heterogeneity in space and time. However, they can be exceptionally recorded in exhumed fault rocks bearing pseudotachylytes (quenched coseismic frictional melts).

Here, for the first time, we provide a measure of the residual elastic stress preserved in the lattice of seismically shocked garnets crosscut by a pseudotachylyte fault vein by means of HR-EBSD (high-angular resolution electron backscattered diffraction). The thin (3 mm-thick) pristine pseudotachylyte was produced during a single seismic event at mid-crustal conditions (ca. 500 MPa, 500 °C) within felsic gneisses in the hanging wall of the Woodroffe Thrust (Musgrave Ranges, central Australia). Centimetric garnets of the host rock are intensely fractured and extremely comminuted close to the pseudotachylyte. A local enrichment in Mn is associated with healing of the cracks close to the pseudotachylyte and with the growth of epitaxial garnet in the cataclastic portions. HR-EBSD maps (ca. 30 x 50 µm2) were acquired in the garnet at increasing distance from the pseudotachylyte and in a cataclastic domain in contact with it. Residual stresses reach up to 5 – 6 GPa in contact with the pseudotachylyte and decrease to a few hundred MPa in less than a millimeter from it. Similar high stresses are recorded also in the clasts of a cataclasite flanking the pseudotachylyte, while newly grown high-Mn garnet surrounding the clasts records lower stresses. High stress domains in the mapped areas, a few micrometers in size, are bounded by straight bands of stress sign inversion that become less regular and more closely spaced towards the pseudotachylyte. Geometrically necessary dislocations (GND) are more abundant close to the pseudotachylyte and are linked with the high-stress domains.

Microstructures, stress gradients and magnitudes all suggest that the extreme residual stresses recorded in proximity of the pseudotachylyte belong to the stage of propagation of the earthquake rupture, in agreement with theoretical predictions of the stress fields at the tip of a propagating fracture. The partial preservation of the stress in the strained lattice of the garnet is made possible by the quasi-instantaneous healing of the cracks that produced a load-bearing framework to maintain the elastic strains and by the presence of high GND densities produced during the high-stress – high-strain rate rupture propagation event.

How to cite: Toffol, G., Pennacchioni, G., Menegon, L., Camacho, A., Faccenda, M., Wallis, D., and Bestmann, M.: High coseismic differential stress preserved in the lattice of seismically shocked garnets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5200, https://doi.org/10.5194/egusphere-egu23-5200, 2023.

EGU23-5259 | ECS | Posters on site | TS3.11

Fe-Si-gel like injections in banded iron formations of the Musselwhite Mine (Canada) 

Friedrich Hawemann, Cees Passchier, and John Biczok

A sample of banded iron formation from a drill core from the Musselwhite Gold Mine, Ontario, Canada, shows millimeter-wide opaque veins at a low angle to the foliation with perpendicular offshoots. The veins are non-crystalline, structureless and chemically homogeneous, with oxide weight percentages of 35 % FeO, 40 % SiO2, 5 % MnO, 5 % MgO and 1 % CaO. The remaining ca. 15 % might be attributed to water content. Despite the water, the composition is very similar to the bulk rock composition, consisting mainly of grunerite and quartz. The overall geometry of the veins resembles the appearance of a pseudotachylyte with injection veins, partly sharp boundaries, and clasts of the host rock. However, no other indicative observations such as flow banding, quenched margins or corrosion of clasts can be made. Instead, the vein is overgrown by euhedral quartz, nucleating from wall rock quartz crystals. Some of the material is emplaced in a calcite vein where the calcite seems to be fragmented. EBSD orientation data show that the fragments have the same orientation as calcite crystals remaining attached to the wall rock. Calcite crystals are therefore not displaced, but rather dissolved or replaced by the vein filling material, but without leaving a chemical signature. We therefore favor an Fe-Si rich gel-like injection origin of the veins. It remains unclear, how the gel was produced and how it is mechanically possible to inject such a gel into a solid rock and replace calcite.

How to cite: Hawemann, F., Passchier, C., and Biczok, J.: Fe-Si-gel like injections in banded iron formations of the Musselwhite Mine (Canada), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5259, https://doi.org/10.5194/egusphere-egu23-5259, 2023.

Fluids in subduction zones play a key role in controlling seismic activity, drastically affecting the rheology of rocks, triggering mineral reactions, and lowering the effective stress. Fluctuating pore pressure is one important parameter for the switch between brittle and ductile deformation, thus impacting seismogenesis. Episodic tremor and slow slip events (ETS) have been proposed as a common feature of the geophysical signature of subduction zones. Their geological record, however, remains scanty. We propose that fluctuating pore pressure linked to metamorphic dehydration reactions steered cyclic and ETS-related brittle and ductile deformation of continental metasediments in the subduction zone of the Apennines (Italy).

Field observations reveal a metamorphosed broken formation composed of boudinaged metaconglomerate enveloped by metapelite displaying a pervasive mylonitic foliation. Dilational shear veins occur in both lithotypes but are more common and laterally continuous in the metapelite. Veins are generally parallel to the metamorphic foliation and are composed of iso-oriented stretched quartz and carpholite fibres, which form single-grains up to several centimetres long. These fibres define a stretching direction mainly consistent with that of the hosting metaconglomerate and metapelite, which is marked by K-white mica and quartz. Thermodynamic modeling constrains the formation of the high-pressure veins and the mylonitic foliation to ~ 1 GPa and 350°C, corresponding to c. 30-40 km depth in the subduction channel1.

Microstructural analysis suggests that dilational hydroshear veins formed by incremental crack-sealing at supralithostatic pore pressure values. Successively, the veins experienced only limited recrystallization of quartz fibres by subgrain rotation recrystallization, with adjacent metapelite bands acting as decollement horizons, likely by slip on the basal plane of phyllosilicates. Blueschist facies mylonites formed mainly by a combination of dissolution-precipitation creep and slip along phyllosilicate bands.

Dilational shear veins in subducted metasedimentary successions have been suggested to be potential records of episodic tremors and slip events2. We propose these microstructures and deformation mechanisms to represent a geological evidence of deep episodic tremor and slow slip events in subducted continental metasediments. Pore pressure cyclically reached supralithostatic values triggering tremors causing fracturing of all involved lithotypes. Likely, slow slip was accommodated preferentially by slip on phyllosilicate bands. Aseismic creep occurred mainly by dislocation creep with subgrain rotation recrystallization in vein quartz, slip on the basal plane of phyllosilicates, and dissolution and precipitation creep in the host rock3.

Our results suggest reconsidering the role of quartz-carpholite veins forming coevally with metamorphic foliation as a possible record of deep ETS in similar geological settings of other convergent orogens 1.

 

1 Giuntoli et al. A likely geological record of deep tremor and slow slip events from a subducted continental broken formation. Sci Rep 12, (2022).

2 Fagerenget al. Incrementally developed slickenfibers — Geological record of repeating low stress-drop seismic events? Tectonophysics 510, 381–386 (2011).

3 Giuntoli et al. Deformation Mechanisms of Blueschist Facies Continental Metasediments May Offer Insights Into Deep Episodic Tremor and Slow Slip Events. J Geophys Res Solid Earth 127, (2022).

 

 

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 839779.

 

 

 

How to cite: Giuntoli, F., Viola, G., and Eske Sørensen, B.: Cyclic brittle-ductile oscillations recorded in exhumed high-pressure continental units: a record of deep episodic tremor and slow slip events?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5348, https://doi.org/10.5194/egusphere-egu23-5348, 2023.

EGU23-5373 | ECS | Orals | TS3.11

Earthquake Nucleation: The formation of rupture fronts and the influence of local conditions 

shahar gvirtzman and Jay fineberg

In recent years, there has been important progress in the experimental study of earthquakes (‘laboratory earthquakes’). Much has been learned about the character and dynamics of rupture fronts propagating along a frictional interface. These fronts are the vehicle with which the contacts composing a frictional interface break, therefore enabling slip. These fronts were shown to be identical to shear cracks, whose propagation characteristics are fully described by the framework of fracture mechanics.

However, the formation of these fronts - the nucleation process - is not yet fully understood. This process is not included in the fracture mechanics framework, which describes only cracks that are above the critical (Griffith) length needed for propagation, and does not provide us an explanation on how a small defect grows and reaches this critical point. In laboratory experiments, obtaining a detailed description of nucleation is a challenge, due to its unpredictable nature.

We use an experimental system in which the real contact area between 2 PMMA blocks is continuously imaged into a fast camera to record the dynamics at the onset of frictional motion and to monitor the propagation of the rupture fronts. In order to overcome the difficulties of the unpredictable nucleation process, a unique experimental technique is used to dictate the nucleation location, thus enabling the direct measurements of the nucleation time and local stresses at the nucleation point. In these controlled experiments, the dynamics of the nucleation process during the slow expansion of a nucleation patch are recorded in detail, as well as the transition to the fast propagation of the newly formed front.

We find that the expansion of the nucleation patch is qualitatively different than the propagation of the fully formed rupture front. It occurs at extremely slow and constant velocities, and it is 2D in nature. Some of the features of this expansion, like self-similar evolution and timescales that are stress-dependent, are general. However, the details of this process are governed by the local conditions at the nucleation region. Due to the slow rates of expansion, local variations in the surface toughness (the ‘fracture energy’) can influence characteristics such as the exact nucleation point, the shape of the patch, and the stress threshold that is needed for nucleation to occur.

As nucleation is not described by the usual frameworks that are used to explain rupture propagation, understanding the driving mechanism of it is of fundamental importance to questions ranging from earthquake nucleation and prediction to processes governing material failure. We propose a possible mechanism for this process and discuss it.

How to cite: gvirtzman, S. and fineberg, J.: Earthquake Nucleation: The formation of rupture fronts and the influence of local conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5373, https://doi.org/10.5194/egusphere-egu23-5373, 2023.

EGU23-6190 | ECS | Posters on site | TS3.11

Effects of water on the brittle to ductile transition of sandstones 

Francesco Lazari, Marie Violay, and Florence Begue

Geothermal energy is one of the renewable energy sources that can help mitigate climate change. Rocks are elasto-plastic materials at low pressure and temperature, and the deformation is accommodated along localized shear bands (brittle behavior); at high pressure and temperature rocks are elasto-visco-plastic and the deformation is homogeneous (ductile behavior); the transition between the two behaviors is called the brittle to ductile transition (BDT). Rocks capable of hosting geothermal fluids hot enough for electricity production (above 100°C) might be at or beyond the BDT.

The importance of the BDT of rocks stems from the fact that the largest earthquakes occur there, and it corresponds to a major decrease in the permeability of the crust. In the literature, the mechanical properties of rocks across the BDT are relatively well known, though only lately the effect of the presence of fluids and their chemical composition has been investigated by few research groups. However, certain fluid compositions might lead to mineral dissolution, precipitation, weakening and alteration, which in turn affect the mechanical properties of rocks.

To investigate the effect of water, fluid chemistry and alteration, triaxial experiments on a porous silicate sandstone (Adamswiller sandstone) with and without water at 100°C were done, to understand in detail the effect of water on deformation. To assess the evolution of the mechanical properties, complex electrical conductivity, permeability and ultrasonic seismic velocity were monitored in situ to fully describe the rock properties across the BDT.

The experiments resulted in a complete characterization of the failure and yield envelopes of Adamswiller sandstone across the BDT, together with the electrical conductivity, permeability and ultrasonic seismic velocities. The presence of water lowers both the peak stress and yield stress. Electrical conductivity decreases beyond the BDT due to porosity reduction, following the reduction of permeability.

How to cite: Lazari, F., Violay, M., and Begue, F.: Effects of water on the brittle to ductile transition of sandstones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6190, https://doi.org/10.5194/egusphere-egu23-6190, 2023.

EGU23-6440 | Posters on site | TS3.11

Experimental reactivation of faults in marble across the brittle ductile transition 

Erik Rybacki, Lu Niu, Youngsheng Zhou, and Xiwei Xu

The reactivation and stability of faults depend on a number of parameters, like rock composition, (effective) normal pressure, fault roughness, and loading rate. However, not much in known about the impact of temperature on faulting behavior. Using a Paterson-type gas deformation apparatus, triaxial compression experiments were conducted on dry Carrara marble samples containing a saw-cut oriented at about 40° to the axial stress direction. The tests were performed at constant axial strain rate of 1x10-5 s-1, confining pressures, P, between 30 and 150 MPa, and temperatures, T, in the range of 20 to 600°C. Under these conditions, intact Carrara marble deforms mainly in the semi-brittle regime and brittle, localized, deformation associated with strain weakening occurs only at room temperature and P < 100 MPa. At similar temperature, saw cut samples show formation of a new fracture zone inclined at 30° to the loading direction at P = 30 MPa and fault reactivation with stable sliding on the preexisting fault at P = 50 MPa. At higher temperatures up to 400°C and pressures < 100 MPa, we observed a mixture of matrix deformation and unstable (stick-slip) sliding on the fault. The peak stress at the onset of fault reactivation increased with P and T, resulting in higher associated peak strain. Also, the peak stress drop increased with increasing peak stress. At high T (>400°C) and P (>100 MPa) the fault remained locked and samples revealed ductile matrix creep with strain hardening, where the strength is almost similar to the strength of intact sample deformed under similar conditions. Microstructural observations reveal intense microcracking at the lowest P-T conditions. Samples exhibiting stick-slip behavior show a thin, discontinuous gouge layer and high twin density in specimens with late (high stress) fault reactivation. Bulk creeping samples reveal less damage and the fault appears to be partially sealed. Electron backscatter diffraction measurements suggest a slightly increasing crystallographic preferred orientation in the direct neighborhood to the fault compared the matrix under most conditions. Our results indicate that the fault reactivation stress of marbles increases with both, pressure and temperature, limited by the frictional strength. Above the brittle-ductile transition, the strength is limited by the bulk flow strength, which depends on total strain due to strain hardening, eventually leading to failure at high strain.

How to cite: Rybacki, E., Niu, L., Zhou, Y., and Xu, X.: Experimental reactivation of faults in marble across the brittle ductile transition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6440, https://doi.org/10.5194/egusphere-egu23-6440, 2023.

EGU23-7412 | ECS | Orals | TS3.11

Seismic and aseismic slip driven by ascending fluids and overpressure pulses on faults 

Danyang Jiang, Luca Dal Zilio, and Antonio P. Rinaldi

It is well known that fault zones are conduits for fluids. In particular, elevated pore-fluid pressure can neutralize the strengthening effect of normal stress and bring the fault system closer to failure. Despite this, most earthquake cycle models prescribe a constant effective normal stress and neglect the evolution of fluid pressure and transport properties. In this study, we present a hydro-mechanical earthquake cycles (H-MECs) model on a 2-D antiplane strike-slip fault with rate-and-state friction, full inertia effects, and poro-visco-elasto-plastic rheology. As a proxy for metamorphic reactions, a source of fluids is imposed at bottom of the fault causing fluids to ascend along the seismogenic zone. We further adopt a permeability evolution law in which permeability increases with fault slip and decreases due to healing and sealing processes. Our results show that fluid overpressure at the base of the seismogenic builds during the late interseismic period, when the fault has low permeability, weakening the fault and triggering slow-slip transients and earthquakes. When the healing time is shorter than the average recurrence interval of earthquakes, overpressure pulses facilitate the propagation of fluid-driven aseismic slip and their ascent through the seismogenic zone, thus causing swarm seismicity. For healing times of the order of a few years, overpressure pulses trigger long-term slow slip events, whereas for even longer healing times, fluid-driven aseismic slip causes a transient unlocking of the fault, without causing any seismic event. As a result, our models show that charge and discharge processes of fluid pressure and relative changes in fault strength influence the timing, slip behavior, stress transfers, stress drop, and other rupture properties. Accounting for viscoelastic deformation and poroelasticity effects incorporating the two-way coupling of solid and fluid phases brings earthquake cycle simulations much closer to reality, allowing greater consistency with experimental and geologic constraints on fault zone structure and dynamics.

How to cite: Jiang, D., Dal Zilio, L., and Rinaldi, A. P.: Seismic and aseismic slip driven by ascending fluids and overpressure pulses on faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7412, https://doi.org/10.5194/egusphere-egu23-7412, 2023.

The deformation sequence recorded in granitoid units of the External Crystalline Massifs (Aar-Gotthard, Mont Blanc) is commonly characterized by a brittle-ductile-brittle evolution. The same evolution is here described for the Rotondo granite (Gotthard Massif) and used to constrain the mechanics, rheology and timing of this brittle-ductile-brittle deformation sequence. Here we present meso- and microstructural, mechanical and petrochronological analyses of the deformation features of the Rotondo granite.

We distinguish four different deformation stages in the Rotondo granite based on structures, cross-cutting relationships, PT conditions and in-situ dating. The earliest structural features are brittle cataclasites and hydraulic breccias that appear to have formed under variable differential stresses and elevated fluid pressures. They host garnets that grew over the sheared texture and record peak metamorphic conditions of 600 ºC and 0.9 GPa. Ductile mylonitic shear zones overprint and exploit these early brittle structures at retrograde conditions (550 ºC and 0.7 GPa, ~18 Ma in-situ Rb-Sr in white mica), at differential stress <40 MPa and elevated fluid pressures during Alpine exhumation exemplified by the development of syn-kinematic, subhorizontal quartz veins. Strike-slip tectonics was dominant afterwards, as exemplified by the occurrence of brittle-ductile shear zones developed sequentially through decreasing fluid pressure and increasing differential stress conditions. The pre-existent mylonitic shear zones were initially partially reactivated during strike-slip shearing (400 ºC and 0.5 GPa, ~14 Ma in-situ Rb-Sr in white mica) and subsequently overprinted by conjugate brittle faults. The latest deformation stage involves zeolite- gouge-bearing faults that exploit pre-existent structural discontinuities, aided by low friction coefficients of the fault gouges. All three youngest deformation stages are interpreted to be Alpine in age and are observed to exploit/reactivate the earliest (presumably Variscan or prograde) breccias and cataclasites.

The structural sequence of the Rotondo granite exemplifies the effects of pre- and syn-orogenic structural inheritance and variable metamorphic fluid conditions on the mechanical evolution, rheology and strain distribution of crystalline (granitoid) basement units of the European continental crust through the Alpine orogenic cycle.

How to cite: Ceccato, A., Behr, W. M., and Zappone, A. S.: The mechanical evolution of the European continental crust through the Alpine orogenic cycle: insights from the Rotondo granite (Gotthard massif, Central Swiss Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8225, https://doi.org/10.5194/egusphere-egu23-8225, 2023.

EGU23-8363 | Posters on site | TS3.11

Investigating the effect of a heavy rainfall episode on the Mw4.9 earthquake of 11 November 2019 at Le Teil (France) 

André Burnol, Antoine Armandine Les Landes, Daniel Raucoules, Hideo Aochi, Julie Maury, Cécile Allanic, and Behrooz Bazargan-Sabet

On 11 November 2019, the Le Teil Mw4.9 earthquake occurred in southeast France, in the vicinity of a surface quarry. We focus this work on the effect of hydraulic recharge linked to the infiltration of meteoric water in the fault zones in the period preceding the earthquake. In the reference simulation, we used the in situ soil moisture at 30 cm depth (Berzème station) as surface boundary conditions.

We describe first the local 3D fault system from an updated geological model and the boundary conditions that are used to calculate the pressure variations at depth using a double permeability model.

The movement of moisture in partially-saturated media is then simulated by the Compass code (1) during the period 2015-2019. A maximum overpressure takes place near the junction of the three-fault system at around 1,200 m depth. Moreover, the calculated increase in pore fluid pressure is maximum during 2015-2019 just before the earthquake of 11 November 2019. Additionally, the surface soil moisture (SSM) data acquired by the SMOS satellite (2) are used to extend the study period between 2010 and 2015.

A sensitivity study carried out on the main hydraulic parameters allows us to estimate that the overpressure linked to the hydraulic recharge of the fault system is between 0.7 and 1 MPa at about 1200 m depth before the seismic event.

Finally, we compare this result with the maximum Coulomb stress change linked to the mass withdrawal from the surface quarry over the two past centuries (3). The conclusion is that the hydraulic effect is about two and a half times larger than the cumulative effect of the mechanical stress release due to the mass removal from the surface quarry.

(1) https://github.com/BRGM/ComPASS

(2) Li, X., Wigneron, J.-P., et al.: The first global soil moisture and vegetation optical depth product retrieved from fused SMOS and SMAP L-band observations, Remote Sensing of Environment 282, 113272, 2022. https://doi.org/10.1016/j.rse.2022.113272

(3) Maury, J., Guillon, T., Aochi, H., Bazargan, B., and Burnol, A.: Assessing the effect of mass withdrawal from a surface quarry on the Mw4.9 Le Teil (France) earthquake triggering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2742, https://doi.org/10.5194/egusphere-egu22-2742, 2022.

How to cite: Burnol, A., Armandine Les Landes, A., Raucoules, D., Aochi, H., Maury, J., Allanic, C., and Bazargan-Sabet, B.: Investigating the effect of a heavy rainfall episode on the Mw4.9 earthquake of 11 November 2019 at Le Teil (France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8363, https://doi.org/10.5194/egusphere-egu23-8363, 2023.

EGU23-8443 | ECS | Posters on site | TS3.11

Transient fluid flow recorded in the Crust-Mantle transition zone of the Oman Ophiolite 

Kazuki Yoshida, Ryosuke Oyanagi, Masao Kimura, Oliver Plümper, Mayuko Fukuyama, and Atsushi Okamoto

Fluid flow in subduction zones is one of the essential factors of seismic activity in subduction zones. However, the timescale of fluid flow and fluid flow velocity in subduction zones is unclear. In this study, we report antigorite veins with brucite-rich reaction zones in the crust-mantle transition zone of the Oman ophiolite and estimate the timescale and fluid flow velocity during vein formation.

In this study, we observed 28 samples in the lower crust to upper mantle section obtained from the Oman Drilling Project Hole CM1A (Kelemen et al., 2020). The lithology of borehole CM1A consists of lower crust (0-160 m depth), crust-mantle transition zone (160-310 m depth), and mantle section (310-404 m depth), which were mainly composed of altered gabbroic rocks (olivine gabbro, troctolite: 5-95% altered) and completely serpentinized dunite and 70-100% serpentinized harzburgite, respectively. Antigorite-chrysotile (Atg-Ctl) vein network was found in dunite at 160-180 m in Hole CM1A. The matrix of the dunite (lizardite, brucite, and magnetite) is cut by antigorite-chrysotile (Atg-Ctl) vein network. Trace element analysis using LA-ICP-MS revealed that the Atg-Ctl vein is enriched in As and Sb compared to the matrix lizardite, suggesting that the Atg-Ctl veins were formed by fluids interacting with subducting sediments. Some of the Atg-Ctl veins are accompanied by brucite-rich reaction zones. The brucite-rich reaction zone was developed at both sides of the antigorite veins with widths of 0.5 – 4 mm. Elemental mapping of the reaction zone using EPMA and TEM show sharp reaction front at scale from micro- to nano- meter.

Mass balance calculations and thermodynamic considerations of the reaction zone suggest that the formation of the reaction zone was caused by the removal of silica from the host rock during the precipitation of antigorite in the veins. Based on a diffusion model, we estimated the fluid activity is short-lived (2.1 × 10–1 to 1.1 × 101 yr), and the fluid flow velocity of 2.7 × 10–3 to 4.9 × 10–2 m s-1, which is much faster than those observed for the intact mantle and crustal rocks. This fluid flow velocity along the fractures within the mantle wedge is similar to the observed propagation velocities of seismic events in subduction zones. These results suggest that fluid flow in the overlying plate occurs as episodic pulses as observed as the migration of seismicity in the present subduction zones.

How to cite: Yoshida, K., Oyanagi, R., Kimura, M., Plümper, O., Fukuyama, M., and Okamoto, A.: Transient fluid flow recorded in the Crust-Mantle transition zone of the Oman Ophiolite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8443, https://doi.org/10.5194/egusphere-egu23-8443, 2023.

EGU23-9750 | ECS | Posters on site | TS3.11

Reconstructing the localized transient high stress state of seismogenic faults in the lower crust, Lofoten, Norway 

Hugo van Schrojenstein Lantman and Luca Menegon

Pseudotachylytes (frictional melts produced during seismic slip) in the metamorphosed anorthosites of the Lofoten archipelago preserve a record of seismic rupture in the dry lower crust at 650–750 °C, 0.8 GPa. Pyroxene deformation microstructures associated with preseismic loading and coseismic fragmentation reveal strongly localized transient stresses that presumably reached GPa-level magnitude. However, such transient high stresses have never been measured in exhumed seismogenic faults. In this work, we use high-angular resolution electron backscatter diffraction (HR-EBSD) on pyroxene grains to obtain spatial datasets of residual stresses retained in the crystal lattice. With these data, we aim to reconstruct the progressive build-up and release of transient high stress as it is recorded in the pyroxenes, and whether this recorded stress is related to preseismic loading or coseismic fragmentation.

The analysed anorthosite wall rock of a pseudotachylyte at the Nusfjord locality consists mostly of plagioclase, diopside, and enstatite, with diopside forming the main target minerals of this study. HR-EBSD maps were obtained in the wall rock at various distances from the pseudotachylyte interface along a 10 mm long transect, and on survivor clasts within the pseudotachylyte.

EBSD reveals that most diopside in the wall rock contains micron-scale deformation twins, except within 50 microns of the pseudotachylyte where it is fragmented. Residual stresses obtained via HR-EBSD vary along the transect, and are generally lower at greater distance from the pseudotachylyte. The highest values approximately coincide with the lithostatic pressure. The residual stresses are not in agreement with the very high transient stresses (>1 GPa) expected during the rupture propagation. Rather, the analysed diopside recorded the progressive build-up of stress during preseismic loading.

How to cite: van Schrojenstein Lantman, H. and Menegon, L.: Reconstructing the localized transient high stress state of seismogenic faults in the lower crust, Lofoten, Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9750, https://doi.org/10.5194/egusphere-egu23-9750, 2023.

EGU23-9809 | ECS | Posters on site | TS3.11

Mechanisms of deep earthquakes unraveled thanks to unsupervised machine learning 

Jiaqi Li, Gilbert Mao, Thomas Ferrand, Brian Zhu, Ziyi Xi, and Min Chen

Although transformational faulting in the rim of the metastable olivine wedge is hypothesized as a triggering mechanism of deep-focus earthquakes, there is no direct evidence of such rim. Variations of the b value – slope of the Gutenberg-Richter distribution – have been used to decipher triggering and rupture mechanisms of deep earthquakes. However, detection limits prevent full understanding of these mechanisms. Using the Japan Meteorological Agency catalog, we estimate b values of deep earthquakes in the northwestern Pacific Plate, clustered in four regions with unsupervised machine learning. The b-value analysis of Honshu and Izu deep seismicity reveals a kink at magnitude 3.7–3.8, where the b value abruptly changes from 1.4–1.7 to 0.6–0.7. The anomalously high b values for small earthquakes highlight enhanced transformational faulting, likely catalyzed by deep hydrous defects coinciding with the unstable rim of the metastable olivine wedge, the thickness of which we estimate at ∼1 km.

How to cite: Li, J., Mao, G., Ferrand, T., Zhu, B., Xi, Z., and Chen, M.: Mechanisms of deep earthquakes unraveled thanks to unsupervised machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9809, https://doi.org/10.5194/egusphere-egu23-9809, 2023.

EGU23-10076 | ECS | Posters on site | TS3.11

Transdisciplinary connections help understand natural mechanisms behind major seismic ruptures 

Thomas P. Ferrand, Lisa Eberhard, Mattia Gilio, and Revathy Parameswaran

For decades, millions of people have been waiting for the "big one" in either Tokyo, Istanbul or Los Angeles. No one is able to predict where and when such a disaster will happen first. People expect it as a self-evident fact, will experience it as a stroke of fate, and will speak of it as a “tragedy”.

Our aim cannot be (yet?) to predict where and when major earthquakes will occur, because that would amount to claiming to be able to announce in advance where and when the lightning strikes. Nevertheless, we believe that our understanding of the seismic process and associated risk should greatly benefit from the following question: what parameters control whether a dynamic rupture nucleates, grows or stops?

It is crucial to understand the processes and conditions causing the initial stages of catastrophic rock tearing under pressure, and the interplay between mineral- and tectonic-scale factors. Both fluid percolation events and transformation-driven stress transfers can trigger mechanical instabilities ultimately causing rupture nucleation. And once a rupture has nucleated, similar processes should also occur within the damage zone and modulate the ability of small ruptures to “self-propagate” towards large seismic events.

Our lack of understanding is considerable about the exact conditions for rupture nucleation and dynamic propagation. While observational methods help image mechanical instabilities, laboratory experiments provide insights on the physics of the lubrication processes enabling seismic faults to grow under pressure. Unfortunately, there remains a significant gap in scientific communication between researchers using different analytical methods or conceptual views.

Here we outline transdisciplinary connections between the contributions to the session. From seismology to electrical conductivity measurements in the laboratory, from field geology to numerical modelling, from machine learning to mineralogy, from geodesy to mineral physics, here we walk on the frontier of knowledge in order to reshape the central questions that we need to ask to further investigate the rupture phenomenon.

How to cite: Ferrand, T. P., Eberhard, L., Gilio, M., and Parameswaran, R.: Transdisciplinary connections help understand natural mechanisms behind major seismic ruptures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10076, https://doi.org/10.5194/egusphere-egu23-10076, 2023.

EGU23-11218 | Orals | TS3.11

Experimental constraints on the controlling mechanisms of tectonic tremors 

Timm John, Sandra Babinski, Julien Gasc, Jörn Kummerow, Markus Ohl, Oliver Plümper, and Alexandre Schubnel

Tectonic (or non-volcanic) tremors have been extensively documented at subduction zones and are considered as the signature of transport processes of dehydration-related fluids in subduction zones, often recorded in close association with geodetically observed shear induced slow-slip events. However, to the best of our knowledge, they have not yet been reproduced in the laboratory at subduction zones P–T conditions in such way that their first-order controlling mechanisms remain enigmatic.  

This work investigates the mechanism of these seismic events by performing dehydration-deformation experiments combined with detailed investigations of mineral reactions and acoustic emissions. Experiments were carried out on chlorite-peridotite powders (Balmuccia peridotite with synthetically added chlorite, a mineral that is typically found in subduction zone lithologies), following a subduction zone geothermal gradient using a high-pressure apparatus (Griggs-type). The experiments were conducted from ambient conditions to maximum pressures of 1.5-3.0 GPa and temperatures of 750-800 °C. Experiments were executed under hydrostatic conditions and an additional one with deformation. An ultrasonic transducer (0.5-10MHz dynamic range) was employed to monitor and detect the micro-seismic events. High-resolution electron beam techniques (EMPA, SEM and TEM) have been applied for analyzing the sample material.

Dehydration of ~15 vol.% of the initial chlorite suffices to trigger acoustic emissions, which display waveforms reminiscent of those of tectonic tremors. The moment distribution statistics of these laboratory tremor-like signals follows the Gutenberg-Richter relationship and a scaling between moment vs. event duration. Finally, we observe a match between the ratios of size and typical frequency of natural over laboratory tremors. Microstructural observations document metamorphic olivine and pyroxene growth in the decomposing chlorite and demonstrate that an almost isochemical dehydration of the chlorite took place. Accordingly, the appearance of the tremor-like acoustic emissions after crossing a temperature of 600 °C can be linked to a dehydration process related to the chlorite breakdown in the sample. Thermodynamic calculations show that a small amount of released fluids (breakdown of ~1.5 vol.% of a hydrous phase) is enough to trigger seismic signals analogues to tremors. The experiment with additional deformation produced no tremor-like acoustic emission suggesting that the large macroscopic shear stress suppressed the development of the processes that lead to acoustic emissions. We conclude that fluid release during dehydration is the cause of tectonic tremors, whereas shear-stress seems to counteract their development with no occurrence of tremors at high rates of deformation. According to the results from this study, the triggering mechanism can be tentatively interpreted as a fluid propagation front resulting in the vibration of grain boundaries.

How to cite: John, T., Babinski, S., Gasc, J., Kummerow, J., Ohl, M., Plümper, O., and Schubnel, A.: Experimental constraints on the controlling mechanisms of tectonic tremors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11218, https://doi.org/10.5194/egusphere-egu23-11218, 2023.

EGU23-13208 | Orals | TS3.11

Planar features, Trace element mobilisation and recrystallization formed during lower crustal CO2 induced seismic deformation of olivine 

Bjørn Eske Sørensen, Eric James Ryan, Rune Larsen, Stefanie Lode, Jostein Røstad, and Thomas B. Grant

Planar deformation features are a common feature in shock-deformed olivine, both experimentally in conditions corresponding to crustal shear zones [1] and impact structures e.g., [2] and in deep crustal shear zones [3, 4].  Hence, the identification of different planes associated with the shock deformation is essential to access the stress levels during deformation, important feature during studies of earthquake deformation.  A combination of optical and EBSD data combined to infer which of the possible crystallographic planes and EPMA to study trace elements to investigate planar deformation features and grain size reduction in olivine. Samples originate from the Reinfjord Ultramafic Complex, exposing lower crustal earthquakes induced by with CO2 bearing magmatic volatiles causing reaction facilitated grainsize reduction and weakening [3, 4].  First, calculated plane traces are compared with the observed plane traces in the free open source Matlab ® toolbox MTEX  [5], then the dip and dip direction of the observations of planes in the optical microscope.  Our results demonstrate: 1) That several planes are active during high stress deformation of lower crustal olivine rich rocks. 2) Some planes develop recrystallization features, whereas others develop later and do not develop recrystallization features. 3) Our results shows that these new olivine grains are a mix of grains with an orientation relationship with the host grains and grains that are far of the orientation of the host grain. 3) Further investigation using trace element mapping shows that P (Phosphorous) is a marker of fluid involvement in the recrystallization. P is mobilized preferably along grain boundaries and sub-grain boundaries involving twist, shown by zones of local P enrichment.

By looking at several grains we found that the developed fractures highly depend on the orientation of the host grain with respect to the external stress field.  Using the demonstrated methodology, it should be possible to map out the relative abundance of planar deformation features along different crystallographic planes in high stress deformed olivine and other transparent silicates.  The method can be refined by calculation of the exact thickness of the sample using interference colours calculated using the code published by [6] now available in MTEX.  This will enable the calculation of exact plane inclinations extracted from multifocal optical images that can be compared with crystallographic planes calculated in MTEX from the EBSD data. Further combination of trace elements reveals that fluid mobilisation is involved in the recrystallization process.

 

 

[1]   Druiventak A, Trepmann C A, Renner J and Hanke K  2011  Earth Planet. Sci. Lett. 311 199‑211

 [2]  Stöffler D, Keil K and Edward R D S  1991  Geochim. Cosmochim. Acta 55 3845-3867

 [3]  Ryan E J, et al.  2021  Infiltration of volatile-rich mafic melt in lower crustal peridotites provokes deep earthquakes.  J. Struct. Geol. 2022

[4]       Sørensen, B.E., et al., In situ evidence of earthquakes near the crust mantle boundary initiated by mantle CO2 fluxing and reaction-driven strain softening. Earth and Planetary Science Letters, 2019.

[5] Bachmann F, Hielscher R and Schaeben H  2010  Solid State Phenomena 160 63-68

[6] Sørensen B E  2013  Eur. J. Mineral. 25 5-10

 

How to cite: Eske Sørensen, B., Ryan, E. J., Larsen, R., Lode, S., Røstad, J., and Grant, T. B.: Planar features, Trace element mobilisation and recrystallization formed during lower crustal CO2 induced seismic deformation of olivine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13208, https://doi.org/10.5194/egusphere-egu23-13208, 2023.

EGU23-13444 | ECS | Posters on site | TS3.11

Fault reactivation by fluid injection: insights from laboratory friction experiments with multiple reactivation sequences 

Stefano Aretusini, Chiara Cornelio, Giuseppe Volpe, Giacomo Pozzi, Elena Spagnuolo, Giulio Di Toro, Cristiano Collettini, Men-Andrin Meier, and Massimo Cocco

Faults can be reactivated by fluid injection and pore pressure increase in the rock volumes surrounding the fault zone. Induced earthquakes represent only one of the possible responses of active faults to pore pressure perturbations, since other strain transients characterize the spectrum of fault-slip behavior. A series of fluid injection experiments, designed and undertaken in the framework of the ERC Fault Activation and Earthquake Ruptures (FEAR) project, will be conducted in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG, Switzerland) to understand fault reactivation processes on a target well-identified fault zone. Small and accessible faults are to be instrumented to monitor deformation and seismicity during both fluid injection and fault reactivation.

The mineralogical, microstructural, and hydraulic properties of the target fault zone are investigated to characterize the fault-slip behavior. Characterization of the frictional response is achieved through a suite of laboratory rock-deformation experiments using both double-direct and rotary experimental apparatuses. Fault stimulation by fluid pressurization was also simulated in laboratory by using an injection protocol reliable for the in-situ hydraulic stimulation and consisting of stepwise pore fluid pressure increase. Experiments undertaken at low velocity with the double-direct apparatus (BRAVA) suggest that the selected fault, composed of mixed phyllosilicate-granular materials, is frictionally stable but yet can be dynamically reactivated by hydraulic stimulation.

Experiments were also performed on the fault gouge from the target fault with the rotary experimental apparatus (SHIVA). First, we apply half of the stresses measured at depth in the underground laboratory to accomplish the operating capability of the apparatus: 12 MPa normal stress, 7.5 MPa confining pressure and 1.5 MPa pore fluid pressure. Second, we imposed a slip rate of 10-5 m/s for 0.01 m to have an equally compacted and textured layer. Third, we applied a shear stress so that an equivalent slip tendency of 0.35 is achieved (ca. 2.7 MPa), and kept it constant. We then increased stepwise the pore fluid pressure by 0.1 MPa every 150 s. This allows the spontaneous nucleation of slip events. After fault reactivation, the maximum slip velocity was set to 0.1 m/s. The fluid injection sequence results in a first reactivation (R1). Thanks to the nominally infinite slip available in SHIVA we run a second injection sequence up to a reactivation (R2).

Our experiments show two different styles of reactivation between R1 and R2. R1 reactivation is abrupt, with slip rate accelerating up to 0.1 m/s. Instead, R2 has a stage in which slip rate oscillates (0.5-3 mm/s) just before the last step of pore pressure increase leads to acceleration to 0.1 m/s. This would suggest a role for the shear fabric developed during the first reactivation, in which extensive grain size reduction might have led to stiffening of the fault, responsible of the oscillatory slip. This frictional behavior suggests the importance of considering the effect of texture development during multiple cycles of seismic slip. The generalization of our data and observations will contribute to shed light on the mechanics of faults and induced earthquakes by fluid pressure increase.

How to cite: Aretusini, S., Cornelio, C., Volpe, G., Pozzi, G., Spagnuolo, E., Di Toro, G., Collettini, C., Meier, M.-A., and Cocco, M.: Fault reactivation by fluid injection: insights from laboratory friction experiments with multiple reactivation sequences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13444, https://doi.org/10.5194/egusphere-egu23-13444, 2023.

EGU23-13491 | ECS | Posters on site | TS3.11

Does the polymorphic transition in quartz trigger lower crustal earthquakes? 

Mattia Gilio, Marta Morana, Ross Angel, Boriana Mihailova, and Matteo Alvaro

Earthquakes are generated through the brittle failure of rocks at depth. While earthquakes are generally caused by far–field tectonic stresses, the atomic–scale mechanisms that actually trigger brittle failure in dry ductile crustal rocks are still uncertain. Quartz, a widespread mineral in the lower crust, undergoes an instantaneous polymorphic transformation from the α to β phase at pressure and temperature conditions compatible with the estimates of several lower–crustal paleo–earthquakes recorded as pseudotachylytes. The α–β quartz transition is displacive, reversible and, as α–quartz approaches the transition temperature at constant pressure, its volume increases non–linearly but without sudden jumps. In contrast, near the phase–transition temperature, the bulk modulus of quartz drops from ~30 GPa to almost zero and then abruptly rises to more than 70 GPa within a temperature range of only 10 K (Lakshtanov et al., 2007).

Due to the confined space, near the α–β transition, a quartz inclusion in a garnet host is expected to develop strong differential strains and consequently will impose strong differential stresses on the surrounding host crystal. To check this hypothesis, we have applied in situ high–temperature Raman spectroscopy to quartz inclusions in garnet to monitor the development of structural deformation via the atomic dynamics at temperatures across the phase transition temperature Tc = 847 K for a free quartz crystal at atmospheric pressure. The temperature behaviour of the phonon wavenumbers ω of a quartz inclusion, in particular the hardening and disappearance of a minimum in ω(T) for the A modes near 208 and 464 cm-1 (involved in the α-β phase transition) as well as the persistence of Raman activity of the modes at ~128 cm-1 and ~355 cm-1 above Tc, reveals the accumulation of abnormally high strain in the confined quartz grains in the vicinity of the expected phase transition. Consequently, the corresponding stored elastic energy in the inclusion is released through the inclusion-host boundary into the host matrix while crossing the α–β transition, causing the garnet around the quartz inclusion to fracture or even, in some cases, shatter due to the large differential stresses developing in the inclusion at its transition.  Inclusions of apatite and zircon in the same garnets remain unchanged at the same conditions, excluding the fracturing being caused by the host garnet itself.

We propose that this process can create sufficient fracturing in lower–crustal garnets, which can in turn accumulate into planar fractures along garnet-rich layers and thus trigger brittle failure and seismicity.

References

Lakshtanov, D.L., Sinogeikin, S.V., Bass, J.D., 2007. High-temperature phase transitions and elasticity of silica polymorphs. Physics and Chemistry of Minerals 34, 11-22.

How to cite: Gilio, M., Morana, M., Angel, R., Mihailova, B., and Alvaro, M.: Does the polymorphic transition in quartz trigger lower crustal earthquakes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13491, https://doi.org/10.5194/egusphere-egu23-13491, 2023.

EGU23-13677 | Orals | TS3.11

Phase transition induced stresses and their implications for deep earthquakes 

Marcel Thielmann, Einat Aharonov, Philippe Yamato, and Thibault Duretz

The nucleation and rupture processes of deep-focus earthquakes have remained enigmatic ever since their discovery. These earthquakes occur mostly within the mantle transition zone where brittle failure is extremely unlikely due to the elevated pressures at these depths. Hence, other mechanisms have to be invoked to explain the occurrence of these events. To date, two main hypotheses have been put forward to explain deep focus earthquakes: transformational faulting (due to the polymorphic phase change of metastable olivine to either wadsleyite or ringwoodite) and thermal runaway (due to the conversion of deformational work to heat). More recently, it has been proposed that the feedback between those two mechanisms may explain the observed two-stage ruptures of large deep-focus earthquakes.

To better understand the potential feedback between transformational faulting and thermal runaway, it is necessary to determine the stresses induced by the phase change due to i) the grain size reduction and corresponding viscosity reduction of the transformed material and ii) the volume reduction of the transformed phase. The former process triggers a stress transfer from the transformed material to the untransformed material, whereas the latter results in elevated stresses around the transformed phase.

In this study, we employ numerical models with a viscoelastic compressible rheology to quantify the stress levels and patterns resulting from both processes. To gain a better understanding of the parameters controlling the stress transfer from transforming regions to the surrounding matrix, we employ simplified