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SM – Seismology

EGU24-9250 | Orals | MAL30-SM | Beno Gutenberg Medal Lecture

Seismic images of the continental lithosphere 

Jaroslava Plomerová

Seismic waves propagating through the Earth sample its structure, carry information about its fabrics and physical characteristics and record its present-day state and evolution. In the past, several velocity discontinuities within the radial Earth, which separate its fundamental regions, were retrieved. The lower mantle-core boundary was named as Gutenberg discontinuity in recognition of the Gutenberg’s discovery of the Earth’s core in 1913. This discontinuity relates to the abrupt decrease in P-velocity and diminishing of S-waves in the liquid core. In present-day terminology, the Gutenberg discontinuity is associated with the bottom of the D’’ layer. An area of low velocities in the Earth’s upper mantle denoted as G-discontinuity, has related to Gutenberg’s name until now. The low velocity zone exists just below the oceanic lithosphere, and its characteristics are often used globally in studies of lithosphere thickness in the view of modern plate tectonics. Gutenberg’s Seismicity of the Earth (1941) became a major influence in later scientists’ efforts to describe the theory of plate tectonics. The accuracy and validity of the Earth models depend on data quality and coverage, i.e., earthquake foci - seismic station ray distribution within the Earth volume studied. Small-sized to large-scale international passive seismic experiments, operated during several recent decades, recorded an unprecedented huge amount of high-quality data, which along with new techniques and computational facilities represent a big step forward in our knowledge of the Earth’s structure. However, many questions still remain unanswered and require further research. Current close international cooperation among seismologists involved in the experiments follow the spirit of Beno Gutenberg’s action as a driving force behind the acceptance of seismology as an international science of earthquake detection and the Earth studies.

We present models of the European lithosphere derived from the propagation of body waves, shear-wave splitting and radial and azimuthal anisotropy of surface waves, including ambient noise. Data for individual studies has been collected from international seismological databases (ISC, EIDA) and from several passive experiments we have organized or participated in. Initial isotropic models are upgraded into anisotropic ones, following the fundamental condition that seismic anisotropy is a 3D phenomenon and thus it has to be evaluated in 3D to get more realistic images of the Earth. We invert/interpret jointly anisotropic parameters of independent observables (directional variations of P-wave travel times, shear-wave splitting parameters) which leads to 3D self-consistent anisotropic models of the continental lithosphere with tilted symmetry axes and characteristic domain-like structure. The individual domains at size from several tenths to several hundreds of kilometers are often sharply bounded and of different thicknesses. We interpret the often sharply bounded domains with systematically oriented dipping fabrics in the continental mantle lithosphere by successive subductions of ancient oceanic plates and their accretions enlarging primordial continent cores. Consequent continental break-ups and assemblages of wandering micro-plates preserve fossil anisotropic fabrics and create patchwork structures of the present-day continents. Supporting arguments for such model exist in petrological and geochemical studies (Babuska and Plomerova, 2020).

How to cite: Plomerová, J.: Seismic images of the continental lithosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9250, https://doi.org/10.5194/egusphere-egu24-9250, 2024.

EGU24-14636 | Orals | MAL30-SM | SM Division Outstanding ECS Award Lecture

Uncovering the tectonic secrets of the Atlantic with broadband ocean-bottom seismology 

Stephen P. Hicks

80% of earthquakes occur underwater, so ocean-bottom seismometers (OBS) are crucial for improving our understanding of earthquake source mechanics along unexplored offshore faults, and fillling key gaps in our images of the deeper solid Earth. Even for ocean islands and island arcs, land stations alone struggle to image underlying structures. Broadband OBSs have been through many design iterations, but many OBS deployments now yield high data recovery rates (>90%). 

Even though my first OBS deployment experience left me feeling seasick, I have since continued to seismically explore the oceans, taking part in several OBS projects. In this talk, I will focus on my recent results from experiments across the Atlantic Ocean. Compared to the faster-spreading and subducting Pacific lithosphere, the less well-studied Atlantic offers a key endmember for refining our knowledge of global tectonics and associated hazards.

In the Lesser Antilles subduction zone, subducting Atlantic lithosphere is heterogeneously hydrated. Local earthquakes recorded by OBSs (VoiLA experiment), allowed me to image seismic attenuation to map fluid and melt pathways through the slab and mantle wedge, showing how slab fluids precondition melt generation and volcanism in arc settings. In the mid-Atlantic, long transform faults can host large M~7 earthquakes in ultra-wide (20-30 km thick) fault zones, allowing a uniquely macro-scale view of how damage zones control seismogenesis. In 2017, OBSs (PI-LAB experiment) recorded a nearby Mw 7.1 earthquake on the Romanche transform fault, triggering detailed teleseismic analysis that show back-propagating rupture fronts, which have since been seen during the 2023 M7.8 Türkiye earthquake. More recently, I analysed a seismic swarm and dyke intrusion in the Azores, which lies on a diffuse transtensional plate boundary. Here, a temporary OBS network (UPFLOW project) installed around the uniquely narrow island of São Jorge yields high-resolution seismicity locations that shed light on magma inflow and drainage along pre-existing faults.

Overall, OBS experiments yield fascinating results, but these results come from vast team efforts, particularly from ship crews and OBS technicians, that often go uncredited. We need to work harder to ensure the long-term sustainability of data from these expensive, often publicly-funded projects, with OBS-specific data preprocessing complications a partial barrier to this.

How to cite: Hicks, S. P.: Uncovering the tectonic secrets of the Atlantic with broadband ocean-bottom seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14636, https://doi.org/10.5194/egusphere-egu24-14636, 2024.

SM1 – General Seismology

EGU24-169 | Posters on site | SM1.1

Dealing with uncertainties related to ground motion prediction models for Georgia, Caucasus Region. 

Nato Jorjiashvili, Ia Shengelia, Tea Godoladze, Irakli Gunia, and Dimitri Akubardia

Georgia is situated in the Caucasus region, which is one of the most seismically active regions in the Alpine-Himalayan collision belt. Analysis of the historical and instrumental seismology of this region shows that it is still of moderate seismicity. The seismicity of the area reflects the general tectonics of the region.

Recently, number of seismic stations and earthquake records in Georgia significantly increased. Thus, we can run more detailed studies regarding ground motion prediction. 

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. In this study ground motion prediction equations are obtained by classical, statistical way, regression analysis. Also, new data and new features such as local soil conditions, fault types, etc. were considered for analysis. In the study models are obtained for PGA (horizontal and vertical), 5%-damped pseudo-absolute-acceleration spectra (SA) are described for periods between 0.01 s and 10 s (for both vertical and horizontal components).

Next stage was to assess the standard deviation and its minimization. Fuzzy Analysis gives a possibility of making optimal decision when available data is insufficient and cannot represent real situation. In our case it is quite difficult to explain all physical processes related to earthquakes. However, it is very important to consider all processes during the hazard assessment. Also, during GMPE assessment it is very difficult to consider site effect very precisely because available data is still insufficient. In this case usage of Fuzzy Analysis is the best solution. We constructed membership functions based on shear wave velocity measurements for each site class. Site classifications were done according to Eurocode8. At the end a significant reduction of uncertainties (~30-40%) was observed.

How to cite: Jorjiashvili, N., Shengelia, I., Godoladze, T., Gunia, I., and Akubardia, D.: Dealing with uncertainties related to ground motion prediction models for Georgia, Caucasus Region., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-169, https://doi.org/10.5194/egusphere-egu24-169, 2024.

For decades, the seismological community has debated the scaling relationships of earthquake sources. The debate centers around whether the scaled energy (ER/M0) remains uniform across all magnitudes, indicating self-similarity, or if there is an increase in scaled energy with seismic moment, M0. To contribute to this discussion, we analyzed coda derived source displacement spectra of 303 local earthquakes that occurred in and around the segments of the North Anatolian Fault Zone (NAFZ) within the Sea of Marmara. Our database includes digital waveform recordings of the events that were occurred between 2018 and 2020 (2.5≤ ML ≤5.7 within a radius of 200 km) and were recorded at 49 seismic stations operated by the Kandilli Observatory and Earthquake Research Institute (KOERI) in the study area. We employed a joint inversion technique to optimize source-, path-, and site-specific factors simultaneously. This was achieved by comparing the observed coda envelope with its physically derived representative synthetic coda envelope based on Radiative Transfer Theory. Our inversion process, conducted across various frequency bands, enabled us to make reliable coda-based seismic moment (M0) and moment magnitude estimates (Mw-coda) consistent with local catalogue magnitudes. The variation of the scaled energy (ER/M0) calculated from the total seismic radiated energy (ER) using coda-derived source displacement spectra for each event tends to increase with seismic moment across most magnitude ranges. This indicates that the crustal earthquakes with Mw-coda 2.5 and Mw-coda 5.7 in this laterally heterogeneous region are likely to follow non-self-similarity. Our findings imply different rupture dynamics working for large earthquakes than small ones and relatively more efficient seismic energy radiation for larger earthquakes along the northwestern part of the NAFZ.

How to cite: Özkan, B., Eken, T., Gaebler, P., and Taymaz, T.: Implications for Non-Self Similar Energy and Moment Scaling of Small-to-Moderate Earthquakes Along the NAFZ: Source Displacement Spectra Derived from Coda Waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-749, https://doi.org/10.5194/egusphere-egu24-749, 2024.

EGU24-1310 | Orals | SM1.1

The seismic source parameters of the South Hangay Fault System in Central Mongolia 

Mungunsuren Dashdondog, Odonbaatar Chimed, Anne Meltzer, and Ankhtsetsteg Dorjsuren

The purpose of the study is to describe a geodynamic process in the study area using its focal mechanism and stress field inversion to characterize precise events along the study area, the rupture zones of the South Hangay Fault System (SHFS). This fault system was activated by four earthquakes which are occurred along the Bayanbulag fault (2012/10/03, Mw=4.7) and Bayankhongor fault (2013/01/05, Mw=4.2, & Mw=4.2; 2013/11/25, Mw=3.9). These earthquakes are the strongest in the fault zone.

From the Mongolian National Data Center's database, it has chosen 2228 occurrences (0.1ML5.4) from the Handay Experiments, which used 72 broadband seismometers to cover Hangay Dome. Using HypoDD with a double-difference technique, its seismic station density provides us with precise hypocenter location along the fault system. Among these events, 47 focal mechanism solutions were determined using the first-motion polarity of the P wave from the experimental seismic networks of Mongolia. Then, we classified the determined focal mechanism parameters. According to classification, three main cluster zones are related to the Bayanbulag (BB), Bayankhongor North (BHN), and Bayankhonor South (BHS) fault zones along the rupture area of the South Hangay Fault System. 

Furthermore, we determined the stress fields, stress regime, and the horizontal maximum (SHmax), and minimum (Shmin) stress orientations for all three zones.  

We concluded that the whole SHFS is a left-lateral strike-slip fault with normal and reverse components, NE-SW shortening, and corresponding NW-SE extension. Its compression orientation in the NE-SW direction is the same as the azimuth direction of the India-Asia collision.

We hope that this stress inversion results can be a useful tool for geodynamic and seismotectonic analysis of this part of Mongolia and it will give a better understanding of different stress regimes.

How to cite: Dashdondog, M., Chimed, O., Meltzer, A., and Dorjsuren, A.: The seismic source parameters of the South Hangay Fault System in Central Mongolia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1310, https://doi.org/10.5194/egusphere-egu24-1310, 2024.

EGU24-1533 | ECS | Orals | SM1.1

Earthquake source characterization in stable continental regions: Application to the Armorican Massif, France 

Marion Alloncle, Antoine Mocquet, and Mickaël Bonnin

The seismic moment M0, the associated moment magnitude Mw, and the corner frequency fc are essential parameters for earthquake studies and seismic risk management. In the context of stable continental regions (SCRs), remote from active plate boundaries, the assessment of these parameters is made difficult by the low energy release associated with each earthquake and the low density of seismological networks.

In the north west of France, the Armorican Massif and its surroundings are part of a SCR, where the densification of the seismological network, completed in 2019, now allows for a reassessment of the regional seismicity. Though characterized by very small strain rates, the region currently displays a high rate of low-to-moderate earthquakes (up to a few Mw lower or equal to 4.0 – 5.0). For such small earthquakes, these assessments are particularly sensitive to the signal-to-noise ratio, to the seismic structure of the region, to its attenuation properties, and to the azimuthal distribution of the regional network with respect to the focal mechanisms.

We attempt to determine the M0, and the fc, of 106 earthquakes, detected in northwestern France between 2015 and 2023, with local magnitudes ML ranging from 2.0 to 5.3, using spectral methods. We obtained a linear relationship between ML and Mw for Mw ranging from 1.5 to 5.0. Our analysis also highlighted the importance of the frequency dependence of attenuation on the assessment of the fc. This study will show the relation between M0 and fc in the region.

How to cite: Alloncle, M., Mocquet, A., and Bonnin, M.: Earthquake source characterization in stable continental regions: Application to the Armorican Massif, France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1533, https://doi.org/10.5194/egusphere-egu24-1533, 2024.

EGU24-1985 | Orals | SM1.1

ProbShakemap: a Python toolbox for urgent earthquake source uncertainty quantification 

Angela Stallone, Jacopo Selva, Louise Cordrie, Licia Faenza, and Alberto Michelini

Seismic urgent computing aims at assessing the potential impact of earthquakes through rapid simulation-based ground-shaking forecasts. However, uncertainty quantification remains a significant challenge in this domain.

While current practice accounts for the uncertainty arising from Ground Motion Models (GMMs), it neglects the uncertainty about the source model, which is only known approximately in the first minutes after an earthquake. Addressing this issue involves propagating earthquake source uncertainty from a multi-scenarios ensemble that captures source variability to ground motion predictions. In principle, this could be accomplished with 3D modelling of seismic wave propagation for multiple earthquake sources. However, full ensemble simulation is unfeasible under emergency conditions with strict time constraints.

Here we present ProbShakemap, a Python toolbox which generates multi-scenario ensembles and delivers ensemble-based forecasts for urgent source uncertainty quantification. It implements GMMs to efficiently propagate source uncertainty from the ensemble of scenarios to ground motion predictions at a set of points, while also accounting for model uncertainty (by accommodating multiple GMMs, if available) along with their intrinsic uncertainty. Notably, ProbShakemap does not rely on any recorded data, and only requires the following event-specific information: latitude, longitude, magnitude and time. ProbShakemap incorporates functionalities from two open-source toolboxes routinely implemented in seismic hazard and risk analyses: the USGS ShakeMap software and the OpenQuake-engine.

We quantitatively test ProbShakemap against past earthquakes, illustrating its capability to rapidly quantify earthquake source uncertainty.

How to cite: Stallone, A., Selva, J., Cordrie, L., Faenza, L., and Michelini, A.: ProbShakemap: a Python toolbox for urgent earthquake source uncertainty quantification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1985, https://doi.org/10.5194/egusphere-egu24-1985, 2024.

EGU24-2254 | Posters on site | SM1.1

Qc, Qp, Qs, Qi, and Qsc attenuation parameters in the southern part of Georgia 

Ia Shengelia, Nato Jorjiashvili, Tea Godoladze, and Albert Buzaladze

Georgia is located in the Caucasus between The black and the Caspian seas and is surrounded by the Greater and Lesser Caucasus. Among the seismic areas of Georgia, the volcanic upland of Javakheti situated in the south of Georgia is notable for its high level of seismicity where three large earthquakes with M6 occurred in the last century. The main goal of the study is to investigate the attenuation properties of the lithosphere in the region using a hundred and twenty local earthquakes in 2008-2020  recorded at five seismic stations equipped with broadband Guralp CMG40T and Trillium 40  seismometers. Earthquake magnitudes varied from 1.5 to 4.1; epicentral distances and depth were smaller than 60 km and 19 km, respectively. The quality factors of coda waves Qcand direct P, S waves Qp,and Qs have been estimated using the single back-scattering model and the extended coda normalization methods, respectively. Wennerberg’s approach has been used to estimate intrinsic Qi and scattering Qs attenuation parameters. The Q values were fitted to a  power-law, of form Q(f)= Q0 (f)n, where Q0 is the quality factor at 1Hz and n is the frequency relation parameter, which depends on the heterogeneity of the medium. The obtained values of Qc, Qp, Qs, Qi, andQsc show the frequency-dependent character in the frequency range of 1.5-24 Hz and are expressed as:

Qc = (47.6±3.8)(1.034±0.048)Qp = (17.4±2.3)𝑓(1.100±0.033), Qs = (28.8±3.3)𝑓(1.048±0.039)

Qi = (62 ± 4) f (0.969±0.052),  Qsc = (177 ± 6) f (0.932±0.051)

The calculated attenuation parameters characterize the entire earth's crust under the Javakheti plateau and the surrounding area. The observed Qc and Qi values are almost identical at different central frequencies and both of them are less than Qsc. This means that the effect of intrinsic attenuation is dominated by scattering attenuation. Comparison of our results for similar lapse times to those obtained in other tectonic and seismic active regions show that the Q values and their frequency-dependent relationships are in an interval of values of tectonically active and highly heterogeneous regions. The results obtained will be useful for source parameter estimation, ground motion prediction, and hazard assessment of the study regions.

How to cite: Shengelia, I., Jorjiashvili, N., Godoladze, T., and Buzaladze, A.: Qc, Qp, Qs, Qi, and Qsc attenuation parameters in the southern part of Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2254, https://doi.org/10.5194/egusphere-egu24-2254, 2024.

EGU24-2853 | ECS | Posters on site | SM1.1

Research on the Importance of Feature Parameters in Seismic Sequence Type Determination Based on Decision Tree 

Xiaoyan Zhao, Youjin Su, and Lingyuan Meng

Based on the catalog of 225 earthquakes with magnitudes 5 or above, the catalog of earthquake sequences, and the focal mechanism of the historical earthquakes in Sichuan-Yunnan region from 1966 to 2021, and referring to the previous research and practice on the estimation of the tendency of the aftershock activity, 10 sample datasets for the judging features of the earthquake sequence types have been constructed. According to the earthquake sequences types—swarm type, mainshock-aftershock type, as well isolated type—three labels have been made. After processing the imbalanced state and the missing state of the feature parameters, a decision tree model was used to study and analyze the importance of feature parameters. The results showed that there were differences in the importance categories of the feature parameters in different periods. As the sequence data increased, sequence type judgment relied more on dynamic sequence data; the parameters related to the main shocks’ focal mechanism and the main shocks’ parameters have a high contribution rate to the sequence classification, while the contribution rate of sequence parameters is extremely low. In overall, the results provided by the model are consistent with the actual empirical prediction methods. The above results can provide some ideas for the preliminary screening, exclusion, and selection of the complex and numerous feature parameters.

How to cite: Zhao, X., Su, Y., and Meng, L.: Research on the Importance of Feature Parameters in Seismic Sequence Type Determination Based on Decision Tree, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2853, https://doi.org/10.5194/egusphere-egu24-2853, 2024.

Through the utilization of P-Alert network data from Taiwan, this study endeavors to estimate earthquake magnitude (Mcaa) using the cumulative absolute absement (CAA) methodology across varying window lengths after the arrival of P-wave. It is differentiated that even the proximity of the nearest 12 stations to the epicenter results in robust magnitude estimations. Notably, the standard deviation between the estimated Mcaa and the moment magnitude (Mw) using 12 stations decreases with the increase in window length and is found minimum for 5s window length. For 3s window the variation between Mcaa and Mw is found ±0.385, whereas, for 5s window it is ±0.313. Consequently, the estimation of Mcaa remains reliable. The magnitude Mpd is alternatively deduced from Pd, utilizing the closest 12 stations situated near the epicenter. The standard deviation of the order of ±0.412 is observed between the estimated Mpd and Mw for 3s window, whereas for 5s window it is ±0.281. A difference is observed using Mpdand Mcaafor comparison with Mw. The standard deviation error decreases for Mcaaand Mpd with increase in window length. While Mpd performs better under a 5s window scenario, it tends to underestimate the magnitude of an earthquake with a magnitude of Mw 7.0. On the other hand, CAA surpasses Pd in magnitude estimation, though with a slightly higher standard deviation compared to Mcaa. As a result, Mcaa is considered a more reliable magnitude indicator.

How to cite: Wu, Y.-M.: Cumulative absolute absement for magnitude determination in earthquake early warning system using low-cost sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2969, https://doi.org/10.5194/egusphere-egu24-2969, 2024.

EGU24-3321 | ECS | Posters on site | SM1.1

Imaging of Crust and Lithospheric Mantle of the Incipient Okavango Rift Zone: Implications on the Rifting Mechanism 

Tuo Wang, Ling Chen, Stephen S. Gao, Kelly H. Liu, Youqiang Yu, Zhichao Yu, and Xu Wang

The Holocene Okavango Rift Zone (ORZ) marks the southern terminus of the Western Branch of the East African Rift System. Detailed knowledge of the crustal and lithospheric mantle structure of the ORZ is essential to decipher the rifting mechanism and nature of the lithosphere of this incipient continental rift. A 3-D shear wave velocity model from the surface to 160-km depth is constructed by jointly inverting the Rayleigh wave phase velocity dispersion and receiver function data through a non-linear Bayesian Monte-Carlo algorism. The crustal thickness estimates from our new velocity model generally agree with previous receiver function investigations of the region. The crust beneath the ORZ is thinned compared with the cratonic regions to both sides of the rift, suggesting a certain degree of continental stretching. Our velocity model also reveals two low velocity anomalies in the crust and upper mantle beneath the incipient rift, respectively. The shallow low velocity anomaly is mainly confined in the upper and middle crust, and the deeper low velocity anomaly extends from the Moho to at least 160 km depth, with a high-velocity lower crust (~4.0 km/s) in between. Although the two low velocity anomalies are probably both caused by rift-related decompression melting, the structural feature imaged suggests that they are generated separately and individually. Based on our observations, we propose that thermal upwelling and decompression partial melting in the upper mantle of the ORZ have a limited contribution to the stretching and thinning of the crust during the initiation of the continental rifting. The crustal rifting could be induced by an intra-plate relative motion between the South African block and the rest of the African continent along a pre-existing weak zone.

How to cite: Wang, T., Chen, L., Gao, S. S., Liu, K. H., Yu, Y., Yu, Z., and Wang, X.: Imaging of Crust and Lithospheric Mantle of the Incipient Okavango Rift Zone: Implications on the Rifting Mechanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3321, https://doi.org/10.5194/egusphere-egu24-3321, 2024.

 In the present study, seismic gaps are identified as periods with no occurrence of M ≥ 4.0 earthquake over dT ≥ 400 days. After examining all records in the Sichuan-Yunnan-Tibet-Qinghai junction area on the southeastern margin of the Tibetan Plateau in 1970−2022, a total of six M ≥ 4.0 seismic gaps were identified. Spatio-temporal images of the seismic gaps had similar characteristics and demonstrated spatial overlapping and statistical significance. The quiet periods of the six seismic gaps included 419−777 days (approximately 580 days on average). The semi-major-axis and semi-minor-axis lengths were in the 880−1050 km (approximately 987 km on average) and 500−570 km (about 533 km on average) ranges, respectively. Case analysis results revealed that the images of M ≥ 4.0 seismic gaps were of high significance in predicting M ≥ 6.7 strong earthquakes in the region, and they could be used as a predictive index on a time scale of about 1-0.5 year or less.

How to cite: Su, Y. and Zhao, X.: Characteristics and predictive significance of spatio-temporal space images of M ≥ 4.0 seismic gaps on the southeastern margin of the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3496, https://doi.org/10.5194/egusphere-egu24-3496, 2024.

EGU24-4004 | ECS | Orals | SM1.1

Full-waveform tomography for the lithospheric structure of southern Tibetan Plateau 

Qiwen Zhu, Nobuaki Fuji, and Li Zhao

The collision of the Indian and Eurasian plates has resulted in high-altitude Tibetan Plateau with active seismicity. In this study, we apply the seismic box tomography to the southern Tibetan Plateau, aiming to obtain a self-consistent and high-resolution (10−20 km) model of the crust and upper mantle beneath the region, including density as well as bulk and shear moduli without a priori constraints, which provides us with crucial constraints on the compositional and thermal structures of a highly deformed lithosphere in southern Tibetan Plateau.

In order to obtain the seismic tomographic model, we perform full-waveform inversion of teleseismic (30°−90°) surface- and body-wave waveforms recorded by the Hi-CLIMB network, a densely distributed (5−10 km station spacing) N-S oriented linear seismic array deployed during 2002 and 2005. In our iterative hierarchical inversion workflow, we calculate the sensitivity kernels based on the adjoint method and the model is updated by the L-BFGS algorithm. Data covariance matrices are introduced to control the data quality and objective weighting functions for different seismic events. We will present our preliminary results of the on-going study with comparison to existing models.

How to cite: Zhu, Q., Fuji, N., and Zhao, L.: Full-waveform tomography for the lithospheric structure of southern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4004, https://doi.org/10.5194/egusphere-egu24-4004, 2024.

EGU24-4895 | Orals | SM1.1

Dynamic responses of a building derived from microtremor and seismic signals 

Ruey-Juin Rau, Cheng-Feng Wu, Ying-Chi Chen, Hung-Yu Wu, and Chin-Jen Lin

We used the liquid-based R2 rotational seismometer in addition to several arrays of translation velocity seismometers on a 12-floor building in the National Cheng Kung University campus to evaluate the dynamic responses of the structure. During the observation period in August-October 2023, we encountered a moderate M 5.6 earthquake sequence 61 km north of the campus and one moderate typhoon passing through this 49-m-long and 12-m-wide building. By examining these data, we investigate the natural frequency and the rotation behavior of the long-strip-shaped building. Both the time-frequency and Fast Fourier Transform analyses of the microtremor and earthquake data show two dominant frequencies of ~1.2 Hz and 1.8 Hz occurred in the horizontal directions. The translation velocity and rotation rate are more significant in the transverse, short-axis direction and at the location away from the elevator of the building. The translation velocity array and rotational seismometer show rotations around the horizontal and vertical axes during the M 5.6 earthquake. The results of two natural frequencies and the corresponding rotational motions are most likely related to the asymmetric design of the building, which resulted in the non-rigid behavior of the structure. These findings may provide insights into improvements that could enhance the building’s resilience to seismic or typhoon events.

How to cite: Rau, R.-J., Wu, C.-F., Chen, Y.-C., Wu, H.-Y., and Lin, C.-J.: Dynamic responses of a building derived from microtremor and seismic signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4895, https://doi.org/10.5194/egusphere-egu24-4895, 2024.

In the continuation of the work carried out over the period 1962-2009 as part of the SI-Hex project, work is on going to revise the seismic catalog of mainland France from 2010 to 2018. This time period is characterized by both an upgrade of short-period stations with broadband stations and a major deployment of new broadband stations as part of the Résif-Epos research infrastructure (now called Epos-France), significantly increasing the amount of detected and processed events.

This catalog will benefit from our advances in the use of new artificial intelligence tools, such as PhaseNet, a deep learning automatic picking method, as well as in the development of a deep learning method for discrimination between earthquakes, quarry blasts and explosions.

This catalog will be built from those of the national observation service BCSF-Renass, CEA/LDG and regional seismological observatories (Isterre, OCA, OMP). The earthquake picks from these catalogs will be supplemented by those automatically obtained by deep learning on all the waveforms from the Epos-France (formerly Résif-Epos) stations daily used by BCSF-Renass (as part of its mission to monitor seismicity in mainland France) including stations from neighboring countries (GB, LU, BE, DE, CH, IT, ES), as well as those from temporary network stations (AlpArray, CifAlps2). 

The process workflow includes several steps. The first one consists in a clustering of picks close in time to reduce the amount of picks to process; duplicated picks are removed and priority is given to the manual ones. The second step is the association of seismic phases to create events, by combining the HDBSCAN algorithm - to merge picks close in time and space - with the PyOcto one - to discard picks that did not follow typical travel-time curves. The third step consists in event location using NonLinLoc algorithm with several regional models chosen based on the prior location obtained from PyOcto. At the last step, a moment magnitude Mw is computed (when possible) from waveform spectral fitting using a modified version of SourceSpec. To compute robust magnitudes in particular for low magnitude events, we include magnitude station corrections computed from statistics on magnitude differences between event and stations. Finally, events information (ie. origins, magnitudes) coming from the various catalogs are integrated into the multi-origin catalog according to the QuakeML standard, with the preferred location being the new one computed on the third step.

This catalog currently under revision will represent an update of seismicity in France over the period 2010-2018. Preliminary results show that it will incorporate a significantly increased number of low-magnitude events, detected thanks to the inclusion of picks from artificial intelligence tools. Event labeling is consolidated using our deep learning discrimination algorithm, and a Mw magnitude is calculated for each event using waveforms.

How to cite: Grunberg, M. and Lambotte, S.: A new workflow for revising the seismicity catalog for mainland France, covering the period 2010-2018, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5100, https://doi.org/10.5194/egusphere-egu24-5100, 2024.

EGU24-5890 | Posters on site | SM1.1

On the temporal variations of near-surface seismic structure of Taiwan and its geological inferences 

Hui-Chu Chen, Yuancheng Gung, Hsin-Yu Lee, and Li-Wei Chen

We report on the temporal variations of the near-surface (< 500 m) seismic structure (Vp, Vs, and Vs anisotropy) of Taiwan using the empirical Green’s functions of body waves between vertical station pairs at 60 borehole sites. In our previous work, the obtained near-surface anisotropy are categorized into stress-aligned anisotropy (SAA) and orogeny parallel anisotropy (OPA). Since all the major geological units of Taiwan are well sampled by borehole arrays, and drilling data for 52 sites are available, we were able to find that OPA is typically stronger than SAA, SAA strength is generally higher in sedimentary rocks, igneous rocks, and gravel sediments compared to fine-grained sediments, and OPA is more pronounced in foliated metamorphic rocks than in dipping sedimentary strata. In this study, we aim to address the following specific questions with the obtained results: (1) How do the temporal variations of near-surface seismic properties in different geological units of Taiwan correlate with seismic activity or nearby earthquake events? (2) Are there distinct patterns in the temporal variations of anisotropy strength based on the specific geological composition? (3) Do sites characterized by OPA exhibit different temporal variations in response to seismic activity compared to sites dominated by SAA?

How to cite: Chen, H.-C., Gung, Y., Lee, H.-Y., and Chen, L.-W.: On the temporal variations of near-surface seismic structure of Taiwan and its geological inferences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5890, https://doi.org/10.5194/egusphere-egu24-5890, 2024.

EGU24-7189 | ECS | Posters on site | SM1.1

Observation of intraplate repeating earthquakes within the fault zone of the 2008 ML 3.6 earthquake 

Seula Jung, Dong-Hoon Sheen, Chang-Soo Cho, and Kwangsu Kim

The repeating earthquake (RE) ruptures a single fault patch repeatedly and generates highly similar waveforms. The RE is often observed in the area of subduction zones (Uchida and Matsuzawa, 2013; Yu et al., 2013; Uchida, 2019). However, even in the intraplate region, the RE has been found in the ruptured fault zones (Li et al., 2007; Li et al., 2011; Bisrat et al., 2012). We searched for REs around the epicenter of the 2008 ML 3.6 Gyerong earthquake that occurred in Mount Gyeryong, the Korean Peninsula, located in a stable intraplate region. In the study area, 48 earthquakes (ML 0.4–3.6) were reported during 2002–2022, while we found 50 earthquakes during 2018–2022 using a template matching. We located the events based on the Hypoellipse (Lahr, 1999), and also refined the hypocenters using the double difference method (hypoDD; Waldhauser and Ellsworth, 2000) to obtain the high-resolution fault geometry. It is found that the epicenters exhibit a linear alignment of the fault striking along WNW-ESE consistent with one of the strikes of the ML 3.6 event which has a strike-slip focal mechanism with a strike of 108° or 198°, a dip of 83° or 88°, and a rake of -2° or -173°, which indicates that the ML 3.6 earthquake occurred with a left-lateral fault slip. We estimated the rupture directivity of the ML 3.6 event from the apparent source time functions obtained by the empirical Green’s function approach. A vast number of microearthquakes including aftershocks of the ML 3.6 event occurred in the rupture direction (i.e. the east-southeast of the epicenter of the ML 3.6 event). We identified REs based on the waveform similarity (cross-correlation coefficient > 0.95) and their locations (co-location) to distinguish them from neighboring earthquakes. We found that the REs occurred within the rupture radius of the ML 3.6 event. Upon categorizing these REs according to their family duration, we identified three swarm-type families that occurred in 2007, 2009, and 2010, along with a continuous-type family spanning from 2011 to 2019. These observations demonstrate the close relationship between the REs and the ML 3.6, specifically highlighting the fault’s rupture and healing process.

How to cite: Jung, S., Sheen, D.-H., Cho, C.-S., and Kim, K.: Observation of intraplate repeating earthquakes within the fault zone of the 2008 ML 3.6 earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7189, https://doi.org/10.5194/egusphere-egu24-7189, 2024.

EGU24-7660 | Orals | SM1.1

Source analysis of the 2022 Nord Stream and 2023 Balticconnector underwater explosions 

Andreas Steinberg, Nicolai Gestermann, Lars Ceranna, Gernot Hartmann, Björn Lund, Eric Dunham, Patrick Hupe, Peter Voss, Tine Larsen, Trine Dahl-Jensen, Andreas Köhler, Johannes Schweitzer, Christoph Pilger, Thomas Plenefisch, Klaus Stammler, Stefanie Donner, Peter Gaebler, and Christian Wiedle

On 26 September 2022 two seismic events near the Danish island of Bornholm in the Baltic Sea were detected. The first event with a magnitude Mw 2.3 occurred at 00:03 UTC 40 km east-southeast of Bornholm. The determined location and the origin time of the event are consistent with data of the pressure decrease on one of the Nord Stream 2 pipelines. Another sequence of events occurred 17 hours later at 17:03 UTC around 60 km north-east of Bornholm with a maximum magnitude of Mw 2.7. It consists of three closely successive, but separable, single events. Using relative localisation methods and the gas pressure inside the pipeline recorded at the landing site in Germany, we can assign the epicentres of the three events to the locations of the leaks in the pipelines of Nord Stream 1 and 2.

Based on comparable events in the region, which include both tectonic earthquakes and explosions, the explosive character of the investigated Nord Stream events can be verified. Infrasound signals associated with the destruction of the Nord Stream pipelines were recorded at two stations (I26DE in the Bavarian Forest and IKUDE near Kühlungsborn) in Germany. Particularly after the event sequence at 17:03 UTC, distinctive signals were registered whose characteristics indicate an explosive event with subsequent gas leakage at the surface.

Our modelling of the sources shows that the measured seismic signals can sufficiently be explained by the instantaneous gas release. Synthetic seismograms for such a source and a subsurface model adapted for the study area show high consistency with the measured signals. Based on the released energy and the characteristics of the recorded waveforms, we conclude that the impulsive gas release from the burst gas pipes constitutes the dominant part of the signal source. The model places an upper limit of approximately 50 kg TNT equivalent on the yield of the chemical explosive component of the events, but we note that smaller yields may also be consistent with the data.

We also carried out an analysis of the seismic signals of the event on the Balticconnector pipeline between Finland and Estonia on 8 October 2023 and found that again the instantaneous gas release can sufficiently explain the observed data. This supports a possible mechanical cause of the damage.

 

How to cite: Steinberg, A., Gestermann, N., Ceranna, L., Hartmann, G., Lund, B., Dunham, E., Hupe, P., Voss, P., Larsen, T., Dahl-Jensen, T., Köhler, A., Schweitzer, J., Pilger, C., Plenefisch, T., Stammler, K., Donner, S., Gaebler, P., and Wiedle, C.: Source analysis of the 2022 Nord Stream and 2023 Balticconnector underwater explosions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7660, https://doi.org/10.5194/egusphere-egu24-7660, 2024.

EGU24-8482 | ECS | Orals | SM1.1

Tracking a Vibroseis Truck and Investigating the Wavefield using 6 Rotational Sensors in Fürstenfeldbruck, Germany  

Gizem Izgi, Eva P.S. Eibl, Frank Krüger, and Felix Bernauer

Six-degree-of-freedom (6-DoF) measurements, which combine rotational sensors and seismometers, provide a comprehensive dataset that allows seismologists to determine the back azimuth of a potentially moving source from a single-point measurement. Our investigation focused on tracking the movement of a vibroseis truck operating from 20 November 2019, 11:00 UTC, to 21 November 2019, 14:00 UTC. Using 480 sweep signals, each lasting 15 seconds and covering a wide frequency range from 7 to 120 Hz, we measured at 160 different locations. Back azimuths for each sweep were derived from the 6-DoF data, and root mean squares were calculated for each component. This procedure was repeated for five additional rotational sensors of the same type.
During the first day, the north component of all sensors recorded larger amplitude signals than the East and Vertical, indicating the dominance of SV (shear-vertical) wave energy. Subsequently, we observed gradually increasing amplitudes on the east component, which was consistent with the direction of the moving vibroseis truck. Although the dominant wave type recorded was SV, and the method of comparing horizontal rotation rates was used to calculate the back azimuth, we observed a relatively decreasing accuracy of direction estimates as the truck moved away from the sensors due to increased scattering. To fully understand the reason for this, we investigated the specific fingerprint of each wave type in the wave field. Our results suggest that direction estimates should be made using only the portion of the wavefield containing SV-type waves when using this method, and then the moving source should be tracked accordingly. This approach provides insight into the trajectory of the truck and improves our understanding of the seismic signals generated during the experiment.

How to cite: Izgi, G., Eibl, E. P. S., Krüger, F., and Bernauer, F.: Tracking a Vibroseis Truck and Investigating the Wavefield using 6 Rotational Sensors in Fürstenfeldbruck, Germany , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8482, https://doi.org/10.5194/egusphere-egu24-8482, 2024.

EGU24-8735 | Orals | SM1.1 | Highlight

Near-real time detection of conflict-related explosions or suspicious events using seismological data  

Bettina Goertz-Allmann, Ben D.E. Dando, Andreas Koehler, Quentin Brissaud, Johannes Schweitzer, and Tormod Kværna

Apart from classical earthquake monitoring, seismological data can also be used to detect explosions in near-real-time on both regional and global scales. We demonstrate how seismic and infrasound data can provide more comprehensive and objective information about conflict-related explosions or suspicious events that might be the result of targeted attacks. We can identify the underwater explosions at the Nord Stream pipeline infrastructure in the Baltic Sea in September 2022. Cross-correlation analysis allowed us to identify sub-events several seconds apart which can be associate with specific locations along the pipelines. Furthermore, we detect a signal at the Finish seismic array in October 2023 which may be associated with the damage along the Balticconnector. The other example is from Ukraine, where we present the ability to automatically identify and locate ground explosions related to the Russia-Ukraine conflict with data from the Malin array (AKASG). Between February and November 2022, we observe more than 1,200 explosions from the Kyiv, Zhytomyr, and Chernihiv provinces. Both seismic and infrasound detections can be used to verify and improve accurate reporting of military attacks and help to provide an unprecedented view of an active conflict zone. We analyze events with a variety of seismo-acoustic signatures and significant differences in explosive yield. These can be associated with various types of military attacks, including artillery shelling, cruise missile attacks, airstrikes, or the destruction of the Kakhovka dam NE of Cherson.

How to cite: Goertz-Allmann, B., Dando, B. D. E., Koehler, A., Brissaud, Q., Schweitzer, J., and Kværna, T.: Near-real time detection of conflict-related explosions or suspicious events using seismological data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8735, https://doi.org/10.5194/egusphere-egu24-8735, 2024.

EGU24-9479 | Orals | SM1.1

Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France 

Mickaël Bonnin, Marion Alloncle, Maxime Bes de Berc, Éric Beucler, Damien Fligiel, Marc Grunberg, Céline Hourcade, Clément Perrin, Olivier Sèbe, Jérôme Vergne, and Dimitri Zigone

On June 16, 2023 at 16h38 UTC, a moderate earthquake of magnitude MW=4.9 stroke western France south of Niort city, near the small village of La Laigne (Charente Maritime). The shaking has been widely felt in the whole NW France and macroseismic intensity (EMS98) of VII was reached at the epicenter. Such an event is relatively rare in continental France and represents the second largest event in the western France in the last century. The epicentral region is located at the northern termination of the Aquitaine basin where 300 m of Mesozoic sediments covers the variscan basement. The focal mechanism obtained from waveform inversion corresponds to a pure dextral strike-slip motion or a pure senestrial strike-slip motion along a EW or NS striking fault plane, respectively.

The fault that ruptured on June 16 is not known. To gain insight on its characteristics, teams of Nantes (Osuna and LPG), of Strasbourg (EOST and ITES) and of the CEA deployed between June 17 and June 22, 2023 for approximately one month, a network of 3-components stations composed of 12 MEMS accelerometers, 104 five hertz geophones and 5 broadband velocimeters in a 40 by 30 km region around the epicenter, with a station inter-distance of approximately 4 km.

We present is this study the first results derived from this unique experiment. In particular, we show that the aftershock sequence (more than 600 events recorded) highlights a planar rupture zone of about 5.4 km2, trending NS and strongly dipping to the East (75°), located between 2 and 5 km depth. Site effect analysis allows us to better understand large ground motion distributions over the area and their link with macroseismic intensities. The installed array also allows us to infer a preliminary 3D VS model of the region. We show the extent to which a dense temporary network is mandatory for studying the fine structure of the fault plane in a region where previous knowledge of active geological structures is limited.

How to cite: Bonnin, M., Alloncle, M., Bes de Berc, M., Beucler, É., Fligiel, D., Grunberg, M., Hourcade, C., Perrin, C., Sèbe, O., Vergne, J., and Zigone, D.: Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9479, https://doi.org/10.5194/egusphere-egu24-9479, 2024.

EGU24-9598 | ECS | Orals | SM1.1 | Highlight

Seismic Precursor for the October 7th Terrorist Attack? 

Asaf Inbal

Seismic waves excited by human activity frequently mask signals due to tectonic processes, and are therefore discarded as nuisance.  Seismic noise-field analysis is, however, a powerful tool for characterizing anthropogenic activities. Here, I apply this analysis to examine seismic precursors to the October 7 Hamas attack on Israel. The precursory activity in Gaza included massive mobilization which took place in the hours leading to the attack, and was  documented on multiple media outlets. Favourable conditions, which arise due to a temporary lack of anthropogenic activity in Israel, allow remote seismic stations to record signals due to Gaza vehicle traffic. I use these seismograms in order to identify anomalous ground-motions, associate them with pre-attack mobilization, and precisely determine their location. By applying array analysis to three seismic stations located tens-of-kilometers from the Gaza strip, I was able to obtain valuable information on the Hamas attack plans. This suggests that embedding seismic noise-field analysis into decision-making protocols could enhance preparedness, thus providing an opportunity to blunt terrorist attacks and reduce the number of casualties.

How to cite: Inbal, A.: Seismic Precursor for the October 7th Terrorist Attack?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9598, https://doi.org/10.5194/egusphere-egu24-9598, 2024.

EGU24-11960 | ECS | Orals | SM1.1

Reassessment of the historical earthquake of 23 February 1887 in Liguria (north-western Mediterranean) on the basis of magnetogram recordings 

Gabriele Tarchini, Daniele Spallarossa, Stefano Parolai, Denis Sandron, and Angela Saraò

In the early morning of 23 February 1887, the ‘Ligurian earthquake’, a devastating seismic event currently estimated at MW 6.3-7.2, shook the towns of the Italian and French Riviera. It is the most devastating earthquake known in this region: it is thought to have claimed at least six hundred lives, displaced twenty thousand people, and destroyed many historic buildings and houses. As a result of the event, a tsunami with a maximum run-up of two meters near Imperia (Italy) also occurred and the record of the tide gauge in the port of Genoa (Italy) has long been considered the only existing record of the event.

However, we found that the 1887 earthquake was also recorded by historical magnetometers in the UK and France. These instruments were used to measure variations in geomagnetic field strength, but were also able to record seismic waves, which were essentially a simple ‘disturbance’. Almost uninterrupted records of this type of variometric data are held by the British Geological Survey (BGS). Traces recorded at Greenwich, Kew, and Falmouth magnetic observatories, which clearly show waveforms related to the event, were used. The Bureau Central de Magnetisme Terrestre (BCMT) also keeps magnetograms: in particular, we used the recordings of the instrument at Le Parc de Saint-Maur (Saint-Maur-des-Fossés, Paris).

The waveforms were digitized and processed according to the theory of Eleman (1966), which describes the response of a classical declinometer and/or a horizontal force instrument to harmonic ground displacement, and according to the work of Krüger et al. (2018).

The location of the epicenter and the magnitude of this historical earthquake are difficult to characterize with high accuracy, and the focal mechanism of the fault responsible for the event remains controversial to this day. We present the preliminary results of our research, which is focused on the revaluation of the Ligurian earthquake in terms of magnitude and focal mechanism. This would lead for the first time to a definition of magnitude on an instrumental basis for this important seismic event, whose macroseismic intensity is usually assessed based on studies conducted immediately after the event to determine the damage it had caused.

How to cite: Tarchini, G., Spallarossa, D., Parolai, S., Sandron, D., and Saraò, A.: Reassessment of the historical earthquake of 23 February 1887 in Liguria (north-western Mediterranean) on the basis of magnetogram recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11960, https://doi.org/10.5194/egusphere-egu24-11960, 2024.

EGU24-12248 | Posters on site | SM1.1

Seismic Data Compression and Telemetry Bandwidth Considerations for Earthquake Early Warning 

Michael Laporte, Michael Perlin, Marian Jusko, and David Easton

Earthquake early warning systems depend on the prompt, reliable arrival of seismic data at network data centers. Network operators invest significant resources into the design, installation and operation of real-time acquisition systems to ensure maximum data completeness and minimum data latency, to allow EEW processing modules to detect events and issue warnings as quickly as possible.

These mission-critical acquisition systems must perform before, during and after earthquakes, as main shocks are frequently preceded by foreshocks and followed by aftershocks, which are often just as dangerous. As such, a key consideration in the design of these systems is the impact that large earthquakes may have. Seismic data is generally encoded using Steim compression, which is a first difference algorithm. During large events the differences between samples grow, requiring more bits to record and, thus, increasing the data volume. This results in a surge in the throughput required during large events. System designers and network operators must be fully aware of this effect and plan for it accordingly.

This study expands on existing work to further characterize the impact of large events on seismic data compression and the corresponding spikes in throughput which must be supported by real-time acquisition systems. The study will examine the relationship between compression and various factors, including station magnitude, hypocentral distance, sample encoding technique, packet size, sample rate and system sensitivity.

How to cite: Laporte, M., Perlin, M., Jusko, M., and Easton, D.: Seismic Data Compression and Telemetry Bandwidth Considerations for Earthquake Early Warning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12248, https://doi.org/10.5194/egusphere-egu24-12248, 2024.

EGU24-12588 | Posters on site | SM1.1

Preliminary estimation of attenuation properties in the High Agri Valley (Southern Apennines, Italy) by the coda attenuation method 

Vincenzo Serlenga, Salvatore Lucente, Salvatore de Lorenzo, Edoardo Del Pezzo, Marilena Filippucci, Teresa Ninivaggi, Tony Alfredo Stabile, and Andrea Tallarico

High Agri Valley is an intermontane basin of the axial portion of Southern Apennines (Southern Italy), characterized by a very strong seismogenic potential. Indeed, a  Mw=7.0  earthquake occurred in 1857. Currently, the seismic networks managed by ENI Oil Company and INGV, installed in the area, continuously record a low-magnitude natural seismicity. Furthermore, two anthropogenic earthquake clusters are documented in two distinct sectors of the valley, located NE and SW of the artificial Pertusillo lake, respectively. The first cluster is related to the fluid-induced microseismic swarms caused by the injection, through the Costa Molina 2 well, of the wastewater produced by the exploitation of the Val d’Agri oilfield. The second cluster is due to a protracted reservoir induced seismicity (RIS) affected by the combined effects of the water table oscillations of the Pertusillo lake, the regional tectonics and likely the poroelastic/elastic stress due to aquifers in the carbonate rocks.

In this study we investigated the attenuation properties of the High Agri Valley crust by the estimation of the S-coda waves Qc-1, as it is widely recognized the role of fluids on this parameter. We selected a dataset of about 1800 events acquired from 2001 to 2015 by the two above mentioned seismic networks, with local magnitude (ML) ranging from 0 to 3.3. We estimated the attenuation of the target area by means of a linear regression analysis of the amplitude decay curves of the envelopes of the seismograms; these were filtered in the frequency ranges centered on 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16 Hz. The Qc estimates were performed by using different time windows for the envelope fitting, starting from the time T1 to the time TL (the lapse time). In detail, we adopted, as T1, 1.0*Ts, 1.5*Ts and 2.0*Ts (being Ts the S wave arrival time), and as TL 10s, 15s, 20s, 25s and 30 s from the event origin time. Only the components for which the condition T1<TL<T2 was fulfilled were considered for the linear regression, being T2 the end-time of the coda envelope; the latter was automatedly found by a proper methodology implemented in this study.

The obtained results show the increase of Qc as a function of f at all the considered TL. Compared with other tectonic regions worldwide, in the High Agri valley the Qc(f) is very low: the Q0, that is the Qc at 1 Hz, ranges between 8 and 57. At greater frequencies, the highest estimated Qc value is lower than 400. These evidences could be interpreted as the effect of fluids in the investigated crust, thus providing a further hint on their possible role in the seismicity of the area. A complete characterization of seismic attenuation of the High Agri Valley will require further investigations, that is the separation of scattering and intrinsic contributions in the total attenuation and a 3D imaging: indeed, the latter could highlight possible overlapping between spatial attenuation anomalies and seismicity distribution in the investigated area.

How to cite: Serlenga, V., Lucente, S., de Lorenzo, S., Del Pezzo, E., Filippucci, M., Ninivaggi, T., Stabile, T. A., and Tallarico, A.: Preliminary estimation of attenuation properties in the High Agri Valley (Southern Apennines, Italy) by the coda attenuation method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12588, https://doi.org/10.5194/egusphere-egu24-12588, 2024.

EGU24-12990 | Orals | SM1.1

Seismic Network Station Infrastructure as the Basis for Multi-Disciplinary Geophysical Stations 

Michael Perlin, Neil Trerice, Ted Somerville, and Marian Jusko

Geophysical monitoring requires the highest level of performance and reliability from purpose-built and tightly integrated instrumentation and infrastructure. Parallel and separate efforts between different scientific disciplines seen in the past came at the expense of duplicated infrastructure, telemetry and power subsystems, and even land use permits. This duplication increases costs, ultimately limiting station counts and reducing “the reach” of monitoring networks. Recent ambitions to combine multi-disciplinary geophysical applications into streamlined deployments led to initiatives such as the European Plate Observing System (EPOS) and the recent amalgamation of the SAGE and GAGE programs in the United States.

Modern seismic dataloggers, such as the Nanometrics Centaur, support a wide range of seismo-acoustic sensor interfaces and sensor types while maintaining ultra-low power consumption, precise timing, and reliable data transport with automatic back-fill features over flexible telemetry mediums. These properties transformed the Centaur’s capabilities to act as a highly versatile foundation in multi-disciplinary geophysical station deployments. 

Despite initially being designed as a high-performance data recorder for seismic applications, Centaur’s applicability has evolved to include data collection for the infrasonic, geodetic, magnetic, and meteorological domains. This triggered the development and addition of purpose-built features to support multi-disciplinary use cases with the same proven performance and reliability of a Centaur seismic station.

Both existing and planned capabilities that enable reliable and efficient multi-disciplinary science are discussed.

How to cite: Perlin, M., Trerice, N., Somerville, T., and Jusko, M.: Seismic Network Station Infrastructure as the Basis for Multi-Disciplinary Geophysical Stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12990, https://doi.org/10.5194/egusphere-egu24-12990, 2024.

Size distribution of earthquakes, characterized by the power law decay (b-value), sometime displays the major earthquakes before their occurrence. The b-value reflect state of stress and proximity of fault failure condition according to previous studies. However, the causes are difficult to separate each other. This study proposes an additional indicator reflecting the proximity. Seismic moment release in a volume by small earthquake indicates inelastic strain. The efficiency of inelastic strain on stress loaded medium exhibits proximity to strength of the medium based on Mohr diagram and Coulomb failure condition. Thus, we adopt the efficiency as the indicator. We examine b-value and the efficiency variation in pre- and post- seismic activity of the 2016 Kumamoto earthquake sequence. Weighted b-value distribution by the efficiency captured the initiation point of the Kumamoto earthquake. The result suggests utilizing both b-value and the efficiency contribute to improving earthquake alerts and disaster mitigation.

How to cite: Matsumoto, S.: Inelastic strain efficiency of small earthquakes as an indicator for proximity of the 2016 Kumamoto earthquake (M7.3), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13440, https://doi.org/10.5194/egusphere-egu24-13440, 2024.

Seismicity records during the 1990’s reveals that large inland earthquakes tend to concentrate near several active volcanoes in the central part of northeastern (NE) Japan (Hasegawa & Yamamoto, 1994 Tectonophysics). The inland seismicity around active volcanoes could be related to localized zones of high strain contraction detected by the GNSS measurements in 1997–2001 (Miura et al., 2004 JGR). Several studies speculated that the localized strain contraction is caused by inelastic deformation of weak lithosphere beneath the active volcanoes (Hasegawa et al., 2004 J. Seismol. Soc.). Such weak lithosphere (i.e., low-viscosity zone or LVZ) is inferred from high heat-flow observations (Tanaka et al., 2004 EPS), lithospheric strength simulation (Shibazaki et al., 2016 GRL; Muto, 2011 Tectonophysics) and seismic-velocity tomography (Hasegawa et al., 2005 JGR). However, because of complex interplay between elastic and inelastic processes during steady-state (i.e., interseismic) crustal deformation, the physical mechanism related to inelastic deformation is still poorly understood.

When the Mw9.0 2011 Tohoku-oki earthquake occurred, strong surface deformations were observed locally near the active volcanoes (Takada & Fukushima, 2013 Nat. Geosci.) and continued for several years after the mainshock (Muto et al., 2016 GRL). Past studies (e.g., Sun et al., 2014 Nature) advocated that the earthquake-related inelastic processes such as viscoelastic mantle relaxation dominates the crustal deformations in the postseismic period. In the present study, we identified localized strain contractions near the active volcanoes by extracting the short-wavelength strain rate (Meneses-Gutierrez & Sagiya, 2016 EPSL) from the GNSS observations during 2012–2014. We explained these localized strain contraction by building three-dimensional rheological models of small-scale LVZs beneath five active volcanoes of NE Japan. We simulated the volumetric deformation of viscoelastic LVZs using power-law Burgers rheology, which previously succeeded to explain the large-scale postseismic deformation of the 2011 Tohoku-oki earthquake (Agata et al., 2019 Nat. Commun.; Muto et al., 2019 Sci. Adv.; Dhar et al., 2022 GJI). The power-law Burgers rheology represents the bi-phasic nature of rock deformations (rapid transient with subsequent steady state) and power-law dependency of strain rate to evolving stress (proxy of dominating dislocation creep in high-stress mantle condition) (Muto et al., 2019 Sci. Adv. and references therein).

We found that the localized strain contraction near the active volcanoes can be explained by small-scale LVZs which have narrow tops of 10–20 km and wide roots of 60–100 km width. Our results conclude the minimum depths of the tops and roots of LVZs are 15 km and 40 km, respectively. The geometries of the LVZs vary (e.g., upright conic or inclined shape) from volcano to volcano. The effective viscosities of the LVZs are in the order of 1017 Pa·s immediately after the earthquake and increases to the order of 1018 Pa·s over the 3 years of postseismic deformation. Our results agree with the results of several past studies (Ohzono et al., 2012 EPS; Hu et al., 2014 EPS; Muto et al., 2016 GRL) who investigated the lithospheric rheology near Mt. Naruko using the postseismic surface displacements of the 2011 Tohoku-oki and 2008 Iwate-Nairiku earthquakes.

How to cite: Dhar, S., Takada, Y., and Muto, J.: Rheology of weak lithosphere beneath active volcanoes of NE Japan: Insights from postseismic deformation of 2011 Tohoku-oki earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13903, https://doi.org/10.5194/egusphere-egu24-13903, 2024.

A large crustal earthquake (Mw=7.5) struck the Noto Peninsula, central Japan, at 16:10 (JST = UT + 9 hours) on New Year's Day, 2024. The main-shock rupture extended ~150 km in length, which covered the source regions of intense swarm activity in the northeastern tip of the peninsula [Amezawa et al., 2023] as well as the previous large crustal earthquakes such as the 2007 (Mw=6.7) and 2023 (Mw=6.3) events. The aftershock distribution of the 2024 event provides fundamental information for understanding the rapture process of the main shock and seismotectonics in the Noto peninsula. Therefore, we relocated the earthquake hypocenters that occurred immediately after the 2024 event by considering the three-dimensional velocity structure [Matsubara et al., 2022]. In the relocation, we applied the method proposed by Shiina and Kano [2022] to the arrival time data on the earthquake catalog compiled by the Japan Meteorological Agency. The applied method utilized the Markov Chain Monte Carlo technique, allowing us to evaluate uncertainty in hypocenter locations. Thus, we can discuss the distributions of the crustal earthquakes in and around the source area of the 2024 event, taking account of the spatial variations in uncertainty in the hypocenters. For example, some aftershocks occurred offshore, indicating that estimation accuracy in that area may get worse due to limited station coverage compared with the inland area. As the result of the relocation considering the three-dimensional structure, the depth of these offshore events was shifted about 5 km shallower. These hypocenters suggested that the aftershocks of the 2024 event occurred mainly between the ground surface and the depth of 15 km.

How to cite: Shiina, T., Horikawa, H., and Imanishi, K.: Relocations of earthquake hypocenters in and around the source area of the 2024 Mw 7.5 Noto Peninsula earthquake, Japan, by Bayesian inference, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14903, https://doi.org/10.5194/egusphere-egu24-14903, 2024.

EGU24-15253 | ECS | Posters on site | SM1.1

Repeating events detection in northeastern Taiwan using a broadband seismometer array 

Chin-Shang Ku, Bor-Shouh Huang, and Cheng-Horng Lin

In this study, we document unusual and recurring events that transpired within one hour on November 17, 2021. These incidents were identified through a seismometer array deployed in the Yilan area and Turtle Island, northeastern Taiwan. Preceding this series of events, a shallow submarine volcano near Turtle Island emitted sulfur smoke from October 28, 2021, lasting until November 22, 2021. This eruption was marked by a significant release of white sulfur smoke from the sea near Turtle Island. It reached a height exceeding 3 meters and extended over 100 meters into the air, making it the most substantial eruption of the year. At first, we proposed that the giant bubble could be generated during the submarine eruption and expanded through the water and into the atmosphere; the collapse of this bubble was considered a potential source of the recurring events. However, a grid-search method utilizing the arrival times of seismic stations indicates that the source location is close to the seacoast of Yilan, still dozens of kilometers away from Turtle Island. Upon further analysis of the seismic waveforms, it was observed that the propagation velocity is close to the speed of sound and only detected by surface stations, not by shallow-hole stations. This suggests that the source likely produced signals that couple well with the atmosphere rather than the solid Earth. The waveforms exhibit high consistency between different events at the same station, indicating that the sources occurred at the exact location several times within one hour. The possibility of an aircraft-induced shock wave was considered but needs more investigation. Trustworthy sources and their mechanisms remain to be clarified, and additional data, such as infrasound and pressure data, will be essential for a more comprehensive understanding shortly.

How to cite: Ku, C.-S., Huang, B.-S., and Lin, C.-H.: Repeating events detection in northeastern Taiwan using a broadband seismometer array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15253, https://doi.org/10.5194/egusphere-egu24-15253, 2024.

When in 1997 we started to compute Regional CMT for seismic events in the Euro-Mediterranean region, we could not expect to create a Catalog that can well describe the seismicity, the seismotectonics of this really active region with such complex characteristics. The RCMT Catalog includes more than 3200 seismic moment tensors for earthquakes with a magnitude starting from 4.5, but for the Italian region also down to M 4.0, for the time span 1997 to 2023. All RCMTs are available on the web, on dedicated pages, with the possibility to select the preferred dataset choosing intervals for time, geography, magnitude, depth and quality factors (http://rcmt2.bo.ingv.it/searchRCMT.html). In the first years the RCMT computation was based only on the modelling of intermediate-period surface waves. After 2002, it has been possible to invert also for body waves, an improvement that for the RCMT computation has been important for events with M greater than 5.0. The homogeneity of the dataset given by the continuous use of the same algorithm is an added value that has been underlined by several comparisons with other regional catalogs. The lower magnitude threshold applied in the Euro-Mediterranean region produces a dataset three times more numerous with respect to what is available with the Global CMT data only. In 1997 RCMTs were the only seismic moment tensors available for earthquakes with M lower than 5.0 in the Euro-Mediterranean region. Later, several regional and local focal mechanisms have been computed, with different methods and for different sub-regions. At present, on average three or more regional solutions appear on the web after a M4.5 earthquake hits the Mediterranean. However, RCMT Catalog is the one with the longer time interval covered by homogeneous data. Today, the Catalog is continuously updated with a few months of delay between definitive and quick solutions, that are however available on the RCMT web pages up to the time the revised solution is ready.

How to cite: Pondrelli, S.: The European Mediterranean RCMT Catalog: more than 25 years of activity and data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15437, https://doi.org/10.5194/egusphere-egu24-15437, 2024.

EGU24-15494 | Orals | SM1.1

Geology and geomorphology of the Jan 1st 2024 Mw 7.6 Noto Peninsula Earthquake: observations and context. 

Luca C. Malatesta, Shigeru Sueoka, Kyoko S. Kataoka, Tetsuya Komatsu, Sumiko Tsukamoto, Lucile Bruhat, and Jean-Arthur Olive

On January 1st 2024, a Mw 7.6 earthquake shook the Noto Peninsula on the Sea of Japan coast of Central Japan causing over 202 casualties and >100 missing (at the time of submission). The quake follows a period of intensifying seismic activity starting in 2020. The Mw 6.3 Oku-Noto earthquake of May 5 2023 was the previous largest event of the sequence. The Jan. 1 2024 Noto Peninsula earthquake significantly impacted the Peninsula. A large number of landslides and rockfalls dissected the road network. Liquefaction damaged infrastructure up to 150 km away from the epicenter. Meter-scale coseismic uplift modified the northern shoreline with displacement of the coastline by up to 200 m seaward discernible on SAR and aerial image data. At the time of abstract submission (Jan. 10 2024) we only have limited preliminary observations. It appears that the Noto Earthquake ruptured the same or adjacent fault to the May 5 2023 Mw 6.5 earthquake and was in the vicinity of the March 25 2007 Mw 6.9 Noto earthquake. Coseismic displacement measured geodetically shows uplift of up to +3–4 m (SAR) in the northwest of the peninsula (Wajima-shi), and +1.06 m (GPS) in the main town of Wajima-shi. The uplift magnitude decreases gradually to the SE. The uplift is near zero (SAR) or -0.3 m (GPS) on Noto Island (Nanao-shi) 30 km to the south of the town of Wajima. Surface deformation goes back to near zero (GPS) a further 20 km to the south.

The coseismic deformation pattern broadly reflects the deformation recorded in the Noto landscape. Long-term moderate rock uplift in the north gives way to a complex history of long-term slow uplift around Noto Island that likely includes sustained episodes of subsidence, highlighted by its sinuous “drowned” coastline. Along the western shore (Shika-machi), marine terraces presumed to be 120 ka (last Interglacial) show a gradient in elevation also decreasing to the south. In the north, the newly emerged platform does not have a higher marine terrace counterpart. This may reflect the relationship between high wave power and moderate rock uplift resulting in the long-term retreat of the coastline and erosion of any terrace. The Noto Peninsula also holds widespread evidence of drainage reorganization that would reflect varying boundary conditions, in particular rock uplift, in deeper time beyond 100’s ka. The similarities between recent landscape morphology and coseismic displacement suggest that the Jan. 1 2024 rupture fits a recent pattern of crustal strain in Noto Peninsula (at least up to 100 ka). Earlier deformation pattern (>100’s ka) likely happened along different faults and/or at different rates as reflected by the transient drainage network.

By conference time, we will present field observations collected after the rescue and emergency work is completed.

How to cite: Malatesta, L. C., Sueoka, S., Kataoka, K. S., Komatsu, T., Tsukamoto, S., Bruhat, L., and Olive, J.-A.: Geology and geomorphology of the Jan 1st 2024 Mw 7.6 Noto Peninsula Earthquake: observations and context., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15494, https://doi.org/10.5194/egusphere-egu24-15494, 2024.

EGU24-15942 | Orals | SM1.1

Insights into the 36 Years of Seismic Activity at Vulcano Island, Italy, preceding the Volcanic Unrest in 2021 

Susanna Falsaperla, Giovanni Barreca, Ornella Cocina, and Salvatore Spampinato

Numerous episodes of volcanic unrest have taken place at Vulcano island (Italy) since its last Vulcanian eruption occurred 133 years ago. Decades-long seismic monitoring has documented some of them. We have collected and examined all available seismic data recorded since 1985, most of which were in analog format and/or dispersed in old repositories. We were able to compile catalogs where three different types of seismic events are considered according to their location and magnitude: events in the Fossa Crater, in the Lipari-Vulcano complex, and earthquakes with M>2.5. The primary goal of this data collection was to identify the main features of seismic activity on and around the island in the 36 years preceding the last volcano unrest, which began in mid-September 2021 with a high occurrence frequency of Very Long Period (VLP) events. Our review of the past seismic activity allows us to contextualize the newly recorded anomalous variations. Furthermore, we sought the connection with the structural framework of the region.

The duration of the episodes of volcanic unrest in 1985 and 1988 was relatively short (lasting just a few months) when compared to the recent one, which ended in December 2023. The source of the seismic events during those past unrests was mainly close to the reference station (now IVCR) with hypocenters mostly beneath the island at shallow crustal depths (up to 5 km below sea level). Their magnitude remained low (<2.5) during both the episodes (i.e., 1985, and 1988).

Overall, the seismicity recorded in and around the island has reached a maximum value of M4.6 both in the 36 years preceding and during the 2021 unrest. Some preliminary insights can be drawn by comparing the seismicity occurred during past and recent unrest episodes: i) the peculiarly long duration of the most recent unrest, and ii) the importance of broadband equipment, which documented the substantial contribution of VLP seismicity during the 2021-2023 episode.

How to cite: Falsaperla, S., Barreca, G., Cocina, O., and Spampinato, S.: Insights into the 36 Years of Seismic Activity at Vulcano Island, Italy, preceding the Volcanic Unrest in 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15942, https://doi.org/10.5194/egusphere-egu24-15942, 2024.

EGU24-17485 | ECS | Orals | SM1.1

Frequency-dependent delay time analysis for Bhutan Himalaya 

Sayan Bala, Abhisek Dutta, and Chandrani Singh

In this study, we have evaluated the scattering nature of the crust beneath the Bhutan Himalaya, located in the eastern part of the Himalayan arc. We have analysed high-quality waveforms of 566 events having magnitude (ML) below 6, recorded by broadband stations of the GANSSER network operated by the Swiss Seismological Service at ETH Zurich from Jan, 2013 to Nov, 2014. We have investigated the peak delay time (tpd), defined as the time interval between the initial S-wave appearance and the peak amplitude of its envelope, for the frequency ranges of 4–8, 6–12, 8–16 and 12–24 Hz. Initially, we have analysed frequency-dependent nature of tpd at 9 stations (BHE01, BHE09, BHE13, BHN02, BHN06, BHN11, BHW01, BHW10 and BHW16). The observed values of Bfreq, which indicates the frequency dependence of the peak delay time, show mostly low positive values up to 0.3. It shows that tpd is independent of frequency which may be associated with the relative proportions of large as well as small scale heterogeneities present in the mediumAt BHE09, Bfreq exhibits a negative value, which might be attributed to the limited sampling of high-frequency signals that capture small portions of the subsurface along their paths. The crust beneath BHE09 experiences reduced scattering, probably due to the absence of a strongly attenuating body in the subsurface. Furthermore, we aim to extend this study for all the stations and to compare the frequency-dependent nature of T5%-75% (time interval between 5% and 75% of the total integrated power value) and the tpd for the study region.

How to cite: Bala, S., Dutta, A., and Singh, C.: Frequency-dependent delay time analysis for Bhutan Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17485, https://doi.org/10.5194/egusphere-egu24-17485, 2024.

The North Anatolian Fault Zone in Turkey spans 1400 km, passing through densely populated areas, including Düzce, which experienced the destructive Mw 7.2 event in 1999 that caused more than 700 lives. On 23 November 2022, for the first time in over 20 years, a moderate Mw 6.1 earthquake struck the city and surrounding area. Despite its moderate magnitude, the event caused unexpectedly severe damage to numerous buildings, as reported by local institutions (Disaster and Emergency Management Presidency; AFAD). Recognizing the potential impact of near-field effects such as ground motion pulses and directivity effects, which are known to increase damage in the vicinity of the fault, we investigate these phenomena using the AFAD-Turkish Accelerometric Database. Our analysis delves into the spatial distribution of ground motion intensities, revealing higher peak ground velocities in certain azimuthal ranges than predicted by existing ground motion models. Surprisingly, our findings challenge outcomes derived from previous studies, suggesting that impulsive ground motions associated with directivity effects mainly occur on the fault-normal component of large-magnitude events. In contrast, our examination of near-fault recordings indicates a concentration of velocity pulses, primarily on the fault-parallel component, and thus questions the widely established understandings of earlier studies.

How to cite: Türker, E., Yen, M.-H., Pilz, M., and Cotton, F.: Importance of Pulse-Like Ground Motions and Directivity Effects in Moderate Earthquakes based on the 23 November 2022, Mw 6.1 Gölyaka-Düzce Earthquake (Turkey)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17715, https://doi.org/10.5194/egusphere-egu24-17715, 2024.

EGU24-18530 | Posters on site | SM1.1

Recalibration of the intensity prediction equation in Italy using the Macroseismic Dataset DBMI15 V2.0 

Barbara Lolli, Paolo Gasperini, and Gianfranco Vannucci

We re-compute the coefficients of the intensity prediction equation (IPE) in Italy using the data of the DBMI15 V2.0 intensity database and the instrumental and combined (instrumental plus macroseismic) magnitudes reported by the CPTI15 V2.0 catalog. We follow the same procedure described in a previous article, consisting of a first step in which the attenuation of intensity I with respect to the distance D from macroseismic hypocenter is referred to the expected intensity at the epicenter IEand a second step in which IEis related to the instrumental magnitude Mi, the combined magnitude Mc, the epicentral intensity I0 and the maximum intensity Imax, using error-in-variable (EIV) regression methods. 

The main methodological difference with respect to the original article concerns the estimation of the uncertainty of IEto be used for EIV regressions, which is empirically derived from the standard deviation of regression between IE and Miand also used for the regressions of IEwith Mc, I0 and Imax. 

In summary, the new IPE determined from DBMI15 V2.0 is

                                        𝐼=𝐼𝐸−0.0081(𝐷−ℎ)−1.072[ln(𝐷)−ln(ℎ)]

 where 𝐷=√(𝑅2+ℎ2), h=4.49 km and IEcan be calculated from the intensity data distribution of the earthquake. If the intensity data distribution is not available, IEcan be calculated from the following relationships

                                        𝐼𝐸=−2.578+1.867𝑀𝑤

                                                      IE=I0

                                       

How to cite: Lolli, B., Gasperini, P., and Vannucci, G.: Recalibration of the intensity prediction equation in Italy using the Macroseismic Dataset DBMI15 V2.0, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18530, https://doi.org/10.5194/egusphere-egu24-18530, 2024.

EGU24-18752 | ECS | Posters on site | SM1.1

The new earthquake catalog of the Gargano (Southern Italy) OTRIONS seismic network. 

Andrea Pio Ferreri, Annalisa Romeo, Rossella Giannuzzi, Gianpaolo Cecere, Salvatore de Lorenzo, Luigi Falco, Marilena Filippucci, Maddalena Michele, Giulio Selvaggi, and Andrea Tallarico

The OTRIONS seismic network (University of Bari Aldo Moro, 2013, FDSN code OT) is a local network installed in the Apulia region (Southern Italy) with the aim of monitoring the seismicity of the Gargano area (Northern Apulia) and the Salento area (Southern Apulia). OT network is managed by the University of Bari Aldo Moro (UniBa) and by the National Institute of Geophysics and Volcanology (INGV). It started to operate in 2013 and in 2019 the recording stations migrated to EIDA (all details can be found in Filippucci et al., 2021a). In 2021 a first database was collected, with the event detection achieved both manually and automatically with SeisComP3 (Helmholtz-Centre Potsdam), and was released (Filippucci et al., 2021a; Filippucci et al., 2021b).

Now, after ten years of operations, we focus on the microseismicity of the Gargano area with the aim of collecting a new seismic database for the period from April 2013 to December 2022, by using a recently acquired software, CASP (Complete Automatic Seismic Processor), for the automatic detection, picking and location of seismic events (Scafidi et al., 2019). The CASP software is installed on a remote server implemented by RECAS-Bari, the computational infrastructure of INFN and UniBa.

Through an appropriate parameter setting, we adapted CASP and NonLinLoc (Lomax et al., 2000) to the Gargano area and to the seismic stations available, both OT and INGV. We used the 1D velocity model of Gargano (de Lorenzo et al., 2017).

The recorded seismic events were organized in two catalogs: the first one is the automatic catalog, obtained from the automatic locations of CASP; the second one is the manual catalog, obtained through a manual revision of P and S waves arrival times. To evaluate the reliability of CASP, a comparison between the automatic and manual catalog was performed.

From a comparison of the manual catalog with the already released catalog of the Gargano seismicity (Filippucci et al., 2021b), the number of events detected by CASP increased a lot. Furthermore, the results show that the choice of the CASP parameters allows us to lower the minimum magnitude threshold of the recorded microseismicity in the Gargano area. Preliminary analysis of the earthquakes foci shows that the seismicity pattern retrace, substancially, the same discussed in the work of Miccolis et al., 2021.

How to cite: Ferreri, A. P., Romeo, A., Giannuzzi, R., Cecere, G., de Lorenzo, S., Falco, L., Filippucci, M., Michele, M., Selvaggi, G., and Tallarico, A.: The new earthquake catalog of the Gargano (Southern Italy) OTRIONS seismic network., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18752, https://doi.org/10.5194/egusphere-egu24-18752, 2024.

EGU24-20056 | ECS | Orals | SM1.1

Deep Scanning of the Bhutan Eastern Himalaya Seismic Dataset for Local Earthquakes 

Zamir Khurshid, Hamzeh Mohammadigheymasi, Dawei Gao, Jianxin Liu, and S. Mostafa Mousavi

Seismic networks monitor seismic activities across the globe, recording distinctive events within specific geographical and temporal frames. Whether old or new, each seismic record preserves valuable information, with its extraction relying mainly on the sophistication of the method. This study presents the implementation of an advanced earthquake detection workflow on a relatively old dataset, the Bhutan Pilot Experiment. This temporary five-station seismic network in Eastern Himalaya comprised a set of Broadband sensors deployed for 14 months from January 2002 to March 2003. However, outdated methodologies have limited the analysis of the recorded data, resulting in the reporting of only 175 local microearthquakes in this area. In this study, we reprocess the data using the recently introduced deep-scan Integrated Pair-Input deep learning and Migration Location workflow [1] to detect and locate local earthquakes. The IPIML employs the well-known Earthquake Transformer (EqT) model as its core function for initial phase picking, followed by a pair-input Siamese EQTransformer (S-EqT) to further mitigate the false negative rate using a pair-wise model. The S-EqT step demonstrated an approximately 40% increase in average detected phases compared to the standard EqT model. The detected phases are associated using the Rapid Earthquake Association and Location (REAL) method through grid searching, providing a preliminary list of detected events. This list encompasses 2458 detected events, several times larger than the previously reported catalog for this dataset. These events primarily cluster in central and eastern Bhutan, particularly along the Golpara lineament, a recognized strike-slip fault. The subsequent phase of this study involves precisely locating these events through the implementation of the Migration Location (MIL) method.

References
[1] H. Mohammadigheymasi et al., "IPIML: A Deep-Scan Earthquake Detection and Location Workflow Integrating Pair-Input Deep Learning Model and Migration Location Method," in IEEE Transactions on Geoscience and Remote Sensing, vol. 61, pp. 1-9, 2023, Art no. 5914109, doi: 10.1109/TGRS.2023.3293914.

How to cite: Khurshid, Z., Mohammadigheymasi, H., Gao, D., Liu, J., and Mousavi, S. M.: Deep Scanning of the Bhutan Eastern Himalaya Seismic Dataset for Local Earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20056, https://doi.org/10.5194/egusphere-egu24-20056, 2024.

EGU24-20889 | Posters on site | SM1.1

Local to moment earthquake magnitude conversion in mainland France and implications for seismic hazard assessment 

Pierre Arroucau, Clara Duverger, Paola Traversa, Guillaume Daniel, Jessie Mayor, and Gilles Mazet-Roux

Modern ground motion prediction equations used in probabilistic seismic hazard assessment studies are now almost exclusively expressed as a function of moment magnitude MW. Yet, earthquake catalogues produced by seismic observatories often provide local magnitude ML only. It is for instance the case for the Laboratoire de Détection Géophysique (LDG) catalogue recently published by Duverger et al. (2021) for mainland France. A conversion relationship was proposed by Cara et al. (2015) from ML (LDG) to MW. It appears however that this relationship does not result in a good fit when compared to recently compiled MW values for France and neighboring areas (Laurendeau et al., 2020). In this work, we propose a new conversion relationship based on the inversion of ML-MW couples for events present in both the LDG catalogue and the compilation of Laurendeau et al. (2021). In order to avoid the choice of an arbitrary number of segments to model the MW=f(ML) relationship, the inverse problem is solved in a Bayesian framework by means of the reversible jump Markov chain Monte Carlo (rj-McMC) algorithm (Green, 1995; Bodin et al., 2012). The number of segments, as well as their respective slopes and intercepts, are jointly invert for. As moment magnitude uncertainty is not known, it is also considered as an unknown, while the ML uncertainties provided in the LDG catalogue are fully accounted for by random sampling during the McMC process. We observe a geographical dependence of the differences between the available MW values and those obtained from calculation so a location-dependent term is also modeled. This allows to account for the regional attenuation variations that can affect ML estimates. The new conversion law is then applied to the full LDG catalogue and its impact on seismic hazard assessment is explored.

How to cite: Arroucau, P., Duverger, C., Traversa, P., Daniel, G., Mayor, J., and Mazet-Roux, G.: Local to moment earthquake magnitude conversion in mainland France and implications for seismic hazard assessment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20889, https://doi.org/10.5194/egusphere-egu24-20889, 2024.

EGU24-22522 | Orals | SM1.3

Foreshock sequence prior to the 2024 M7.6 Noto-Hanto earthquake, Japan 

Aitaro Kato and Takuya Nishimura

A destructive M7.6 earthquake occurred on January 1st, 2024, at shallow depths along the northern coast of Noto Peninsula on the back-arc side of Central Japan. The earthquake rupture started from an area where an intensive seismic swarm has lasted for more than 3 years (from December 2020). The seismic swarm consisted of numerous small planar faults dipping toward the southeast. In May 2023, an M6.5 event, that was the largest event before the M7.6 rupture, emanated from the swarm area toward shallow depths, resulting in the subsequent increase in the seismicity in the swarm area (Kato 2024 GRL). Then, the seismicity had gradually decayed to a level before the 2023 M6.5 event. Here we have explored the seismic and geodetic data to revel the nucleation process of the M7.6 event. Approximately two weeks before the M7.6 event, seismic activity exhibited a weak localization around the point of rupture initiation. After that, a foreshock sequence commenced roughly one hour before the occurrence of the M7.6 event, concentrated in proximity to the epicenter (within a 1-kilometer epicentral distance). The tightly clustered foreshock sequence consisted of around 20 events, including an M5.5 event 4 minutes prior and an M3 class event 1 second before the onset of M7.6 event. The M7.6 rupture nucleated from the deep side of one of planar clusters that were dominantly dipping toward the southeast direction. The growth process of the rupture in the M7.6 event is characterized by a complicated nature.

How to cite: Kato, A. and Nishimura, T.: Foreshock sequence prior to the 2024 M7.6 Noto-Hanto earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22522, https://doi.org/10.5194/egusphere-egu24-22522, 2024.

EGU24-22523 | Orals | SM1.3 | Highlight

The Impact of the 2024 Noto Peninsula Earthquake Tsunami 

Shunichi Koshimura, Bruno Adriano, Ayumu Mizutani, Erick Mas, Yusaku Ohta, Shohei Nagata, Yuriko Takeda, Ruben Vescovo, Sesa Wiguna, Takashi Abe, and Takayuki Suzuki

The tsunami generated by the Mw7.6 earthquake of Noto Peninsula, Japan left widespread impact. We analyzed multi-modal information and data to elucidate its impact.

We modeled the tsunami propagation and inundation with multiple tsunami source models based on GNSS-based crustal movement and tsunami waveform data to understand its propagation and inundation characteristics. The model results are verified by using post-tsunami field survey data. Preliminary tsunami modeling results implied that severe tsunami impacts were around Noto Peninsula (Shika to Nanao). Through the visualization of tsunami propagation model, we found that the remarkable tsunami refraction around the continental shelf of Noto Peninsula were responsible for high tsunamis in Suzu City. This distinctive sea bottom topography also affected the directivity of tsunami energy toward the Japan sea coasts, especially Joetsu city, Nigata Prefecture. Tsunami in Toyama bay had long duration of oscillation caused by multiple-reflection. The leading (negative) tsunami wave could not be explained by fault rupture and this implied the possibility of submarine landslides.

The post-tsunami field survey teams at Suzu City preliminarily found tsunami run-ups of 3 m or higher with flow depths of 2.5m or higher. Inside the tsunami inundation zone around Noto Peninsula, we found at least 648 houses out of 3398 were destroyed by both the strong ground motion and tsunami.

The cellphone-based population data (Mobile Spatial Statistics) were used to analyze the exposed population in the aftermath of the event. The hourly population estimates with 500m spatial resolution in the coastal communities implied how people reacted and were affected. Approximately 2500 population increase were found in the areas above 10 m after the major tsunami warning was issued.

How to cite: Koshimura, S., Adriano, B., Mizutani, A., Mas, E., Ohta, Y., Nagata, S., Takeda, Y., Vescovo, R., Wiguna, S., Abe, T., and Suzuki, T.: The Impact of the 2024 Noto Peninsula Earthquake Tsunami, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22523, https://doi.org/10.5194/egusphere-egu24-22523, 2024.

This presentation will report preliminary results of multifaceted analyses for the geomorphological aspects of the Mw 7.5 earthquake struck northern tip of the Noto Peninsula, Japan, at 16:10JST on January 1, 2024. The earthquake caused significant uplift of the northern coastal areas of the peninsula, accompanying a tsunami observed widely in the surrounding coastline, along with extensive tectonic deformations observed inland. Spatial extent of the crustal movements accords generally with the relief structures and distribution of marine terraces in the Noto Peninsula, implying the long-term tectonic forcing on the landscape evolution in this region. Numerous coseismic landslides occurred in steep mountainous terrains, which yield vast volume of sediment from hillslopes into fluvial channels. Inventory mapping revealed the localized distribution of the landslides, regulated most probably by geologic and topographic conditions. Areal density of the landslides can be explained by coupled factors of lithological susceptibility of the hillslopes to the seismic shaking and amplification of ground motion at the hilltops.

How to cite: Matsushi, Y.: Geomorphological consequences of the 2024 Noto Peninsula Earthquake: tectonic deformations, coseismic landslides, and their implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22535, https://doi.org/10.5194/egusphere-egu24-22535, 2024.

Since November 30, 2020, an intense earthquake swarm with over 22,000 M≥1 earthquakes and transient deformation have been continuously observed in the Noto Peninsula, central Japan, which is a non-volcanic/geothermal area far from major plate boundaries. During the earthquake sequence, Mw6.2 and Mw7.5 earthquakes occurred on May 5, 2023, and January 1, 2024, respectively. We report the transient and coseismic deformation related to the earthquake sequence by a combined analysis of multiple Global Navigation Satellite System (GNSS) observation networks, including one operated by a private sector company (SoftBank Corp.), relocated earthquake hypocenters, and tectonic settings. The start of the transient deformation coincides with a burst-type activity of small earthquakes in late 2020. A total displacement pattern in the first two years shows horizontal inflation and uplift of up to ~60 mm around the source of the earthquake swarm. The overall deformation rate gradually decreased with time except for the coseismic displacement of the Mw 6.2 earthquake and its postseismic displacement. On January 1, 2024, the coseismic horizontal and vertical displacements reached ~2 m at several GNSS sites. The pattern of the postseismic displacement for the first three weeks is similar to that of the coseismic displacement, though spatial decay of the postseismic displacement from the epicentral area is much gentler than that of the coseismic displacement. Viscoelastic relaxation of the mantle and/or lower crust is probably an important factor in explaining the observed deformation. In order to explain the transient deformation before the Mw6.2 and Mw7.5 earthquakes, we assumed a southeast-dipping fault plane based on the observed seismicity and regional tectonics and estimated the distribution of both reverse-slip and tensile components on the fault plane. In the first three months, a significant tensile component with a small slip component was estimated around a depth of ~15 km. The estimated volumetric increase is ~1.4 x 107 m3. Over the next 15 months, the observed deformation was well reproduced by shear-tensile sources, which represent an aseismic reverse-type slip and the opening of the southeast-dipping fault zone at a depth of 14–16 km. These slips and openings of the fault are estimated mainly at the down-dip extension of the intense earthquakes. We suggest that the upwelling fluid spread at a depth of ~16 km through an existing shallow-dipping permeable fault zone and then diffused into the fault zone, triggering a long-lasting sub-meter aseismic slip below the seismogenic depth. The aseismic slip further triggered intense earthquake swarms including the Mw6.2 and Mw7.5 earthquakes at the updip.

Acknowledgments: We are grateful to SoftBank Corp., ALES Corp., and GSI for providing us with GNSS data.

How to cite: Nishimura, T., Hiramatsu, Y., and Ohta, Y.: Deformation of the 2020-2024 Noto Peninsula earthquake sequence revealed by combined analysis of multiple GNSS observation networks in central Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22539, https://doi.org/10.5194/egusphere-egu24-22539, 2024.

EGU24-22540 | Orals | SM1.3

Ground motions and geotechnical aspects of the Noto Peninsula earthquake, Japan 

Hiroyuki Goto, Ayaka Nakatsuji, Dongliang Huang, and Silvana Montoya-Noguera

The Noto Peninsula earthquake (MJ7.6, MW7.5) caused extensive damage to buildings and infrastructure in the Noto Peninsula located in the northern part of Ishikawa prefecture, Japan. The hypocenter was within the area of the earthquake swarm that started in 2020. However, the source fault bilaterally ruptured over a length of 150 km beyond this area. The main residential areas in Wajima, Suzu, and Anamizu are located almost above the western segment of the reverse fault. The geographical features of the Noto Peninsula pose significant challenges for aid and support, particularly due to embankment and soil failures that caused main road closure or limited access. This has led to increased traffic on the few accessible routes, further delaying the arrival of support. The situation has hindered the restoration of essential services such as water and sewage systems and has slowed down the process of demolishing buildings deemed dangerous.

Valuable strong motions were observed during this event. The maximum Peak Ground Acceleration (PGA) in the horizontal component reaching 2.78g was recorded at the K-NET ISK006 station, a location known for significant site amplification around 0.2s. This value aligns with the dominant period in the Spectral Acceleration (Sa), thus the extreme PGA was probably due to the enhanced short-period component in the shallow soil amplification. In addition, K-NET ISK002 and ISK005 recorded large PGVs of 1.31 m/s and 1.59 m/s, respectively, and observed the remarkable Sa with 1.3g and 2.2g at T=1.0s, respectively, which are similar to the damage-prone record in the 1995 Kobe earthquake (JR Takatori record).

In the main residential areas of Anamizu and Wajima, two seismic stations are operated. One is located on the stiff soil ground, and the other is located in zones where residential damage was most severe. In both Anamizu and Wajima, the records at the damage site were amplified in the periods of 1-4 s, suggesting that the residential damage is related to the site amplification. Since the spectral ratio of the weak motions shows the amplification at periods of less than 1s, the major reason for the amplification at periods of 1 to 4 seconds during the main event is due to the nonlinear response of the soil ground.

How to cite: Goto, H., Nakatsuji, A., Huang, D., and Montoya-Noguera, S.: Ground motions and geotechnical aspects of the Noto Peninsula earthquake, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22540, https://doi.org/10.5194/egusphere-egu24-22540, 2024.

EGU24-22541 | Orals | SM1.3

Extensive liquefaction and building damage on the Niigata Plain due to the 1 January 2024 Noto Peninsula Earthquake: Geomorphological and geological aspects and land-use in coastal and lowland areas 

Kyoko Kataoka, Atsushi Urabe, Ryoko Nishii, Takane Matsumoto, Hirofumi Niiya, Naoki Watanabe, Katsuhisa Kawashima, Shun Watabe, Yasuhiro Takashimizu, Norie Fujibayashi, and Yasuo Miyabuchi

The Niigata (Echigo) Plain facing the Sea of Japan is located downstream of two large rivers (the Shinano-gawa River and the Agano-gawa River), and has three sand dune ridges which formed along the coastal areas during the Holocene. Niigata city, with a population of ~770,000, lies in the lower catchment of the alluvial-coastal system. Despite the city being approximately 160 km away from the epicenter of the January 1st 2024 Mw 7.6 Noto Peninsula Earthquake, extensive damage to houses, buildings, and infrastructure occurred throughout Niigata city due to pervasive liquefaction (resulting from the earthquake) in the coastal and lowland areas.

Our field investigation focuses on the Nishi-ku (west ward) of the city, where much of the liquefaction-induced building damage (~ 700 houses at the time of submission of the abstract) is concentrated. Although our “ground truth” fieldwork is still ongoing, we have manually mapped the distribution of damaged houses/buildings, road deformation, sand boiling (sand volcanoes), cracks, slides, groundwater springs and other related phenomena onto map sheets, before then digitising these data using GIS.  The distribution of damage is concordant with geomorphology—such as the Holocene sand dunes (and associated landforms) and buried meander loop of the Shinano-gawa River—as well as with subsurface geology (e.g. the location of the water table). Some damage areas are coincident with artificially modified landforms.

Liquefaction conspicuously occurred on natural (i.e. not artificially modified) gentle slopes of the Holocene coastal sand dunes and interdune swale/lowland. In particular, ground was liquefied in the lower parts of the landward slope of the sand dune (formed ~1800­–900 years ago) which has a lateral extension of ~7 km at the elevation of ~0–3 m above sea level. Sandy subsurface geology and high groundwater level of the Holocene sand dune, together with the force of gravity on the slopes, were probable contributors to liquefaction.

Evidence for liquefaction —including damage to houses—was observed in modern residential areas developed above the buried meander loops of the Shinano-gawa River, which have been historically filled in artificially with sandy material. Damage was also noted in houses built upon an artificially buried pond. However, there was no liquefaction on the natural levee along the abandoned meander loops where relatively old settlements are present.

Similar liquefaction occurred in Niigata city on the sand dune slopes and associated lowlands at the time of the M 7.5 Niigata Earthquake in 1964; the epicenter was in the Sea of Japan, approximately 60 km from the city.  Despite the Noto Peninsula Earthquake occurring remotely from Niigata, the aftermath of the earthquake indicates that certain geomorphologic and geological factors, coupled with particular seismic conditions, can result in repeated liquefaction. 

The field observation is still ongoing after the earthquake. Therefore this abstract is based on tentative results and analysis of our investigation so far. Further information on liquefaction related to the geomorphology and subsurface geology in this area will be available by the time of the 2024 EGU General Assembly.

How to cite: Kataoka, K., Urabe, A., Nishii, R., Matsumoto, T., Niiya, H., Watanabe, N., Kawashima, K., Watabe, S., Takashimizu, Y., Fujibayashi, N., and Miyabuchi, Y.: Extensive liquefaction and building damage on the Niigata Plain due to the 1 January 2024 Noto Peninsula Earthquake: Geomorphological and geological aspects and land-use in coastal and lowland areas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22541, https://doi.org/10.5194/egusphere-egu24-22541, 2024.

EGU24-22563 | ECS | Orals | SM1.3

The 2024 Mw 7.5 Noto Earthquake, shallow rupture with a stagnant initiation in a fluid-rich immature fault zone 

Haipeng Luo, Zhangfeng Ma, Hongyu Zeng, and Shengji Wei

Seismic hazard evaluation at critical infrastructures, such as nuclear power plant, urges deeper understanding on the fundamental physics that govern the initiation, propagation and termination of damaging earthquakes. The 2024 moment magnitude (Mw) 7.5 Noto Peninsula earthquake produced great hazards and exhibited complex rupture process. We derive high-resolution 3D surface deformation of the event using dense space geodetic observations, which reveal two major deformation zones separated by ~40 km along the coast of the Peninsula. Two large (>10m) shallow slip asperities with over 10 MPa stress drop on the thrust faults explain excellently the geodetic observations. A calibrated back-projection using teleseismic array high-frequency data shows that the rupture was stagnant around the hypocentre for ~20s before it propagated bilaterally at the speed of 3.4 km/s and 2.8 km/s towards southwest and northeast, respectively. The slow start of the rupture coincides with the seismic swarm surged since 2020 due to lower crust fluid supply, suggesting low normal stress (high pore fluid pressure) at the bottom edge of the seismogenic zone slowed down the initial rupture. The first major asperity of the rupture was accompanied with intense high frequency seismic radiation, and such radiation is even stronger from the largest asperity located at the southern edge of the Peninsula where the Peak-Ground-Acceleration (PGA) exceeding 2.6G at a site that is less than 40km away from the nuclear power plant. Large stress accumulation together with rough fault geometry and/or friction are likely responsible for the exceedingly large high-frequency radiation, which is mostly responsible for devasting damages.

How to cite: Luo, H., Ma, Z., Zeng, H., and Wei, S.: The 2024 Mw 7.5 Noto Earthquake, shallow rupture with a stagnant initiation in a fluid-rich immature fault zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22563, https://doi.org/10.5194/egusphere-egu24-22563, 2024.

SM2 – Computational, Theoretical and Data-Intensive Seismology

The propagation of rupture at the interface between a layer and a half-space, arising from their relative slipping, is commonly observed in geophysics and in technological materials. Fault ruptures develop as a consequence of ongoing aseismic interfacial movement caused by geological forces; and accumulation of stress over time ultimately leads to a sudden stress release resulting in seismic phenomena. In mathematical terms, it is a highly nonlinear and multiscale phenomenon that necessitates the accurate solution of elastodynamic equations and interfacial fault friction across an extensive domain over an extended time period. The most numerically efficient algorithm for simulating this process is the Boundary Integral Equation Method (BIEM). It computes field quantities at the fracture plane and reduces domain dimensionality of the problem by one, but its current applicability is mostly limited to planar interfaces and to unbounded geometries. BIEM computes elastodynamic fields at the fracture plane from a space-time traction history by utilizing suitable convolution kernels (dependent on the geometry and the material/bi-material characteristics across the interface). Applying BIEM to a geometry involving a layer over a half space presents significant challenges, particularly due to the difficulty in analytically deriving convolution kernels for finite geometry and in-plane deformations. Here, we develop an integrated approach, combining the traction formulation of BIEM (Ranjith, 2015) with the Finite Difference Method (FDM), to overcome these challenges. A hybrid FDM-BIEM has previously been used by Hajarolasvadi and Elbanna (2017) using the velocity formulation of BIEM (Geubelle and Rice, 1995) for unbounded geometries. In the present work, a fourth-order staggered-grid FDM is employed to model dynamic rupturing in a layer. The layer is adjoined by an elastic half-space. The elastodynamic equations in the half-space are handled using a BIEM. The FDM region incorporates a slip-weakening friction law at the fault interface using a thick fault zone model consisting of two grid rows (Madariaga, Olsen and Archuleta, 1998). By applying traction boundary conditions, it computes updated velocities in the domain, and passes them to BIEM. BIEM, in turn, responds with updated tractions at the boundary, utilizing convolution kernels derived by Ranjith (2015). We utilized the hybrid FDM-BIEM numerical algorithm to study the effect of finite layer thickness on rupture propagation, considering both homogeneous and bi-material fault interfaces. The results suggest that the present method has the capacity to effectively deal with a wide array of problems in finite domains often countered in both geophysics and technological domains.

How to cite: Painuly, A. and Kunnath, R.: Dynamic Slip Rupture at a Layer-Half-space Interface: A Hybrid Finite Difference and Spectral Boundary Integral Equation Method for Numerical Simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4263, https://doi.org/10.5194/egusphere-egu24-4263, 2024.

EGU24-4424 | Posters on site | SM2.1

Improving Seismic Hazard Assessment in Southeast Spain through CyberShake: A Physics-Based Approach 

Natalia Zamora, Marisol Monterrubio, Otilio Rojas, Rut Blanco, Cedric Bhihe, and Josep de la Puente

The Eastern Betic Shear Zone (EBSZ) experiences slow seismic deformation that leads to relatively low seismicity rates. Due to this, historical records underscore the substantial impact that earthquakes have had on local communities. The dearth of comprehensive data on moderate to large seismic events in this area, limits the accurate generation of seismic hazard and risk maps, posing a significant challenge for seismic risk planning. A way to address these limitations is leveraging physics-based earthquake simulations in the Southeast Iberian Peninsula. These simulations first require integrating paleoseismic data, models of fault distribution –such as the Quaternary-Active Faults Database of Iberia, seismic source characterizations and historical seismic catalogs, to construct an Earthquake Rupture Forecast (ERF), where likelihood of each fault rupture is weighted by an occurrence probability. Our study focuses on developing physics-based rupture scenarios and shake maps using CyberShake. CyberShake is designed to perform physics-based probabilistic seismic hazard assessments (PB-PSHA) by simulating a vast set of synthetic ground-motion time histories from kinematic rupture scenarios on the ERF three-dimensional finite-fault array. Originally tailored for PB-PSHA studies in Southern California by the SCEC (Southern California Earthquake Center); this research represents the first CyberShake application for Southeast Spain. The resulting shake maps represent an alternative basis for updating regional probabilistic seismic hazard maps and also could support crucial decision-making processes following a local earthquake, offering valuable insights for effective response strategies.

How to cite: Zamora, N., Monterrubio, M., Rojas, O., Blanco, R., Bhihe, C., and de la Puente, J.: Improving Seismic Hazard Assessment in Southeast Spain through CyberShake: A Physics-Based Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4424, https://doi.org/10.5194/egusphere-egu24-4424, 2024.

The Central Italy area close to the town of Amatrice was hit by a seismic sequence that started with a Mw 6.2 mainshock and lasted more than 1 year, with the highest event being the Mw 6.5 earthquake in Norcia. Reliable prediction of ground motion is difficult due to the limited data available particularly in the near-source; for this reason, we need realistic simulations of near-source broadband ground motion for seismic hazard assessment. Such simulations should be accurate and computationally efficient. In this work, we performed physics-based simulations to investigate ground motion variability for the Amatrice and Norcia earthquakes. Using the Frequency-Wavenumber (FK) technique we generated broadband ground motion time histories up to 10 Hz for both earthquakes. We exploited accurate source rupture models and various sets of Green’s functions generated with 1D velocity models obtained by slightly modifying the 1D velocity model of the Central Apennine Area proposed by Hermann et al. (2011). First, we employed the Graves and Pitarka (2016) technique to generate kinematic rupture models. Then, FK Green's functions are computed using the propagator matrix method proposed by Zhu and Rivera (2002). Using the RotD50 SA goodness of fit (GoF) between the recorded and simulated ground motion, we conducted 1D velocity model sensitivity analysis. Overall, the simulated time histories match well the recorded ground motion. We found that the 1D velocity model of the Central Apennine Area, modified for the inclusion of thin near-surface sedimentary layers, performed better than the other 1D velocity models considered in the GOF analysis. Our ground motion simulations suggest that the FK-based simulation approach can effectively reproduce the recorded ground motion in the frequency range of 0-10 Hz. Consequently, this approach holds promise for the seismic hazard assessment in Central Italy, enabling significant computer time savings compared to more complex methodologies that involve 3D wave propagation modeling.

How to cite: Artale Harris, P., Pitarka, A., and Akinci, A.: Broadband Ground Motions Simulations for M≥6.0 Earthquakes in the 2016/2017 Central Italy Seismic Sequence through a 1D Frequency-Wavenumber Approach: a Velocity Models Sensitivity Analysis , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5129, https://doi.org/10.5194/egusphere-egu24-5129, 2024.

EGU24-5475 | ECS | Posters on site | SM2.1

Scattered wave and coda reliability in 3D elastic seismic simulation: new insights for the advancement of inversion studies. 

Mirko Bracale, Ludovic Margerin, Romain Brossier, and Michel Campillo

In this study we investigate the behavior of seismic waves in a high-scattering medium using numerical simulations of the full wavefied based on the Spectral Element Method solutions of the wave equation. The simulated 3D elastic medium was designed to have Laplacian correlated heterogeneity, creating a realistic representation of the complexities present in natural seismic environments. We conducted analyses on three distinct cases, each characterized by increasing levels of heterogeneity fluctuation, ranging from 10% to 25% standard deviation.
We checked the consistency between theoretical results and simulations with regard to the value of the mean free path, the asymptotic behavior at long times and the partitioning of energy between compressional and shear modes. Excellent agreements were obtained, indicating the reliability of the numerical models of coda waves used here.  Our analyses are made both at depth and at the free surface, allowing us to compare the behavior of seismic waves under varying conditions. Additionally, we validated our findings by conducting independent numerical simulations of wave energy densities that used Monte Carlo methods to solve the Radiative Transfer Equation, thus corroborating the robustness and accuracy of our results for long lapse times.
We show that under specific conditions, existing simulation codes can effectively replicate wave propagation in a highly scattered medium. This implies that a greater part of the waveform, namely the late envelops, could be employed in inversion processes, thus opening up new possibilities in the realm of inversion studies. Furthermore, we used these simulations to investigate the behavior of the wavefield and its gradient, exploring the information that can be extracted from their evolution over time to improve characterization of environmental heterogeneity.

How to cite: Bracale, M., Margerin, L., Brossier, R., and Campillo, M.: Scattered wave and coda reliability in 3D elastic seismic simulation: new insights for the advancement of inversion studies., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5475, https://doi.org/10.5194/egusphere-egu24-5475, 2024.

EGU24-6202 | ECS | Orals | SM2.1

The influence of gouge formation on seismicity and fault slip behavior.  

Miguel Castellano, Enrico Milanese, Camilla Cattania, and David Kammer

Through the progression of seismic activity, natural fault zones undergo a complex evolution characterized by the accumulation of damage and the formation of gouge within the fault core across multiple scales. Even though this is believed to be among the key factors affecting the evolution of fault seismicity over time, a deep understanding of the mechanisms at play is still missing. In this study, we explore the role of gouge production in the self-organization process of loaded rough faults, focusing on the evolving dynamics of earthquake nucleation, recurrence and moment partitioning during the seismic cycle. We model the stress and sliding dependence of gouge evolution by linearly coupling Archard's wear law with rate-and-state friction through the critical slip distance ( Dc ). Including this new formulation in 2D quasi-dynamic, elastic simulations of rough faults, we can reproduce the effects of spatially and temporally heterogeneous gouge evolution. Following the build-up of gouge over many cycles, we observe a progressive transition from cascade-driven to creep-dominated nucleation processes, marked by an increase of precursory slow slip and foreshock activity. A clear shift in the moment partitioning from faster to slower slip rates becomes evident as heterogeneity grows larger, followed by a reduction of the total cumulative moment released. Finally, the recurrence interval is observed to grow initially, then drop abruptly and become more unpredictable as the amplitude of Dc continues to rise. Incorporating a new formulation of gouge production in earthquake cycles simulations, this work sheds light on the role of gouge accumulation in the maturation process of natural faults, offering critical insights for seismic risk assessment and mitigation.

How to cite: Castellano, M., Milanese, E., Cattania, C., and Kammer, D.: The influence of gouge formation on seismicity and fault slip behavior. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6202, https://doi.org/10.5194/egusphere-egu24-6202, 2024.

In a three-dimensional Cartesian coordinate system, the deformation of the medium around a particle includes strain, translation, and rotation. Rotational motion is an important aspect of current seismological research. Seismologists have recognized the importance of rotational motion in dynamic response and damage of structures caused by certain earthquakes, through investigations into earthquake damage. In rapid earthquake intensity reports, it is essential to not only consider factors such as earthquake location, source depth, magnitude, and fault rupture model, but also to emphasize the analysis of the amplification effect of shallow media. We discuss the attenuation characteristics and difference between seismic translational and rotational components by medium viscoelasticity through two-dimensional numerical simulation, analyze the amplification effect of shallow viscoelastic low-velocity layer on ground motion by the reference site spectral ratio (RSSR), and discuss the difference of the amplification caused by different low-velocity layer factors. The results show that the seismic primary frequency decreases more with increasing viscoelasticity, and the energy of rotational component attenuates more significantly than that of translational component. The elastic low-velocity layer amplifies high-frequency signals of body waves greater than the viscoelastic low-velocity layer, especially in rotational component. When shallow low-velocity layers consist of multilayered sediments compared to a single sediment, the amplification of surface wave is stronger, particularly in rotation. We follow the research method used for seismic translation to discuss the amplification effect of shallow viscoelastic medium on seismic rotation, which is important for performance-based seismic design and earthquake damage analysis.

How to cite: Li, W., Zhang, Y., and Wang, Y.: Attenuation and amplification effects of seismic translational and rotational components in shallow media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7150, https://doi.org/10.5194/egusphere-egu24-7150, 2024.

We focus on the main rupture process of the Mw7.8 Februrary 6th 2023 01:17 UTC Pazarcık, Turkey, propagating to the south-west direction where more than ten acceleration stations recorded the ground motions within a distance of a few kilometers from the fault. On one hand, we estimate the frictional parameters directly from the waveforms of the acceleration records. Several stations are sufficiently close enough to characterize the cohesive zone length, and the estimated critical displacement (Dc) ranges from 90 cm to 150 cm. On the other hand, we carry out the dynamic rupture simulations along the constructed non-planar fault and also simulate the ground motions in the surrounding, using boundary integral equation and finite difference methods.  Upon the constructed standard model, we prepare different models of Dc distribution both along dip and strike. Our numerical simulations show that a longer Dc is necessary in the shallowest depth (2-3 km depth) than in the deep seismogenic zone. The observed ground motion pattern in terms of PGV (Peak Ground Velocity) shows a strong correlation with the estimated strike-variated Dc and the rupture process controlled by the fault geometry.

How to cite: Aochi, H. and Cruz-Atienza, V.: Characterization of shallow fault parameters from the near-field ground motion data and non-planar dynamic rupture simulations for the Mw7.8 February 6th Pazarcık, Turkey, earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7928, https://doi.org/10.5194/egusphere-egu24-7928, 2024.

EGU24-8160 | Orals | SM2.1

Inferred source models for Alpine Fault Earthquake Scenarios and influence on seismic hazard. 

Caroline Holden, John Townend, Calum Chamberlain, Emily Warren-Smith, Carmen Juarez-Garfias, Olivia Pita-Sllim, Kasper Van Wijk, and Marine Denolle

As part of the Southern Alps Long Skinny Array (SALSA) project, ~35+ seismometers have been deployed with 10–12 km spacing along a 450 km-long   section of the Alpine Fault. SALSA is focused on determining the ground motions likely to be produced by a future Alpine Fault earthquake. This project is addressing three principal objectives: (1) Determine the Alpine Fault’s subsurface geometry, present-day slip rates, and spatial variations in how tectonic stresses are currently accumulating on the fault, (2) Estimate the ground shaking that would be recorded at seismometers throughout central and southern New Zealand by localised slip at different points on the Alpine Fault, focusing on the synthesis of long-period Green's functions  representing accurate path effects between sources distributed along the fault and population centres throughout the South Island, and (3) Calculate the ground shaking hazard from geologically informed earthquake rupture scenarios. In this presentation we will address the influence of inferred Alpine Fault source models derived from empirical data as well as current knowledge of the fault geological and geophysical parameters on regional seismic hazard.

How to cite: Holden, C., Townend, J., Chamberlain, C., Warren-Smith, E., Juarez-Garfias, C., Pita-Sllim, O., Van Wijk, K., and Denolle, M.: Inferred source models for Alpine Fault Earthquake Scenarios and influence on seismic hazard., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8160, https://doi.org/10.5194/egusphere-egu24-8160, 2024.

Earthquakes that nucleate at depths shallower than a few km are very rare but pose high near-fault hazard despite moderate magnitudes. Some very shallow earthquakes have been associated with surface mass removal processes, both natural (e.g. glacier melting) and anthropogenic. A notable recent case is the November 11 2019 Mw 4.9 Le Teil, France earthquake. It called strong public attention because of its very shallow depth (slip shallower than 2 km), very strong ground motion (>1 g) affecting the near-fault population, and proximity to nuclear power plants. It has been proposed that this earthquake could have been triggered by mass removal from a large cement quarry located close to the epicenter. Indeed, the estimated Coulomb stress change induced by the quarry activity on the fault is of several 100 kPa. Here, we further evaluate the mechanical viability of the quarry-triggering hypothesis through 3D earthquake cycle simulations.

We consider a dipping fault governed by rate-and-state friction, with velocity-weakening steady-state behavior, and a realistic mass removal history constrained by analyses of aerial optical images across ~180 years of quarry activity. To account for uncertainties about the recurrence time of natural earthquakes on the fault and the timing of the previous natural event, we consider mass-removal loads starting at different times relative to the simulated natural earthquake cycle. Our simulations show that realistic mass removal rates can advance the failure time by thousands of years. Simulations with a constant mass-removal rate but same cumulative removed mass at 180 years produce a similar triggering timing. This indicates that the induced clock advance mostly depends on the cumulative load, rather than on its rate. The dependence on loading rate manifests through the following mechanism: the model with constant rate can trigger slow slip events instead of regular earthquakes, which postpones the next regular earthquake by a long time, whereas the model with realistic loading history (and higher load rates) always triggers regular earthquakes. The quarry's proximity to the fault and the frictional heterogeneity on the fault also play important roles. For example, clock advance is higher if the quarry location is closer to the edge of the velocity-weakening zone and lower in the middle. Also, the model with the classical rate-and-state model shows negligible impact if the quarry is at the top of a steady-state behavior zone and far away from the velocity weakening zone.

While these models confirm the possibility that mass removal can trigger shallow earthquakes on velocity-weakening faults, we will also report on additional simulations that examine whether such triggering can occur on a fault with velocity-strengthening behavior at shallow depth or it requires a more sophisticated fault rheology, such as friction with a transition from velocity-strengthening to velocity-weakening at increasing slip rate. These modeling efforts will be further constrained by ongoing laboratory experiments on representative materials of the fault that ruptured in the Le Teil earthquake.

How to cite: Sopaci, E. and Ampuero, J. P.: Triggering of very shallow earthquakes by surface mass removal processes - case study of the 2019 Mw4.9 Le Teil, France earthquake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9827, https://doi.org/10.5194/egusphere-egu24-9827, 2024.

The Mw 7.8 and Mw 7.5 doublets of the 2023 Turkey seismic sequence show strong velocity pulses that may have caused extensive damage to buildings and structures. We analyze the velocity pulses from the empirical data (both raw and processed) to understand the causes of these for these doublets. The analysis includes a comparison with the velocity pulses from the synthetic data of the Jia et al. (2023) dynamic rupture simulation available for the first Mw 7.8 event and an analysis of the variability of large instrumented earthquakes of the last 30 years. We characterize the properties of the ground motion pulses (e.g., period, velocity, and orientation) using the algorithm proposed by Shahi and Baker (2014). The identified pulses in the synthetic data show the main characteristics of the pulses (periods, PGV). However, the pulse properties in the synthetic data show less variability than the natural variability found in the empirical data, particularly a random behavior in the pulse orientation. The results then indicate that the pulse characteristics in the near-fault regions of large-magnitude earthquakes exhibit a significant variability and that this variability is similar to the one observed in past large earthquakes. This pronounced variability can be attributed to various factors, including directivity effects and site effects. This suggests that the full complexity of earthquake rupture processes and site configurations should be taken into account to be able to capture the high variability in pulse properties.

How to cite: Yen, M.-H., Türker, E., and Cotton, F.: An analysis of strong velocity pulses from the empirical data and dynamic rupture simulations of the 2023 Kahramanmaras earthquake doublets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9916, https://doi.org/10.5194/egusphere-egu24-9916, 2024.

EGU24-10403 | ECS | Orals | SM2.1

Thermal runaway as driving mechanism of deep earthquakes – Constraints from numerical modeling 

Arne Spang, Marcel Thielmann, and Daniel Kiss

Deep-focus earthquakes occur at depths of 300-700 km below the surface where brittle failure is unlikely due to the large lithostatic pressure. Instead, they require a ductile localization mechanism that can significantly reduce rock strength and create highly localized shear zones. The feedback loop of shear heating, temperature-dependent viscosity and localization is called thermal runaway and has been linked to deep-focus earthquakes.

We present one- and two-dimensional (1D and 2D) numerical, thermomechanical models that investigate the occurrence, nucleation and temporal evolution of thermal runaway in a simple shear setting. The models are characterized by a visco-elastic rheology where viscous creep is accommodated with a composite rheology of diffusion and dislocation creep as well as low-temperature plasticity. We utilize the pseudo-transient iterative method in combination with a viscosity regularization and adaptive time stepping to solve this nonlinear system of equations and avoid resolution dependencies.

Varying eight input parameters, we observe two distinct types of behavior. After elastic loading, models either release stress over hundreds to thousands of years, accompanied by low slip velocities and moderate temperature increase, or they release stress within seconds to minutes while slip velocity and temperature increase drastically – Thermal runaway occurs. With nondimensional scaling analysis, we unite the eight different input parameters into two nondimensional numbers that allow inferring the behavior. The ratio tr/td describes the competition between heat generation by viscous dissipation and heat loss due to thermal diffusion whereas the ratio Uel/Uth compares the elastic and thermal energy density before stress relaxation.

2D experiments show that thermal runaway allows highly localized ductile ruptures to nucleate at small heterogeneities and propagate like brittle fractures. The ruptures accelerate during propagation and reach the highest velocities when two tips link up. Rupture trajectories are usually parallel to the direction of background deformation but bend in the vicinity of other ruptures to allow for a link up. The results demonstrate that thermal runaway can create highly localized, propagating shear zones that reach slip velocities in line with slow earthquakes at upper mantle and transition zone conditions.

How to cite: Spang, A., Thielmann, M., and Kiss, D.: Thermal runaway as driving mechanism of deep earthquakes – Constraints from numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10403, https://doi.org/10.5194/egusphere-egu24-10403, 2024.

EGU24-10632 | ECS | Orals | SM2.1

A quantum computing concept for 1-D elastic wave simulation 

Malte Schade, Cyrill Bösch, Vaclav Hapla, and Andreas Fichtner

We present a quantum computing concept for 1-D elastic wave propagation in heterogeneous media with two components: a theoretical formulation and an implementation on a real quantum computer. The method rests on a finite-difference approximation, followed by a transformation of the discrete elastic wave equation to the Schrödinger equation, which can be simulated directly on a gate-based quantum computer. An implementation on an error-free quantum simulator verifies our approach and forms the basis of numerical experiments with small problems on an actual quantum computer. As the presented approach promises exponential speedup compared to classical numerical wave propagation methods, it has the potential to significantly push the limits of global full-waveform inversion, particularly maximum feasible frequencies, on future quantum computers.

How to cite: Schade, M., Bösch, C., Hapla, V., and Fichtner, A.: A quantum computing concept for 1-D elastic wave simulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10632, https://doi.org/10.5194/egusphere-egu24-10632, 2024.

Natural faults exhibit complex geometry. In this study, we model cycles of earthquake ruptures on non-planar faults governed by a friction formulation that combines rate and state friction for low slip velocity and enhanced weakening friction in the form of flash heating for high slip velocity, both consistent with rock friction experiments. The numerical method allows non-matching meshes across the fault, continuously updates the fault geometry, and employs variable time steps with quasi-static and fully dynamic time integration schemes during slow and fast deformation stages, respectively. To prevent the development of large stresses on the fault, the model also accounts for fault wear and inelastic off-fault deformation. We investigate the effect of macro-scale roughness on the fault slip behavior and rupture dynamics in terms of event magnitude, stress drop, and rupture style and speed. We analyze the relationship between the fault geometry, stresses from the preceding earthquakes, and rupture characteristics.

The simulation results show a significant increase in event variability with roughness levels, with both small partial ruptures and ruptures significantly more intense than those on planar faults. The planar faults host a sequence of earthquakes that rupture the entire fault, exhibiting similar magnitudes and stress drops. The substantial reduction in friction enables the ruptures to propagate under a low background shear-to-normal stress ratio as self-healing slip pulses, with a sub-Rayleigh rupture speed. Faults with low roughness levels generally show a similar pattern. Prior to some events, the stress ratio along the fault slightly increases, leading to ruptures with secondary slip pulses and larger magnitudes. As roughness increases, stresses become more heterogeneous, resulting in a more complex sequence of ruptures, some of which arrest at restraining bends with a low stress ratio. However, stress accumulation and slip deficit during these partial ruptures result in high stress ratios on the unruptured fault segments. These are eventually released by large events of crack-like ruptures with supershear propagation speed and stress drops and slip significantly larger than a typical event on a planar fault. Therefore, while fault roughness can cause rupture arrest, consistent with previous studies, it can also substantially increase earthquake magnitudes. This factor should be accounted for in earthquake hazard assessments.

How to cite: Tal, Y.: Rupture Dynamics and Characteristics During Earthquake Cycles on Nonplanar Faults with Strongly Rate-Weakening Friction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11379, https://doi.org/10.5194/egusphere-egu24-11379, 2024.

EGU24-13834 | Orals | SM2.1

CyberShake simulation of strike-slip earthquakes on the Southwest Iceland transform zone 

Otilio Rojas, Farnaz Bayat, Marisol Monterrubio-Velasco, Claudia Abril, Scott Callaghan, Juan E. Rodríguez, Milad Kowsari, Benedikt Halldórsson, Kim Olsen, Alice-Agnes Gabriel, and Josep de la Puente

The Statewide Southern California Earthquake Center (SCEC) has designed and implemented CyberShake (CS), a high-performance computing (HPC) workflow to undertake Physics-Based Probabilistic Seismic Hazard Analysis (PB-PSHA) in California (CA). Here, we have ported CS from CA to the South Iceland Seismic Zone (SISZ) and the Reykjanes Peninsula Oblique Rift (RPOR), which experience sinistral transform motion and pose a very high earthquake risk to about 2/3 of the Iceland population. We consider a realization of the 3D SISZ-RPOR fault system, where fault areas are estimated from event magnitude through a scaling law (Mai & Beroza, 2017),  that fits maximum fault extents observed from slip inversions and surface mappings. The magnitude variability across the modeling region (~63.8°- 64.1°N, ~20°-23°W) is Mw 5-7. In this work, we employ CS to model ~2100 kinematic earthquake ruptures and quantify the resulting ground motion (GM) in terms of Pseudo Spectral Acceleration (PSA) intensity measures. An important computational milestone is the software development of an open-source in-house workflow manager at the Marenostrum Supercomputer that replaces the one used in CA by SCEC based on Pegasus and HTCondor. This new workflow manager handles input data (fault-plane geometries, rupture magnitudes, surface stations for GM recording and hazard studies), orchestrates the execution of CS components, and stores results (particle velocity seismograms and hazard curves). Among these components, the Graves-Pitarka (GP) kinematic rupture generator is used to produce finite-fault source descriptions characterized by a few large asperities. The other important component is the open-source fourth-order finite-difference staggered-grid AWP-ODC earthquake simulation code that allows for reciprocity and efficiently simulates rupture and seismic wave propagation in 3D heterogeneous Earth models. CS uses an adjoint computational procedure in which simulations of wave propagation are performed using a polarized delta source to compute the Strain Green Tensors (SGTs) at each fault point. The convolution of SGTs with GP ruptures yields particle-velocity seismograms at each station. SGT time histories are memory demanding, but the adjoint calculations are completely independent and therefore embarrassing parallel, making CS a highly efficient earthquake simulation tool. In this study, SGTs are constructed using a source frequency range of 0-1.0 Hz, generating ground motion synthetics resolved up to 0.5 Hz. CS rotation-invariant PSA values (3 and 5 sec periods) computed from our study show a good agreement with updated Bayesian ground motion prediction equations (Kowsari et al, 2022). This study is a first step towards a PB-PSHA in the SISZ-RPOR region and to routinely apply Cybershake outside of California.

REFERENCES:

Mai, M., & Beroza, G. Source scaling properties from finite-fault-rupture models. Bulletin of the Seismological Society of America, 90(3), 604-615, 2000.

Kowsari, M., Sonnemann, T., Halldorsson, B., Hrafnkelsson, B., Snæbjörnsson, J. &  Jonsson, S. Bayesian inference of empirical ground motion models to pseudo-spectral accelerations of South Iceland Seismic Zone earthquakes based on informative priors. Soil Dynamics and Earthquake Engineering, 132, 106075, 2020.

How to cite: Rojas, O., Bayat, F., Monterrubio-Velasco, M., Abril, C., Callaghan, S., Rodríguez, J. E., Kowsari, M., Halldórsson, B., Olsen, K., Gabriel, A.-A., and de la Puente, J.: CyberShake simulation of strike-slip earthquakes on the Southwest Iceland transform zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13834, https://doi.org/10.5194/egusphere-egu24-13834, 2024.

Friction plays a crucial role in rupture dynamics and yet its precise nature remains elusive. Consequently, a friction law must be assumed to model rupture. Commonly used constitutive laws for modeling friction include slip-weakening laws which are characterized by a drop from static to dynamic frictional strength. Within this framework, the prevailing understanding asserts that the frictional behaviour is solely controlled by the fracture energy - the area beneath the frictional strength versus the cumulated slip curve. In particular, it is claimed that the curve's shape itself has no influence on the system's response. Here we perform fully dynamic rupture simulations to challenge prevailing beliefs by demonstrating that the constitutive law shape exerts an intimate control over rupture profiles. For a consistent fracture energy but varying constitutive law shapes, the velocity profile is different: each abrupt slope transition leads to the localization of a distinct velocity peak. For example, in the case of a dual slip-weakening law featuring two different slopes, the rupture exhibits two distinct velocity peaks. This distinction significantly influences how a rupture responds to a stress barrier. These results are derived through two separate numerical schemes (spectral boundary integral and finite element methods) ensuring their independence from the computational approach employed.

How to cite: Ferry, R. and Molinari, J.-F.: Unveiling the influence of slip-weakening laws' shapes on rupture dynamics: beyond fracture energy in controlling rupture profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15557, https://doi.org/10.5194/egusphere-egu24-15557, 2024.

EGU24-16751 | ECS | Orals | SM2.1

Differences in breakdown work and fracture energy in slip weakening constitutive laws 

Chiara Cornelio, Shane Murphy, Elena Spagnuolo, Stefan Nielsen, and Massimo Cocco

Earthquakes are associated with the propagation of a dynamic rupture, which radiates elastic energy through seismic waves. The generation of seismic radiation is related to dynamic weakening of shear stress and stress drop. In modeling dynamic ruptures, shear stress evolution is commonly imposed through a constitutive law, such as the widely adopted slip weakening laws. According to these constitutive laws, shear stress evolves as a function of slip in each point of the rupturing fault, prescribing strength excess, stress drop and dynamic weakening.

Here, we compare two well-known slip weakening laws: namely, the classic Ida’s (1972) and the Ohnaka’s (1996) slip weakening laws. The former prescribes that fault stress increases from the initial stress to the peak stress with zero slip and then linearly decreases from the peak value to a residual value over a slip-distance Dc (dynamic weakening). The latter assumes that the initial stress hardening phase occurs over a non-negligible slip-distance Da and that shear stress decrease from the peak value is not linear. The Ohnaka’s law was validated with numerous laboratory experiments. The evolution of shear stress with slip allows the estimate of the breakdown work Wb, i.e. the excess of work above a minimum stress level with slip from 0 to Dc.

We collected data from high-velocity friction experiments to quantify yield, peak and residual stresses, Da and Dc distances for bare-rock samples of Carrara Marble and Gabbro deformed under various experimental conditions (room humidity, vacuum, pressurized fluids) and normal stress (from 5 to 40 MPa). The ratio Da/Dc is much lower for Carrara marble (0.015) than for Gabbro (0.12). We implemented the Ohnaka’s constitutive law in a 2D finite difference code for spontaneous dynamic ruptures characterized by a fault in a homogeneous elastic material.  We perform simulations using the two different slip weakening laws. We kept constant Dc, and we compared the results of the simulations in terms of rupture style, rupture velocity, breakdown work, and cohesive zone size. As expected both laws yield crack-like ruptures. Moreover, Ohnaka’s law in comparison to the linear slip weakening law produces:

  • rupture velocity ~2 % higher;
  • breakdown work (Wb) up to 60 % lower. Moreover, dividing the breakdown work into the energy dissipated between the yield stress and the peak stress over the slip-distance Da (Wba), we notice that Wba can reach up to the 30% of the total Wb in case of Gabbro (Da/Dc = 0.12).
  • a cohesive zone size (defined as the portion of the fault in which the slip velocity is higher than zero and the stress is higher than its residual value) up to 50% larger.

Therefore, Ohnaka’s law generates more energetic ruptures (i.e. faster rupture velocity and peak slip-rate) despite having a larger cohesive zone due to the lower breakdown energy dissipated during rupture propagation. We discuss our results in terms of the difference between breakdown highlighting the implications on dynamic rupture propagation and earthquake energy budget. We emphasize that common interpretations of energy dissipated during rupture propagation are model-dependent.

How to cite: Cornelio, C., Murphy, S., Spagnuolo, E., Nielsen, S., and Cocco, M.: Differences in breakdown work and fracture energy in slip weakening constitutive laws, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16751, https://doi.org/10.5194/egusphere-egu24-16751, 2024.

EGU24-18840 | Orals | SM2.1

Taiwan Non-Ergodic Ground Motion Prediction Equations for Spectral Accelerations and Instantaneous Powers 

Shu-Hsien Chao, Jyun-Yan Huang, Chiao-Chu Hsu, Che-Min Lin, Chih-Hsuan Sung, and Chun-Hsiang Kuo

Currently, available Taiwan ground motion prediction equations were developed based on ergodic assumption, which means that the same ground motion prediction equation is applicable to any ground motion scenarios occurred in Taiwan no matter what locations of earthquake sources are; what paths from sources to sites are, and what locations of sites are. However, several recent studies have shown that the regional differences of source, path and site effects of ground motion in Taiwan are significant. As a result, the prediction for some specific ground motion scenarios in Taiwan may be biased, and the aleatory uncertainty of the ground motion may be over-estimated by using current available Taiwan ground motion prediction equations. Based on it, the aim of this study is to develop new Taiwan ground motion prediction equations for spectral accelerations and instantaneous powers based on non-ergodic assumption which are depended on the source and site locations to consider the regional differences of source, path and site effects of ground motion in Taiwan by using available ground motion records, 3-D velocity models, and horizontal-to-vertical Fourier spectra ratios. A better ground motion prediction result with higher accuracy and lower uncertainty will be achieved based on the proposed non-ergodic Taiwan ground motion prediction equations in this study. Structural damage induced by a scenario-based earthquake can be estimated more precisely by using the proposed non-ergodic ground motion prediction models for spectral acceleration and instantaneous power at fundamental period simultaneously.

How to cite: Chao, S.-H., Huang, J.-Y., Hsu, C.-C., Lin, C.-M., Sung, C.-H., and Kuo, C.-H.: Taiwan Non-Ergodic Ground Motion Prediction Equations for Spectral Accelerations and Instantaneous Powers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18840, https://doi.org/10.5194/egusphere-egu24-18840, 2024.

EGU24-19294 | ECS | Orals | SM2.1

One-way linking of 3D long-term geodynamic models and short-term earthquake dynamic rupture models 

Anthony Jourdon, Nicolas Hayek, Dave May, and Alice-Agnes Gabriel

Tectonic deformation plays a crucial role in shaping the Earth's surface, with strain localization resulting in the formation of shear zones in depth and faults on the surface. These structures accommodate a significant portion of the displacement between tectonic plates. While long-term deformation can be approximated as continuous visco-plastic processes, earthquakes involve cycles of stress loading and unloading that trigger rapid and catastrophic elasto-plastic deformation. Earthquake dynamic rupture models offer valuable insights into studying and comprehending earthquakes. However, these models heavily rely on initial conditions that are often challenging to obtain solely from observations. Particularly, a mechanically self-consistent prestress state loading a fault prior a seismic event and 3D fault geometry, especially in depth, are commonly poorly constrained. Nonetheless, the prestress state and the fault geometry significantly impact earthquakes initiate, propagate, and arrest and the associate radiation of seismic waves and ground shaking.

To address the lack of information on stress and fault geometry, one promising approach is to use long-term geodynamic numerical simulations. In this study, we employ pTatin3D, a visco-plastic finite element software, to simulate the evolution of strike-slip deformation in 3D over geological time scales. To ensure a physically consistent long-term model, the fault geometry is not prescribed but solved for based on the lithospheric rheology and tectonic plate velocities. However, the geodynamics model describes faults as continuous volumetric fields of finite deformation and strain-rate, rendering them 3D objects, while earthquake dynamic rupture models typically represent faults as 2D interfaces.

In this study, we outline a new and versatile method to link 3D geodynamic simulations to rupture dynamics earthquake and seismic wave propagation modelling. We first extract 3D volumetric shear zones from the geodynamic model and automatically convert them into surface representations. Next, we generate meshes including these as faults for dynamic rupture models. Finally, we showcase 3D dynamic rupture models utilizing the stress states and faults self-consistently as derived from the long-term geodynamic model as initial conditions.

How to cite: Jourdon, A., Hayek, N., May, D., and Gabriel, A.-A.: One-way linking of 3D long-term geodynamic models and short-term earthquake dynamic rupture models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19294, https://doi.org/10.5194/egusphere-egu24-19294, 2024.

EGU24-19464 | ECS | Posters on site | SM2.1

A first look at the ground motion characteristics unveiled by accelerometric data: the case of Campi Flegrei area (Italy) 

Claudia Pandolfi, Donato Talone, Giusy Lavecchia, Giovanni Costa, Veronica Pazzi, Simone Francesco Fornasari, Luisa Filippi, Elisa Zambonelli, Alfredo Ammirati, Sebastiano Sirignano, Aybige Akinci, and Rita de Nardis

Campi Flegrei is a volcanic region in Southern Italy of great interest for volcanic risk due to the presence of a potentially dangerous caldera collapse structure in a very densely populated area. In historical times, the Campi Flegrei area experienced explosive eruptions (the most recent – the Monte Nuovo eruption, 1538 CE), and in recent times (from 1969 to 1972 and from 1982 to 1984) critical seismic activity and bradyseism crises. Since 2020 the increase of seismicity related with the acceleration of ground uplift is a matter of the scientific and civil protection debate, given the vulnerability of the urban settlements under the effect of the volcanic phenomena. The recent bradyseism crisis climaxed in September 2023, with a high number of seismic events per month (1000 events per month) and a maximum magnitude (Md) of 4.2— the strongest event recorded in the last forty years. In general, predicting attenuation law in volcanic areas poses a significant challenge due to the limited availability of strong motion records, the predominance of lower magnitude events, and the distinct characteristics of waveforms compared to tectonic earthquakes. Moreover, additional challenges arise from the potential anisotropic behavior of the area, which could lead to high seismic impact for specific directions of seismic wave propagation. This makes it difficult to establish predictive models for ground motion, hindering the development of reliable risk scenarios and the effective implementation of civil protection measures. Since September 2023, the Civil Protection Department started improving the station coverage of the accelerometric network (RAN, Rete Accelerometrica Nazionale) by installing 3 new seismic stations along coastal areas and around Pisciarelli locality. The accelerometric data, recorded from the 18th of September 2018 to the 4th of October 2023 by 12 accelerometric stations of the RAN, fill a gap of information and represent an important contribution in adding new constraints to ground motion characterization. Specifically, we analyzed 3771 three-component records whose 186 exhibit a magnitude exceeding 3.5. We derived the engineering interest parameters (e.g., Peak Ground Acceleration, PGA; Peak Ground Velocity, PGV; Housner Intensities, HI; Arias Intensities, AI; significant duration, Td; Spectral accelerations) and compared them with the available ground motion prediction equations defined in the tectonic and volcanic areas in Italy and abroad. For the two events >= 3.8 we perform a comprehensive analysis. Our results unveil a trend similar to that predicted in the ground motion prediction equations in the near field but with a steeper attenuation recorded beyond approximately 5 km of distance. Furthermore, a relevant result is the existence of elevated peaks in PGA (Peak Ground Acceleration) at considerable distances also for low magnitude values underscoring the potential existence of preferential directions in propagation. These findings are crucial for understanding the region's seismic impact and enhancing risk assessment and civil protection strategies in this densely populated volcanic area.

How to cite: Pandolfi, C., Talone, D., Lavecchia, G., Costa, G., Pazzi, V., Fornasari, S. F., Filippi, L., Zambonelli, E., Ammirati, A., Sirignano, S., Akinci, A., and de Nardis, R.: A first look at the ground motion characteristics unveiled by accelerometric data: the case of Campi Flegrei area (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19464, https://doi.org/10.5194/egusphere-egu24-19464, 2024.

Discrimination of underground explosions from naturally occurring earthquakes and other anthropogenic sources is one of the fundamental challenges of nuclear explosion monitoring. In an operational setting, the number of events that can be thoroughly investigated by analysts is limited by available resources. The capability to rapidly screen out events that can be robustly identified as not being explosions is, therefore, of great potential benefit. Nevertheless, possible mis-classification of explosions as earthquakes currently limits the use of screening methods for verification of test-ban treaties. Moment tensors provide a physics-based classification tool for the characterisation of different seismic sources and have enabled the advent of new techniques for discriminating between earthquakes and explosions. Following normalisation and projection of their six-degree vectors onto the hypersphere, existing screening approaches use spherically symmetric metrics to determine whether any new moment tensor may have been an explosion. Here, we show that populations of moment tensors for both earthquakes and explosions are anisotropically distributed on the hypersphere. Distributions possessing elliptical symmetry, such as the scaled von Mises-Fisher distribution, therefore provide a better description of these populations than the existing spherically symmetric models. We describe a method that uses these elliptical distributions in combination with a Bayesian classifier to achieve successful classification rates of 99% for explosions and 98% for earthquakes using existing catalogues of events from the western United States. Application of the method to the 2006–2017 nuclear tests in the Democratic People's Republic of Korea yields 100% identification rates. The approach provides a means to rapidly assess the likelihood of an event being an explosion and can be built into monitoring workflows that rely on simultaneously assessing multiple different discrimination metrics.

How to cite: Hoggard, M., Scealy, J., and Delbridge, B.: Improved classification of explosive moment tensors using elliptical distribution functions on the hypersphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2978, https://doi.org/10.5194/egusphere-egu24-2978, 2024.

EGU24-3453 | ECS | Posters on site | SM2.2

Identification of strong-velocity pulses in seismic ground motion signals 

Junhao Wang and Qingming Li

Seismic ground motions in the near-fault region produce strong pulses in the velocity-time history, resulting in severe damage to structures. To accurately and effectively monitor these ground motion signals with strong pulses, Shock-Waveform (SW) method is introduced to quantitatively extract the largest velocity pulse from a given ground motion. SW method is an energy-based and adaptive signal analysis method, which has proven capability of analyzing different physical and engineering signals initiated by sudden actions. It is suitable to identify pulse components in the signal with low error and high efficiency. Three variables are proposed to classify ground motions, which is combined with the Principal Component Analysis (PCA) for data dimensionality reduction and subsequent analysis. In addition, an optimum classification standard on pulse-like and non-pulse-like ground motion is established. To avoid the subjective judgement induced by manual selection, unsupervised machine learning classification method and Support Vector Machine (SVM) are used successively to find the decision boundary. In this study, about 100 pulse-like ground motions with large-velocity pulses are identified from approximately 1000 near-fault ground motion recorded in PEER Next Generation Attenuation-West2 database. It shows that most of the pulse-like ground motions are caused by the directivity effect. Based on the proposed classification approach, new models are developed to forecast the possibility of a single pulse, multi-pulses, and pulse period for a given earthquake event. 

How to cite: Wang, J. and Li, Q.: Identification of strong-velocity pulses in seismic ground motion signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3453, https://doi.org/10.5194/egusphere-egu24-3453, 2024.

EGU24-4186 | ECS | Orals | SM2.2 | Highlight

The frontiers of distributed acoustic sensing for seismological applications 

Ettore Biondi, Jiaxuan Li, Jessie Saunders, Allen Husker, and Zhongwen Zhan

Distributed acoustic sensing (DAS) is proving to be an effective technology for seismological applications. Its success is due to the ability to deploy DAS instrumentation on the existing ever-growing telecommunication fiber networks across the globe. However, the benefits of DAS are hindered by the sheer volume of data commonly recorded from single-instrument deployments, which can easily reach tens of TBs. Additionally, since DAS measures along fiber strain, new data analysis paradigms are necessary to exhaustively exploit all the information contained within these large datasets. 

We showcase successful applications of DAS experiments using existing fiber cables located in different scenarios, from volcanic systems to densely populated urban environments. To harness the information within these novel datasets, we combine machine-learning tools with efficient algorithms running on high-performance computing architectures. For example, we showcase how the arrival times obtained from PhaseNet-DAS can provide real-time earthquake detection and localization, allowing for the inclusion of DAS data within earthquake early warning systems. Moreover, we demonstrate the capability of integrating real-time streamed DAS channels within seismic network operations. Our processing paradigm is proving to be an effective ground for discoveries and for creating the next generation of seismic monitoring frameworks.

How to cite: Biondi, E., Li, J., Saunders, J., Husker, A., and Zhan, Z.: The frontiers of distributed acoustic sensing for seismological applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4186, https://doi.org/10.5194/egusphere-egu24-4186, 2024.

EGU24-4268 | Posters on site | SM2.2

Deep learning forecasting of induced earthquakes through the analysis of precursory signals 

Vincenzo Convertito, Fabio Giampaolo, Ortensia Amoroso, and Francesco Piccialli

The current limited knowledge about Earth system prevents deterministic earthquake prediction. This will probably continue for the foreseeable future. However, the improved capability of identifying reliable precursory phenomena can allow geoscientists to comprehend if the monitored system is evolving toward an unstable state. Among the premonitory phenomena preceding earthquakes, foreshocks represent the most promising candidate. Physically, two hand-member mechanisms have been proposed to interpret foreshocks. The first considers the failing of populations of small patches of fault that eventually but not necessarily become large earthquakes whereas the second assumes that foreshocks are a part of the nucleation process which ultimately leads to the mainshock. The prompt identification of foreshocks with respect to background seismicity is an issue and the task is worsened when dealing with low-magnitude earthquakes. However, the use of Artificial Intelligence (AI) can help real-time seismology to effectively discriminate precursory signals.

In the present study, we propose a deep learning method named PreD-Net (Precursor Detection Network) to address the precursory signal identification of induced earthquakes through the analysis of several statistical features. PreD-Net has been trained on data related to two induced seismicity areas, namely The Geysers, located in California, USA, and Hengill in Iceland. Notably, the network shows a suitable model generalization, providing considerable results on samples that were excluded from the training dataset of all the sites. The performed tests on related samples of induced relatively large events demonstrate the possibility of setting up a real-time warning strategy to be used to avoid adverse consequences during field operations.

This work is supported by project D.I.R.E.C.T.I.O.N.S. - Deep learning aIded foReshock deteCTIOn Of iNduced mainShocks, project code: P20229KB4F - - Next Generation EU (PRIN-PNRR 2022, CUP D53D23022800001)

How to cite: Convertito, V., Giampaolo, F., Amoroso, O., and Piccialli, F.: Deep learning forecasting of induced earthquakes through the analysis of precursory signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4268, https://doi.org/10.5194/egusphere-egu24-4268, 2024.

GEObit Instruments are proud to announce the market release of a new low-cost and low -latency seismic accelerograph, the GEO-T200, for earthquake monitoring, early waring applications, and structural monitoring. The device mainly consists of two sections, the triaxial sensor sensor and the digitizer. The architecture and the hardware is based on the GEObit GEOtiny platform.

The sensing elements are based in a re-designed previous generation GEObit force balance acceleration sensor unit [1], providing very high dynamic range 160+dB, and wide bandwidth, flat response DC to 260Hz. The acceleration range is user configurable and can be set between +/-4g to +/-0.5g but other ranges are also available upon request.

The digitizer is based on a 24bit ADC and provides high effective dynamic range 140dB, high sampling rate up to 4000sps, integrates seedlink server and the earthworm chain. The device is based on a locally running open-source components ported on ARM Linux board. It is able to apply local signal processing and trigger detection based on multiple schemes (amplitude, STA/LTA etc.) through open-source components ported from the Earthworm toolchain and transmit pick times over MQTT with ultra-low latency based signaling for trigger event distribution supporting multiple centralized or distributed schemes.

It Supports ethernet port and Wi-Fi. Also supports continuous data stream, triggered data stream (level, LTA/LTA, both) or both.

The device is housed into a small cylindrical enclosure, aluminum made, IP68 with dimensions 120mm diameter and 143mm height. Three leveling legs are provided along with a central bolt for proper mounting of the device. An bright OLED lcd screen reports the user about the instrument operation and state of health. The SOH stream is also transmitted in real time over TCP.

 

References:

[1]: Design, Modeling, and Evaluation of a Class-A Triaxial Force-Balance Accelerometer of Linear Based Geometry” N. Germenis, G. Dimitrakakis, E. Sokos, and P. Nikolakopoulos Seismol. Res. Lett. 93, 2138–2146, doi: 10.1785/0220210102

How to cite: Germenis, N.: A new low latency and low-cost force-balance accelerograph for earthquake and structural monitoring and for early waring applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5299, https://doi.org/10.5194/egusphere-egu24-5299, 2024.

GeoSphere Austria (GA, formerly ZAMG), the Italian National Institute of Oceanography and Applied Geophysics (OGS) and the Slovenian Environment Agency (ARSO) are the agencies dedicated to real-time seismological monitoring of Austria, north-eastern Italy and Slovenia, in cooperation with the respective civil protection authorities. In 2014, GA (then ZAMG), OGS and ARSO founded the “Central and Eastern Europe Earthquake Research Network” (CE3RN, http://www.ce3rn.eu/) to 1) formally establish the cross-border network, 2) define the rules of conduct for the management, improvement, extension and expansion of the network, 3) improve seismological research in the region and 4) support civil protection activities. As part of CE3RN, GA, OGS and ARSO have adoptd the “Antelope” software package for collecting, archiving, analysing and sharing seismological data.
In 2022, the international AdriaArray experiment was launched, following on from the previously successful AlpArray experiment. AdriaArray is a multinational effort to map the Adriatic plate and its active margins in the central Mediterranean with a dense regional array of seismic stations to understand the causes of active tectonics and volcanic fields in the region. GA, OGS and ARSO are actively involved in the AdriaArray experiment by providing data from their seismic monitoring networks and - in the case of OGS - also by installing and managing dedicated seismic stations. As part of the AdriaArray experiment, several additional seismic stations have been set up in Austria and north-eastern Italy. It is therefore to be expected that the additional seismic stations installed will improve the earthquake localization capabilities of GA, OGS and ARSO. This certainly applies to Austria and north-eastern Italy, but also to Slovenia, as a large part of its seismicity lies on the border with Italy.
The GOAT-CASE experiment aims to quantify the improvement in earthquake localization capability across the entire area. The underlying methodology is to locate earthquakes also using the additional seismic stations and to compare the results. The workload for the detections is distributed among the three partners, while the mapping is done centrally. An attempt will be made to use artificial intelligence to detect earthquakes and compare the results with the standard routines of the agencies.
The AdriaArray experiment is planned for a duration of 3 years starting around mid-2022. In this presentation we will illustrate the results of the first year of the experiment, from 01/07/2022 to 30/06/2023.

How to cite: Pesaresi, D., Horn, N., and Pahor, J.: GA-OGS-ARSO Transfrontier CE3RN AdriaArray Seismicity Experiment (GOAT-CASE): results of the first year of data collection and analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5459, https://doi.org/10.5194/egusphere-egu24-5459, 2024.

EGU24-5936 | ECS | Posters on site | SM2.2

A workflow for synthetic DAS data generation 

Giacomo Rapagnani, Sonja Gaviano, Davide Pecci, Giorgio Carelli, Gilberto Saccorotti, and Francesco Grigoli

Distributed Acoustic Sensing (DAS) is an emerging data acquisition technology that utilises an optical fiber to measure dynamic strain along its axis. Composed by an optical fiber and an interrogator unit (IU), the system emits laser pulses into the fiber and detects phase shifts in the backscattered light, converting them into strain or strain rate measurements. DAS is becoming popular in many seismological applications and, in particular, for logistically challenging environments such as offshore areas, boreholes, glaciers, and volcanic settings, where deploying conventional monitoring is challenging. Spatial and temporal sampling of DAS systems is much higher than traditional seismological instruments, offering a detailed picture of the recorded seismic wave field. This high spatial and temporal sampling of DAS systems results in massive data generation, especially over extended acquisition periods. For instance, a single day's data collected with a 1 km fiber, featuring inter-channel distances of approximately 1m and a temporal sampling rate of 0.5 ms, can easily reach 2 TB. This highlights the need for efficient data analysis procedures in Distributed Acoustic Sensing (DAS) with methods that are both computationally fast and capable of exploiting the extensive information embedded in such data. As DAS data acquisition experiments are still few in numbers, generating and using synthetic data becomes essential for evaluating performance across diverse DAS acquisition geometries and testing new data analysis techniques. Despite the constant growth of DAS systems, there is a lack of standard modelling and analysis tools that can be used within routine procedures. To address this issues, we formulated a versatile workflow designed to generate synthetic DAS data based on the convolutional model. A central component of this workflow is a travel-time calculator based on the solution of the Eikonal equation, accommodating various data acquisition geometries, including scenarios involving optical fibers deployed in deep boreholes—whether vertical or oblique. Synthetic DAS seismograms are subsequently generated by using the computed travel times, for both P and S phases, with the convolutional model. These seismograms contain several information, such as the radiation pattern of the source and the directivity of the fiber, with the possibility of selecting an arbitrary wavelet. While DAS synthetics computed using the convolutional model may be less realistic than those generated with methods like the reflectivity or the spectral element method, their computational speed is much higher. This efficiency becomes particularly crucial when dealing with the generation of extensive DAS synthetic datasets. The synthetic generation workflow can be used for 1) testing new seismic event detection and location methods for DAS data and 2) training machine learning models. Lastly, this work includes a comparative analysis of synthetics obtained through our workflow against those generated using the spectral element method, followed by an application with a waveform-based DAS event detector.

How to cite: Rapagnani, G., Gaviano, S., Pecci, D., Carelli, G., Saccorotti, G., and Grigoli, F.: A workflow for synthetic DAS data generation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5936, https://doi.org/10.5194/egusphere-egu24-5936, 2024.

EGU24-6310 | ECS | Orals | SM2.2

Accounting for shallow sedimentary layers for accurate earthquake localization using submarine Distributed Acoustic Sensing 

Alister Trabattoni, Marie Baillet, Martijn van den Ende, Clara Vernet, and Diane Rivet

Distributed Acoustic Sensing (DAS) technology facilitates the instrumentation of areas that are challenging to access with conventional instruments. In Chile, the presence of offshore submarine telecommunication cables offers a unique opportunity to instrument a major subduction zone close to the trench. Here we report an analysis of DAS data collected during a one–month campaign, sensing a commercial telecom cable connecting Concón to La Serena positioned several dozen kilometers off the coast.  

The earthquake recordings displayed P and S arrivals along with an additional Ps arrival, which is the result of the conversion of the P-wave at the bedrock/sediment interface. These three phase arrivals were identified and manually picked taking advantage of the spatial continuity of DAS measurements. To correctly account for the presence of the sediment layer in the localization procedure we introduced sedimentary corrections, which are a modification of the conventional station corrections. Instead of introducing an arbitrary constant time delay for each station and each phase, the corrections are derived from a physical first order modeling of the wave propagation in the sediments. The estimation of sedimentary parameters relies on: (i) the observed delay between the transmitted P-phase and the converted Ps-phase that give an indication of the sediment thickness; (ii) an inversion of the P- and S-wave speed in the sediments which is made possible thanks to the high sensor spatial density.   

We show that sedimentary corrections: (i) can represent most of the observed pick residual bias while only requiring the inversion of two global parameters (compared to station correction that requires three parameters per station); (ii) allow one to retrieve the sediment thickness and wave speed values that are consistent with common values for sediments; (iii) reduces the residuals of the earthquake hypocenter localization. The proposed correction method should improve the hypocenter estimation quality, facilitating the analysis of geological structures, and will contribute to a more detailed view of seismic activity in the studied area. 

How to cite: Trabattoni, A., Baillet, M., van den Ende, M., Vernet, C., and Rivet, D.: Accounting for shallow sedimentary layers for accurate earthquake localization using submarine Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6310, https://doi.org/10.5194/egusphere-egu24-6310, 2024.

EGU24-6552 | ECS | Posters on site | SM2.2

HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity 

Matteo Bagagli, Francesco Grigoli, and Davide Bacciu

Machine Learning (ML) applications in geoscience are growing exponentially, particularly in the field of seismology. ML has significantly impacted traditional seismological observatory tasks, such as phase picking and association, earthquake detection and location, and magnitude estimation. However, despite promising results, ML-based classical workflows still face challenges in analyzing microseismic data

Leveraging recent advances in Deep Learning (DL) methods, we present HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity. This tool utilizes an attention-based, spatiotemporal graph-neural network for seismic event detection and employs a waveform-stacking approach for event location, using output probability functions over a dense regular grid.

We applied HEIMDALL to a one-month dataset (December 2018) from the publicly available Hengill Geothermal Field in Iceland, collected during the COSEIMIQ project (active from December 2018 to August 2021). This dataset is ideal for testing seismic event detection and location algorithms due to its high seismicity rate (over 12,000 events in about two years) and the presence of burst sequences with very short interevent times (e.g., less than 5 seconds).

We assessed the methodology's performance by comparing our catalog with those obtained by two recent DL methods and one manually compiled by ISOR for the same period. The DL algorithms we considered are: (i) MALMI, a waveform-based location algorithm, and (ii) the recent GENIE graph-neural-network algorithm. For GENIE, we conducted a full repicking of continuous waveforms using the PhaseNet picking algorithm and subsequent retraining of its model to adapt it to the new seismic network.

Finally, we highlight the pros and cons of each method and discuss potential improvements for microseismic event detection and location, with a particular focus on induced seismicity monitoring operations at EGS sites.

How to cite: Bagagli, M., Grigoli, F., and Bacciu, D.: HEIMDALL: a grapH-based sEIsMic Detector And Locator for microseismicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6552, https://doi.org/10.5194/egusphere-egu24-6552, 2024.

EGU24-7863 | ECS | Orals | SM2.2

The advantages of Standardization and Data Sharing: a swift compilation of a high-quality data set for seismological studies in the East Anatolian Fault Zone 

Leonardo Colavitti, Gabriele Tarchini, Daniele Spallarossa, Davide Scafidi, Matteo Picozzi, Antonio Giovanni Iaccarino, Dino Bindi, Patricia Martínez-Garzón, Fabrice Cotton, and Riccardo Zaccarelli

On 6 February 2023 at 01:17 UTC, the Mw 7.8 Pazarcık earthquake struck south-eastern Türkiye and Syria along the East Anatolian Fault Zone (EAFZ), in the province of Kahramanmaraş. The Mw 7.6 Elbistan earthquake occurred about 9 hours later, with an epicenter located about 95 km north-northeast of the Mw 7.8 quake. The combination of these two shocks produced a devastating effect with nearly 55,000 confirmed deaths and about 1.5 million people left homeless.

In this work, we describe the Complete Automatic Seismic Processor (CASP) procedure that has been implemented to develop a large and comprehensive data set consisting of about 63,000 events of magnitude greater than 2.0, that occurred in south-eastern Türkiye between January 2019 and June 2023. The starting catalogue contains about 3.8 million waveforms recorded by 262 velocimetric and accelerometric instruments (network codes KO, TK and TU). The earthquakes were located using the Non-Linear Location technique (NLLOC) with a regional 1-D velocity model, based on the precise picking of P- and S-wave arrivals provided by the RSNI-Picker2 implemented in CASP. After several quality controls, the final high quality catalogue contains 8,475 well-located earthquakes, with a significant difference in depth with respect to the AFAD catalogue.

We present the spatio-temporal distribution of earthquakes before and after the two mainshocks, as well as the distribution of strong-motion parameters, such as peak ground acceleration (PGA), peak ground velocity (PGV), and Fourier amplitude spectra (FAS). Furthermore, preliminary results on earthquake source parameters obtained by spectral decomposition applied separately to background and clustered seismicity are also discussed.

The compiled data set can serve as a basis for studying seismic sequences during seismic crises and identifying the preparatory phase of strong earthquakes in geologically active areas.

How to cite: Colavitti, L., Tarchini, G., Spallarossa, D., Scafidi, D., Picozzi, M., Iaccarino, A. G., Bindi, D., Martínez-Garzón, P., Cotton, F., and Zaccarelli, R.: The advantages of Standardization and Data Sharing: a swift compilation of a high-quality data set for seismological studies in the East Anatolian Fault Zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7863, https://doi.org/10.5194/egusphere-egu24-7863, 2024.

EGU24-8614 | ECS | Orals | SM2.2

Recent Advances in Earthquake Monitoring in Madagascar 

Andriniaina Tahina Rakotoarisoa and Hoby N. T. Razafindrakoto

Earthquakes are acknowledged as a potent force of nature that can cause substantial harm to populations and result in widespread damage. Therefore, having a seismic public alerting system is crucial for swiftly broadcasting warnings to the public and relevant risk agencies in the event of an earthquake. The system will send instantaneous notifications to users, allowing them to quickly implement protective measures for risk agencies, as well as offer feedback on individuals’ situations during the earthquake. In this regard, this study aims to build a wrapper for near-real-time earthquake monitoring. Our development includes four steps: (1) improvement of earthquake detection using PhaseNet (Zhu & Beroza, 2018) with PhasePApy (Chen & Holland, 2016) and the Rapid Earthquake Association and Location (REAL, Zhang et al., 2019) for picks association, (2) earthquake location refinement using the HYPOINVERSE program (Klein, 2002), (3) event classification with the CNN classification method, and (4) rapid earthquake notification through email and a locally designed application called SeismicBox2 for smartphones that include earthquake information and USGS shakemap. We conduct testing and validation of the system using earthquake data from Madagascar (archive and near-realtime)

How to cite: Rakotoarisoa, A. T. and Razafindrakoto, H. N. T.: Recent Advances in Earthquake Monitoring in Madagascar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8614, https://doi.org/10.5194/egusphere-egu24-8614, 2024.

EGU24-9715 | ECS | Orals | SM2.2

Automatic detection and characterization of Very Long-period seismic events for volcanic monitoring applications. 

Sergio Gammaldi, Dario Delle Donne, Pasquale Cantiello, Antonella Bobbio, Walter De Cesare, Rosario Peluso, and Massimo Orazi

Real-time seismological applications are now crucial for the monitoring and surveillance of active volcanoes, as they are useful tools for the early detection of volcanic unrest. In open-vent active volcanoes,  Very Long Period (VLP) seismicity, typically associated with mild and persistent explosive activity, is of crucial importance for volcano monitoring, as its variations in occurrence rate and magnitude may prelude a phase of unrest.  Here we show a new method for the automatic real-time detection and characterization of  VLP seismicity at Stromboli active volcano (Italy).

The detection algorithm is based on the Three-Component Amplitude (TCA) obtained from waveform polarization and spectral analysis of the continuous recording, providing time of detection,  azimuth,  incidence,  amplitude, and frequency of the detected VLP events. The VLP amplitudes derived at all stations of the monitoring network, provided as peak-to-peak amplitudes and mean square amplitudes, are also used to perform an automatic localization of VLP source.

VLP detections and characterizations derived from our automatic detection algorithm are compared with detection derived from manual and automatic inspections of the seismic record and with VLP time histories from available published VLP datasets.

From this comparison, it turns out that the VLP detection time series produced by the automatic algorithm tracks fluctuations in the  VLP activity well,  as manually detected by the operators over a  ~20-year period, thus allowing us to include it into the real-time processing framework operating at Stromboli for volcano surveillance.

How to cite: Gammaldi, S., Delle Donne, D., Cantiello, P., Bobbio, A., De Cesare, W., Peluso, R., and Orazi, M.: Automatic detection and characterization of Very Long-period seismic events for volcanic monitoring applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9715, https://doi.org/10.5194/egusphere-egu24-9715, 2024.

EGU24-9764 | Orals | SM2.2

Creating an Inventory of Seismic Signals at Vulcano Island, Italy, using Unsupervised Learning Techniques 

Horst Langer, Susanna Falsaperla, Ferruccio Ferrari, and Salvatore Spampinato

The island of Vulcano gives its name to the so-called “Vulcanian eruptions”, an eruptive style with strong explosive characteristics and observed there for the first time. The last eruptive activity occurred between 1888 and 1890. Starting from mid-September 2021, an unrest, marked by relevant variations in geochemical and geophysical parameters, affected the island. Here, we analyze the seismic signals recorded from the onset of the unrest until December 2022. An increasing number of Very Long Period events was detected from September 2021 onwards, enhancing concerns linked to other measured anomalies, such as increasing CO2 emissions and fumarole temperatures. Numerous types of signals were generally recorded on the island, partly caused by various man-made sources, such as the close-by passage of ships, dropping anchors, etc. The large variety of the seismic signals made standard amplitude-based monitoring techniques, such as RSAM, questionable. We therefore focused on creating an inventory of the recorded signals exploiting unsupervised machine learning techniques, namely Self-Organizing Maps and Cluster Analysis. We were able to identify various classes of seismic events related to volcanic dynamics and to distinguish exogenous signals, such as anthropic noise. This allowed us to visualize the development of signal characteristics efficiently. This classification can help build an effective alert tool to automatically identify different types of seismic signals, useful for surveillance purposes. Furthermore, it is a preparative step for other studies, such as event location and source process modeling.

How to cite: Langer, H., Falsaperla, S., Ferrari, F., and Spampinato, S.: Creating an Inventory of Seismic Signals at Vulcano Island, Italy, using Unsupervised Learning Techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9764, https://doi.org/10.5194/egusphere-egu24-9764, 2024.

EGU24-10651 | ECS | Posters on site | SM2.2

Contribution of SeismoCitizen Raspberry Shake dense network in monitoring induced seismicity in northern Alsace (France) 

Mathieu Turlure, Marc Grunberg, Fabien Engels, Hélène Jund, Antoine Schlupp, and Jean Schmittbuhl

PrESENCE ANR project (2022-2025) focuses on seismic hazards induced by deep geothermal operations in northern Alsace, France, and their associated societal perception. Seismological observations are obtained using a large number of low cost internet-connected equipment (Raspberry Shake seismic station and associated open access data). The breakthrough strategy of the project relies on the deployment of the stations in residences or administrative buildings of non-seismologist volunteer citizens or authorities. The aim is to use those stations to densify the french permanent seismic network, and to improve the detection and location of seismic events, in particularly small ones. Our presentation will be focused on the Soultz-sous-Forêts and Rittershoffen areas (northern Alsace, France), which are sites of deep geothermal operations. 

 

The topology of the seismological network was determined by the location of permanent stations, from Epos-France permanent network (4) and public stations belonging to geothermal operators (2), the number of low-cost stations (35) to be deployed in the region, the location of deep geothermal power plants (Soultz and Rittershoffen) and the location of volunteer citizen hosts. Volunteer citizens were selected initially by word of mouth, then by a call for applications (through social networks, flyers, local newspapers). Twenty-one stations are currently (end of 2023) hosted in the area. About ten additional stations are planned to be deployed early 2024 in the area.

 

Based on our past experience in deploying similar networks in other contexts and regions (Mayotte, Vosges massif, Mulhouse, etc.), we have consolidated the installation of these stations to ensure reliable data acquisition and, in particular, to achieve better data completeness (acquisition directly at the station using the Seedlink protocol via a VPN, hardware watchdog). We use Ansible (an open source IT automation platform) to facilitate the deployment of Raspberry Shake stations configuration and management tasks, ensuring rapid and consistent production deployment.

 

The workflow for building the seismicity catalog benefits from our advances in the use of new artificial intelligence tools, such as PhaseNet, a deep learning automatic picking method, as well as in the development of a deep learning method for discrimination between earthquakes, quarry blasts and explosions. Our tests over the year 2023 show that even if the stations are installed in urban areas (and therefore in a noisy environment), the network is able to automatically detect and locate many small induced earthquakes, including around 250 with a high level of confidence, compared with the ten detected or so by the standard procedure of BCSF-Renass, the French National Observation Service.

How to cite: Turlure, M., Grunberg, M., Engels, F., Jund, H., Schlupp, A., and Schmittbuhl, J.: Contribution of SeismoCitizen Raspberry Shake dense network in monitoring induced seismicity in northern Alsace (France), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10651, https://doi.org/10.5194/egusphere-egu24-10651, 2024.

EGU24-10668 | ECS | Posters on site | SM2.2

A workflow for building an automatic earthquake catalog from near-real time DAS data recorded on offshore telecommunications cable in central Chile. 

Marie Baillet, Alister Trabattoni, Martijn van den Ende, Clara Vernet, and Diane Rivet

Distributed Acoustic Sensing (DAS) is of critical value for the offshore expansion of seismological networks. The work presented here is part of the 5-years ERC ABYSS project, which aims at building a permanent seafloor seismic observatory leveraging 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, constituting more than 37,500 virtual sensors sampled at 125 Hz. We develop a workflow to detect more than 3500 local, regional and teleseismic events with local magnitudes down to ML = 0.5, automatically processing over 72 TB of data. We show that applying those methods to DAS data combined with data from the national onland seismic network greatly increases the accuracy of the earthquake hypocenter localizations. As a first step, we perform automatic seismic phase arrival picking using PhaseNet pretrained on conventional seismological stations, followed by phase association with GaMMA. We then apply a correction of the phase picks to account for shallow sedimentary layers and invert for the event hypocenter with VELEST. Finally, we estimate a local magnitude based on peak ground displacements.  

The ABYSS project near-real time data collection started the 30th of September 2023 using three DAS units to sense two offshore telecommunications cables connecting the cities of Concón to La Serena and La Serena to Caldera. The DAS data covers over 500 km of cable, comprising 30,000 virtual sensors sampled at 62.5 Hz. These data are synchronized once a day with a storage server located in France, the volume of which is anticipated to reach an estimated 608 TB by the end of the project. By applying our workflow, tested and validated on the POST experiment, to our daily data, we are able to process data in near-real time to build a catalog that will span 5 years, and that will be used as a reference for subsequent studies within the framework of the ABYSS project. Furthermore, the size of our catalog, enriched with numerous offshore events is a significant improvement over the existing regional catalogs, which may aid future studies of the Chilean margin subduction zone seismicity. 

How to cite: Baillet, M., Trabattoni, A., van den Ende, M., Vernet, C., and Rivet, D.: A workflow for building an automatic earthquake catalog from near-real time DAS data recorded on offshore telecommunications cable in central Chile., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10668, https://doi.org/10.5194/egusphere-egu24-10668, 2024.

EGU24-10893 | ECS | Posters on site | SM2.2

Exploring the application of Characteristic Functions on DAS data and their influence in event detection performance. 

Sonja Gaviano, Giacomo Rapagnani, Davide Pecci, Juan Porras, Estelle Rebel, and Francesco Grigoli

Distributed Acoustic Sensing (DAS) has emerged as a powerful tool in seismological applications, transforming fiber-optic cables into dense arrays of geophones that can continuously sample seismic wavefields across several kilometers. DAS data acquisition presents a versatile approach, utilizing either ad hoc installations with specific cables or leveraging existing telecommunication optical fiber-network infrastructure. Its adaptability makes DAS particularly advantageous for seismic monitoring in logistically challenging environments like volcanoes or offshore areas, where traditional seismometers may face limitations.

 

Conventional seismological techniques struggle to effectively process DAS data due to its unique characteristics—typically, wavefields are sampled at 1 m spacing with frequencies exceeding 1 kHz. As a result, this technology provides a detailed mapping of the seismic wavefield across the length of the fiber, and it also generates a significant amount of data compared to the sparse seismometer installations. In order to efficiently analyze these data, we introduced HECTOR, a waveform-based detection method designed specifically for DAS data (Porras et al. 2024).

 

In this study, we investigate the capabilities of HECTOR following preprocessing of DAS data using various characteristic functions (CF). We explore non-negative functions, including Short Term Average to Long Term Average (STALTA), Energy, and Envelope, whose peculiarity is to preserve noise. Conversely, zero-mean characteristic functions such as Short Term Average to Long Term Average derivative (STALTA derivative), Kurtosis, and Kurtosis derivative enhance signals and mitigate noise. Our objective is to assess HECTOR's performance when analyzing preprocessed data compared to raw data.

 

To validate our findings, we initially test the detector on synthetic data. These simulations encompass diverse optical fiber geometries, source configurations, and locations. Subsequently, we apply the algorithm to real data collected in two distinct scenarios. The first scenario involves the FORGE experiment situated in Utah, US, which entails a borehole installation of 1 km optical fiber deployed above a geothermal reservoir characterized by induced seismic activity. The second scenario involves a 90 km horizontal optical fiber deployed in the Pyrenees region. The area is characterized by natural earthquake activity with magnitudes (2.01≥ML≥0.02), alongside anthropic events due to quarry blasts. 

Our evaluation focuses on quantifying the enhancement in HECTOR's performance following the application of CFs compared to analyzing raw data.

Through this comprehensive exploration, we aim to advance the understanding of DAS data processing, demonstrating the efficacy of HECTOR across diverse scenarios. 

We would like to thank TotalEnergies for sharing this data set with us as well as Febus Optic for providing the DAS interrogator used for the data acquisition.

 

References: 

A Semblance-based Microseismic Event Detector for DAS Data.

  • Porras, D. Pecci, G. Bocchini, S. Gaviano, M. De Solda, K. Tuinstra, F. Lanza, A. Tognarelli, E. Stucchi, F. Grigoli. Geophysical Journal International (GJI) 2024 (Accepted)

How to cite: Gaviano, S., Rapagnani, G., Pecci, D., Porras, J., Rebel, E., and Grigoli, F.: Exploring the application of Characteristic Functions on DAS data and their influence in event detection performance., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10893, https://doi.org/10.5194/egusphere-egu24-10893, 2024.

EGU24-12443 | ECS | Posters on site | SM2.2

Unveiling coupling properties of subduction zones with novel telesismic waveform approaches 

Francesco Rappisi, Tim Craig, and Sebastian Rost

Subduction zones are among the most active tectonic areas on the planet. Their primary characteristic is the enormous amount of stress accumulated at the interface between the subducting oceanic plate and the overriding plate. The release of this stress is accommodated by a wide range of behaviours, ranging from aseismic slip (slip at speeds too slow to radiate seismic energy), through the spectrum of slow slip and tremor, to seismic slip capable of generating major earthquakes. The main investigative tools for subduction zones to map out this range of behaviour, and to assess the coupling properties of the subduction interface, involve the direct observation of ground movements through geodesy (either terrestrial or satellite-based) or through local seismic surveillance using near-field instrumentation, all of which are logistically complex, and typically only feasible on land.

Utilizing the recent expansion of seismic arrays in continental regions, we propose an alternative approach for the study of subduction zones that bypasses the aforementioned limitations through the use of teleseismic waves—recorded at a distance between 30º and 90º from the epicenter—based on the identification of the presence (or absence) of highly reflective layers at the megathrust interface. Previous studies using local seismic data have observed the presence of highly reflective layers, characterized by strong impedance contrasts, located at the megathrust interface, capable of producing a reflection in the wavefield that results into the presence of precursors of depth phases. Since impedance contrasts in the solid Earth are linked to variations in the elastic properties of the medium, reflectivity offers a window into the rheology of the plate interface. Understanding the reasons behind such strong impedance contrasts, their potential variability over time and space, could pave the way for understanding why the degree of coupling of subduction interfaces varies, whether it is related to transient processes, or if it is stable over time.

Here, we present an automated waveform processing approach designed to detect such reflections in remote seismic data, and illustrate this with a test region from the Central America subduction zone.  We analyse waveforms produced by seismic events with magnitudes ranging from 4.5 to 5.5 occurring at different times and recorded by small aperture seismic arrays. Our observations in Central America prove to be an excellent tool for studying the coupling properties of the megathrust interface. This work represents a first attempt, with the ultimate goal of mapping subduction zones and their coupling properties, even in currently inaccessible submarine areas, allowing for a better understanding of the seismic risk that subduction zones represent.

How to cite: Rappisi, F., Craig, T., and Rost, S.: Unveiling coupling properties of subduction zones with novel telesismic waveform approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12443, https://doi.org/10.5194/egusphere-egu24-12443, 2024.

EGU24-13591 | ECS | Posters on site | SM2.2

Automatic determination of focal depth with the optimal period of Rayleigh wave amplitude spectra and uncertainty assessment in 3D velocity model 

Xiaohui He, Peizhen Zhang, Sidao Ni, Wenbo Wu, Risheng Chu, Yi Wang, and Kaiyue Zheng

Focal depth of earthquakes is essential for studies of seismogenic processes and seismic hazards. Surface waves are usually the strongest seismic phases at local and regional distances, and its excitation is sensitive to source depth. We observe that the optimal period (the period corresponding to the maximum amplitude) of Rayleigh waves at local distances shows an almost linear correlation with focal depth, based on which we propose a method for resolving the focal depth of local earthquakes. We propose an automated data processing workflow, and applications to earthquakes in diverse tectonic settings demonstrate that reliable focal depth with uncertainty of 1~2 km can be determined even with one or a few seismic stations. Then, we use the Longmenshan region as a case study to systematically assess the impact of the 3D velocity model on the results through forward simulation. A total of 191 events at depths ranging from 5 to 20 km are simulated. The standard deviation between the focal depths determined by this method and the input values is approximately 1.5 km, with 95% events having errors within 2 times the standard deviation. This indicates that the method exhibits good applicability even in regions with complex velocity structures, and highlights the applicability of the method in scenarios characterized by sparse network coverage or historical events.

How to cite: He, X., Zhang, P., Ni, S., Wu, W., Chu, R., Wang, Y., and Zheng, K.: Automatic determination of focal depth with the optimal period of Rayleigh wave amplitude spectra and uncertainty assessment in 3D velocity model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13591, https://doi.org/10.5194/egusphere-egu24-13591, 2024.

EGU24-15414 | ECS | Posters on site | SM2.2

Passive Assessment of Geophysical Instruments Performance using Electrical Network Frequency Analysis 

Mathijs Koymans, Elske de Zeeuw-van Dalfsen, Läslo Evers, and Jelle Assink

The electrical network frequency (ENF) of the alternating current operated on the power grid is a well-known source of noise in digital recordings. The noise (i.e., signal) is widespread and appears not just in close proximity to high-voltage power lines, but also in instruments simply connected to the mains powers grid. This omnipresent, anthropogenic signal is generally perceived as a nuisance in the processing of geophysical data. Research has therefore been mainly focused on its elimination from data, while its benefits have gone largely unexplored. It is shown that mHz fluctuations in the nominal ENF (50 - 60Hz) induced by variations in power usage can be accurately extracted from geophysical data. This information represents a persistent time-calibration signal that is coherent between instruments over national scales. Cross-correlation of reliable reference ENF data published by electrical grid operators with estimated ENF data from geophysical recordings allows timing errors to be resolved at the 1s level. Furthermore, it is shown that a polarization analysis of particle motion at the ENF may assist in the detection of instrument orientation anomalies at the surface. Furthermore, it is explored whether this method can be applied to determine orientations of geophones inside seismic boreholes.

How to cite: Koymans, M., de Zeeuw-van Dalfsen, E., Evers, L., and Assink, J.: Passive Assessment of Geophysical Instruments Performance using Electrical Network Frequency Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15414, https://doi.org/10.5194/egusphere-egu24-15414, 2024.

EGU24-17429 | ECS | Orals | SM2.2

Relative methods of localization and their differences in results on the REYKJANET seismic network in Iceland 

Diana Konrádová, Jana Doubravová, Bohuslav Růžek, and Josef Horálek

Accurate earthquake localization is essential for advancing seismic processing and understanding geological structures. In this study, we explore the application of relative relocation methods—HypoDD (HD), GrowClust (GC), and Master Event (ME)—to refine event locations and analyze their implications beyond specific fault structure determination. While the primary focus is not exclusively on geological structures, the outcomes also serve broader purposes, contributing to critical aspects of seismic processing.
Our investigation employs a dataset from the REYKJANET seismic network located on the Reykjanes Peninsula in Iceland. The comparative assessment of these methods reveals significantly focused clusters in contrast to absolute event locations. Notably, individual event locations exhibit variations dependent on the chosen relocation method.
Furthermore, it is essential to note that Master Event (ME) is a program developed for event localization, offering the unique capability of sequential use. This feature proves valuable, especially in dynamic geological settings, such as the Reykjanes Peninsula in Iceland, where volcanic eruptions occur.
Additionally, we delve into the influence of control parameters for HD, GC, and ME on final location results, aiming to optimize these parameters while considering computational and memory demands. This research contributes to a comprehensive understanding of relative localization methods, emphasizing their broader applications and significance in seismic event analysis within the REYKJANET network.

How to cite: Konrádová, D., Doubravová, J., Růžek, B., and Horálek, J.: Relative methods of localization and their differences in results on the REYKJANET seismic network in Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17429, https://doi.org/10.5194/egusphere-egu24-17429, 2024.

Faults zones in the Earth’s crust alter permeability architecture relative to country rock and can function as fluid conduits. Documented cases of long-distance earthquake interactions suggest that pore-pressure gradients resulting from conduit flow can activate seismic slip where receiver faults might be sensitive to external forcing. When external stress forcing can be quantified, for example, in the form of ground motions that can be converted to stress, it provides an opportunity to measure the stress perturbation required to nucleate slip in cases where fault activation is triggered.  

 

In this study, we investigate the stress state of faults in the Lower Rhine Embayment (LRE), western Germany. We do so by quantifying the occurrence of remote dynamic triggering by transient stresses imparted by passing waves of distant mainshocks. The LRE hosts a system of normal faults with mean estimated slip rates of 0.1 mm/yr and moderate seismicity. We use the continuous Bensberg catalog starting in 1990 to estimate the statistical significance of seismicity rate changes surrounding teleseismic mainshocks identified as triggering candidates. We identify 21 teleseismic mainshocks with ML > 7 (1990 – 2015) and ML > 6 (2016 – present) that generate a theoretical peak-ground velocity (PGV) >0.02 cm/s within the study area. Two mainshocks associate with statistically significant seismicity-rate increases following the passing of their surface waves: the 1992 Roermond, and the 2021 M8.2 Chignik, Alaska earthquakes. Both mainshocks generated PGV values > 0.017 cm/s at 30s and have back-azimuths that are roughly parallel to the dominant strike of LRE faults. We observe a migrating sequence of earthquakes in the 10 days following the Roermond earthquake, where roughly half occur outside of the classical aftershock zone of ~2-3 fault lengths. We infer dynamic triggering to play a role in the generation of the migrating sequence, as migration outpaces diffusion time scales assuming realistic crustal diffusivity values of up to 3 m2/s. The July 2021 Alaska earthquake likely triggered a sequence of ~16 locatable earthquakes. The observed surface PGV values of the Alaska and Roermond earthquakes correspond to peak dynamic stress values of 1.4 kPa and < 30 kPa, respectively. Thus, stress values at the hypocentral depth of the triggered sequence of ~16 events inferred from 30s Rayleigh waves of the Alaska earthquake would correspond to 50-66% of the observed surface value.

 

Using remote dynamic triggering as a stress-meter to estimate stress thresholds that can potentially activate faults has important implications for earthquake physics, as well as for society. The LRE is being targeted for geothermal energy production. Prior work documents a series of 14 earthquakes of Mw > 5.0 since the 14th century, including the 1992 Mw 5.3 Roermond earthquake. Therefore, quantifying the triggerability of faults at a future energy production site prior to operation should be a key step in assessing the potential for fault reactivation.

How to cite: Roth, M. P. and Harrington, R. M.: Using remote dynamic earthquake triggering as a stress-meter of the Lower Rhine Embayment fault system in western Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20910, https://doi.org/10.5194/egusphere-egu24-20910, 2024.

EGU24-4154 | ECS | Posters on site | SM2.3

Clustering distributed acoustic sensing signals via curvelet transform and unsupervised deep learning 

Bolin Li, Sjoerd de Ridder, and Andy Nowacki

Distributed acoustic sensing (DAS), a technology that exhibits great potential for subsurface monitoring and imaging, has been regarded as a preeminent instrument for vibration measurements. In light of the tremendous amount of seismic data, numerous channels, and elevated noise levels, it becomes imperative to suggest an appropriate denoise procedure that is compatible with DAS data. In this regard, unsupervised deep learning with data clustering generally exhibits superior performance in facilitating the efficient analysis of sizable unlabeled data sets devoid of human bias. In addition, the clustering method is capable of detecting seismic waves, microseismic turbulence, and even unidentified new types of negligible seismic events, in contrast to a number of conventional denoising techniques. While current approaches reliant on f-k analysis remain valuable, they fail to fully exploit the information present in the wavefield due to their inability to identify the characteristic moveout observed in seismic data. In order to denoise DAS data more effectively, we investigate the capacity of the curvelet transform to extend existing deep scattering network methodologies. In this paper, we propose a novel clustering approach for the denoise processing of DAS data that utilises the Gaussian Mixture Model (GMM), curvelet transform, and unsupervised deep learning. 

The DAS data are initially subjected to the curvelet transform in order to derive the curvelet coefficients at various scales and orientations, which can be regarded as the first layer of extracted features. Following this, a deeper layer of features is obtained by applying the curvelet transform to the coefficients in the first layer. The aforementioned process continues in this manner until the depth of the layer satisfies the algorithm-determined expectation. By concatenating the curvelet coefficients from each layer, the original DAS data's features are generated. Afterwards, the signal is reduced to two dimensions using principal component analysis (PCA), which simplifies its interpretation by projecting the high-dimensional features onto two principal components, which facilitates the clustering of the features by GMM for achieving the final clustered results.

This methodology operates without the need for labels of DAS data and is highly appropriate for managing the substantial quantity and numerous channels of DAS. We used a variety of approaches, such as Bayesian information criteria and silhouette analysis, to determine the optimal number of clusters in GMM and evaluate the algorithm's clustering performance. We demonstrate the method on downhole data acquired during stimulation of the Utah FORGE enhanced geothermal system, and the results appear quite satisfactory, indicating that it can be utilised effectively to denoise DAS signals.

How to cite: Li, B., de Ridder, S., and Nowacki, A.: Clustering distributed acoustic sensing signals via curvelet transform and unsupervised deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4154, https://doi.org/10.5194/egusphere-egu24-4154, 2024.

EGU24-4807 | ECS | Posters on site | SM2.3

Implementation of the Random Forest Algorithm for Magnitude Prediction in the Matano Fault Indonesia  

Madona, Mohammad Syamsu Rosid, Djati Handoko, Nelly Florida Riama, and Deni Saiful

Studying earthquake prediction is an interesting academic area. Earthquakes are classified as natural disasters that have the potential to inflict significant damage.  The magnitude of an earthquake provides substantial benefits, both immediately after the event and in the future, for risk assessment and mitigation. This study employs the Random Forest algorithm to predict the magnitude of earthquakes occurring on the Matano Fault in Sulawesi, Indonesia. The prediction is derived from the historical seismic data collected between 1923 and 2023, obtained from the BMKG and USGS Catalogs. The area of interest is situated along the Matano Fault in Sulawesi, Indonesia, with coordinates ranging from 2.99°S to 1.66°S and from 120.50°W to 122.47°W. The dataset comprises six attributes and is split into training and testing sets at a ratio of 70% and 30%, respectively. The variables employed in this investigation encompass origin time, latitude, longitude, magnitude, and magnitude type.  The investigation yields an RMSE score of 0.1929. Overall, the prediction model has outstanding performance, with a high degree of accuracy in predicting values that quite match the actual values. Additionally, the Root Mean Square Error (RMSE) value is 0.1929, indicating a low level of error in the predictions. this work attempts to propose an alternative approach, characterized by a straightforward and practical technique, to solve problems in the geophysics field, for instance in the area of earthquake prediction.

How to cite: Madona, , Rosid, M. S., Handoko, D., Riama, N. F., and Saiful, D.: Implementation of the Random Forest Algorithm for Magnitude Prediction in the Matano Fault Indonesia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4807, https://doi.org/10.5194/egusphere-egu24-4807, 2024.

EGU24-5031 | ECS | Posters on site | SM2.3

SeisPolar: Seismic Wave Polarity Module for the SeisBlue Deep Learning Seismology Platform 

I-Hsin Chang, Chun-Ming Huang, and Hao Kuo-Chen

Responding to challenges from increasing seismic data, our study leverages deep learning to enhance seismic data processing's automation and efficiency. Recognizing Taiwan's unique geological structure, we have developed deep learning models using data from dense seismic arrays since 2018. We have integrated the Transformer model with GAN training techniques for phase picking. Our latest system, SeisBlue, has evolved from phase picking and earthquake location to include magnitude and focal mechanism estimation, primarily using SeisPolar, a CNN model for P-wave polarity classification, crucial for focal mechanism analysis. Additionally, our redesign of the seismic monitoring process emphasizes data pipelines and integrates software engineering technologies, including hardware, system environment, database, data pipelines, model version control, task monitoring, data visualization, and Web UI interaction. The model shows high proficiency in identifying P-wave polarity and deciphering focal mechanisms, with an accuracy of 85%, and precision and recall rates for three categories [positive, negative, undecidable] at [87%, 77%, 53%] and [84%, 80%, 54%], respectively. It notably achieves about 70% Kagan angle under 40 degrees for focal mechanism analysis. This semi-automated workflow, from data processing to phase picking, earthquake location, magnitude determination, focal mechanism estimation and Web UI, significantly boosts seismic monitoring's efficiency and accuracy. It facilitates quicker and more meaningful engagement for researchers in subsequent studies, marking a notable advancement in seismic monitoring and deep learning application.

How to cite: Chang, I.-H., Huang, C.-M., and Kuo-Chen, H.: SeisPolar: Seismic Wave Polarity Module for the SeisBlue Deep Learning Seismology Platform, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5031, https://doi.org/10.5194/egusphere-egu24-5031, 2024.

EGU24-5044 | Posters on site | SM2.3

Event-based features: An improved feature extraction approach to enrich machine learning based labquake forecasting 

Sadegh Karimpouli, Grzegorz Kwiatek, Patricia Martínez-Garzón, Georg Dresen, and Marco Bohnhoff

Earthquake forecasting is a highly complex and challenging task in seismology ultimately aiming to save human lives and infrastructures. In recent years, Machine Learning (ML) methods have demonstrated progressive achievements in earthquake processing and even labquake forecasting. Developing a more general and accurate ML model for more complex and/or limited datasets is obtained by refining the ‘ML models’ and/or enriching the ‘input data’. In this study, we present an event-based approach to enrich the input data by extracting spatio-temporal seismo-mechanical features that are dependent on the origin time and location of each event. Accordingly, we define and analyze a variety of features such as: (a) immediate features, defined as the features which benefit from very short characteristics of the considered event in time and space, (b) time-space features, based on the subsets of acoustic emission (AE) catalog constrained by time and space distance from the considered event, and (c) family features, extracted from topological characteristics of the clustered (family) events extracted from clustering analysis in different time windows. We use AE catalogs recorded by tri-axial stick-slip experiments on rough fault samples to compute event-based features. Then, a random forest classifier is applied to forecast the occurrence of a large magnitude event (MAE>3.5) in the next time window. Results show that to obtain a more accurate forecasting model, one needs to separate background and clustered activities. Based on our results, the classification accuracy when the entire catalog data is used reaches 73.2%, however, it shows a remarkable improvement for separated background and clustered populations with an accuracy of 82.1% and 89.0%, respectively. Feature importance analysis reveals that not only AE-rate, seismic energy and b-value are important, but also family features developed from a topological tree decomposition play a crucial role for labquake forecasting.

How to cite: Karimpouli, S., Kwiatek, G., Martínez-Garzón, P., Dresen, G., and Bohnhoff, M.: Event-based features: An improved feature extraction approach to enrich machine learning based labquake forecasting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5044, https://doi.org/10.5194/egusphere-egu24-5044, 2024.

EGU24-5148 | ECS | Posters on site | SM2.3

Toward a Polarity Focal Mechanism Estimation via Deep Learning for small to moderate Italian earthquakes 

Flavia Tavani, Pietro Artale Harris, Laura Scognamiglio, and Men-Andrin Meier

One of the main tasks in seismology is the source characterization after an earthquake, in particular the estimate of the orientation of the fault on which an earthquake occurs and the direction of the slip. Currently, most seismological observatories compute moment tensor solutions for earthquakes above a certain magnitude threshold, but, for small to moderate earthquakes (i.e. aftershock sequences), or for large but close in time events, focal mechanism by first arrival polarities are often the only source information available (Sarao et al., 2021).

Focal mechanisms are important to better define the activated faults, to help in understanding the seismotectonic process, to improve the predicted ground shakings for early warning, the tsunami alert and the seismic hazard assessment. For these purposes, it becomes essential to produce and disseminate an estimate of the earthquake source parameters even for small events. Recently, machine learning techniques have gained significant attention and usage in various fields, including seismology where these algorithms have emerged as powerful tools in providing new insight into the earthquakes data analysis such as the prediction of the seismic wave's first arrivals polarities which can be used to compute focal mechanisms.

We present here a workflow developed to obtain earthquake focal mechanisms starting from the first p-wave polarities estimated through the method proposed by Ross et al (2018).

Our procedure consists of two stages: in the first stage, we use a combination of the available INGV web services (Bono et al., 2021) and the ObsPy functions to download the earthquake hypocentral location. We recover the waveforms recorded by the stations in the 0 -120 km distance range, and we create an input file with the appropriate information required for the prediction of the polarities for each waveform. We then use the convolutional neural network (CNN) proposed in Ross et al (2018) to obtain the polarities for each waveform, which can be UP, DOWN, or UNKNOWN. The second stage of the developed procedure aims to use the polarities that have been predicted to determine the focal mechanisms of the selected earthquakes. To do this, we use a modern Python implementation of HASH code (originally proposed in Fortran by Hardebeck et al. 2002, 2003) called SKASH (Skoumal et al. submitted). Finally, we present an application of this procedure to the September 2023, Marradi (Central Italy), seismic sequence that has been characterized by a magnitude Mw 4.9 mainshock followed by over 70 aftershocks in the magnitude range 2 - 3.4. Here, we focused on the estimation of the focal mechanism for events down to M 2.0. The application of the presented workflow permits to gain useful information about the kinematics of the earthquakes in the sequence, obtaining thus a more precise characterization of the activated structures.

How to cite: Tavani, F., Artale Harris, P., Scognamiglio, L., and Meier, M.-A.: Toward a Polarity Focal Mechanism Estimation via Deep Learning for small to moderate Italian earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5148, https://doi.org/10.5194/egusphere-egu24-5148, 2024.

Dynamic source inversion of earthquakes consists of inferring frictional parameters and initial stress on a fault consistent with co-seismic seismological and geodetic data and dynamic earthquake rupture models. In a Bayesian inversion approach, the nonlinear relationship between model parameters and data (e.g. seismograms) requires a computationally demanding Monte Carlo (MC) approach. As the computational cost of the MC method grows exponentially with the number of parameters, dynamic inversion of a large earthquake, involving hundreds to thousands parameters, shows problems with convergence and sampling. We introduce a novel multi-stage approach to dynamic inversions. We divide the earthquake rupture into several successive temporal (e.g. 0-10 s, 10-20 s, …) and spatial stages (e.g., 100 km, 200 km, …). As each stage requires only a limited number of independent model parameters, their inversion converges relatively fast. Stages are interdependent: earlier stage inversion results are a prior for a later stage inversion. Our main advancement is the use of Generative Adversarial Networks (GAN) to transfer the prior information between inversion stages, inspired by Patel and Oberai (2019). GAN are a class of machine learning algorithms originally used for generating images similar to the training dataset. Their unsupervised training is based on a contest between a generator that generates new samples and a critic that discriminates between training and generator’s images. The resulting generator should generate synthetic images/samples with noise in a low-dimensional latent space as an input. We train GANs on samples of dynamic parameters from an earlier stage of the inversion and use the GAN to suggest the dynamic parameters in a later stage of inversion. We show a proof of concept dynamic inversion of a synthetic benchmark, comparing performance of direct MC dynamic inversion with parallel tempering with our GAN approach. We efficiently handle large ruptures by adopting a 2.5D approximation that solves for source properties averaged across the rupture depth. The 2.5D modeling approach accounts for the 3D effect of the finite rupture depth while keeping the computational cost the same as in 2D dynamic rupture simulations. Additionally we show current results on the dynamic inversion of 2023 Mw 7.8 Kahramanmaraş, Turkey, earthquake.

How to cite: Premus, J. and Ampuero, J.-P.: Dynamic earthquake source inversion with GAN priors, with application to the 2023 Mw 7.8 Kahramanmaraş, Turkey earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6072, https://doi.org/10.5194/egusphere-egu24-6072, 2024.

EGU24-6371 | Posters on site | SM2.3

Detailed clustering of continuous seismic waveforms with deep scattering networks: a case study on the Ridgecrest earthquake sequence 

Reza Esfahani, Michel Campillo, Leonard Seydoux, Sarah Mouaoued, and Qing-Yu Wang

Clustering techniques facilitate the exploration of extensive seismogram datasets, uncovering a variety of distinct seismic signatures. This study employs deep scattering networks (Seydoux et al. 2020), a novel approach in deep convolutional neural networks using fixed wavelet filters, to analyze continuous multichannel seismic time-series data spanning four months before the 2019 Ridgecrest earthquake sequence in California. By extracting robust physical features known as scattering coefficients and disentangling them via independent component analysis, we cluster different seismic signals, including those from foreshock events and anthropogenic noises. We investigate the variability of intracluster (dispersion within each cluster) and examine how it correlates with waveform properties and feature space. The methodology allows us to measure this variability, either through distance to cluster centroids or 2D manifold mapping. Our findings reveal distinct patterns in the occurrence rate, daily frequency, and waveform characteristics of these clusters, providing new insights into the behavior of seismic events versus anthropogenic noises.

How to cite: Esfahani, R., Campillo, M., Seydoux, L., Mouaoued, S., and Wang, Q.-Y.: Detailed clustering of continuous seismic waveforms with deep scattering networks: a case study on the Ridgecrest earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6371, https://doi.org/10.5194/egusphere-egu24-6371, 2024.

As the amount of seismic data increasing drastically worldwide, there are ever-growing needs for high-performance automatic seismic data processing  methods and high-quality, standardized professional datasets. To address this issue, we recently updated the 'DiTing' dataset, one of the world's largest seismological AI datasets with ~2.7 million traces and corresponding labels,  with 1,089,920 three-component waveforms from 264,298 natural earthquakes in mainland China and adjacent areas, and 958,076 Pg, 780603 Sg, 152752 Pn, 25956 Sn earthquake phase arrival tags, in addition to 249,477 Pg, 41610 Pn first motion polarity tags from 2020 to 2023. We also collected 15375 non-natural earthquake waveforms in mainland China from 2009 to 2023 and a manually labeled noise dataset containing various typical noise signals from the China Seismological Network. With the support of the 'DiTing' dataset, we developed and trained several deep learning models referred as 'DiTingTools' for automatic seismic data processing. In the continuous waveform detection and evaluation of more than 1,000 stations over a year across China, 'DiTingTools' has achieved an average recall rate of 80% for event detection, mean square error ±0.2s for P phase picking, and ±0.4s for S, the average identification accuracy rate of Pg first motion polarity reached 86.7% (U) and 87.9% (D), and 75.1% (U) and 73.1% (D) for Pn first motion polarity, the average magnitude prediction error of a single station is mainly concentrated at ±0.5. The remarkable generalization capabilities of 'DiTingTools' were demonstrated through its application on the China Seismic Network. Specifically, 'DiTingPicker', a model within 'DiTingTools' designed for earthquake detection and phase picking, was employed to analyze the M 6.8  earthquake that struck Luding County, Sichuan Province, in 2022. This tool was instrumental in automatically processing data to examine the main shock and intricate fault structures of the aftershocks. The effectiveness of 'DiTingTools' in earthquake prevention and disaster reduction was further validated through these practical applications.

How to cite: Zhao, M., Xiao, Z., Zhang, B., Zhang, B., and Chen, S.: 'DiTing' and 'DiTingtools':a large multi-label dataset and algorithm set for intelligent seismic data processing established based on the China Seismological Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7119, https://doi.org/10.5194/egusphere-egu24-7119, 2024.

EGU24-7309 | Posters on site | SM2.3

Deep learning-based earthquake catalogs extracted from threebroadband/nodal seismic arrays with different apertures in Taiwan bySeisBlue 

Sheng-Yan Pan, Wei-Fang Sun, Chun-Ming Huang, and Hao Kuo-Chen

SeisBlue, a deep-learning-based earthquake monitoring system, is one of the solutions to deal with massive continuous waveform data and create earthquake catalogs. The SeisBlue workflow contains waveform data preprocessing, phase arrival detection by AI modules, phase associator, earthquake locating, earthquake catalog generation, and data visualization. The whole process can be done automatically and efficiently reduces the labor and time costs. In this study, SeisBlue is applied to three different regional seismic networks: the Formosa Array for the observation of magma chamber beneath the Tatun volcanic area, Taiwan (aperture ~80 km with 148 broadband stations and station spacing 5 km), the Chihshang seismic network (CSN) for monitoring micro-seismicity of Chihshang, Taiwan (aperture ~150 km with 14 broadband stations and station spacing 20 km), and the temporary dense nodal array for capturing the aftershock sequence of the 18 th Sep. 2022 Mw6.9 Chihshang earthquake, Taiwan (aperture ~70 km with 46 nodal stations and station spacing 3 km). The 2020 annual SeisBlue catalog of the Formosa Array contains 2,201 earthquakes, as background seismicity, compare to the 1,467 earthquakes listed in the standard catalog of the Central Weather Administration (CWA), Taiwan. The two-month SeisBlue catalog of the 2022 Mw6.9 Chihshang earthquake sequence, September to October, contains 14,276 earthquakes using the CSN dataset; however, the CWA standard catalog only lists 1,247 earthquakes during the same time period. By using waveform data of 18 th Sep. to 25 th Oct. 2022, SeisBlue detects 34,630 and 12,458 earthquakes extracted from the datasets of the dense nodal array and CSN, respectively. SeisBlue can effectively detects both background and aftershock seismicity and extracts small earthquakes via dense arrays.

Keywords: AI earthquake monitoring system, deep learning, AI earthquake catalog, SeisBlue, automatic waveform picking

How to cite: Pan, S.-Y., Sun, W.-F., Huang, C.-M., and Kuo-Chen, H.: Deep learning-based earthquake catalogs extracted from threebroadband/nodal seismic arrays with different apertures in Taiwan bySeisBlue, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7309, https://doi.org/10.5194/egusphere-egu24-7309, 2024.

EGU24-8233 | Posters on site | SM2.3

Double Acoustic Emission events detection using U-net Neural Network 

Petr Kolar, Matěj Petružálek, Jan Šílený, and Tomáš Lokajíček

In the past decade, the development of the Deep Neural Network formalism has emerged as a promising approach for addressing contemporary task in seismology, particularly in the effective and potentially automated processing of extensive datasets, such as seismograms. In this study, we introduce a 4D Neural Network (NN) based on the U-Net architecture, capable of simultaneously processing data from the entire seismic network. Our dataset comprises records/seismograms of Acoustic Emission (AE) events obtained during a laboratory loading experiment on a rock specimen. While AE event records share similarities with real seismograms, they exhibit simplifications in certain features.
To assess the capability of the proposed NN in handling complex data, including occurrences of multiple events observed during experiments, we generated double-event seismograms through the augmentation of unambiguous single-event seismograms. These augmented datasets were employed for training, validation, and testing of the NN. Despite the individual station detection rate being approximately 30%, the simultaneous processing of multiple stations significantly increased efficiency, achieving an overall detection rate of 97%.
In this work, we treat seismograms as "images," adopting an approach that proves to be fruitful. The simultaneous processing of seismograms, coupled with this image-based treatment, demonstrates high potential for reliable automatic interpretation of seismic data. This approach (possibly combined with other methodologies), holds promise for seismogram processing.

How to cite: Kolar, P., Petružálek, M., Šílený, J., and Lokajíček, T.: Double Acoustic Emission events detection using U-net Neural Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8233, https://doi.org/10.5194/egusphere-egu24-8233, 2024.

EGU24-8913 | ECS | Posters on site | SM2.3

Benchmarking seismic phase associators: Insights from synthetic scenarios 

Jorge Antonio Puente Huerta, Jannes Münchmeyer, Ian McBrearty, and Christian Sippl

In seismology, accurately associating seismic phases to their respective events is crucial for constructing reliable seismicity catalogs. This study presents a comprehensive benchmark analysis of five seismic phase associators, including machine learning based solutions, employing synthetic datasets tailored to replicate the seismicity characteristics of real seismic data in a crustal and a subduction zone scenario.

The synthetic datasets were generated using the NonLinLoc raytracer, using real station distributions and velocity models and simulating a large range of seismic events across different depths. In order to generate sets of picks with quality and diversity similar to a real-world dataset, some modifications such as adjustments to arrival times simulating picking errors, selective station exclusion, incorporation of false picks, were included. Such a controlled environment allowed for the assessment of associator performance under a range of different conditions.

As part of project MILESTONE, we compared the performance of five state-of-the-art seismic phase associators (PhaseLink, GaMMA, REAL, GENIE, and PyOcto) across multiple scenarios, including low-noise environments, high-noise background activity, out-of-network events, and complex aftershock sequences. Each associator's accuracy in identifying and associating true events amidst noise picks and its ability to handle overlapping sets of arrival times from different events were rigorously evaluated.

Additionally, we conducted a systematic comparison of the advantages and disadvantages of each associator, attempting a fair and unbiased evaluation. This included assessing their processing times, a critical factor in operational seismology. Our findings reveal significant differences in the precision and robustness of these associators.

This benchmark study not only underscores the importance of robust phase association in seismological research but also paves the way for future enhancements in seismic data processing techniques. The insights gained from this analysis are expected to significantly contribute to the ongoing efforts in seismic monitoring and hazard assessment, particularly in the realm of machine learning applications.

How to cite: Puente Huerta, J. A., Münchmeyer, J., McBrearty, I., and Sippl, C.: Benchmarking seismic phase associators: Insights from synthetic scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8913, https://doi.org/10.5194/egusphere-egu24-8913, 2024.

EGU24-8924 | Orals | SM2.3

Revealing and interpreting patterns from continuous seismic data with unsupervised learning 

Léonard Seydoux, René Steinmann, Sarah Mouaoued, Reza Esfahani, and Michel Campillo

Exploring large datasets of continuous seismic data is a challenging task. When targeting signals of interest with a good a priori knowledge on the signal's properties, it is possible to design a dedicated processing pipeline (earthquake detection, noise reduction, etc.). Many other sources can sign up in the data, with characteristics that differ from the targetted ones (changes in noise frequency, modulating signals, etc.). In this case, it is difficult to design a processing pipeline that will be robust to all the possible sources. In this work, we propose to use unsupervised learning to explore the data and reveal patterns in an interpretable way. We extract relevant features of continuous seismic data with a deep scattering network —a deep convolutional neural network with interpretable feature maps— and experiment various classical machine learning tools (clustering, dimensionality reduction, etc.) to reveal and interpret patterns in the data. We apply this method to various cases including to a decade of continuous data in the region of Guerrero, Mexico, and interpret the results in terms of seismicity and external datasets.

How to cite: Seydoux, L., Steinmann, R., Mouaoued, S., Esfahani, R., and Campillo, M.: Revealing and interpreting patterns from continuous seismic data with unsupervised learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8924, https://doi.org/10.5194/egusphere-egu24-8924, 2024.

EGU24-9120 | ECS | Posters on site | SM2.3

An up-to-date seismic catalogue of the 2020 Mw6.4 Petrinja (Croatia) earthquake sequence using machine learning 

Dinko Sindija, Marija Mustac Brcic, Gyorgy Hetenyi, and Josip Stipcevic

Identifying earthquakes and selecting their arrival phases are essential tasks in earthquake analysis. As more seismic instruments become available, they produce vast amounts of seismic data. This necessitates the implementation of automated algorithms for efficiently processing earthquake sequences and for recognising numerous events that might go unnoticed with manual methods.

In this study, we employed the EQTransformer, trained on the INSTANCE dataset, and utilised PyOcto for phase association, focusing specifically on the Petrinja earthquake series. This series is particularly interesting for its initial phase, which was marked by a limited number of seismometers in the epicentral area during the onset of the sequence in late December 2020. This limitation was subsequently addressed by the swift deployment of five additional stations near the fault zone in early January 2021, followed by a gradual expansion of the seismic network to over 50 instruments.

Our analysis covers the Petrinja earthquake series from its onset on December 28, 2020, up to present, offering a complete and up-to-date view of the seismic activity as the seismic activity is still higher than in the interseismic period. We compare our findings from the machine learning-generated catalogue with a detailed manual catalogue. Focusing on the first week of the series, when the seismic network was sparse and there was a high frequency of overlapping earthquakes, we achieved a recall of 80% and a precision of 81% for events with local magnitude greater than 1.0. In contrast, for the subsequent six months of processed data, a period still characterised by a high frequency of earthquakes but with the fully expanded network, our recall improved dramatically to 95% with over 20,000 detected events. This comparison allows us to demonstrate the challenges, evolution, and effectiveness of automatic seismic monitoring throughout the earthquake sequence.

How to cite: Sindija, D., Mustac Brcic, M., Hetenyi, G., and Stipcevic, J.: An up-to-date seismic catalogue of the 2020 Mw6.4 Petrinja (Croatia) earthquake sequence using machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9120, https://doi.org/10.5194/egusphere-egu24-9120, 2024.

The use of P-wave receiver function and surface wave dispersion data is crucial in exploring the structure of the Earth's crust and upper mantle. Typically, to address the ambiguity resulting from using a single type of dataset for inversion, these two types of seismic data, which have different sensitivities to shear wave velocity structure, are jointly inverted to achieve a detailed velocity structure. However, methods that rely on a linearized iterative joint inversion approach depend on the initial model selection, while non-linear joint inversion frameworks based on model parameter space search are computationally intensive. To address these challenges, this study suggests employing a deep learning strategy for the joint inversion of P-wave receiver function and surface wave dispersion data. Two distinct neural networks are developed to extract features from the P-wave receiver function and surface wave dispersion data, and different loss functions are tested to train the proposed neural network. The proposed method has been applied to actual seismic data from South China, and the results are comparable to those obtained by jointly inverting body wave first travel-time, P-wave receiver function, and surface wave dispersion data.

How to cite: Hu, J.: Joint inversion of P-wave receiver function and surface wave dispersion data based on deep learning. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9621, https://doi.org/10.5194/egusphere-egu24-9621, 2024.

Objectives and Scope:

Deep learning's efficacy in seismic interpretation, including denoising, horizon or fault detection, and lithology prediction, hinges on the quality of the training dataset. Acquiring high-quality seismic data is challenging due to confidentiality, and alternative approaches like using synthetic or augmented data often fail to adequately capture realistic wavefield variations, ambient noise, and complex multipathing effects such as multiples. We introduce an innovative seismic data augmentation method that incorporates realistic geostatistical features and synthetic multiples, enhancing the training and transferability of deep neural networks in multi seismic applications.

Methods and Procedures:

Our method comprises two primary steps: (1) Creating augmented impedance models from existing seismic images and well logs, and (2) Simulating seismic data from these models. The first step merges Image-Guided Interpolation (IGI, Hale et al., 2010) and Sequential Gaussian Simulation (SGS) to generate models that retain original structural features of the input seismic image and introduce random small-scale features aligned with the geostatistical properties of the input seismic data. The second step employs reflectivity forward modeling method (Kennett, 1984) to simulate both primary and multiple seismic data trace-by-trace. This approach, summing up infinite order internal multiples, effectively reproduces the full properties of reflection wavefields, which is a good approximation in areas without rapidly changing structures.

Results and Observations:

Our numerical tests validate the method's effectiveness. The IGI technique interpolates well log data into gridded velocity models, maintaining seismic horizons and smoothing fault features. The SGS method then generates stochastic velocity model implementations preserving the geostatistical distribution of the input seismic data. The resulting reflectivity forward modeling successfully distinguishes between multiples and primaries, facilitating the creation of nuanced training datasets and labels.

Further tests involve training two Transformer-based seismic fault detection neural networks: one with conventional data lacking multiples and another with our augmented data incorporating multiples. While both networks exhibit similar validation performance, their generalization capabilities differ markedly. The network trained with conventional data shows reduced accuracy and fault detection reliability on synthetic field data. In contrast, the network trained with our augmented data demonstrates better precision, accuracy, and recall on the same dataset.

Significance and Novelty:

Our approach generates augmented seismic data that retains the original seismic cubes' and well logs' geostatistical features and multiples, crucial for training deep learning models with high transferability for various seismological tasks. This method's novelty lies in its consideration of geostatistical characteristics, wavelet fluctuations, and multiples. The resulting data is more complex, varied, and realistic compared to conventional augmentation methods. Neural networks trained on this data exhibit enhanced transferability over those trained with traditional synthetic data incorporating only random noise. This advancement represents a significant leap in seismic data processing and interpretation, particularly for deep learning applications in geophysics.

How to cite: Zhou, T.: Seismic data augmentation with realistic geostatistical features and synthetic multiples for multi deep learning tasks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10219, https://doi.org/10.5194/egusphere-egu24-10219, 2024.

EGU24-12197 | Orals | SM2.3

Failures, successes and challenges of machine-learning-based engineering ground-motion models 

Fabrice Cotton, Reza Esfahani, and Henning Lilienkamp

The exponential growth of seismological data and machine learning methods offer new perspectives for analysing the factors controlling seismic ground motions and predicting earthquake shaking for earthquake engineering. However, the first models (e.g. Derras et al., 2012) using "simple" neural networks to predict seismic motions did not convince the earthquake engineering community, which continued to use more conventional models. We analyse the weaknesses (from the perspective of engineering seismology) of this first generation of ML-based ground motion models and explain why this first generation did not provide sufficient added value compared to conventional models.  Based on this experience, we propose two evolutions and new methods that have advantages over conventional methods and therefore have greater potential.  A first class of models (e.g. Lilienkamp et al., 2022), based on a U-net neural network, predicts spatial variations in seismic motions (e.g. site effects in three-dimensional basins) by considering seismic motions in map form. A second class of approaches) combines AI methods (conditional generative adversarial networks,  Esfahani et al., 2023) and hybrid databases (observations and simulations selected for their complementarity) to train simulation models capable of generating not only a few parameters (e.g. PGA) describing ground motions, but the full acceleration time histories. We will discuss the potential advantages of this new generation of ML-based methods compared to conventional methods, but also the challenges (and proposed solutions) to best combine simulations and observations, and to calibrate both the best estimate and the variability of future ground motions.

How to cite: Cotton, F., Esfahani, R., and Lilienkamp, H.: Failures, successes and challenges of machine-learning-based engineering ground-motion models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12197, https://doi.org/10.5194/egusphere-egu24-12197, 2024.

EGU24-12357 | ECS | Orals | SM2.3

Deep learning prediction of measured earthquake waveforms from synthetic data 

Alexander Bauer, Jan Walda, and Conny Hammer

Seismic waveforms of teleseismic earthquakes are highly complex since they are a superposition of numerous phases that correspond to different wave types and propagation paths. In addition, measured waveforms contain noise contributions from the surroundings of the measuring station. The regional distribution of seismological stations is often relatively sparse, in particular in regions with low seismic hazard such as Northern Germany. However, a detailed knowledge of the seismic wavefield generated by large earthquakes can be crucial for highly precise measurements or experiments that are carried out for instance in the field of particle physics, where seismic wavefields are considered noise. While synthetic waveforms for cataloged earthquakes can be computed for any point on the Earth’s surface, they are based on a highly simplified Earth model. As a first step towards the prediction of a dense seismic wavefield in a region with sparsely distributed stations, we propose to train a convolutional neural network (CNN) to predict measured waveforms of large earthquakes from their synthetic counterparts. For that purpose, we compute synthetic waveforms for numerous large earthquakes of the past years with the IRIS synthetics engine (Syngine) and use the corresponding actual measurements from stations in Northern Germany as labels. Subsequently, we test the performance of the trained neural network for events not part of the training data. The promising results suggest that the neural network is able to largely translate the synthetic waveforms to the more complex measured ones, indicating a means to overcome the lack of complexity of the Earth model underlying the synthetic waveform computation and paving the way for a large-scale prediction of the seismic wavefield generated by earthquakes.

 
 

 

 

How to cite: Bauer, A., Walda, J., and Hammer, C.: Deep learning prediction of measured earthquake waveforms from synthetic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12357, https://doi.org/10.5194/egusphere-egu24-12357, 2024.

EGU24-14134 | ECS | Posters on site | SM2.3

Recipe For Regular Machine Learning-based Earthquake Cataloging: A Systematic Examination in New Zealand, from Local to Regional Scale 

Wu-Yu Liao, En-Jui Lee, Elena Manea, Florent Aden, Bill Fry, Anna Kaiser, and Ruey-Juin Rau

Machine learning-based algorithms are emerging in mining earthquake occurrences from continuous recordings, replacing some routine processes by human experts, e.g., phase picking and phase association. In this study, we explore the combination of phase picker and phase associator with challenging application scenarios: the complex seismogenic structure, wide study area (15 degrees of both longitude and latitude and a depth of 600 km), hundreds of stations, and intensive seismicity during the 2016 Mw7.8 Kaikōura earthquake that correlates with at least seven faults. The deep learning-based phase pickers usually follow the prototype of PhaseNet, which maps the phase arrivals into truncated Gaussian functions with a customized model. Recent studies have shown poor generalizability of the advanced models on data out of the training distribution. In this study, we argue that appropriate data augmentation enables the RED-PAN model, trained on the Taiwanese data, to generalize well on New Zealand data even under intense seismicity. We applied RED-PAN on year-long continuous recordings over 439 stations of the GeoNet during 2016 and 2017. RED-PAN produces approximately three million P-S pairs over the New Zealand-wide network, enabling the exploration of the advanced phase associators' robustness on local and regional scales and under intense seismicity, e.g., back-projection, GaMMA, and PyOcto. Finally, we developed a six-stage automatic pipeline producing a high-quality earthquake catalog: phase picking, phase association, 3-D absolute location by NonLinLoc, magnitude estimation, weighted template matching, and 3-D relative location by GrowClust. 

How to cite: Liao, W.-Y., Lee, E.-J., Manea, E., Aden, F., Fry, B., Kaiser, A., and Rau, R.-J.: Recipe For Regular Machine Learning-based Earthquake Cataloging: A Systematic Examination in New Zealand, from Local to Regional Scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14134, https://doi.org/10.5194/egusphere-egu24-14134, 2024.

EGU24-14239 | ECS | Orals | SM2.3

Deep learning to predict time to failure of lab foreshocks and earthquakes from fault zone raw acoustic emissions 

Laura Laurenti, Christopher Johnson, Elisa Tinti, Fabio Galasso, Paul Johnson, and Chris Marone

Earthquake forecasting and prediction are going through achievements in short-term early warning systems, hazard assessment of natural and human-induced seismicity, and prediction of laboratory earthquakes.

In laboratory settings, frictional stick-slip events serve as an analog for the complete seismic cycle. These experiments have been pivotal in comprehending the initiation of failure and the dynamics of earthquake rupture. Additionally, lab earthquakes present optimal opportunities for the application of machine learning (ML) techniques, as they can be generated in long sequences and with variable seismic cycles under controlled conditions. Indeed, recent ML studies demonstrate the predictability of labquakes through acoustic emissions (AE). In particular, Time to Failure (TTF) (defined as the time remaining before the next main labquake and retrieved from recorded shear stress) has been predicted for the main lab-event considering simple AE features as the variance.

A step forward in the state of the art is the prediction of Time To Failure (TTF) by using raw AE waveforms. Here we use deep learning (DL) to predict not only the TTF of the mainshock with raw AE time series but also the TTF of all the labquakes, foreshocks or aftershocks, above a certain amplitude. This is a great finding for several reasons, mainly: 1) we can predict TTF by using traces that don’t contain EQ (but only noise); 2) we can improve our knowledge of seismic cycle predicting also TTF of foreshocks and aftershocks.

This work is promising and opens new opportunities for the study of natural earthquakes just by analyzing the continuous raw seismogram. In general laboratory data studies underscore the significance of subtle deformation signals and intricate patterns emanating from slipping and/or locked faults before major earthquakes. Insights gained from laboratory experiments, coupled with the exponential growth in seismic data recordings worldwide, are diving into a new era of earthquake comprehension.

How to cite: Laurenti, L., Johnson, C., Tinti, E., Galasso, F., Johnson, P., and Marone, C.: Deep learning to predict time to failure of lab foreshocks and earthquakes from fault zone raw acoustic emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14239, https://doi.org/10.5194/egusphere-egu24-14239, 2024.

EGU24-14438 | ECS | Posters on site | SM2.3

A deep learning-based earthquake simulator: from source and geology to surface wavefields 

Fanny Lehmann, Filippo Gatti, Michaël Bertin, and Didier Clouteau

Recent advances in scientific machine learning have led to major breakthroughs in predicting Partial Differential Equations’ solutions with deep learning. Neural operators, for instance, have been successfully applied to the elastic wave equation, which governs the propagation of seismic waves. They give rise to fast surrogate models of earthquake simulators that considerably reduce the computational costs of traditional numerical solvers.

We designed a Multiple-Input Fourier Neural Operator (MIFNO) and trained it on a database of 30,000 3D earthquake simulations. The inputs comprise a 3D heterogeneous geology and a point-wise source given by its position and its moment tensor coordinates. The outputs are velocity wavefields recorded at the surface of the propagation domain by a grid of virtual sensors. Once trained, the MIFNO predicts 6.4s of ground motion velocity on a domain of size 10km x 10km x 10km within a few milliseconds.

Our results show that the MIFNO can accurately predict surface wavefields for all earthquake sources and positions. Predictions are assessed in several frequency ranges to quantify the accuracy with respect to the well-known spectral bias (i.e. degradation of neural networks’ accuracy on small-scale features). Thanks to its efficiency, the MIFNO is also applied to a database of real geologies, allowing unprecedented uncertainty quantification analyses. This paves the way towards new seismic hazard assessment methods knowledgeable of geological and seismological uncertainties.

How to cite: Lehmann, F., Gatti, F., Bertin, M., and Clouteau, D.: A deep learning-based earthquake simulator: from source and geology to surface wavefields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14438, https://doi.org/10.5194/egusphere-egu24-14438, 2024.

EGU24-15571 | ECS | Orals | SM2.3

Self-Supervised Learning Strategies for Clustering Continuous Seismic Data 

Joachim Rimpot, Clément Hibert, Jean-Philippe Malet, Germain Forestier, and Jonathan Weber

Continuous seismological datasets offer insights for the understanding of the dynamics of many geological structures (such as landslides, ice glaciers, and volcanoes) in relation to various forcings (meteorological, climatic, tectonic, anthropic) factors. Recently, the emergence of dense seismic station networks has provided opportunities to document these phenomena, but also introduced challenges for seismologists due to the vast amount of data generated, requiring more sophisticated and automated data analysis  techniques. To tackle this challenge, supervised machine learning demonstrates promising performance; however, it necessitates the creation of training catalogs, a process that is both time-consuming and subject to biases, including pre-detection of events and subjectivity in labeling. To address these biases, manage large data volumes and discover hidden signals in the datasets, we introduce a Self-Supervised Learning (SSL) approach for the unsupervised clustering of continuous seismic data. The method uses siamese deep neural networks to learn from the initial data. The SSL model works by increasing the similarity between pairs of images corresponding to several representations (seismic traces, spectrograms) of the seismic data. The images are positioned in a 512-dimensional space where possible similar events are grouped together. We then identify groups of events using clustering algorithms, either centroid-based or density-based. 

The processing technique is applied to two dense arrays of continuous seismological datasets acquired at the Marie-sur-Tinée landslide and the Pas-de-Chauvet rock glacier, both located in the South French Alps. Both datasets include over a month of continuous data from more than 50 stations. The processing technique is then applied to the continuous data streams from either a single station or from the whole station network. The clustering products show a high number of distinct clusters that could potentially be considered as produced by different types of sources. This includes the anticipated main types of seismicity observed in these contexts: earthquakes, rockfalls, natural and anthropogenic noises as well as potentially yet unknown sources. Our SSL-based clustering approach streamlines the exploration of large datasets, allowing more time for detailed analysis of the mechanisms and processes active in these geological structures.

How to cite: Rimpot, J., Hibert, C., Malet, J.-P., Forestier, G., and Weber, J.: Self-Supervised Learning Strategies for Clustering Continuous Seismic Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15571, https://doi.org/10.5194/egusphere-egu24-15571, 2024.

EGU24-16930 | ECS | Orals | SM2.3

How to Limit the Epistemic Failure of Machine Learning Models? 

Alexandra Renouard, Peter Stafford, Saskia Goes, Alexander Whittaker, and Stephen Hicks

The intelligible understanding of natural phenomena such as earthquakes is one of the main epistemic aims of science. Its very aims are shaped by technological discoveries that can change the cognitive fabric of a research field. Artificial intelligence, of which machine learning (ML) is one of the fundamental pillars, is the cutting-edge technology that promises the greatest scientific breakthroughs. In particular, great hopes are placed in ML
models as a source of inspiration for the formulation of new concepts or ideas, thanks to their ability to represent data at different levels of abstraction inaccessible to humans alone.
However, the opacity of ML models is a major obstacle to their explanatory potential. Although efforts have recently been made to develop ML interpretability methods that condense the complexity of ML models into human-understandable descriptions of how they work and make decisions, their epistemic success remains highly controversial. Because they are based on approximations of ML models, these methods can generate misleading explanations that are overfitted to human intuition and give an illusory sense of scientific understanding.
In this study, we address the question of how to limit the epistemic failure of ML models. To answer it, we use the example of an ML model trained to provide insights into how to better forecast newly emerging earthquakes associated with the expansion of hydrocarbon production in the Delaware Basin, West Texas. Through this example, we show that by changing our conception of explanation models derived from interpretability methods,
i.e. idealised scientific models rather than simple rationalisations, we open up the possibility of revealing promising hypotheses that would otherwise have been ignored. Analysis of our interpreted ML model unveiled a meaningful linear relationship between stress perturbation distribution values derived from ML decision rules and earthquake probability, which could be further explored to forecast induced seismicity in the basin and beyond. This observation also helped to validate the ML model for a subsequent causal approach to the factors underlying earthquakes.

How to cite: Renouard, A., Stafford, P., Goes, S., Whittaker, A., and Hicks, S.: How to Limit the Epistemic Failure of Machine Learning Models?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16930, https://doi.org/10.5194/egusphere-egu24-16930, 2024.

EGU24-17061 | ECS | Posters on site | SM2.3

Further investigations in Deep Learning for earthquake physics: Analyzing the role of magnitude and location in model performance 

Gabriele Paoletti, Laura Laurenti, Elisa Tinti, Fabio Galasso, Cristiano Collettini, and Chris Marone

Fault zone properties can evolve significantly during the seismic cycle in response to stress changes, microcracking, and wall rock damage. Distinguishing subtle changes in seismic behavior prior to earthquakes, even in locations with dense seismic networks, is challenging. In our previous works, we applied Deep Learning (DL) techniques to assess alterations in elastic properties before and after large earthquakes. To do that, we used 10,000 seismic events that occurred in a volume around the October 30th 2016, Mw 6.5, Norcia earthquake (Italy), and trained a DL model to classify foreshocks, aftershocks, and time-to-failure (TTF), defined as the elapsed time from the mainshock. Our model exhibited outstanding accuracy, correctly identifying foreshocks and aftershocks with over 90% precision and achieving good results also in time-to-failure multi-class classification.

To build upon our initial findings and enhance our understanding, this follow-up investigation aims to thoroughly examine the model's performance across various parameters. First, we will investigate the influence of earthquake magnitude on our model, specifically assessing whether and to what extent the model's accuracy and reliability are maintained across varying minimum magnitude thresholds included in the catalog. This aspect is crucial to understand whether the model's predictive power remains consistent at different magnitudes of completeness. In terms of source location, our study will extend to evaluate the model's reliability by selectively excluding events from specific locations within the study area, and alternatively, by expanding the selection criteria. This approach allows us to discern the model's sensitivity to spatial variations and its ability to adapt to diverse seismic activity distributions. Furthermore, we’ll pay particular attention to the analysis of null-results. This involves meticulously analyzing cases where the model does not perform effectively, producing low-precision or inconclusive results. By carefully examining these scenarios, our goal is to further assess and confirm the high-performance results obtained from previous works.

Our results highlight the promising potential of DL techniques in capturing the details of earthquake preparatory processes, acknowledging that while complexities of machine learning models exist, ML models have the potential to open hidden avenues of future research.

How to cite: Paoletti, G., Laurenti, L., Tinti, E., Galasso, F., Collettini, C., and Marone, C.: Further investigations in Deep Learning for earthquake physics: Analyzing the role of magnitude and location in model performance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17061, https://doi.org/10.5194/egusphere-egu24-17061, 2024.

EGU24-18303 | Posters on site | SM2.3

Machine learning based rapid earthquake characterization using PEGS in Alaska 

Quentin Bletery, Kévin Juhel, Andrea Licciardi, and Martin Vallée

A signal, coined PEGS for Prompt Elasto-Gravity Signal, was recently identified on seismograms preceding the seismic waves generated by very large earthquakes, opening promising applications for earthquake and tsunami early warning. Nevertheless, this signal is about 1,000,000 times smaller than seismic waves, making its use in operational warning systems very challenging. A Deep Learning algorithm, called PEGSNet, was later designed to estimate, as fast as possible, the magnitude of an ongoing large earthquake from PEGS recorded in real time. PEGSNet was applied to Japan and Chile and proved capable of tracking the magnitude of the Mw 9.1 Tohoku-oki and Mw 8.8 Maule earthquakes within a few minutes from the events origin times. Here, we apply this algorithm to a very well instrumented region: Alaska. We find that, applied to such a dense seismic network, the performance of PEGSNet is drastically improved, with robust performances obtained for earthquakes with magnitudes down to 7.8. The gain in resolution also allows us to estimate the focal mechanism of the events in real time, providing all the information required for tsunami warning within less than 3 minutes.

How to cite: Bletery, Q., Juhel, K., Licciardi, A., and Vallée, M.: Machine learning based rapid earthquake characterization using PEGS in Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18303, https://doi.org/10.5194/egusphere-egu24-18303, 2024.

SM3 – Seismic Instrumentation and Infrastructure

EGU24-414 | ECS | Posters on site | SM3.1

Subsurface characterization using Distributed Acoustic Sensing (DAS) on an offshore fiber between Denmark and Norway 

Jonas Damsgård, Thomas Hansen, Peter Voss, Henrik Hansen, Simon Steffansen, Egon Nørmark, and Michael Fyhn

In April 2023 a seismic survey was carried out in southern Skagerrak using a towed-streamer and airgun setup. The aim of the survey was investigating the suitability of the Jammerbugt structure for CO2 storage. A fiber-optic cable is co-located with the Skagerrak 4 high-voltage interconnector cable between Denmark and Norway. The fiber was crossed multiple times by the surveying ship. Relative strain was measured along a 80 km section of the fiber using Distributed Acoustic Sensing (DAS) during the active seismic survey. 

Seismic arrivals from the airgun shots were clearly recorded by the fiber. The DAS data also contains a large number of other signals caused by passing ships and wave interactions. Shot-gathers were extracted from the DAS data using the timing and location of airgun shots. These were subsequently processed and compared with traditional shot-gathers recorded by the towed-streamer. The DAS data contains distinguishable direct, refracted and surface wave arrivals from the airgun shots. Reflection hyperbolas are also observed in the DAS data at larger receiver-offsets, but only when the source is close to the fiber.

The comparison indicates that DAS is able to at least partially record the same wavefield from an active source as that recorded by hydrophones. Consequently the DAS data can be used for imaging and subsurface characterization.

The utilized DAS interrogator unit is owned by the danish transmission system operator, Energinet, who provided the DAS data for this study. Data processing is carried out using MatLab and Promax.

How to cite: Damsgård, J., Hansen, T., Voss, P., Hansen, H., Steffansen, S., Nørmark, E., and Fyhn, M.: Subsurface characterization using Distributed Acoustic Sensing (DAS) on an offshore fiber between Denmark and Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-414, https://doi.org/10.5194/egusphere-egu24-414, 2024.

Ubiquitous acoustic gravity waves in the atmosphere lead to elastic deformations of the Earth’s surface via ambient barometric pressure variations at ground level. The induced ground deformations are composed of vertical and horizontal displacements as well as ground tilts or equivalently ground rotations around horizontal axes. To make inferences about background levels of rotational ground motions we exploit the fact that ground tilts are sensed by both suitably oriented gyroscopes, as well as horizontal component accelerometers through tilt coupled gravity.  Based on 20 years of data from the Global Seismic Network (GSN) we estimate coherence and admittance between ambient atmospheric pressure and horizontal acceleration from collocted sensors.

Since atmospheric acoustic gravity waves propagate too slowly to efficiently excite Rayleigh waves in the Earth, we attribute horizontal accelerations which are coherent with pressure to tilt coupled gravity. Based on this line of reasoning and by restricting the analysis to time windows with high coherence, we can estimate lower bounds of background tilt and background rotation rate for all GSN stations and for the GSN as a whole. We find that below 20mHz and in the least noisy time windows the  pressure induced background rotation rate is 30dB higher than similar estimates based on the assumption that the terrestrial noise floor for rotations around a horizontal axis is defined by Rayleigh wave motion.

A notable consequence of the above findings is that for frequencies below 20 mHz  atmospheric pressure induced ground tilts lead not only to the well established large difference between background noise levels for vertical and horizontal seismic accelerations, but also for rotations around vertical and horizontal axes.  We will present preliminary new rotational low noise models valid for frequencies below the band of the marine microseisms. The caveat for such models is that they are drived from inertial seismometers and not from gyroscopes. Data from the ROMY gyroscope are analyzed in a companion poster by Brotzer et al. in this same session SM3.3

How to cite: Widmer-Schnidrig, R. and Brotzer, A.: On the limit imposed by variable atmospheric pressure for the observation of small terrestrial rotations around horizontal axes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1797, https://doi.org/10.5194/egusphere-egu24-1797, 2024.

EGU24-2514 | Orals | SM3.1 | Highlight

Photonic Seismology: A New Decade of Distributed Acoustic Sensing in Geophysics from 2012 to 2022 

Feng Cheng, Ke Zhao, Longfeng Zhao, and Jonathan Ajo-Franklin

This work delivers an in-depth bibliometric analysis of Distributed Acoustic Sensing (DAS) research within the realm of geophysics, covering the period from 2012 to 2022 and drawing on data from the Web of Science. By employing bibliographic and structured network analysis methods, including the use of VOSviewer®, the study highlights the most influential scholars, leading institutions, and pivotal research contributions that have significantly shaped the field of DAS in geophysics. The research delves into key collaborative dynamics, unraveling them through co-authorship network analysis, and delves into thematic developments and trajectories via comprehensive co-citation and keyword co-occurrence network analyses. These analyses elucidate the most robust and prominent areas within DAS research. A critical insight gained from this study is the rise of 'Photonic Seismology' as an emerging interdisciplinary domain, exemplifying the fusion of photonic sensing techniques with seismic science. The paper also discuss certain limitations inherent in the study, and concludes with implications for future research.

How to cite: Cheng, F., Zhao, K., Zhao, L., and Ajo-Franklin, J.: Photonic Seismology: A New Decade of Distributed Acoustic Sensing in Geophysics from 2012 to 2022, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2514, https://doi.org/10.5194/egusphere-egu24-2514, 2024.

EGU24-2827 | Orals | SM3.1 | Highlight

Overview of distributed fibre-optic sensing in geophysical applications. 

Arthur Hartog

The technology of distributed fibre-optic sensors (DFOS) has developed over more than four decades, initially confined to temperature sensing, which remains a valuable tool. In the last 15 years, however, the addition of distributed vibration/acoustic sensing has vastly increased the use of DFOS in geophysical applications.

The combination of acoustic, temperature and static strain measurement has provided a deeper insight in the subterranean and subsea realms, ranging from hydrocarbon and geothermal energy production, earthquake monitoring to oceanography and glaciology. Spare or disused capacity on long-distance fibre-optic communications links has opened up many opportunities for sensing the environment, especially in oceanography. Techniques developed for oil and gas exploration and production have led to reliable methods for conveying optical fibres in the very hostile found in boreholes and this has extended the applications of DFOS to understanding tectonic movements and also to decarbonising the energy supply industry, e.g. in carbon sequestration and geothermal production.

The talk will provide a brief overview of the instrumentation used for DFOS and it will discuss some of the key applications in geophysics. It will also examine some of the untapped opportunities and how technological improvements might enable these to be realised.  

How to cite: Hartog, A.: Overview of distributed fibre-optic sensing in geophysical applications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2827, https://doi.org/10.5194/egusphere-egu24-2827, 2024.

The reliable estimation of earthquake magnitude and stress drop are key in seismology. The novel technology of distributed acoustic sensing (DAS) holds great promise for source parameter inversion owing to the measurements' high spatial density. Here, I demonstrate the robustness of DAS for magnitude and stress drop estimation using the empirical Green's function deconvolution method. This method is applied to nine co-located earthquakes recorded in Israel following the 2023 Turkey earthquakes. Spectral ratios were stacked along the fiber, and fitted with a relative Boatwright source spectral model. Excellent fits were obtained even for similar sized earthquakes. Stable seismic moments and stress drops were calculated assuming the moment of one earthquake is known. DAS derived estimates were found to be more stable and reliable than those obtained using a dense accelerometer network. The results demonstrate the great potential of DAS for source studies.

How to cite: Lior, I.: Accurate Magnitude and Stress Drop Using the Spectral Ratios Method Applied to Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3214, https://doi.org/10.5194/egusphere-egu24-3214, 2024.

EGU24-3331 | ECS | Posters on site | SM3.1

Earthquake Coda Magnitude with Distributed Acoustic Sensing at Ridgecrest, California 

Peng Ye and Xin Wang

Distributed Acoustic Sensing (DAS) has emerged as a transformative technology in recent years, effectively converting optical fibers into dense seismic arrays. Numerous studies have demonstrated the widespread applications of DAS in seismology, including earthquake detection and subsurface structure imaging. In terms of earthquake source studies using DAS, the conventional approach for determining earthquake magnitudes primarily relies on maximum amplitude measurements. However, this approach faces limitations, such as unknown cable couplings and instrument responses, single-component sensing, complex source radiation patterns, and uncommon amplitude saturation behaviors. To overcome these challenges, we propose a novel method that calculates earthquake magnitudes based on coda waves using DAS. Utilizing a 10 km-long DAS array deployed in Ridgecrest, California, we derive coda wave energy decay to estimate source amplitude terms. Our findings reveal a strong linear correlation between these estimates and seismic magnitudes estimated using broadband seismic network. Furthermore, our study provides insights into the attenuation structure beneath the DAS array, aligning well with shallow velocity structures. This study not only advances our understanding of seismic source characterization using DAS, but also paves the way for more accurate earthquake magnitude estimation using DAS.

How to cite: Ye, P. and Wang, X.: Earthquake Coda Magnitude with Distributed Acoustic Sensing at Ridgecrest, California, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3331, https://doi.org/10.5194/egusphere-egu24-3331, 2024.

EGU24-3466 | ECS | Orals | SM3.1

Differential arrival times for source location with DAS arrays: tests on data selection and automatic weighting procedure 

Emanuele Bozzi, Nicola Piana Agostinetti, Gilberto Saccorotti, Andreas Fichtner, Lars Gebraad, Tjeerd Kiers, and Takeshi Nishimura

Distributed Acoustic Sensing (DAS) technology is currently used to monitor seismic activity, offering a unique spatially-dense representation of the along-the-cable strain wavefield. Traditional seismic networks typically rely on the timing of specific seismic phases to estimate source locations. In this context, DAS arrays may fail to provide accurate traveltimes because of spatially-heterogeneous waveforms. The motivations are (but not limited to) the directional sensitivity, the heterogeneous cable ground-coupling and the enhanced sensitivity to lateral variations in the medium elastic properties. The resulting fluctuations in signal-to-noise ratios of the dense DAS channels pose significant challenges in the automatic picking of body phases, e.g., P-wave Absolute Arrival Times (P-ARTs). Consequently, the complex distribution of the estimated traveltimes impacts the accuracy of event locations, especially if incorrect assumptions on error statistics (e.g., Normal distribution) are considered. In this study, we address this issue by exploiting the intrinsic DAS measurements' spatial density and testing selected P-wave Differential Arrival Times (P-DATs) for source location. We estimate P-DATs for all the possible DAS channel pairs by identifying the time delay corresponding to the peak of each cross-correlation function. Subsequently, we select P-DATs based on two criteria: interchannel distance and cross-correlation index value. This procedure is often employed to reduce the risk of mixing delay times from coherent and incoherent waveforms. As a first test, using a probabilistic inversion (Hamiltonian Monte Carlo method), we demonstrate how the selected P-DATs provide a better constraint on the event's azimuthal direction compared to P-ARTs. Then, as a second experiment, we move from a subjective selection of P-DATs. To do so, we test a fully-automated and data-driven covariance matrix weighting procedure, in a probabilistic inversion scheme. Specifically, we compute posterior probability distributions for both the physical parameters (event location) and hyperparameters related to data features (interchannel distance and cross-correlation index thresholds). In this scheme, the hyperparameters define each weight along the diagonal of the covariance matrix. These tests offer useful insights into the utilization of P-DATs for event location with DAS. Moreover, we provide an automatic approach to avoid subjective biases based on pre‐conceptions in the a-priori data selection.

How to cite: Bozzi, E., Piana Agostinetti, N., Saccorotti, G., Fichtner, A., Gebraad, L., Kiers, T., and Nishimura, T.: Differential arrival times for source location with DAS arrays: tests on data selection and automatic weighting procedure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3466, https://doi.org/10.5194/egusphere-egu24-3466, 2024.

EGU24-4418 | Orals | SM3.1

Smart Grid Optical Fiber Network for Earthquake Early Warnings 

Hasan Awad, Fehmida Usmani, Emanuele Virgillito, Rudi Bratovich, Stefano Straullu, Roberto Proietti, Rosanna Pastorelli, and Vittorio Curri

Optical fiber networks, commonly known for data communications, could be extended beyond their conventional use. In our research, we propose a groundbreaking method by leveraging these existing terrestrial optical networks as wide distributed array sensors for earthquakes early detection. This approach is centered around the use of light polarization changes within the fiber cable, analyzed through a robust machine learning model that provide early warning alerts upon Primary earthquake waves arrival that induce strain, and precede earthquake’s destructive Surface waves. Unlike previous methods such as Distributed Acoustic Sensing and Frequency Interferometric Techniques, our approach avoids the use of expensive and specialized hardware. We introduce a centralized smart grid system that exploits the network’s existing terrestrial infrastructure, yet ensure cost effective and high efficient network modeling for initiating emergency plans and earthquake countermeasures. Our initial studies started by conducting experimental tests on a deployed fiber ring in Turin, Italy, using commercial Intensity Modulated – Direct Detection transceivers and polarimeters as polarization sensing devices, yield in promising results. Additionally, we identified the Primary waves arrival for a real 4.9 magnitude earthquake struck in the Marradi region, central Italy, with a 98% accuracy rate. This achievement was the result of a python-based waveplate model empowered by machine learning algorithm.  

Basically, when an earthquake occurs, networks nodes communicates with a centralized optical network controller that detects alterations in the light’s state of polarization by leveraging a pre-trained machine learning model. Upon the model confirmation, the controller activates early warning system in accordance with a predetermined emergency response mechanism. Building up on these findings, our current objective is to explore the impact of earthquake depth on seismic wave characteristics and their influence on light’s polarization to further investigate the potential of this advanced smart grid methodology. We aim to analyze real ground motion waves generated by two distinct earthquakes with same magnitudes but different depths. This knowledge is crucial in refining our machine learning model, which in turn will refine model prediction capabilities. Our approach promises more efficient optical network, by transforming the network into long range seismic sensors.

How to cite: Awad, H., Usmani, F., Virgillito, E., Bratovich, R., Straullu, S., Proietti, R., Pastorelli, R., and Curri, V.: Smart Grid Optical Fiber Network for Earthquake Early Warnings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4418, https://doi.org/10.5194/egusphere-egu24-4418, 2024.

EGU24-5900 | ECS | Orals | SM3.1

Noise analysis of Distributed Acoustic Sensing (DAS) systems in borehole installations 

Davide Pecci, Simone Cesca, Giacomo Rapagnani, Sonja Gaviano, Gian Maria Bocchini, Giorgio Carelli, Eusebio Stucchi, Renato Iannelli, and Francesco Grigoli

In recent years, there has been an increasing interest in Distributed Acoustic Sensing (DAS) technology for microseismic monitoring, especially in operations involving borehole installations. Despite the widespread adoption of DAS systems in such contexts, many questions regarding the data quality of the recordings are still open. Is the DAS self-noise higher than traditional systems? How does the ambient noise recorded by a DAS system attenuate with the depth as observed with traditional geophones? It is known that various noise types, including optical, thermal, and mechanical noise coupled with the fiber, affect DAS data. Additionally, the noise frequency band often overlaps with the signal frequency band, making frequency filtering alone inadequate for denoising. Therefore, specialized noise reduction workflows, such as FK Filtering and SVD, are necessary. Mitigating the impact of noise on DAS data remains a primary challenge for the seismological and geophysical community. This study aims to examine and characterize the noise influencing DAS data collected in borehole installations, with a specific focus on the data recorded at the Frontier Observatory for Research in Geothermal Energy site in Utah, USA. We use Power Spectral Density analysis to assess depth-dependent noise reduction and its temporal variations. Furthermore, the depth dependence of the signal-to-noise ratio for various microseismic events is evaluated. Finally, a comparison is drawn with geophones data colocated with the fiber, offering a comprehensive exploration of the advantages and disadvantages of the two data acquisition technologies.

How to cite: Pecci, D., Cesca, S., Rapagnani, G., Gaviano, S., Bocchini, G. M., Carelli, G., Stucchi, E., Iannelli, R., and Grigoli, F.: Noise analysis of Distributed Acoustic Sensing (DAS) systems in borehole installations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5900, https://doi.org/10.5194/egusphere-egu24-5900, 2024.

EGU24-6263 | ECS | Orals | SM3.1

Full-waveform modelling of coupling and site effects for DAS cables 

Nicolas Luca Celli, Christopher J. Bean, and Gareth S. O'Brien

The use of optical fibre cables to sense ground motion is one of the most researched topics in seismology at present day. By using the technique of Distributed Acoustic Sensing (DAS), a single fibre can be turned into thousands of seismic sensors, providing unprecedented spatial resolution. The instrument response of optical fibre cables, however, is largely unknown and difficult to separate from source, path, and directivity effects on seismic records, preventing us from using the information from the full seismic waveform.

Here we present a full-waveform simulation scheme developed to model the DAS instrument response using a particle-based Elastic Lattice Model (ELM-DAS). The scheme allows us to simulate a virtual cable embedded in the medium and made of a string of connected particles. By measuring the strain along these particles, we are able to replicate the axial strain natively measured by DAS as well as the effects of irregular cable geometries. The scheme allows us to easily simulate complex properties of the material around the cable (e.g., unconsolidated sediments, nonlinear materials) as well as different degrees of cable-ground coupling, both of which are believed to be the key factors controlling the DAS instrument response.

By simulating DAS cables in 2D, 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. By expanding the scheme to 3D, we can accurately include the effects of realistic, complex–and at times sub-wavelength—cable geometries and how they influence DAS records. Our observations 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., and O'Brien, G. S.: Full-waveform modelling of coupling and site effects for DAS cables, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6263, https://doi.org/10.5194/egusphere-egu24-6263, 2024.

EGU24-6576 | ECS | Posters on site | SM3.1

Deep Learning Driven DAS Strain Conversion to Geophone Ground Motion 

Basem Al-Qadasi and Umair Bin Waheed

Distributed Acoustic Sensing (DAS) has become a revolutionary observational technology for different geophysical applications. DAS, known for its high spatial resolution, environmental resilience, and ease of deployment, which make it a potential replacement to the traditional physical sensors that have been used for decades in seismology. The primary distinction between DAS and conventional seismic sensors lies in the fact that DAS inherently captures strain (or strain rate), in contrast to seismic instruments which record translational ground motions. However, the problem of strain directional sensitivity poses challenges for its direct use in standard seismic analysis. Therefore, several physics-based methods have been proposed to convert DAS strain to ground motion response (displacement, velocity, or acceleration). Efficient conversion of strain to ground motion using physics-based methods relies on accurate estimation of phase velocity along the DAS cable which is unavailable in most cases. To overcome this problem, we introduce a novel deep learning (DL) approach to convert high-resolution Distributed Acoustic Sensing (DAS) strain measurements into ground motion (GM).  The DL model employs a Bidirectional Long Short-Term Memory (BiLSTM) network. The model is trained and evaluated utilizing data from the PoroTomo project at Brady Hot Springs Geothermal Natural Laboratory. This dataset includes earthquake waveforms recorded by collocated DAS channels and geophones. The model’s performance is evaluated using the Root Mean Squared Error (RMSE) metric. It demonstrated an average RMSE of 0.41 for training and 0.95 for testing, indicating the model's efficacy in transforming DAS strain to particle velocity. The comparison results of predicted and original geophone waveforms further validated the model's accuracy within the relevant frequency range. This study marks a significant advancement in adapting high-resolution DAS strain data for use with conventional seismic data analysis techniques, thereby expanding the capabilities of seismic monitoring and interpretation.

How to cite: Al-Qadasi, B. and Bin Waheed, U.: Deep Learning Driven DAS Strain Conversion to Geophone Ground Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6576, https://doi.org/10.5194/egusphere-egu24-6576, 2024.

EGU24-6610 | ECS | Orals | SM3.1

Towards back-projection earthquake rupture imaging with ocean bottom distributed acoustic sensing data  

Yuqing Xie, Jean-Paul Ampuero, Martijn van den Ende, Alister Trabattoni, Marie Baillet, and Diane Rivet

Distributed Acoustic Sensing (DAS) along seafloor fiber optic cables offers high-density and wide-aperture seismic data close to seismic sources, at a lower cost than conventional cabled ocean bottom seismic networks. It is thus a very promising approach to develop offshore monitoring systems for hazard mitigation and to obtain deeper insights into earthquake mechanics. We introduce a workflow for back-projection earthquake rupture imaging based on ocean bottom DAS data off the Chilean coast, taking full advantage of DAS data features to greatly refine the resolution and accuracy of source parameter estimation of local earthquakes. 

The workflow includes a number of steps that improve the back-projection performance. To reduce the negative effects of wave scattering on waveform coherence, we apply spatial integration to convert DAS strains into displacements. We refine travel time accuracy through shallow-sediment time corrections. We apply array processing on multiple overlapping cable segments (sub-arrays) to get the apparent slowness. The information from all sub-arrays is used jointly to locate the earthquakes using a 1D local velocity model.

Through systematic synthetic tests, utilizing the 120-km-long cable configuration off the coast of Chile, we identified a ‘high-precision, high-resolution source region”, which is also less sensitive to uncertainties of the velocity structure. This region extends to about 80 km laterally from the cable and reaches depths of up to 15 km, a range likely attributable to optimal signal focusing from various angles and that can be extended by increasing the cable length. We apply our method to data of roughly 50 local earthquakes with magnitudes from 1.5 to 3. We consistently obtain sharp back-projection images with high spatial accuracy, within 1 to 4 km, for earthquakes occurring within this defined region. Such precision is comparable to the location uncertainties of the seismic catalog.

The true strength of our approach is its potential for imaging the rupture process of larger earthquakes. We apply our method to the synthetic waveforms of a magnitude 7 earthquake constructed from multiple empirical Green's functions. We demonstrate that strong coda waves do not compromise the precise detection and location of subsequent sub-sources, if we apply a travel time calibration. The rupture speeds and locations of sub-sources are accurately recovered, even for concurrent multiple sources. We are currently improving the calibration of travel times to increase the location accuracy and resolution. These include waveform alignment with static calibration, 3D velocity model travel time tables, and slowness bias measurements and calibrations for each source-subarray pair. Collectively, these methods will increase the resolution and accuracy of our method, along with more sophisticated back-propagation methods for individual arrays. Our work holds promise for the development of earthquake and tsunami early warning, provided that we can effectively address the issue of amplitude saturation of DAS data.

How to cite: Xie, Y., Ampuero, J.-P., van den Ende, M., Trabattoni, A., Baillet, M., and Rivet, D.: Towards back-projection earthquake rupture imaging with ocean bottom distributed acoustic sensing data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6610, https://doi.org/10.5194/egusphere-egu24-6610, 2024.

EGU24-7603 | ECS | Posters on site | SM3.1 | Highlight

Advances in Avalanche Monitoring in Norway: Insights from Distributed Acoustic Sensing 

Antoine Turquet, Andreas Wuestefeld, Finn Kåre Nyhammer, Espen Nilsen, and Vetle Refsum

Snow avalanches pose significant risks in mountainous regions. Traditional detection methods often lack the precision and timely responsiveness crucial for effective risk management. This study introduces an innovative approach using Distributed Acoustic Sensing (DAS) to detect snow avalanches in Norway. The monitoring site is located along a road in Holmbuktura in northern Norway, close to Tromsø. The cable path is composed of two segments: In segment one (0 – 850 m) an existing telecommunication cable is used, while for segment two (850 - 1450 m) a new cable was installed. The pilot road was frequently impacted by avalanches. Over three winters, the system captured both avalanche occurrences and anthropogenic noises (e.g., vehicles, wind, sea waves, etc.). 

The area is monitored with an OptoDAS interrogator with a sampling frequency of 500Hz and 10m gauge length. A 5m channel spacing results in 270 virtual channels along the monitored road stretch. Our automatic detection process distinguishes is based on classical signal processing techniques. We can confidently detect avalanches that hit road level, and additionally determine snow deposit on the road. Furthermore vehicles are detected with exact location and speed, which is used to alert emergency units in case of trapped vehicles. In this project, the focus of the installation is to detect avalanches that hit the road and determine whether any vehicles were trapped under the avalanches. For the winter season of 2022-2023 eight avalanches hit the road. The DAS-based monitoring system managed to successfully detect and classify these avalanches.

Compared to conventional methods like radar, infrared, and camera-based systems DAS offers distinct advantages in avalanche monitoring. DAS excels in providing real-time, continuous monitoring with high sensitivity and precision over extensive areas, unaffected by visual obstructions and less impacted by adverse weather conditions. Its robustness and low maintenance needs stand out, particularly when compared to radar systems' high installation costs and limited area coverage, camera's susceptibility to weather/light conditions.

The application of DAS technology offers a promising avenue for real-time, accurate avalanche detection, potentially enhancing safety measures in high-risk areas. Furthermore, this concept, when fully operational, could detect the risk of collision between avalanches and vehicles and alert authorities in real-time, which would be crucial for time-sensitive rescue operations.

How to cite: Turquet, A., Wuestefeld, A., Nyhammer, F. K., Nilsen, E., and Refsum, V.: Advances in Avalanche Monitoring in Norway: Insights from Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7603, https://doi.org/10.5194/egusphere-egu24-7603, 2024.

EGU24-7791 | ECS | Orals | SM3.1

Enhancing 1D and 2D passive seismic imaging of urban ambient noise DAS recordings 

Leila Ehsaninezhad, Christopher Wollin, Verónica Rodríguez Tribaldos, Benjamin Schwarz, and Charlotte Krawczyk

Ambient noise tomography Derived from Distributed Acoustic Sensing (DAS) deployed on existing telecommunication networks provides an opportunity to image the urban subsurface at local to regional scales and high resolution effectively with a small footprint. This capability can contribute to the assessment of the urban subsurface's potential for sustainable and safe utilization in countless applications, such as geothermal development of an area. However, extracting coherent seismic signals from the DAS ambient wavefield in urban environments remains a challenge. One obstacle is the presence of complex noise sources in urban environments, which may not be homogeneously distributed. Consequently, long-duration recordings are required to calculate high-quality virtual shot gathers, which entails significant time and computational cost.

 

In this study, we present the analysis of 15 days of passive DAS data recorded on a pre-existing fiber optic cable (dark fibers) running along an 11~km long major road in urban Berlin (Germany). We identify anthropogenic activities, mainly traffic noise from vehicles and trains, as the dominant seismic source and use it for ambient noise interferometry. To retrieve Virtual Shot Gathers (VSGs), we apply interferometric analysis based on the cross-correlation approach. Before stacking, we designed a selection scheme to carefully identify high-quality VSGs, which optimizes the resultant stacked VSG . Moreover, we modify the conventional ambient noise interferometry workflow by incorporating a coherence-based enhancement approach designed for wavefield data recorded with large-N arrays. We then conduct Multichannel Analysis of Surface Waves (MASW) to retrieve 1D shear-wave velocity models of the subsurface along consecutive portions of the array and validate them against local lithologic models. Finally, a 2D velocity model of the subsurface is obtained by concatenation of individual 1D velocity models from overlapping array subsections. The expansion into 2D requires an automatic identification of high-quality VSGs based on unsupervised learning, such as clustering, to exclude transient incoherent noise in the process of selective stacking.

 

The clustering results reveal distinct groups of VSGs that exhibit similar patterns. These distinct groups provide valuable insights into the temporal variations in human activities and allow a better understanding and interpretation of the recorded DAS ambient noise data. We find that recordings obtained predominantly during rush hour are viable for further processing and improve the accuracy of dispersion measurements, in particular for traffic-induced noise data. Moreover, the resulting 1D velocity models correspond well with available lithographic information. The modified workflow yields improved dispersion spectra, particularly in the low-frequency band (< 1 Hz) of the signal. This improvement leads to an increased investigation depth along with lower uncertainties in the inversion result. Additionally, these enhanced results were achieved using significantly less data than required using conventional processing schemes, thus opening the opportunity for reduced acquisition times and efforts.

How to cite: Ehsaninezhad, L., Wollin, C., Rodríguez Tribaldos, V., Schwarz, B., and Krawczyk, C.: Enhancing 1D and 2D passive seismic imaging of urban ambient noise DAS recordings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7791, https://doi.org/10.5194/egusphere-egu24-7791, 2024.

EGU24-8486 | ECS | Posters on site | SM3.1

Exploring Unsupervised Clustering of Seismic Noise Sources in Urban DAS Data: A Methodology Guide 

Antonia Kiel, Céline Hadziioannou, and Conny Hammer

Seismic measurements record the superposition of many seismic sources, with anthropogenic ones dominating frequencies above 1 Hz. While the anthropogenic seismic vibrations in urban areas are too small to influence daily human life, measurements in high precision physics experiments, such as those carried out at the Deutsche Elektronen-Synchrotron (DESY) particle accelerators in Hamburg can be negatively influenced by these vibrations. To gain insight into the seismic wavefield at DESY, distributed acoustic sensing measurements were started in the WAVE initiative (www.wave-hamburg.eu). 

The goal of this study is to utilize unsupervised machine learning tools to detect and identify different anthropogenic seismic noise sources. Two different approaches were tested: the seismic measurements are clustered using a temporal average of one second on time-frequency representations and a deep embedded clustering technique. For the first method, the clustering methods fuzzy-c-means, Gaussian mixture model (GMM), hierarchical clustering and hierarchical density-based spatial clustering of applications with noise (HDBSCAN) were used. The clustering performance of all methods was compared using car signals on a short DAS fiber section as our ground truth data. Furthermore, the usage of spectrograms and continuous wavelet transforms was compared on the ground truth data set, with the continuous wavelet transform giving better results.

In a next step, the best-performing clustering methods GMM and HDBSCAN of the temporal average and deep embedded clustering were applied to the entire 12 km fiber to cluster seismic noise sources. Based on the results, the respective advantages and disadvantages of the different approaches were determined. The study was concluded with a "recipe'' on how to approach unseen DAS data based on scientific objectives and physical properties of interest, paving the way for an optimized DAS data analysis. 

How to cite: Kiel, A., Hadziioannou, C., and Hammer, C.: Exploring Unsupervised Clustering of Seismic Noise Sources in Urban DAS Data: A Methodology Guide, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8486, https://doi.org/10.5194/egusphere-egu24-8486, 2024.

EGU24-9254 | Posters on site | SM3.1

Locating mine explosions in shallow waters from hydroacoustic waves using DAS 

Emil Fønss Jensen, Jonas F. Damsgård, Peter H. Voss, Thomas Funck, and Thomas Mejer Hansen

Of the roughly 50.000 mines that were deployed in Danish waters during the First and Second World Wars, the Royal Danish Navy estimates that 4.000 to 6.000 units remain unexploded. Naval mines are to this day regularly found by fishermen or during surveys related to offshore construction work and reported to the Royal Danish Navy who then undertakes their controlled detonation. Seismic and hydroacoustic signals from naval mine explosions have been recorded by distributed acoustic sensing (DAS) on subsea fiber optic cabling where the hydroacoustic waves are readily identified. We have developed a simple technique that uses inversion of the travel time of hydroacoustic signals to determine the location of explosions. The technique has also been tested on hydroacoustic waves from a marine air gun seismic survey that crosses a fiber cable in shallow water monitored by DAS. We present the inversion results in addition to the data processing and analysis.

How to cite: Jensen, E. F., Damsgård, J. F., Voss, P. H., Funck, T., and Hansen, T. M.: Locating mine explosions in shallow waters from hydroacoustic waves using DAS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9254, https://doi.org/10.5194/egusphere-egu24-9254, 2024.

EGU24-9611 | ECS | Orals | SM3.1

A new formulation for source parameters estimation from DAS native strain data. 

Claudio Strumia, Alister Trabattoni, Mariano Supino, Marie Baillet, Diane Rivet, and Gaetano Festa

Distributed Acoustic Sensing (DAS) is establishing as a promising technique in Seismology. This novel system turns a fibre optic cable into a continuous single component array with very dense spatial sampling. Simplicity of installation and availability of telecommunication cables (dark fibres) make the technique very advantageous for investigating harsh environments like seafloors, sensing up to hundreds of kilometres of fibre with fine spatial resolution. Given the high potential, the technology has been successfully tested in recent years for several earthquake monitoring tasks, such as location, subsurface characterization, focal mechanism determination, tomography, or source back projection. 
The transferability of standard seismological tools to DAS data is straightforward when working with time picking, while analysis of the amplitude content of the signal demands further research. This is the case of earthquake source characterization, where standard approaches require conversion of strain rate data into more classical kinematic quantities (i.e. acceleration or velocity). In this work we develop a new formulation that allows to estimate source parameters without the need for conversion. We start from the description of the far-field strain radiation emitted from a circular seismic rupture, showing that the time integral of the strain is related to the Source Time Function. Using this quantity, we develop the spectral modelling allowing for frequency domain inversion of DAS data for estimation of moment magnitude and corner frequency. The formulation accounts for the unique azimuthal sensitivity of the cable in the radiation pattern average, and explicitly shows DAS enhanced sensitivity to slow scattered waves propagating beneath the fibre.
We validated the proposed approach on two case-studies, for events in local magnitude range  0.4 - 4.3, comparing the results with estimates from standard seismic instruments. Earthquakes recorded on a 150km long cable offshore the coast of central Chile during a 1-month DAS survey exhibit scale invariant stress drops, with an average of Δσ=(0.8±0.6)MPa. Also, moment magnitude estimates agree with results from standard seismic instruments. The analysis of small magnitude events (ML<2.5) recorded on a 1km long fiber during a 5-month DAS survey in the Italian southern Appenines shows agreement of moment magnitude estimates when compared with local seismic network estimations. Nevertheless, site effects dominate the high frequency domain resulting in an apparent corner frequency around 5Hz and masking the actual event size. An appropriate modelling of site effects using a parametric EGF approach was thus adopted to estimate corner frequencies for the highest magnitude events in the catalogue. 
This study shows the possibility to work with raw DAS data to retrieve information about earthquake source and highlights the high potential of these systems in characterizing the seismic moment and the size of earthquakes in a wide magnitude range.

How to cite: Strumia, C., Trabattoni, A., Supino, M., Baillet, M., Rivet, D., and Festa, G.: A new formulation for source parameters estimation from DAS native strain data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9611, https://doi.org/10.5194/egusphere-egu24-9611, 2024.

EGU24-9645 | ECS | Posters on site | SM3.1

Tremor analysis on dense network using Distributed Fiber Optic Sensing at La Palma 

Olivier Fontaine, Corentin Caudron, Thomas Lecocq, Luca D'Auria, and José Barrancos

The fast rise of Distributed Fiber Optic Sensing (DFOS, also known as DAS) technology in seismology has enabled to reach new horizons in volcano monitoring for example by its ability to attain hardly accessible environment and its high spatial and temporal resolution. Such advantages are extremely valuable for observatories located on islands where the ocean complicates the installation of traditional seismic networks and would require deploying ocean bottom seismometers.

In this research, we bring DFOS to a well-studied eruption that occurred in 2021 at La Palma (Canary Islands) by using a dark fiber, an unused telecom optic fiber, joining the islands together. The cable was interrogated using an HDAS (from Aragon Photonics) operated by INVOLCAN producing a 50 km-long array reaching outward from the island in the sea.

By using a combination of traditional seismic preprocessing and array detection methods such as CovSeisNet1, we recover low frequency signals across the entire fiber. These steps enable us to detect and locate episodes of tremor linked to the volcanic activity which we compare with complementary observables.

https://covseisnet.gricad-pages.univ-grenoble-alpes.fr/covseisnet/

How to cite: Fontaine, O., Caudron, C., Lecocq, T., D'Auria, L., and Barrancos, J.: Tremor analysis on dense network using Distributed Fiber Optic Sensing at La Palma, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9645, https://doi.org/10.5194/egusphere-egu24-9645, 2024.

EGU24-10033 | ECS | Posters on site | SM3.1

Constraining 6C-observed seismic anisotropy from seasonal ambient seismic noise 

Le Tang, Heiner Igel, and Jean-Paul Montagner

Our recent theory shows that the 6C ground motion (three-component translation and three-component rotation) of ambient seismic noise is capable of measuring the local seismic anisotropy using azimuth-dependent 6C-based cross-correlation functions. However, seasonal variations in ambient seismic noise result in large uncertainties in local velocity measurements due to inaccurate corrections in the azimuth of wave propagation. Here, we show that the time-dependent small azimuth variation of ambient seismic noise can be visualized using horizontal rotation-based cross-correlation functions, which can be applied to constrain the local seismic anisotropy of Rayleigh waves. We apply this approach to a small seismic array (deployed to retrieve the rotational motions of seismic ambient noise) of Pinon Flat Observatory in Southern California. The estimated anisotropy is compatible with results calculated based on azimuth-dependent 6C cross-correlation functions from multiple pairs of stations, demonstrating the applicability of the proposed method.

How to cite: Tang, L., Igel, H., and Montagner, J.-P.: Constraining 6C-observed seismic anisotropy from seasonal ambient seismic noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10033, https://doi.org/10.5194/egusphere-egu24-10033, 2024.

EGU24-10120 | Orals | SM3.1

An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy 

Simone Donadello, Cecilia Clivati, Aladino Govoni, Lucia Margheriti, Maurizio Vassallo, Daniele Brenda, Marianna Hovsepyan, Elio Bertacco, Roberto Concas, Filippo Levi, Alberto Mura, Andrè Herrero, Francesco Carpentieri, and Davide Calonico

Optical fiber sensing represents a promising technology for seismological monitoring, leveraging the widespread deployment of optical networks, and representing an important opportunity for the development of early warning systems. While so far Distributed Acoustic Sensing (DAS) has been widely employed in geosciences, this technology shows some limitations, like a restricted working range, requirement of dedicated fibers and criticalities in the management of big datasets. We focus on an alternative technique, coherent interferometry relying on ultrastable lasers, which is characterized by high sensitivity, long range, and full compatibility with the existing telecommunication infrastructure. The method allows detecting perturbations induced by seismic events through the measurement of the phase accumulated by an optical signal along the fiber path. The best performances are obtained employing narrow-linewidth lasers inherited from metrological applications due to their high coherence. While the technique was initially demonstrated on subsea cables, its application to on-land fibers poses new challenges. Indeed, the phase measurement integrates all the perturbations occurring along the fiber: this means that anthropic activities, such as vehicle traffic, represent important noise sources that must be taken into account. 

We present the details of an in-field implementation over a commercial fiber deployed in a highly seismic region in central Italy and connecting two populated towns. The experimental setup employs self-heterodyne interferometry detection, utilizing a continuous wave laser stabilized to an optical cavity through the Pound-Drever-Hall technique. The laser operates within a single channel of the Dense Wavelength Division Multiplexing (DWDM) grid, sharing the fiber with standard internet services. We show the results of continuous observations performed over a period of two years. We demonstrate the detection of about one hundred earthquakes, distinguishing them from typical noise sources such as acoustic interference and infrastructure oscillations. The results include the detection of both local and distant earthquakes, demonstrating the robustness of the technique. This allowed us to characterize for the first time the sensitivity curve of the technique, described by the probability of the event detection as a function of its magnitude and epicenter distance. We also show the correlation between the source magnitude and signal spectral analysis.

In conclusion, we present an operational fiber-based earthquake observatory, highlighting the compatibility of coherent interferometry with the existing telecommunication infrastructures and its effectiveness in seismic monitoring. The results are promising for the development of scalable sensing networks utilizing the extensive optical fiber infrastructure already in place, which can conveniently integrate in real-time the data acquired with the existing networks of classical seismological sensors.

How to cite: Donadello, S., Clivati, C., Govoni, A., Margheriti, L., Vassallo, M., Brenda, D., Hovsepyan, M., Bertacco, E., Concas, R., Levi, F., Mura, A., Herrero, A., Carpentieri, F., and Calonico, D.: An Earthquake Observatory based on Coherent Interferometry over the Optical Fiber Network in Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10120, https://doi.org/10.5194/egusphere-egu24-10120, 2024.

EGU24-10604 | Posters on site | SM3.1

On DAS-recorded strain amplitude 

Thomas Forbriger, Nasim Karamzadeh, Jérôme Azzola, Rudolf Widmer-Schnidrig, Emmanuel Gaucher, and Andreas Rietbrock

The power of distributed acoustic sensing (DAS) lies in its ability to sample deformation signals along an optical fiber at hundreds of locations with one interrogator only. While the interrogator is calibrated to record ‘fiber strain’, the properties of the cable and its coupling to the rock control the ‘strain transfer rate’ and hence how much of ‘rock strain’ is represented in the recorded signal.

We use DAS recordings carried out with a Febus A1-R interrogator in an underground installation colocated with an array of strainmeters in order to measure the ‘strain transfer rate’ in situ. A tight-buffered cable and a standard loose-tube telecommunication cable (running in parallel) are used, where a section of both cables covered by sand and sandbags is compared to a section, where cables are just unreeled on the floor.

Signals from the Mw 7.7 and Mw 7.6 earthquakes that took place on the East Anatolian Fault on February 6th 2023 allow us a proper comparison of signals in the frequency-band between 50 mHz and 0.2 Hz. At lower frequencies the DAS signal-to-noise ratio is insufficient. At higher frequencies the invar-wire strainmeters show a parasitic response to vertical ground motion. For frequencies up to 1 Hz we use seismometer recordings to estimate strain for an incoming plane wave, based on the ray parameter and in this way extend the bandwidth of the comparison. The ray parameter varies along the recording but is sufficiently well known and can be validated against the strainmeter recording.

The ‘strain transfer rate’ is largely independent of frequency in the band from 0.05 Hz to 1 Hz and varies between 0.15 and 0.55 depending on cable and installation type. The sandbags show no obvious effect and the tight-buffered cable generally provides a larger ‘strain transfer rate’. The noise background for ‘rock strain’ in the investigated band is found at about an rms-amplitude of 0.1 nstrain in 1/6 decade for the tight-buffered cable. This allows a detection of the marine microseisms at times of high microseism amplitude.

How to cite: Forbriger, T., Karamzadeh, N., Azzola, J., Widmer-Schnidrig, R., Gaucher, E., and Rietbrock, A.: On DAS-recorded strain amplitude, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10604, https://doi.org/10.5194/egusphere-egu24-10604, 2024.

EGU24-10764 | Orals | SM3.1 | Highlight

SUBMERSE: Exploring the planet with live submarine telecommunications cables. 

Chris Atherton and the SUBMERSE Project

The integration of state-of-the-art fibre optic sensing technologies with telecommunication systems has not yet been achieved. There are many challenges which need to be overcome to allow for a pan-continental research instrument, all of which requires international collaboration. Such international collaborations would allow for the creation of novel applications and research into Earth science, such as cetology and abiotic and biotic marine interactions, oceanography, seismology, volcanology, and soundscape monitoring, to name but a few.

Over the past 5 years, research teams from National seismic and oceanographic infrastructures, together with National Research and Education Networks (NRENs), and partners from universities, research institutes and industry have pioneered sensing techniques to use submarine optical telecommunication fibres to monitor the Earth and its systems.

Fibre sensing technology and collaborations created by developing these techniques have now reached a level where a new paradigm shift can occur. This presentation will discuss the SUBMERSE project (SUBMarinE cables for ReSearch and Exploration), which is creating and delivering a pilot research instrument which could serve as a blueprint for continuous monitoring upon many more existing submarine fibre optic cables in the future.

The SUBMERSE project, which started in May 2023, is a Horizon Europe-funded, 36-month long initiative which is investigating the combined acquisition of SOP (State-of-Polarisation) and DAS (Distributed Acoustic Sensing) data from live telecom cables, with the aim to then make that data available to researchers globally and F.A.I.R. The project team, consisting of 24 organisations, uses existing fibre-optic infrastructure deployed across multiple national research infrastructures to create a pan-European research instrument.

Our presentation will discuss the latest field deployments of DAS and SOP technologies across 5 geographic locations on 3 cable systems, which are spread across the European continent and Atlantic Ocean. It will offer a first glimpse of the effects of running a DAS in the L-and C- Bands on a live DWDM telecoms system, in combination with SOP, in a submarine and terrestrial environment.

The aim of the SUBMERSE project is to disseminate the data following FAIR principles through established community data centres. The main challenges we have faced relate to ensuring compliance to security restrictions and handling huge data quantities generated by DAS.  The approaches to down sampling, frequency filtering, and potentially time-and-space-gating will also be presented.  We will discuss the approaches taken for acquiring, streaming from remote sites, data staging, pre-processing and raw file retention. We will also highlight the tools and approaches that we have adopted to develop best practices for running such a multi-national, distributed, sensing instrument which must take these elements into account.

Our work has shown that a pragmatic approach, with collaboration at heart, is needed to address these challenges. Without a strong commitment and collaboration between research communities and research infrastructure providers, the potential to lose valuable research data is high. This risk can be mitigated by focusing on datasets which are valuable to communities and ensuring the long-term availability of those data sets in a F.A.I.R manner.

How to cite: Atherton, C. and the SUBMERSE Project: SUBMERSE: Exploring the planet with live submarine telecommunications cables., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10764, https://doi.org/10.5194/egusphere-egu24-10764, 2024.

EGU24-10925 | Orals | SM3.1

Denoising DAS data in urban volcanic areas through a Deep Learning Approach 

Martina Allegra, Flavio Cannavo, Miriana Corsaro, Gilda Currenti, Philippe Jousset, Simone Palazzo, Michele Prestifilippo, and Concetto Spampinato

The notable benefits of Distributed Acoustic Sensing (DAS) technology—high coverage, high resolution, low cost—have led to its widespread application in the geophysical domain for high-quality data recording. Among possible applications, the ability to interrogate telecommunication cables has enabled the detection of a variety of seismic-volcanic events in poorly instrumented environments, such as densely populated urban areas.

Nevertheless, the sensing of commercial fiber optic cables has to deal with the presence of anthropogenic noise that frequently corrupts the seismic signal. Indeed, vibrations induced directly or indirectly by anthropogenic activities significantly reduce the signal-to-noise ratio by masking target events.

Taking advantage of the high spatiotemporal resolution of the DAS data, a deep learning approach has been adopted for noise removal. The architecture of the neural network together with the training strategy have enabled the extraction and preservation of salient information while neglecting anthropogenic noise.

The validation on real low-frequency seismic events recorded during the 2021 Vulcano Island unrest  has provided encouraging results, demonstrating the potential of the proposed approach as a pre-processing step to facilitate subsequent DAS signal analysis.

How to cite: Allegra, M., Cannavo, F., Corsaro, M., Currenti, G., Jousset, P., Palazzo, S., Prestifilippo, M., and Spampinato, C.: Denoising DAS data in urban volcanic areas through a Deep Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10925, https://doi.org/10.5194/egusphere-egu24-10925, 2024.

EGU24-11389 | ECS | Orals | SM3.1

Adjoint-Source Inversion of Microseismic Sources with DAS in Boreholes 

Katinka Tuinstra, Federica Lanza, Sebastian Noe, Andreas Fichtner, Antonio Pio Rinaldi, Pascal Edme, Martina Rosskopf, Anne Obermann, Marian Hertrich, Hansruedi Maurer, Domenico Giardini, and Stefan Wiemer and the Bedretto Team

Microseismic source processes can be closely monitored during hydraulic stimulations with optical fiber deployed behind borehole casing, using Distributed Acoustic Sensing (DAS). The Bedretto Underground Laboratory for the Geosciences and Geoenergies (BULGG) provides a test site at the scale of hundreds of meters (meso-scale), where multiple boreholes are instrumented with fibers around a stimulation well. This enables the characterization of source properties of induced seismicity thanks to the dense sampling of the wavefield close to the stimulated region.

In 2023 various stimulation activities in the BedrettoLab produced M<-1 events that were recorded on three fibers surrounding the stimulated region. The interrogated fibers are running through the stimulated seismicity zone, and surround the majority of the events. Some of these events are recorded with high coherency and signal-to-noise ratio, making them suitable for further source characterization, such as location and moment tensor inversion. These events were at the same time recorded with other co-located point sensors such as geophones and acoustic emission sensors, which enables comparison to other instruments.

In this work, we select and process a subset of events with clear DAS recordings, and invert for their location, source time and moment tensor components using an adjoint inversion method. This includes computing the full forward and adjoint wavefield and gradient using a spectral-element solver. Using the full waveforms to invert for these events greatly improves the resolution of the source estimates, allows for incorporation of the full velocity model, and only two simulations per iteration are required: a forward and adjoint simulation, and gradient computation. The receiver coverage of the focal spheres by the surrounding optical fibers is an excellent test bed for the method, and the simulated domain remains on the order of hundreds of meters, which means that the simulation can be pushed to high frequencies (>100 Hz). This study provides a step forward to monitoring microseismicity in hydraulic stimulations with fiber-optic measurements.

How to cite: Tuinstra, K., Lanza, F., Noe, S., Fichtner, A., Rinaldi, A. P., Edme, P., Rosskopf, M., Obermann, A., Hertrich, M., Maurer, H., Giardini, D., and Wiemer, S. and the Bedretto Team: Adjoint-Source Inversion of Microseismic Sources with DAS in Boreholes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11389, https://doi.org/10.5194/egusphere-egu24-11389, 2024.

EGU24-12344 | ECS | Posters on site | SM3.1

Groundwater monitoring in an alluvial aquifer with an underwater DAS cable recording urban seismic noise: Application to the Crépieux-Charmy Wellfield in France 

Destin Nziengui Bâ, Aurélien Mordret, Olivier Coutant, and Camille Jestin

Seismic interferometry applied to Distributed Acoustic Sensing (DAS) arrays is an increasingly common approach for subsurface investigations. In this study, we show that analysis of urban seismic noise acquired on a linear underwater DAS array can be used to track depth-dependent seismic velocity variations caused by groundwater level changes in an alluvial aquifer.

We apply our methodology to the Crépieux-Charmy wellfield, a strategic site for the water supply of the Lyon metropolitan area in France. We analyze 4 weeks of ambient noise recorded during a water infiltration experiment along a 200m DAS cable placed at the bottom of an infiltration basin.

Using ambient noise interferometry, we derived time-lapse phase velocity variations (dc(f)/c(f)) of Rayleigh waves and inverted them for depth-dependent shear wave velocity variations (dVs(z)/Vs(z)) in the first 50 m of the subsurface. The obtained seismic velocity changes appear to be associated with variations in water saturation and effective pore pressure for different compartments of the aquifer.

Our results suggest that DAS combined with noise-based passive monitoring provides a solution to track the dynamics of an alluvial aquifer and estimate hydrological parameters relevant for effective groundwater resource management.

How to cite: Nziengui Bâ, D., Mordret, A., Coutant, O., and Jestin, C.: Groundwater monitoring in an alluvial aquifer with an underwater DAS cable recording urban seismic noise: Application to the Crépieux-Charmy Wellfield in France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12344, https://doi.org/10.5194/egusphere-egu24-12344, 2024.

EGU24-12679 | Posters on site | SM3.1

On the influence of ambient atmospheric pressure on multi-component, direct observations of rotational ground motion 

Andreas Brotzer, Rudolf Widmer-Schnidrig, and Heiner Igel

A high-sensitive, large-scale ring laser gyroscope provides access to direct observations of local rotational ground motions. A tetrahedral configuration of ring laser gyroscopes, such as ROMY (ROtational Motions in seismologY), located in a Geophysical Observatory near Munich, Germany, enables to redundantly observe all three components of the rotation vector.
For seismic accelerations below 30 mHz, the separation of low noise background levels between vertical and horizontal component are well established and understood to result from local tilts driven by atmospheric pressure variations. The promise of multi-component rotational observations is that ideally they can be used to decontaminate a co-located horizontal component acceleration sensor from contributions of ground tilt. Moreover, knowing and understanding the background levels for vertical and horizontal rotational ground motions at long periods is essential as benchmarks for instrument development towards higher sensitivity.
We use several months of multi-component data of vertical and horizontal rotation rates by ROMY and a co-located atmospheric pressure sensor to derive the pressure compliance for both vertical and horizontal rotational motions. Focusing on frequencies below 20 mHz, we find that time windows with energetic weather patterns consistently lead to high coherence of atmospheric pressure and horizontal rotations, but only little coherence between the atmospheric pressure and vertical rotation.
We consider this as a first indication that atmospheric pressure induced ground tilts are detected by the ROMY horizontal components. Different effects of ambient atmospheric pressure changes on the optical gyroscope itself, such as cavity deformation, are discussed. A small aperture barometer array surrounding ROMY to detect lateral pressure gradients is currently being deployed to provide additional constraints on ground deformations from atmospheric pressure waves.

Here we focus on a detailed analysis of ROMY gyroscope data, while accelerometer data are analyzed in a companion poster by Widmer-Schnidrig et al. in this same session SM3.3.

How to cite: Brotzer, A., Widmer-Schnidrig, R., and Igel, H.: On the influence of ambient atmospheric pressure on multi-component, direct observations of rotational ground motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12679, https://doi.org/10.5194/egusphere-egu24-12679, 2024.

EGU24-13091 | Posters on site | SM3.1

 Long-term monitoring of seismic and volcanic activity using distributed fibre optic sensing: examples in Iceland (2015-2024) and Italy (2018-2024). 

Philippe Jousset, Gylfi Hersir, Gilda Currenti, Christopher Wollin, Sergio Díaz-Meza, Martina Allegra, Regina Maass, Michele Prestifilippo, Egill Gudnason, Rosalba Napoli, and Charlotte Krawczyk

Monitoring of seismic activity around volcanoes has been conventionally performed using data from continuous seismic and deformation networks, which give real-time information on the status of a volcano at any time. In case of a volcanic crisis, the number of earthquakes often increases with time and conventional networks are completed by deployment of additional sensors, which allow for a better hazard assessment, e.g., by lowering the detection threshold and improving earthquake locations. The deployment of such additional sensors is labour intensive and may be dangerous due to increased volcanic hazard.

Existing fibre optic telecommunication cables can be used with distributed dynamic strain sensing interrogators to density and complement the monitoring network. It has been demonstrated that the usage of fibre optic sensing allows for a rapid response and the acquisition of crucial data describing a developing crisis (e.g., at Vulcano, Italy). However, fibre optic interrogators are rarely deployed as permanent interrogating systems, despite the capability of such systems for long-term monitoring as demonstrated during a 7 months continuous recording on the Reykjanes Peninsula, Iceland, in 2020. Instead, interrogators are usually deployed for limited time periods when the activity occurs, ideally before new activity starts. For example, we connected an iDAS interrogator on the telecommunication 16-km long cable running between the Reykjanes and Svartsengi (“Blue Lagoon”) geothermal power plants in 2015 for an initial test of 10 days, in 2020 for 7 months (GFZ rapid response to the seismic crisis and precursory activity to the 2021 and 2022 eruptions of Fagradalsfjall volcano), and in November 2023 (recording still on 10.01.2024) as a GFZ rapid response before the 18 december 2023 eruption.

In this work, we investigate the possibility to use repetitive campaign-based measurements of dynamic strain sensing performed in the course of multiple years on the Reykjanes Peninsula (2015; 2020; 2023-2024) and at Etna volcano (2018; 2021; 2022; 2023-2024). Analysing earthquakes and ambient noise, we search for differences and similarities in the strain-rate response between the different and disjunct recording periods. We report preliminary results.

How to cite: Jousset, P., Hersir, G., Currenti, G., Wollin, C., Díaz-Meza, S., Allegra, M., Maass, R., Prestifilippo, M., Gudnason, E., Napoli, R., and Krawczyk, C.:  Long-term monitoring of seismic and volcanic activity using distributed fibre optic sensing: examples in Iceland (2015-2024) and Italy (2018-2024)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13091, https://doi.org/10.5194/egusphere-egu24-13091, 2024.

Distributed Acoustic Sensing (DAS) is a technology that enables continuous, realtime measurements along the entire length of a fiber optic cable. The low-frequency band of DAS can be used to analyze hydraulic fracture geometry and growth. In this study, the low-frequency strain waterfall plots with their corresponding pumping curves were analyzed to obtain information on fracture azimuth, propagation speed, number of fractures created in each stage, and re-stimulation of pre-existing fractures. We also use a simple geomechanical model, described in full detail in Ortega Perez and Van der Baan (Geophysics, 2024), to predict fracture growth rates while accounting for changes in treatment parameters. As expected, the hydraulic fractures principally propagate perpendicular to the treated well, that is, parallel to the direction of maximum horizontal stress. During many stages, multiple frac hits are visible indicating that multiple parallel fractures are created and/or re-opened. Secondary fractures deviate towards the heel of the well, likely due to the cumulative stress shadow caused by previous and current stages. The presence of heart-shaped tips reveals that some stress and/or material barrier is overcome by the hydraulic fracture. The lobes of the heart are best explained by the shear stresses at 45-degree angles from the fracture tip instead of the tensile stresses directly ahead of the tip. Antennas ahead of the fracture hits indicate the re-opening of pre-existing fractures. Tails in the waterfall plots provide information on the continued opening, closing, and interaction of the hydraulic fractures within the fracture domain and stage domain corridors. Analysis of the low-frequency DAS plots thus provides in-depth insights into the rock deformation and rock-fluid interaction processes occurring close to the observation well.

How to cite: van der Baan, M. and Ortega Perez, A.: Interpretation of low-frequency DAS data acquired during hydraulic fracturing treatments based on geomechanical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13428, https://doi.org/10.5194/egusphere-egu24-13428, 2024.

EGU24-13660 | Posters on site | SM3.1

Effect of ambient temperature fluctuation on DAS observation with a submarine cable 

Hiroyuki Matsumoto, Eiichiro Araki, and Takashi Yokobiki

Long-term Distributed Acoustic Sensing (DAS) using a submarine cable is being conducted in the Nankai Trough, Japan. The first long-term DAS observation shows that the apparent strain is observed along the relatively shallow water depth section (i.e., < water depth 1000 m) on the submarine cable, suggesting a periodic temperature fluctuation up to about 6 degrees Celsius associated with the ocean tide takes place in this region (Ide et al., 2021). However, it is difficult to discuss how the ambient temperature changes, or how the ambient temperature affects the submarine cabled DAS observation because of the lack of the in-situ observation. For this reason, we installed temperature sensors near the submarine cable by a Remotely Operation Vehicle (ROV). We did not discover the submarine cable at the seafloor, and therefore the detailed location of the temperature sensors, i.e., the accurate cable position could not be constraint so far. Simultaneous observations of the DAS and the long-term ambient temperature were conducted for a period from 16 August 2021 to 04 October 2021, i.e. about 50 days. A cross-correlation analysis between the DAS and the ambient temperature by dividing into the 5-day dataset has speculated the position of the temperature sensors to be 24.75 km of the submarine cable. Additionally, the strain coefficient of the optical fiber w.r.t. the temperature change has been determined to be 7 micro-strain per 1 degree Celsius, which is comparable to the previous experimental study (Zumberge et al., 2018). Finally, the temperature correction was performed, but the phase delay still remains, suggesting that the thermal measurement should be conducted beside the submarine cable.

How to cite: Matsumoto, H., Araki, E., and Yokobiki, T.: Effect of ambient temperature fluctuation on DAS observation with a submarine cable, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13660, https://doi.org/10.5194/egusphere-egu24-13660, 2024.

EGU24-14922 | Orals | SM3.1

Challenges of Rotational Ground Motion Measurements in the Local Distance Range 

Stefanie Donner, Johanna Lehr, Frank Krüger, Mathias Hoffmann, Manuel Hobiger, and Sebastian Heimann

Since almost two decades, there is a fast and steady progress in understanding the rotational part of the seismic wavefield and exploring possible applications. These achievements are based on studies using simulated data, array-derived measurements, and direct measurements of large (M > 5), teleseismic earthquakes by ringlasers. Since only a couple of years, direct measurements of smaller (M < 3) earthquakes in the local distance range are also feasible. This was made possible due to new instrumentation developments such as portable rotation sensors.

From experience with translational measurements, seismology has developed a relatively simple description of the seismic wavefield, as long as the observation is recorded in the source far-field, and site-effects at the point of observation can be neglected by choosing an appropriate frequency range for the analysis.

Within the NonDC-BoVo project two portable rotational sensors have been installed in the Vogtland/West-Bohemia earthquake swarm region with the goal to incorporate the rotational waveform data into the inversion for seismic moment tensors. Both sensors are located in an epicentral distance of ~10 km to the center of the swarm activity. So far, we have recorded 197 events with ML ≥ 1 and 6 events with ML ≥ 2.5.

Although we are positively surprised how well we can record rotational ground motion of earthquakes with even very small magnitudes, we encountered challenges in the details of the waveform recordings. At the sensor location in Landwüst (D) we recorded events down to ML ~ 0.5 with good signal-to-noise ratio in a frequency range of 5 to 25 Hz. At the second location in Skalna (CZ) the signal-to-noise ratio is worse and we recorded earthquakes only with ML ≥ 1.5. Relocating the sensor to Wernitzgrün (D), about 25 km to the North of Skalna, did not improve the quality of the waveform recordings. Technical issues with the sensor can be ruled out for both locations.

Here, we want to present details of the challenges with the rotational ground motion data from these small and local earthquake recordings. First analyses hint to a much stronger effect of local site conditions onto rotational than translational ground motion data. In addition, with the above-mentioned setting, we have to consider the complexities of the near-field part of the wavefield as well. With our contribution we aim to add another aspect to the understanding of the rotational wavefield.

How to cite: Donner, S., Lehr, J., Krüger, F., Hoffmann, M., Hobiger, M., and Heimann, S.: Challenges of Rotational Ground Motion Measurements in the Local Distance Range, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14922, https://doi.org/10.5194/egusphere-egu24-14922, 2024.

EGU24-15284 | ECS | Orals | SM3.1

Distributed Acoustic Sensing automated classifiers design via transfer learning for seismology 

Mathieu Donnadille, Antoine Turquet, Clément Hibert, and Cédric Richard

For a decade, Distributed Acoustic Sensing (DAS) has become an exciting new tool for research in geophysics. However, the vast amount of data produced by hundreds of virtual sensors presents a challenge, and the lack of labeled data hampers the training of new automated classifiers based on machine learning methods from scratch. Automatic classifiers are essential tools for labeling observations across large, complex, and continuous datasets. They are commonly used in seismology to classify all the geophysical events recorded by seismic stations with a high degree of accuracy. Transfer learning is a machine learning technique where a model trained on one task is repurposed on a second related task. This method is particularly beneficial as it allows for the reuse of pre-existing, labeled datasets, significantly reducing the need for new data collection and annotation. This approach is a promising way to create efficient DAS classifiers without requiring a lot of resources. We built three different classifiers: the first classifies events based on their location, distinguishing local earthquakes from distant events; the second differentiates anthropogenic events from natural ones, specifically quarry blasts from earthquakes; and the third is capable of identifying all three types of events - local earthquakes, distant events, and anthropogenic quarry blasts - simultaneously. We used random forest models to train our classifiers using a labeled dataset of 14345 seismometer signals from the NOA network made for seismological research and nuclear monitoring. We studied the transferability of those classifiers to DAS data from a new NORSAR facility called NORFOX. This infrastructure consists of 8 km of cables located in Norway with a sampling frequency of 100Hz. Its multidirectional cable configuration makes it ideal for seismological surveys. We built a small test dataset of 543 signals using 20 channels equally distributed along the array. Our approach succeeded in reaching F1 score thresholds above 76%. We also showed, by fine-tuning feature selection according to their correlations between the seismic and DAS domains, that these results can be improved. In this way, we were able to increase the scores of our models from 5.89% to 11.36%. Several transfer learning approaches were also explored and discussed. Those encouraging results highlight the potential of a transfer learning approach to build new DAS classifiers. By leveraging historical seismometer catalogs, this approach facilitates the creation of DAS classifiers, thereby saving substantial time and avoiding the need for creating specialized datasets exclusively for DAS. Several strategies for improving score thresholds for future classifiers based on these transfer learning methods can be derived.

How to cite: Donnadille, M., Turquet, A., Hibert, C., and Richard, C.: Distributed Acoustic Sensing automated classifiers design via transfer learning for seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15284, https://doi.org/10.5194/egusphere-egu24-15284, 2024.

EGU24-15616 | ECS | Orals | SM3.1

On the variation of ocean surface waves with wind speed and direction: A case study from offshore Svalbard, Norway 

Robin André Rørstadbotnen and Martin Landrø

Distributed Acoustic Sensing (DAS) has become increasingly popular due to its capacity of extremely high spatial and temporal strain sensing over long distances. Due to the long reach of the current fiber sensing technology, and that all the electronic components are placed on land, it holds great potential in marine applications. This presentation shows how DAS can be used to observe ocean surface waves inside Kongsfjord and in the open ocean West of Svalbard.

A well-known problem when monitoring ocean phenomena is the sensor undersampling in the world’s oceans. This problem limits observations of fundamental scientific questions, like the dynamics of the oceans (Sladen et al., 2019). Fiber optic sensing has already been used to observe numerous ocean phenomena, such as tides, OSGW (Ocean-Surface-Gravity-Wave), and internal waves (Lindsey et al., 2019, Ide et al, 2021, Williams et al., 2023).

A comprehensive DAS data set is being collected at the Centre for Geophysical Forecasting’s (CGF) research lab in Ny-Ålesund, Svalbard. Data has been collected continuously since June 2022 providing the possibility of investigating oceanographic signals over a long time period in different marine environments. In this presentation, we focus on how ocean surface wave signals are influenced by local wind conditions and how the signal changes characteristics as a function of wind speed and direction.

The results from analyzing this data will be presented, and it will be demonstrated how the local wind-induced waves interact with the background swell signal which hit West Svalbard from a South-West direction. The difference between the portion of the fiber located inside Kongsfjorden will be compared to the portions in open ocean. Additionally, the obtained results will be compared to previous studies from the area (e.g., Wojtysiak et al., 2018). Finally, we use the well-known dispersion relation for OSGW to compute the associated phase velocity along the whole stretch of the fiber cable.

How to cite: Rørstadbotnen, R. A. and Landrø, M.: On the variation of ocean surface waves with wind speed and direction: A case study from offshore Svalbard, Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15616, https://doi.org/10.5194/egusphere-egu24-15616, 2024.

EGU24-16151 | ECS | Orals | SM3.1

Near Surface Imaging with Zig-Zag shaped DAS Arrays Based on Cross Correlation of Ambient Noise 

Peng Wu, Chen Gu, Yichen Zhong, Zhi Yuan, Zhuoyu Chen, and Borui Kang

Distributed Acoustic Sensing (DAS) has effectively transformed traditional telecommunication fiber-optic cables into highly efficient, dense seismic arrays. In this paper, we perform cross-correlation and stacking on the signals recorded by DAS fiber arrays in a Zig-Zag pattern, which increases the spatial coverage and improves the ability to detect and analyze various seismic waves modes. We observed that the resulting signals include both Rayleigh and Love waves. Additionally, the propagation characteristics of the wave field exhibit a Zig-Zag distribution pattern, consistent with the spatial distribution of the fibers. The challenge arises from the need to distinguish and accurately interpret the overlapping signals of Rayleigh and Love waves, which have different propagation characteristics. To address these challenges, we propose an inversion method specifically tailored for the near surface imaging with DAS array data when the fiber-optic cables are not laid in straight lines. We also conducted an on-site experiment using Zig-Zag shaped DAS arrays with known subsurface velocity model. This experiment was designed to record ambient noise signals over a week and analyze the propagation characteristics of both Rayleigh and Love waves within the surface waves captured by the DAS system. The inversion results obtained from the analysis of the recorded data showed a high degree of consistency with the ground truth subsurface structure of the test area. This demonstrates the effectiveness of the proposed method in overcoming the limitations of traditional dispersion curve-based inversion techniques, particularly in the context of non-linear fiber layouts. This research provides strong support for the practical application of dark fibers in near surface imaging, demonstrating the potential of dark fibers.

How to cite: Wu, P., Gu, C., Zhong, Y., Yuan, Z., Chen, Z., and Kang, B.: Near Surface Imaging with Zig-Zag shaped DAS Arrays Based on Cross Correlation of Ambient Noise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16151, https://doi.org/10.5194/egusphere-egu24-16151, 2024.

EGU24-16375 | Orals | SM3.1

Sensing enabled submarine telecom networks for seismology 

Jan Petter Morten, Susann Wienecke, Ole Henrik Waagaard, Jan Kristoffer Brenne, and Erlend Rønnekleiv

Distributed acoustic sensing (DAS) on submarine fiber optic cables will contribute to resilient societies by significantly enhancing environment and hazard monitoring. Recent studies have emphasized applications to earthquake and tsunami early warning, volcanic eruptive events observation, and characterizing climate change effects. Widespread deployment of DAS instrumentation on the existing cable networks traversing the coastal zones and oceans can vastly expand data coverage with real-time capabilities at low cost. 


The use of DAS in existing long-haul telecommunication systems has so far been limited since most DAS interrogators rely on optical wavelengths that interfere with the existing telecom traffic. Recent developments in DAS technology enable co-existence of telecom traffic with the sensing application. Lab and field investigations have demonstrated that there is no detrimental effect from the interrogation on the transmission line performance when the DAS instrument is configured to operate at sufficiently separated wavelength channels. Thus, it is possible to utilize all existing cable networks for sensing applications in unison with continued telecom transmission without sacrificing any capacity in the link and maintaining high-quality DAS measurements.


This study describes a DAS deployment on a submarine cable system with live telecom traffic. The interrogation scheme facilitates consistent high sensing sensitivity exceeding 120 km range. The data quality and interrogator performance are quantified, and the localization and characterization for a representative set of environmental and anthropic signal sources is shown. We will describe real-time processing and detection implementations that transform such sensing enabled submarine telecom networks into measurement arrays suitable for seismic monitoring. Moreover, the technical solutions for DAS installation with existing terminal equipment and the practical aspects of data sharing will be described.

How to cite: Morten, J. P., Wienecke, S., Waagaard, O. H., Brenne, J. K., and Rønnekleiv, E.: Sensing enabled submarine telecom networks for seismology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16375, https://doi.org/10.5194/egusphere-egu24-16375, 2024.

EGU24-16414 | ECS | Orals | SM3.1

Distributed Fiber Optic Sensing and Artificial Intelligence: preliminary results on the Campi Flegrei caldera unrest 

Miriana Corsaro, Martina Allegra, Flavio Cannavò, Gilda Currenti, Gaetano Festa, Philippe Jousset, Daniele Pellegrino, Simone Palazzo, Michele Prestifilippo, Eugenio Privitera, Mario Pulvirenti, Patrizia Ricciolino, Concetto Spampinato, Francesco Scotto di Uccio, and Anna Tramelli

Since 2005 the Campi Flegrei caldera (Southern Italy) has been experiencing a long-term unrest characterized by a recent increase in seismicity and ground uplift rate. In August and September 2023, the unrest showed a sudden intensification in the number and maximum magnitude of earthquakes, culminated with the occurrence of a Md 4.2 event. In an effort to strengthen the monitoring activity, two Distributed Acoustic Sensing (DAS) devices were connected from October 2023 to telecommunication fiber optic cables in the densely populated Campi Flegrei area. The DAS interrogators are set up inside two TELECOM central offices in the city center of Naples and in Bagnoli. Dynamic strain rate data are continuously acquired with a gauge length of 10 m at an average spatial sampling of 4 and 5 m. In this framework, an automated real-time workflow has been implemented comprising both DAS data downsampling and transferring to INGV data processing center. 

From the beginning of the DAS acquisition (19 October 2023), more than 300 seismic events have been recorded by the INGV local seismic network, including a Md 3.0 earthquake occurred on 23rd November 2023. Unknown cable installation conditions, poor coupling of the fiber optic cable with the ground, intense traffic and anthropogenic activities make the DAS data highly noisy and, hence, pose challenges for the application of traditional seismic data processing algorithms. In this study, we propose and apply AI based algorithms to improve and fasten earthquake detection and seismic phase picking on the large data volume associated with the high number of DAS channels.  In particular, the compared algorithms cover recently published state-of-the-art deep learning networks. We show preliminary results that demonstrate the ability of the synergy between DAS and AI to contribute to the rapid response to volcanic crises.

How to cite: Corsaro, M., Allegra, M., Cannavò, F., Currenti, G., Festa, G., Jousset, P., Pellegrino, D., Palazzo, S., Prestifilippo, M., Privitera, E., Pulvirenti, M., Ricciolino, P., Spampinato, C., Scotto di Uccio, F., and Tramelli, A.: Distributed Fiber Optic Sensing and Artificial Intelligence: preliminary results on the Campi Flegrei caldera unrest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16414, https://doi.org/10.5194/egusphere-egu24-16414, 2024.

EGU24-17020 | ECS | Posters on site | SM3.1

Towards Fiber-optics-based, Next-generation Observational Platforms for Investigating the Urban Subsurface: the InDySE Project 

Verónica Rodríguez Tribaldos, Charlotte Krawczyk, Leila Ehsaninezhad, Patricia Martínez-Garzón, and Marco Bohnhoff

Urban sustainable development and improved resilience to geohazards requires an exhaustive understanding of the geological structure, physical properties and dynamics of the shallow subsurface underneath urbanized areas at the sub-kilometer scale. Yet, our current understanding of the urban subsurface is limited by our ability to image its structure and temporal variations at high resolution using classical geophysical approaches. Recently, the application of conventional ambient noise interferometry analysis to dynamic strain data recorded using Distributed Acoustic Sensing (DAS) deployed on unused telecommunication fiber-optic cables (dark fibers) has emerged as an attractive alternative for cost-efficient, regional scale (10’s of km) seismic imaging and monitoring at high spatial and temporal resolution. Still, its application to urban environments remains vastly underutilized. One of the most significant hurdles is the lack of adequate and efficient data exploration and processing tools to address and harness the unique challenges associated with DAS-based urban seismic noise recordings, which include the complexity of the noise field, unconventional array geometries and non-uniform coupling conditions, and increasingly massive data volumes.

The InDySE project (Interrogating the Dynamic Shallow Earth) aims at addressing these challenges to develop and validate the next-generation of subsurface imaging and monitoring platforms in urban areas based on the combination of existing fiber-optic networks and high-frequency infrastructure noise. The project comprises (1) developing high-performance computational tools, advanced processing workflows and machine learning approaches for efficient data exploration, selection and processing using existing datasets, (2) field experiments in target areas to retrieve high-resolution velocity models and monitor changes in seismic velocities, (3) integrating the resultant high-resolution seismic models with complementary datasets such as deformation maps derived from InSAR measurements. One of the selected study areas is the highly populated metropolitan area of Istanbul (Turkey), where understanding the structure, properties and dynamics of the shallow subsurface at high-resolution is critical for evaluating geohazard exposure. Among our objectives will be illuminating potential hidden faults underneath the city, obtaining high-resolution maps of geological materials and subsurface properties that can be translated into maps of local site response to large earthquakes, and tracking seismic velocity changes linked to hydrological dynamics that are known to be responsible for ground movements such as landsliding and subsidence. Ultimately, InDySE aims at developing efficient approaches for using dark fiber and ambient noise in urban subsurface investigations with implications in geohazard assessment.

How to cite: Rodríguez Tribaldos, V., Krawczyk, C., Ehsaninezhad, L., Martínez-Garzón, P., and Bohnhoff, M.: Towards Fiber-optics-based, Next-generation Observational Platforms for Investigating the Urban Subsurface: the InDySE Project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17020, https://doi.org/10.5194/egusphere-egu24-17020, 2024.

EGU24-17284 | ECS | Orals | SM3.1

A complete feature set for classification of seismic sources with Distributed Acoustic Sensing (DAS) in the context of long-range monitoring 

Camille Huynh, Clément Hibert, Camille Jestin, Jean-Philippe Malet, and Vincent Lanticq

Distributed Acoustic Sensing (DAS) exploits Rayleigh light backscattering to extract images of seismic wave propagation along a fiber optic in time and distance. The spatial distribution of virtual point sensors represents an opportunity to develop innovative methods for seismic event sources detection and identification. We develop in this study a method based on Machine Learning solutions for events classification.

This method relies on the development of features which translate the characteristics of the signals we observe into quantities that can be processed by machine learning algorithms to achieve the source classification. Three families of features investigating temporal and spatial characteristics and similarity of the signal are proposed, such as spatial and temporal analysis of the standard deviation, kurtosis or skewness of the signal or cross-correlation and dynamic time warping characterization and enables to quantify their individual contribution. Then we use a supervised machine learning model named XGBoost to perform classification based on these developed features. We tested this approach with a dataset recorded along a 91 km-long fiber optic deployed in the Pyrenees in France. The data acquisition has been achieved using a FEBUS A1-R DAS interrogator and with the support of TotalEnergies, from August 30 to September 20, 2022. During this period, 11 earthquakes and 6 quarry blasts have been recorded.

The trained model is validated using cross-validation techniques. Our Machine Learning processing chain successfully detect and classify 13 regional events from continuous background noise made by natural and anthropogenic activities. In particular, spatial features help to reduce the contribution of moving vehicles, whose presence is unavoidable along existing long-distance telecommunication fiber sections installed alongside roads.  In the continuity of this study, we investigate the potential of transfer learning from geophones deployed along the studied cable to DAS data or to another fiber optic cable installed in the same area.

How to cite: Huynh, C., Hibert, C., Jestin, C., Malet, J.-P., and Lanticq, V.: A complete feature set for classification of seismic sources with Distributed Acoustic Sensing (DAS) in the context of long-range monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17284, https://doi.org/10.5194/egusphere-egu24-17284, 2024.

EGU24-17595 | Orals | SM3.1

Analysis of DAS and slow strain measurements recorded during circulation tests at the FORGE geothermal underground laboratory 

Frantisek Stanek, Ismael Vera Rodriguez, Joseph Wolpert, David Podrasky, Anna Stork, Michal Chamarczuk, Matt Becker, and Jonathan Ajo-Franklin

FORGE (Frontier Observatory for Research in Geothermal Energy) is an underground field laboratory located in Utah, western United States, and sponsored by the US Department of Energy. The FORGE site is situated above a young, hot granitoid formation. The site has been used as a testbed for institutions interested in enhanced geothermal systems. As part of recent research work conducted at the site, a new deviated well was drilled adjacent to a previously stimulated well. Both wells were drilled into the granite volume. Circulation tests were performed over a period of approximately two days following completion of the second well. The circulation tests were monitored with two distributed optical sensing systems. One of the systems was recording in the new well and included measurements of distributed acoustics (DAS), temperature (DTS) and strain (DSS). The other system recorded from a preexisting well located about 500 m away and consisted of DAS measurements in a vertical cable.

Over the duration of the circulation tests, the two DAS systems detected on the order of 250 microseismic events in the close vicinity of the new well. A preliminary analysis of this group of events in terms of their hierarchical clustering allowed the selection of a small subset of them, which was used for the joint inversion of their absolute location and a layered velocity model for the site. The two-well DAS data of some of the events with absolute location was then used as a reference to estimate relative locations for the rest of the event’s catalogue. The estimated relative locations display a SW-NE alignment approximately perpendicular to the orientation of the new deviated well within the depth range of about 2300m to 2500m measured from the ground level. The location uncertainties more often show longer horizontal elongations suggesting a better depth constraint compared to the epicentral locations.

DTS data was analyzed in conjunction with slow strain data derived from the DAS data. Following the circulation tests, a ramp-like feature was observed beginning at approximate 1500m migrating upward throughout time in the slow strain data potentially indicating preferential fluid flow at this depth. Slow strain data is inextricably tied to temperature due to the thermal elongation of fiber, and as such, a thermal anomaly with similar characteristics is also observed at this depth. However, similar warming trends exist at various intervals throughout the well without the accompanied slow strain response indicating a truly anomalous interval that features unique DTS and slow strain response.

How to cite: Stanek, F., Vera Rodriguez, I., Wolpert, J., Podrasky, D., Stork, A., Chamarczuk, M., Becker, M., and Ajo-Franklin, J.: Analysis of DAS and slow strain measurements recorded during circulation tests at the FORGE geothermal underground laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17595, https://doi.org/10.5194/egusphere-egu24-17595, 2024.

EGU24-17644 | Orals | SM3.1

Understanding non-linear ground response with Distributed Dynamic Strain Sensing (DDSS) at Mt. Etna volcano, Sicily. 

Sergio Diaz-Meza, Philippe Jousset, Gilda Currenti, Lucile Costes, and Charlotte Krawczyk

Mt. Etna, the largest volcano in Europe, is known for its almost persistent activity and complex seismic wavefield, making it an attractive location for examining volcanic explosions and testing new instrumentation in seismology (e.g., rotational sensors, strain-meters, fiber optic sensing). In 2018, a study was conducted at the Pizzi Deneri (PDN) observatory, situated near Mt. Etna’s summit to understand new instrumentation responses to the local seismo-acoustic wavefield. During volcanic explosions the released energy is mainly partitioned into seismic waves traveling through the ground, and sound waves traveling through the atmosphere. To capture this phenomenon, a temporary multi-parameter network comprised of infrasound sensors, broad-band seismometers (BB) and a fiber optic cable buried within the local loosed granular medium (scoria layer). The fiber optic cable was connected to a Distributed Dynamic Strain Sensing (DDSS) interrogator.

At Etna, volcanic explosions were observed at co-located BB, infrasound and DDSS virtual sensors. A notable example(visible in both BB and DDSS data) is the successive occurrence of a 1-2 Hz seismic signal with a duration of ~4 seconds, followed by a ~2 Hz acoustic signal originating from the explosion, recorded at infrasound sensors. Unusually, simultaneous to the arrival of the acoustic signal observed at the infrasound sensors, DDSS and BB sensors record a signal with a frequency content of 15-20 Hz with a duration of ~2 seconds. We hypothesize that the 15-20 Hz signal is resulting from a non-linear ground response due to the air-to-ground coupling of the air pressure wave.

In order to better characterize this phenomenon, a second experiment was conducted in 2019 at PDN with a similar instrumentation as in 2018, but with a different spatial arragenment. During three months the infrasound sensors recorded each about 65000 volcanic explosions. In this work we analyze the respective ground responses of volcanic explosions observed in the DDSS records of the 2019 campaign. We observe similar phenomenon as in 2018 (non-linear ground response), nevertheless, not all explosion can trigger this response. We first characterize the explosion events from both infrasound and DDSS records, and then classify them using their waveform similarity. The preliminary results provide a broad characterization of the non-linear ground response phenomenon and an insight into the physical properties and processes that are necessary for a pressure wave to trigger a non-linear ground response. The outcomes of this work provide a better understanding of acoustic-to-ground energy coupling in volcanic environments and their potential to trigger other hazards.

How to cite: Diaz-Meza, S., Jousset, P., Currenti, G., Costes, L., and Krawczyk, C.: Understanding non-linear ground response with Distributed Dynamic Strain Sensing (DDSS) at Mt. Etna volcano, Sicily., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17644, https://doi.org/10.5194/egusphere-egu24-17644, 2024.

EGU24-17953 | Orals | SM3.1 | Highlight

Using Distributed Acoustic Sensing, Seismic and Infrasonic Observation to Track Pyroclastic Flows at Stromboli Volcano (Italy)  

Jean-Philippe Métaxian, Francesco Biagioli, Alister Trabattoni, Eléonore Stutzmann, Giorgio Lacanna, Gilda Risica, Pascal Bernard, Yann Capdeville, Anne Mangeney, Vadim Monteiller, Gianluca Diana, Lorenzo Innocenti, and Maurizio Ripepe

Pyroclastic flows are highly hazardous phenomena demanding precise detection, localization, and comprehensive characterization for effective volcanic risk management. During October and December 2022, the volcanic activity of Stromboli produced more than 60 pyroclastic flows. The flows propagated from the craters (~700 m a.s.l.) to the sea, resulting in tsunami waves ranging from centimetres to meters in height. These events coincided with an experiment involving distributed acoustic sensing (DAS) data acquisition with a dedicated 4-kilometer-long fibre-optic cable. A 3-component array consisting of 27 geophones and the multi-parameter monitoring network managed by the Laboratory of Experimental Geophysics (LGS) at the University of Florence were active simultaneously. We study two distinct pyroclastic flows of varying intensities. Using array processing techniques applied to DAS, seismic, and infrasonic measurements, we estimate back-azimuths that consistently track flows moving at velocities between 40 and 50 m/s from the craters to the shoreline. Validation of these measurements was accomplished through georeferenced images obtained by a visible camera, affirming their accuracy. These results demonstrate the effectiveness of the three datasets in monitoring pyroclastic flows and the need for multi-parametric observations for a better interpretation of volcanic phenomena.

How to cite: Métaxian, J.-P., Biagioli, F., Trabattoni, A., Stutzmann, E., Lacanna, G., Risica, G., Bernard, P., Capdeville, Y., Mangeney, A., Monteiller, V., Diana, G., Innocenti, L., and Ripepe, M.: Using Distributed Acoustic Sensing, Seismic and Infrasonic Observation to Track Pyroclastic Flows at Stromboli Volcano (Italy) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17953, https://doi.org/10.5194/egusphere-egu24-17953, 2024.

EGU24-18170 | Posters on site | SM3.1

Near-source T-wave observations in the North Atlantic using Distributed Acoustic Sensing 

David Schlaphorst, Afonso Loureiro, Luis Matias, Susana Custódio, Carlos Corela, and Rui Caldeira

T phases are acoustic waves that propagate in the low velocity zone of the oceanic sound channel that acts as a waveguide, the SOFAR channel. They are generated by earthquakes through the conversion of seismic energy at the solid-liquid interface, but the exact processes involved are still under debate.

Due to their low attenuation and slow propagation velocity, these arrivals are especially useful for the detection and characterisation of small earthquakes in marine basins, as they can improve the location of the event while their waveforms can yield information on source rupture.

In October 2023, a Distributed Acoustic Sensing (DAS) interrogator was installed on the GeoLab dark fibre in the Atlantic, starting at the Praia Formosa CLS, in Madeira Island, Portugal. The instrumentation of this cable is part of a project by ARDITI and the Oceanic Observatory of Madeira where oceanographic data recorded by buoys and autonomous vessels are combined with DAS data to obtain a global view of the underwater environment of Madeira Island in all its physical, chemical and biological aspects, including the characterisation of regional seismicity. This initiative is also linked to the SUBMERSE project, as the Madeira cable is a pilot site to establish continuous DAS monitoring along many more submarine fibre-optic cables.

On October 27th, a near-source (<40 km) M2.9 earthquake was recorded by the DAS interrogator along the entire cable. The epicentre of the earthquake was east of the Desertas Islands, southeast of Madeira. Besides the P and S phases, very clear T phases are also visible. The recorded T waves have strain values larger than those of P and S waves. However, multiple T phases are identifiable, suggesting different points of conversion or even possible reflections.

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 (DOI: 10.54499/UIDB/50019/2020), UIDP/50019/2020 (DOI: 10.54499/UIDP/50019/2020) and LA/P/0068/2020 (DOI: 10.54499/LA/P/0068/2020), and by ERC project SUBMERSE, HORIZON-INFRA-2022-TECH-01-101095055.

How to cite: Schlaphorst, D., Loureiro, A., Matias, L., Custódio, S., Corela, C., and Caldeira, R.: Near-source T-wave observations in the North Atlantic using Distributed Acoustic Sensing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18170, https://doi.org/10.5194/egusphere-egu24-18170, 2024.

EGU24-18371 | ECS | Posters on site | SM3.1

Earthquake Early Warning Systems based on Fiber Optic Distributed Acoustic Sensing in the Sea of Marmara 

Zeynep Coşkun, Havva Gizem Özgür, Berkay Koç, Meryem Ece Dal, Erkan Özkan, Tayfun Erkorkmaz, Niyazi Bedri Pamukçu, Ramazan Can Şahin, Süleyman Tunç, Doğan Kalafat, Ali Pınar, Kadri Buldanlı, and Haluk Özener

The Istanbul Natural Gas Distribution Company (İGDAŞ) has recently embarked on utilizing existing Fiber-Optic (F/O) cables to enhance disaster prevention and mitigation efforts in Istanbul. We are exploring the potential of a novel technology called F/O Distributed Acoustic Sensing (DAS) for earthquake early warning systems. The strategic placement of the F/O cable, which crosses the North Anatolian Fault in the Marmara Sea, presents a unique opportunity for monitoring seismic activity. While seismic stations exist around the Marmara Sea, the absence of online operating Ocean Bottom Seismometer (OBS) stations makes the F/O cable the only sensor positioned across the fault lines expected to rupture during a major earthquake.

The monitored F/O cable, originally intended for telecommunications, spans 60 kilometers in the Sea of Marmara. Over the past 7 months starting in June 2023, more than 160 earthquakes ranging from magnitudes 1.0 to 7.5 have been recorded through the F/O cable. Notably, the F/O DAS system successfully captured significant distant events, notably the February 6, 2023, M7.8 and M7.5 earthquakes in Kahramanmaraş. This initiative highlights the critical stages, obstacles, and best practices associated with deploying this technology. It underscores the importance of precise cable layout, optimal sensor density, range optimization, and the conduction of shaking table tests.

Shaking table experiments were conducted to compare noise levels across various sampling rates. By subjecting a Force-Balanced Accelerometer (FBA) and F/O cable to simulated seismic activity resembling the 1999 Sakarya Earthquake (M6.9) with sine signals at frequencies of 0.25 Hz, 0.5 Hz, 1.5 Hz, 2 Hz, and 3 Hz, observations revealed that reducing the sample rate to 200 sps significantly lowered the interrogator's instrumental noise compared to 2000 sps. Hence, a lower sample rate proved advantageous in achieving a better Signal-to-Noise Ratio (SNR).

Through the analysis of acoustic signal variations along the F/O cable, the DAS systems can accurately pinpoint and characterize earthquake events, facilitating timely warnings. F/O DAS technology boasts distinct advantages in earthquake detection due to its capacity to capture a broad spectrum of seismic signals, ranging from low-frequency tectonic shifts to high-frequency ground vibrations. The effectiveness of F/O DAS measurements relies on proper coupling, ensuring the efficient transfer of acoustic signals to the optical fiber, thereby ensuring precise detection and interpretation of seismic activity.

How to cite: Coşkun, Z., Özgür, H. G., Koç, B., Dal, M. E., Özkan, E., Erkorkmaz, T., Pamukçu, N. B., Şahin, R. C., Tunç, S., Kalafat, D., Pınar, A., Buldanlı, K., and Özener, H.: Earthquake Early Warning Systems based on Fiber Optic Distributed Acoustic Sensing in the Sea of Marmara, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18371, https://doi.org/10.5194/egusphere-egu24-18371, 2024.

EGU24-19403 | ECS | Posters on site | SM3.1

Distributed Acoustic Sensing measurements in a box: a case-study for laboratory landslide test 

Micol Fumagalli, Nicola Piana Agostinetti, and Giovanni Battista Crosta

Distributed Acoustic Sensing (DAS) is a novel technology for monitoring seismic waves that shake fiber optic cables (FOC) buried in the ground, at unprecedented spatial resolution as low as 20 cm. Such technology can be in principle applied to laboratory experiments aimed to reproduce landslide phenomena. Here we present a preliminary study of DAS measurements in a 2m x 1m sand-box, where piles of sand act as landslide analogues. Our preliminary results demonstrate the capability of DAS recordings in locating seismic events occurring in the sand-box, related to the growth of the sand piles. This study opens to the possibility of using DAS technology to monitor large-scale (1-10m) laboratory analogue experiments aimed to reproduce geophysical and tectonic processes.

How to cite: Fumagalli, M., Piana Agostinetti, N., and Crosta, G. B.: Distributed Acoustic Sensing measurements in a box: a case-study for laboratory landslide test, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19403, https://doi.org/10.5194/egusphere-egu24-19403, 2024.

EGU24-19804 | ECS | Orals | SM3.1

A Fiber-Optic Approach for Cement Placement Monitoring of Deep Boreholes 

Johannes Hart, Berker Polat, Felix Schölderle, Toni Ledig, Martin P. Lipus, Christopher Wollin, Thomas Reinsch, and Charlotte Krawzcyk

Reliable well completion technologies are mandatory for the safe and sustainable use of subsurface reservoirs. Achieving subsurface well integrity requires displacing the entire drilling mud with homogenous cement. For this purpose, surface pump parameters (rate, density, pressure, and volume) are generally measured, yielding average values along the borehole. Here, distributed fiber-optic sensing offers new continuous monitoring options with dense spatial sampling within a borehole.

In the GFK-monitor project (https://gfk-monitor.de/en/), we investigated the primary cementation of an 874 m surface casing at a geothermal well in Munich, Germany. A 699 m long fiber optic cable, implemented by the Geothermie Allianz Bayern (GAB), was attached to the outside of the casing in the annulus between the casing and formation and cemented. This allowed for monitoring distributed dynamic strain rate (DDSS or DAS) throughout cement placement with a sampling rate of 1000 Hz and a spatial resolution of 1 m.

We analyzed the average vibration energy in the borehole by DDSS data using a root mean square approach in rolling windows for different frequency bands. Linear features with two different characteristics appear prominently in the frequency band between 0.2-0.3 Hz. One feature, which we named the “slow feature”, shows a varying slope resulting in velocities ranging from 2.5 to 6 m/s. In contrast, the accordingly called “fast feature” indicates a relatively constant velocity of around 6 m/s.

To better understand these features, a theoretical model was developed that simulates the rising velocity of fluids along the annulus. This model uses a cumulative approach and considers the cement pumping rate, borehole geometry, and timings from the daily reports. We assume, that the predicted minimum velocity is required to fill the whole breakout volume. This means that the faster the velocity the smaller the flow paths cross section.

A comparison of data and models reveals that the varying velocities of the "slow feature" correlate with velocities predicted by using the borehole geometry from the caliper log. The rather constant “fast feature” correlates instead with the predicted velocity of the model based on a uniform borehole geometry with the smallest possible radius, the drill diameter, which thus neglects all breakouts.

In summary, due to the nearly constant pumping rate during the monitoring campaign, we hypothesize that different rising velocities result from variations in the cross-sectional area of the flow path.  Based on our observations, the majority of the water spacer does not flush the borehole breakouts. With a good match to the minimum required velocity, these breakouts are filled by the first arriving cement. The following cement, with the same density, rises again on the fastest track. Thus, measuring the cement rising velocities with fiber optics and comparing them to the minimum required velocity from modeling might be a new tool to assess displacement efficiency in real-time.

How to cite: Hart, J., Polat, B., Schölderle, F., Ledig, T., Lipus, M. P., Wollin, C., Reinsch, T., and Krawzcyk, C.: A Fiber-Optic Approach for Cement Placement Monitoring of Deep Boreholes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19804, https://doi.org/10.5194/egusphere-egu24-19804, 2024.

EGU24-20360 | ECS | Posters on site | SM3.1

Towards a real-time railway monitoring system based on Distributed Acoustic Sensing and a Convolutional Neural Net 

Kevin Growe, Anna Tveit, Hefeng Dong, Susann Wienecke, Martin Landrø, and Joacim Jacobsen

Distributed Acoustic Sensing (DAS) enables cost-efficient retrieval of wavefield information alongside large linear infrastructure elements, such as pipelines, cables or railways. The massive datasets require automated approaches to detect and classify anomalies which can trigger further investigation through an operator, if necessary.

 

Within this work we exploit one week of DAS data from a fiber-optic cable co-located with a 50 km long railway line south of Trondheim, in the center of Norway. The data were acquired with a temporal sampling of 2 kHz and channel spacing of 4 m, resulting in 12500 channels. Treating the DAS time-space domain matrices like images we can make use of well-established techniques from the field of computer vision. We compute sliding RMS windows of 60 s and 1.5 km with 50 percent overlap and use them as input images for a Convolutional Neural Network. The network classifies events such as trains, cars, unknown events as well as different noise classes and artefacts. In order to thoroughly train the network, we labeled approximately 1000 RMS images per class and further applied a variety of data augmentation techniques to finally obtain about 5000 labeled images per class. Once trained, we can simply apply a forward pass through the network every 30 s for all the 1.5 km overlapping segments to obtain a live-classification of events along the entire railway line.

 

We present our workflow as well as initial results and discuss the potential of DAS for future railway monitoring and the challenges that we encounter. If successful, these methods can open up an opportunity to exploit a large amount of fibers co-located with railway lines enabling automatization of real-time railway monitoring.

Acknowledgements:

We acknowledge Bane NOR and Alcatel Submarine Networks for conducting the data acquisition for this project. This work is supported by the SFI Centre for Geophysical Forecasting under grant No. 309960.

How to cite: Growe, K., Tveit, A., Dong, H., Wienecke, S., Landrø, M., and Jacobsen, J.: Towards a real-time railway monitoring system based on Distributed Acoustic Sensing and a Convolutional Neural Net, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20360, https://doi.org/10.5194/egusphere-egu24-20360, 2024.

EGU24-1332 | Posters on site | SM3.2

Seismicity in the Bransfield Strait, Antarctica, using temporal Ocean Bottom Seismographs data 

Jinhoon Jung, Yongcheol Park, Won Sang Lee, and Seewon Park

The Bransfield Basin, located between the South Shetland Island and the Antarctic Peninsula in Western Antarctica, is formed by slab rollback of the South Shetland Trench and complementary extensional. The region also has large and small active volcanoes like the Orca volcano. Various earthquakes have occurred due to tectonic movement and volcanic activities. Since the Mw 4.9 earthquake struck at a depth of 10 km in the vicinity of South Shetland Islands on 29 August 2020 (USGS), moderate earthquakes have constantly been reported adjacent to Bransfield Basin like an earthquake swarm.The Extreme Geoscience Team (EGG) at the Korea Polar Research Institute (KOPRI) has been operating a seismic station at the King Sejong station. Other countries have been running their seismic stations in the South Shetland Islands, such as the Antarctic Seismographic Argentinean Italian Network (ASAIN) and Chilean seismic stations, to monitor local earthquakes associated with back-arc spreading and submarine volcanic activities in this area. However, these seismic stations are located on the islands, and the inter-station distance is over 50 km. To make up for the poor coverage of seismic stations, we installed 5 OBSs in the earthquake swarm area between 2020 and 2021.

Using cross-correlation with onland seismic data and OBSs data, we conducted the template matching analysis and detected 67,952 events from August 29, 2020, to December 31, 2021. We relocated 2,313 epicenters of the seismic events by manually picking the first arrival of the P-wave. We found that the earthquake swarm’s epicenters were mainly concentrated in the central basin of the Bransfield Strait.

We categorize the characteristics of the earthquake near Bransfield Basin. We will contribute to understanding the dynamics and evolution of subduction zones in Bransfield Basin.

 

How to cite: Jung, J., Park, Y., Lee, W. S., and Park, S.: Seismicity in the Bransfield Strait, Antarctica, using temporal Ocean Bottom Seismographs data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1332, https://doi.org/10.5194/egusphere-egu24-1332, 2024.

EGU24-2816 | ECS | Orals | SM3.2

SurfQuake (SQ): A new Python toolbox for the workflow process of seismic sources 

Roberto Cabieces, Thiago C. Junqueira, and Jesús Relinque

surfQuake is a new software designed to overcome the workflow process that involves the estimation of seismic source parameters. The complete set of toolboxes inside surfQuake allows the user the complete automation of seismic phases arrival times estimation and events association, event locations, magnitudes and attenuation, slowness vector, and moment tensor inversion.

The software is programmed in Python 3 and offers the users the possibility of three programming levels. From the core library, which allows the user to integrate the core of surfQuake into his own scripts, to the Command Line Interface, which gives the user access to an upper layer that simplifies the use of the core. Finally, surfQuake core is wrapped by a Graphical User Interface (GUI) and connected to a SQL Lite database to store all the results. The user has direct access to query the database tables to extract important information through the object Relational Mapper SqlAlchemy directly managed from the GUI.

The software has been fully tested with the earthquake cluster that occurred during the eruption of La Palma in 2021-22. The source parameters resulting from the eruption and the basic statistics associated with them are displayed using the database toolbox. Additionally, we offer a web tutorial with the documentation of surfQuake and a set of usage examples for the three programming levels.

How to cite: Cabieces, R., Junqueira, T. C., and Relinque, J.: SurfQuake (SQ): A new Python toolbox for the workflow process of seismic sources, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2816, https://doi.org/10.5194/egusphere-egu24-2816, 2024.

EGU24-4409 | Orals | SM3.2

Clock skew corrections of a large-aperture OBS array in the Atlantic Ocean reveal the need to include non-linear drift corrections 

Frank Krueger, Roberto Cabieces, Katrina Harris, Ana Ferreira, Maria Tshekmistrenko, Stephen Hicks, Wolfram Geissler, Katrin Hannemann, and Mechita Schmidt-Aursch

Accurate timing corrections for seismic data recorded by ocean bottom seismometers (OBS) are essential for a wide range of applications. The synchronization of internal OBS clocks with Global Positioning System (GPS) is only possible prior and subsequently to deployment in the seafloor. Thus, untracked, possibly nonlinear clock errors in seismic data may accumulate over the deployment period. The measurement of the clocks offset from GPS at retrieval, referred to as `skew’, can be used to correct the data solely under the assumption of a uniform rate of clock drift throughout the whole deployment. We estimate OBS clock drift curves for 40 OBSs of the large-scale UPFLOW amphibian array in the Madeira-Azores-Canaries region that lasted ~14 months in 2021-22. We use the relative shift of daily Empirical Green Functions obtained from seismic ambient noise recorded by all available data channels to track clock error. We find that 95% of our OBS clock drift observations have a substantial non-linear component, notably in the first months of the deployment. Overall, our estimated time-dependent clock drift curves accurately predict the final skew, with an average difference of ~160 ms to GPS skew values obtained at retrieval. We test our skew curves by using them to correct examples of recordings of teleseismic earthquakes and of local-regional seismicity. Uncertainty analysis of the skew curves gives a mean skew error of ~110 ms, indicating the suitability of the corrected data for future seismological studies such as for seismic tomography, seismicity analysis and moment tensor inversions. A dedicated open-source Graphical User Interface toolbox in Python 3 has been developed to facilitate OBS clock synchronization using seismic ambient noise.

How to cite: Krueger, F., Cabieces, R., Harris, K., Ferreira, A., Tshekmistrenko, M., Hicks, S., Geissler, W., Hannemann, K., and Schmidt-Aursch, M.: Clock skew corrections of a large-aperture OBS array in the Atlantic Ocean reveal the need to include non-linear drift corrections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4409, https://doi.org/10.5194/egusphere-egu24-4409, 2024.

EGU24-4486 | Orals | SM3.2

Pacific Array: international collaboration for large-scale array experiment in the Pacific basin 

Takehi Isse, Hitoshi Kawakatsu, Sang-Mook Lee, Bang-Yuan Kuo, and James B. Gaherty

             Constructing a seismic network in the oceans has been one of the most difficult challenges in seismology. Almost 70 % of the Earth's surface is covered by the ocean, so such a network is necessary for investigating the Earth's interior. Because the Pacific Ocean is the largest ocean basin, it was considered impractical to establish a large-scale dense seismic array.

              However, in 2014, Kawakatsu and colleagues proposed a new array concept (Kawakatsu et al., 2014). Deploying ~15+ BBOBS as an array unit for 1-2-year observation period, and repeating such observations in a leap-frog fashion for a decade or so, would enable us to cover a large portion of the Pacific Ocean. International collaboration was essential to successfully implement this strategy, and since 2015, the concept has been realized as "Pacific Array" via international collaboration between partners in Japan, U.S.A, EU, South Korea, Taiwan, and China.

              Since then, many array units have been funded, providing broadband data from across the Pacific. Oldest-1 (Japan-S. Korea), Oldest-2 (Japan-Taiwan), Young- and Old-ORCA, and OHANA (U.S.A) have all been completed; Galapagos and SaLOON (U.S. A.) are currently deployed; and HEB (Japan-Germany), GTJ, and EPIC (U. S. A.) will be deployed in the near future. Although each of these observations have their own scientific goals, they contribute to the larger international Pacific Array structure. We summarize recent progress of the Pacific Array and some of scientific result in each array.

How to cite: Isse, T., Kawakatsu, H., Lee, S.-M., Kuo, B.-Y., and Gaherty, J. B.: Pacific Array: international collaboration for large-scale array experiment in the Pacific basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4486, https://doi.org/10.5194/egusphere-egu24-4486, 2024.

EGU24-4563 | ECS | Posters on site | SM3.2

Seismic Activity in the Zabargad Fracture Zone (Red Sea): Insights from an Amphibious Seismic Network 

Hasbi Ash Shiddiqi, Laura Parisi, Eduardo V. Cano, P. Martin Mai, Nico Augustin, and Sigurjón Jónsson

The Zabargad Fracture Zone (ZFZ), located between 23.5o N – 26o N is the largest rift-axis offset in the Red Sea. The ZFZ is a fundamental tectonic element of ~100 km rift-axis offset that marks the transition between the northern and central Red Sea. Due to data scarcity, our understanding of the seismic activity and the potential presence of transform faults or non-transform offsets in the ZFZ area is limited. Local seismological datasets so far have been restricted to the onshore recordings, thus hampering the ability to study the ZFZ's role in the Red Sea’s tectonic evolution and to assess its potential seismic hazard associated with transform faults accommodating the rift-axis offset in the Red Sea.

To fill this data gap, we deployed 14 broadband Ocean Bottom Seismometers (OBS) and four land stations for 12 months within the ZFZ to collect continuous waveforms. The newly collected data span the period 11/2021 to 11/2022. First, we corrected recorded OBS-waveforms for clock drift using skew values measured at the time of the OBS recovery and time-shifts measured from ambient noise cross-correlations for stations whose skews could not be measured. Next, we applied a deep-learning-based algorithm to automatically detect earthquakes and pick P and S phases. We verified and, if necessary, manually corrected these phase picks; this approach identified more than 3500 local earthquakes.

To obtain reliable hypocentral locations, we inverted for an optimum crustal 1-D seismic velocity model of the ZFZ and station delays simultaneously. Using as reference a nearby land station installed on Precambrian bedrock, we obtained positive OBS station delays of up to 2 seconds. These delays correspond to late phase arrivals, most likely due to thick sedimentary and salt deposits. Our local magnitude (ML) calculations show that OBS-station ML values are up to 1.5 units larger than for the land stations. We find that station delays and ML deviations are correlated, highlighting the importance to account for the variability of shallow geological and bathymetric properties for accurate earthquake location and magnitude estimation.

Our seismicity analysis reveals two major distinct spatial clusters of earthquakes, in the southern (23.95 o N – 24.53 o N) and northern (24.68 o N – 25.43o N) parts of the ZFZ. Seismicity in the south higher seismicity rate and spatially concentrated than in the north. We also identified three seismic swarms in the south and one seismic swarm in the north lasted for one to three weeks each. Our preliminary analyses document the potential of this new dataset to address key questions on the seismotectonics and seismic activity of the ZFZ.

How to cite: Shiddiqi, H. A., Parisi, L., Cano, E. V., Mai, P. M., Augustin, N., and Jónsson, S.: Seismic Activity in the Zabargad Fracture Zone (Red Sea): Insights from an Amphibious Seismic Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4563, https://doi.org/10.5194/egusphere-egu24-4563, 2024.

EGU24-4888 | Posters on site | SM3.2

The Design of a Low-Angle Active Leveling Device for Short-Period Ocean Bottom Seismometer 

Chin-Heng Yang, Ching-Ren Lin, Yuancheng Gung, Feng-Sheng Lin, and Kun-Hui Chang

In this study, we focus on developing a low-angle active leveling device of geophone for Ocean Bottom Seismometers (OBS). The deployment of OBS in varied underwater environments poses a significant challenge due to unpredictable terrains, which often affect the positioning and orientation of these instruments. In such scenarios, the role of a leveling device becomes crucial, especially for self-floating OBS. Most of the leveling devices are designed with a 360° range, resulting in high costs and limited versality, our approach is informed by previous OBS positional data, suggesting that a limited corrective angle is adequate for underwater conditions. Our innovative leveling mechanism resembles a joystick in its transmission system, topped with a platform to enhance versatility. The control rod below the platform is controlled by two DC motors combined with worm gears, adjusting the rod along the X and Y axes with an approximate corrective angle of 30 degrees. For seismic sensing, our system utilizes one vertical and two horizontal geophones, housed in a custom sensor box to ensure the three axes are orthogonal to each other. This design simplifies the complexity of parts, combining off-the-shelf and custom components, offering a significant size and cost advantage. We have also tested its performance, with a focus on eliminating signal interference from resonance frequencies and assessing the system's stability. This includes a comparative analysis with older leveling mechanisms.

How to cite: Yang, C.-H., Lin, C.-R., Gung, Y., Lin, F.-S., and Chang, K.-H.: The Design of a Low-Angle Active Leveling Device for Short-Period Ocean Bottom Seismometer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4888, https://doi.org/10.5194/egusphere-egu24-4888, 2024.

EGU24-5502 | ECS | Posters on site | SM3.2

Empirical insights into ocean acoustic wave propagation and source localization using ocean-bottom seismometers 

Clara Gómez-García and Christopher J. Bean

Human activities in the marine environment coupled with the efficient propagation of acoustic waves, have significantly increased ocean noise levels. This rise poses a threat to marine biodiversity, especially impacting vocal-dependent marine mammals. Therefore, obtaining a more comprehensive understanding of the complex ocean soundscape, shaped by both natural and anthropogenic sources, is essential.

Ocean-bottom seismometer (OBS) datasets present an opportunity to explore the marine acoustic noise field. OBS hydrophones can be used to effectively study regional marine soundscapes. Additionally, the three-component OBS seismometers capture acoustic-to-seismic conversions from the water column, enabling the detection and localization of acoustic events.

Through the analysis of OBS hydrophone recordings from the NE Atlantic offshore Ireland, we develop a frequency-dependent empirical sound propagation model for the area. The model provides information on (1) the spectral amplitude decay of sound sources in the region and (2) the distance between OBSs and acoustic sources.

To construct the model, we consider ship noise from individual vessels recorded by OBSs at known distances from the source, using Automatic Identification System (AIS) ship-tracking data. As a ship moves away from its closest point of approach (CPA) to an OBS, the hydrophone records the evolution of the frequency-dependent ship's acoustic signal spectral amplitude with distance. This enables us to compute amplitude decay curves for narrow frequency bands from different vessel signals recorded at various OBSs. We apply a signal-to-noise ratio (SNR) quality control criterion and consider ships sailing along 'straight' paths at a constant speed (< 2 kn variation). After normalizing and scaling the CPAs of the different curves to a reference, we stack them for each frequency band and compute polynomial fits for the stacked amplitude decay curves. We analyse the number of vessel tracks needed to build a reliable empirical model. Numerical simulations are computed to further understand the acoustic propagation properties from our empirical model.

The goal is to investigate (1) how spectral amplitudes at different frequencies behave with distance from the sound sources, (2) the efficiency of frequency-dependent sound propagation in the ocean in regions with variable seafloor morphologies, and (3) the potential use of the empirical model to obtain distances to other sound sources with unknown locations, such as Baleen whales. To achieve this, we compute ratios of spectral amplitudes for pairs of different frequency bands using the fitted amplitude decay curves. We test the model's ability to locate other vessels with known AIS positions before using it to locate different sound sources with unknown positions. Locating a sound source employing the distance provided by the empirical model is valuable when OBSs are too far apart for 'traditional' multi-sensor methods. In such cases, the incoming direction of the sound source is determined by rotating the horizontal-component OBS seismic data to point to the source back-azimuth. Also, the amplitude decay information provided by the model has multiple applications in other areas where noise pollution may be a concern (e.g., marine infrastructure construction).

How to cite: Gómez-García, C. and Bean, C. J.: Empirical insights into ocean acoustic wave propagation and source localization using ocean-bottom seismometers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5502, https://doi.org/10.5194/egusphere-egu24-5502, 2024.

EGU24-6052 | ECS | Posters on site | SM3.2

Re-location and integration into the ISC Bulletin of earthquakes recorded by hydro-acoustic MERMAID instruments freely floating in the South Pacific Ocean 

Dalija Namjesnik, Karin Sigloch, Joel D. Simon, Tom Garth, James Harris, Dmitry Storchak, Frederik. J. Simons, Sébastien Bonnieux, Yong Yu, and Masayuki Obayashi

We present the analysis of more than 9000 hydro-acoustic earthquake records, recorded by a network of 50 instruments called Mobile Earthquake Recording in Marine Areas by Independent Divers (MERMAIDs), which are freely floating in the South Pacific Ocean. This network is part of the collaborative South Pacific Plume Imaging and Modeling (SPPIM) project. Our analysis focuses on evaluating how the MERMAID stations complement the conventional worldwide network of stations reporting to the ISC, comprising records of globally distributed seismic stations. In the context of routine earthquake (re)location, we evaluate the improvement of results of earthquake location estimates, particularly focusing on the Tonga-Kermadec subduction zone, where current distribution of seismic land stations is extremely sparse. MERMAIDs are often the closest “station” to earthquakes occurring in the Tonga subduction zone, and frequently fill significant station azimuthal gaps.

We matched the MERMAID records from June 2018 to December 2023 to more than 3000 earthquakes which are reported to the ISC by many international agencies worldwide, allowing us to construct the MERMAID catalogue, complimented with additional parametric data such as MERMAIDs locations, observed direct P-phase picks and travel time residuals with respect to ak135 model, as well as their corrections for bathymetry. These data were integrated into the existing ISC Bulletin, and relocated using the ISC hypocentre relocation algorithm ISCLoc. The results of this successful first integration of MERMAID data into ISC routines presents an important step towards routinely including MERMAID traveltime picks in ISC Bulletin.

How to cite: Namjesnik, D., Sigloch, K., Simon, J. D., Garth, T., Harris, J., Storchak, D., Simons, F. J., Bonnieux, S., Yu, Y., and Obayashi, M.: Re-location and integration into the ISC Bulletin of earthquakes recorded by hydro-acoustic MERMAID instruments freely floating in the South Pacific Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6052, https://doi.org/10.5194/egusphere-egu24-6052, 2024.

EGU24-6977 | Posters on site | SM3.2

Reprocessing of the ocean bottom seismic data of the TYDE experiment using modern techniques. 

Marco Calò, José Antonio Gamez Lindoro, Francesca Di Luccio, and Karina Bernal Manzanilla

During the TYrrhenian Deep-sea Experiment (TYDE) 14 Ocean Bottom stations were deployed in the period December 2000-May 2001 on the southern Tyrrhenian seafloor around the Aeolian islands All the stations were equipped with Hydrophones (OBH) and six of them with 3-component geophones (OBS). This experiment represented one of the first and most important passive ocean bottom data acquisition ever realized in southern Tyrrhenian and the records were mainly used to perform receiver functions, modeling of the seismic velocity field, and detect and locate seismicity.

In this work we present a reprocessing of these old data using modern techniques of analysis to improve the quality of the signals and extract more information of what has been already published.

We show the workflow used for cleaning the records together with Machine Learning approaches to improve the detection of small events and the application of methods that were not common at that time, such as the Ambient Noise analyses.

 

Work supported by the “Pianeta Dinamico” call, 2023–2025 CAVEAT

How to cite: Calò, M., Gamez Lindoro, J. A., Di Luccio, F., and Bernal Manzanilla, K.: Reprocessing of the ocean bottom seismic data of the TYDE experiment using modern techniques., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6977, https://doi.org/10.5194/egusphere-egu24-6977, 2024.

EGU24-8185 | Posters on site | SM3.2

HALIOS  an innovative and clever Broad Band OBS. 

Yann Hello, Charles Rebour, Karin Sigloch, Sebastien Bonnieux, and Olivier Philippe

A fruitful close collaboration between teams of researchers and engineers of Geoazur, a research laboratory specializing in seismic observation, and Osean, a dynamic company combining the talents of engineers in low-noise, low-power electronics specialized in underwater acoustics, gives this instrument a guarantee of robustness, reliability and innovation by capitalizing on all their knowledge in their respective fields. Halios has an autonomy of 18 months, dimensions of 1.1 x 1.1 x 1m and a total weight with ballast of 346 kg. Electrical power is supplied by lithium or alkaline batteries. Halios is made entirely from corrosion-resistant materials. The 4-panel, mortise-and-tenon structure naturally creates a well in which the seismometer is protected. This well is covered by two flaps that open when the OBS sinks into the water, and close when the OBS stops on the bottom. During descent, the seismometer is suspended in the well. Once the OBS is in place, the seismometer is released automatically or by an acoustic command to land on the ground without any mechanical contact with the structure. This type of coupling is ideal, and protects the sensor from underwater currents. Communication with the OBS is possible via Ethernet, Wi-fi or acoustics once in the water by non-specialists. An acoustic module makes it possible to retrieve a health report on demand, which groups together the essential parameters of the station, and to modify some of them once the OBS is in the water. Halios incorporates precise clock or a CSAC-type atomic clock, if time precision is required.The seismometer is a compact Nanometrics Trillium, integrated in a dedicated container which also houses an accelerometer. An hydrophone, a precision temperature sensor and an absolute pressure sensor complete the range of sensors integrated on Halios. An dedicated acoustic modem also enables partial data retrieval from the surface.To retrieve the OBS, an acoustic command activates a mechanical release which frees the ballast. Dynamic assistance from leaf springs accelerates the positive thrust provided by the OBS's high-density syntactic foam. This foam is injected into a PHD shell, which effectively protects the whole unit and, thanks to its compact shape, provides effective anti-shock protection. The ascent of the OBS into the water column can be monitored by the acoustic module.Once at the surface, the time difference between the OBS clock and the GPS datum is automatically calculated. The OBS sends its GPS coordinates to the ship by VHF to facilitate recovery. At night, an LED flashing light can also be used to pinpoint its position. Halios is equipped with an interface that enables it to be connected to a real-time cable network, making it a versatile OBS of the highest performance and innovation.

How to cite: Hello, Y., Rebour, C., Sigloch, K., Bonnieux, S., and Philippe, O.: HALIOS  an innovative and clever Broad Band OBS., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8185, https://doi.org/10.5194/egusphere-egu24-8185, 2024.

EGU24-10807 | Posters on site | SM3.2

Pushing Boundaries with Ocean Bottom Seismometers (OBS) with a Pool-Ready System: Güralp Aquarius 

Aaron Clark, James Lindsey, Phil Hill, Connor Foster, Federica Restelli, Neil Watkiss, Ella Price, Mladen Nedimović, and Graeme Cairns

Cabled ocean bottom seismometer (OBS) solutions are financially and logistically challenging and autonomous OBS systems do not provide operators with seismic data until recovery. To address this issue Güralp has developed Aquarius, an ultra-low-power, free-fall OBS system, operational at any angle and with the ability to transmit seismic data in near-real-time from the seafloor without the use of cables.

The Güralp Aquarius incorporates seafloor-to-surface acoustic communication technology that allows state-of-health and noise performance interrogation during installation followed by retrieval of seismic data throughout the deployment period.

Omnidirectional broadband seismometer components allow the Aquarius to land and operate on steep slopes without requiring a gimbal mechanism that inherently introduces noise and failure modes. Raw data is recorded uncorrected for orientation to allow users to correct during post-processing.

These unique features allow the sensor to function on uneven seafloor as well as transmitting seismic data to the surface where the operator can use noise characteristics, location, and orientation data to determine if the landing site is suitable.

Intelligent battery design allows for typical 18-month deployments, with charging being possible alongside data transfer. This allows recharging, download and configuration simultaneously on the ship in between deployments.

Ease of configuration, deployment and recovery followed by simple data processing are all central themes to the Aquarius. The capital investment required to purchase OBS systems often means that the OBS instrument must be adaptable to a range of use-cases.

The Aquarius is in use in 6 different countries and is the unit of choice for the Canadian OBS pool, comprising 120 units for deployment around the globe. Aquarius units have been successfully deployed in the Mediterranean, North Atlantic as well as the North and South Pacific. Here, we focus on the mechanics of deployment and recovery for demonstrating to experienced and prospective principle investigators how this system simplifies and improves confidence in deployment.

How to cite: Clark, A., Lindsey, J., Hill, P., Foster, C., Restelli, F., Watkiss, N., Price, E., Nedimović, M., and Cairns, G.: Pushing Boundaries with Ocean Bottom Seismometers (OBS) with a Pool-Ready System: Güralp Aquarius, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10807, https://doi.org/10.5194/egusphere-egu24-10807, 2024.

EGU24-11062 | Orals | SM3.2

Successful Deployment of a 21km SMART Cable with Force-Feedback Seismometer and Accelerometers in the Mediterranean Sea 

Federica Restelli, John O'Neill, Bruce Nicholson, Neil Watkiss, Giuditta Marinaro, Francesco Simeone, Davide Embriaco, Ella Price, Connor Foster, and Aaron Clark

Autonomous Ocean Bottom Seismometer (OBS) deployments have often involved a degree of “drop-and-hope” due to the inherent lack of seismic data communication during installation as well as waiting extended periods before data collection. Cabled solutions provide real-time data during and immediately after deployment, sometimes with opportunity to adjust the instrument before it is left to operate remotely. However, cabled solutions are inherently financially and logistically challenging both in terms of seismic hardware and arguably more significantly, deployment hardware (ships, ROVs, cables etc.). The geographical reach of these experiments is also often limited to within a few hundred kilometres of the coast. These constraints often mean cabled OBS are beyond the scope of most scientific bodies.

Güralp Systems, in collaboration with INGV, has successfully manufactured and demonstrated a method of reducing financial and logistical constraints and extending geographical range by utilising force-feedback seismic instrumentation in cabled OBS systems. The recent successful deployment of the InSEA Wet Demo SMART (Science Monitoring And Reliable Telecommunications) cable displays a world first in how science can partner with industry to achieve this.

SMART cables are primarily telecommunication cables that secondarily serve as hosts for scientific monitoring equipment. Commercial viability for these systems relies on the cable being laid as if the science element did not exist, thereby minimising additional deployment costs and reducing barriers to cooperation with cable laying companies. GSL and INGV deployed 3 seismometer-accelerometer pairs housed inline repeaters along the 21km cable length using standard cable-laying techniques to show proof of concept.

This pioneering installation using telecommunication cables marks a significant step towards drastically improving local knowledge of inaccessible oceanic regions as well as global azimuthal coverage for teleseismic events, all in real time.

How to cite: Restelli, F., O'Neill, J., Nicholson, B., Watkiss, N., Marinaro, G., Simeone, F., Embriaco, D., Price, E., Foster, C., and Clark, A.: Successful Deployment of a 21km SMART Cable with Force-Feedback Seismometer and Accelerometers in the Mediterranean Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11062, https://doi.org/10.5194/egusphere-egu24-11062, 2024.

EGU24-11074 | ECS | Posters on site | SM3.2

Waveform tomography of the upper mantle beneath the North Atlantic region using regional seafloor and global data. 

Janneke I. de Laat, Sergei Lebedev, Raffaele Bonadio, Maria Thsekhmistrenko, and Nicolas L. Celli and the SEA-SEIS Team

The Iceland hotspot and its interaction with the Mid-Atlantic Ridge have strongly influenced the structure and evolution of the North Atlantic region. The Iceland hotspot has been linked to the presence of the underlying Iceland plume, rising from the deep mantle below Iceland. Due to the sparsity of the seismic data coverage in the North Atlantic Ocean, the structure and dynamics of the underlying plume, as well as its influence on the surrounding North Atlantic region, remain a topic of debate. As part of the project SEA-SEIS (Structure, Evolution And Seismicity of the Irish offshore), a network of ocean bottom seismometers was deployed across a large part of the North Atlantic Ocean—from Ireland and Britain to near Iceland—in September 2018. Over a period of 19 months, they recorded seismic data on the seafloor. 14 OBSs were retrieved in May 2020, of which 12 successfully recorded 19 months of seismic data. The data was thoroughly preprocessed, including the reduction of compliance and tilt noise on the vertical-component waveforms of teleseismic events. These waveforms were individually inverted for surface, S- and multiple S-waves using the Automated Multimode Inversion (AMI), extracting structural information on the lithosphere and underlying mantle.

Here, we combine this new seafloor seismic data with a massive global dataset of waveform fits for almost 1.5 million seismograms, with the coverage maximised in the hemisphere around the North Atlantic, and compute a new seismic waveform tomography model of the North Atlantic upper mantle: NA24. The tomography capitalises on the improved data coverage and reveals both the S-wave velocity and the azimuthal anisotropy structure below the Iceland hotspot, the adjacent mid-ocean ridge, and the entire North Atlantic region at a new level of detail. It shows low seismic velocities below Iceland and the adjacent Reykjanes Ridge and Kolbeinsey Ridge down to ~260 km depth, below which they merge into one low-velocity body located west of Iceland at around 330 km depth. Around 410 km depth, the low-velocity body is present below eastern Greenland where it remains throughout the transition zone. This observation implies that the Iceland plume is located below eastern Greenland in the transition zone, moving eastward as it rises in the upper mantle. In the shallow upper mantle, a strong ridge-parallel azimuthal anisotropy structure is revealed along the full length of the Reykjanes Ridge. This implies a strong channelled horizontal flow from the Iceland plume towards the south below the ridge axis, while any sign of a radial outward flow of the plume is absent.

How to cite: de Laat, J. I., Lebedev, S., Bonadio, R., Thsekhmistrenko, M., and Celli, N. L. and the SEA-SEIS Team: Waveform tomography of the upper mantle beneath the North Atlantic region using regional seafloor and global data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11074, https://doi.org/10.5194/egusphere-egu24-11074, 2024.

EGU24-11876 | ECS | Posters on site | SM3.2

Integrated Bayesian Approach for Station Location and Orientation in Marine Active-Source Seismic Shear Wave Studies 

Morgan Cryder, Robert Dunn, and Chong Xu

Since the introduction of the ocean bottom seismograph (OBS), it has played a pivotal role in the expansion of our comprehension of the Earth’s interior structure and dynamics. Typically deployed through free-fall from a ship, the position of the OBS on the seafloor and its orientation are initially unknown. When using airgun shots to locate and orient an instrument, a severe downside is the often-limited azimuthal distribution of shots around the OBS, possibly leading to large location and, subsequently, orientation errors. We introduce a novel and efficient method aimed at enhancing the accuracy of station locations in active-source seismic experiments. The approach uses airgun shots recorded as part of the experiment, and integrates both acoustic wave travel time information and waveform polarizations. The inverse problem of station location is formulated in terms of Bayesian inference. At each location of a search grid, the misfit of observed and theoretical water wave travel times and the clustering of polarization data are combined into one probabilistic formulation to map the relative likelihood of a station’s position and orientation. We demonstrate the practical utility of the method via application to the location and orientation of OBS deployed during a recent seismic experiment located across the Hawaiian Ridge. Thereafter, we will use the results to compute radial seismograms, extract the travel times of crustal and mantle S waves, and develop S-wave models of the oceanic lithosphere across the Hawaiian Ridge.

How to cite: Cryder, M., Dunn, R., and Xu, C.: Integrated Bayesian Approach for Station Location and Orientation in Marine Active-Source Seismic Shear Wave Studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11876, https://doi.org/10.5194/egusphere-egu24-11876, 2024.

EGU24-13081 | ECS | Posters virtual | SM3.2

How did the Largest Oceanic Plateau modify the Normal Oceanic Lithosphere? 

Ziqi Zhang and Tolulope Olugboji

The Ontong Java Plateau (OJP), formed around 120 Ma, represents a significant event in the Earth’s geologic history. It is the largest preserved Large Igneous Province (LIP) by volume on the Earth. The voluminous and rapid magmatism placed a thick 30-40 km crust on a normal oceanic lithosphere in submarine conditions. The lithosphere has since experienced low subsidence suggesting only modest thermal perturbation. Several hypotheses have been proposed to explain the unique emplacement history, including a hot mantle plume, meteorite impact, or passive mantle upwelling close to a fast-spreading ridge. In this study, we image the crust and upper mantle structure beneath the OJP using body waves and surface waves. A challenge of body wave imaging in submarine environments is the severe reverberations generated in the water column and seafloor sediments. Additionally, multiple reflections from shallow interfaces (e.g., Moho and intra-crustal layers) may interfere with deeper upper mantle phases, making interpretation ambiguous. In this work, we obtain high-resolution Ps-RFs at 17 OBS (ocean bottom seismometer) stations in the OJP region using a transdimensional hierarchical Bayesian deconvolution approach. We then take advantage of two recently developed techniques: (1) FADER (Fast Automated Detection and Elimination of Echoes and Reverberations), which uses autocorrelation and cepstral analysis to identify and remove water and sediment reverberations, and (2) CRISP-RF (Clean Receiver function Imaging with SParse Radon Filters), which uses sparse Radon transforms to eliminate multiples and incoherent noise. We anticipate applying our novel ideas to traditional seismic imaging will provide robust constraints on the discontinuities detected beneath the OJP, shedding new light on its lithospheric structure and origin.

How to cite: Zhang, Z. and Olugboji, T.: How did the Largest Oceanic Plateau modify the Normal Oceanic Lithosphere?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13081, https://doi.org/10.5194/egusphere-egu24-13081, 2024.

EGU24-14905 | Orals | SM3.2

Removing low frequency ocean bottom seismometer tilt noise using simple sensor reorientation 

Wayne Crawford, Gabi Laske, Nicholas Harmon, and Catherine Rychert

Ocean bottom seismometer data are strongly affected by noise from seafloor currents.  Techniques based on the transfer function between noise on the horizontal and vertical channels are commonly used to “clean” this noise from low-frequency (< 0.1 Hz) vertical channel data, but questions remain about the efficiency of this technique and its effect on seismological signals.  We present a method to “pre-clean” the vertical data through simple rotation of the seismometer to minimize the noise on the vertical channel.  The rotation is nearly identical to that indicated by the transfer function method, but has the advantage of losing no information.  Once this pre-cleaning is performed, transfer-function based cleaning can still be performed, generally resulting in lower noise levels than those obtained using the transfer function method alone and the remaining transfer function may provide information beyond that of the instrument’s mis-alignment with the gravitational field.  We will present examples from datasets around the world and discuss new information revealed.

How to cite: Crawford, W., Laske, G., Harmon, N., and Rychert, C.: Removing low frequency ocean bottom seismometer tilt noise using simple sensor reorientation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14905, https://doi.org/10.5194/egusphere-egu24-14905, 2024.

EGU24-16613 | ECS | Posters on site | SM3.2

Surface wave mantle anisotropy tomography of the Azores-Madeira-Canaries region using UPFLOW data: initial results 

Katrina Harris, Michael Witek, Ana M. G. Ferreira, Sung-Joon Chang, and Miguel Miranda

Upward mantle flow is key to understand global mantle geodynamics yet its imaging remains challenging due to potential associated low velocity contrasts and small lateral dimensions. In this study we use the UPFLOW ocean bottom seismometer (OBS) dataset to build images of radial anisotropy to constrain the patterns of mantle upwellings in the Azores-Madeira-Canary Islands region. We use the partitioned waveform inversion (PWI) method whereby non-linear waveform fitting of surface waves filtered between T~ 16 s and T~ 300 s is performed using a successive series of time-frequency windows in two stages. Firstly, the surface wave fundamental mode is extracted via phase match filtering and is used to obtain path average perturbations in shear radial anisotropy and isotropic shear wave velocity from a smoothed combination of the 1-D mantle model ak135 and the crustal model CRUST1.0. These perturbations establish a new initial model, which is subsequently used to estimate the path averaged radial anisotropy model that leads to the best fit between the observed trace and the synthetic waveform obtained by summing all overtones (up to n = 20). An iterative, regularized least squares inversion is used to invert for 3-D radially anisotropic mantle structure. Uncertainties are automatically quantified and used to interpret resolved seismic structures. Preliminary results are compared to previous tomographic models of the Atlantic region.

How to cite: Harris, K., Witek, M., Ferreira, A. M. G., Chang, S.-J., and Miranda, M.: Surface wave mantle anisotropy tomography of the Azores-Madeira-Canaries region using UPFLOW data: initial results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16613, https://doi.org/10.5194/egusphere-egu24-16613, 2024.

EGU24-19546 | Posters on site | SM3.2

Decoding Ocean Depths: Machine Learning Insights into Tidal Dynamics with UPFLOW’s OBS Data 

Carlos Corela, Alex Saoulis, Maria Tsekhmistrenko, Afonso Loureiro, Miguel Miranda, and Ana Ferreira

The iReverb project explores technical methodologies employed in the UPFLOW project, which addresses the challenges associated with tidal-induced noise on Ocean Bottom Seismometers (OBS) deployed in the North Atlantic Ocean. OBS sensors, unlike those on land stations, are exposed to oceanic currents, whose coupling with the instruments induces reverberations in the recordings. This project showcases a method for exploration of reverberations of tidally-modulated current-induced noise across different OBS types around the Azores, Madeira and Canaries region. The overarching objective is to present a comprehensive technical framework to enhance our understanding of Ocean Bottom Circulation (OBC), providing insights for calibrating current models. A central aspect of this project is the proposed utilisation of machine learning (ML) algorithms for automating the mapping of resonances and obtaining a proxy for OBC.

Here, we present the iReverb methodology, involving manual curation of a pixel-level annotated spectrogram dataset, after this, a ML classifier is trained to identify features in each spectrogram (known as supervised semantic segmentation). To begin with, 15-minute spectrograms between 1-20 Hz are manually annotated using an open-source labelling tool. A deep Convolutional Neural Network (CNN), consisting of a ResNet Encoder, a UNet decoder, and a pixel-wise classification head, is then trained to classify features in each spectrogram using supervised learning. We explore the various factors, such as architecture changes to the CNN, that contribute to improving the model performance for annotating key features. We also discuss insights into attempted alternatives to standard supervised learning (semi-supervised and synthetic labels).

Finally, we discuss the results and evaluate the effectiveness of the ML/DL approach in mapping resonances, demonstrating its potential in utilising resonances as signals for tracking ocean currents (and whales). 

This project was funded by the UPFLOW project (ERC grant 101001601). This work was partially funded by FCT I.P./MCTES through PIDDAC (UIDB/50019/2020, UIDP/50019/2020 and LA/P/0068/2020).

How to cite: Corela, C., Saoulis, A., Tsekhmistrenko, M., Loureiro, A., Miranda, M., and Ferreira, A.: Decoding Ocean Depths: Machine Learning Insights into Tidal Dynamics with UPFLOW’s OBS Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19546, https://doi.org/10.5194/egusphere-egu24-19546, 2024.

EGU24-21685 | Orals | SM3.2

Imaging of the West Indian Ocean Subsurface using Compliance from Ocean-Bottom Stations  

Mohammad-Amin Aminian, Eleonore Stutzmann, Wayne C Crawford, and Jean-Paul Montagner

This research focuses on deriving the compliance function from data collected by broadband ocean-bottom stations (OBS) during the RHUM- RUM experiment in the Indian Ocean. The primary objective is to determine the shear velocity structure beneath the ocean floor, a task essential for understanding the geological features of regions where data is sparse. The methodology revolves around analyzing the compliance function, a measure of the seafloor’s deformation in response to infra-gravity pressure signals at low frequencies (0.003 to 0.04 Hz). The compliance function, which represents the transfer function between vertical displacement and pressure, is greatly influenced by the shear velocity of the oceanic sub-structure beneath the station.

Our approach included several processing steps applied to the OBS data. These steps encompassed the removal of glitches, filtering out global and local seismic events, minimizing tilt effects, calibrating pressure gauges, and performing a linear search in the frequency and coherence domains to identify the optimal data window. The compliance function was computed using data recorded over 13 months in 2012 by the RHUM-RUM experiment’s broadband OBS near La Reunion Island, strategically placed at depths ranging from 3 to 5 km, predominantly over the central and southwest Indian Ridge.

Subsequently, we performed depth-velocity inversion of the compliance function using the Metropolis-Hastings algorithm and determined the oceanic crustal shear velocity structure up to a depth of 8 km.

This inversion process verified the compliance function’s stability and reliability throughout the observation period. Additionally, we developed specialized software, ’Compy’ designed to automate the processing steps required for this study, thereby enhancing efficiency and accuracy in seafloor compliance analysis. This research contributes significantly to our understanding of subsurface structures in marine environments, particularly in regions with limited data availability.

How to cite: Aminian, M.-A., Stutzmann, E., Crawford, W. C., and Montagner, J.-P.: Imaging of the West Indian Ocean Subsurface using Compliance from Ocean-Bottom Stations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21685, https://doi.org/10.5194/egusphere-egu24-21685, 2024.

EGU24-3477 | Posters on site | SM3.4

Status and Outlook of ORFEUS Data Services, Products and Activities to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region and Beyond 

Carlo Cauzzi, John Clinton, Wayne Crawford, Susana Custódio, Sebastiano D'Amico, Christos Evangelidis, Christian Haberland, Anastasia Kiratzi, Lucia Luzi, Petr Kolínský, Zafeiria Roumelioti, Jonathan Schaeffer, Karin Sigloch, Reinoud Sleeman, and Angelo Strollo

ORFEUS (Observatories and Research Facilities for European Seismology, http://orfeus-eu.org/) is a non-profit foundation that promotes seismology in the Euro-Mediterranean area and beyond through the collection, archival and distribution of seismic waveform data, metadata, and associated services and products. The data and services are collected or developed at national level by more than 60 contributing Institutions. They are further developed, integrated, standardised, homogenised and promoted through ORFEUS. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in managing digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and data management; (d) the promotion of open access to seismic waveform data, products and services for the broader solid Earth science community. These goals are achieved through the development and maintenance of data services targeted to a broad community of seismological data users, ranging from earth scientists to earthquake engineering practitioners. Three Service Management Committees (SMCs) are consolidated within ORFEUS, devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated waveform Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/); the European mobile instrument pools (https://orfeus-eu.org/data/mobile/). Products and services for computational seismologists are also considered for integration in the ORFEUS domain. ORFEUS services currently provide access to the waveforms acquired by ~ 24,000 stations, including dense temporary experiments (e.g. AdriaArray; https://orfeus.readthedocs.io/en/latest/adria_array_main.html), with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by the various ORFEUS institutions. Web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear policies and licenses, and acknowledging the crucial role played by data providers, who are part of the ORFEUS community. There are significant efforts by ORFEUS participating institutions to enhance the existing services to tackle the challenges posed by Big Data, with emphasis on data quality, improved user experience, and implementation of strategies (e.g. Cloud) for scalability, high-volume data access and archival. ORFEUS actively encourages interoperability and integration of multidisciplinary datasets in seismological and Earth Science workflows. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group (UAG), which comprises selected European Earth scientists with expertise on a broad range of disciplines. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal (https://www.ics-c.epos-eu.org/). ORFEUS is one of the founding Parties and a fundamental pillar of EPOS Thematic Core Service (TCS) for Seismology. ORFEUS and its community are actively involved in EC projects (http://www.orfeus-eu.org/organization/projects/), notably Geo-INQUIRE (https://www.geo-inquire.eu/) and DT-GEO (https://dtgeo.eu/) in 2024.

How to cite: Cauzzi, C., Clinton, J., Crawford, W., Custódio, S., D'Amico, S., Evangelidis, C., Haberland, C., Kiratzi, A., Luzi, L., Kolínský, P., Roumelioti, Z., Schaeffer, J., Sigloch, K., Sleeman, R., and Strollo, A.: Status and Outlook of ORFEUS Data Services, Products and Activities to Coordinate Access to Seismic Waveform Data in the Euro-Mediterranean Region and Beyond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3477, https://doi.org/10.5194/egusphere-egu24-3477, 2024.

EGU24-4414 | ECS | Posters on site | SM3.4

Initiation of the Seismic Network Expansion and Modernization in Ukraine 

Liudmyla Farfuliak, Tetiana Amashukeli, Andrea Chiang, Kevin Mackey, Oleksandr Haniiev, Bohdan Kuplovskyi, Kasey Aderhold, Daniel Burk, Vasyl Prokopyshyn, and Kostiantyn Petrenko

The seismic hazard department and department of the Carpathian region seismicity of the Subbotin Institute of Geophysics of the National Academy of Science of Ukraine, with the support and collaboration of the U.S. Department of Energy, Lawrence Livermore National Laboratory, Michigan State University, and the EarthScope Consortium had done first steps to expand the Ukrainian National Seismic Network (UT) through the installation of permanent broadband seismic stations in the territory of Ukraine.

The main goal of the Seismic Network Expansion and Modernization in Ukraine is to improve regional network coverage by making high-quality data from new stations openly available to the global scientific community in real time. It will strengthen national seismic monitoring and earthquake response capabilities in Ukraine by upgrading and expanding the national networks with high-quality broadband seismometers and strong motion sensors. It will emphasize data quality, real-time data exchange, and network sustainability through training in best practices on station site selection, installation, data management, and network operation.

To maximize the effectiveness of investigating existing and new seismic sites, multiple factors must be considered during the initial selection, preparation, and installation of new seismic stations. One critical component during the site selection process of any seismic network is an assessment of the seismic noise level at potential sites. The capacity of any seismic station to detect earthquakes and record high quality waveforms will be determined by the signal and noise characteristics of the site. Proper site selection is strongly related to the network's region and can be a critical issue. Besides the earth’s natural background noise, there are other noise sources to consider like those related to infrastructure close by (roads, traffic, mining activity, tenants, etc.). The goal of this work is to conduct noise surveys that can be quickly deployed in order to efficiently evaluate potential sites for the installation permanent seismic stations.

An initial noise survey was conducted at two sites: one at an existing site LUBU (near Liubeshka village, Lviv district) and one at a new site SUGL (near Mala Uhol`ka village, Zakarpattia district). We analyzed, and report the data in the form of both time-history examples and standardized Probability Density Function noise plots. Seismic spectral analysis based on the calculation of Power Spectral Density distribution using a Probability Density Function by McNamara approach.

How to cite: Farfuliak, L., Amashukeli, T., Chiang, A., Mackey, K., Haniiev, O., Kuplovskyi, B., Aderhold, K., Burk, D., Prokopyshyn, V., and Petrenko, K.: Initiation of the Seismic Network Expansion and Modernization in Ukraine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4414, https://doi.org/10.5194/egusphere-egu24-4414, 2024.

EGU24-7986 | ECS | Posters on site | SM3.4

SDQ (Seismic Data Quality): a Python project for seismo-accelerometric data quality check 

Fabio Varchetta, Marco Massa, Rodolfo Puglia, Peter Danececk, Sandro Rao, Alfonso Mandiello, and Davide Piccinini

In recent years, significant attention has been devoted both to seismic data processing and data quality procedures. At the Italian scale, EIDA Italia (https://eida.ingv.it/it/getdata) and ISMDq (http://ismd.mi.ingv.it/quality.php) represent the web portals currently available for checking seismic data quality. In this work, we introduce the SDQ (Seismic Data Quality) project, a new open-source Python-based tool, designed for the automatic data quality check of sismo-accelerometric stations considering both selected earthquakes and continuous data streams. Regarding earthquake data, the quality of individual waveforms is assessed by initially comparing – at first - the ground motion parameters derived from co-located accelerometers and velocimeters. SDQ operates by using a simple external input file including the INGV event-id and both station and network codes. Event information, station metadata, and waveforms are obtained from FDSN (https://www.fdsn.org) web services (https://www.fdsn.org/webservices/). Each single waveform is assigned to a quality class ranging from A (high quality) to D (data to be rejected) based on time- and frequency-dependent algorithms. Classification thresholds were empirically obtained by combining visual signal inspection and statistical analysis considering 15.000 waveforms recorded in Italy from 2012 to 2023 by IV (National Seismic Network, https://www.fdsn.org/networks/detail/IV/) and MN (MedNet network, https://www.fdsn.org/networks/detail/MN/) sismo-accelerometric stations. Concerning continuous data streams, mini-seed recording signals are analyzed at each selected station to set empirical thresholds considering several data metrics (i.e. frequency-dependent Root Mean Square, RMS, and Power Spectral Density, PSD) and data availability information (i.e. % gap and data availability, sum of gaps, maximum gap etc.) to build a station-quality archive. Users can select and build target time histories for each network, station, data stream and single ground motion component related to the selected input data included in a local mini-seed archive representing the starting point of the procedure. SDQ finally provides summary tables for both earthquake and continuous data, collecting all relevant parameters for each processed waveform and data stream, along with explanatory text files (log and warning files), allowing the user to better evaluate the results. Although SDQ is currently under development, now it is freely available and  downloadable at  https://gitlab.rm.ingv.it/EIDA/quality/sdq

How to cite: Varchetta, F., Massa, M., Puglia, R., Danececk, P., Rao, S., Mandiello, A., and Piccinini, D.: SDQ (Seismic Data Quality): a Python project for seismo-accelerometric data quality check, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7986, https://doi.org/10.5194/egusphere-egu24-7986, 2024.

EGU24-12258 | Posters on site | SM3.4

The automatic seismic event bulletin of the Swedish National Seismic Network 

Michael Roth, Gunnar Eggertsson, Peter Schmidt, Hossein Shomali, Behzad Oskooi, and Björn Lund

The Swedish National Seismic Network (SNSN) currently operates 67 permanent and 13 temporary broadband seismic stations. All stations transmit continuous realtime data to the data centre in Uppsala, and data streams of about 40 stations are automatically forwarded to subscribing institutes in the neighboring countries and to ORFEUS. In addition to the SNSN stations we receive realtime data from about 120 stations located in Norway, Finland, Denmark, Germany, Poland, the Baltic States, and Russia. 

SNSN processes the waveform data of this virtual network of about 200 stations using the SeisComp and Earthworm systems in parallel. Both systems are set up to be very sensitive in order to detect as small events as possible, which also increases the probability of generating spurious events. In order to screen out spurious events we generate a common bulletin which contains events that have been located by both systems independently. Our common bulletin is very reliable (no spurious events during the last 1.5 years), captures events down to about ML = 1 and contains almost all events with ML > 1.5 in Fennoscandia.

All events in the common bulletin are automatically classified by an artificial neural network as earthquakes, blasts or mining-induced events. The classifier has been developed in the framework of a PhD project, and was implemented into the SNSN processing queue during 2023 (Eggertsson et al, "Earthquake or Blast? Classification of Local-Distance Seismic Events in Sweden using Fully-Connected Neural Networks", accepted GJI 2024). It has been thoroughly tested, and, comparing the automatic classification with analyst-reviewed classification, we found a 97% match

Since December 2023, SNSN provides the automatic common bulletin as a simple webpage https://www.snsn.se/combullUTC/ - mainly for the general public and for quick reference. For the seismological community, SNSN has set up an automatic real-time forwarding of complete event parameters for all events with ML >= 2 to the European-Mediterranean Seismological Centre.

How to cite: Roth, M., Eggertsson, G., Schmidt, P., Shomali, H., Oskooi, B., and Lund, B.: The automatic seismic event bulletin of the Swedish National Seismic Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12258, https://doi.org/10.5194/egusphere-egu24-12258, 2024.

EGU24-12520 | Posters on site | SM3.4

Data quality of large dense seismic networks – lessons learnt from AlpArray and application to AdriaArray 

Petr Kolínský, Luděk Vecsey, Johannes Stampa, Felix Eckel, Tena Belinić Topić, the AlpArray Working Group, and the AdriaArray Seismology Group

Large dense seismic networks popping up around the world in the last two decades enable studying the wave propagation and structure of the Earth with unprecedented details. Hundreds of broadband seismic stations spaced by tens of kilometers produce large amounts of data, which is usually processed by automatic routines. The data is no longer supervised by seismologists on a detailed level of every record as thousands of hours of data are handled at once. Ensuring the quality of data and accompanying metadata is nowadays a discipline by and of itself. Besides the classical techniques, which investigate the properties of data at a single station, large dense seismic networks allow for a multi-station approach to review the quality of the data. The diagnostic tools of multi-station methods are based on the detection of outlying stations/records among many others. Properties of the wavefield of wavelengths longer than the station spacing vary smoothly and hence comparing the measurement at neighboring stations allows for identifying anomalous behaviors. These methods work under the assumption that most of the (meta-) data is correct, and therefore a small number of outliers can be detected. Thus, not only do large dense seismic networks contribute to research, which is their primary goal, but thanks to the design of these networks, data quality can also be tested more precisely than before. We review both types of techniques, showing examples of the AlpArray experiment (2015 - 2022), and discussing the development of the approaches over the years to what is nowadays applied to the AdriaArray Seismic Network. AdriaArray experiment started in 2022 and encompasses now around 1000 permanent as well as over 430 temporary broadband stations. We show how the availability and retrievability of the data are checked, how amplitude and phase information from the ambient and deterministic wavefields are used to assess the correctness of metadata and how we represent the results of these tests in maps and tables. The purpose of these tests is aimed in both directions: towards the users, so that they are aware of potential issues, as well as towards the station operators so that they can be notified and asked to fix the detected problems.

How to cite: Kolínský, P., Vecsey, L., Stampa, J., Eckel, F., Belinić Topić, T., Working Group, T. A., and Seismology Group, T. A.: Data quality of large dense seismic networks – lessons learnt from AlpArray and application to AdriaArray, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12520, https://doi.org/10.5194/egusphere-egu24-12520, 2024.

EGU24-12895 | Posters on site | SM3.4

MUDA: the dynamic geophysical and geocehmical multiparametric database 

Marco Massa, Elisa Ferrari, Andrea Rizzo, Sara Lovati, and Lucia Luzi

MUDA (geophysical and geochemical MUltiparametric DAtabase) is a new infrastructure of the National Institute of Geophysics and Volcanology (INGV, www.ingv.it) serving geophysical and geochemical multiparametric data, designed and developped in the framework of Dynamic Planet -Working Earth project (https://progetti.ingv.it/it/pian-din).

MUDA is a dynamic and relational database based on MySQL (https://www.mysql.com) with a web interface realised in php (https://www.php.net) using a responsive design technique. The multi-parametric data are stored and organised using a table-structure able of correlating different types of data that allow possible future integration with new type of data acquired through both real-time and off-line transmission vectors.

MUDA collects information from different types of sensors, such as seismometers, accelerometers, hydrogeochemical sensors, sensors for measuring the flux of carbon dioxide on the ground (CO2), sensors for detecting the concentration of Radon gas and weather stations with the aim of making possible correlations between seismic phenomena and variations in environmental parameters such as the level of groundwater as well as its temperature and electrical conductivity.

MUDA archives and publishes data of multiparametric stations belonging both to permanent (i.e. the National Seismic Network, RSN, https://www.fdsn.org/networks/detail/IV/) or temporary (e.g. PDnet, Massa et al., 2021, https://www.fdsn.org/networks/detail/ZO_2021/) INGV seismic networks, as well as data from a multi-parametric Salse di Nirano Reserve (MO) site in cooperation with the PD PROMUD 2023-2025 (Definition of a multidisciplinary monitoring PROtocol for MUD volcanoes) project and two additional multi-parametric sites installed in the inter-mountain basin of Norcia, as a part of the GEMME 2023-2025 project. Data from Radon stations belong to the INGV-IRON national network (Italian Radon Monitoring Network, https://www.ingv.it/en/monitoring-and-infrastructure/monitoring-networks/ingv-and-its-networks/iron).

MUDA daily publishes multi-parametric data updated to the previous day and offers the chence to view and download dynamic time series for all available data and for different periods, up to a maximum of 30 days. For longer periods, users can request data to muda@ingv.it.

MUDA is now published at http://muda.mi.ingv.it

How to cite: Massa, M., Ferrari, E., Rizzo, A., Lovati, S., and Luzi, L.: MUDA: the dynamic geophysical and geocehmical multiparametric database, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12895, https://doi.org/10.5194/egusphere-egu24-12895, 2024.

EGU24-13131 | Posters on site | SM3.4

Towards a community standard for DAS metadata: Latest advances within the Geo-INQUIRE project 

Javier Quinteros, Gilda Currenti, Michele Prestifilippo, John Clinton, Pascal Edme, Christopher Wollin, Diane Rivet, Shane Murphy, Jonathan Schaeffer, Helle Pedersen, and Angelo Strollo

In the last 5 years, the seismological community has experienced an impressive growth in the novel Distributed Acoustic Sensing (DAS) technique, in terms of both the number of experiments and the generated data volume. DAS experiments can generate data at a much finer resolution in space and time, than is seen with standard acquisition techniques. This creates challenges not only for data centres regarding the data management, but also for users that need to access and process this data. The current seismological standards for data and metadata formats, as well as community services specifications, are not capable of handling these datasets in an effective way - not unexpected considering that data volumes and ‘station’ numbers are orders of magnitude larger than typical broad-band experiments.

Within the context of the “Geosphere INfrastructures for QUestions into Integrated REsearch” project (Geo-INQUIRE, https://www.geo-inquire.eu/), we have defined a roadmap to advance towards community standards for some of these aspects. The main objective of improving the FAIRness of these datasets was separated in 3 steps. First, we defined how to archive downsampled versions of the datasets in standard community formats (i.e. miniseed and StationXML). Second, we wanted to support the definition (and foster the adoption) of a new metadata standard for DAS experiments based on the outcome of the DAS Research Coordination Network group (DAS-RCN), an initiative led by US researchers. And finally, we wanted to work on the definition of a data format capable of providing fast processing on the data centre side, as well as being able to provide the data to the user to be processed elsewhere.

We worked with 3 datasets from the Global DAS Month (February 2023), acquired by INGV, ETH and GFZ. These datasets had been published and made available in different non-standard formats. We used these experiments as test cases to later apply this workflow to the datasets generated by the Transnational Access Calls of this project at a variety of Research Infrastructures across Europe (e.g. at Etna, Bedretto, Ligurian, Madeira, Irpinia, and others).

Regarding the data volume and lack of standardisation, we have improved “dastools”, a software package developed at GFZ, to read DAS data in proprietary formats from different manufacturers and convert it to standard miniseed. Downsampling in time and space it provides a reduced version ready to be archived in seismological data centres.

Regarding metadata formats, we included in “dastools” the support for the DAS-RCN proposal, discussed and agreed within the community during the last 3 years. We can generate a first draft version of the metadata based on the information available in the raw data of the experiment. We also added a converter to StationXML (still beta) in order to support each step of the archival of a downsampled version of the DAS data.

We plan to work soon on the definition of a data format for this type of experiment as it is a key part of our project.

In parallel, we’ve just started the development of a Seedlink plugin (real-time transmission) to be deployed and tested at interrogators.

How to cite: Quinteros, J., Currenti, G., Prestifilippo, M., Clinton, J., Edme, P., Wollin, C., Rivet, D., Murphy, S., Schaeffer, J., Pedersen, H., and Strollo, A.: Towards a community standard for DAS metadata: Latest advances within the Geo-INQUIRE project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13131, https://doi.org/10.5194/egusphere-egu24-13131, 2024.

EGU24-13158 | Posters on site | SM3.4

The prospects of the Ukrainian seismic network:  Introducing a Low-Cost Seismic Network Initiative in Ukraine 

Tetiana Amashukeli, Luca Malatesta, Liudmyla Farfuliak, Oleksandr Haniiev, Bogdan Kuplovskyi, Vasyl Prokopyshyn, and Kostiantyn Petrenko

Seismic activity in Ukraine varies across regions with notable active zones in the Carpathians and Crimean-Black Sea segments. Southwest Ukraine is affected by the Vrancea seismic zone (Romania) and demands attention, alongside rare but potentially powerful seismic events in the stable Ukrainian shield. Mining and industrial activities also induce ground vibrations (Mw 2.5–4) in otherwise stable areas. Although major destructive earthquakes in Ukraine are infrequent, the cumulative impact of smaller seismic events can shape the geological and geophysical landscape of the region.

An effective seismic network is crucial for safety and research in Ukraine. Yet, the existing seismic network at the Institute of Geophysics of National Academy of Science of Ukraine faces numerous challenges, limiting its capacity to provide accurate seismic information. In addition, the Institute of Geophysics faces a demographic imbalance, with a critical shortage of younger scientists entering the field. This knowledge gap poses implications for the future of scientific research in Ukraine.

In response to these challenges, and considering the Russian invasion, we opted to distribute 28 budget Raspberry Shake Seismographs across schools and universities in Ukraine. Initially, these budget seismometers serve as a short-term solution for seismic data collection. Acknowledging the pros and cons of these stations in contrast to broadband sensors, it's noteworthy that their simplicity in installation, low cost, and near-real-time data transmission make them as a suitable option during the conflict in identifying and characterizing local and regional events.

This initiative also directly supports science teaching from middle to high school in Ukraine. Integrating seismometers into schools cultivates education based on real-time seismic records, familiarizing students with scientific data. The aim is to ignite students’ interest, nurturing a curiosity not only in seismology but also in science as a whole. This goal is accomplished not just through presentations and lessons but also through hands-on involvement, allowing students to take ownership by installing a seismometer and consistently monitoring its output. The analysis of time series seismic signals, regardless of their source – whether earthquakes or artificial noise – forms a fundamental component of any seismology-focused educational program. Currently, such initiatives are lacking in Ukrainian educational institutions.

Raspberry Shake 3D Seismographs have been installed at the Institute of Geophysics in Kyiv, Lviv Polytechnic National University, and Ivan Franko National University of Lviv. Two RS seismometers are at the Mykolaiv Water Hub to support the establishment of the Mykolaiv Innovation Lab in south Ukraine. In November 2023, educational materials for seismology at middle and high school levels in Ukraine were created with the assistance of the GFZ German Research Centre for Geosciences. This approach not only will help students develop practical skills but also provides a starting point for exploring numerical methods and coding at the university level.

How to cite: Amashukeli, T., Malatesta, L., Farfuliak, L., Haniiev, O., Kuplovskyi, B., Prokopyshyn, V., and Petrenko, K.: The prospects of the Ukrainian seismic network:  Introducing a Low-Cost Seismic Network Initiative in Ukraine, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13158, https://doi.org/10.5194/egusphere-egu24-13158, 2024.

EGU24-14842 | ECS | Posters on site | SM3.4

Development of the new seismic network of the IGS, Armenia 

Gevorg Babayan, Elya Sahakyan, Hektor Babayan, Mikayel Gevorgyan, and Lilit Sargsyan

The Republic of Armenia and the neighboring areas are located in the central part of theArabia-Eurasia collision zone, which is characterized by active seismicity.Over the past decade, the Institute of Geological Sciences (IGS) of NAS RA has developed an advanced and dense seismic network.To develop the local seismic network, the Institute of Geological Sciences in collaboration with the National Taiwan University and Institute of Earth Sciences, Academia Sinica (Taiwan) established 11 seismic stations with broadband seismometers and 6 cGPS (continuous) stations. Data from the existing seismic stations were collected, archived and treated, and main earthquake parameters were determined; the conducted works included catalogue maintenance, recalculation of the main earthquake data, calculation of seismic tomography with the input of recalculated and updated data, and adjustment of the three-dimensional (3D) velocity model for the area of the RA.

Starting from 2017, the Institute of Geological Sciences has participated in two partner ISTC projects: A-2334 Project (Transect) “The Uplift and Seismic Structure of the Greater Caucasus” and KR-2452 Project (SNECCA) “Seismic Network Expansion in the Caucasus and Central Asia” with support from the U.S. Department of Energy.  In the framework of the indicated projects, 32 seismic stations with broadband seismometers were established along with 8 seismic borehole stations with fully broadband seismometers (Real Time) and 8 strong motion sensors. These two projects are implemented through the Seismic Targeted Initiative of the International Science and Technology Center and the Science and Technology Center in Ukraine.The records collected from the eight (8) already operational permanent seismic stations of the indicated network are in real-time mode sent to the International Seismology Center of the IRIS (Incorporated Research Institutions for Seismology). To download and archive the database of seismic stations, a new computer server was acquired under the project, and all required configurations were made to provide for its uninterrupted operation. Seiscomp software set is applied to produce automatic solutions for earthquakes recorded within the region. Adjustments and recalculations of the automatic earthquake solutions are implemented to produce the resulting main earthquake parameters with uncertainties reduced to the rate as low as possible. The collected data from all existing stations are widely used to determine and to re-estimate the main parameters of earthquake occurring in Armenia and in surrounding territories. These data are included in local bulletins and catalogues.For strong motions, the on-going research includes processing of design accelerograms, preparation and analysis of hazard response spectra (RS), selection of the actually recorded (real) acceleration time-history, and spectral matching of the time-history to the hazard response spectrum with application of Seismosoft (Earthquake Engineering Software Solutions, SeismoMatch, SeismoSignal, SeismoSelect, SeismoSpec) software set.All the results obtained from the data seismic stations mentioned above are used for the purposes of scientific research and are summarized in articles.

How to cite: Babayan, G., Sahakyan, E., Babayan, H., Gevorgyan, M., and Sargsyan, L.: Development of the new seismic network of the IGS, Armenia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14842, https://doi.org/10.5194/egusphere-egu24-14842, 2024.

EGU24-17386 | Posters on site | SM3.4

Güralp Data Centre Software for Easy Mass Data Acquisition and Station Metadata Monitoring 

Neil Watkiss, Philip Hill, Ella Price, Connor Foster, Aaron Clark, Federica Restelli, and James Lindsey

Güralp Data Centre (GDC) interface offers ‘one click’ tools to configure instruments to stream data to a central (typically cloud based) server where it is saved in miniSEED in configurable folder structures. This application is particularly important for operators dealing with large volumes of seismic waveform data from regional/national networks.

Additionally, the data can be transmitted to downstream processors such as Earthworm or SeisComP for more advanced seismic monitoring and data analysis. GDC has a simple interface to set up and monitor the operation of the network and is easy to implement into existing systems and networks with minimal configuration as industry standard protocols are employed throughout.

An integrated VPN/Tunnel circumvents Network Address Translations (NATs) present in internet modems and ADSL connections, providing the facility to remotely update digitizer firmware and upload configuration files to multiple units simultaneously.

Long term latency monitoring, network outages and bandwidth usage are captured and displayed in a number of applets that further simplify maintenance of large networks. The GDC dashboard allows network managers to view data integrity over time so that latency performance can be monitored.

Trigger events from instruments can be recorded and displayed on a map as part of a range of features dedicated to EEW implementations. This information is conveyed using the open Common Alert Protocol (CAP). The CAP messages are created by individual station or sub-network triggers and contain important parameters such the on-site recorded PGA, PGV and PGD, providing the lowest possible latency for network early warning.

How to cite: Watkiss, N., Hill, P., Price, E., Foster, C., Clark, A., Restelli, F., and Lindsey, J.: Güralp Data Centre Software for Easy Mass Data Acquisition and Station Metadata Monitoring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17386, https://doi.org/10.5194/egusphere-egu24-17386, 2024.

EGU24-17749 | ECS | Posters on site | SM3.4

The Italian multiparametric network for detection and monitoring of earthquake-related crustal fluids alterations 

Elisa Ferrari, Marco Massa, Andrea Luca Rizzo, Sara Lovati, and Federica Di Michele

Seismic signals coupling to physical (e.g., temperature, pH, Eh, electrical conductivity, flow rate) and geochemical changes in ground and spring waters as well as variations in soil flux regimes (e.g., CO2, CH4, radon) represent a valuable tool to better understand the interaction between tectonics and crustal fluids dynamics (e.g., Italiano et al., 2001, 2004; Wang and Manga, 2021; Chiodini et al., 2020; Gori and Barberio, 2022 and references therein). Pre-, co- and post-seismic modifications are markers of the local tectonic stress acting in the crust and are extremely site-specific due to the local geological and lithological features besides being simultaneously influenced by other environmental conditions (e.g., meteorological and climatic). Therefore, local continuous monitoring of all the involved parameters is needed to delineate crustal fluids response to seismicity site by site.
Multiparametric stations have been set up in Italy starting from the end of 2021, placed on the major seismogenic structures, and widely distributed among the Alps, Apennines and Pianura Padana. They are equipped with: (i) sensors installed in water wells measuring water level, temperature, and electrical conductivity; (ii) meteorological sensors measuring atmospheric pressure, temperature, rain, humidity, wind speed and direction; (iii) seismic sensors providing accelerometric and velocimetric datasets; (iv) radon sensors; (v) CO2 soil flux chamber. 
Data are transmitted in near real-time to an ad hoc developed dynamic relational database (MUDA-geophysical and geochemical MUltiparametric DAtabase) and displayed in a dedicated website (http://muda.mi.ingv.it). The built-in philosophy is to easily compare distinct parameters from the various sensors and possibly recognize cause-effect relationships among them. 
To our knowledge, our new multiparametric network is the first developed in Italy showing all these features.
A statistic approach is also applied to the time-series to investigate intra-annual and inter-annual trends and correlations among different parameters. Alternative methods (e.g., signal decomposition, spike detection) will be presented and discussed. 

References
-Chiodini G., Cardellini C., Di Luccio F., Selva J., Frondini F., Caliro S., Rosiello A., Beddini G., Ventura G., 2020: Correlation between tectonic CO2 Earth degassing and seismicity is revealed by a 10-year record in the Apennines, Italy. Science Advances, https://www.science.org/doi/10.1126/sciadv.abc2938
-Gori F., Barberio M.D., 2022: Hydrogeochemical changes before and during the 2019 Benevento seismic swarm in central-southern Italy. Journal of Hydrology, 604:127250
-Italiano F., Martinelli G., Nuccio P.M., 2001: Anomalies of mantle-derived helium during the 1997 – 1998 seismic swarm of Umbria-Marche, Italy. Geophysical Research Letters, 28(5):839-842
-Italiano F., Martinelli G., Rizzo A., 2004: Geochemical evidence of seismogenic-induced anomalies in the dissolved gases of thermal waters: A case study of Umbria (Central Apennines, Italy) both during and after the 1997–1998 seismic swarm. Geochemistry, Geophysics, Geosystems, 5:11, doi:10.1029/2004GC000720
-Wang C.-Y., Manga M., 2021: Water and Earthquakes. Lecture Notes in Earth System Sciences, Springer Cham, 387 pp., https://doi.org/10.1007/978-3-030-64308-9 

How to cite: Ferrari, E., Massa, M., Rizzo, A. L., Lovati, S., and Di Michele, F.: The Italian multiparametric network for detection and monitoring of earthquake-related crustal fluids alterations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17749, https://doi.org/10.5194/egusphere-egu24-17749, 2024.

EGU24-17890 | Posters on site | SM3.4

The mobile Finnish Seismic Instrument Pool 

Roméo Courbis, Gregor Hillers, Emilia Koivisto, Päivi Haapanala, Ilmo Kukkonen, Yinshuai Ding, Thomas Fordell, Suvi Heinonen, Niina Junno, Anssi Juntunen, Kari Komminaho, Elena Kozlovskaya, Jussi Leveinen, Kari Moisio, Jyri Näränen, Tahvo Oksanen, Pietari Skyttä, Eija Tanskanen, and Timo Tiira

We report on establishing the Finnish mobile seismic instrument pool that is owned and operated by seven Finnish academic and research institutions. The pool infrastructure is funded by the Research Council of Finland, through the FLEX-EPOS project and under the FIN-EPOS umbrella. It is financing the build-up stage and started in 2021 with an end in 2024. By then the seismic instrumentation is anticipated to include 46 Güralp broadband seismometers, 5 Güralp accelerometers, and 1197 and 70 Geospace and SmartSolo self-contained geophone units, respectively. It is making this probably the largest coherent mobile seismic instrument pool in Europe in the public sector. The pool supports domestic and international collaborative projects of temporary deployments to enhance data-driven subsurface and environmental applications. Those deployments are for active or passive experiments and can last a few days up to a few years. The acquisition of such pool is motivated and facilitated by the advent of efficient data storage and transmission and powerful computing systems; progress in the understanding of the seismic wavefield coupled with the development of new types of analysis techniques and algorithms; and the manufacturing of sensitive, affordable data-dense sensor systems. Despite these game-changing and promising developments, the access to many seismic sensors for large-N deployments is not pervasive. Even in developed countries, it is challenging for a single institution to acquire and maintain a sufficiently large mobile pool of instruments and ensure sustainable data production and distribution. Our report on the equipment, facilities, ownership, and governance structure, project management, and data systems is essential background information for the access to and utilization of the pool instruments, and the interaction with the support community. A discussion about best practices for establishing and maintaining a mobile pool infrastructure can benefit from our experience of building such an extensive public seismic infrastructure from the ground up, and it provides relevant information for communities considering similar research infrastructure projects. Among the many challenges and opportunities associated with establishing effective pool management and operations, we highlight the lack of a coherent community protocol to store, find, disseminate, and analyze the associated large datasets. The Finnish mobile seismic instrument pool actively engages with ORFEUS/EIDA and the Geo-INQUIRE project to contribute to developing community solutions for data discovery and accessibility.

How to cite: Courbis, R., Hillers, G., Koivisto, E., Haapanala, P., Kukkonen, I., Ding, Y., Fordell, T., Heinonen, S., Junno, N., Juntunen, A., Komminaho, K., Kozlovskaya, E., Leveinen, J., Moisio, K., Näränen, J., Oksanen, T., Skyttä, P., Tanskanen, E., and Tiira, T.: The mobile Finnish Seismic Instrument Pool, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17890, https://doi.org/10.5194/egusphere-egu24-17890, 2024.

EGU24-24 | Orals | NP4.1

The fractional Sinusoidal wavefront Model (fSwp) for time series displaying persistent stationary cycles 

Gael Kermarrec, Federico Maddanu, Anna Klos, and Tommaso Proietti

In the analysis of sub-annual climatological or geodetic time series such as tide gauges, precipitable water vapor, or GNSS vertical displacements time series but also temperatures or gases concentrations, seasonal cycles are often found to have a time-varying amplitude and phase.

These time series are usually modelled with a deterministic approach that includes trend, annual, and semi-annual periodic components having constant amplitude and phase-lag. This approach can potentially lead to inadequate interpretations, such as an overestimation of Global Navigation Satellite System (GNSS) station velocity, up to masking important geophysical phenomena that are related to the amplitude variability and are important for deriving trustworthy interpretation for climate change assessment.

We address that challenge by proposing a novel linear additive model called the fractional Sinusoidal Waveform process (fSWp), accounting for possible nonstationary cyclical long memory, a stochastic trend that can evolve over time and an additional serially correlated noise capturing the short-term variability. The model has a state space representation and makes use of the Kalman filter (KF). Suitable enhancements of the basic methodology enable handling data gaps, outliers, and offsets. We demonstrate our method using various climatological and geodetic time series to illustrate its potential to capture the time-varying stochastic seasonal signals.

How to cite: Kermarrec, G., Maddanu, F., Klos, A., and Proietti, T.: The fractional Sinusoidal wavefront Model (fSwp) for time series displaying persistent stationary cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-24, https://doi.org/10.5194/egusphere-egu24-24, 2024.

On some maps of the first military survey of the Habsburg Empire, the upper direction of the sections does not face the cartographic north, but makes an angle of about 15° with it. This may be due to the fact that the sections were subsequently rotated to the magnetic north of the time. Basically, neither their projection nor their projection origin is known yet.

In my research, I am dealing with maps of Inner Austria, the Principality of Transylvania and Galicia (nowadays Poland and Ukraine), and I am trying to determine their projection origin. For this purpose, it is assumed, based on the archival documentation of the survey, that these are Cassini projection maps. My hypothesis is that they are Graz, Cluj Napoca or Alba Julia and Lviv. I also consider the position of Vienna in each case, since it was the main centre of the survey.

The angle of rotation was taken in part from the gufm1 historical magnetic model back to 1590 for the assumed starting points and year of mapping. In addition, as a theoretical case, I calculated the rotation angle of the map sections using coordinate geometry. I then calculated the longitude of the projection starting point for each case using univariate minimization. Since the method is invariant to latitude, it can only be determined from archival data.

Based on these, the starting point for Inner Austria from the rotation of the map was Vienna, which is not excluded by the archival sources, and since the baseline through Graz also started from there, it is partly logical. The map rotation for Galicia and Transylvania also confirmed the starting point of the hypothesis.  Since both Alba Julia and Cluj Napoca lie at about the same longitude, the method cannot make a difference there; and the archival data did not provide enough evidence. In comparison, the magnetic declination rotations yielded differences of about 1°, which may be due to an error in the magnetic model.

On this basis, I have given the assumed projections of the three maps with projection starting points, and developed a method for determining the projection starting points of the other rotated grid maps. The results suggest that there is a very high probability that the section network was rotated in the magnetic north direction, and thus provide a way to refine the magnetic declination data at that time.

With this method I managed to give new indirekt magnetic declinations data from Central-East Europe, which can help to improve the historical magnetic field models. The main reason for this is that we don’t have any measurement from that region.

Furthermore the difference beetwen the angle of the section north and the declination data from gufm1 always 0.8-1°. Maybe there are systematical data error at that region.

Supported by the ÚNKP-23-6 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.

How to cite: Koszta, B. and Timár, G.: A possible cartographical data source for historical magnetic field improvement: The direction of the section north of the Habsburg first military survey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-582, https://doi.org/10.5194/egusphere-egu24-582, 2024.

EGU24-1988 | ECS | Posters on site | NP4.1

Predictive ability assessment of Bayesian Causal Reasoning (BCR) on runoff temporal series 

Santiago Zazo, José Luis Molina, Carmen Patino-Alonso, and Fernando Espejo

The alteration of traditional hydrological patterns due to global warming is leading to a modification of the hydrological cycle. This situation draws a complex scenario for the sustainable management of water resources. However, this issue offers a challenge for the development of innovative approaches that allow an in-depth capturing the logical temporal-dependence structure of these modifications to advance sustainable management of water resources, mainly through the reliable predictive models. In this context, Bayesian Causality (BC), addressed through Causal Reasoning (CR) and supported by a Bayesian Networks (BNs), called Bayesian Causal Reasoning (BCR) is a novel hydrological research area that can help identify those temporal interactions efficiently.

This contribution aims to assesses the BCR ability to discover the logical and non-trivial temporal-dependence structure of the hydrological series, as well as its predictability. For this, a BN that conceptually synthesizes the time series is defined, and where the conditional probability is propagated over the time throughout the BN through an innovative Dependence Mitigation Graph. This is done by coupling among an autoregressive parametric approach and causal model. The analytical ability of the BCR highlighted the logical temporal structure, latent in the time series, which defines the general behavior of the runoff. This logical structure allowed to quantify, through a dependence matrix which summarizes the strength of the temporal dependencies, the two temporal fractions that compose the runoff: one due to time (Temporally Conditioned Runoff) and one not (Temporally Non-conditioned Runoff). Based on this temporal conditionality, a predictive model is implemented for each temporal fraction, and its reliability is assessed from a double probabilistic and metrological perspective.

This methodological framework is applied to two Spanish unregulated sub-basins; Voltoya river belongs to Duero River Basin, and Mijares river, in the Jucar River Basin. Both cases with a clearly opposite temporal behavior, Voltoya independent and Mijares dependent, and with increasingly more problems associated with droughts.

The findings of this study may have important implications over the knowledge of temporal behavior of water resources of river basin and their adaptation. In addition, TCR and TNCR predictive models would allow advances in the optimal dimensioning of storage infrastructures (reservoirs), with relevant substantial economic/environmental savings. Also, a more sustainable management of river basins through more reliable control reservoirs’ operation is expected to be achieved. Finally, these results open new possibilities for developing predictive hydrological models within a BCR framework.

How to cite: Zazo, S., Molina, J. L., Patino-Alonso, C., and Espejo, F.: Predictive ability assessment of Bayesian Causal Reasoning (BCR) on runoff temporal series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1988, https://doi.org/10.5194/egusphere-egu24-1988, 2024.

EGU24-3857 | ECS | Posters on site | NP4.1 | Highlight

Spatial-Temporal Analysis of Forest Mortality 

Sara Alibakhshi

Climate-induced forest mortality poses an increasing threat worldwide, which calls for developing robust approaches to generate early warning signals of upcoming forest state change. This research explores the potential of satellite imagery, utilizing advanced spatio-temporal indicators and methodologies, to assess the state of forests preceding mortality events. Traditional approaches, such as techniques based on temporal analyses, are impacted by limitations related to window size selection and detrending methods, potentially leading to false alarms. To tackle these challenges, our study introduces two new approaches, namely the Spatial-Temporal Moran (STM) and Spatial-Temporal Geary (STG) approaches, both focusing on local spatial autocorrelation measures. These approaches can effectively address the shortcomings inherent in traditional methods. The research findings were assessed across three study sites within California national parks, and Kendall's tau was employed to quantify the significance of false and positive alarms. To facilitate the measurement of ecosystem state change, trend estimation, and identification of early warning signals, this study also provides "stew" R package. The implications of this research extend to various groups, such as ecologists, conservation practitioners, and policymakers, providing them with the means to address emerging environmental challenges in global forest ecosystems.

How to cite: Alibakhshi, S.: Spatial-Temporal Analysis of Forest Mortality, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3857, https://doi.org/10.5194/egusphere-egu24-3857, 2024.

Iram Parvez1, Massimiliano Cannata2, Giorgio Boni1, Rossella Bovolenta1 ,Eva Riccomagno3 , Bianca Federici1

1 Department of Civil, Chemical and Environmental Engineering (DICCA), Università degli Studi di Genova, Via Montallegro 1, 16145 Genoa, Italy (iram.parvez@edu.unige.it,bianca.federici@unige.it, giorgio.boni@unige.it, rossella.bovolenta@unige.it).

2 Institute of Earth Sciences (IST), Department for Environment Constructions and Design (DACD), University of Applied Sciences and Arts of Southern Switzerland (SUPSI), CH-6952 Canobbio, Switzerland(massimiliano.cannata@supsi.ch).

3 Department of Mathematics, Università degli Studi di Genova, Via Dodecaneso 35, 16146 Genova, Italy(riccomag@dima.unige.it).

The deployment of hydrometeorological sensors significantly contributes to generating real-time big data. The quality and reliability of large datasets pose considerable challenges, as flawed analyses and decision-making processes can result. This research aims to address the issue of anomaly detection in real-time data by exploring machine learning models. Time-series data is collected from IstSOS - Sensor Observation Service, an open-source software that stores, collects and disseminates sensor data. The methodology consists of Gated Recurrent Units based on recurrent neural networks, along with corresponding prediction intervals, applied both to individual sensors and collectively across all temperature sensors within the Ticino region of Switzerland. Additionally, non-parametric methods like Bootstrap and Mean absolute deviation are employed instead of standard prediction intervals to tackle the non-normality of the data. The results indicate that Gated Recurrent Units based on recurrent neural networks, coupled with non-parametric forecast intervals, perform well in identifying erroneous data points. The application of the model on multivariate time series-sensor data establishes a pattern or baseline of normal behavior for the area (Ticino). When a new sensor is installed in the same region, the recognized pattern is used as a reference to identify outliers in the data gathered from the new sensor.

How to cite: Parvez, I.: Exploring Machine Learning Models to Detect Outliers in HydroMet Sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4280, https://doi.org/10.5194/egusphere-egu24-4280, 2024.

EGU24-5268 | ECS | Orals | NP4.1

Unveiling Geological Patterns: Bayesian Exploration of Zircon-Derived Time Series Data 

Hang Qian, Meng Tian, and Nan Zhang

For its immunity to post-formation geological modifications, zircon is widely utilized as chronological time capsule and provides critical time series data potential to unravel key events in Earth’s geological history, such as supercontinent cycles. Fourier analysis, which assumes stationary periodicity, has been applied to zircon-derived time series data to find the cyclicity of supercontinents, and wavelet analysis, which assumes non-stationary periodicity, corroborates the results of Fourier Analysis in addition to detecting finer-scale signals. Nonetheless, both methods still prognostically assume periodicity in the zircon-derived time-domain data. To stay away from the periodicity assumption and extract more objective information from zircon data, we opt for a Bayesian approach and treat zircon preservation as a composite stochastic process where the number of preserved zircon grains per magmatic event obeys logarithmic series distribution and the number of magmatic events during a geological time interval obeys Poisson distribution. An analytical solution was found to allow us to efficiently invert for the number and distribution(s) of changepoints hidden in the globally compiled zircon data, as well as for the zircon preservation potential (encoded as a model parameter) between two neighboring changepoints. If the distributions of changepoints temporally overlap with those of known supercontinents, then our results serve as an independent, mathematically robust test of the cyclicity of supercontinents. Moreover, our statistical approach inherently provides a sensitivity parameter the tuning of which allows to probe changepoints at various temporal resolution. The constructed Bayesian framework is thus of significant potential to detect other types of trend swings in Earth’s history, such as shift of geodynamic regimes, moving beyond cyclicity detection which limits the application of conventional Fourier/Wavelet analysis.

How to cite: Qian, H., Tian, M., and Zhang, N.: Unveiling Geological Patterns: Bayesian Exploration of Zircon-Derived Time Series Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5268, https://doi.org/10.5194/egusphere-egu24-5268, 2024.

Semi-enclosed freshwater and brackish ecosystems, characterised by restricted water outflow and prolonged residence times, often accumulate nutrients, influencing their productivity and ecological dynamics. These ecosystems exhibit significant variations in bio-physical-chemical attributes, ecological importance, and susceptibility to human impacts. Untangling the complexities of their interactions remains challenging, necessitating a deeper understanding of effective management strategies adapted to their vulnerabilities. This research focuses on the bio-physical aspects, investigating the differential effects of spring and summer light on phytoplankton communities in semi-enclosed freshwater and brackish aquatic ecosystems.

Through extensive field sampling and comprehensive environmental parameter analysis, we explore how phytoplankton respond to varying light conditions in these distinct environments. Sampling campaigns were conducted at Müggelsee, a freshwater lake on Berlin's eastern edge, and Barther Bodden, a coastal lagoon northeast of Rostock on the German Baltic Sea coast, during the springs and summers of 2022 and 2023, respectively. Our analysis integrates environmental factors such as surface light intensity, diffuse attenuation coefficients, nutrient availability, water column dynamics, meteorological data, Chlorophyll-a concentration, and phytoplankton communities. Sampling encompassed multiple depths at continuous intervals lasting three days.

Preliminary findings underscore significant differences in seasonal light availability, with summer exhibiting extended periods of substantial light penetration. These variations seem to impact phytoplankton abundance and diversity uniquely in each ecosystem. While ongoing analyses are underway, early indications suggest distinct phytoplankton responses in terms of species composition and community structure, influenced by the changing light levels. In 2022 the clear water phase during spring indicated that bloom events have occurred under ice cover much earlier than spring, while in the summer there were weak and short-lived blooms of cyanobacteria. The relationship between nutrient availability and phytoplankton dynamics, however, remains uncertain according to our data.

This ongoing study contributes to understanding the role of light as a primary driver shaping phytoplankton community structures and dynamics in these environments.  Our research findings offer insights for refining predictive models, aiding in ecosystem-specific eutrophication management strategies, and supporting monitoring efforts of Harmful Algal Blooms.

How to cite: Kaharuddin, A. and Kaligatla, R.: Comparative Study of Spring and Summer Light Effects on Phytoplankton Communities in Semi-Enclosed Fresh- and Brackish Aquatic Ecosystems., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5733, https://doi.org/10.5194/egusphere-egu24-5733, 2024.

EGU24-6065 | ECS | Orals | NP4.1

Magnetospheric time history:  How much do we need for forecasting? 

Kendra R. Gilmore, Sarah N. Bentley, and Andy W. Smith

Forecasting the aurora and its location accurately is important to mitigate any potential harm to vital infrastructure like communications and electricity grid networks. Current auroral prediction models rely on our understanding of the interaction between the magnetosphere and the solar wind or geomagnetic indices. Both approaches do well in predicting but have limitations concerning forecasting (geomagnetic indices-based model) or because of the underlying assumptions driving the model (due to a simplification of the complex interaction). By applying machine learning algorithms to this problem, gaps in our understanding can be identified, investigated, and closed. Finding the important time scales for driving empirical models provides the necessary basis for our long-term goal of predicting the aurora using machine learning.

Periodicities of the Earth’s magnetic field have been extensively studied on a global scale or in regional case studies. Using a suite of different time series analysis techniques including frequency analysis and investigation of long-scale changes of the median/ mean, we examine the dominant periodicities of ground magnetic field measurements at selected locations. A selected number of stations from the SuperMAG network (Gjerloev, 2012), which is a global network of magnetometer stations across the world, are the focus of this investigation.

The periodicities retrieved from the different magnetic field components are compared to each other as well as to other locations. In the context of auroral predictions, an analysis of the dominating periodicities in the auroral boundary data derived from the IMAGE satellite (Chisham et al., 2022) provides a counterpart to the magnetic field periodicities.

Ultimately, we can constrain the length of time history sensible for forecasting.

How to cite: Gilmore, K. R., Bentley, S. N., and Smith, A. W.: Magnetospheric time history:  How much do we need for forecasting?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6065, https://doi.org/10.5194/egusphere-egu24-6065, 2024.

EGU24-6151 | Posters on site | NP4.1

Using information-theory metrics to detect regime changes in dynamical systems 

Javier Amezcua and Nachiketa Chakraborty

Dynamical systems can display a range of dynamical regimes (e.g. attraction to, fixed points, limit cycles, intermittency, chaotic behaviour) depending on the values of parameters in the system. In this work we demonstrate how non-parametric entropy estimation codes (in particular NPEET) based on the Kraskov method can be applied to find regime transitions in a 3D chaotic model (the Lorenz 1963 system) when varying the values of the parameters. These infromation-theory-based methods are simpler and cheaper to apply than more traditional metrics from dynamical systems (e.g. computation of Lyapunov exponents). The non-parametric nature of the method allows for handling long time series without a prohibitive computational burden. 

How to cite: Amezcua, J. and Chakraborty, N.: Using information-theory metrics to detect regime changes in dynamical systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6151, https://doi.org/10.5194/egusphere-egu24-6151, 2024.

EGU24-9367 | ECS | Orals | NP4.1

Fractal complexity evaluation of meteorological droughts over three Indian subdivisions using visibility Graphs 

Susan Mariam Rajesh, Muraleekrishnan Bahuleyan, Arathy Nair GR, and Adarsh Sankaran

Evaluation of scaling properties and fractal formalisms is one of the potential approaches for modelling complex series. Understanding the complexity and fractal characterization of drought index time series is essential for better preparedness against drought disasters. This study presents a novel visibility graph-based evaluation of fractal characterization of droughts of three meteorological subdivisions of India. In this method, the horizontal visibility graph (HVG) and Upside-down visibility graph (UDVG) are used for evaluating the network properties for different standardized precipitation index (SPI) series of 3, 6 and 12 month time scales representing short, medium and long term droughts. The relative magnitude of fractal estimates is controlled by the drought characteristics of wet-dry transitions. The estimates of degree distribution clearly deciphered the self-similar properties of droughts of all the subdivisions. For an insightful depiction of drought dynamics, the fractal exponents and spectrum are evaluated by the concurrent application of Sand Box Method (SBM) and Chhabra and Jenson Method (CJM). The analysis was performed for overall series along with the pre- and post-1976-77 Global climate shift scenarios. The complexity is more evident in short term drought series and UDVG formulations implied higher fractal exponents for different moment orders irrespective of drought type and locations considered in this study. Useful insights on the relationship between complex network and fractality are evolved from the study, which may help in improved drought forecasting. The visibility graph based fractality estimation evaluation is efficient in capturing drought and it has vast potential in the drought predictions in a changing environment.

Keywords:  Drought, Fractal, SPI, Visibility Graph

How to cite: Rajesh, S. M., Bahuleyan, M., Nair GR, A., and Sankaran, A.: Fractal complexity evaluation of meteorological droughts over three Indian subdivisions using visibility Graphs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9367, https://doi.org/10.5194/egusphere-egu24-9367, 2024.

EGU24-9537 | Posters on site | NP4.1

Wavelet-Induced Mode Extraction procedure: Application to climatic data 

Elise Faulx, Xavier Fettweis, Georges Mabille, and Samuel Nicolay

The Wavelet-Induced Mode Extraction procedure (WIME) [2] was developed drawing inspiration from Empirical Mode Decomposition. The concept involves decomposing the signal into modes, each presenting a characteristic frequency, using continuous wavelet transform. This method has yielded intriguing results in climatology [3,4]. However, the initial algorithm did not account for the potential existence of slight frequency fluctuations within a mode, which could impact the reconstruction of the original signal [4]. The new version (https://atoms.scilab.org/toolboxes/toolbox_WIME/0.1.0) now allows for the evolution of a mode in the space-frequency half-plane, thus considering the frequency evolution of a mode [2]. A natural application of this tool is in the analysis of Milankovitch cycles, where subtle changes have been observed throughout history. The method also refines the study of solar activity, highlighting the role of the "Solar Flip-Flop." Additionally, the examination of temperature time series confirms the existence of cycles around 2.5 years. It is now possible to attempt to correlate solar activity with this observed temperature cycle, as seen in speleothem records [1].

[1] Allan, M., Deliège, A., Verheyden, S., Nicolay S. and Fagel, N. Evidence for solar influence in a Holocene speleothem record, Quaternary Science Reviews, 2018.
[2] Deliège, A. and Nicolay, S., Extracting oscillating components from nonstationary time series: A wavelet-induced method, Physical Review. E, 2017.
[3] Nicolay, S., Mabille, G., Fettweis, X. and Erpicum, M., A statistical validation for the cycles found in air temperature data using a Morlet wavelet-based method, Nonlinear Processes in Geophysics, 2010.
[4] Nicolay, S., Mabille, G., Fettweis, X. and Erpicum, M., 30 and 43 months period cycles found in air temperature time series using the Morlet wavelet, Climate Dynamics, 2009.

How to cite: Faulx, E., Fettweis, X., Mabille, G., and Nicolay, S.: Wavelet-Induced Mode Extraction procedure: Application to climatic data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9537, https://doi.org/10.5194/egusphere-egu24-9537, 2024.

EGU24-10258 | Orals | NP4.1

New concepts on quantifying event data 

Norbert Marwan and Tobias Braun

A wide range of geoprocesses manifest as observable events in a variety of contexts, including shifts in palaeoclimate regimes, evolutionary milestones, tectonic activities, and more. Many prominent research questions, such as synchronisation analysis or power spectrum estimation of discrete data, pose considerable challenges to linear tools. We present recent advances using a specific similarity measure for discrete data and the method of recurrence plots for different applications in the field of highly discrete event data. We illustrate their potential for palaeoclimate studies, particularly in detecting synchronisation between signals of discrete extreme events and continuous signals, estimating power spectra of spiky signals, and analysing data with irregular sampling.

How to cite: Marwan, N. and Braun, T.: New concepts on quantifying event data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10258, https://doi.org/10.5194/egusphere-egu24-10258, 2024.

EGU24-10415 | ECS | Orals | NP4.1

Application of Transfer Learning techniques in one day ahead PV production prediction 

Marek Lóderer, Michal Sandanus, Peter Pavlík, and Viera Rozinajová

Nowadays photovoltaic panels are becoming more affordable, efficient, and popular due to their low carbon footprint. PV panels can be installed in many places providing green energy to the local grid reducing energy cost and transmission losses. Since the PV production is highly dependent on the weather conditions, it is extremely important to estimate expected output in advance in order to maintain energy balance in the grid and provide enough time to schedule load distribution. The PV production output can be calculated by various statistical and machine learning prediction methods. In general, the more data available, the more precise predictions can be produced. This poses a problem for recently installed PV panels for which not enough data has been collected or the collected data are incomplete. 

A possible solution to the problem can be the application of an approach called Transfer Learning which has the inherent ability to effectively deal with missing or insufficient amounts of data. Basically, Transfer Learning is a machine learning approach which offers the capability of transferring knowledge acquired from the source domain (in our case a PV panel with a large amount of historical data) to different target domains (PV panels with very little collected historical data) to resolve related problems (provide reliable PV production predictions). 

In our study, we investigate the application, benefits and drawbacks of Transfer Learning for one day ahead PV production prediction. The model used in the study is based on complex neural network architecture, feature engineering and data selection. Moreover, we focus on the exploration of multiple approaches of adjusting weights in the target model retraining process which affect the minimum amount of training data required, final prediction accuracy and model’s overall robustness. Our models use historical meteorological forecasts from Deutscher Wetterdienst (DWD) and photovoltaic measurements from the project PVOutput which collects data from installed solar systems across the globe. Evaluation is performed on more than 100 installed PV panels in Central Europe.

How to cite: Lóderer, M., Sandanus, M., Pavlík, P., and Rozinajová, V.: Application of Transfer Learning techniques in one day ahead PV production prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10415, https://doi.org/10.5194/egusphere-egu24-10415, 2024.

EGU24-11897 | Posters on site | NP4.1

Results of joint processing of magnetic observatory data of international Intermagnet network in a unified coordinate system 

Beibit Zhumabayev, Ivan Vassilyev, Zhasulan Mendakulov, Inna Fedulina, and Vitaliy Kapytin

In each magnetic observatory, the magnetic field is registered in local Cartesian coordinate systems associated with the geographic coordinates of the locations of these observatories. To observe extraterrestrial magnetic field sources, such as the interplanetary magnetic field or magnetic clouds, a method of joint processing of data from magnetic observatories of the international Intermagnet network was implemented. In this method, the constant component is removed from the observation results of individual observatories, their measurement data is converted into the ecliptic coordinate system, and the results obtained from all observatories are averaged after the coordinate transformation.

The first data on joint processing of measurement results from the international network of Intermagnet magnetic observatories in the period before the onset of magnetic storms of various types, during these storms and after their end are presented. There is a significant improvement in the signal-to-noise ratio after combining the measurement results from all observatories, which makes it possible to isolate weaker external magnetic fields. A change in the shape of magnetic field variations is shown, which can provide new knowledge about the mechanism of development of magnetic storms.

How to cite: Zhumabayev, B., Vassilyev, I., Mendakulov, Z., Fedulina, I., and Kapytin, V.: Results of joint processing of magnetic observatory data of international Intermagnet network in a unified coordinate system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11897, https://doi.org/10.5194/egusphere-egu24-11897, 2024.

We introduce the CLEAN algorithm to identify narrowband Ultra Low Frequency (ULF) Pc5 plasma waves in Earth’s magnetosphere. The CLEAN method was first used for constructing 2D images in astronomical radio interferometry but has since been applied to a huge range of areas including adaptation for time series analysis. The algorithm performs a nonlinear deconvolution in the frequency domain (equivalent to a least-squares in the time domain) allowing for identification of multiple individual wave spectral peaks within the same power spectral density. The CLEAN method also produces real amplitudes instead of model fits to the peaks and retains phase information. We applied the method to GOES magnetometer data spanning 30 years to study the distribution of narrowband Pc5 ULF waves at geosynchronous orbit. We found close to 30,0000 wave events in each of the vector magnetic field components in field-aligned coordinates. We discuss wave occurrence and amplitudes distributed in local time and frequency. The distribution of the waves under different solar wind conditions are also presented. With some precautions, which are applicable to other event identification methods, the CLEAN technique can be utilized to detect wave events and its harmonics in the magnetosphere and beyond. We also discuss limitations of the method mainly the detection of unrealistic peaks due to aliasing and Gibbs phenomena.

How to cite: Inceoglu, F. and Loto'aniu, P.: Using the CLEAN Algorithm to Determine the Distribution of Ultra Low Frequency Waves at Geostationary Orbit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12928, https://doi.org/10.5194/egusphere-egu24-12928, 2024.

EGU24-12938 | Posters on site | NP4.1

Applying Multifractal Theory and Statistical Techniques for High Energy Volcanic Explosion Detection and Seismic Activity Monitoring in Volcanic Time Series 

Marisol Monterrubio-Velasco, Xavier Lana, Raúl Arámbula-Mendoza, and Ramón Zúñiga

Understanding volcanic activity through time series data analysis is crucial for uncovering the fundamental physical mechanisms governing this natural phenomenon.

In this study, we show the application of multifractal and fractal methodologies, along with statistical analysis, to investigate time series associated with volcanic activity. We aim to make use of these approaches to identify significant variations within the physical processes related to changes in volcanic activity. These methodologies offer the potential to identify pertinent changes preceding a high-energy explosion or a significant volcanic eruption.

In particular, we apply it to analyze two study cases. First, the evolution of the multifractal structure of volcanic emissions of low, moderate, and high energy explosions applied to Volcán de Colima (México years 2013-2015). The results contribute to obtaining quite evident signs of the immediacy of possible dangerous emissions of high energy, close to 8.0x10^8 J. Additionally, the evolution of the adapted Gutenberg-Richter seismic law to volcanic energy emissions contributes to confirm the results obtained using multifractal analysis. Secondly, we also studied the time series of the Gutenberg-Richter b-parameter of seismic activities associated with volcanic emissions in Iceland, Hawaii, and the Canary Islands, through the concept of Disparity (degree of irregularity), the fractal Hurst exponent, H, and several multifractal parameters. The results obtained should facilitate a better knowledge of the relationships between the activity of volcanic emissions and the corresponding related seismic activities.  

How to cite: Monterrubio-Velasco, M., Lana, X., Arámbula-Mendoza, R., and Zúñiga, R.: Applying Multifractal Theory and Statistical Techniques for High Energy Volcanic Explosion Detection and Seismic Activity Monitoring in Volcanic Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12938, https://doi.org/10.5194/egusphere-egu24-12938, 2024.

EGU24-13593 | ECS | Posters on site | NP4.1

Characterizing Uncertainty in Spatially Interpolated Time Series of Near-Surface Air Temperature 

Conor Doherty and Weile Wang

Spatially interpolated meteorological data products are widely used in the geosciences as well as disciplines like epidemiology, economics, and others. Recent work has examined methods for quantifying uncertainty in gridded estimates of near-surface air temperature that produce distributions rather than simply point estimates at each location. However, meteorological variables are correlated not only in space but in time, and sampling without accounting for temporal autocorrelation produces unrealistic time series and potentially underestimates cumulative errors. This work first examines how uncertainty in air temperature estimates varies in time, both seasonally and at shorter timescales. It then uses data-driven, spectral, and statistical methods to better characterize uncertainty in time series of estimated air temperature values. Methods for sampling that reproduce spatial and temporal autocorrelation are presented and evaluated. The results of this work are particularly relevant to domains like agricultural and ecology. Physical processes including evapotranspiration and primary production are sensitive to variables like near-surface air temperature, and errors in these important meteorological inputs accumulate in model outputs over time.

How to cite: Doherty, C. and Wang, W.: Characterizing Uncertainty in Spatially Interpolated Time Series of Near-Surface Air Temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13593, https://doi.org/10.5194/egusphere-egu24-13593, 2024.

EGU24-13879 | ECS | Posters on site | NP4.1

Understanding the role of vegetation responses to drought in regulating autumn senescence 

Eunhye Choi and Josh Gray

Vegetation phenology is the recurring of plant growth, including the cessation and resumption of growth, and plays a significant role in shaping terrestrial water, nutrient, and carbon cycles. Changes in temperature and precipitation have already induced phenological changes around the globe, and these trends are likely to continue or even accelerate. While warming has advanced spring arrival in many places, the effects on autumn phenology are less clear-cut, with evidence for earlier, delayed, or even unchanged end of the growing season (EOS). Meteorological droughts are intensifying in duration and frequency because of climate change. Droughts intricately impact changes in vegetation, contingent upon whether the ecosystem is limited by water or energy. These droughts have the potential to influence EOS changes. Despite this, the influence of drought on EOS remains largely unexplored. This study examined moisture’s role in controlling EOS by understanding the relationship between precipitation anomalies, vegetation’s sensitivity to precipitation (SPPT), and EOS. We also assess regional variations in responses to the impact of SPPT on EOS.

The study utilized multiple vegetation and water satellite products to examine the patterns of SPPT in drought and its impact on EOS across aridity gradients and vegetation types. By collectively evaluating diverse SPPTs from various satellite datasets, this work offers a comprehensive understanding and critical basis for assessing the impact of drought on EOS. We focused on the Northern Hemisphere from 2000 to 2020, employing robust statistical methods. This work found that, in many places, there was a stronger relationship between EOS and drought in areas with higher SPPT. Additionally, a non-linear negative relationship was identified between EOS and SPPT in drier regions, contracting with a non-linear positive relationship observed in wetter regions. These findings were consistent across a range of satellite-derived vegetation products. Our findings provide valuable insights into the effects of SPPT on EOS during drought, enhancing our understanding of vegetation responses to drought and its consequences on EOS and aiding in identifying drought-vulnerable areas.

How to cite: Choi, E. and Gray, J.: Understanding the role of vegetation responses to drought in regulating autumn senescence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13879, https://doi.org/10.5194/egusphere-egu24-13879, 2024.

EGU24-16981 | ECS | Orals | NP4.1

A machine-learning-based approach for predicting the geomagnetic secular variation 

Sho Sato and Hiroaki Toh

We present a machine-learning-based approach for predicting the geomagnetic main field changes, known as secular variation (SV), in a 5-year range for use for the 14th generation of International Geomagnetic Reference Field (IGRF-14). The training and test datasets of the machine learning (ML) models are geomagnetic field snapshots derived from magnetic observatory hourly means, and CHAMP and Swarm-A satellite data (MCM Model; Ropp et al., 2020). The geomagnetic field data are not used as-is in the original time series but were differenced twice before training. Because SV is strongly influenced by the geodynamo process occurring in the Earth's outer core, challenges still persist despite efforts to model and forecast the realistic nonlinear behaviors (such as the geomagnetic jerks) of the geodynamo through data assimilation. We compare three physics-uninformed ML models, namely, the Autoregressive (AR) model, Vector Autoregressive (VAR) model, and Recurrent Neural Network (RNN) model, to represent the short-term temporal evolution of the geomagnetic main field on the Earth’s surface. The quality of 5-year predictions is tested by the hindcast results for the learning window from 2004.50 to 2014.25. These tests show that the forecast performance of our ML model is comparable with that of candidate models of IGRF-13 in terms of data misfits after the release epoch (Year 2014.75). It is found that all three ML models give 5-year prediction errors of less than 100nT, among which the RNN model shows a slightly better accuracy. They also suggest that Overfitting to the training data used is an undesirable machine learning behavior that occurs when the RNN model gives accurate reproduction of training data but not for forecasting targets.

How to cite: Sato, S. and Toh, H.: A machine-learning-based approach for predicting the geomagnetic secular variation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16981, https://doi.org/10.5194/egusphere-egu24-16981, 2024.

EGU24-17344 | Posters on site | NP4.1

Introducing a new statistical theory to quantify the Gaussianity of the continuous seismic signal 

Éric Beucler, Mickaël Bonnin, and Arthur Cuvier

The quality of the seismic signal recorded at permanent and temporary stations is sometimes degraded, either abruptly or over time. The most likely cause is a high level of humidity, leading to corrosion of the connectors but environmental changes can also alter recording conditions in various frequency ranges and not necessarily for all three components in the same way. Assuming that the continuous seismic signal can be described by a normal distribution, we present a new approach to quantify the seismogram quality and to point out any time sample that deviates from this Gaussian assumption. To this end the notion of background Gaussian signal (BGS) to statistically describe a set of samples that follows a normal distribution. The discrete function obtained by sorting the samples in ascending order of amplitudes is compared to a modified probit function to retrieve the elements composing the BGS, and its statistical properties, mostly the Gaussian standard deviation, which can then differ from the classical standard deviation. Hence the ratio of both standard deviations directly quantifies the dominant gaussianity of the continuous signal and any variation reflects a statistical modification of the signal quality. We present examples showing daily variations in this ratio for stations known to have been affected by humidity, resulting in signal degradation. The theory developed can be used to detect subtle variations in the Gaussianity of the signal, but also to point out any samples that don't match the Gaussianity assumption, which can then be used for other seismological purposes, such as coda determination.

How to cite: Beucler, É., Bonnin, M., and Cuvier, A.: Introducing a new statistical theory to quantify the Gaussianity of the continuous seismic signal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17344, https://doi.org/10.5194/egusphere-egu24-17344, 2024.

EGU24-17566 | ECS | Posters on site | NP4.1

Unveiling Climate-Induced Ocean Wave Activities Using Seismic Array Data in the North Sea Region 

Yichen Zhong, Chen Gu, Michael Fehler, German Prieto, Peng Wu, Zhi Yuan, Zhuoyu Chen, and Borui Kang

Climate events may induce abnormal ocean wave activities, that can be detected by seismic array on nearby coastlines. We collected long-term continuous array seismic data in the Groningen area and the coastal areas of the North Sea, conducted a comprehensive analysis to extract valuable climate information hidden within the ambient noise. Through long-term spectral analysis, we identified the frequency band ranging from approximately 0.2Hz, which appears to be associated with swell waves within the region, exhibiting a strong correlation with the significant wave height (SWH). Additionally, the wind waves with a frequency of approximately 0.4 Hz and gravity waves with periods exceeding 100 seconds were detected from the seismic ambient noise. We performed a correlation analysis between the ambient noise and various climatic indexes across different frequency bands. The results revealed a significant correlation between the North Atlantic Oscillation (NAO) Index and the ambient noise around 0.17Hz.

Subsequently, we extracted the annual variation curves of SWH frequency from ambient noise at each station around the North Sea and assembled them into a sparse spatial grid time series (SGTS). An empirical orthogonal function (EOF) analysis was conducted, and the Principal Component (PC) time series derived from the EOF analysis were subjected to a correlation analysis with the WAVEWATCH III (WW3) model simulation data, thereby confirming the wave patterns. Moreover, we conducted the spatial distribution study of SGTS. The spatial features revealed that the southern regions of the North Sea exhibit higher wind-wave energy components influenced by the Icelandic Low pressure system and topography, which explains the correlation between ambient noise in the region and the NAO index. Furthermore, spatial features disclosed a correlation between the first EOF mode of the North Sea ocean waves and the third mode of sea surface temperature anomalies. This research shows the potential of utilizing existing off-shore seismic monitoring systems to study global climate variation and physical oceanography.

How to cite: Zhong, Y., Gu, C., Fehler, M., Prieto, G., Wu, P., Yuan, Z., Chen, Z., and Kang, B.: Unveiling Climate-Induced Ocean Wave Activities Using Seismic Array Data in the North Sea Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17566, https://doi.org/10.5194/egusphere-egu24-17566, 2024.

EGU24-18061 | ECS | Orals | NP4.1

A new methodology for time-series reconstruction of global scale historical Earth observation data 

Davide Consoli, Leandro Parente, and Martijn Witjes

Several machine learning algorithms and analytical techniques do not allow gaps or non-values in input data. Unfortunately, earth observation (EO) datasets, such as satellite images, are gravely affected by cloud contamination and sensor artifacts that create gaps in the time series of collected images. This limits the usage of several powerful techniques for modeling and analysis. To overcome these limitations, several works in literature propose different imputation methods to reconstruct the gappy time series of images, providing complete time-space datasets and enabling their usage as input for many techniques.

However, among the time-series reconstruction methods available in literature, only a few of them are publicly available (open source code), applicable without any external source of data, and suitable for application to petabyte (PB) sized dataset like the full Landsat archive. The few methods that match all these characteristics are usually quite trivial (e.g. linear interpolation) and, as a consequence, they often show poor performance in reconstructing the images. 

For this reason, we propose a new methodology for time series reconstruction designed to match all these requirements. Like some other methods in literature, the new method, named seasonally weighted average generalization (SWAG), works purely on the time dimension, reconstructing the images working on each time series of each pixel separately. In particular, the method uses a weighted average of the samples available in the original time series to reconstruct the missing values. Enforcing the annual seasonality of each band as a prior, for the reconstruction of each missing sample in the time series a higher weight is given to images that are collected exactly on integer multiples of a year. To avoid propagation of land cover changes in future or past images, higher weights are given to more recent images. Finally, to have a method that respects causality, only images from the past of each sample in the time series are used.

To have computational performance suitable for PB sized datasets the method has been implemented in C++ using a sequence of fast convolution methods and Hadamard products and divisions. The method has been applied to a bimonthly aggregated version of the global GLAD Landsat ARD-2 collection from 1997 to 2022, producing a 400 terabyte output dataset. The produced dataset will be used to generate maps for several biophysical parameters, such as Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), normalized difference water index (NDWI) and bare soil fraction (BSF). The code is available as open source, and the result is fully reproducible.

References:

Potapov, Hansen, Kommareddy, Kommareddy, Turubanova, Pickens, ... & Ying  (2020). Landsat analysis ready data for global land cover and land cover change mapping. Remote Sensing, 12(3), 426.

Julien, & Sobrino (2019). Optimizing and comparing gap-filling techniques using simulated NDVI time series from remotely sensed global data. International Journal of Applied Earth Observation and Geoinformation, 76, 93-111.

Radeloff, Roy, Wulder, Anderson, Cook, Crawford, ... & Zhu (2024). Need and vision for global medium-resolution Landsat and Sentinel-2 data products. Remote Sensing of Environment, 300, 113918.

How to cite: Consoli, D., Parente, L., and Witjes, M.: A new methodology for time-series reconstruction of global scale historical Earth observation data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18061, https://doi.org/10.5194/egusphere-egu24-18061, 2024.

EGU24-18197 | ECS | Orals | NP4.1 | Highlight

The regularity of climate-related extreme events under global warming 

Karim Zantout, Katja Frieler, and Jacob Schewe and the ISIMIP team

Climate variability gives rise to many different kinds of extreme impact events, including heat waves, crop failures, or wildfires. The frequency and magnitude of such events are changing under global warming. However, it is less known to what extent such events occur with some regularity, and whether this regularity is also changing as a result of climate change. Here, we present a novel method to systematically study the time-autocorrelation of these extreme impact events, that is, whether they occur with a certain regularity. In studies of climate change impacts, different types of events are often studied in isolation, but in reality they interact. We use ensembles of global biophysical impact simulations from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) driven with climate models to assess current conditions and projections. The time series analysis is based on a discrete Fourier transformation that accounts for the stochastic fluctuations from the climate model. Our results show that some climate impacts, such as crop failure, indeed exhibit a dominant frequency of recurrence; and also, that these regularity patterns change over time due to anthropogenic climate forcing.

How to cite: Zantout, K., Frieler, K., and Schewe, J. and the ISIMIP team: The regularity of climate-related extreme events under global warming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18197, https://doi.org/10.5194/egusphere-egu24-18197, 2024.

EGU24-18210 | ECS | Posters on site | NP4.1

Long-term vegetation development in context of morphodynamic processes since mid-19th century 

Katharina Ramskogler, Moritz Altmann, Sebastian Mikolka-Flöry, and Erich Tasser

The availability of comprehensive aerial photography is limited to the mid-20th century, posing a challenge for quantitatively analyzing long-term surface changes in proglacial areas. This creates a gap of approximately 100 years, spanning the end of the Little Ice Age (LIA). Employing digital monoplotting and historical terrestrial images, our study reveals quantitative surface changes in a LIA lateral moraine section dating back to the second half of the 19th century, encompassing a total study period of 130 years (1890 to 2020). With the long-term analysis at the steep lateral moraines of Gepatschferner (Kauner Valley, Tyrol, Austria) we aimed to identify changes in vegetation development in context with morphodynamic processes and the changing climate.

In 1953, there was an expansion in the area covered by vegetation, notably encompassing scree communities, alpine grassland, and dwarf shrubs. However, the destabilization of the system after 1980, triggered by rising temperatures and the resulting thawing of permafrost, led to a decline in vegetation cover by 2020. Notably, our observations indicated that, in addition to morphodynamic processes, the overarching trends in temperature and precipitation exerted a substantial influence on vegetation development. Furthermore, areas with robust vegetation cover, once stabilised, were reactivated and subjected to erosion, possibly attributed to rising temperatures post-1980.

This study demonstrates the capability of historical terrestrial images to enhance the reconstruction of vegetation development in context with morphodynamics in high alpine environments within the context of climate change. However, it is important to note that long-term mapping of vegetation development through digital monoplotting has limitations, contingent on the accessibility and quality of historical terrestrial images, as well as the challenges posed by shadows in high alpine regions. Despite these limitations, this long-term approach offers fundamental data on vegetation development for future modelling efforts.

How to cite: Ramskogler, K., Altmann, M., Mikolka-Flöry, S., and Tasser, E.: Long-term vegetation development in context of morphodynamic processes since mid-19th century, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18210, https://doi.org/10.5194/egusphere-egu24-18210, 2024.

EGU24-19601 | ECS | Posters on site | NP4.1

Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform 

Palangio Paolo Giovanni and Santarelli Lucia

Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform

  • Palangio1, L. Santarelli 1

1Istituto Nazionale di Geofisica e Vulcanologia L’Aquila

3Istituto Nazionale di Geofisica e Vulcanologia Roma

 

Correspondence to:  lucia.santarelli@ingv.it

 

Abstract

In this paper we present an application of  the SSA Transform to the detection and reconstruction of  very weak geomagnetic signals hidden in noise. In the SSA Transform  multiple subspaces are used for representing and reconstructing   signals and noise.  This analysis allows us to reconstruct, in the time domain, the different harmonic components contained in the original signal by using  ortogonal functions. The objective is to identificate the dominant  subspaces that can be attributed to the  signals and the subspaces that can be attributed to the noise,  assuming that all these  subspaces are orthogonal to each other, which implies that the  signals and noise  are independent of one another. The subspace of the signals is mapped simultaneously on several spaces with a lower dimension, favoring the dimensions that best discriminate the patterns. Each subspace of the signal space is used to encode different subsets of functions having common characteristics, such as  the same periodicities. The subspaces  identification was performed by using singular value decomposition (SVD) techniques,  known as  SVD-based identification methods  classified in a subspace-oriented scheme.The  quasi-periodic variations of geomagnetic field  has been investigated in the range of scale which span from 22 years to 8.9 days such as the  Sun’s polarity reversal cycle (22 years), sun-spot cycle (11 years), equinoctial effect (6 months), synodic rotation of the Sun (27 days) and its harmonics. The strength of these signals vary from fractions of a nT to tens of nT. Phase and frequency variability of these cycles has been evaluated from the range of variations in the geomagnetic field recorded at middle latitude place (covering roughly 4.5 sunspot cycles). Magnetic data recorded at L'Aquila Geomagnetic observatory (geographic coordinates: 42° 23’ N, 13° 19’E, geomagnetic coordinates: 36.3° N,87°.2 E, L-shell=1.6) are used from 1960 to 2009.

 

 

How to cite: Paolo Giovanni, P. and Lucia, S.: Discrimination of  geomagnetic quasi-periodic signals by using SSA Transform, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19601, https://doi.org/10.5194/egusphere-egu24-19601, 2024.

EGU24-22262 | ECS | Posters on site | NP4.1

Temporal Interpolation of Sentinel-2 Multispectral Time Series in Context of Land Cover Classification with Machine Learning Algorithms 

Mate Simon, Mátyás Richter-Cserey, Vivien Pacskó, and Dániel Kristóf

Over the past decades, especially since 2014, large quantities of Earth Observation (EO) data became available in high spatial and temporal resolution, thanks to ever-developing constellations (e.g.: Sentinel, Landsat) and open data policy. However, in the case of optical images, affected by cloud coverage and the spatially changing overlap of relative satellite orbits, creating temporally generalized and dense time series by using only measured data is challenging, especially when studying larger areas.

Several papers investigate the question of spatio-temporal gap filling and show different interpolation methods to calculate missing values corresponding to the measurements. In the past years more products and technologies have been constructed and published in this field, for example Copernicus HR-VPP Seasonal Trajectories (ST) product.  These generalized data structures are essential to the comparative analysis of different time periods or areas and improve the reliability of data analyzing methods such as Fourier transform or correlation. Temporally harmonized input data is also necessary in order to improve the results of Machine Learning classification algorithms such as Random Forest or Convolutional Neural Networks (CNN). These are among the most efficient methods to separate land cover categories like arable lands, forests, grasslands and built-up areas, or crop types within the arable category.

This study analyzes the efficiency of different interpolation methods on Sentinel-2 multispectral time series in the context of land cover classification with Machine Learning. We compare several types of interpolation e.g. linear, cubic and cubic-spline and also examine and optimize more advanced methods like Inverse Distance Weighted (IDW) and Radial Basis Function (RBF). We quantify the accuracy of each method by calculating mean square error between measured and interpolated data points. The role of interpolation of the input dataset in Deep Learning (CNN) is investigated by comparing Overall, Kappa and categorical accuracies of land cover maps created from only measured and interpolated time series. First results show that interpolation has a relevant positive effect on accuracy statistics. This method is also essential in taking a step towards constructing robust pretrained Deep Learning models, transferable between different time intervals and agro-ecological regions.

The research has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the KDP-2021 funding scheme.

 

Keywords: time series analysis, Machine Learning, interpolation, Sentinel

How to cite: Simon, M., Richter-Cserey, M., Pacskó, V., and Kristóf, D.: Temporal Interpolation of Sentinel-2 Multispectral Time Series in Context of Land Cover Classification with Machine Learning Algorithms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22262, https://doi.org/10.5194/egusphere-egu24-22262, 2024.

SM4 – Earthquake Sources, Deformation and Faulting (incl. seismotectonics, geodynamics, earthquake source physics)

EGU24-2384 | ECS | Orals | EMRP1.6

Frictional slip sequences in homogeneous and bimaterial interfaces 

Songlin Shi, Meng Wang, Yonatan Poles, and Jay Fineberg

Earthquake-like ruptures disrupt the frictional interface between contacting bodies and initiate frictional motion (stick-slip). The interfacial slip (motion) immediately resulting from a rupture during each stick-slip event is usually much smaller than the total slip recorded during the duration of the event. Slip after the onset of friction is generally attributed to the continuous motion of global ‘dynamic friction’. Here, we demonstrate that numerous hitherto invisible secondary ruptures are initiated immediately after each initial rupture by directly measuring the contact area and slip at the frictional interface. Each secondary rupture generates incremental slip that, when not resolved, may appear as steady sliding of the interface. Each slip increment is linked, via fracture mechanics, to corresponding variations of contact area and local strain. Cumulative interfacial slip can only be described if the effects of these secondary ruptures are taken into account. These weaker slip sequences can also be observed in bimaterial interfaces and exhibit strong directional effects. In addition, the seismic moments we estimate based on slip sequences are consistent with the Gutenberg-Richter (G-R) law. These results have important implications for our fundamental understanding of frictional motion and the important role of aftershocks within natural faults in generating earthquake-mediated slip/afterslip.

How to cite: Shi, S., Wang, M., Poles, Y., and Fineberg, J.: Frictional slip sequences in homogeneous and bimaterial interfaces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2384, https://doi.org/10.5194/egusphere-egu24-2384, 2024.

EGU24-3912 | ECS | Orals | EMRP1.6

Back-Propagating Rupture: Nature, Excitation, and Applications 

Xiaotian Ding, Shiqing Xu, Eiichi Fukuyama, and Futoshi Yamashita

In recent years, an intriguing feature of back-propagating rupture (BPR) has been reported during some earthquakes (Ide et al., 2011; Houston et al., 2011; Hicks et al., 2020; Okuwaki et al., 2021; Vallée et al., 2023). The occurrence of BPR challenges the classical interpretation of rupture propagation as a “forward” problem, while remaining less understood by the earthquake science community. Here, using fracture mechanics, we first argue that BPR is nothing but an intrinsic component of rupture propagation; however, its observability is usually masked by the superposition effect of interfering waves behind the primary, forward-propagating rupture front. We then suggest that perturbation to an otherwise smooth rupture process can break the superposition effect and hence can make BPR observable. To test our idea, we report results of mode-II rupture propagation from both numerical simulations and laboratory observations. By introducing a variety of perturbations (lateral variation in bulk or interfacial properties along the fault, singular stress drop, coalescence of two rupture fronts, etc.) during rupture propagation, we show that prominent phases of BPR indeed can be successfully excited. We further classify BPR into two modes: higher-order rupture or interface wave, depending on whether the already-ruptured fault is quickly healed and whether additional stress drop can be produced. Lastly, we propose several application potentials for BPR, such as constraining the velocity structure of fault zones, probing the mechanical state of faults, and studying the stability of perturbed slip along a homogeneous or bimaterial interface. Our study refines the understanding of the nature and complexity of rupture process, and can help improve the assessment of earthquake hazards.

How to cite: Ding, X., Xu, S., Fukuyama, E., and Yamashita, F.: Back-Propagating Rupture: Nature, Excitation, and Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3912, https://doi.org/10.5194/egusphere-egu24-3912, 2024.

EGU24-5187 | Orals | EMRP1.6

The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes  

Fabio Corbi, Giacomo Mastella, Elisa Tinti, Adriano Gualandi, Laura Sandri, Matthias Rosenau, Silvio Pardo, and Francesca Funiciello

Modeling the seismic cycle requires multiple assumptions and parameters. Providing a quantitative assessment of the model behavior is pivotal for determining the degree of similarity between different scales and modeling strategies and for exploring dependencies with respect to selected parameters. Here we compare stick-slip ruptures nucleating spontaneously in scaled seismotectonic models (i.e., laboratory experiments capturing the first-order physics of the seismic cycle of subduction megathrusts) with slow earthquakes in nature. We rely on two non-dimensional parameters, namely the Ruina number (Ru) and system dimension (D) to quantify model behavior. Ru is proportional to the ratio of the asperity size to the critical nucleation size. Within the rate- and state friction framework, for velocity weakening asperities Ru controls the behavior of the system, which can be either periodic or not, and it can exhibit both slow and fast ruptures. D measures how complicated the system evolution is. D reveals how many variables are required to describe the seismic cycle because it tells us the minimum dimension needed to embed the observed dynamics. 

By coupling the Simulated Annealing algorithm and quasi-dynamic numerical simulations, we retrieve rate and state friction parameters characterizing single asperity models with different lateral extent of the velocity weakening patch. Similarly to slow earthquakes, we found optimal rate and state parameters indicative of low (< 4) Ru. We also found a direct proportionality between Ru and the lateral extent of the asperity. 

Next, we implement tools from non-linear time-series analysis and Extreme Value Theory to compute D from models of different sizes, materials, deformation rates and frictional configurations (single or twin asperities along strike). Our analysis supports the existence of a low dimensional attractor (D<5) describing the dynamics of scaled seismotectonic models. In particular, our models display D=3.0-4.2, which is remarkably similar to D=3.2 of slow earthquakes identified along the Cascadia subduction zone. Under the explored conditions, D appears more affected by the material behavior of the analog upper plate (i.e., gelatin vs. foam rubber) than by the lateral frictional segmentation of the megathrust.

Despite the different spatio-temporal scales, our results support a scenario where scaled seismotectonic models and slow earthquakes share similar dynamics.



How to cite: Corbi, F., Mastella, G., Tinti, E., Gualandi, A., Sandri, L., Rosenau, M., Pardo, S., and Funiciello, F.: The similarity between ruptures in scaled laboratory seismotectonic models and slow earthquakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5187, https://doi.org/10.5194/egusphere-egu24-5187, 2024.

EGU24-5767 | ECS | Posters on site | EMRP1.6

Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity  

Pierre Romanet, Marco Scuderi, Stéphanie Chaillat, Jean-Paul Ampuero, and Frédéric Cappa

Numerical modeling of Discrete Fracture Networks (DFNs) is commonly used to assess the behavior and properties of hydraulic diffusion and seismicity in the Earth’s crust within a network of fractures and faults, and to study the hydromechanical evolution of fractured reservoirs stimulated by hydraulic injection and production. The modelling of such fractures is typically carried out under a quasi-static approximation, and occasionally accounting for elasto-dynamics in single-rupture studies that assume a slip-weakening friction law. 

In this work, we develop a 2D DFN model to simulate fluid-induced seismicity that couples hydraulic diffusion and slip governed by rate-and-state friction on multiple interacting faults. The main goal of this numerical model is to establish a connection between laboratory derived friction parameters and field observations, enabling the inference of the long-term evolution of fractured reservoirs and crustal fault systems undergoing multiple earthquakes and (slow) slip events induced by fluid pressure perturbations.

In the model, the elastic interactions are computed with a boundary element method, accelerated by the hierarchical matrix method. We assessed the convergence of the method at fracture junctions and verified it does not create unphysical singularities. The use of rate-and-state friction makes it possible to model several seismic events over the injection duration.

The simulations will be later used to fit measurements of permeability and friction collected in laboratory experiments, in-situ observations of fault slip and opening from fluid injection experiments at decametric scale, and finally, induced seismicity at reservoir scale.

 

How to cite: Romanet, P., Scuderi, M., Chaillat, S., Ampuero, J.-P., and Cappa, F.: Towards a 2D model of Discrete Fracture Network with permeability and friction evolution for modeling fluid-induced seismicity , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5767, https://doi.org/10.5194/egusphere-egu24-5767, 2024.

EGU24-6284 | ECS | Posters on site | EMRP1.6

Fault drainage state and frictional stability in response to shearing rate steps in natural gouge 

Raphael Affinito, Derek Elsworth, and Chris Marone

Elevated pore fluid pressures are frequently implicated in governing fault zone seismicity. While substantial evidence from geodetic and geological studies supports this notion, there is a notable scarcity of experimental observations of how fluid pressure influences fault stability during shear. Understanding the precise interplay between porosity, fault slip rate, and frictional stability is pivotal for assessing the significance of processes like dilational strengthening or thermal pressurization in the context of seismic hazards. Here, we prepare fault gouges from the Utah FORGE enhanced geothermal field injection well 16A at depths corresponding to seismic events (between 2050 – 2070m). Experiments were conducted inside a pressure vessel and loaded under a true-triaxial stress state, replicating in-situ stress conditions observed at the Utah FORGE site. The applied fault normal stress and during the experiments were held constant at 44MPa. Pore fluid pressure was varied between successive experiments (13, 20, and 27 MPa) to span a range of effective stresses to examine impacts on fault dilation/compaction and the successive frictional stability. Different fluid pressure boundary conditions: constant volume or pressure were applied to explore how changes in shearing rate influence gouge stability thought the fault drainage state. Our data indicate that the Utah FORGE samples are velocity-neutral and transition to velocity-weakening behavior at elevated pore pressure and shear strains >7. We find dilatancy coefficients e = ∆f/∆ln(v), where f is porosity and v is fault slip velocity, consistent with quartz-feldspathic-rich rocks ranging from 5–12^10-4, indicating a conditionally unstable regime. Furthermore, our results demonstrate that the boundary conditions for pore fluids influence frictional stability viachanges in effective normal stress. For example, when pore volume has zero flux, an expansion in the void volume during slip results in a decrease in pore pressure, transitioning the system towards frictional stability. Our results indicate that the connectivity of pore conduits may be more important than the imposed pore pressure conditions when considering the impact on fault stability. We suggest that the interplay between fault slip and fluid mobility within a fault is a delicate balance for predicting and managing seismic hazards.

How to cite: Affinito, R., Elsworth, D., and Marone, C.: Fault drainage state and frictional stability in response to shearing rate steps in natural gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6284, https://doi.org/10.5194/egusphere-egu24-6284, 2024.

EGU24-7508 | Orals | EMRP1.6

A granular numerical model for the friction and wear of a lab-scale fault asperity 

Guilhem Mollon, Adriane Clerc, Amandine Ferrieux, Lionel Lafarge, and Aurelien Saulot

Seismic faults are often represented using two different and self-excluding conceptual models. In the first representation, seismic faults are seen as the interface between two surfaces of bare rock, with a roughness extending at all scales. These surfaces interact mechanically through a certain number of “asperities” which constitute the “real contact area”. When adopting this view, attention is paid on the statistics of the asperities population in the fault plane. Faults are thus considered as 2D objects, since their thickness is disregarded.

In the second representation, seismic faults are seen as mathematical planes separated by a certain thickness of granular gouge created by abrasive wear of the surfaces during previous slips. This view is analogous to the tribological “third body” theory, and is supported by field observations and experimental evidences of gouge creation in rotary shear and triaxial experiments. It is convenient to adopt this perspective when weakening phenomena within the gouge are to be spatially resolved in the direction orthogonal to the fault plane. Variations along this plane are then ignored, as well as fault roughness, and faults are mostly seen as 1D objects.

Unification of these two representations requires a better understanding of the interactions between geometrical asperities and a layer of gouge, and in particular of the phenomena that lead to the creation of the latter through the wear of the former. In this communication, we present a numerical model which aims at reproducing lab tests of millimetric single-asperity friction and wear. The model is essentially granular in order to represent the progressive degradation of the asperity along sliding, the separation of powdery matter, its successive ejection and reinjection by the contact (thanks to a periodicity in boundary conditions), and the build-up of a gouge layer. It also includes a coupling with continuum mechanics in order to maintain a meaningful stress field in the asperity beyond the region of degradable rock.

Numerical results show that: (i) the rate of wear of the asperity and the counterface are directly linked to the normal load applied to the contact; (ii) an established layer of gouge develops in the interface and controls the friction coefficient; (iii) a constant level of surface roughness is established after a sufficient sliding distance, both for the asperity and the counterface; (iv) an accurate control of the asperity boundary conditions is necessary in order to obtain repeatable friction and wear. These results are a first step towards a better understanding of the wear kinetics as a function of asperity geometry, load, and roughness, before the introduction of thermal aspects (including melting) in a future version of the model.

How to cite: Mollon, G., Clerc, A., Ferrieux, A., Lafarge, L., and Saulot, A.: A granular numerical model for the friction and wear of a lab-scale fault asperity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7508, https://doi.org/10.5194/egusphere-egu24-7508, 2024.

EGU24-7803 | ECS | Posters on site | EMRP1.6

Fluid driven seismic cycle modelling in subduction zones 

Betti Hegyi, Taras Gerya, Luca Dal Zilio, and Whitney Behr

The role of fluid flow in triggering earthquakes in subduction zones is a critical yet complex aspect in seismology. Despite extensive study through geological, geophysical observations, and laboratory experiments, fully understanding and modelling these processes within a coupled solid-fluid interaction framework remain challenging. This study employs a coupled seismo-hydro-mechanical code (i2elvisp) to simulate fluid-driven earthquake sequences in a simplified subduction megathrust environment. We incorporate non-uniform grid resolution, enhancing the resolution of seismic events within the subduction channel. The code integrates solid rock deformation with fluid dynamics, solving mass and momentum conservation equations for both phases, alongside gravity and temperature-dependent viscosity effects. Brittle/plastic deformation is modelled through a rate-dependent strength formulation, with slip instabilities governed by compaction-induced pore fluid pressurisation. Our approach demonstrates the significant impact of fluid pressurisation on deformation localization, achieving slip rates up to metres per second in a fully compressible poro-visco-elasto-plastic medium. By refining the vertical model resolution in the subduction channel to less than or equal to 200 metres, we ensure convergence in terms of event recurrence interval and slip velocity. The models successfully replicate various slip modes observed in nature, ranging from regular earthquakes (including partial and full ruptures) to transient slow slip phenomena and aseismic creep. This research focuses on the parameters influencing the dominant slip mode, their distributions, and interactions along a modelled subduction interface. Our findings indicate that the dominant slip mode and the earthquake sequences are significantly influenced by porosity, permeability, and temperature-dependent viscosity. We explore two distinct viscosity gradients in the subduction channel to represent subduction zones with differing thermal profiles. In 'hot' subduction models, the brittle-ductile transition commences at shallower depths than in 'cold' subduction cases, influencing the nucleation depth of seismic events. These viscosity variations markedly impact model evolution; regular earthquakes exhibit higher velocities and slip rates in 'hot' scenarios, which are also more conducive to hosting aseismic creep or slow slip events. In conclusion, our study elucidates the pivotal role of fluid pressure evolution in seismicity within subduction zones and provides deeper insights into earthquake source processes. Through comprehensive modelling and analysis, we enhance understanding of the complex dynamics governing fluid-induced seismic activity and contribute to the broader field of earthquake source processes. 

How to cite: Hegyi, B., Gerya, T., Dal Zilio, L., and Behr, W.: Fluid driven seismic cycle modelling in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7803, https://doi.org/10.5194/egusphere-egu24-7803, 2024.

EGU24-8381 | Posters on site | EMRP1.6

Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure 

Lei Zhang, Changrong He, and Sylvain Barbot

To investigate the frictional behavior of basalt under hydrothermal conditions, we apply sliding experiments using basalt gouge under the temperature of 100-600ºC, effective normal stress of 150MPa, and fluid pressure of 30MPa and 100MPa, respectively. Experiment results under 30MPa pore pressure show that basalt exhibits velocity-strengthening behavior at 100-200ºC and changes to velocity-weakening behavior at 400-600ºC; meanwhile, at 400ºC, velocity dependence of basalt evolves with slip from initial velocity weakening to velocity-strengthening. Results under 100MPa fluid pressure show a similar transition of velocity dependence at 300ºC; however, at higher temperatures of 400-600ºC, velocity strengthening behavior occurs, accompanied by strong slip weakening behavior at the slowest loading rate (0.04μm/s). During the velocity step, the experiment exhibits a rate-dependent creep without transient evolution with slip. Microstructure observation reveals significant differences between samples sheared under 30MPa and 100MPa fluid pressure. At higher fluid pressure and temperatures of 400-600ºC, the porosity of the basalt gouge layer is significantly reduced, and deformation is characterized by pervasive shear with no apparent localization. Such results suggest that the healing process/plastic deformation is activated at higher fluid pressure, leading to slip stability transition and slip-weakening of frictional strength.

How to cite: Zhang, L., He, C., and Barbot, S.: Transition from Unstable Slip to Rate-Dependent Creep Controlled by High Fluid Pressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8381, https://doi.org/10.5194/egusphere-egu24-8381, 2024.

EGU24-8887 | ECS | Posters on site | EMRP1.6

High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge 

Jianhua Huang, Bo Zhang, Junjie Zou, Honglin He, Jiaxiang Dang, and Jinjiang Zhang

        Abundant cherts (nodules and bands) were discontinuously hosted by dolostones of the Mesoproterozoic group Strata (∼1.5 Ga) in the Shanxi graben system, North China, where earthquakes are common. Measurements of the shear strength and stability of granular quartz reveal that quartz is a typical tectosilicate which exhibits high frictional strength and velocity-weakening properties. Conversely, dolomite is usually frictionally weak but velocity strengthening. The two minerals also behave differently during coseismic slip. Due to the high temperature generated by frictional heating, the thermal decomposition of dolomite usually results in calcite, periclase nanoparticles and carbon dioxide. However, quartz melts by friction at high temperatures. In order to investigate the role of quartz in dolomite fault rock during the process of coseismic slip, high velocity shear experiments were conducted on the quartz-bearing dolomite fault gouge taken from Yuguang Basin South Margin Fault (YBSMF), northeast of the Shanxi graben system. Also, we carried out high velocity experiments with the synthetic quartz-dolomite gouge with different mass ratio. For a slip velocity ≥ 0.1 m/s and normal stresses from 1.0 to 1.5 MPa, the friction values of the gouge decrease exponentially from a peak value of more than 0.5 to a steady-state value from 0.1 to 0.4. This high-velocity weakening feature was observed in the synthetic quartz-dolomite gouge as well as in the YBSMF gouge. With the increase of quartz content, the slip weakening distance (Dw) increases from 4.27 to 13.24 m, and the steady-state friction coefficient increases from 0.2 to 0.4 at 1.0 MPa normal stress and 1.0 m/s slip velocity. The textures of the gouge are characterized by grain comminution, R shear planes and localized deformation zone in the friction weakening stage. The slip surfaces are characterized by mirror-like smooth surface and nanoparticle aggregates. The theoretical calculation results show that the temperature inside the gauge layer did not exceed 300 °C during the experiments. However, the microstructures present that the dolomite experienced thermal decomposition, indicating that the temperature at the asperity exceeds 550 ℃. We suggest that thermal decomposition together with flash heating may lead to the slip-weakening behavior of quartz-bearing dolomite gauge, and the addition of quartz will increase of the strength of the dolomite gouge.

How to cite: Huang, J., Zhang, B., Zou, J., He, H., Dang, J., and Zhang, J.: High-velocity frictional behavior and microstructure evolution of quartz-bearing dolomite fault gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8887, https://doi.org/10.5194/egusphere-egu24-8887, 2024.

EGU24-9165 | ECS | Posters on site | EMRP1.6

Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland) 

Wei-Hsin Wu, Wei Feng, Rodrigo Gomila, Telemaco Tesei, Marie Violay, Anette K. Mortensen, and Giulio Di Toro

Fault’s frictional strength and particularly its ability to heal during the interseismic period (fault frictional healing Δμ) is critical to understand the seismic cycle, yet the understanding of temperature and phase-dependent healing characteristics of natural geothermal conditions remains limited. Here we examined the frictional healing of both simulated fresh and chlorite-altered basaltic gouge from Krafla geothermal field (Iceland) under realistic geothermal conditions of water temperature Tf = 100-400 ˚C and pressure Pf = 10-30 MPa (water in liquid, vapor and supercritical state) by performing Slide-Hold-Slide (SHS) experiments. All experiments were performed under a constant effective normal stress of 10 MPa and initiated with a 5-mm run-in slip at a loading point slip rate V of 10 mm/s before the SHS sequence. For each SHS sequence, shearing was held from 3 s to 10,000 s, separated by a slip interval of 1mm. Our mechanical results indicate that frictional healing, the difference between peak friction reached upon re-shear and the steady-state friction before the hold, increases with increasing logarithm of hold time in all experiments, as suggested by previous studies. Meanwhile, frictional healing rate (β = Δμ/log(1+ thold/tcutoff)), commonly regarded as the quantification of the rate of healing, increases with increasing temperature for both fresh and altered basalt. For fresh basalt, β increases from 0.007 at Tf = 100 ˚C to 0.060 at Tf = 300 ˚C (liquid) before dropping to 0.036 at Tf = 400 ˚C (vapor) and eventually increases to 0.096 at Tf = 400 ˚C (supercritical). For altered basalt, β  increases continuously from 0.003-0.007 at Tf = 100 ˚C to 0.013-0.022 at Tf = 300 ˚C and reaches its maximum value of β = 0.024-0.035 at Tf = 400 ˚C (vapor) and β = 0.030 at Tf = 400 ˚C (supercritical). Besides this temperature-dependent relationship, the dramatic decrease of β in fresh basalt to values similar to those of altered basalt when water changed from liquid to vapor state also suggests that the physical state of water can control the healing rate. Subsequent microanalytical analyses (XRPD, XRF, SEM-EDS) performed on the deformed gouges from altered basalts suggest an increase in hydrothermal alteration with increasing temperature, as shown by a depletion in K2O at Tf ≥ 300 ˚C. SEM-BSE images of fine platy matrices in shear bands formed at Tf = 400 ˚C point towards a dissolution of quartz, pyroxene and plagioclase. Therefore, we suggest that the healing rate of both fresh and altered basalt not only scales with the ambient temperature but is also affected by the physical state of water, particularly in the case of fresh basalt, potentially related to more intense fluid-rock interactions with increasing temperature.

Keywords: frictional healing, frictional healing rate, hydrothermal fluids, basaltic gouge, Krafla geothermal field

How to cite: Wu, W.-H., Feng, W., Gomila, R., Tesei, T., Violay, M., Mortensen, A. K., and Di Toro, G.: Temperature and Physical State of Water Controls Frictional Healing of Basaltic Gouges from Krafla (Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9165, https://doi.org/10.5194/egusphere-egu24-9165, 2024.

EGU24-9541 | Posters on site | EMRP1.6

Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures 

Marco Scuderi, Nathalie casas, Giuseppe Volpe, and Cristiano Collettini

Mineralogy, fabric, and frictional properties are fundamental aspects of natural and experimental faults that concur in controlling the fault strength and the fault slip behavior. Mineralogy controls the fabric evolution influencing the micro-mechanisms at play during fault deformation and needs an in-depth investigation to better understand and foresee the frictional response of experimental faults. Classically, this investigation has been conducted by relating the fault frictional behavior to the post-experimental microstructures. However, this “classical” approach provides a direct but static view of the fault deformation where the evolution of fabric with deformation can be only speculated.

To investigate in “real-time” the deformation micro-mechanisms at play during the experiments, the recording and analyses of Acoustic Emissions (AEs) produced by the deforming fault gouge can provide new insights.

In this study, we present a systematic study of microstructural, mineralogical, frictional, and AEs analysis coming from a suite of frictional experiments in a double direct shear configuration (biaxial apparatus, BRAVA2). We conducted experiments on gouges made of bi-disperse and layered mixtures of quartz and phyllosilicate. These experiments were performed at a constant normal stress of 52MPa and under 100% humidity. The friction evolves with the phyllosilicate content from µ ~ 0.6 for 100% quartz to µ ~ 0.4 for 100% phyllosilicates. At the end of the experiments samples were carefully collected and prepared for microstructural analysis. The fabric of the experimental samples show an evolution from localized to distributed and foliated fabric with increasing amount of phyllosilicate content.

We then integrate specific features of AEs, such as amplitude and AE rate, to unveil the micro-mechanisms at play during the experimental fault deformation. Our results show that the overall AE behavior is controlled by mineralogy. Deformation of quartz gouge produces the largest number of AEs whereas phyllosilicates are almost not producing AEs. Furthermore, the AE behavior of bi-disperse mixtures of quartz and phyllosilicates is strongly controlled by the amount of phyllosilicates. In fact, increasing the amount of phyllosilicate, the number, the rate, and the amplitude of AEs decrease. This behavior could be explained by the lubricant role of phyllosilicates which hinder the interaction between quartz grains favoring foliation sliding as main deformation mechanism and thus reducing the frictional strength. These results suggest that for bi-disperse mixtures the AEs reflect the frictional behavior of the mixture. Layered quartz-phyllosilicates mixtures show instead a non-trivial acoustic emission behavior which cannot be directly related to the measured frictional strength of the layered mixture: friction is controlled by the frictionally weaker mineral phase, whereas the AEs are probably dependent by the interplay between the stronger and weaker phase of the layered mixture.

Our results show that fault fabric together with mineralogy strongly control the micro-mechanisms at play during deformation and therefore the frictional response. Our findings support the use of the AE analysis as a new tool for the investigation of the micro-mechanisms at play during deformation, improving our interpretation of the mechanical behavior of fault gouges.

How to cite: Scuderi, M., casas, N., Volpe, G., and Collettini, C.: Unraveling the micro-mechanics of shear deformation through acoustic attributes of quartz-muscovite mixtures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9541, https://doi.org/10.5194/egusphere-egu24-9541, 2024.

EGU24-9941 | ECS | Posters on site | EMRP1.6

Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge 

Michele De Solda, Michele Mauro, Federico Pignalberi, and Marco Scuderi

In the last decades, rock mechanics laboratory experiments have allowed framing earthquake physics as a frictional problem. When the accumulated stress on a fault exceeds the frictional forces holding it in place, a rapid acceleration occurs. This movement can be stable or unstable, involving phases of adhesion (stick) and rapid sliding (slip). In these terms, an earthquake results from the release of mechanical energy during one of these slip phases.

 

Modern friction theories propose that the frictional forces holding the fault in place are controlled by small asperities defining the real contact area (RCA). Therefore, understanding the mechanics of contacts on the fault and their evolution under stress and velocity changes can shed light on the microphysical processes underlying earthquakes.

 

In the laboratory, it is now possible to investigate the dynamics of experimental faults, predicting their instability behavior based on Rate and State Friction theory and its experimentally obtainable parameters (a-b, Dc). However, these parameters lack an explicit relationship with contact mechanics, necessitating additional measurements complementing the system's state information. One of the most widely used techniques for studying RCA during laboratory experiments involves investigating changes in acoustic transmissivity (velocity, amplitude) of generated and recorded ultrasonic waveforms (UW) passing through the sample during the deformation. At a given wavelength, analytical expressions for these quantities depend on the elastic properties and densities of the fault portion crossed by the wave. Simultaneous knowledge of stress conditions and elastic properties allows the formulation of constitutive laws for the evolution of contacts between fault asperities.

 

In double direct shear experiments (DDS) within biaxial apparatuses, the sample dimensions (gouge) impose stringent limits on the spatial and temporal resolution of the signal. These limits highlight the current sensor technology's deviation from the ideal behavior.

 

Here, we present a methodology and a waveform recording and synchronization protocol

implemented on the biaxial apparatus BRAVA2 in the Rock Mechanics and Earthquake Physics laboratory at Sapienza University of Rome. We focus on the types of sensors used and their specifications to provide accurate measurements of the deformation processes occurring within the gouge layers.

 

Several studies have conducted DDS experiments using UW, but they rarely take into account the characterization of the impulse signal, various reflections in the sample assembly, and conversion modes of the generated waveforms. These are all essential components to identify the interaction of the experimental system with the propagation of the ultrasonic waves, to exploit the received signal in its entirety.

We believe that a careful signal characterization is necessary to fully understand the physical processes during deformation within the sample and, consequently, to attempt upscaling to natural earthquakes.

How to cite: De Solda, M., Mauro, M., Pignalberi, F., and Scuderi, M.: Strengthen and limitations of ultrasonic wave testing: examples from Double Direct Shear experiments on gouge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9941, https://doi.org/10.5194/egusphere-egu24-9941, 2024.

EGU24-10564 | Posters on site | EMRP1.6

An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions 

Yu-Han Wang and Elías Rafn Heimisson

The interactions between fluids and fault structures play a pivotal role in understanding fault slip behavior. Over the years, various numerical methods have been developed to simulate these interactions. Volume-based methods, like the finite difference method (FDM), excel in their capacity to handle the intricacies of real-world fault structures, including material heterogeneity. On the other hand, the spectral boundary integral method (SBIM) is renowned for its computational efficiency. Recently, a hybrid approach has garnered significant attention, offering the benefits of both volume-based and SBI methods. This hybrid method allows for the consideration of fault structures' heterogeneity while maintaining computational efficiency. In this study, we introduce a novel hybrid method that bridges the SBIM and the FDM to model fluid migration in fault structures. Through rigorous model verification, we establish that our hybrid method can achieve a remarkable speedup of up to one thousand times compared to the FDM. Furthermore, we conducted two parametric studies to address open questions in fluid migration modeling within fault structures. First, we investigate the mobility contrast ratio between the host rock and the damage zone to determine the limits under which we can assume a zero-leak-off interface. Second, we explore the role of fault zone width in maintaining the validity of this zero-leak-off assumption. Building upon these foundational investigations, we demonstrate the possibility of extending the numerical framework to describe fault-fluid interactions considering poroelastic coupling.

How to cite: Wang, Y.-H. and Rafn Heimisson, E.: An efficient hybrid SBI-FD method for modeling fluid migration and fault-fluid interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10564, https://doi.org/10.5194/egusphere-egu24-10564, 2024.

The slip behavior of crustal faults is known to be controlled by the mineralogic composition of the fault gouge. The exact properties determining the frictional behavior of geologic materials, including diverse remains an important question. Here, we use a geochemical approach considering the role of water-rock interactions. As a mechanism, we suspect that the mineral surface charge allows attractive and repulsive forces (Van Der Waals type), and that those forces may influence the static mechanical behavior of clays (cohesion, static friction).  On the other hand, we suspect that the water bound to the mineral surfaces may play a role during shearing.  To address these ideas, we measured the cation exchange capacity (CEC) of 10 different rock and mineral types, including non-clays and a range of phyllosilicate minerals, using CEC as a proxy for the mineral surface charge and the ability to bind water to the mineral surfaces.  For these materials, we conducted laboratory shearing experiments measuring the pre-shear cohesion, peak friction coefficient, residual friction coefficient, post-shear cohesion, and velocity-dependent friction parameters under 10 MPa effective normal stress.  
Our results show that low CEC materials (< 3 mEq/100g) tend to exhibit high friction, low cohesion, and show velocity-weakening frictional behavior. The phyllosilicate minerals exhibit larger CEC values up to 78 mEq/100g and correspondingly lower friction coefficients, higher cohesion, and velocity-strengthening frictional behavior. Zeolite exhibits a relatively high CEC value typical of phyllosilicates, but its strength and frictional characteristics are that of a non-clay with low CEC. This suggests that grain shape and contact asperity size may be more important for non-phyllosilicates. For phyllosilicates, we suggest that the systematic patterns in strength and frictional behavior as a function of CEC could be explained by water bound to the mineral surfaces, creating bridges of hydrogen or van der Waals bonds when the particles are in contact. Such bonding explains the large cohesion values for high-CEC materials under zero effective stress, whereas surface-bound water trapped between the particles under load explains low friction.  Beyond the results of this study, CEC appears to be a controlling factor for other properties such as permeability and even the amount of bound DNA in sediments.

 

How to cite: Ikari, M. and Conin, M.: Cation Exchange Capacity Quantifies the Link Between Mineral Surface Chemistry and Frictional-Mechanical Behavior of Simulated Fault Gouges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10969, https://doi.org/10.5194/egusphere-egu24-10969, 2024.

During natural and induced seismic activities, pore fluid pressure within fault zones and their surrounding rock may respond differently to stress variations, introducing additional complexities to seismic hazard assessment. While theoretical investigations have recognized the influence of such poroelastic heterogeneity on fault instability, incorporating phenomena like slip-induced dilation or compaction, the chosen poroelastic properties in these studies lack robust constraints from experimental measurements. Addressing this gap, our study focuses on quantifying the heterogeneity of poroelastic properties in the presence of a fresh fault, aiming to elucidate the coupling between poroelasticy and fault dilatancy during fault slip.

In our experimental investigation, we examined the evolving dynamics of pore pressure both on- and off-fault in initially intact Westerly granite samples. Applying confining stress of 100 MPa and a pore pressure of 60 MPa at two sample ends to replicate crustal settings, we induced a sliding fault plane through loading to failure under a constant strain rate. In the faulted samples, we measured the pore pressure response under sudden step loading in the direction of the maximum compression σ1. Each loading step of around 5 MPa was imposed incrementally increasing the differential stress from 5 MPa to approximately 80 MPa (frictional resistance) after achieving pore pressure equilibrium. Detailed measurements, including displacement, bulk deformation, differential stress, local pore pressure and acoustic emissions were recorded throughout these tests. A spring-slider model coupled with 1-D fluid diffusion was used to try to simulate experimental observations.

Our results indicate that both the shear zone and the bulk exhibit a diminishing Δp/Δσ1 with increasing differential stress. Measurements within the fault zone consistently yield positive values, surpassing those off the fault, with the discrepancy more pronounced at lower stress levels. In regions farther away from the shear zone, the off-fault response Δp/Δσ1 presents a smaller value compared to locations proximal to the fault zone and may even exhibit slight negativity. During fault slip, on-fault measurements exhibit an instantaneous increase upon step loading followed by a gradual decrease, as a result of the interplay between poroelasticity and fault dilatancy. These observations were effectively reproduced by the numerical model integrating the poroelastic measurements and rate-and-state fault friction with slip-dependent dilatancy. The implications of this investigation extend to an enriched understanding of the heterogeneity in poroelastic responses between fault zones and host rocks, serving as valuable benchmarks for informing future numerical simulations, particularly in the context of naturally formed fresh faults. 

How to cite: Liu, D. and Brantut, N.: Poroelastic heterogeneity in the presence of a fresh fault: experimental insights and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10998, https://doi.org/10.5194/egusphere-egu24-10998, 2024.

EGU24-11200 | Orals | EMRP1.6

Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front 

Francois Passelegue, Pierre Dublanchet, Nicolas Brantut, and Hervé Chauris

A growing amount of evidence indicate that aseismic transients driven by overpressure play an important role in the triggering of induced seismicity. Understanding the physical control on aseismic slip development is thus important for seismic hazard assessment. We conducted an investigation into the propagation dynamics of a fluid-driven slip front along a laboratory frictional interface composed of granite. The experiments were carried out under a confining pressure of 90 MPa, with an initial uniform fluid pressure of 10 MPa. Fault reactivation was initiated by injecting fluids through a borehole directly connected to the fault.

Our findings reveal that the peak fluid pressure at the borehole leading to reactivation exhibits an increase proportionate to the injection rate. Employing three fluid pressure sensors and eight strain gauges strategically positioned around the experimental faults, we performed an inversion analysis to image the spatial and temporal evolution of (i) hydraulic diffusivity and (ii) kinematic fault slip during each injection experiment. Our inversion methods integrated both deterministic and Bayesian procedures, facilitating the tracking of the fluid pressure front along the fault interface and the subsequent propagation of the slip front over time.

The migration pattern shares many similarities with natural slow slip events suspected to play a role in the development of natural and induced earthquake swarms or aftershock sequences.  We demonstrate that increasing the fluid injection rate induces a transition from a quasistatic propagation of the slip front correlated with the increase in fluid pressure to a dynamic scenario where the slip front outgrows the fluid pressure front, accelerating during its propagation. Furthermore, we establish that temporarily shutting off fluid pressure during injection induces the propagation of a pore-pressure back-front, which halts the propagation of the slip front, aligning with theoretical expectations.

How to cite: Passelegue, F., Dublanchet, P., Brantut, N., and Chauris, H.: Influence of Injection rate and slip-induced dilatancy on the propagation of fluid-driven slip front, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11200, https://doi.org/10.5194/egusphere-egu24-11200, 2024.

EGU24-11407 | ECS | Posters on site | EMRP1.6

Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear 

Sofia Michail, Paul Antony Selvadurai, Markus Rast, Antonio Felipe Salazar Vásquez, Patrick Bianchi, Claudio Madonna, and Stefan Wiemer

Faults in nature exhibit complex surface characteristics with patches of the fault (asperities) that may slip dynamically while other sections are more prone to creep (Beeler et al., 2011). Asperities forming in nature may be due to the geometric interactions between surfaces within a fault that contribute to complex stress states that are not well understood. Fault roughness is believed to play an important role in the control of the contact conditions established by asperities, directly affecting its potential to slip unstably. How the asperities are formed and how their seismogenic properties evolve due to wear is an important question with implications to slip budget and earthquake potential.

In this study, we performed a triaxial experiment at sequentially increasing confining pressures (Pc = 60, 80, 100 MPa) on a saw-cut sample of Carrara marble. We analysed the quasi-static frictional response that benefited from novel arrays of distributed strain sensors (DSS) obtained using fiber optics. This sensor offered unique insight into the axial strain with a spatial resolution of 2 mm. The frictional behaviour during the first confining pressure step exhibited a dynamic instability in the form of a stick-slip event (SS) that produced a measurable stress drop. In the subsequent confining pressure stages, where an increase in confining pressure translated to increased normal stress, the fault behaved in a stable manner and no dynamic instabilities were produced. This observation is inconsistent with frictional stability theory (e.g. Rubin and Ampuero, 2005) and required pre- and post-mortem campaigns into the surface characteristics and their evolution to explain this abnormal behaviour. Therefore, we employed experimental techniques (pressure sensitive film (PSF), optical and stylus profilometry) along with finite element (FE) model in ABAQUS to characterize the pressure and roughness.

The DSS array showed extensional axial strain closer to the edges of the fault, while only compression was expected in this triaxial loading test. The pre-experimental profilometry revealed an asperity located at the centre of the fault with a curvature ratio of h/L=0.1% inherited from the hand-lapping preparation, which dominated the initial contact conditions prior to the SS and explained the DSS observations. The DSS results were confirmed using a FE model which justified the effect of the fault geometry (h/L) on the strain response. After the SS, wear and smoothening of the central asperity was seen in roughness measurements. The profilometric measurements showed that gouge was deposed adjacent to the high normal stress asperity center (PSF) and were characterized by increased RMS roughness. These small amounts of gouge on the fault surface were sufficient to suppress the seismic response of the asperity. These findings show that the seismic potential of a carbonate (softer) asperity, may be highly influenced by the debris produced during wear. Its impact on earthquake nucleation could provide insight into large-scale earthquake preparation processes on carbonate faults in nature.

 

References:

  • Beeler, M., Lockner, D. L. and Hickman, S. H. (2001), Bull. Seis. Soc. Am., 91 (6): 1797–1804
  • Ampuero, J.-P. and Rubin, A. M. (2008), J. Geophys. Res., 113, B01302

How to cite: Michail, S., Selvadurai, P. A., Rast, M., Salazar Vásquez, A. F., Bianchi, P., Madonna, C., and Wiemer, S.: Laboratory Insight into the Evolution of the Seismic Potential of an Asperity due to Wear, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11407, https://doi.org/10.5194/egusphere-egu24-11407, 2024.

EGU24-11536 | Orals | EMRP1.6 | Highlight

Fault activation from up close 

Men-Andrin Meier, Domenico Giardini, Stefan Wiemer, Massimo Cocco, Florian Amann, Elena Spagnuolo, Paul Selvadurai, Elisa Tinti, Luca Dal Zilio, Alba Zappone, Giacomo Pozzi, Mohammadreza Jalali, and Valentin Gischig and the FEAR science team

Our understanding of earthquake rupture processes is generally limited by the resolution of available observations. In all but exceptional cases, earthquake observations are made at comparatively large distances from the rupture itself, which puts a limit on what spatial scales can be resolved. At the same time, it is clear that small scale processes may play a crucial, if not dominant, role for various seismogenic processes, including rupture nucleation, co-seismic weakening and stress re-distribution.

The Fault Activation and Earthquake Rupture ('FEAR') project aims at collecting and interpreting a multitude of earthquake-relevant observations from directly on and around the process zone of an induced earthquake. To this end, we attempt to activate a natural granitic fault zone in the BedrettoLab, at a depth of ~1km, after instrumenting the fault zone with a multi-domain and multi-scale monitoring system. The goal is to observe and study earthquake rupture phenomena in a natural setting, from unusually close distance.

In this talk, we outline the project status, the science goals, and the plans for the main experiments, which are scheduled for the years 2024 - 2026. Notable milestones we report on include

  • the identification and detailed characterisation of the target fault zone
  • the beginning of niche and tunnel excavations
  • laboratory experiments that characterise the frictional and mechanical behaviour of both gauge material and host rock of the target fault zone
  • development of numerical models for 2D and 3D dynamic rupture propagation
  • development of tailored monitoring methods for seismicity, strain, temperature, pressure, bio-geo-chemistry and other relevant observables
  • development of remote experiment control methods
  • test stimulations in a nearby rock volume of similar geology, with an already existing monitoring system, where we tested the influence of pre-conditioning injection protocols
  • similar test stimulations in the same volume where we aim at triggering a larger event (target Mw~0)
  • active seismic experiments in an underground salt mine, to calibrate the very- to ultra-high frequency (1k Hz - 500k Hz) acoustic emission sensors

Together, these and other efforts constitute the necessary ingredients we need for interpreting the near-source observations that we will collect during the fault activation experiments.

How to cite: Meier, M.-A., Giardini, D., Wiemer, S., Cocco, M., Amann, F., Spagnuolo, E., Selvadurai, P., Tinti, E., Dal Zilio, L., Zappone, A., Pozzi, G., Jalali, M., and Gischig, V. and the FEAR science team: Fault activation from up close, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11536, https://doi.org/10.5194/egusphere-egu24-11536, 2024.

EGU24-12986 | ECS | Posters on site | EMRP1.6

Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations 

Elvira Latypova, Fabio Corbi, Giacomo Mastella, Jonathan Bedford, and Francesca Funiciello

The short seismic record with respect to the return time of large subduction earthquakes and the spatial fragmentation of available geophysical data represent unfavourable conditions for robust hazard assessment. Over the last decade, data from scaled seismotectonic models have become useful in filling the observational gaps of seismic and geodetic networks. Such models allow reproducing hundreds of analogue seismic cycles in a few minutes of experimental time and with the advantage of known and controllable boundary conditions. 

Here we present experimental results from Foamquake – an established 3D seismotectonic model, which simulates megathrust subduction. Recent technical advances in experimental monitoring have allowed us to include into our research a high-frequency camera to record model surface deformation at 50 Hz and a network of 5 accelerometers (located on the model surface) that measure the three components of acceleration at 1 kHz. To analyse the camera data, we used particle image velocimetry (PIV) to derive surface displacements, such as in a dense, homogeneously distributed geodetic network spanning updip to scaled depths that are often offshore and, therefore, typically under-monitored in natural subduction zones.

We performed 33 experiments exploring 10 different geometrical configurations of asperities along the analog megathrust. In particular, we varied the number of asperities, their size, location, and extra normal load. We observed that the rupture pattern of analogue earthquakes predictably changes as the extra normal load varies and the distribution of asperity configurations becomes more complex. Depending on the number and size of the asperities and the size of the barrier between them, we noticed different ratios between full and partial ruptures with different recurrence time (Rt) intervals. In some experiments we detected cascades of ruptures. We used the coefficient of variation (CoV) of recurrence time to quantify analog earthquakes periodicity. Most of our models display quasi-periodic analog earthquakes recurrence with CoV<0.5, but multi-asperity experiments with variable-size and extra normal load lean toward random behaviour as testified by CoV~0.8.

Future investigations include the following steps – exploring this great volume of data using machine learning, looking for spatial and temporal relationships between accelerometer and PIV displacements, and tracking in detail the aseismic processes that may precede and follow earthquake rupture.

How to cite: Latypova, E., Corbi, F., Mastella, G., Bedford, J., and Funiciello, F.: Exploring earthquake recurrence and nucleation processes with Foamquake and a variety of asperity configurations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12986, https://doi.org/10.5194/egusphere-egu24-12986, 2024.

EGU24-13117 | ECS | Posters on site | EMRP1.6

A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach 

Ludovico Manna, Giovanni Toscani, Matteo Maino, Leonardo Casini, and Marcin Dabrowski

The 2D, plane strain, Finite Element Method-based linear elastic model that I present aims to assess the differential stress response to variations in the geometric configuration of a system of multiple collinear elliptic cracks intercepting a body of rock undergoing elastic deformation. The assumption underlying this simulation is that a collection of thin voids in a continuum medium can replicate the features observed in a system consisting of rough fault profiles in partial contact subjected to shear. The linear elastic model is designed to reproduce the stress and displacement fields around a rough fault, with a specific focus on stress concentration around its contact asperities. The model also allows to record the principal stress field on the domain for a wide range of scales and geometric properties of the system of collinear cracks embedded in the deforming rock. Analyzing the dependence of differential stress on parameters describing the geometry of rough fractures allows for considerations on the primary factors influencing brittle failure. Additionally, the examination of principal stresses around the tips of the cracks helps evaluate the potential orientation of new fracture patterns that may emerge when the yield strength of the deforming material is locally exceeded. The magnitude and orientation of the principal stresses are also crucial for the understanding of fracture coalescence and frictional reactivation of shear cracks in an elastic rock, which in turn is one of the main factors that govern the seismic cycle of natural faults. Furthermore, a comparison of the results of the present model with recent wing crack models of brittle creep suggest that our code may also be useful to obtain estimates of the critical distance between cracks for their interaction to coalesce into larger fractures. The process is assumed to indefinitely continue at greater scales, which offers the chance to propose a model for fault formation and propagation.

How to cite: Manna, L., Toscani, G., Maino, M., Casini, L., and Dabrowski, M.: A model for the formation and propagation of faults from the coalescence of smaller-scale systems of cracks: Finite Element Method-based numerical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13117, https://doi.org/10.5194/egusphere-egu24-13117, 2024.

EGU24-13433 | Orals | EMRP1.6

The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading 

Michele Fondriest, Fabio Arzilli, Benoit Cordonnier, Michael Carroll, and Mai-Linh Doan

The propagation of earthquake fault ruptures in the crust involve the generation of unloading stress pulses sufficiently large to induce dynamic failure of water-saturated rocks under tensional stresses and hydrofracturing. Similar processes are also activated during underground rock mass excavation activities in mines and tunnels. The current knowledge about rock fracturing via dynamic unloading is mainly limited to empirical records and numerical simulations, while there is a general paucity of experimental studies, due to difficulties in reproducing large instantaneous decompressions on rock samples using standard triaxial rigs. Until now rapid decompression and fracturing of large rock samples in dry conditions was reported only by using an unconventional gas-confined vessel.

Here, we report rock-fracture results for newly conceived rock decompression experiments, completed through the innovative use of a “cold-seal pressure vessel” (CSPV) apparatus which is routinely employed in experimental petrology. We applied instantaneous large decompressions on water-saturated rock samples equilibrated at high confinement (up to 200 MPa) and temperatures (up to 540°C). The tested rock samples were fine-grained Westerly granite, coarse-grained tonalite and micritic limestone. During the decompressions the rock samples hydrofractured due to the confinement dropping faster than the pore pressure within the rock. Porosity measurements, SEM imaging and X-ray µCT acquired before and after the tests suggest that the magnitude of dynamic fracturing not only positively correlates with the pressure drops but it mostly increases when the decompression is associated to a phase change of the pore water (e.g. supercritical fluid to subcritical gas) . Water vaporization or degassing imply an instantaneous volume expansion (up to 70 times) which critically enhances dynamic fracture propagation along rock grain boundaries. The induced fractures span from mm-long transgranular cracks to microcracks with submicrometric aperture. Therefore, synchrotron light high-resolution microtomography (final pixel resolution of 0.3 µm) was employed to fully resolve and quantify the 3D fracture networks of these deformed rock samples. Such unique dataset allowed us to determine at different scales the fracture intensity, aperture and connectivity of the dynamically induced fracture networks and to assess the key contribution of pore-water physical state changes on the initial stages of dynamic fracturing in rocks at crustal conditions. Such results will contribute to close a current knowledge gap in rock mechanics.

How to cite: Fondriest, M., Arzilli, F., Cordonnier, B., Carroll, M., and Doan, M.-L.: The effect of pressure drop and fluid expansion during rock fracturing by dynamic unloading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13433, https://doi.org/10.5194/egusphere-egu24-13433, 2024.

Establishing a constitutive law for fault friction is a crucial objective of earthquake science. However, the complex frictional behavior of natural and synthetic gouges in laboratory experiments eludes explanations. Here, we present a constitutive framework that elucidates the slip-rate, state, temperature, and normal stress dependence of fault friction under the relevant sliding velocities and temperatures of the brittle lithosphere during seismic cycles. The competition between healing mechanisms explains the low-temperature stability transition from steady-state velocity-strengthening to velocity-weakening as a function of slip-rate and temperature. In addition, capturing the transition from cataclastic flow to semi-brittle creep accounts for the stabilization of fault slip at elevated temperatures. The brittle behavior is controlled by the real area of contact, which is a nonlinear function of normal stress, leading to an instantaneous decrease of the effective friction coefficient upon positive normal stress steps. The rate of healing also depends on normal stress, associated with an evolutionary response. If these two effects do not compensate exactly, steady-state friction follows a nonlinear dependence on normal stress. We calibrate the model using extensive laboratory data covering various relevant tectonic settings. The constitutive model consistently explains the evolving frictional response of fault gouge from room temperature to 600º for sliding velocities ranging from nanometers to millimeters per second, and normal stress from atmospheric pressure to gigapascals. The frictional response of faults can be uniquely determined by the in situ lithology and the prevailing hydrothermal conditions.

How to cite: Barbot, S.: Constitutive behavior of rocks during the seismic cycle in non-isothermal, non-isobaric conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14003, https://doi.org/10.5194/egusphere-egu24-14003, 2024.

EGU24-14504 | Posters on site | EMRP1.6

The role of poroelasticity in rupture dynamics across fault stepovers 

Luyuan Huang, Luca Dal Zilio, and Elías Rafn Heimisson

Understanding earthquake rupture propagation across fault stepovers is pivotal for assessing the seismic hazard, offering vital insights into dynamic rupture processes within intricate fault geometries. However, the role of poroelastic effects within strike-slip fault systems featuring stepovers remains unexplored in dynamic models simulating Sequences of Earthquakes and Aseismic Slip (SEAS). Many existing models neglect poroelastic effects, and among those that consider them, a typical standard value of 0.8 is adopted for Skempton's coefficient B. Furthermore, a single dynamic rupture simulation is unable to address the frequency at which ruptures propagate through the stepover. Instead, these simulations only provide a binary status, indicating whether the ruptures jump or arrest. Thus, the investigation into how poroelasticity influences the likelihood of an earthquake jumping through a stepover emerges as a significant area of study. In response, we introduce a quasi-dynamic boundary element model that simulates 2D plane-strain earthquake sequences. This model incorporates undrained pore pressure responses affecting the fault's clamping and unclamping mechanisms and is governed by rate-and-state friction, with state evolution defined by the aging law. We first illustrate that dynamic rupture occurring in either left-lateral or right-lateral fault stepovers leads to a dynamic decrease (unclamping) or increase (clamping) in the effective normal stress. Dynamic variations of the effective normal stress depend on Skempton's coefficient. Consequently, higher Skempton's coefficients can promote rupture jumping across fault segments even for larger stepover distances. We then conduct a thorough parameter space study, evaluating the effects of Skempton's coefficient variations and stepover width on fault interactions within a fluid-filled porous environment. The likelihood of rupture jumping involves a trade-off between Skempton's coefficient and stepover width. We validate the numerical model by comparing it to an analytical solution that involves a plane strain shear dislocation on a leaky plane within a linear poroelastic, fluid-saturated solid. This validation demonstrates that a simple analytical solution, primarily dependent on fault dislocation and Skempton's coefficient, has the potential to effectively predict the pore pressure change. The critical jumping width for 50% chance of rupture jumping predicted by our model explains the threshold dimension of the fault step, above which ruptures do not propagate. This study highlights the significance of incorporating poroelastic effects on- and off-fault in understanding the dynamic variations of the effective normal stress, which could significantly alter the overall length of fault rupture.

How to cite: Huang, L., Dal Zilio, L., and Rafn Heimisson, E.: The role of poroelasticity in rupture dynamics across fault stepovers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14504, https://doi.org/10.5194/egusphere-egu24-14504, 2024.

EGU24-14566 | Posters on site | EMRP1.6

Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions 

Weifeng Qin, Lu Yao, Tongbin Shao, Wei Feng, Jianye Chen, and Shengli Ma

The frictional properties of faults are primarily controlled by their mineral composition, as well as ambient and deformation conditions, such as temperature, pore fluid, normal stress, and slip displacement. While many studies have been conducted to decipher how temperature and pore fluid may affect the frictional behavior of faults, less attention has been paid to the slip displacement effects, especially under hydrothermal conditions. By employing a rotary shear apparatus equipped with an externally-heated hydrothermal pressure vessel, we conducted large-displacement (up to 521 mm) friction experiments on chlorite under temperature (T) of 25 to 400℃ and pore water pressure (Pp) of 30MPa. The imposed effective normal stresses were 200 MPa and the slip rates ranged from 0.4 to 10 μm/s. The experiments unveiled significant slip strengthening in chlorite within the temperature range of 25 to 400 °C. Moreover, with increasing temperatures, there was an overall increasing trend in both the rate of slip strengthening and the ultimate frictional strength. For example, under T = 25 °C, the friction coefficients at displacements of 5, 90, and 521 mm were 0.33, 0.49, and 0.59, respectively, in contrast to 0.46, 0.79, and 0.88, respectively, at the same three displacements under T =400 °C. Under all the temperature and displacement conditions, chlorite exhibited velocity strengthening behavior without discernible temperature dependence, although the velocity-dependence parameter (a-b) increased with slip displacement. Microstructural analysis revealed that, the entire layer of the chlorite gouge experienced pervasive and intense shear deformation after slip of 521 mm, with extremely remarkable grain-size reduction. The thermogravimetrical and FTIR data of the deformed chlorite samples, together with the microstructural data, suggest that the dehydroxylation and the distortion of crystal structure of chlorite might occur during the friction experiments conducted at T ≥ 200 °C. Such changes may explain the more pronounced slip strengthening of chlorite with increasing temperatures towards 400 °C. This explanation can be further demonstrated by a comparative experiment conducted under varying temperatures (400°C for the first 100 mm of slip, followed by 25°C for the rest of 100 mm slip), wherein the friction coefficient at T = 25°C during the latter stage of slip remains as high as that at T = 400°C. These findings highlight the importance of slip displacement in controlling the frictional strength and its variations of chlorite-bearing faults at depths, and have profound implications for understanding the fault slip behaviors and earthquake mechanisms in subduction zones.

How to cite: Qin, W., Yao, L., Shao, T., Feng, W., Chen, J., and Ma, S.: Frictional behavior of chlorite in large-displacement experiments under hydrothermal conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14566, https://doi.org/10.5194/egusphere-egu24-14566, 2024.

EGU24-15205 | ECS | Posters on site | EMRP1.6

Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults 

Federica Paglialunga, Francois Passelegue, and Marie Violay

Many aspects of earthquake physics are still not completely understood given its intrinsically complex nature. Among the others, the nucleation process; when and where an earthquake will occur, as well as its magnitude. Seismology is a commonly used method for studying earthquakes, but it faces challenges in accessing precise information about the physical processes taking place on the fault plane.

Here, we show how laboratory seismology can directly shed light on fault plane dynamics. Our approach involves reproducing in the laboratory on a large biaxial apparatus with a fault length of 2.5 m generated by two analog (PMMA) samples brought into contact. The experimental setup allows to impose both a heterogeneous loading distribution through the use of independent pistons loading the fault in the normal direction and specific boundary conditions (i.e. by modifying stopper and puncher dimensions). The stress state is measured through strain gauges at high frequency (40 KHz) along 15 locations along the fault. The experiments provide insights into two crucial aspects of laboratory earthquakes: (i) the nucleation location of ruptures and (ii) the complexity of the seismic cycle.

Our findings reveal that the initial on-fault stress distribution plays a significant role in both aspects. We observe that ruptures consistently nucleate in locations where the stress ratio τ/σn is the highest. Notably, such values change among experiments, challenging the widespread notion that a friction coefficient solely governs the onset of instability. Furthermore, we demonstrate how the heterogeneity of the initial prestress distribution along the fault controls the complexity of the seismic cycle. In certain cases, the seismic cycle manifests as system-size events with complete ruptures occurring regularly in time, devoid of precursors. Conversely, other initial stress distributions generate more complex cycles, characterized by multiple precursors before a main rupture, predominantly occurring in zones of elevated τ/σn (referred to as 'friction asperity'). The complexity of the seismic cycle can be described in terms of the number of precursory events, inter-event time, and the size of finite ruptures.

This study, carried out in a long laboratory fault, highlights the complexities that emerge when heterogeneous, hence more realistic, stress conditions are applied, providing valuable insights into the physics of natural earthquakes.

How to cite: Paglialunga, F., Passelegue, F., and Violay, M.: Initial stress distribution dictates nucleation location and complexity of the seismic cycle of long laboratory faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15205, https://doi.org/10.5194/egusphere-egu24-15205, 2024.

EGU24-15273 | ECS | Orals | EMRP1.6

Impact of multiscale heterogeneities on the nucleation of earthquakes 

Mathias Lebihain, Thibault Roch, Marie Violay, and Jean-François Molinari

Earthquake nucleation is traditionally described using cascading or slow pre-slip models. In the latter, nucleation occurs as the sudden transition from quasi-static slip growth to dynamic rupture propagation. This typically occurs when a region of the fault of critical size Lc, often called nucleation length, is sliding. This transition is relatively well-understood in the context of homogeneous faults. Yet, faults exhibit multiple scales of heterogeneities that may emerge from local changes in lithologies or from its self-affine roughness. How these multiscale heterogeneities impact the overall fault stability is still an open question.

Combining the nucleation theory of [Uenishi and Rice, JGR, 2003] and concepts borrowed from statistical physics, we propose a theoretical framework to predict the influence of brittle/ductile asperities on the nucleation length Lc for simple linear slip-dependent friction laws. Model predictions are benchmarked on two-dimensional dynamic simulations of rupture nucleation along planar heterogeneous faults. Our results show that the interplay between frictional properties and the asperity size gives birth to three (in)stability regimes: (i) a local regime, where fault stability is controlled by the local frictional properties, (ii) an extremal regime, where it is governed by the most brittle asperities, and (iii) a homogenized regime, in which the fault behaves at the macroscale as if it was homogeneous and the influence of small-scale asperities can be averaged.  

Using this model, we explore the overall stability of rough faults, featuring multiscale distributions of frictional properties. We also investigate the stability of velocity-neutral faults that features brittle asperities. Overall, our model provides a theoretical basis to discriminate which heterogeneity scales should be explicitly described in a comprehensive modelling of earthquake nucleation, and which scales can be averaged.

How to cite: Lebihain, M., Roch, T., Violay, M., and Molinari, J.-F.: Impact of multiscale heterogeneities on the nucleation of earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15273, https://doi.org/10.5194/egusphere-egu24-15273, 2024.

EGU24-18100 | ECS | Posters on site | EMRP1.6

Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods 

Nico Bigaroni, Julian Mecklenburgh, and Ernest Rutter

During interseismic periods a fault at depth can experience non-constant effective normal stress due to fluctuations in the pore-fluid pressure. Pore-pressure oscillations may influence the healing capability of the fault and ultimately affect its reactivation. Thus, studying the behaviour of faults during interseismic periods is a critical factor in understanding the seismicity. Triaxial tests were conducted using saw-cut (45o) samples of Pennant Sandstone to investigate the influence of pore-pressure oscillations during slide-hold-slide (SHS) tests (th = 900 – 7300s) on its frictional behaviour and fault reactivation. The cylindrical samples were hydrostatically compacted at 30 MPa and pore-pressurized with argon gas at 5, 10 and 18 MPa resulting in effective normal stress (σ’n) 25, 20 and 12 MPa, respectively. Then the saples were deformed at a constant shear displacement rate ≈ 4.5 μm/s. To overcome the displacement hardening tendency of the sample geometry, we servo-controlled the confining pressure so that the resolved normal stress on the sliding surface is kept constant. Experimental observations revealed a significant influence of pore-pressure oscillation on the frictional behaviour resulting in an increase in both frictional healing and creep relaxation. Moreover, this effect was enhanced as the effective normal stress was increased further. To understand better the underling mechanism(s) that influences these time-dependent processes we coupled the frictional results with permeability measured using the oscillating pore pressure method during the SHS tests. Finally, we tested how the pore-pressure oscillation affected the fault reactivation by conducting creep experiments at constant shear stress while the fault was brought to reactivation via progressive increase in fluid pressure. Our results demonstrated how non-constant effective normal stress history during interseismic periods deeply affects the fault behaviour, with important implications for natural and human-induced seismicity.

How to cite: Bigaroni, N., Mecklenburgh, J., and Rutter, E.: Frictional Response of Clay-rich Sandstone to Pore-Pressure Oscillation Throughout Interseismic Periods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18100, https://doi.org/10.5194/egusphere-egu24-18100, 2024.

EGU24-19397 | Orals | EMRP1.6

The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model 

Fabian Barras, Einat Aharonov, and François Renard

Observations suggest that large earthquakes often propagate as self-healing slip pulses but the mechanical reason of this ubiquity remains debated. Pulse-like ruptures differ from the classical crack-like dynamics by the fact that the slipping portion of the fault is limited to the immediate vicinity of the propagating tip. In this work, we first propose a minimal model describing the dynamics of large earthquakes. In its simplest form, the model contains only two free parameters: a dimensionless stress parameter characterizing the initial state of stress along the fault and a ratio of elastic moduli. The model illuminates how self-healing slip pulses can be produced by the paucity of elastic strain energy that arises once the rupture dynamics interplays with the finite geometry of fault zones—even in the absence of additional mechanisms such as rate-dependent friction.

Next, we discuss the example of faults surrounded by a damage zone whose reduction in elastic wave velocity restricts the flow of strain energy to the rupture tip and promotes pulse-like rupture. Using the proposed model, we demonstrate how the contrast in wave velocities and the initial stress level in the fault zone mediate the propagation mode of the earthquake.

How to cite: Barras, F., Aharonov, E., and Renard, F.: The pulse-like dynamics of large earthquakes illuminated by a minimal elastodynamic model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19397, https://doi.org/10.5194/egusphere-egu24-19397, 2024.

EGU24-249 | ECS | Posters on site | TS1.11

Competitive methane bubble growth in aquatic muds 

Xiongjie Zhou and Regina Katsman

Methane (CH4) bubbles developed in shallow aquatic muds present a significant environmental risk. Macroscopic CH4 gas content in the muds is accommodated in discrete bubbles that grow from below the pore scale size to the maximum size defined by muddy sediment mechanical properties. The bubbles force out the water within the pores and distort the structure of the muddy sediment by moving the grains apart at their growth above the pore scale. However, the interaction between growing bubbles was not understood. This study uses a mechanical/reaction-transport numerical model to simulate the interaction of competitive CH4 bubbles paired with fracture-driven growth of varying initial sizes in aquatic muds. It reveals that mechanical and solute transport dynamics play a crucial role at different stages of bubble growth, particularly hindering the development of smaller bubble growth in competition. The stress from the larger bubble impacts the inner pressure and diffusive CH4 flux to the smaller bubble, slowing its initial growth (at t < 40 s). Additionally, the larger bubble later diverts CH4 from the smaller one, further inhibiting its growth expansion. This interaction may cause more horizontally oriented smaller bubbles and significant deformations in the larger bubble, especially as the distance between the bubble pair decreases. Such competitive bubble growth may explain the bubble size distributions observed in lab experiments and in situ, promoting CH4 retention in muddy sediments and the formation of gas domes, which are precursors to pockmarks that can cause abrupt gas releases to the water and potentially the atmosphere. The study provides a foundation for upscaling to different models of gassy muddy sediment acoustic characteristics and models of gas retention evolution, while maintaining single bubble growth metrics. It contributes to better evaluating and potentially reducing long-persisting uncertainties around CH4 emissions from shallow aquatic sediments.

How to cite: Zhou, X. and Katsman, R.: Competitive methane bubble growth in aquatic muds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-249, https://doi.org/10.5194/egusphere-egu24-249, 2024.

EGU24-392 | Orals | TS1.11

Dykes and their magma overpressure 

Tridib Kumar Mondal and Sirshendu Kumar Biswas

Dykes are essentially magma filled fractures within the earth’s crust often formed by the pressure imparted by the intruding magma. Magnitude of the magma overpressure has been traditionally determined utilizing elastic properties of the host rock and the complete dimension i.e., full length and maximum width of the fractures. Full exposures of dykes (from tip to tip) are rare, however, as most of the dyke bodies encountered in the field are subject to erosion or disruption along its length as a result of geological time, making estimation of aspect ratios challenging.

We propose a new method of estimating total length and maximum width of dykes from their partial outcrops featuring at least one exposed tip. Taking into account the fact that majority of dykes form as dominantly opening mode fractures with an elliptical shape of opening, the method involves solving the equation of this ellipse using every conceivable combination of a pair of ground points recorded on the dyke margin considering the visible tip as the origin. Validity of the method has been checked using published data obtained from incomplete dyke outcrops exposed in the caldera walls of Miyake-jima volcano in Japan. The calculated estimates are in line with the results acquired through a previous published method. The present method has been effectively utilized to calculate the aspect ratios of partially exposed mafic dykes emplaced within the younger granite of the Chitradurga Schist Belt in the western Dharwar craton of peninsular India. We discuss the ranges of their magma overpressure and depths of origin as well as the stress intensity factors associated with the host granite.

 

How to cite: Mondal, T. K. and Biswas, S. K.: Dykes and their magma overpressure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-392, https://doi.org/10.5194/egusphere-egu24-392, 2024.

EGU24-782 | ECS | Posters on site | TS1.11

(Un)certainties in tectonic stylolite stress inversion 

Saskia Köhler and Daniel Koehn

Over the last two decades application of stylolite roughness inversion has become a common tool to reconstruct paleostress-fields, stress magnitudes and burial depth. While the orientation of the highest principal stress is free of any doubt, there are uncertainties coming along with tectonic stylolite inversion that require a differentiated debate. This includes data quality, rock physical parameters, timing of stylolite growth and burial depth.

We present results of statistical data analysis, showing that data quality depends on the number of samples as well as on the sample size. Thus, the dataset can be of very high quality and stable in outcrop scale. This is faced by field and microscopic observations and results of the stress inversion itself, that demonstrate that some common assumptions, i.e. that modelled paleodepth can be used for tectonic stylolite inversion, are not generally valid. We want to open the discussion towards the question of how we can refine such assumptions and parameters for our paleo stress models and better prediction of recent deformations.

 

How to cite: Köhler, S. and Koehn, D.: (Un)certainties in tectonic stylolite stress inversion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-782, https://doi.org/10.5194/egusphere-egu24-782, 2024.

Observations of crustal stress orientation from the regional inversion of earthquake focal mechanisms often conflict with those from borehole breakouts. In particular, stress orientations from focal mechanism inversion tend to show little heterogeneity on length scales of kms to 10s of km, while borehole stress measurements often exhibit substantial short-length-scale heterogeneity.  Some of the difference may be because the two methods sample different locations within the crust, possibly indicating local stress heterogeneity, either laterally or with depth. We attempt to reconcile these two types of stress measurements, and investigate the implications for crustal stress heterogeneity. We compiled SHmax estimates from previous studies for 57 near-vertical boreholes with measured breakout azimuths across the Los Angeles region. We identified subsets of earthquake focal mechanisms from established earthquake catalogs centered around each borehole with various criteria for maximum depth and maximum lateral distance from the borehole. Each subset was independently inverted for 3-D stress orientation, and the SHmax direction compared with the corresponding borehole breakout-derived estimate. We find good agreement when both methods sample the basement stress (breakouts are close to the sediment-basement interface), or when both methods sample the mid- basin stress (sufficient earthquakes are present within a sedimentary basin). Along sedimentary basin margins, in contrast, we find acceptable agreement only when focal mechanisms are limited to shallow and close earthquakes, implying short-length-scale heterogeneity of <20 km. While the region as a whole shows evidence of both lateral and vertical stress orientation heterogeneity, we find a more homogeneous stress state within basement rock, over length scales of 1–35 km. These results reconcile the apparently conflicting observations of short-length-scale heterogeneity observed in boreholes, which sample primarily the basins, with the relative homogeneity of stress inferred from focal mechanisms, which sample primarily the basement.

How to cite: Hardebeck, J. and Luttrell, K.: A Unified Model of Crustal Stress Heterogeneity from Borehole Breakouts and Earthquake Focal Mechanisms , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3672, https://doi.org/10.5194/egusphere-egu24-3672, 2024.

EGU24-3863 | ECS | Orals | TS1.11

Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction 

Jean-baptiste Jacob, Benoît Cordonnier, Jonathan Wright, and François Renard

Understanding the mechanisms controlling brittle rock failure at the grain to sub-grain scale is a fundamental challenge in geosciences. Recent advances in triaxial compression and dynamic shock experiments combined with dynamic X-ray microtomography provide unparalleled insights into the 3D strain field evolution within deforming rocks. However, these methods do not accurately predict the heterogeneous internal stress field prior to failure, which is crucial for predicting microfracture initiation and propagation, leading to macroscopic failure. In the past decade, efforts have focused on developing synchrotron X-ray diffraction techniques leveraging the high penetrative capacity of hard X-rays from the last generations of synchrotron light sources. These techniques offer spatially resolved information on crystal phase orientation and elastic strain within a 3D volume. The local orientation and elastic strain tensor is reconstructed grain-by-grain, with precision down to approximately 10-3 radian for orientation and 10-4 for strain. Stress is then calculated using Hooke's law for anisotropic materials and the elastic constants of the crystal phases. We employed 3D X-ray diffraction to investigate the internal stress field evolution in a rock core sample deformed under triaxial compression in the Hades apparatus. A 5mm-diameter core of Berea sandstone was subjected to axial step loading under constant radial stress of 10 MPa, reaching brittle failure at around 90 MPa differential stress. Elastic strain of individual quartz grains were measured at different load steps, and elastic stresses were calculated, providing maps of the internal strain and stress field in the sample. Results reveal progressive elastic shortening of quartz grains parallel to the compression axis and elongation in orthogonal directions due to the Poisson’s effect. Reorientation of principal stress components is also observed with increasing axial stress, which tend to align with the macroscopic stress field. Internal stresses distribution varies within a range of ca. 300 MPa, suggesting local stress amplifications occurred interpreted as force chains, potentially favoring crack nucleation. This experiment is among the first ones to characterize in-situ the stress distribution in a natural rock under compressive loading, and demonstrates the potential of synchrotron diffraction techniques for investigating strain and stress in geological materials.

How to cite: Jacob, J., Cordonnier, B., Wright, J., and Renard, F.: Mapping internal stress field in deforming rocks using synchrotron high-energy X-ray diffraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3863, https://doi.org/10.5194/egusphere-egu24-3863, 2024.

Abstract

The shale reservoir in the Lower Permian Fengcheng Formation of Mahu Sag, the Junggar Basin is prospective in hydrocarbon exploration and development. Due to the complex structures of the study area and the strong heterogeneity of shale reservoirs, the distribution of in-situ stress in the research area has always been poorly understood. Previous studies on in-situ stress are mostly limited to mechanical experiments, logging calculation and simple 2D numerical simulations. Nevertheless, this study combines multiple technical means to simulate the complex 3D in-situ stress in a more accurate and precise way. In this study, a detailed geological model was established by utilizing the method of ant tracking. Post-stack acoustic impedance, logging data and acoustic emission tests were used to jointly invert the accurate 3D geomechanical model. The orientation of the in-situ stress in the study area was determined by digesting the information from FMI (Formation MicroScanner Image) while the boundary condition was fixed by acoustic emission experiments. Finally, the in-situ stress distribution of the study area was clarified through finite element numerical simulation. As is shown by the simulation results, the in-situ stress modeling revealed that the complicated stress state, stress differences, and stress difference coefficients, all of which can provide valuable guidance for well deployment optimization and hydraulic fracturing in the study area, are closely related to burial depth, faults, and rock mechanics parameters. The stress regime in the research area is mainly reverse faulting type. However, as the burial depth increases, the stress regime will change accordingly, transforming from reverse faulting stress regime to strike-slip faulting stress regime. In the same time, the existence of faults will also affect the stress regime to a certain degree. In addition, most faults in the research area are stable and show little tendency of slippage, but there may be a higher risk of slippage in the deep strata. Therefore, it is advisable to avoid these areas as much as possible during geological exploration.

Keywords: 3D in-situ stress field, numerical simulation, shale reservoir, Mahu Sag

How to cite: Chen, P., Qiu, H., and Chen, X.: 3D numerical simulation of complex in-situ stress fields in shale reservoirs: A case study in the northwestern Junggar Basin of China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4458, https://doi.org/10.5194/egusphere-egu24-4458, 2024.

Knowledge of the present‐day stress field in the Earth's crust is key for understanding the mechanical behaviour of rocks and structures under tectonic forces. The study of stress fields therefore remains a pivotal area for understanding the mechanical behaviour of rocks, fluid flow at depth and in revealing mechanisms that cause tectonic plates to creep, fail, or rupture. stress patterns in the Earth's crust appear on different scales: first order (plate scale), second order (regional scale), and third order (local scale). The latter is mainly controlled by basin geometry, topography, local inclusions, density contrasts, and active faults and can mask regional and plate stress patterns.

In this contribution, a couple of examples of stress states at the local, regional and large scale are presented using borehole breakouts as main stress indicator for the current stress field orientation.

In order to understand the influence of stress field evolution at local scale, a case study in Hawai´i concerns the effects of the two large overlapping shield volcanoes on the stress field at depth. The analysis reveals that the two-competing gravitational loads primary control the orientation of the present-day stress field, which deviates significantly from the plate and regional tectonic stress field. Therefore, knowledge of local and shallow stress fields can have a significant impact on future borehole planning. From a more regional point of view, an example of current stress orientation in Sweden is presented. The main objectives are to constrain the orientation of horizontal stresses using borehole data, and to discuss implications for geothermal exploration. Thus, obtaining detailed and accurate data on the stress state is of paramount significance to optimise the design of underground installations in order to maximise fluid flow and minimise the risks of wellbore instability. Finally, a large-scale study in Italy investigates the stress field at plate scale to reveal whether the orientation of horizontal stresses may change with depth or laterally indicating stress perturbations and heterogeneities related to areas with complex geo-tectonic setting.

In conclusion, this contribution aims to illustrate and emphasise the relevance of determining the horizontal stress orientation at depth in order to improve the understanding of subsurface stress fields and their applications in different fields of geosciences and different geological settings.

How to cite: Pierdominici, S.: Reconstruction of the state of stress in the upper crust by borehole breakouts stress indicators, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5744, https://doi.org/10.5194/egusphere-egu24-5744, 2024.

Transient stress perturbations caused by passing waves of distant earthquakes have been observed to activate fault slip. Observations of remotely triggered earthquakes at distances greater than ~2-3 mainshock fault lengths suggest that certain conditions promote fault activation, including large-amplitude shaking at periods below ~ 10 seconds within a geothermal setting and extensional and/or transtensional tectonics. Yet, it is still unclear if remote dynamic triggering is ubiquitous. An additional complication to determining the prevalence of triggering is that there are likely many small-magnitude earthquakes within sparsely instrumented regions that are uncataloged. Additionally, large mainshock signals can mask smaller local events that also are missing from the local catalogs. As a result, possible triggering mechanism(s) remain enigmatic. Bounding the necessary physical conditions for remote triggering, such as determining the upper or lower bounds of stress or strain amplitudes, the orientation of the seismic wave’s traversal with respect to the local stress field or fault geometry, or the geologic properties conducive to triggering can help provide clues about the physics of remote triggering. 

            The northern Chilean subduction margin provides an ideal setting to study remote dynamic triggering. Its dense instrumentation provides a long history of both seismic and aseismic deformation in both the subduction system and forearc faults, including the Atacama fault system. Our investigation combines a new, detailed regional earthquake catalog (2007-2021) from Sippl et al., (2023) and documented cases of triggered aseismic slip in the Atacama fault system (Victor et al., 2018). We use a twofold approach to determine the prevalence of earthquake triggering by candidate mainshocks that produce strains at our target location ranging from 1 to ~140 microstrain. The approach uses 1) a difference-of-means test of cataloged seismicity outside of the mainshock cluster (including foreshocks and aftershocks), and 2) a waveform-based approach to look for earthquake triggering at seismic stations located close to creepmeters that recorded triggered aseismic slip events.  We find a lack of evidence of persistent, statistically significant seismicity increases outside of the mainshock cluster associated with any of the candidate mainshocks.  Notably, there is an absence of significant seismicity changes outside of clustered foreshock or aftershock seismicity associated with the series of 11 M6.2-8.2 earthquakes that produced high-strain-rate events during the 2014 Iquique sequence. Seismic recordings of the 2011 M9.1 Japan earthquake at stations CX.PB01-CX.PB14 located near creep meter stations CAR3 and CH01 on the Mejillones peninsula near the Chomache fault reveal evidence of remote triggering. We observe local, uncataloged earthquakes that are only visible after applying a high pass filter that removes the mainshock signal that otherwise overprinted and swamped the local signals.  The uniformity of particle motions (circular or oblong) generated by local earthquakes on multiple stations (N=9) is lacking in most non-triggering mainshocks. This uniformity suggests that the orientation of transient stress perturbations imparted by the mainshock waveforms, in relation to the local fault orientations, may play a role in the triggering process. 

How to cite: Harrington, R. M., Kilb, D., Verdecchia, A., and Victor, P.: Putting faults into motion by remote dynamic triggering: local ground-motion orientations seem to eclipse strain in the northern Chilean subduction forearc crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6650, https://doi.org/10.5194/egusphere-egu24-6650, 2024.

EGU24-6837 | Posters on site | TS1.11

Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary  

Mojtaba Rajabi, Moritz Ziegler, Oliver Heidbach, and Malte Ziebarth

The complex interplay between the Pacific and Australian plates in New Zealand offers a unique opportunity to investigate the present-day stress field in a tectonically active area. This study examines the present-day stress pattern of New Zealand through the analysis and compilation of data from 289 boreholes, 4291 earthquake focal mechanism solutions, and 72 neotectonic geological structures. Utilizing the Moho depth of New Zealand, we developed both crustal and mantle stress maps. Stress data above the Moho depth is categorized as the crustal stress map, while data below the Moho is classified as the mantle stress map.

The crustal stress map reveals a consistent ESE-WNW orientation of the maximum horizontal stress (SHmax) across much of the South Island, presenting a high angle to the strike of major active strike-slip faults. In the North Island, the crustal SHmax pattern is variable, highlighting the predominant role of the Pacific Plate subduction beneath the Australian Plate along the Hikurangi Margin. Within the Hikurangi Subduction Zone, both the crustal and mantle SHmax orientations are variable. However, the Taupo Rift Zone exhibits completely different stress pattern in mantle and crust, highlighting the Moho as a strong decoupling horizon in this region.

An examination of neotectonic stress regimes, derived from the neotectonic fault database, in comparison with the present-day stress regime from our stress database across 28 tectonic domains in New Zealand indicates a correlation between observed faults, faulting styles, and the stress field. Nevertheless, discrepancies emerge in certain domains, where the acting stress field diverges from the one expected according to the observed faults, suggesting non-optimal fault orientations.

How to cite: Rajabi, M., Ziegler, M., Heidbach, O., and Ziebarth, M.: Neotectonic stress characterization of New Zealand along the Australia–Pacific plate boundary , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6837, https://doi.org/10.5194/egusphere-egu24-6837, 2024.

The Sichuan-Yunnan region of the SE and E margin of the Tibetan Plateau, situated at the transitional nexus between the seismically-active intensely-deformed Tibetan Plateau and the tectonically stable Yangzi block with comparatively low seismicity, has experienced substantial geological transformations during the Quaternary. Given the pronounced seismicity, there is an escalating imperative for an accurate and refined distribution of the stress field in the region. To unravel the contemporary stress state within major active blocks and along active faults in the study area, an elaborate computation of their tectonic stress field is undertaken by comprehensive updated earthquake focal mechanisms catalog. The tectonic stress field in Sichuan-Yunnan region exhibits obvious lateral variations, with the principal compressive stress direction demonstrating a notable correlation with the azimuth of the P axis. The directions of the stress field show a variation from north to south at ~ 28°N. The directions of the maximum and minimum principal compressive stress in the north show nearly E-W compression and N-S tension, respectively. Conversely, in the south, there is a discernible clockwise rotation trend from east to west. Localized normal faulting stress regimes are observed in the middle section of Xianshuihe fault and southwest side of Litang fault. The extensional environment of the former may be attributed to the tectonic activities such as block translation, clockwise rotation and vertical uplift, as well as the clockwise rotation of the Xianshuihe fault from NW-SW to NNW-SSE. The latter may be related to the extensional structures, rift basins and the normal fault movements in the crust formed by the detachment of the plates and delamination of the mountain roots at the end of Triassic. We also found that the tectonic stress field under the large faults, such as Longmenshan fault, Red River fault, Xiaojiang fault and Lijiang-Xiaojinhe fault, show segmented variation. The findings yield invaluable insights into the intricate dynamics of tectonic deformation along the SE margin of the Tibetan Plateau [supported by NSFC Projects 42330311, 42074065 & 41730212].

How to cite: Tian, J., Gao, Y., and Li, Y.: Present-day stress field in Sichuan-Yunnan region based on comprehensive updated earthquake focal mechanisms catalog, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7176, https://doi.org/10.5194/egusphere-egu24-7176, 2024.

EGU24-7664 | Orals | TS1.11

Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021 

Rostislav Melichar, Ivo Baroň, Matt Rowberry, Jan Jelének, Ľuboš Sokol, Maria del Puy Papí Isaba, Christiane Freudenthaler, Helmut Hausmann, Lukas Plan, Bernhard Grasemann, Josef Stemberk, Richard A. Schultz, and Roland Bürgmann

Short-term earthquake prediction remains one of the primary goals of seismotectonics. Here detailed observations of unusual fault kinematic behaviour and near-surface crustal stress variations are presented from before, during, and shortly after an earthquake series which culminated with two Mw 4.6 and 4.4 events near Breitenau, Vienna Basin, Austria, on 30 March 2021 and 19 April 2021, respectively. The oblique normal NNE-SSW trending Pitten Fault is exposed in Altaquelle Cave close to the southern margin of the Vienna Basin in the eastern Alps, which is known to have hosted several historical earthquakes of Mw = > 5. This cave has developed in Triassic marbles of the Central Alpine Permomesozoic. The observed branch of this active steeply dipping fault is associated with the seismogenic sinistral Vienna Basin Fault and the NE-SW trending Mur-Mürz Fault. To investigate the fault activity, TM71 moiré extensometers have been used to obtain precise three-dimensional records of fault kinematic behaviour at the micron scale while the recently developed SMB2018 protocol has been used to define the stress state associated with each fault reactivation event. The observations were then compared to the Copernicus European Ground Motion Service InSAR time series derived from Sentinel-1 data. From late 2018 to early 2021, the three-dimensional kinematic behaviour of the fault comprised a variety of different on-plane as well as out-of-plane hanging block displacements ranging in magnitude from 3 to 19 μm. Then, around the time of the earthquake series in 2021, four significant displacement events were recorded: (i) 0.186 mm along a vector of 186/-12° (i.e. upward) on 16 March; (ii) 0.615 mm along a vector of 177/-88° (upward) on 26 March; (iii) 0.066 mm along a vector of 013/26° (downward) on 30 March; and (iv) 0.022 mm along a vector of 308/54° (downward) on 11 May. The third of these events occurred on the same day as the largest earthquake. These events are all much larger than any other record of fault displacement recorded in the Eastern Alps since 2013. This contribution details this unusual fault displacement behaviour and compares the calculated stress states with both the focal solutions for each earthquake and InSAR maps of E-W and vertical ground motion. A comprehensive understanding of this important seismotectonic event helps to shed further light on potential earthquake precursory phenomena.

How to cite: Melichar, R., Baroň, I., Rowberry, M., Jelének, J., Sokol, Ľ., del Puy Papí Isaba, M., Freudenthaler, C., Hausmann, H., Plan, L., Grasemann, B., Stemberk, J., Schultz, R. A., and Bürgmann, R.: Unusual fault kinematic behaviour and near-surface crustal stress variations before and during an earthquake series in the Vienna Basin (Austria) in spring 2021, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7664, https://doi.org/10.5194/egusphere-egu24-7664, 2024.

EGU24-9228 | Orals | TS1.11

Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust 

Luca Menegon, Giovanni Toffol, Hugo W. van Schrojenstein Lantman, David Wallis, Giorgio Pennacchioni, and Bjørn Jamtveit

Field studies established that seismicity in the lower crust is linked to brittle failure of dry, strong rocks. Failure of these strong rocks implies build-up of differential stresses to gigapascal (GPa) levels, but this requirement contrasts with current models of continental lithosphere deformation, which favour distributed flow of weak viscous lower crust. Although several mechanisms have been proposed to generate transiently high stresses, direct measurements are lacking. Recent advancements in microanalytical techniques (i.e., high-angular resolution electron backscatter diffraction, HR-EBSD) have proven successful at measuring the residual stress resulting from elastic strain retained in mineral grains.

We investigated with HR-EBSD the residual stresses in garnet and diopside from exhumed faults containing pseudotachylytes (quenched frictional melts produced during seismic slip). The samples come from Lofoten (Norway), Holsnøy (Bergen Arcs, Norway), and Musgrave Ranges (Central Australia). Pseudotachylytes from all three localities represent single earthquake events and formed at lower-crustal conditions (T = 500–720 °C, P = 0.5–1.0 GPa). Pseudotachylytes from Holsnøy show an asymmetric damage distribution, where host-rock garnet is pulverized nearby the fault on the side subjected to predominantly tensional stresses during rupture propagation, while garnet is intact on the other side. This asymmetry provides an opportunity to compare the residual stresses on both sides of the fault.

All samples preserve intragrain residual stress heterogeneities reaching 100s of MPa to GPa levels due to local high density of unrecovered lattice defects (dislocations). However, the timing of formation of lattice defects with respect to the seismic event differs. In samples from the Musgrave Ranges, the absence of any later deformation along with the sluggish mobility of dislocations in garnet at the ambient deformation conditions (500 °C, 0.5 GPa) allowed preservation of the high dislocation density produced during the earthquake rupture propagation, recording stress heterogeneities of as much as 6 GPa. In Holsnøy, residual stress heterogeneities of up to 1 GPa are only measured in pulverized grains and are also associated with unrelaxed dislocations generated during the earthquake rupture propagation. Intact garnet grains from the less damaged side of the fault show a limited range of intragrain stress heterogeneities, generally within 100 MPa, and a low density of dislocations. Residual stresses in diopside from Lofoten are only elevated (600 MPa) within 200 µm of the pseudotachylyte. Diopside recorded the progressive build-up of stress during interseismic loading, as suggested by the presence of coseismic cracks crosscutting lattice undulations that preserve the greatest stress heterogeneities. However, the ability of diopside to build up stress is limited, as stress is efficiently dissipated by the development of deformation twins.

In conclusion, great stress heterogeneities can be preserved in mineral grains that experienced the earthquake cycle in the lower crust. Different mineral phases can preserve stress heterogeneities to different extents, depending on the mobility of dislocations after their formation and on other relaxation mechanisms (e.g., twinning). Information on residual stress have important implications for the energy budget of an earthquake, the earthquake cycle deformation, and crustal rheology.

How to cite: Menegon, L., Toffol, G., van Schrojenstein Lantman, H. W., Wallis, D., Pennacchioni, G., and Jamtveit, B.: Earthquake induced residual stresses preserved in fault rocks exhumed from the lower crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9228, https://doi.org/10.5194/egusphere-egu24-9228, 2024.

EGU24-9630 | ECS | Posters on site | TS1.11

Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye) 

Gian Maria Bocchini, Patricia Martínez-Garzón, Armin Dielforder, Luca Smeraglia, Rebecca M. Harrington, and Marco Bohnhoff

The Armutlu Peninsula in north western Türkiye, a horst zone in an active transtensional pull-apart basin, is bounded by two major sub-branches of the North Anatolian Fault zone and host high rates of seismicity in the northern part. The ~25-station SMARTnet surface seismic network was installed in 2019-2020 with the purpose of augmenting permanent seismic stations in the northern part of the Armutlu Peninsula and to help increase the detection of small-magnitude earthquakes. Here, we employ a waveform-based clustering method that integrates detailed information from the seismicity and focal mechanism distribution enabled by the added station coverage to investigate the geometry and kinematics of the seismically active structures. We start by using an enhanced earthquake catalog of >4,000 double-difference-relocated events and >150 focal mechanisms obtained using P-wave polarities and amplitudes in the time period between January 2019 and February 2020. We perform a formal inversion of the stress field orientation from focal mechanisms to investigate the regional deviatoric stress field and its relation with activated fault structures. The stress-field inversion uses input data that combines the enhanced focal-mechanism catalog from background seismic events together with published focal mechanisms of M≥2.5 events that occurred between 1999 and 2019. Stress inversion results show an extensional stress regime for the broader northern Armutlu Peninsula and a transtensional stress regime for a narrow region of ~80 km2, referred to as the Esenköy Seismic Zone (ESZ). Within the ESZ, the minimum principal stress (σ3) is approximately horizontal and NE-trending, while the maximum (σ1) and intermediate (σ2) principal stresses are close in magnitude and vary between near vertical and near horizontal. We observe clusters of normal and strike-slip faulting events identified in the ESZ through waveform-based clustering analysis that are optimally oriented with respect to the stress field we derive for the area. The minimum principal stress in the ESZ is rotated clockwise by ~10-15° with respect to the minimum principal stress inferred for the broader Armutlu Peninsula and eastern Sea of Marmara. Based on the Mohr-Coulomb failure criterion, we quantify the relative and absolute magnitudes of the principal stresses, determine the local crustal stress and strength conditions, and will present a discussion of the implications for regional tectonic forces.

How to cite: Bocchini, G. M., Martínez-Garzón, P., Dielforder, A., Smeraglia, L., Harrington, R. M., and Bohnhoff, M.: Quantitative constraints on crustal stress and strength from seismological observations in the Armutlu Peninsula (northwestern Türkiye), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9630, https://doi.org/10.5194/egusphere-egu24-9630, 2024.

EGU24-10591 | ECS | Posters on site | TS1.11

Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes 

Thomas P. Ferrand, Jacques Précigout, David Sifré, Frédéric Savoie, Rémi Champallier, and Fabrice Gaillard

Electrical conductivity measurements on well-characterized materials in the laboratory allow accurate interpretations of electrical anomalies within the lithosphere and asthenosphere. But so far, most measurements have been performed statically, and hence, the effect of deformation and/or differential stress on electrical conductivity remains largely unknown. Here we report the first successful deformation experiments performed in a new-generation Griggs-type apparatus adapted for electrical conductivity measurements. The experiments were conducted on samples of Åheim dunites at a confining pressure of 1 GPa and temperatures of 500, 650 and 800°C. In silicate polycrystals, electrical charges are known to preferentially travel through grain boundaries, which act as high-diffusivity pathways. Our results show that stress and strain can significantly impact the electrical conductivity of peridotites by changing the thickness and the number of grain boundaries, respectively. At fixed P-T conditions, the electrical conductivity varies within an order of magnitude during deformation. This motivates to reappraise interpretations of electrical anomalies in mantle rocks, at least in tectonically active regions. The design presented in this study is fully stable at 1 GPa (≈ 30 km depth) and should be stable up to 2 GPa at least, and to average temperatures as high as 1000°C. Further developments should soon enable similar measurements at pressures up to 4 GPa (120 km depth). These experimental achievements open a new research field, which will help to understand electrical anomalies and strain localization processes in rocks under stress at depth, notably within the lower crust, the upper mantle, and subducting slabs.

How to cite: Ferrand, T. P., Précigout, J., Sifré, D., Savoie, F., Champallier, R., and Gaillard, F.: Electrical conductivity in a Griggs apparatus: a new experimental geophysical tool to investigate geological processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10591, https://doi.org/10.5194/egusphere-egu24-10591, 2024.

EGU24-10900 | Orals | TS1.11

The development of kinematic shear-stress free faults  

Daniel Koehn, Daniel Hafermaas, and Saskia Koehler

Faults are normally thought to present shear fractures that develop at an angle to the main principal stresses, so that they have shear stresses active parallel to the fault plane and thus move. Here we present two “fault” features that deviate from this principle, they develop not due to stress but during kinematic movement, they are both oriented parallel to two of the main principle stresses and as such have no shear stresses in their planes. On the large tectonic plate scale one of these features are the well known transform faults between mid ocean ridges. The ridges themselves are extensional features with the lowest principle stress perpendicular to the ridge. Transform faults are oriented perpendicular to the ridges and show movement only or mainly between the ridges where the plates move in opposite directions. These are faults that do not develop due to shear stress, they develop only because of differential movement and are therefore only or mainly kinematic. On the small scale a very similar feature is the side of a stylolite tooth. Stylolites are dissolution features, they are thus in a way the opposite to mid ocean ridges and have the largest principal stress oriented perpendicular to the stylolite plane. Due to differential movement and growth of the stylolite roughness they develop steep teeth where the sides of teeth become oriented perpendicular to the stylolite plane. These are also movement surfaces or “faults” that have no shear stress.

What does this mean for stress inversion analysis? At least stylolite teeth show a quite pronounced set of striations on their sides and slikolites are also often developed on fault planes, at least in limestone. How do we separate a purely kinematic from a stress-related fault? This discussion and the potential consequences for stress inversion studies is not new, but remains to be very important and should be debated.

How to cite: Koehn, D., Hafermaas, D., and Koehler, S.: The development of kinematic shear-stress free faults , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10900, https://doi.org/10.5194/egusphere-egu24-10900, 2024.

Understanding the stress conditions of active subduction zones has been a longstanding hurdle with critical implications for natural disasters considering stress/strain orientations and magnitudes can control shallow earthquakes and tsunamigenesis. The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines is an exhumed subduction channel with exposures of up to 9 km paleodepth, having reached up to 200°C. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twin data from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation.

During subduction, the maximum principal stress axis was oriented at a low angle to the subduction interface and the minimum principal stress axis oriented at a high angle, indicating N/NE directed compression. As subduction ceased and exhumation initiated, stress orientations inverted with the maximum principal stress axis becoming oriented at a high angle to the subduction interface and the minimum principal stress axis oriented at a low angle, indicating N/NE directed extension driven by primarily the weight of overburden material. These findings are consistent with theoretical orientations for both of these tectonic regimes and agree with previous studies interpreting subduction zone stress orientations. Calcite twin paleopiezometry and geothermometry suggests the rotation of principal stresses coincides with higher differential stresses during early exhumation. Based on the interpreted differential stresses and the reconstructed paleostress orientations, we model different possible explanations including contrasting mechanical strength between the contractional and extensional faults or changes in pore fluid pressure conditions between the two different tectonic regimes.

How to cite: Williams, S., French, M., and Rubin, C.: Determining the deformation temperatures and paleostress conditions of the Sestola-Vidiciatico Unit in the Northern Apennines, an exhumed shallow subduction zone, using calcite deformation twins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14306, https://doi.org/10.5194/egusphere-egu24-14306, 2024.

EGU24-15071 | Posters on site | TS1.11

Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines 

Silvia Mittempergher, Francesca Remitti, Telemaco Tesei, and Giancarlo Molli

During their activity, faults experience multiple seismic cycles, implying that faults recover strength between subsequent failures. Fault strengthening after failure (“fault healing”) occurs through processes having different space and time scales, including fault rock compaction, contact strengthening, contact area increase, fracture self-healing and precipitation of minerals in fractures (sealing). The efficiency of different processes varies depending on the geological setting, fault mechanics and availability and geochemistry of fluids. Here, we present preliminary data from a field-based study of the healing mechanisms of thrust faults inside the Sestola Vidiciatico Unit (SVU) in the Northern Apennines, a tectonic unit interpreted as the plate boundary shear zone between the Ligurian complex and the underthrusting Adria microplate during early-to-middle Miocene, active at temperatures up to 150°C.

The thrusts are sharp surfaces lined by calcite shear veins juxtaposing hectometer to kilometer-sized tectonic slices consisting of marls, shales, sandstones and mud-rich mass transport deposits. The marls and shales of the SVU bear a penetrative deformation pattern of fractures and incipient cleavage planes bounding oblate lithons, whose flattening planes define a foliation approximately parallel to the tectonic contacts. In the marls and shales adjacent to the main thrusts decimetric to metric-thick sheared domains may be observed showing an oblique foliation compatible with the sense of transport of the thrusts. Subvertical extensional calcite veins are common in the competent rock lithons. Multiple generations of normal faults lined by calcite shear veins crosscut the thrust faults, the oldest being rotated and deflected within the thrust-related shear zones. Calcite shear veins, in both thrusts and normal faults, display crack and seal domains and implosion breccias.

The lack of cataclastic rocks along faults indicates that the thrusts and normal faults were active at low differential stresses and high fluid pressures. Normal faults and subvertical extensional veins mutually crosscutting with thrusts are compatible with episodes of post-failure switching from reverse to normal fault stress regimes. Fault healing is dominated by calcite precipitation, which occurs both during fault slip (in crack and seal veins and implosion breccias), and after failure into subvertical extensional veins. Thrust compaction due to stress rotation is likely to be a factor promoting fault compaction and healing. Furter investigations will be conducted to constrain the origin of fluids involved in the vein cementation and the role of stress rotation in promoting different healing mechanisms.

How to cite: Mittempergher, S., Remitti, F., Tesei, T., and Molli, G.: Healing and strength cycling in a regional scale overthrust: insights from the Sestola Vidiciatico Unit in the Northern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15071, https://doi.org/10.5194/egusphere-egu24-15071, 2024.

EGU24-15970 | Posters on site | TS1.11

Paleostress inversion of fault slip data: what is the problem? 

Christophe Pascal

Paleostress inversion methods based on fault slip data (i.e. “fault slip inversion methods” or FSIMs) were formalised fifty years ago to become, shortly after, classical tools in structural geology and tectonics. The great popularity quickly gained by the methods was as remarkable as the enduring scepticism they prompted in the geological community. FSIMs belong to the rather narrow collection of methods, which allow for bridging traditional field observations and measurements (of fault planes and their respective slickenlines in the present case) to the stress tensor, a complex mathematical object. The latter statement highlights the originality of the approach and, perhaps, the roots of FSIM scepticism: stress are “observed” (or derived from observation of the nature) and not “measured” with the help of physical instrumentation, as it is traditionally done.

FSIMs are thus methods that involve mathematical processing of field data after adequate encoding of these. They rely primarily on the so-called “Wallace-Bott hypothesis”, which assumes parallelism between the measured fault stria and the computed maximum resolved shear stress, and on additional background conditions. The purpose of the present contribution is to discuss the limits of FSIMs in the light of their theoretical background and of realistic geological situations. The discussion will mostly focus on key-issues (e.g. is the stress restored by FSIMs in agreement with the formal definition of mechanical stress?) and will try to propose some future research tracks.

How to cite: Pascal, C.: Paleostress inversion of fault slip data: what is the problem?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15970, https://doi.org/10.5194/egusphere-egu24-15970, 2024.

EGU24-16586 | Posters on site | TS1.11

The recent crustal stress state of Germany - results of a new geomechanical–numerical model 

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

Knowledge of the recent crustal stress state is crucial for a better understanding of crust stability. However, the amount of available stress data in Germany is low. Therefore, a reliable and comprehensive prediction of the complete stress tensor is not possible with these only. However, 3D geomechanical-numerical models, which represent the geometry of the subsurface and its mechanical properties and are calibrated to stress data, allow a continuum-mechanics based prediction of the complete stress tensor and its lateral and vertical variability. A new geomechanical-numerical model of Germany provides new insights into the recent crustal stress field. In contrast to previous models, an improved geological model with a significantly higher stratigraphic resolution is used, a high vertical resolution of ~40 m allows a better mechanical representation of individual units and mechanical inhomogeneities and new data records are used for calibration.

The results provide a comprehensive prediction of the complete stress tensor for Germany and can be used for a wide range of scientific questions and applications. Examples are the prediction of the fracture potential, the slip tendency of faults or as boundary conditions for small-scale models usable for example for engineering applications.

How to cite: Ahlers, S., Reiter, K., Henk, A., Hergert, T., Röckel, L., Morawietz, S., Heidbach, O., Ziegler, M., Müller, B., and Kuznetsova, V.: The recent crustal stress state of Germany - results of a new geomechanical–numerical model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16586, https://doi.org/10.5194/egusphere-egu24-16586, 2024.

Seismicity studies on both fast- and slow-spreading ridge systems have found along-strike variations in mantle mechanical behavior on oceanic transform faults (OTFs), at pressure and temperature conditions above the long-term brittle-ductile transition of peridotites at ~700°C. Plate motion on some sections of the fault is accommodated by aseismic slip only (ductile deformation), whereas motion on other sections is by slip and deep swarms of microearthquakes (semi-brittle deformation) of mantle rocks (e.g., McGuire et al., 2012; Yu et al., 2021). To explore the mechanisms responsible for lateral variations in mantle mechanical behavior and the occurrence of this deep mantle microseismicity, we carried out an integrated study on peridotite mylonites dredged from two OTFs on the Southwest Indian Ridge that record deformation at 700-1000°C.

The samples show variable degrees of deformation, ranging from proto- to ultra-mylonitic textures. The most deformed zones of the mylonites are characterized by an increase in the proportion of fine grained (<10 micron) mylonitic shear bands compared to coarse grained (millimeter) porphyroclasts inherited from the protolith. These shear bands contain syn-deformation chlorine-rich amphibole indicating seawater-peridotite interaction during shear band formation.

Olivine and pyroxene porphyroclasts in protomylonites contain evidence for intense brittle deformation. The presence of subgrain walls, high aspect ratios, and internal misorientations crosscut by fractures imply that they deformed by low-temperature plasticity before brittle deformation. Fractures are sealed by the fine-grained shear bands present in the samples. In (ultra)mylonites, porphyroclasts also show evidence of fracturing after flowing through low-T plasticity. Fracturing was coeval with viscous flow of surrounding weak and hydrated mylonitic shear bands and triggered by hardening of larger grains due to dislocation accumulation. From existing flow laws, such brittle deformation of peridotite minerals necessitates high strain rate deformation, from 10-9 to 10-5s-1, similar to strain rates associated with slow slip events.

From these results we propose that swarms of microseismicity on OTFs are triggered by deformation of a heterogeneous mantle. Seismic rupture occurs in lenses of coarse-grained peridotites, possibly driven by aseismic creep of surrounding hydrated mylonitic shear zones. Importantly, observations also suggest plastic flow of brittle (seismic) patches before rupture.

How to cite: Cécile, P. and Jessica, W.: Origin of brittle deformation and microseismicity in the ‘ductile’ mantle on oceanic transform faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16752, https://doi.org/10.5194/egusphere-egu24-16752, 2024.

EGU24-16807 | ECS | Orals | TS1.11

First-order global stress patterns inferred from hierarchies of upper mantle flow models 

Jorge Nicolas Hayek Valencia, Ingo Leonardo Stotz, Hans-Peter Bunge, Sara Carena, and Sia Ghelichkhan

Understanding the intricate dynamics of mantle flow and their influence on lithospheric stress patterns is critical for assessing reservoir responses to potential CO2 or nuclear waste storage, as well as for hazard and risk assessment. Stress patterns play a first-order control in the mechanical response within inherited tectonic structures, with varying stress sources governing different spatiotemporal scales. Our understanding of the present-day mantle flow state has much improved over the past decades, reflected in models that are consistent with first-order features. The World Stress Map (WSM) project serves as a primary observational dataset to validate our understanding of Earth's dynamics through a global compilation of crustal stress indicators.

Here we study mantle flow models as a simplified superposition of Couette and Poiseuille flow types, which have been useful in explaining sub-continental scale deformation in the lithosphere. We aim to understand the role of mantle flow as a stress driver by generating stress fields from an analytical representation of upper mantle flow, derived from the superposition of steady-state flow models. Our approach allows us to build first-order expectations and conduct fast hypothesis testing for upper mantle flow states.

How to cite: Hayek Valencia, J. N., Stotz, I. L., Bunge, H.-P., Carena, S., and Ghelichkhan, S.: First-order global stress patterns inferred from hierarchies of upper mantle flow models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16807, https://doi.org/10.5194/egusphere-egu24-16807, 2024.

EGU24-16849 | ECS | Orals | TS1.11

Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust 

Alix Osinchuk, Brendan Dyck, Dave Wallis, and Alfredo Camacho

Strength-depth profiles for ductile portions of continental crust are derived from either extrapolation of flow laws from deformation experiments or paleopiezometric estimates in deformed and nominally hydrated plate margins. Lower continental crust in intracontinental settings, in contrast, is relatively dry and should be considerably stronger than the lower crust of hydrated plate margins. The relative strengths of dry quartz and feldspar are poorly constrained by experiments and paleopiezometric estimates from such rocks are sparse. As such, the strength of intracratonic lower crust is difficult to ascertain. Here, we use a recently calibrated subgrain-size piezometer to estimate paleostresses from feldspar and quartz deformed in relatively dry (<20 ppm H2O) lower continental crust of the Musgrave Ranges in central Australia. Neocrysts of plagioclase, K-feldspar, and quartz mantle partially recrystallized porphyroclasts, which is indicative of bulging and subgrain-rotation recrystallization. Using crystallographic preferred orientations and plotting misorientation axes of subgrain boundaries of each phase, we infer that dislocation creep involved the slip systems (010)[100] and (010)[001] for plagioclase, (010)[101] for K-feldspar, and (0001)<11-20> and {01-10}<0001> for quartz. Titanium in quartz and gradients in concentration of Ca and K in feldspars within neocrysts and along subgrain boundaries verify that subgrains in all three phases were formed at a temperature of ~650°C under dry, eclogite-facies conditions. Subgrain sizes of 10.6–18.1 µm in quartz, 11.5–16.9 µm in plagioclase, and 12.0–17.5 µm in K-feldspar correspond to differential paleostresses between 22–36 MPa and are consistent with a single mean paleostress of 28 MPa. Our results demonstrate that there is minimal stress partitioning between dry quartz, plagioclase and K-feldspar under typical crustal thermal gradients. Moreover, the differential stress accommodated by felsic rocks in the Davenport shear zone is lower than predicted by previous strength-depth profiles of lower cratonic crust.

How to cite: Osinchuk, A., Dyck, B., Wallis, D., and Camacho, A.: Subgrain-size piezometry of feldspar and quartz records a single paleostress from dry lower continental crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16849, https://doi.org/10.5194/egusphere-egu24-16849, 2024.

EGU24-16995 | ECS | Posters on site | TS1.11

Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India   

Subha Kundu, Uddipta Mohanta, and Sudheer Kumar Tiwari

Paleostress analysis is commonly used to understand the brittle exhumation process of deeper crustal rocks to the surface. In this research, we have assessed different stress fields and associated tectonic events in the southern part of Chotanagpur Gneissic Complex (CGC) using fault slip data. The southern CGC comprises two significant crustal-scale shear zones: South Purulia Shear Zone (SPSZ) and the North Purulia Shear Zone (NPSZ), along and across which our fault slip data has been collected. These shear zones exhibit high-grade (amphibolite to granulite) facies Proterozoic rocks consisting mainly of felsic gneisses and migmatites in which low-grade metapelite of North Singhbhum Mobile Belt (NSMB), calc-silicate and mafic granulites of CGC occur as enclaves.

 There has not been any previous study to determine the major stress orientations during brittle exhumation acting upon the Proterozoic rocks in the study area. Thus, our main aim in this study is to understand the variation in stress regime along and across these shear zones and also try to reconstruct the paleostress orientation to determine the history of brittle exhumation of the lower crustal rocks during major orogenic stages of the Proterozoic period. Almost 1000 homogeneous fault slip data have been analyzed using Win-Tensor software. The primary fault data within both shear zones exhibits an approximate E-W orientation, whereas other sets range from NW-SE to NE-SW. Reconstructing stress fields using the age, overprinting relationship and sense of fault movements show that during the Neoproterozoic period (1.0-0.95 Ga), the direction of the compressional stress regime was in N-S orientation. This indicates an oblique-slip movement (thrusting and sinistral strike-slip fault) of the northern CGC block with respect to the NSMB resulting in crustal thickening. The evidence of E-W striking, orogen-parallel normal faults was produced from an N-S directed extensional stress and is primarily responsible for brittle exhumation of these widely distributed granulite facies rocks especially the CGC gneisses in the Purulia region through crustal extension and thinning at 0.95–0.85 Ga.

How to cite: Kundu, S., Mohanta, U., and Tiwari, S. K.: Paleostress reconstruction from fault slip data along the Purulia Shear Zone, Chotanagpur Gneissic Complex, India  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16995, https://doi.org/10.5194/egusphere-egu24-16995, 2024.

EGU24-17092 | ECS | Posters on site | TS1.11

Record of high-stress deformation before and during an earthquake at intermediate-depth conditions 

Giovanni Toffol, Giorgio Pennacchioni, Marco Scambelluri, and Luiz Fernando Grafulha Morales

Exhumed pseudotachylytes (quenched coseismic frictional melts) and their wall-rocks represent a source of information to investigate earthquake mechanics at hypocentre depth. Pseudotachylytes produced at eclogite-facies conditions in subducted oceanic rocks are of particular interest as they open a window into the elusive mechanics of intermediate-depth earthquakes1.

Here we present observations from pseudotachylytes hosted in oceanic gabbros and peridotites from Moncuni (Lanzo Massif, W Alps). These pseudotachylytes record seismic faulting occurred at ca. 70 km of depth during subduction of oceanic lithosphere and have been explained as the result of brittle failure under high differential stress in dry rocks2,3.

We focus on the pervasive damage surrounding pseudotachylytes within olivine-bearing gabbros. Brittle deformation comprises aseismic (cataclasite bands and foliated cataclasites) and coseismic (pulverized domains with shattering in-situ) features associated with the pseudotachylyte veins. Fluid-absent conditions promoted preservation of the pristine brittle features, including pseudotachylyte glass, throughout the exhumation path.

Pseudotachylyte veins and the associated sharp micro-faults are commonly bound by cataclastic domains. Locally, these domains develop an S-C fabric with ultracataclasites along the shear planes. This fabric shows a progressive localization of strain toward the core pseudotachylyte that cut through the S-C fabric, with the cataclastic aggregates proximal to the pseudotachylyte frequently impregnated by melt. Wall-rock olivine grains show evidence of low-temperature plasticity (deformation lamellae and undulatory extinction) and microfracturing. Both deformation lamellae and microfractures are oriented perpendicular to olivine c-axis. These deformation microstructures are also shown by olivine clasts within the cataclasites bounding the pseudotachylytes suggesting a temporal sequence of (i) crystal plastic deformation and (ii) shattering and pulverization. The small olivine clasts in contact with the sharp margin of the pseudotachylyte show substructures a few hundred nanometres in size and are characterized by absence of Kikuchi diffraction patterns. The lack of diffraction bands is interpreted as evidence of extremely high density of dislocations leading to amorphization of the material.

We interpret the low temperature plasticity of olivine and the progressive evolution of the S-C fabric to represent the precursory stage of stress localization predating the abrupt propagation of the seismic rupture, whose instantaneous high stress pulse is recorded by the shattered olivine clasts.

 

[1] Toffol et al., Earth and Planetary Science Letters, 2020, 578: 117289

[2] Scambelluri et al., Nature Geoscience, 2017, 10.12: 960-966

[3] Pennacchioni et al., Earth and Planetary Science Letters, 2020, 548: 116490

How to cite: Toffol, G., Pennacchioni, G., Scambelluri, M., and Grafulha Morales, L. F.: Record of high-stress deformation before and during an earthquake at intermediate-depth conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17092, https://doi.org/10.5194/egusphere-egu24-17092, 2024.

EGU24-17191 | ECS | Orals | TS1.11

Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks  

Natalia Nevskaya, Alfons Berger, Holger Stünitz, Weijia Zhan, Oliver Plümper, Marcus Ohl, and Marco Herwegh

To comprehend the rheology of the Earth's crust and the relevant rock properties, one key approach is to deform rocks and minerals at elevated pressures and temperatures and then extrapolate the measured stress and strain rate values to natural conditions using constitutive equations. Laboratory experiments are mostly conducted on monomineralic rocks, with quartz being considered as the weakest constituent of the middle continental crust. However, field observations suggest that this is an oversimplification, and polymineralic fault rocks may be weaker than monomineralic quartz rocks. This study presents the first experiments on fine-grained, solid, natural rock samples, containing their natural homogeneities and inhomogeneities, demonstrating that granitoid rocks may be weaker than quartz at mid-crustal conditions. It also highlights the importance of pre-existing faults and polymineralic fine-grained zones for strain localisation and proposes values for extrapolation to natural conditions and their use in numerical models of the deformation of the granitoid crust.

Cylindrical granitoid ultramylonite samples, composed of qtz + ab + K-fsp + bt + ep, with grain sizes of 125-15 μm are deformed in a Grigg’s type apparatus at T=650°C, confining P=1.2 GPa, strain rates=10-3 to 10-5s-1, and 0.2 wt% H2O added. Mechanical data are combined with light microscope, SEM, TEM, and quantitative image analysis to connect microstructures with stress and strain evolution. We show that polymineralic granitoid rocks deform through other mechanisms than monomineralic quartz aggregates at pressure and temperature conditions characteristic for the middle crust: Ultra-fine grain size reduction down to <50nm is developed by nucleation and growth of new grains in a polymineralic mixture. Grain size remains small because of pinning processes. We therefore refer to the deformation mechanism as pinning-controlled dissolution-precipitation creep (P-DPC).

Furthermore, we establish a new constitutive equation for this P-DPC, based on an exponential diffusion creep flow law, to model our experiments and tackle the extrapolation to various natural conditions. This flow law is supported by the microstructural evidence for the deformation mechanisms. Extrapolations show that the shear zones of the granitoid middle crust may be magnitudes weaker than extrapolated so far, and deformation may occur at magnitudes faster rates. The brittle to viscous transition may be shifted to shallower levels. This may have implications for the seismogenic zone and/or stress fields below geothermal reservoirs. Most importantly, we show the necessity to take polymineralic rocks into consideration for various numerical model applications.

How to cite: Nevskaya, N., Berger, A., Stünitz, H., Zhan, W., Plümper, O., Ohl, M., and Herwegh, M.: Implications for the strength of the Earth’s middle crust from novel experiments on natural fine-grained granitoid rocks , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17191, https://doi.org/10.5194/egusphere-egu24-17191, 2024.

EGU24-19186 | Orals | TS1.11

Could earthquakes cause rapid dehydration of serpentinite? 

Lucie Tajčmanová, Sebastian Cionoiu, and Dan Schuppenhauer

Dehydration reactions can influence the occurrence of earthquakes at a range of depths, highlighting the importance of understanding these reactions in the study of seismic activity. We have performed several pilot experiments that included the construction of a controllable fast pressure drop unit attached to the piston-cylinder apparatus. This setup makes it possible to simulate conditions that represent a fast pressure drop during an earthquake event. We focused on serpentinite dehydration because 1/ it plays an important link between the deep geodynamic processes occurring in subduction zones and the seismic and volcanic activity and 2/ the interplay between serpentinite dehydration and deformation during the earthquake cycle is not yet fully understood. To test the experimental setting, we first performed a series of static experiments under the conditions that are already in the olivine stability field. After the static experiments at high pressure (1.1 GPa), we performed the controlled fast pressure drop experiments to 0.3 GPa as well as the ramping experiments, in which a series of pressure build-ups and drops were performed maintaining the high temperatures (570 to 640 °C) to simulate the earthquake cycle. In these experiments, olivine was an order of magnitude more abundant than in the one-hour low-pressure static experiment. The pressure drop occurs in seconds. The ramping experiment lasted only 10 mins before cooling down. The results may challenge conventional wisdom about the timescales of mineral reactions under extreme conditions, such as during earthquakes.

How to cite: Tajčmanová, L., Cionoiu, S., and Schuppenhauer, D.: Could earthquakes cause rapid dehydration of serpentinite?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19186, https://doi.org/10.5194/egusphere-egu24-19186, 2024.

EGU24-19980 | ECS | Posters on site | TS1.11

Eurasian plate-scale stress model considering driving and resistive forces 

Renato Gutierrez Escobar and Rob Govers

Our goal is to constrain magnitudes and directions of forces that may explain present-day natural stresses within the Eurasian plate. Driving forces such as horizontal gravitational stresses (HGSs), mantle convective tractions including dynamic topography, and plate interaction tractions with bounding plates are considered. HGS resulting from lateral variations in gravitational potential energy 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 illustrate that recently published models of lithospheric density including lateral variations in the lithosphere-asthenosphere boundary result in significantly different HGSs. Furthermore, we include observed major faults into a 2D spherical cap elastic model of the Eurasian plate. We present results of forward FEM calculations and compare them with observed stress directions from the world stress map. We propose different objective functions that determine 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 analysis represents a first step towards a Bayesian inference workflow to constrain the dynamics of the Eurasian plate.

How to cite: Gutierrez Escobar, R. and Govers, R.: Eurasian plate-scale stress model considering driving and resistive forces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19980, https://doi.org/10.5194/egusphere-egu24-19980, 2024.

EGU24-20499 | Posters on site | TS1.11

Three-dimensional numerical modelling of drilling-induced tensile wall fractures 

Martin Schöpfer, Mario Habermüller, Nicola Levi, and Kurt Decker

Drilling-induced tensile fractures (DITFs) form due to stress concentrations around a wellbore and are in vertical wells typically parallel to the largest horizontal far-field stress and normal to the least horizontal far-field stress. The peak pressure in the wellbore exerted by the drilling mud that the wall rock can sustain is given by the so-called Hubbert-Willis (H-W) criterion, which predicts that wall rock failure takes place when the circumferential effective stress at the borehole wall reaches the tensile strength of the wall rock. However, even though the H-W criterion is a valuable fracture-initiation criterion, it cannot predict if and how an initiated fracture propagates. Linear elastic fracture mechanics (LEFM) can provide a solution to these questions under simple loading conditions, e.g. a vertical borehole in a rock mass that is under an Andersonian stress state. Predicting the initiation and propagation of DITFs in more complex settings, such as inclined boreholes or wellbores in mechanically layered sequences, however, necessitates three-dimensional numerical modelling.

Here we present results of three-dimensional numerical Rigid Body Spring Network (RBSN) lattice modelling. The model comprises so-called rigid blocks (tetrahedra in the present study), that interact with each other and can be bonded at their contacts; these bonds fail when the effective normal stress exceeds the bonds tensile strength, which corresponds to micro-fracture of the wall rock. Coalescence of these micro-cracks leads to the formation of macroscopic fractures. Wellbore failure is modelled by means of a hollow cylinder discretised by these bonded rigid blocks. The remote (tectonic) stress is applied to the hollow cylinder’s outer surface whilst the pressure exerted by the drilling mud is applied to its inner surface. Fractures connected to the wellbore receive the same internal pressure as the wellbore and quasi-static fracture propagation is achieved by gradually increasing the pressure on the borehole wall.

Validation of the numerical model under simple loading conditions illustrates that fracture lengths and associated aperture profiles as a function of wellbore pressure correspond well with LEFM predictions. Numerical models of moderately inclined boreholes exhibit stepping DITFs, where fracture stepping is most pronounced when the wellbore is inclined towards the least horizontal stress direction and no fracture stepping occurs when the wellbore is inclined towards the greatest horizontal stress direction. In mechanically layered sequences comprised of layers with different Young’s modulus, DITFs first nucleate in the stiff beds. Complex fracture geometries emerge in mechanically layered sequences, such as fracture stepping within individual beds or at layer boundaries. The detailed evolution of these more complex DITFs depends on several factors, such as the orientation of the remote principal stresses and layering relative to the wellbore axis. Our numerical modelling approach permits to systematically investigate the effects of these different factors on the geometry of DITFs and therefore offers a new tool that can assist in construing the mechanical genesis of fractures imaged in borehole logs and the current stress in the Earth’s crust.

How to cite: Schöpfer, M., Habermüller, M., Levi, N., and Decker, K.: Three-dimensional numerical modelling of drilling-induced tensile wall fractures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20499, https://doi.org/10.5194/egusphere-egu24-20499, 2024.

The 1D Geomechanical Models (1DGM) were done for four vertical boreholes in the Early Paleozoic shale sequences of the Baltic Basin in Poland. The models assumed an elastic rock behaviour with anisotropy in VTI symmetry. The far-field horizontal stresses were calculated as the sum of two components: the vertical stress derivative acting on the horizontally constrained rock column and the effect of elastic tectonic strains. Local stresses in the borehole wall were assumed to induce breakouts (BBs) and drilling-induced tensile fractures (DITFs). Hydraulic fracturing tests additionally validated the stress modelling results.

Micro-resistivity images from XRMI logging revealed irregular BBs, usually confined to individual layers, often non-symmetrical, and with a tendency to encompass the entire borehole wall. Despite their irregularity, statistical analysis of their orientation provides a good quality and stable stress orientation.

The initial modelling results, balancing the cumulative length of the modelled (BBM) and observed (BBO), revealed a systematic misfit between BBm and BBo locations. A detailed comparison between the BBm and BBo intervals concluded that the artificial degradation of Young's modulus and Poisson's ratio is caused by the perturbation of the velocity of the acoustic wave from the dipole acoustic tool passing through the intervals with irregular BBs. This makes it impossible to model the BBs in the places where they are present. To deal with this, the initial stress models were recalculated to the final models in which the BBm were avoided in intervals where there were no BBO.

The initial and final stress models differ significantly in terms of the tectonic strain values and the combined length of the BBm. Still, their stress profiles are similar due to the small contribution of tectonic strain to the far-field stresses. We concluded that irregular BBs developed due to small differential horizontal stresses, causing abrupt BB failure with rapidly growing angular width. The stress layering between lithostratigraphic units was obtained with a dominance of the normal faulting stress regime in the lower borehole sections and the reverse faulting present in the upper sections. The minor regional elastic tectonic strain value for the shale sequence was determined to be an order of magnitude lower than the strain in the crystalline basement, as determined from the satellite geodetic strain rate. We expect that this discrepancy could be explained by a higher rate of viscous relaxation in the shale sequence with > 60% of the clay mineral content. This suggests the need to implement the viscous relaxation into the 1DGM of sedimentary sequences.

How to cite: Jarosinski, M., Bobek, K., and Pachytel, R.: Geomechanical models of the shale sequence of the Baltic Basin (Poland): possible case of elastic properties degradation and viscous stress relaxation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20951, https://doi.org/10.5194/egusphere-egu24-20951, 2024.

EGU24-21427 | Orals | TS1.11

Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting 

Giulia Mingardi, Julien Gasc, Robert Farla, and Alexandre Schubnel

Numerous studies have illustrated that mineral transformations have the capability to induce faulting at elevated pressure and temperature (PT), circumstances in which ductile flow would typically dominate. This mechanism, commonly known as transformational faulting, emerges as a plausible explanation for the puzzling phenomenon of deep-focus earthquakes occurring at depths up to 700 km. Currently, the debate partly revolves around determining why certain phase transformations lead to faulting while others do not. To better understand this phenomenon, we can compare different transformations taking place in similar experimental conditions and see how they do or do not cause strain localization and faulting. In this regard, we conducted a series of five deformation experiments in the large volume press at the PB61 beamline at DESY synchrotron. Two of these experiments involved deforming germanium-olivine samples as they transformed into ringwoodite (the high-pressure phase). The other three experiments were carried out on quartzite (novaculite) samples while they were transforming to coesite. Throughout the experiments, we collected X-ray diffraction patterns and images concurrently with the collection of Acoustic Emissions (AEs).

The results indicate, in both quartz and olivine experiments, the growth of the high-pressure phase at various rates depending on PT conditions and equilibrium overstep. Specifically, we observed rapid olivine-ringwoodite kinetics at elevated PT, far from equilibrium, while slower kinetics were noted for the quartz-coesite transformation. Thousands of AEs were collected in each experiment, and their locations reconstructed using arrival times on the six transducers used. Interestingly, the spatial distribution of these AEs revealed that for some quartz-coesite experiments, AEs originated from fault planes that formed within the initially intact rock cores. Furthermore, an analysis of the AE catalogues, focusing on the magnitude-frequency distribution, revealed a wide range of b-values influenced by varying PT conditions and transformation kinetics. This observation underscores the different underlying mechanisms since the obtained b-values are high when transformation and strain are distributed and lower when strain is localized (i.e., when a fault plane develops).

Our study supports the major role of mineral transformations in inducing faulting under high PT. These findings will help better quantify the intricate relationships between mineral transformations and faulting and in turn contribute to a better understanding of the fundamental geological processes behind deep and intermediate earthquakes.

How to cite: Mingardi, G., Gasc, J., Farla, R., and Schubnel, A.: Combining synchrotron and acoustic emission techniques to reveal the secrets of high PT faulting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21427, https://doi.org/10.5194/egusphere-egu24-21427, 2024.

EGU24-428 | ECS | Orals | TS1.6

AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS 

Efe T. Ayruk, Muhammed Turğut, İlay Farımaz, Mehmet Köküm, Roger Bilham, and Uğur Doğan

The Mw 7.8 earthquake of 2023 ruptured the southern (main) branch of the East Anatolian Fault (EAF), followed by the Mw 7.6 earthquake on the northern (Çardak Fault) branch of the EAF nine hours later. In March, we installed ten carbon-rod extensometers across segments of the main and northern branches of the ruptured faults, where potential slip deficits were considered possible, to investigate if afterslip continues. It is important to measure afterslip to understand the behaviour of a fault, if any, resulting from stresses associated with local coseismic slip deficits.  Seven of these extensometers recorded less than a few millimetres of slip since March. In Göksun near the western end of the Çardak fault, we recorded more than a 25 mm of accelerating afterslip preceding local aftershocks of magnitude ≤Mw5.1.

The Mw 6.8 Elazığ-Sivrice earthquake of January 24, 2020, and the Mw 7.8 Kahramanmaraş earthquake of February 6, 2023, stopped in the Pütürge region, where it is named as Pütürge Gap. To understand why these two earthquakes terminated there, an array of five extensometers were ultimately deployed. One of the extensometers, which is 52 m long, shows that slip > 3.8 mm/yr continues at depth. Extensometers spaced 45 km apart recorded an eastward propagating subsurface creep event in September 2023. Four cGPS stations recording at 5 Hz were installed in an array to better investigate the subsurface evolution of aseismic slip on the Pütürge Fault in the village of Taşmış.

How to cite: Ayruk, E. T., Turğut, M., Farımaz, İ., Köküm, M., Bilham, R., and Doğan, U.: AFTERSLIP of 6 FEBRUARY 2023 KAHRAMANMARAS EARTHQUAKE SEQUENCE : PRELIMINARY RESULTS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-428, https://doi.org/10.5194/egusphere-egu24-428, 2024.

EGU24-2299 | ECS | Posters on site | TS1.6

Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults 

Silvia Aldrighetti, Giulio Di Toro, and Giorgio Pennacchioni

Earthquakes are the result of propagation at ∽km s-1 of a rupture and associated slip at ∽m s-1 along a fault. The total energy involved in a seismic event is unknown, but qualitatively most of it is dissipated by rock fracturing and frictional heat. Seismic fracture energy G (J m-2) is the energy dissipated in the rupture propagation and can be estimated by the inversion of seismic waves. However, its physical significance remains elusive. G may include the contributions of both rock fracturing (energy to form new rock surfaces US, J m-2) and fault frictional heating (Q, J m-2) per unit fault area. Here we determine both US and Q in natural and experimental pseudotachylyte-bearing faults, following the approach used by Pittarello et al. (2008). In fact, in pseudotachylytes, or solidified frictional melts produced during seismic slip, (i) US is proportional to the surface of new fragments produced in both the slip zone and in the wall rocks, and (ii) Q is proportional to the volume of frictional melt.

The selected natural pseudotachylytes belong to the east-west-striking, dextral, strike-slip Gole Larghe Fault Zone (Adamello, Italian Alps). To estimate US we employed Electron Back-Scatter Electrons (EBSD), High Resolution Mid Angle Back-Scattered Electrons (HRMABSD) and Cathodoluminescence-Field Emission Scanning Electron Microscopy (CL-FESEM). In particular, CL-FESEM imaging reveals a microfracture network in the wall rocks that cannot be detected with the other techniques. In the pseudotachylyte-bearing fault, the microstructural analysis reveals (i) a high degree of fragmentation of the wall rock adjacent to the pseudotachylyte fault vein (formed along the slip surface), with clast size down to <90 nm in diameter, and (ii) a systematic difference in fracture density and orientation of the microfractures in the two opposite wall rock sides of the fault. In fact, in the northern wall rock the fracture density is low and the microfractures are oriented preferentially east-west, while in the southern wall rock the fracture density is high and oriented preferentially north-south. Instead, this asymmetric microfracture pattern is absent in the experimental pseudotachylytes produced by shearing pre-cut cylinders of tonalite (the rock that hosts natural pseudotachylytes) in the absence of a propagating seismic rupture. Thus, the formation of the asymmetric microfracture pattern is associated with the propagation of the seismic rupture and, therefore, can be used to estimate US.

In natural pseudotachylytes, fracture density decreases exponentially from the pseudotachylyte-wall rock contact towards the wall rock. The rock volumes with highest coseismic damage at the contact with the pseudotachylytes were assumed to represent the host-rock damage preceding frictional melting along the slip zone. Based on this assumption, US was estimated in the range 0.008-1.35 MJ m-2, while Q was estimated from the thickness of the pseudotachylyte vein to be ∽32 MJ m-2. In the case of the Gole Larghe Fault, numerical modelling of seismic rupture propagation yields fracture energies G in the range 8-67 MJ m-2 suggesting that US is a subordinate component of G and that most of the seismological fracture energy is heat.

How to cite: Aldrighetti, S., Di Toro, G., and Pennacchioni, G.: Estimate of seismic fracture surface energy from pseudotachylyte-bearing faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2299, https://doi.org/10.5194/egusphere-egu24-2299, 2024.

EGU24-3922 | ECS | Orals | TS1.6

Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence 

Fengjiang Ju, Haoran Meng, Xiaofei Chen, and Chunquan Yu

Advancing our understanding of earthquake nucleation process can shed lights on earthquake prediction, early warning, and hazard assessment. Foreshocks, which usually refer to smaller earthquakes that occur before an earthquake, exhibit good temporal and spatial correlations with the mainshock. Investigating the relationship between foreshocks and mainshocks can therefore provide valuable insights into earthquake nucleation mechanisms and contribute to the improvement of earthquake prediction and early warning capabilities.

A recent study on the 2019 Mw 7.1 Ridgecrest earthquake sequence suggests that immediate foreshocks often share similar waveforms to the P-waves of subsequent earthquakes, differing only in amplitude. This similarity is believed to arise from the fractal nature of fault fracture processes. Consequently, there might be many immediate foreshocks with similar waveforms hidden in ambient noise that have gone undetected. Two methods have been proved to be effective in detecting small events: the Matched Filter Technique (MFT) and the Source-Scanning Algorithm (SSA). The MFT relies on template events to detect small events by stacking cross-correlograms between the waveforms of the templates and potential events. The conventional MFT, however, requires that the small events be located in the vicinity of one of the template events and does not provide the accurate locations of detected events. On the other hand, SSA is a migration-based approach that involves stacking non-negative waveforms, envelopes, and their extended characteristic functions. However, due to their tendency to provide absolute locations, SSA are heavily influenced by the accuracy of the velocity model and struggle to accurately detect earthquakes that are obscured by noise.

In our study, we prioritize the accuracy of relative event locations when studying the relationship between foreshocks and mainshocks. To address this concern, we have developed an advanced method that combines the strengths of cross-correlation and beamforming analyses. This method allows us to detect and relatively locate small seismic events simultaneously using dense array data. For the 2021 Ms 6.4 Yangbi  aftershock sequence, we first compute the cross-correlograms of the contentious records with the P-waves/S-waves of the target earthquake, respectively. We then grid searches around the hypocenter using N-th root stacking to detect and locate the immediate foreshocks. Upon detecting numerous immediate foreshocks, we proceed to statistically quantify the earthquake nucleation process or investigate the nucleation mechanism.

How to cite: Ju, F., Meng, H., Chen, X., and Yu, C.: Detection of Immediate Foreshocks Using Dense Seismic Array: A Case Study of the 2021 Ms 6.4 Yangbi aftershock sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3922, https://doi.org/10.5194/egusphere-egu24-3922, 2024.

EGU24-4427 | Orals | TS1.6

Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults 

Kevin P. Furlong, Matthew W. Herman, and Kirsty A. McKenzie

A general correlation between maximum co-seismic fault slip and fault length has been well constrained by observations from numerous earthquakes occurring on many crustal faults. In spite of this global consistency, there are notable examples of co-seismic fault slip magnitudes that far exceed the expected maxima for the fault dimensions.  Two instances of extreme fault slip that occurred on short-to-moderate length upper-plate faults in subduction systems, where the megathrust lies at shallow depths are the 2016 Kaikoura (New Zealand) earthquake, and the 1855 Wairarapa (New Zealand) earthquake. In both cases, co-seismic fault slip was 5 to 10 times greater than expected from the rupture length - fault slip scaling relationships. The typical crustal fault model  is a fault with a brittle-to-ductile transition at depth; in this scenario, co-seismic slip is inhibited by viscous resistance from the deeper, ductile component of the fault.  In contrast, the tectonic characteristics of faults that experience extreme co-seismic slip, involve upper plate faults that truncate against the megathrust at seismogenic depths (i.e. are fully frictionally coupled over their entire depth extent). During a megathrust earthquake, the plate interface unlocks and upper-plate faults that extend to the ruptured plate interface transiently experience free-slip boundary conditions on both their upper (surface) and lower (megathrust) ends. As a result, such upper-plate faults can potentially experience full strain release (and therefore maximum slip), independent of their length. For appropriately oriented faults, this effect may be enhanced by co-seismic stress changes associated with the megathrust earthquake. 

Geologic evidence of large displacement (and/or displacement rate) upper-plate faults in other subduction systems indicates this process may commonly occur. One example is a set of upper-plate faults along the Cascadia margin (near Newport, Oregon), that have strike-slip geologic slip rates, averaged over 10s of thousands of years, exceeding tens of mm/yr and approaching local plate convergence rates. These upper-plate Cascadia faults are also located where the plate interface is sufficiently shallow and seismogenic, indicating that these high-slip, upper-plate faults are likely frictionally locked over their entire depth range. In spite of the high overall slip rates of these upper-plate faults, because they are locked along their entire depth extent between earthquakes,  they may be unrecognized by inter-seismic geodetic observations.

How to cite: Furlong, K. P., Herman, M. W., and McKenzie, K. A.: Big Slip on Small Faults - How Does Extreme Fault Slip Occur on Short-to-Moderate Length Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4427, https://doi.org/10.5194/egusphere-egu24-4427, 2024.

EGU24-4550 | Posters on site | TS1.6

Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations 

Yariv Hamiel and Roger Bilham

We use geodetic measurements to characterize aseismic deformation along the western boundary fault of the Dead Sea pull-apart basin, which is located at the southern part of the sinistral Dead Sea Fault. This research provides constraints on patterns and timescales of deformation and its dependence on regional tectonics and the rheology of the upper crust. We use creepmeter, GNSS, InSAR and airborne LiDAR observations and show transient aseismic slip on the western boundary fault of the Dead Sea basin. A biaxial creepmeter with a 30 s sampling interval was installed in early 2021 showing high extensional deformation (an average rate of ~8.6 mm/yr), which is consistent with the ~30 cm of subsidence recorded 2017-2019 differential LiDAR data. The data imply modulated slip on a 60° dipping normal fault with maximum slip rates of ~0.5 µm/hour starting in late August and varying close to zero in late April. We attribute these large movements to local tectonics, sediment compaction, thermo-elastic response and dissolution of subsurface salt responsible for the formation of sink-holes in the region. The creepmeter measurements also show some sinistral deformation with an average rate of ~2.1 mm/yr, comparable to the rate of 2.5±0.4 mm/yr that was observed for the Sedom Fault, the southernmost segment of the western boundary fault, using GNSS data. Several minor creep events were detected by the creepmeter. The 19 Feb 2022 creep event lasted more than an hour following heavy rain in this area with abrupt sinistral slip of ~2.5 mm preceding dilation and dip-slip by 20 minutes. Small Baseline Subset (SBAS) analysis of InSAR data reveals up to 7mm/yr of line-of-sight deformation across the western boundary fault, north of the creepmeter. It also reveals high subsidence rate (up to ~20 mm/yr) along the southern shores of the Dead Sea Lake that can be explained by high compaction rate of clay sediments and reduction of pore pressure along the lake shores. This high subsidence rate is also observed in our near shore GNSS stations. Our results indicate that deformation within the Dead Sea basin is not solely controlled by the active tectonics. The observed vertical deformation is apparently modulated by the response of sediments to seasonal variations of local conditions.

How to cite: Hamiel, Y. and Bilham, R.: Characterizing shallow creep along the Dead Sea pull-apart basin using geodetic observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4550, https://doi.org/10.5194/egusphere-egu24-4550, 2024.

EGU24-4561 | Orals | TS1.6

Boso seismicity swarm propagation driven by slow slip stress change 

Baptiste Rousset, Asaf Inbal, Roland Bürgmann, Naoki Uchida​​, Anne Socquet, Lou Marill, Takanori Matsuzawa, and Takeshi Kimura

The interactions between aseismic slip and seismicity is mostly studied during postseismic afterslip associated with the generation of aftershocks following large earthquakes. However because of the large stress perturbations produced by the coseismic rupture, it remains difficult to distinguish the contribution of the coseismic stress perturbation and the effects of stresses induced by the afterslip on the triggering of aftershocks. Studying seismicity triggered by slow slip events enables us to understand the direct effect of aseismic slip on the generation of the seismicity. While most subduction slow slip events are deep-seated, at the down-dip edge of seismogenic zones accompanied by tectonic tremors, some are also observed at shallower depths associated with seismic swarms. Among them are the well-studied Boso slow slip events located on the Sagami trough, between 10 and 20 km depth. Recorded every ~4 years since 1996, they are always accompanied by swarms of Mw 1 to 5 earthquakes on their northern and western flanks. Being located right beneath the Boso Peninsula coastline, the kinematics of these slow slip events is particularly well imaged by dense GNSS and tiltmeter networks. In this study, we model the time dependent aseismic slip of the 2018 Boso slow slip event, with the largest moment released of all Boso slow slip events, by inverting time step by time step the slip on the fault with joint GNSS and tiltmeter data. We do not impose arbitrary temporal smoothing in the inversion and find that the well constrained fault slip is first growing and then migrating southwestward with a migration speed of ~ 2 km/day. In order to model the interaction with the seismicity, we compute the Coulomb stress change due to the transient slip on receiver faults located in 9 cubes centered in the seismicity swarm and parallel to the subduction interface. From June 2nd to June 18th, the seismicity is migrating up-dip at a rate of 1 km/day. This migration period coincides with the peak slip rate and with Coulomb stress produced by the slow slip migrating updip together with the seismicity, indicating a causal relationship. Adopting a rate and state friction formalism to explain the nucleation of the seismicity, we finally investigate the ensemble of parameters, in particular the constitutive parameter that relates changes in stress to logarithmic changes of slip velocity, the effective normal stress and the tectonic stressing rates, that can explain the seismicity rate. 



How to cite: Rousset, B., Inbal, A., Bürgmann, R., Uchida​​, N., Socquet, A., Marill, L., Matsuzawa, T., and Kimura, T.: Boso seismicity swarm propagation driven by slow slip stress change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4561, https://doi.org/10.5194/egusphere-egu24-4561, 2024.

EGU24-5061 | ECS | Orals | TS1.6

Complex Frictional Behavior of Clay and Implications for Slow Slip  

Giuseppe Volpe, Cristiano Collettini, Jacopo Taddeucci, Chris Marone, and Giacomo Pozzi

The shallowest region of subduction megathrust accommodates deformation by a spectrum of seismic modes including continuous aseismic creep and peculiar seismic phenomena as slow slip events. However, the mechanisms behind these phenomena remain enigmatic because they are not explained by conventional frictional models. This because the shallowest regions of subduction zones are characterized by unconsolidated, clay-rich lithologies that, nominally, cannot nucleate seismic events due to their frictionally weak and rate-strengthening attributes. Here we present laboratory friction experiments showing that clay-rich experimental faults with bulk rate strengthening behavior and low healing rate can contemporaneously creep and nucleate slow slip events. These instabilities are self-healing, slow ruptures propagating within a thin shear zone and driven by structural and stress heterogeneities. We propose that the bulk rate-strengthening frictional behavior promotes the observed long-term aseismic creep whereas local frictional mechanism causes slow rupture nucleation and propagation. Our results illustrate the complex behavior of clay-rich lithologies, providing a new paradigm for the interpretation of the genesis of slow slip as well as significant implications for seismic hazard.

How to cite: Volpe, G., Collettini, C., Taddeucci, J., Marone, C., and Pozzi, G.: Complex Frictional Behavior of Clay and Implications for Slow Slip , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5061, https://doi.org/10.5194/egusphere-egu24-5061, 2024.

The acoustic emissions (AEs) produced during the shearing of granular materials reflect the accumulation and release of stress, offering valuable insights into the failure mechanisms of seismic faults and stick-slip-controlled landslides. While various characteristics such as amplitude, energy, counts, and frequency of AE signals generated by stick-slip have been studied, the stress changes corresponding to different frequency AEs at various stages of the stick-slip process remain unclear. This knowledge gap hinders our understanding of the precursory signals leading to stick-slip failure. In order to enhance our comprehension of the physical mechanisms underlying granular stick-slip, we conducted monitoring of both mechanical and AE signals using high-frequency (2 MHz) synchronous acquisition. This was done during the constant-speed shearing of packs containing uniform glass beads of different sizes under varying normal stresses. Our findings revealed an accelerated release rate of AE energy in tandem with sample volume dilatation. Additionally, the stress drop during stick-slip increased with higher normal stress and particle size. This study identified three distinct events during a single cycle of stick-slip: main slip, minor slip, and microslip. We analyzed the AE frequency spectra associated with each of these events. Main slip and minor slip correlated with stress drop, generating high-frequency AEs (approximately several hundred kHz). In contrast, microslip produced lower AE frequencies (around tens of kHz) and exhibited stress strengthening. These characteristics, overlooked in prior studies due to low-frequency acquisition, suggest that microslip is primarily a result of sliding on grain contacts, while main slip and minor slip arise from the breakage and reformation of force chains. The low-frequency AEs from microslip may serve as a crucial precursor to seismic faults and landslides, providing a deeper understanding of the granular stick-slip phenomenon.

How to cite: Gou, H. and Hu, W.: Detection of Stick-Slip Nucleation and Failure in Homogeneous Glass Beads Using Acoustic Emissions in Ring-Shear Experiments: Implications for Recognizing Acoustic Signals of Earthquake Foreshocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5252, https://doi.org/10.5194/egusphere-egu24-5252, 2024.

EGU24-5921 | ECS | Posters on site | TS1.6

Interaction of fault slip with fast fluid pressure transients in subduction zones 

Avinash Gupta, Nikolai M. Shapiro, Jean-Paul Ampuero, Gaspard Farge, and Claude Jaupart

This study investigates the dynamic interplay between fluids and fault slip transients in the portion of subduction zones subject to slow earthquakes. The permeable subduction interface in this region is believed to be saturated with fluids supplied by metamorphic dehydration reactions in the downgoing plate. Following Farge et al. (2021), we consider a model of a heterogeneous subduction channel filled with low-permeability plugs that behave as elementary fault-valves. Such a system is characterized by an intermittent fluid transport and rapid and localized pressure transients. Episodic rapid build-ups and releases of the fluid pressure affect the frictional strength on the fault and can result in transient slip accelerations. To study the possible effect of episodic fast fluid pressure variations on fault slip, we use numerical simulations in a 2D in-plane shear geometry. The fault is governed by rate-and-state friction, with velocity-strengthening steady-state properties, and is forced with time and spatially variable pore fluid pressure. In an initial set of tests, we show that periodic pore pressure oscillations can accelerate the fault slip akin to observed slow slip events. We then investigate how the fault slip responds to more complex and “realistic” pore pressure histories generated by the dynamic permeability model of Farge et al. (2021). Our results underscore the possible role of input fluid flux and permeability structure in determining the variations of fault slip and, in particular, in facilitating the slow slip events. 

How to cite: Gupta, A., Shapiro, N. M., Ampuero, J.-P., Farge, G., and Jaupart, C.: Interaction of fault slip with fast fluid pressure transients in subduction zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5921, https://doi.org/10.5194/egusphere-egu24-5921, 2024.

EGU24-7813 | Posters on site | TS1.6

The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia 

Manel Prada, Sara Martínez-Loriente, Jonas B. Ruh, and Valentí Sallarès

The present-day Eurasia-Africa plate convergence offshore SW Iberia gives rise to a diffuse plate boundary marked by deep lithospheric thrust and strike-slip faults. The Horseshoe Abyssal Plain Thrust (HAT) stands out as a key structure accommodating plate convergence, and it has been the site of deep (> 30 km depth) and large magnitude (Mw > 6) earthquakes. Additionally, the HAT has been proposed to be the source of the 1755 Lisbon earthquake (estimated Mw≥8.5), one of the most destructive earthquakes and tsunami in the history of Europe. The geometry of the fault and the physical properties of rocks surrounding it have been determined through tomographic models derived from controlled-source seismic data. Although large earthquakes along the HAT primarily occur at considerable depths within the peridotitic mantle (~40 km depth), the fault intersects a region of serpentinized mantle at shallower depths (10-20 km depth). In contrast to peridotite that undergoes seismic deformation, the frictional behaviour of serpentinized peridotite depends on factors such as pressure, water content, temperature, and slip velocity. Laboratory measurements indicate that serpentinite transitions from rate-strengthening behaviour at plate tectonic rates to rate-weakening at seismic slip rates. This dual nature suggests that large deep earthquakes, nucleated in pristine peridotite, could rupture seismically through the weaker serpentinized peridotite. While this mechanism has been proposed to explain the HAT's potential to generate large tsunamigenic earthquakes, it remains untested. In this study, we use dynamic rupture numerical simulations to investigate the role of serpentinized peridotite in the rupture process and the tsunamigenic potential of the HAT. In particular, we explore various frictional scenarios to determine the slip pattern necessary to account for the previously estimated tsunamigenic uplift associated with the 1755 Lisbon earthquake.

How to cite: Prada, M., Martínez-Loriente, S., B. Ruh, J., and Sallarès, V.: The role of serpentinized mantle on thrust-fault earthquake dynamics offshore SW Iberia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7813, https://doi.org/10.5194/egusphere-egu24-7813, 2024.

Topographic features such as seamounts can influence the buoyancy of the slab and the short- and long-timescale mechanical properties of the subduction interface. How seamounts in the trench interact with the upper plate accretionary wedge during subduction— their stress field, their potential for ‘decapitation’, and their ability to host large megathrust earthquakes— is not fully understood. We utilize exhumed rocks to investigate seamount–upper plate interactions at shallow subduction interface conditions. 

We focus on a 250-m-thick cross-section of deformed, weakly metamorphosed basalt, limestone, chert, argillite and greywacke exposed in the inboard part of the Chugach accretionary complex near Grewingk glacier, southern Alaska. Temperatures from Raman spectroscopy on graphite yield ~260°C, suggesting deformation and metamorphism down to ~15-20 km depth. Detrital zircon data from greywacke lenses within and outside the shear zone overlap within error suggesting emplacement over less than ~1 m.y. at ~167 Ma. 

Basalts in the shear zone are dismembered into ~3 slices up to 35 m thick, all of which contain limestone patches suggesting the basalt is derived from the seamount’s very top (limited decapitation). The basalt slices are bounded by high-strain melange-like shear zones up to 25 m thick, interpreted to represent décollements along which the seamount slices were underplated. These mélange belts exhibit a block-and-matrix texture with a macroscopically ductile argillite and chert matrix, and pervasively disaggregated and brittlely deformed greywacke and basalt lenses. Both the matrix and the blocks show several generations of dilational and shear veins, suggesting high fluid pressures and low differential stresses. Features suggesting deformation at fast (potentially seismic) strain rates include fluidized cataclasites, but these do not extend along strike for more than 0.25 m and do not occur within the larger (m-to-dm-scale) basalt lenses, suggesting that large-magnitude earthquakes were limited during seamount underplating. Instead, the observed mix of brittle and macroscopically ductile deformation at high fluid pressures is more consistent with a potential record of shallow tremor and slow slip.

Our findings support geophysical observations and numerical models that suggest relatively weak mechanical and seismic coupling between seamounts and the overriding plate, and are consistent with recent suggestions (e.g. for the Hikurangi margin) that sediment envelopes around subducting seamounts are conducive to slow slip and tremor.

How to cite: Behr, W., Akker, I. V., and Rast, M.: Deformation processes during seamount dismemberment and underplating along the shallow subduction interface: a case study from the Chugach Complex, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8244, https://doi.org/10.5194/egusphere-egu24-8244, 2024.

EGU24-8731 | ECS | Posters on site | TS1.6

Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet 

Xinze Li, Yongsheng Zhou, Lining Cheng, and Jianfeng Li

A large number of tourmaline fault mirrors are exposed in the north-south normal fault system in the southern part of the Tibetan Plateau. Microstructure analysis shows that the tourmaline fault mirror has the characteristics of co-seismic high speed friction sliding and high temperature plastic rheology. In order to reveal the mechanical process of friction-rheological strength and co-seismic slip of tourmaline fault, the frictional and rheological experiments were carried out on the gas-medium triaxial high temperature and high pressure experimental system using undeformed tourmaline in southern Tibet to determine the formation conditions of tourmaline fault mirror. The effective normal stress of frictional experiments is 100Mpa.The pore water pressure is 30MPa. The temperature is 25-500℃, and the shear slip rate is switched between 1μm·s-1, 0.2μm·s-1, 0.04μm·s-1. The experimental results show that stick-slip occurs at 200-350℃, and the speed weakens at 400℃ and 500℃. The rheological experiment temperature is 850-950℃. The pressure is 300MPa, and the strain rate is switched between 2*10-5s-1, 1*10-5s-1, 5*10-6s-1, 7.5*10-6s-1. The experimental results show that the natural tourmaline sample is mainly fractured flow under the experimental conditions. The strength of hot-pressed dry tourmaline sample decreases with increasing temperature. The rheological strength of water samples synthesized by hot pressing was significantly reduced.

How to cite: Li, X., Zhou, Y., Cheng, L., and Li, J.: Implications of tourmaline frictional and rheological experiments on fault strength and sliding stability in southern Tibet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8731, https://doi.org/10.5194/egusphere-egu24-8731, 2024.

EGU24-8767 | ECS | Posters on site | TS1.6

A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data 

Roxane Tissandier, Adriano Gualandi, Lauro Chiaraluce, Enrico Serpelloni, Mike Gottlieb, Catherine Hanagan, and Chris Marone

Low-angle normal faults (i.e. with a dip < 30°) were assumed to have a very low seismic potential (Sibson et al., 1985). However, several observations have shown that earthquakes and aseismic slip can occur along such faults. For instance, the Alto Tiberina Fault (ATF), a 60-km long normal fault with a 15° low angle dip located in the active sector of the Northern Apennines (Italy), is seismically active as well as is actively accommodating part of the Apennines extensional strain. However, the relative contribution of seismic and aseismic slip on it is still unclear. The central and northern Apennines experienced several seismic sequences in the recent decades and a Mw ∼ 4.6 aseismic event accompanied by a seismic swarm of similar or smaller size was also recorded in 2013-2014 along two synthetic and antithetic fault in the hanging-wall of the ATF (Gualandi et al., 2017). The interactions between such minor conjugate faults and the ATF compose a system undergoing complex behavior making the area an ideal candidate to improve our understanding of interactions between different slipping modes. We benefit from data of the Alto Tiberina Near Fault Observatory (TABOO-NFO; Chiaraluce et al., 2014) looking for aseismic events on the ATF and its surrounding faults. The dense network of GNSS, seismometers and borehole strainmeters provides a rarely attained high spatial (inter-distance < 10km) and temporal (from 2009 to nowadays) resolution framework enabling the study of the ATF fault system slip history. We search for transients with a semi-automatic detection tool of slow slip events based on kinematic inversions of strainmeters time series. We also test if these events interact with larger seismic events of the region. We present the strain time series processed with the EarthScope Strain Tools (EarthScope Consortium) and the preliminary signals detected with our tool. The fine analysis of the ATF would help better constraining the behavior of faults and more generally large events. 

How to cite: Tissandier, R., Gualandi, A., Chiaraluce, L., Serpelloni, E., Gottlieb, M., Hanagan, C., and Marone, C.: A semi-automatic detection for transient events in northern Apennines using strainmeters and GNSS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8767, https://doi.org/10.5194/egusphere-egu24-8767, 2024.

EGU24-9007 | Orals | TS1.6 | Highlight

A mechanical insight into the continuous chatter of a fault volume 

Harsha Bhat, Michelle Almakari, Navid Kheirdast, Carlos Villafuerte, and Marion Thomas

In recent decades, there has been a proliferation of observations related to spatiotemporally intricate slip events occurring in fault systems. These events encompass a spectrum of transient energy releases, ranging from slow slip events to low-frequency earthquakes (LFEs) and tremors, in addition to the more familiar creep and fast ruptures. The prevailing focus in recent research has been to interpret these events by considering variations in frictional behavior along the fault plane.

However, it is crucial to acknowledge the inherent geometric complexity of fault systems across multiple scales. Recent studies have illuminated the significance of incorporating a fault volume or damage zone surrounding the fault in the analysis of slip dynamics. In the context of this study, we endeavor to investigate the influence of "realistic" fault geometry on the dynamics of slip events. To achieve this, we approach the problem from three interrelated perspectives:

  • Forward Source Modeling: We employ forward source modeling techniques to simulate and understand the behavior of slip events.
  • Bridging Source Modeling and Observations: We establish a connection between our source modeling and observed data by generating synthetic surface records that can be compared to actual observations.
  • Energy Budget Analysis: We meticulously analyze the variations in the energy budget that occur throughout the earthquake cycles to gain insights into the mechanics of slip events.

Our primary objectives include deciphering how deformation within the volume is accommodated by both the off-fault damage zone and the primary fault. Specifically, we aim to determine the proportion of the supplied moment rate that is absorbed by off-fault fractures during an earthquake cycle. Additionally, we seek to unravel how the diverse sequences of complex behavior observed on the fault plane manifest in the signals recorded by seismic stations. This entails assessing the distinct contributions of the main fault and off-fault fractures to the radiated signals detected at the monitoring stations. Lastly, we delve into the evolution of the medium's energy budget throughout the earthquake cycles and evaluate the dissipative contribution of off-fault fractures to ascertain their energetic role in the context of earthquake cycles.

How to cite: Bhat, H., Almakari, M., Kheirdast, N., Villafuerte, C., and Thomas, M.: A mechanical insight into the continuous chatter of a fault volume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9007, https://doi.org/10.5194/egusphere-egu24-9007, 2024.

EGU24-9169 | ECS | Posters on site | TS1.6

A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle 

Silvio Pardo, Elisa Tinti, Martijn Van den Ende, Jean-Paul Ampuero, and Cristiano Collettini

Fluid induced seismicity represents a significant issue for numerous activities related to geo-energy production. Enhanced geothermal systems, enhanced oil recovery, disposal of wastewater and carbon dioxide capture and storage are associated with subsurface fluid injection that can change the state of stress within the crust and can induce or trigger earthquakes. In several regions, M>3 earthquakes occurred following fluid injection, whereas in others seismicity has been accompanied by slow slip events. Although several mechanisms have been proposed to explain slow slip associated with fluid injection, the conditions leading to the observed spectrum of fault slip behavior still remain elusive. Here we used a quasi-dynamic boundary element method, the QDYN earthquake cycle simulator, to model the response of a fault governed by rate-and-state friction to fluid injection within a reservoir. We imposed low long-term loading rates to simulate a fault located in an area of slow active deformation, leading to natural earthquake cycles with very long recurrence times. We then imposed fluid pressure perturbations (one-way coupling) at different stages of the seismic cycle, to evaluate pore-pressure effects on the triggering of the next event. 

Our results show that for injection at high fluid pressure, earthquakes are in general immediately triggered (during injection or soon after) irrespective of the stage (early or late) of the seismic cycle, whereas at lower fluid pressure fast triggering is observed only when injecting in the late stages of the seismic cycle. Our models produce a spectrum of fault slip behavior, from regular to slow earthquakes. The latter are observed for specific fluid pressure, flow rate and injection time relative to the seismic cycle. The physics underlying this complex slip behavior remain to be explained, and further studies are required to define the injection conditions that favor the occurrence of slow slip instead of regular earthquakes.

How to cite: Pardo, S., Tinti, E., Van den Ende, M., Ampuero, J.-P., and Collettini, C.: A spectrum of fault slip behaviors induced by fluid injection on a rate-and-state fault depending on time of injection relative to its natural fault cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9169, https://doi.org/10.5194/egusphere-egu24-9169, 2024.

EGU24-9437 | Orals | TS1.6

Creeping sections on continental strike slip faults as the signature of deep fluid upwelling 

Romain Jolivet, Dmitry Garagash, Dublanchet Pierre, and Jorge Jara

Aseismic slip has been recognized over the last 50 years as one of the modes of elastic stress accommodation by large tectonic faults. Long strike slip faults have been imaged with InSAR and scrutinized with GNSS networks and creepmeters, revealing the strikingly ubiquitous occurrence of aseismic slip globally. From the 600-km-long creeping section of the Chaman to the 70 km-long Ismetpasa creeping section along the North Anatolian Fault, geodetic imaging illustrates the rich behavior of such aseismic slip, from mm-scale transient episodes of slip to seemingly continuously sliding fault segments.

Most models explaining the occurrence of aseismic slip along continental faults rely entirely on an ad hoc parameterization of the frictional rheology of the fault. While the friction law governing slip along faults has been determined from laboratory experiments, the inference of the constitutive parameters of such friction law entirely derives from reproducing geodetic data in most cases. In particular, most creeping sections are interpreted as the signature of rate-strengthening material, diffusing stress through stable sliding. However, most rocks at seismogenic depths exhibit a rate-weakening behavior and some even show transient episodes of slip incompatible with purely strengthening properties. In addition, other mechanisms, including complex geometric configuration of faults or fluid circulation may offer the conditions for slow slip. Therefore, the direct inference of constitutive properties of a fault zone from kinematic observations may not be simple.

We propose here a model in which upwelling of fluids sourced in the upper mantle through a vertical fault zone leads to the conditions for slow slip, irrespective of the fault constitutive properties. We map aseismic slip along three different fault zones, including the North Anatolian Fault (Turkiye), the San Andreas Fault (USA) and the Leyte fault (Philippines) and find a systematic relationship between the effective locking depth and the occurrence of aseismic slip. Our model explains this modulation of locking depth along strike and the subsequent modulation of surface shear stressing rate with the along strike variation in the mantle fluid source. This model applied to fault segments with relatively high mantle fluid source leads to low effective normal stress, large nucleation size of a frictional instability, and predicts occurrences of shallow aseismic slip. We perform numerical modeling to show that the critical parameter is the flux of upwelling fluid through the fault zone, which increase leads to the widening of the near-surface region of aseismic slip and transition to full-fault aseismic slip at large enough flux. We finally discuss the potential sources of fluids explaining such behavior.

How to cite: Jolivet, R., Garagash, D., Pierre, D., and Jara, J.: Creeping sections on continental strike slip faults as the signature of deep fluid upwelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9437, https://doi.org/10.5194/egusphere-egu24-9437, 2024.

EGU24-9595 | Orals | TS1.6

Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments 

Corentin Noël, Pierre Dublanchet, and François Passelègue

Deformation within the upper crust is mainly accommodated through slip on fault systems. These systems can accommodate slip via different modes, going from aseismic creep (i.e., stable motion) to dynamic earthquake (i.e., unstable motion). Notably, a single fault is not confined to a specific slip mode, as recent geodetic observations have indicated that a single fault can exhibit both stable and unstable motions. The distinct slip behaviours have been attributed to fault spatial heterogeneity of the frictional properties, rheological transitions, or geometrical fault complexities.

To comprehensively characterize the impact of frictional heterogeneities, we deformed heterogeneous fault samples in a triaxial apparatus, at confining pressure ranging from 30 to 90 MPa. The fault planes, sawcut at a 30° angle from the sample axis, consisted of two materials: granite and marble. Experiments were conducted for both marble asperities embedded in granite and vice versa, alongside homogeneous fault samples of single lithology. The selection of granite and marble was based on their different mechanical and frictional characteristics, with granite exhibiting seismic behaviour, while marble demonstrated aseismic behaviour across the pressure range tested.

Our findings reveal that the stress drops of seismic events are dependent on fault composition, with faults containing higher granite content exhibiting larger seismic events. In addition, by coupling the inversion of the kinematic slip from strain-gauge measurements and the records of acoustic activity during experiments, we demonstrate that the nucleation and propagation of seismic events are significantly influenced by lithological heterogeneity on the fault plane. In the case of homogeneous faults, the seismic event nucleation is relatively straightforward, initiating in the highest stressed region and propagating uniformly. Conversely, heterogeneous faults display more intricate nucleation patterns, often featuring multiple nucleation regions converging into a major dynamic event. The dynamic event propagation is expedited when traversing granite areas and more restrained within the marble. Remarkably, our experiments demonstrate that heterogeneities are required in order to induce earthquake afterslip. These results emphasize the crucial role of fault heterogeneity in earthquake nucleation and propagation, highlighting that even minor lithological heterogeneities are sufficient to complicate laboratory earthquake dynamics.

How to cite: Noël, C., Dublanchet, P., and Passelègue, F.: Exploring the impact of frictional heterogeneities on the seismic cycle: Insights from laboratory experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9595, https://doi.org/10.5194/egusphere-egu24-9595, 2024.

EGU24-9961 | Orals | TS1.6 | Highlight

Do earthquakes start with precursory slow aseismic slip? 

Quentin Bletery and Jean-Mathieu Nocquet

The existence of an observable precursory phase of aseismic slip on the faults before large earthquakes has been debated for decades. We conducted a global search for short-term precursory slip in GPS data. We summed the displacements measured by 3026 high-rate (5-minutes sample) GPS time series—projected onto the displacements expected from precursory slip at the hypocenter—during 48 hours before 90 (moment magnitude ≥7) earthquakes. Our approach revealed a ≈2-hour-long exponential acceleration of slip before the ruptures, suggesting that large earthquakes do start with a precursory phase of slip acceleration. The results have since been questioned as being due to an unfortunate combination of common mode noise in GPS time series. We investigate this possibility along with complementary tests to quantify the likelihood of the proposed pre-slip and the common mode hypotheses.

How to cite: Bletery, Q. and Nocquet, J.-M.: Do earthquakes start with precursory slow aseismic slip?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9961, https://doi.org/10.5194/egusphere-egu24-9961, 2024.

EGU24-10783 | Orals | TS1.6

Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening. 

Einat Aharonov, Pritom Sarma, Renaud Toussaint, and Stanislav Parez

Many previous studies have explored the role of granular media in controlling friction of faults. A gap exists though in understanding the failure process and sliding of a fluid-saturated fault gouge. Here we use a coupled 2D DEM-fluid code to simulate fault-gouge as a layer of grains, sheared by a constant stress boundary. We explore and compare two scenarios: 1) a dry granular layer, in which shear stress on the top wall is incrementally increased, or 2) a fluid-saturated granular layer, into which fluid is injected, so that fluid pressure is incrementally increased. Once the applied stress/pressure is high enough, the layer fails and starts accelerating, until it reaches a steady-state sliding rate (determined by the layers’ velocity-strengthening friction). We next incrementally step-down the shear stress or fluid pressure. Consequently, the slip-rate is observed to slow down linearly with decreasing stress/pore-pressure, until the layer finally stops, at a stress/pressure lower than that required to initiate the failure. Both the dry and fluid-saturated granular systems exhibit two main behaviors: 1) velocity-strengthening friction, following the mu(I) rheology, 2) a hysteresis effect between friction and velocity, porosity and grain coordination numbers. The hysteresis and strain-rate dependence agree with previous experimental, numerical and theoretical results in dry granular media, yet our work suggests these behaviors extend to fluid-filled granular media. We theoretically predict the transient and steady-state observations for dry and fluid-saturated layers, using the mu(I) friction rheology with an added component of hysteresis. Importantly, we show that fluid-filled faults exhibit a process which is absent in dry systems: fluid-injected layers may exhibit failure delay, with some time passing between pressure rise and failure. We link this delay to pre-failure creeping dilative strain, interspersed by small dilative slip events. Our numerical and analytical results may explain: (i) field measurements of fault creep triggered by fluid pressure rise (e.g. via injection), (ii) fault motion which is triggered by fluid-injection but continues even after fluid pressure returns to its pre-injection level. (iii) observed delay prior to failure in fluid-injection experiments.

How to cite: Aharonov, E., Sarma, P., Toussaint, R., and Parez, S.: Fluid-induced failure and sliding of a gouge-filled fault zone: Hysteresis, creep, delay and shear-strengthening., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10783, https://doi.org/10.5194/egusphere-egu24-10783, 2024.

EGU24-10887 | Orals | TS1.6

Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks 

Paul Antony Selvadurai, Antonio Felipe Salazar Vasquez, Patrick Bianchi, Claudio Madonna, Leonid Germanovich, Alexander M. Puzrin, Carlo Rabaiotti, and Stefan Wiemer

A growing number of observations made using geodetic approaches have been able to detect large preparatory regions that experience accelerated deformation prior to and in close proximity to an earthquake’s hypocenter. An uptick in localized seismicity has also been observed in these regions and represents an opposite end-member of the spectra of deformation, in both space and time, from the opposite broad and slow process. If and how these preparatory observations are linked are not well understood. To study this, we conducted a triaxial experiment on a granitic rock sample instrumented with calibrated acoustic emission (AE) sensors and a distributed strain sensing (DSS) method using fibre optics. These two technologies were sensitive to seismic (100 kHz to 1 MHz) and aseismic (DC to 0.4 Hz) deformation at our sample scale and these were monitored as it was loaded and experienced brittle shear failure. DSS measurement allowed us to visualize the emergence of slow, heterogeneous strain fields that localized well before the failure of the sample. In the early stages of localized deformation, the regions exhibiting preferential damage were growing and doing so without producing seismicity. However, when approaching failure, these regions accommodating slow deformation began to accelerate and now produced clusters of seismicity. The cumulative seismic moment of the precursory seismicity was a fraction of the total anelastic deformation (< 0.1%) precluding the runaway dynamic failure. We also examined the clustering and frequency-magnitude distribution of the seismicity with respect to the localized strain field. In the later stages, moments prior to nucleation, the b-value begins to drop and becomes anti-correlated to the rapidly accelerating average volumetric strain rate measured using the DSS array. This observation better constrains the hypothesis that dilation of the relatively large preparation zone can host larger precursory earthquakes therein. These findings can help constrain models that better replicate the physics associated with the large spectrum of brittle deformation and will in turn help with our understanding of preparatory earthquake processes.

How to cite: Selvadurai, P. A., Salazar Vasquez, A. F., Bianchi, P., Madonna, C., Germanovich, L., Puzrin, A. M., Rabaiotti, C., and Wiemer, S.: Localizing slow deformation holds crucial information related to seismicity patterns precluding brittle failure in crystalline rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10887, https://doi.org/10.5194/egusphere-egu24-10887, 2024.

Natural fault zone are complex objects. They not only consist of a fine-grained narrow fault core where the extensive shearing is observed, but it is also surrounded by pervasively fractured rocks, within an intricate 3-D geometry. If fault slip behavior is intrinsically linked to the properties of the fault core, the complex structure of fault zone systems impacts the rheological properties of the bulk, which influence the modes of deformation, and slip, as underlined by recent observations. Fault zone structure is therefore of key importance to understand the mechanics of faulting. Within the framework of a micromechanics based constitutive model that accounts for off-fault damage at high-strain rates, this numerical study aims to assess the interplay between earthquake ruptures along non-planar fault and the dynamically evolving off‐fault medium. We consider 2D inplane models, with a 1D self-similar fault having a root mean square (rms) height fluctuations of order 10-3 to 10-2 times the profile length. We explore the dynamic effect of fault-roughness on off-fault damage structure and on earthquake rupture dynamics. We observe a high‐frequency content in the radiated ground motion, consistent with strong motion records. It results from the combined effect of roughness-related accelerations and decelerations of fault rupture and slip rate oscillations due to the dynamic evolution of elastic moduli. These scenarios underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes, with a particular emphasis on seismic hazard assessment.

How to cite: Thomas, M. Y. and S. Bhat, H.: Combined Effect of Brittle Off-Fault Damage and Fault Roughness on Earthquake Rupture Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12095, https://doi.org/10.5194/egusphere-egu24-12095, 2024.

EGU24-12752 | Posters on site | TS1.6

Healing of fault surfaces: a field vs. experimental perspective 

Telemaco Tesei, Giancarlo Molli, Silvia Mittempergher, Giacomo Pozzi, and Francesca Remitti

“Fault healing” is the ability of fault rocks to recover strength after rupture, due to a combination of several physical processes that include cementation, compaction, asperity growth etc. Healing is fundamental in the earthquake physics because it allows for the repeated accumulation of energy along faults over multiple seismic cycles. Fault healing is commonly studied in the laboratory, through Slide-Hold-Slide (SHS) tests and cementation experiments. However, laboratory measurements and the microstructures of experimental fault rocks are difficult to compare with natural rocks, due to the difference in kinetics of physical mechanisms and the small spatio-temporal scale of experiments.

Here, we review the field and microstructural evidence of various processes of fault healing along a carbonatic fault surface, taking advantage of an outstanding case study: the Pietrasanta Normal Fault (NW Tuscany, Italy). In the field, the most common evidence of fault healing is the occurrence of cohesive fault rocks (cataclasites) and veins, but other fault surface properties may influence the re-strengthening of fault surfaces: e.g. adhesion phenomena (sidewall ripouts and fault surface patches) and geometrical complexity.

We compare these observations with frictional healing experiments carried out on carbonatic fault rocks, in which both fault gouges and cohesive slip surfaces were used. We propose that a fault surface composed by “patches” of cohesive fault rocks bounded by anastomosing slip zones are the result of complex cycles of gouge formation and healing, which modulate the interplay of adhesion and localization along the fault surface.

How to cite: Tesei, T., Molli, G., Mittempergher, S., Pozzi, G., and Remitti, F.: Healing of fault surfaces: a field vs. experimental perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12752, https://doi.org/10.5194/egusphere-egu24-12752, 2024.

In earthquake research, the discovery and ongoing investigation of interseismic transient processes has revealed that faults are non-steady between large earthquakes. These transients are typically identified in continuously operating tectonic GNSS stations, whereby an acceleration away from the average interseismic rates of displacement can be identified with a variety of time series analysis methods. However, the features of these transients can vary depending on the processing strategy employed to derive displacement time series from the raw GNSS observables.

In the processing strategy, the definition of the geodetic datum is necessary to determine global terrestrial reference frames (TRFs), providing an accurate and stable absolute reference of Earth's locations. It is essential for comprehending the dynamic changes in Earth's geometry driven by factors like tidal and non-tidal loading, plate tectonic seismic activity, and ongoing climate change. Therefore, just as geodesy aims for accuracy and stability in the TRF, the datum definition—i.e., the realization of the TRF-defining parameters origin, orientation, and scale—may emerge as a critical factor in processing GNSS networks for geodynamic purposes.

The purpose of this study is to assess up to what extent the transient velocities obtained from GNSS-derived displacement time series change under different regional and global datum definitions for the Cascadia subduction zone and Hikurangi margin; regions with very well-known catalog of interseismic transient tectonic events. In our study, we process data from Cascadia to produce network solutions both NNR (No-Net-Rotation) and NNR+NNT (No-Net-Translation) constraint for regional and global datum definition, respectively. We employed dual-frequency ionosphere-free linear combination observations from 125 GNSS stations for the time between 2015 and 2020. The same GNSS processing strategy is then followed for the Hikurangi subduction zone using a set of 72 stations from the GeoNet project as well as the same control stations used for Cascadia spanning from 2002 to 2010.

For the Cascadia displacement time series, we find variations in transient velocities under different datum definitions emphasizing the need for a comprehensive understanding of its impact on dynamic geophysical processes. Processing and analyses of the New Zealand data is ongoing and results will be presented, along with recommendations for both regions on how to reduce the occurrence of likely non-tectonic transients in the displacement time series. Ultimately, our results may have implications for improving the estimate of the slip budget at plate boundaries that is released aseismically.

How to cite: Garcia, C., Bedford, J., Männel, B., and Glaser, S.: Impact of datum definition on transient velocities from GNSS displacement time series in Networks mode: A Case Study of Cascadia Subduction Zone and Hikurangi margin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12979, https://doi.org/10.5194/egusphere-egu24-12979, 2024.

EGU24-13514 | ECS | Posters on site | TS1.6

Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction 

Lin Zhang, Jianye Chen, Bowen Yu, and Miao Zhang

It is believed that seismic failure conditions are sensitive to strain-softening behavior of nominal rock or fault gouge, and that precursors prior to a big earthquake (i.e., tectonic trains, water level changes, and Vp/Vs anomalies, etc) are provided by the acceleration of local slip. Previous studies of earthquake nucleation on laboratory faults show that the initiation of unstable fault slip is spatiotemporal dependent and consists of an interval of fault preslip (or creep) that localizes and accelerates to a dynamically propagating rupture. We pose that perturbation-type experiments can provide a natural condition to help analyze the potential mechanisms between instability events and the stress loading. In this study, we conducted three sets of double-direct shear experiments on a 300 mm long fault filled with gypsum-rich gouges, under normal stress of 10 MPa superimposed with perturbations of various amplitudes (i.e., 0-0.5 MPa) and a fixed frequency (0.1 Hz). The result showed that during each cycle of the stick slip behavior, the applied normal stress perturbations were redistributed along the fault zone as revealed by the along-fault strain measurement in the normal direction. As such, the fault can be divided into different zones characterized by varied coupling with respect to the applied perturbations. We found, coincidently, nucleation of the final instability, as revealed by the strain measurement in the shear direction, tended to occur at the boundary between the so-called strong and weak coupling zones (‘Transition Zone). Moreover, local normal stress near the nucleation zone also showed some weakening prior to the instability, which was similar to that seen in the local shear stress, and hereafter referred to as ‘normal failure’. Based on these observations, we proposed an empirical equation to fit the normal strain or stress data, giving the distribution of the coupling coefficient (c-value) and the anomaly (a-value) along the simulated fault. Finally, we applied the proposed equation to fit the water level data from 6 monitoring stations along the fault that hosted a nature earthquake (~ML 4). The fitting results predicted a Transition Zone, which was close to the hypocenter. In the end, we propose that this approach can be tested widely to natural observations of various precursory signals, especially those considered to be sensitive to fault-normal deformation (“dilatation” or “compaction”), such as water level, soil gas, and Vp/Vs anomalies. Hopefully, the results can shed some lights on the location of the earthquake nucleation zone. 

How to cite: Zhang, L., Chen, J., Yu, B., and Zhang, M.: Discrepant stress distributions around instability regions: A new view for earthquake nucleation zones prediction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13514, https://doi.org/10.5194/egusphere-egu24-13514, 2024.

EGU24-13838 | ECS | Posters on site | TS1.6

Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones 

Jun Xie, Xiaotian Ding, and Shiqing Xu

A rich spectrum of slip behaviors, spanning from aseismic creep (mm/yr) to seismic slip (m/s), has been observed in many subduction zones and some strike-slip faults. Slow earthquakes, intermediate between these two end-member modes, exhibit transitional slip behaviors in fault sections adjacent to the seismogenic zone. Focusing on subduction zones, it is shown that they experience deformation not only along discrete fault planes but also over distributed frictional-viscous shear zones, the latter of which are thought to be responsible for the observed diverse slip behaviors. Here we employ a frictional-viscous mélange model consisting of brittle blocks surrounded by a viscous matrix to investigate its influence on slip behaviors. By varying the mélange's rheological and frictional properties, we observe a diverse range of slip behaviors. We also reproduce the source scaling relations observed in natural faults, including the relation between seismic moment and duration and that between moment magnitude and stress drop. Additionally, we find a close link between the modeled shear zone deformation patterns and the various geological structures observed in natural fault zones. Our study demonstrates that the interaction between the frictional and viscous compositions of the mélange is responsible for the resulting slip behaviors and their transitions under different compositional ratios. These results provide useful clues for constraining the environmental and rheological conditions of different subduction zone sections from the observed slip behaviors.

How to cite: Xie, J., Ding, X., and Xu, S.: Slip Behaviors Controlled by Rheological and Frictional Properties of A Two-Phase Mélange in Subduction Shear Zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13838, https://doi.org/10.5194/egusphere-egu24-13838, 2024.

EGU24-15197 | ECS | Posters on site | TS1.6

Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea 

Sejin Jung, Ji-Hoon Kang, Youngwoo Kil, and Haemyeong Jung

The 5.5 magnitude (Mw) earthquake in Pohang, South Korea in 2017 was one of the largest triggered earthquakes at an enhanced geothermal system (EGS) site. Faults that ruptured in Pohang were not identified by preliminary geological investigations or geophysical surveys, and the subsequent study of the fault rocks at the Pohang EGS site was limited to depths of 3790–3816 m. In this study, we present new observations of fault rocks from drill cuttings retrieved from the Pohang EGS. The drill cuttings obtained from 3256 to 3911 m contained “mud balls,” which showed a clay matrix with foliation and a cataclastic texture, indicating a typical fault gouge or breccia. Furthermore, the mud ball samples retrieved from depths of 3256 m and 3260 m contained black fragments. Scanning and transmission electron microscopy revealed that the black fragments consisted of glass-like material, which is indicative of frictional melting during coseismic slip (Jung et al., 2023). The presence of these black fragments suggests that at least one seismic event had occurred at the Pohang EGS site prior to the hydraulic stimulation test.

Jung, S., J. -H. Kang, Y. Kil and H. Jung, 2023, Evidence of frictional melting in fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea. Tectonophysics, 862, 229964.

How to cite: Jung, S., Kang, J.-H., Kil, Y., and Jung, H.: Deformation microstructure of the fault rock drill cuttings from the enhanced geothermal system site in Pohang, South Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15197, https://doi.org/10.5194/egusphere-egu24-15197, 2024.

EGU24-15878 | ECS | Orals | TS1.6

Fault orientation in earthquake seismic precursors: insights from the laboratory 

Carolina Giorgetti and Nicolas Brantut

Faults in the brittle crust lie at any orientation to the far-field stress. However, laboratory experiments designed to investigate earthquake physics commonly simulate favorably oriented faults, potentially overlooking the complexity of natural fault behavior. Here, we assess the role of stress field orientation in fault reactivation and earthquake precursors by conducting triaxial saw-cut experiments with laboratory faults oriented at different angles to the maximum principal stress, ranging from 30° to 70°. The samples were instrumented with strain gauges and piezo-electric sensors. Laboratory well-oriented faults describe a rather simple system in which the elastic energy is stored via the deformation of the surrounding host rock during the inter-seismic period and released via on-fault slip during the co-seismic phase with associated precursor acoustic activity. Consistent with previous laboratory data, an abrupt increase in the on-fault acoustic emission rate occurs shortly before the laboratory earthquake. A more complex picture emerges when deforming laboratory misoriented faults. Particularly, acoustic emissions and strain gauge data indicate that when the fault is misoriented, off-fault permanent deformation occurs well before fault reactivation. The stress state in the host rock surrounding the fault is indeed far beyond the one required for the onset of inelastic deformation. In this case, acoustic activity distributed in the rock volume during the pre-seismic phase is associated with permanent deformation in the critically stressed host rock and is not a direct precursor to the following laboratory earthquake. Unlike well-oriented faults, laboratory mis-oriented faults lack detectable seismic precursors. The laboratory-observed increase in acoustic activity prior to, but not precursor of, mis-oriented fault reactivation impacts our understanding of earthquake precursors in natural faults.

How to cite: Giorgetti, C. and Brantut, N.: Fault orientation in earthquake seismic precursors: insights from the laboratory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15878, https://doi.org/10.5194/egusphere-egu24-15878, 2024.

EGU24-16581 | ECS | Posters on site | TS1.6

Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series 

Rens Elbertsen, Ivan Vasconcelos, and André Niemeijer

Laboratory stick-slip experiments are a simple analogue for the earthquake cycle. The acoustic emissions (AE) of these experiments have been shown to contain hidden patterns. Machine Learning (ML) can extract these patterns and information on the fault state can be inferred (e.g. shear stress and time to failure). Two different ML approaches have been used in the past: 1) ensemble tree models, which are relatively easy to evaluate why they made a certain prediction, but only look at a snapshot in time and 2) deep neural networks using Long Short-Term Memory (LSTM), which have the ability to find patterns in the temporal changes in the signal, but act more as a black-box model, so the final predictions are hard to evaluate. Here we introduce an additional step in the workflow that can be used to allow the ensemble tree models information about the temporal changes of the input features. Furthermore, it is able to quantify and visualize whether a pattern is repetitive or not. Like earlier studies we start by calculating (statistical) features using a rolling window on the AE. The features are not directly used as the input of the model, but are placed in a larger Hankel matrix, where the consecutive time windows are the rows of the matrix. Using Principal Component Analysis (PCA) and Uniform Manifold Approximation and Projection (UMAP) we create an embedded version of this array that holds temporal information of features calculated in the previous step. Visual inspection of these embeddings shows that some features map to very distinct patterns that are repetitive over the majority of the stick-slip cycles. The advantage of this method is that an inverse mapping is easily available, allowing for an interpretable embedding of the data.

How to cite: Elbertsen, R., Vasconcelos, I., and Niemeijer, A.: Interpretable Embedding of Laboratory Stick-Slip Acoustic Emission Time Series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16581, https://doi.org/10.5194/egusphere-egu24-16581, 2024.

EGU24-18746 | ECS | Posters on site | TS1.6

Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed 

Navid Kheirdast, Harsha Bhat, Michelle Almakari, Carlos Villafuerte, and Marion Thomas

Seismic observations confirm that natural fault systems radiate waves across a continuum of frequency and amplitude. Within this spectrum, faulted systems exhibit a continuous range of slip rates, allowing them to irreversibly dissipate energy stored in rocks over a broad range of seismic moment. Despite advancements in observations and numerical modeling models, the question on how a given fault system can host such a wide range of ruptures, including slow ruptures, VLFEs, LFEs, and fast earthquakes needs a careful attention. Addressing this question requires a framework rooted in fracture mechanics, which explores the rate at which energy provided to a crack drives the rupture front forward and how this process radiates energy throughout the medium.

This work delves into the question of how frictional instability and mechanical interactions between faults and fractures, particularly concerning the geometrical distribution of off-fault damage, can generate observed rupture patterns in seismic catalogs. A model of a representative fault system is proposed, featuring a main fault embedded within a fractured zone where all fractures can slip independently. The length distribution of the off-fault fractures follows a power-law. The study then explores the fracture processes within the system, examining rupture speed from an energetic standpoint and exploring the impact of the damaged zone on the supply or reduction of energy to the process zone, ultimately influencing whether ruptures propagate rapidly or slowly.

The influence of this process is further examined by analyzing the amount of energy radiated away from the fault system. Moment-radiated energy and moment-fracture energy scaling relationships will be presented as mechanical quantities that both slow and fast earthquakes adhere to on a common curve. We will discuss radiation efficiency as a function of rupture speed to illustrate how a fault adjusts its rupture speed according to the energy provided to it and the amount of its breakdown work. The effect of damage on the process zone of the rupture will be discussed to examine how interactions between multiple fractures supply or detract energy to an active process zone, affecting its rupture speed and, consequently, the fast or slow advancement of the front.

How to cite: Kheirdast, N., Bhat, H., Almakari, M., Villafuerte, C., and Thomas, M.: Analyzing Earthquake Energy: Unveiling the Spectrum of Fault Behavior in Terms of Moment, Duration, and Rupture Speed, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18746, https://doi.org/10.5194/egusphere-egu24-18746, 2024.

EGU24-20753 | Posters on site | TS1.6

Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System 

David Essing, Kaan Cökerim, Gian Maria Bocchini, and Rebecca M. Harrington

The Hellenic Subduction System (HSS) in the eastern Mediterranean is the oldest active subduction margin on earth. It is a segmented boundary that hosts the continuum of faulting styles over a ~200km range in depth and can generate large earthquakes with high tsunamigenic potential.  The complexity of deformation styles and rates leave key aspects of the system poorly understood. For example, historical records of Mw<8 earthquakes fail to explain the current observed convergence rate (~35mm/year), and recent geodetic measurements suggest that the degree of locking within the system is heterogeneous. The density of geodetic measurements is increasing rapidly, nevertheless, the inherent time lag required to accumulate data that will enable identifying regions that undergo slower (than seismic) deformation transients will necessitate inferences from seismic signals. In this work, we aim to further close the observational gap between heterogeneous deformation styles and rates using the features of seismicity distributions to infer where deformation rates, and by inference, locking, vary most.   

To that scope, we will present new results of an enhanced earthquake catalog that we will use to explore the spatio-temporal distribution of seismicity features (e.g., b-value, effective stress drop, seismic-moment-release skewness) to infer variability in deformation rates and loading. Catalog enhancement exploits data from the temporary (EGELADOS) broadband seismometer network that operated between 2005 until 2007 combined with permanent stations leading to a station spacing of ~40 km and covering the entire southern Aegean Sea. We first use the combined network to detect earthquakes using machine learning approaches (EQTransformer, PhaseLink) for detection, phase picking and association. After performing initial locations using NonLinLoc combined with a 1D velocity model and quality control procedure, we enhance the number of small-magnitude detections using a multi-station template-matching approach. Next, we scan the enhanced high-resolution catalog for distinct spatial and temporal patterns of seismicity using unsupervised clustering. We then quantify the clustered seismicity using b-value, effective stress drop, and seismic-moment-release skewness (among other parameters). We will present our clustering results in the context of the variability in slip phenomena related to earthquake-earthquake interactions (e.g., static and dynamic triggering) as well as in the context of external forcing (e.g., aseismic triggering or fluid migration).  

The preliminary results that we will present will provide a basis for our more broad-scale study of interplay between seismic and aseismic deformation. In particular, where the latter is gradually becoming increasingly resolvable using GNSS data within the HSS, this work will provide a basis for links with geodetically observed deformation in the future.  

How to cite: Essing, D., Cökerim, K., Bocchini, G. M., and Harrington, R. M.: Using small-magnitude earthquakes to investigate the interplay between seismic and aseismic deformation along the Hellenic Subduction System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20753, https://doi.org/10.5194/egusphere-egu24-20753, 2024.

EGU24-20908 | ECS | Posters on site | TS1.6

Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction  

Giacomo Mastella, Federico Pignalberi, Carolina Giorgetti, and Marco Scuderi

Double direct shear experiments serve as established methods for delving into the physics of laboratory earthquakes. Using a biaxial shearing apparatus with dual fault configurations, these friction experiments simulate real Earth faults' behaviors during loading and failure. 

Despite the presence of distinct layers, double direct shear experiments are commonly perceived as a unified fault system, where the evolution of fault zone properties captured through passive or active seismic imaging can be correlated with the instantaneous stress state affecting both layers uniformly. To further explore the physics of seismic cycles generated in this setup, we perform friction experiments aiming to independently monitor the behavior of each fault layer. In our experiments, we use granular quartz (medium grain size 40 µm) to simulate fault gouge, amd we vary the normal load and shear velocity, allowing us to modify the apparatus's loading stiffness, which relies on the critical fault rheologic stiffness (kc). In the Rate-and-State framework, increasing the normal load results in an  increase of kc, pushing the system towards instability, occurring when k/kc <1, where k is the fault stiffness. Under 50 MPa of  normal loads and 10 µm/s of loading rate, these conditions result in highly non-cyclic seismic cycles marked by significantly variable stress drops and recurrence times. This situation offers an exceptional opportunity to investigate stress partitioning between the two layers and understand their interactions. Experiments are monitored using high-frequency calibrated piezoelectric sensors with a sampling rate of 6 MHz, placed on each of the two forcing blocks. Such a sampling rate allows us to clearly distinguish the time delay between the Acoustic Emissions (AEs) generated from microslip events in different layers. Phase arrivals are detected using retrained, Deep Learning-based algorithms. By associating these phase arrivals using the DBSCAN clustering algorithm, we classify events as occurring on a single gouge layer or on both layers. Subsequently, we analyze the catalog of AEs,, and single seismic waveforms, in terms of general characteristics and frequency content, to look for differences in the physical sources generating them. Unsupervised clustering may help identify classes of AEs linked to specific stages within seismic cycles. By potentially using established supervised Machine Learning technique, it would be possible to verify the relation between AEs variance for each layer and macroscopic apparatus features, like instantaneous friction or time to failure. All of these techniques reveal differences in acoustic energy released before failure for each layer, observations that can be associated to changes in fault physical properties, asperity scale processes and/or  grains sliding or fracturing. In conclusion, our findings demonstrate that double-direct shear experiments can emulate a system of interacting double faults. In such a context, the continuous monitoring of AEs can provide insights into the stress partitioning between the two layers, a process that may guide the nucleation of major slip events as well as the long term behavior of the system. Additionally, our analysis may be helpful to investigate processes like fault interactions, faults synchronization, static, and dynamic stress triggering.

How to cite: Mastella, G., Pignalberi, F., Giorgetti, C., and Scuderi, M.: Double Direct Shear Experiments as an interacting two fault system:  insights from laboratory seismic cycles on fault interaction , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20908, https://doi.org/10.5194/egusphere-egu24-20908, 2024.

EGU24-1239 | Posters on site | TS2.1

Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements 

Young-Gyun Kim, Jong Kuk Hong, Young Keun Jin, and Byung Dal So

The Amerasia Basin, one of two major basins that comprise the Arctic Ocean, is thought to have a more complex formation history than its counterpart, the Eurasian Basin. Because the harsh conditions for marine expeditions last the entire year, there is a lack of observational data for constraining the tectonic history of the Chukchi Basin. Thus, there are multiple existing hypotheses for its tectonic history, with contrasting formation ages ranging from Mesozoic to Cenozoic and crustal types ranging from hyper-extended continental crust to oceanic crust. Recently, during the 2018 and 2021 Arctic expeditions of the Korean ice-breaking research vessel Araon, we obtained the new marine heat flow data along the east-west and northeast-southwest transect lines from the abyssal plain to the continental slope/shelf of the basin. These data may play an important role in constraining the formation age of the basin, as the extending axis among the hypotheses is likely oriented from north-south. Assuming an oceanic crust, the formation age can be inferred to be Late Cretaceous. This information concerning the formation age enhances our understanding of the underestimated complex tectonic history of the Amerasia Basin, because such inferred timing aligns with the formation age of the adjacent Chukchi Borderland.

How to cite: Kim, Y.-G., Hong, J. K., Jin, Y. K., and So, B. D.: Constraints on the Formation Age of the Chukchi Basin, Arctic Ocean, inferred from Marine Heat Flow Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1239, https://doi.org/10.5194/egusphere-egu24-1239, 2024.

EGU24-1615 | ECS | Orals | TS2.1

Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece 

Costantino Zuccari, Francesco Mazzarini, Enrico Tavarnelli, Giulio Viola, Luca Aldega, Roelant Van der Lelij, and Giovanni Musumeci

Extensional detachments are commonly considered key structures in accommodating the exhumation of deeply buried or subducted crustal slivers, and in facilitating the syndeformation emplacement of plutons during the evolution of wide rift systems (i.e., Basin and Range type). In those settings, ductile shear zones and brittle faults may act for several million years to accommodate important vertical and horizontal displacements such that multiply reactivated and highly complex shear zones and faults may form. The analysis of these complexities, together with the possibility to constrain the age of strain and deformation localisation, is thus pivotal in reconstructing the onset and evolution of the processes that steer(ed) the crustal extension.

Aiming at better understanding these structural/chronological intricacies, we have studied the brittle Mykonos Detachment (MD), which is thought to have facilitated the emplacement of the Mykonos granite starting in the Middle Miocene (~14-9 Ma) and following the activation of the earlier (ductile) Livada Detachment (LD) that would have favoured the beginning of pluton cooling during the structuring of the Aegean rifting. The Mid. Miocene age of the MD is, however, only loosely constrained by the stratigraphic age of syn-tectonic siliciclastic deposits in the hanging wall of the fault. No absolute ages exist yet on the activation of the brittle MD or the ductile LD, and a detailed description of the internal architecture of the MD is still not available.

Aiming to fill this gap(s), we carried out a detailed study that couples a Brittle Structural Facies – based structural analysis with K-Ar dating on authigenic illite from fault gouge(s) that compose the MD fault core. Fault gouges normally rest on and are cut by the MD principal slip surface (PSS), which reasonably postdates the gouge formation and represents the effects of the latest fault activity. We have obtained a 7.1 ± 0.1 Ma K-Ar age from a fault gouge suggesting that the MD activation postdated the widely accepted ~14-9 Ma of the granite cooling, also considering that the PSS postdates the 7.1 Ma gouge, as indicated by field evidence. On this ground, together with published thermochronological data showing that the granite experienced a rapid cooling from ~14 to ~11 Ma before experiencing slow cooling until ~9 Ma, we can state that most of the granite exhumation cannot be ascribed to the MD, the activation of which postdates the late stage of the granite cooling.

These new geochronological data (which are soon to be implemented with new K-Ar dates) and the description of the architectural evolution of the MD fault zone, stress the role of the detachment during the unroofing of the Mykonos granite in the Aegean rifting context. In this perspective, the granite exhumed is mostly assisted by the ductile LD, which acted before the MD. The latter acted instead only at a later stage when it juxtaposed the Miocene siliciclastic against an already cooled and unroofed granite, which had reached a temperature of ~40°C about 2Ma before the latest Late Miocene activation of the MD, as shown by our preliminary age constraint.

How to cite: Zuccari, C., Mazzarini, F., Tavarnelli, E., Viola, G., Aldega, L., Van der Lelij, R., and Musumeci, G.: Evolution and activation of an orogen-scale shear zone in the northern Aegean Rift System: insights from the Mykonos Detachment, Cyclades, Greece, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1615, https://doi.org/10.5194/egusphere-egu24-1615, 2024.

A new onshore-offshore 3-D constrained gravity inversion methodology that incorporates onshore topography and laterally variable inversion mesh depths is used to determine the crustal density distributions, Moho depths, and crustal thicknesses of Iberia, Morocco, and their respective rifted continental margins. The results largely show an excellent correspondence with crustal characteristics determined from sparsely distributed controlled-source and passive seismic experiments, while also allowing the layered density structure of the region to be explored and analyzed in terms of upper, middle, and lower crustal layers. These detailed regional views as a function of depth can improve characterization of crustal types (continental versus oceanic versus transitional), and the resulting interpretations can be directly compared against equivalently derived crustal characteristics for onshore-offshore Atlantic Canada, which encapsulates both Iberia’s and Morocco’s conjugate rifted margins. Collectively, the conjugate 3-D crustal-scale density models allow for the extraction of mega-transects across both sides of the southern North Atlantic, joined together back through geological time using kinematic plate reconstructions.

How to cite: Welford, J. K.: Crustal structure of onshore-offshore Iberia, Morocco, and their rifted continental margins, from constrained 3-D gravity inversion using variable mesh depths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3196, https://doi.org/10.5194/egusphere-egu24-3196, 2024.

EGU24-3979 | ECS | Posters on site | TS2.1

Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin 

Jie Chen, Sylvie Leroy, Louise Watremez, and Adam Robinson

Continental rifting is the Earth’s fundamental tectonic process that may result in a new plate boundary, i.e., mid-ocean ridges, with the accretion of new oceanic crust. At present, continental rifted margins are classified into two end-members based on the amount of magmatism that occurred during the rifting process: magma-rich and magma-poor. However, various factors influence the formation of these margins, such as the inheritance of segmentation, extension obliquity, syn-rift magmatism, and sedimentation. The Gulf of Aden represents a good example for understanding such spatial variations in the formation of rifted margins. It consists of an oblique rifting system, with young and segmented margins (34-17.6 Ma) and thin sediments. In addition, the Gulf of Aden exhibits magma-rich margins in the west, related to the Afar hotpot, and magma-poor margins in the east, with a possible zone of exhumed continental mantle.

In this study, we develop a 3-D P-wave velocity model across the north-eastern Gulf of Aden continental margin, using wide-angle seismic refraction data from a combined onshore-offshore survey with 35 ocean-bottom seismometers and 13 land seismometers. Approximately 187,000 P-wave first arrivals were picked and inverted in 3-D, with the modelling informed by constraints from previously published 2-D velocity models. Here, we present our preliminary tomographic results that illustrate the spatial variations in the crustal velocity structure of the continent, continent-to-ocean transition (COT), and oceanic domains, as well as the comparison between our 3-D and the published 2-D velocity structures of the north-eastern Gulf of Aden continental margin.

How to cite: Chen, J., Leroy, S., Watremez, L., and Robinson, A.: Three-dimensional crustal velocity structure of the north-eastern Gulf of Aden continental margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3979, https://doi.org/10.5194/egusphere-egu24-3979, 2024.

During the final stages of breakup at magma-poor rifted margins, mantle rocks are commonly exhumed and altered to serpentinite due to the ingress of ocean water. This mantle exhumation phase is followed by an increase in magmatism as new oceanic crust begins to form. However, the degree to which serpentinisation is focused at faults and whether the onset of magmatism is abrupt or gradual are both unclear. These processes are difficult to untangle with seismic data alone because the P wave velocities of mafic crustal rocks and partially serpentinised mantle rocks can be similar. However, serpentinised mantle rocks are generally more conductive, often by about an order of magnitude, than mafic crustal rocks, so controlled source electromagnetic (CSEM) and magnetotelluric (MT) techniques provide a promising route to resolve controversies around the structure of lithosphere formed during the onset of seafloor spreading.

To take advantage of the complementary information provided by seismic and electromagnetic data, in September 2023 we acquired a coincident and densely sampled wide-angle seismic, CSEM and MT datasets across the continent-ocean transition at Goban Spur, southwest of the UK. Our c. 200-km profile is coincident with a pre-existing high-quality seismic reflection profile. It extends from thinned continental crust, whose nature is confirmed by drilling, across a broad zone that is inferred on the basis of a previous wide-angle seismic experiment to be composed of exhumed and serpentinised mantle, and into oceanic crust, evidenced by the presence of the prominent seafloor-spreading magnetic anomaly A34. Along this profile, we deployed 49 seafloor instruments at c. 4-km spacing that were each capable of recording seismic, electric field and magnetometer data, plus an additional two instruments recording the inline electric field on 200-m dipoles. These instruments were on the seafloor for about two weeks. During this time we acquired two wide-angle seismic profiles: one using a 5200 cu. in. airgun array shot at 90-s intervals and a second using a 3900 cu. in. airgun array shot at 30-s intervals. We also acquired a frequency-domain  CSEM profile using a transmitter towed c. 100 m above the seabed that powered a 300-m electric dipole with a c. 100-A current at a fundamental frequency of 0.25 Hz. Preliminary data analysis showed that seismic signals were recorded to c. 90 km offset and CSEM signals to c. 8 km offset, while high-quality MT data were recorded at periods of 20-10000 s.

Thus we expect to recover coincident high-resolution images of the seismic velocity and resistivity structure of the upper few km of the basement, sufficient to image patterns of serpentinisation and mafic intrusion. We also expect to recover lower-resolution images of the resistivity to tens of km below the seabed and thus to distinguish continental mantle lithosphere from depleted oceanic lithosphere. We will present examples of the data acquired and the results of some preliminary analysis.    

How to cite: Minshull, T., Bayrakci, G., and Constable, S.: An integrated seismic, controlled source electromagnetic and magnetotelluric study of the continent-ocean transition southwest of the UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6227, https://doi.org/10.5194/egusphere-egu24-6227, 2024.

EGU24-6331 | ECS | Orals | TS2.1

How developing grabens dictate volcanism shifts in rifts 

Gaetano Ferrante, Eleonora Rivalta, and Francesco Maccaferri

Volcanism in continental rifts is generally observed to shift over time from the inside of the graben to its flanks and back. These patterns are commonly observed across rifts from different tectonic contexts, different abundance of melt, and regardless of the rifts' specific complexities, suggesting a common control. However, despite recent advances, the mechanisms governing the spatio-temporal evolution of rift magmatism are still poorly understood. Here we test the hypothesis that the spatio-temporal evolution of rift volcanism is controlled by the crustal stresses produced during the development of the rift basin. To do so, we couple a gravitational unloading model of crustal stresses with a boundary element dike propagation code to investigate the effect of a deepening graben on the evolution of magma trajectories in rifts. We find that the progressive deepening of a graben rotates the direction of the principal stresses in the crust, deflecting ascending dikes. This causes a relatively sudden shift of volcanism from the inside of the graben to its flanks during the early stages of rifting. The intensification of this stress pattern, caused by further deepening of the basin, promotes the formation of lower crustal sill-like intrusions. These horizontal bodies can stack under the rift, shallowing the depth at which dikes nucleate, eventually causing a late stage of in-rift axial volcanism, which can alternatively be induced by compensation of graben unloading by sediment infill. Our model reproduces the general patterns of volcanism in rifts and provides a framework to explain their commonalities and account for possible differences. Given the agreement between our model results and observations, we conclude that the evolution of the stresses generated by a developing rift basin can account alone for the major aspects of the spatio-temporal evolution of rift magmatism.

How to cite: Ferrante, G., Rivalta, E., and Maccaferri, F.: How developing grabens dictate volcanism shifts in rifts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6331, https://doi.org/10.5194/egusphere-egu24-6331, 2024.

EGU24-6401 | ECS | Posters on site | TS2.1

Reactivation of inherited faults in rift basins: insight from analogue modeling 

Pauline Gayrin, Daniele Maestrelli, Giacomo Corti, Sascha Brune, and Chiara Del Ventisette

Continental rifts accommodate shallow extensional stresses both by brittle deformation (normal faulting) and volcanism (i.e. dykes and lava flows). Lava flows, together with clastic sedimentation reshape the topography of the rift floor, forming fresh new layers of rock that cover ancient faults. Therefore, the influence of the inherited buried faults on the development of the new faults and the processes of linkage at depth between them remain difficult to investigate. Here we use analogue brittle-ductile modeling with orthogonal extension to elucidate fault growth and reactivation modes, and then compare the results with data from natural rift systems.

In our models, deformation is produced above an elastic band placed between a fixed and a moving wall controlled by a stepper motor. A  layer of viscous material distributes the deformation within the model. On top of the viscous material we use a  layer of sand mixture to simulate the brittle properties of the upper crust. A first phase of extension develops an entire normal fault network, which is then carefully buried under a variable thickness of sand, simulating a cover of sedimentary or volcanic deposits. A second phase of extension allows us to study the mode of reactivation of the inherited faults.The progress of the deformation is tracked using top view images and digital elevation models interpolated from perspective images. At the very end of the model, cross sections cut at regular intervals show the faults at depth by overlaying coloured brittle layers. The high quality of the images allow us to map and analyze the network semi-automatically. We derive displacement/length profiles to characterize the style of fault growth and propagation mode.

Model results show the development of normal faults creating systems of fault-bounded basins, horst-graben structures and conjugated faults. The setup creates a gradient of deformation from the moving wall, where the faults nucleate first near the fixed wall. We thus observe the coexistence of faults of slightly different ages on the same model, as would occur in nature over time. The cross-section shows an upward propagation and the propagation of faults from depth to surface. The preliminary results indicate different styles of reactivation depending on the stage of fault development: reactivation according to a propagating fault mode where faults still have space at tips to develop and a constant-length fault mode where the network is already fully developed. In addition, we find that the surface overlying the inherited structures first bends, then fractures (without observable vertical displacement), and finally develops from the fracture into a proper fault before it finally propagates to connect laterally within the network. This latter growth mode is consistent with the process observed in Iceland by Braham et al. (2021). Understanding the processes of fault network inheritance holds broader applications to many areas where lava or sediments cover faults, layer after layer, such as magma rich rifts like the Eastern Africa Rift or Iceland.

How to cite: Gayrin, P., Maestrelli, D., Corti, G., Brune, S., and Del Ventisette, C.: Reactivation of inherited faults in rift basins: insight from analogue modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6401, https://doi.org/10.5194/egusphere-egu24-6401, 2024.

EGU24-6489 | Orals | TS2.1

Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs 

Laurent Jolivet, Laurent Arbaret, and Romain Augier

Rifting in back-arc basins is characterized by large extension rates, low-angle normal faults and metamorphic core complexes (MCC) displaying partially molten cores and granitic intrusions. The Aegean metamorphic core complexes (MCC) were exhumed underneath crustal-scale detachments accommodating large displacements of the order of 50-100 km and were intruded by Miocene syn-kinematic granites. A common finite geometry and kinematics of all these detachment/pluton systems is recognized with asymmetric intrusive bodies extracted from anatectic lower crust, whose internal structure is controlled by the large-scale dynamics, from the magmatic stage to mylonitization and final exhumation in brittle conditions. Detachments are organized in sets of structures working sequentially evolving from ductile to brittle, the successive branches of the detachment being progressively inactivated by emplacing plutonic batches. The Mykonos-Delos-Rheneia (MDR) MCC shows these interactions between lower crustal migmatites and different syn-kinematic plutons. Our new detailed map of Delos (1/5000) shows geometrical and kinematic relationships between the different magmatic venues during deformation. A strong internal orientation of granites is observed from the magmatic stage until the last ultramylonites below the upper detachments. The deepest magmatic batches are rich in high-grade rocks septae and mafic enclaves, also oriented parallel to regional stretching. Evidence for magma mixing and mingling further indicates interactions with mafic venues at the base of the crust from the mantle. Large high-grade rocks septae are intensely molten and the contact zone between host gneiss and plutons shows intense migmatitization with a foliation parallel to the granite magmatic foliation. Characteristic banded facies marking the contacts between the different intrusions result from high-temperature shearing at the magmatic stage. At all scales foliation and lineation in magmatic rocks and surrounding gneisses are parallel, suggesting a similar weak rheology. Delos shows the roots of these intrusions emplaced as a large-scale sheath-fold whose axis is parallel to the regional stretching direction. The quality of outcrops in Delos, Rheneia and Mykonos, as well as the links between magma emplacement and regional tectonics makes the MDR MCC a natural laboratory for studying the interactions between magmatic intrusions and crustal deformation in tectonically active and hot contexts. In such contexts magmatic and tectonic processes in the lower and middle crusts appear closely interconnected, working at a similar pace and interacting with mantle deformation and melting.

How to cite: Jolivet, L., Arbaret, L., and Augier, R.: Continental back-arc extension, molten lower crust and syn-kinematic granites: insights from Cycladic MCCs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6489, https://doi.org/10.5194/egusphere-egu24-6489, 2024.

EGU24-6912 | ECS | Orals | TS2.1

Upper mantle anisotropy under the strike-slip Dead Sea rift 

Huikai Xu, Youqiang Yu, and Jiaji Xi

Continental rifting is one of the fundamental tectonics of the Earth evolution while our current knowledge on the dynamic mechanism of the strike-slip ones are seriously limited. Here, a systematically shear-wave splitting investigation has been performed in the typical strike-slip Dead Sea rift to illuminate the upper mantle azimuthal anisotropic status across a transform boundary. Totally, 1855 well-defined anisotropic measurements are observed from 102 stations with dominantly N-S fast orientation, which is parallel to the rift strike but deviate from the absolute plate motion direction, mainly result from the plate-driven mantle flow deflected by the thick lithosphere of the eastern Arabian plate. Additionally, the significant fluctuation patterns of splitting times are identified on both the rift-parallel and rift-orthogonal profiles, among which the relatively large splitting times are generally concentrated at the rift zone and attributed to additional coupling lithospheric deformation from the shearing-oriented melt pockets. The consistent rift-parallel fast orientations, combined with the other geoscientific evidences, rule out the role of mantle plume or edge-driven convection in the rift development and further infer the Dead Sea rift to evolve in a passive mode.

How to cite: Xu, H., Yu, Y., and Xi, J.: Upper mantle anisotropy under the strike-slip Dead Sea rift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6912, https://doi.org/10.5194/egusphere-egu24-6912, 2024.

EGU24-7884 | ECS | Posters on site | TS2.1

A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand 

Malte Froemchen, Ken McCaffrey, Tom Phillips, Mark Allen, and Jeroen van Hunen

The evolution of continental rifts is influenced by the pre-rift rheology of the lithosphere and discrete lithospheric structures that segment the rift. The Great South Basin, offshore New Zealand, is a Cretaceous rift system that formed across heterogenous basement terranes which influence the rift architecture. Faults locally rotate or splay and segment along these terrane boundaries. While the impact of terrane boundaries on rift architecture is well understood, the temporal evolution of these rotated faults is poorly constrained. Here we use 3D reflection seismic data to investigate the timing and slip rate evolution of the rotated and segmented faults along two terrane boundaries. Our results show that these have a significant but variable impact on rift evolution and architecture: Faults in the Murihiku terrane show asymmetric throw-length profiles and are rotated along the terrane boundary to the Dun Mountain-Maitai terrane, as they detach into shallow crustal fabrics. Faults in the DMM terrane show less evidence of rotation and more symmetric throw-length profiles but are segmented along the DMM and Caples terrane boundary. The curving faults of the Murihiku terrane likely formed early on but remained as isolated segments only linking up during later stages of rifting when other faults became inactive. These results show the influence of the terrane boundaries was not only active early during initial segmentation but also during the linkage of curved fault segments in the later stages of rifting. These results may help understand the temporal evolution of lithospheric and crustal inheritance on rift evolution in other regions around the world like East Africa or North China.  

How to cite: Froemchen, M., McCaffrey, K., Phillips, T., Allen, M., and van Hunen, J.: A tale of two terrane boundaries – variable impact of terrane boundaries on rift geometry in the Great South Basin, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7884, https://doi.org/10.5194/egusphere-egu24-7884, 2024.

Lithospheric extension leads to rift formation and may continue to the point of breakup, with oceanic ridge initiation and the formation of two conjugate rifted margins. In some settings, extension can cease, and the rift may be abandoned. These so-called failed rifts archive snapshots of early phases of deformation, with geometries that may help better constrain the parameters that can prevent a rift from reaching breakup, such as lithospheric rheology, thermal state, rift opening direction and rate, inheritance.

This contribution summarizes a study of the Norwegian Continental Shelf which includes the North Sea Rift and the Møre and Vøring rifted margins. We proceeded to the interpretation of a new dataset of deep penetrating seismic reflection profiles and worked at the regional scale, deliberately ignoring local particularities, to focus on the large-scale structural picture. The aim is to list architectural similarities and differences between the failed rift and the successful rifted margins.

The mapping shows that the North Sea structural geometries and basement seismic facies are very similar to the observations listed for the adjacent Møre and Vøring rifted margins. Various types of tectonic structures are observed, from thick anastomosing shear zones possibly evolving into core-complex geometries, to composite large-scale detachment faults and standard high-angle normal faults. These are categorized into five classes and interpreted as exemplifying the rift tectonic evolution through distinct generations of deformation structures that can activate, de-activate and re-activate. Based on these observations, rift failure dynamics are discussed, and it is proposed that the North Sea rift abandonment may not be related to pre-rift local conditions but rather to the ability to initiate specific tectonic structures such as distal breakaway complexes.

How to cite: Peron-Pinvidic, G.: Structural observations of the northern North Sea: insights into rift failure dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7915, https://doi.org/10.5194/egusphere-egu24-7915, 2024.

EGU24-8883 | Posters on site | TS2.1

Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe 

David Ulicny, Vladimír Cajz, Karel Mach, Lenka Špičáková, Matěj Machek, Stanislav Čech, Radomír Grygar, Jan Mrlina, and Filip Havlíček

The present-day surface morphology and fabric of the lithosphere of west-central Europe in the foreland of the Alpine orogen have been significantly affected by formation of a system of rifts and associated volcanic domains during the Oligocene and Neogene, known as the European Cenozoic Rift System (ECRIS). In order to better understand the geodynamic causes of formation of ECRIS and its volcanism, it is important to improve the knowledge of chronology of tectonic events in the entire ECRIS, and to test the validity of existing palaeostress interpretations. The Oligo-Miocene Eger Rift, so far the least-studied part of ECRIS, has the potential to bring new clues to some persisting controversies.

The axis of the Eger Rift roughly follows the trend of a major Variscan lithosphere-scale boundary, the Teplá-Barrandian/ Saxothuringian suture (TSS) formed during the collisional phases about 380-320 Ma. Following the Variscan collision, the lithosphere of the Bohemian Massif was affected by formation of a Late Paleozoic extensional basin system which in the western part of the Bohemian Massif largely follows the NE strike of the TSS. Another major structure in the basement underlying the Eger Rift is the WNW-striking Elbe Zone, with main periods of activity during the Paleozoic and Mesozoic through early Cenozoic.

We present a synthesis of presently available structural and stratigraphic data and a resulting first-order interpretation of tectonic evolution of central and eastern Eger Rift. The main data sources were borehole, outcrop, seismic reflection data, targeted field mapping, digital elevation models, and gravity data from both public and industry sources. Several stratigraphic levels (within the Neogene, Cretaceous, and top of Late Palaeozoic) were used as structural datums.

Analysis of fault populations in central and eastern Eger Rift shows that overall, the Late Paleozoic fracturation of the upper crust of the Bohemian Massif was key for localization of the main fault systems of the Eger Rift. This includes dextral shearing within the Elbe Zone that affected the basement structural grain responsible for segmentation of the Eger Rift during the Cenozoic. Changes between oblique and orthogonal extension modes are interpreted from the geometries and temporal relationships of key structures - both in time, likely due to a changing regional paleostress field, and in space, due to different orientations of basement structures between the rift segments.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Ulicny, D., Cajz, V., Mach, K., Špičáková, L., Machek, M., Čech, S., Grygar, R., Mrlina, J., and Havlíček, F.: Structural inheritance and the evolution of an incipient rift: interaction between the Eger Graben and the Elbe Zone, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8883, https://doi.org/10.5194/egusphere-egu24-8883, 2024.

Ocean closure and collisional orogeny frequently enrich the lithospheric mantle in incompatible chemical elements. The most intensive enrichment usually occurs during the subduction of continent-derived sediments and continental crust. Radioactive isotopes of uranium and thorium are part of the HFSE (high-field-strength elements) group of incompatible elements and, therefore, can be also characterized by increased concentration within the post-orogenic lithospheric mantle in comparison to the common lithospheric mantle. The anomalously high content of uranium and thorium within the post-orogenic mantle lithosphere is reflected by the composition of potassic and ultrapotassic magmas, which are sometimes extremely enriched in these radioactive elements. This enrichment is well documented by numerous studies and, therefore, cannot be ignored during the numerical modelling of rifting processes.

According to pure conductive thermal modelling, the anomalously increased content of radioactive elements within the post-orogenic lithospheric mantle causes a time-dependent rise in temperature, providing favourable conditions for intracontinental rifting more than 20-100 million years after the closure of the ocean. A time gap between the orogeny and highly increased temperature within the lithosphere is controlled by two major factors: (1) the amount of thorium and uranium and (2) the size of the anomalous lithospheric mantle. According to numerical thermo-mechanic modelling, the post-orogenic increase in temperature not only weakens the lithosphere but also causes thermal expansion of the lithosphere which can be sufficient to initiate the first stage of intracontinental rifting without involving regional extensional forces.

Therefore, we propose a new concept of intracontinental rift initiation as a result of time-dependent temperature increase and thermal expansion of the post-orogenic mantle lithosphere due to the decay of radioactive elements. The described rather simple mechanism of rift formation provides a significant advance in our understanding of both local rift processes and global tectonic cycles on our planet.

How to cite: Maystrenko, Y. and Slagstad, T.: Post-orogenic radiogenic initiation of intracontinental rifting within the lithospheric mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9325, https://doi.org/10.5194/egusphere-egu24-9325, 2024.

EGU24-9513 | Posters on site | TS2.1

Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia 

Michal Rajchl, Karel Mach, Filip Havlíček, David Uličný, and Matěj Machek

The present-day geological and morphological expression of the Cenozoic Eger Rift in central Europe is dominated by the faulted edge of the Krušné Hory (Erzgebirge) Mts., a plateau uplifted to c. 1 km above sea level following the mid-Miocene, resulting in partial deformation and erosion of parts of the Eger Rift sedimentary and volcanic infill. The main phase of the uplift is considered to have occurred in Plio-Quaternary times, but details of this process and its relation to the Eger Rift itself remain unclear.

The Oligo – Miocene Most Basin is the most extensive sedimentary basin preserved within the Eger Rift. The basin, bounded at the NW by the Krušné Hory uplift, is characterized by an economically important coal seam, up to 35 m thick. Previous research has shown that during the formation of the basinwide swamps in early Miocene the basin was hydrologically open, with at least one but probably more outlets draining its area toward the North and Northwest, across today’s Krušné Hory (Erzgebirge) Fault Zone (KHFZ). During the earliest Miocene times, most of the region of today’s Krušné Hory / Erzgebirge uplifted block was thus a generally low-relief area. Paleogeographic changes in the Most Basin suggest an increasing activity of its marginal faults, some of which were predecessors of the present-day KHFZ, still during the early to mid-Miocene. For understanding the formation of this major fault zone it is important to answer the question of the timing, magnitude and character of initial relief growth along the nw. edge of the Eger Rift.

The stratigraphic and structural record exposed recently at the KHFZ provides evidence of a small-scale relay ramp that formed between two overlapping normal faults of E-W general strike and breached later by a normal fault of NE strike. Debris-flows conglomerates were found interbedded with carbonaceous mudstones and lignite layers belonging to the early Miocene main coal seam, in the close vicinity of the lower bounding fault containing boulders from a tectonic breccia of the fault damage zone. This fact indicates the existence of a prominent fault scarp developed along the fault plane of the above fault and considered the source of coarse-grained clastics during the initial, coal-bearing, phase of the basin formation. The subsequent acceleration of the Most Basin subsidence that resulted in basin-wide expansion of the swamp environment, can be explained by linkage of the border faults accompanied by breaching and drowning of some relay ramps.

The studied sedimentary record provides evidence of faulted relief with an elevation of tens of metres that contributed to the supply of clastic material to the incipient rift during early Miocene time. The subsequent breakage and drowning of the relay ramp provide evidence for syn-sedimentary activity some of NE-SW segments of the KHFZ previously thought to be a manifestation of later, post-rift deformation.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S. We acknowledge support by the Severní energetická, a.s., and Ing. Petr Šulcek in conducting research in the Důl ČSA Mine.

How to cite: Rajchl, M., Mach, K., Havlíček, F., Uličný, D., and Machek, M.: Early relief growth at the edge of an incipient rift – the Eger Graben, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9513, https://doi.org/10.5194/egusphere-egu24-9513, 2024.

EGU24-9770 | Posters on site | TS2.1

Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe 

Filip Havlíček, David Uličný, Ondřej Krýza, Matěj Machek, Michael Warsitzka, and Prokop Závada

Continental lithosphere undergoing the process of rifting has typically previously experienced a complex deformation history resulting in a highly heterogeneous mechanical structure. This structural inheritance can affect the developing continental rift across all scales, from rift localization and segmentation to individual fault geometries. Assessing the impact of such inherited structures on extensional basin geometries can be difficult, especially in the case of fossil rifts where uncertainties may arise about the orientation of regional stresses during extension. One such example is the Eger Rift which developed during the Oligocene to early Miocene as the easternmost branch of the European Cenozoic Rift System (ECRIS). Earlier interpretation proposed a two-phase extensional history for the rift.

We use a series of crustal-scale, brittle-viscous analogue models, based on the geometry of the central and eastern parts of the Eger Rift, to explore the development of a segmented rift in a multiphase setting with evolving extension direction. Our model crust rests on a basal velocity discontinuity (VD), a discrete boundary of a mobile base plate simulating a reactivated basement weakness localizing our model rift. The geometry of this weakness is a simplified representation of the geometry of older, mainly Upper Paleozoic basins, which are hypothesized to have greatly influenced the localization and geometry of principal fault systems and rift segments that they define. The VD thus consists of 3 segments oriented at various angles with respect to extension direction. The Model surface is imaged by stereoscopic cameras and analyzed by Particle Image Velocimetry (PIV) techniques to track surface deformation and topography evolution during the run.

Our results confirm that in a setting with an abrupt change in extension direction, the first extensional phase plays a key role in defining the final observed fault pattern with new second-phase faults generally being few in number and of limited length. This effect is enhanced above a segmented VD. If a larger portion of the VD is optimally oriented with respect to the first-phase extension, the final fault pattern is dominated by first-phase structures with the growth of second-phase faults being nearly inhibited. In a contrasting scenario, where most of the VD is initially oblique to extension direction, second-phase faults are more abundant, leading to a bimodal final fault pattern. By comparing our results with newly mapped fault populations in the Eger Rift we conclude that the proposed two-phase history for the rift is plausible with a major role of the initial phase of approximately N-S extension.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Havlíček, F., Uličný, D., Krýza, O., Machek, M., Warsitzka, M., and Závada, P.: Modelling the effects of changing extension directions in a segmented rift: application to the Eger Rift, Central Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9770, https://doi.org/10.5194/egusphere-egu24-9770, 2024.

EGU24-9947 | ECS | Orals | TS2.1

New results on the crustal configuration of the Newfoundland margin: Implications for rifting 

Laura Gómez de la Peña, César R. Ranero, Manel Prada, Donna Shillington, and Valentí Sallarès

Driven by discovery of contrasting structures of Continent to Ocean Transition (COT) discovered at rifted continental margins during the 90’s, several high-quality seismic datasets were acquired in these margins during the early 2000 to unravel the structure of unexplored regions. Despite the fact that some of these datasets are basically comparable to modern data in quality, the processing, imaging and modelling methodologies at the time of acquisition can be now refined and improved. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with enhanced resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve. 

We focused on the Newfoundland margin and applied up-to-date methodologies to the high-quality SCREECH dataset (2000). These data include three primary transects with coincident multichannel seismic (MCS) reflection data acquired with a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~15 km. We reprocessed the streamer data and also performed the join inversion of streamer and wide-angle OBS/OBH seismic data, using reflections and refraction arrivals, which significantly improved the resolution of the velocity model. We performed a statistical uncertainty analysis of the resulting model, supporting the reliability of the observed features. In particular the new velocity model provides a detailed definition of the top of the basement where the largest abrupt velocity change occurs. The comparatively high-resolution velocity model obtained from the joint tomography allowed to properly perform a Pre-Stack Depth Migration of the MCS. The improved velocity model and seismic images permit to characterize the different crustal domains of the margin with less uncertainty that previous attempts, and relate them to the tectonic structure.

The different domains reveal previously undetected crustal characteristics that change over short distances. The reprocessing of the MCS data allowed to a better understanding of the crustal structure, as the Moho is imaged for the first time under the slope domain.

Comparison of these new results on the Newfoundland margin with the most modern data on the West Iberian margin, acquired during FRAME (2018) and ATLANTIS (2022) cruises provides a new view of the evolution of the North Atlantic opening.

How to cite: Gómez de la Peña, L., R. Ranero, C., Prada, M., Shillington, D., and Sallarès, V.: New results on the crustal configuration of the Newfoundland margin: Implications for rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9947, https://doi.org/10.5194/egusphere-egu24-9947, 2024.

EGU24-11403 | Posters on site | TS2.1

The story of double spreading centers formed during continental rifting in 2D 

Laetitia Le Pourhiet and Fan Zhou

It is common wisdom, based on many years of published simulations of continental rifting followed by spreading that in 2D when a mid-oceanic ridge form in a numerical simulation of continental rifting, extension stops and spreading take over the extension. This is generally due to the complete loss of strength of the mantle lithosphere that cannot transmit forces horizontally across the spreading zone anymore. Actually, in general even the onset of mantle lithosphere necking in a simulation can cause the end of the extension and for many years, I actually claimed very load in the past that two active necking system must be the signature of some obliquity causing 3D extensional conditions. However, recently, a whole series of 2D simulations produced systematically two spreading centers active at the same time. These results surprised me a lot. These simulations were very complex, including a lot of inheritance, the first easy conclusion could have been to say that inheritance causes multiple spreading… But we spent some time and effort to understand if this behavior was due to inheritance or something else. Simplifying our model set-up to the strict minimum, we found it was not inheritance, but a quite cold mantle temperature which permitted a larger shear coupling between the upper mantle dynamics and the mantle lithosphere.  A 50°C difference in mantle temperature radically change the results of the simulation and thanks to our failure, we have found the embryo of an alternative explanation to 3D interactions for the occurrence multiple active necking zones.

How to cite: Le Pourhiet, L. and Zhou, F.: The story of double spreading centers formed during continental rifting in 2D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11403, https://doi.org/10.5194/egusphere-egu24-11403, 2024.

EGU24-11494 | ECS | Posters on site | TS2.1

The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data 

Silvia Foiada, Marta Neres, Pedro Brito, Laura Gomez de la Peña, Irene Merino, and César Ranero

The FRAME geophysical cruise, conducted in 2018 onboard the Spanish R/V Sarmiento de Gamboa, acquired new multichannel seismic reflection (MCS) data on the SW Iberia and NW Moroccan margins. MCS data were acquired with a 6 km long solid-state digital streamer Sercel SENTINEL towed at 19 m water depth, and a 3920 c.i. source with two sub-arrays with 20 guns towed at 10 m depth. The system was designed to provide high penetration and map the entire crust and the upper mantle structure and retain enough resolution to image well the stratigraphy.

In this work we present a 220 km long seismic line acquired on the NW Moroccan margin, from the shallow continental shelf across the continental slope and extending across the deep abyssal plain of the Gulf of Cadiz. The NW Africa margin was selected because the region was the focus of several geophysical campaigns, and several DSDP drill sites that drilled into the synrift strata.  However, limited modern data has imaged the crustal-scale tectonic structure to unravel the late Triassic - early Jurassic rift history of the region.

We applied a seismic processing flow tailored to the attenuation of the multiple energy, signal designature and for the creation of a detailed macro-velocity model to image the lateral changes of the synrift tectonic structure and stratigraphy. The high-quality image of the structure of this rifted margin reveals a complex tectonic structure from the shelf to the deep-water basin where a deep basement containing salt bodies across the entire profile extension. These new results are of high importance for the understanding of the rifting and continent-ocean transition (COT) processes on the northern Central Atlantic and Neothetys domains, as well as for the subsequent compressive deformation processes in the Gulf of Cadiz related to the Africa-Eurasia plate collision.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds through the project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020).

How to cite: Foiada, S., Neres, M., Brito, P., Gomez de la Peña, L., Merino, I., and Ranero, C.: The seismic structure of the NW Moroccan margin, Gulf of Cadiz, from new high-quality multichannel seismic reflection data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11494, https://doi.org/10.5194/egusphere-egu24-11494, 2024.

EGU24-11825 | ECS | Posters on site | TS2.1

Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin 

Mateus Rodrigues de Vargas, Geoffroy Mohn, Julie Tugend, Nick Kusznir, and Andrew Lin

The wide rifting mode that preceded the opening of the South China Sea (SCS) in the Cenozoic generated a set of Paleogene rift basins presently buried under thick post-rift sedimentary infill. Much of the tectonostratigraphic evolution of the South China Sea is now relatively well-constrained (e.g., Pearl River Mouth Basin). However, the SCS's northeasternmost part (i.e., the Tainan margin sensu lato), which might represent the oldest passive margin segment, remains to be integrated into the framework of the rifting and opening of the SCS.

This work aims to review and revisit the tectonostratigraphic evolution of the Tainan margin. To do so, an integrative approach has been used combining the analysis of seismic reflection and gravity data. We use 3D gravity inversion to determine the distribution of Moho depth and crustal thickness within this margin segment. The gravity inversion scheme incorporates a lithosphere thermal gravity anomaly correction, which is critically important because of the elevated geothermal gradient within the young oceanic lithosphere of the South China Sea and its continental margins. In the Tainan margin, results show contrasted crustal domains from the continental shelf, to the distal margin and oceanic domain.

Only limited crustal thinning is observed over the continental shelf where a succession of rift basins is documented (i.e., Taihsi, Nanjihtao, and Penghu basins) that are part of the Northern Rift System. In contrast, the distal Tainan margin shows greater crustal thinning to less than 10 km thick under an aborted breakup basin, thereby forming the Southern Rift System. To the south, this basin is separated from the unambiguous oceanic domain (6 to 8 km thick) by a comparatively thicker crustal block (~ 10 to 15 km thick). This crustal block forms the Southern High where numerous volcanic edifices and magmatic intrusions are observed or inferred.

Half-grabens of the Northern Rift System are controlled by counter-regional faults and filled by Paleocene to Eocene syn-rift sediments. For the distal domain, no well calibration is available. There, we identified several seismic units bounded by regional unconformities. Our results show relatively thin syn-rift sediments locally controlled by a low-angle normal fault system in the Southern Rift System. In contrast, thick post-rift sequences are observed except over the Southern High.

Based on our results, we propose a review of structural style and age correlations from the continental shelf to the distal domains of the Tainan margin. To illustrate along-strike variations of the crustal structure and stratigraphic style, we build an array of regional geological cross-sections that are further compared with existing observations in the adjacent Pearl River Mouth Basin.

How to cite: Rodrigues de Vargas, M., Mohn, G., Tugend, J., Kusznir, N., and Lin, A.: Tectonostratigraphic evolution of the Tainan Margin (NE South China Sea): comparison with the Pearl River Mouth Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11825, https://doi.org/10.5194/egusphere-egu24-11825, 2024.

EGU24-11854 | Posters on site | TS2.1

Rifting style and continental breakup of Marginal Seas 

Geoffroy Mohn, Jean-Claude Ringenbach, Etienne Legeay, Julie Tugend, William Vetel, and François Sapin

Marginal Seas are extensional basins formed in a convergent setting near active subduction zones. They are characterized by a short life (<25 Ma), as well as unstable and changing directions of seafloor spreading. However, the processes related to their formation from rifting to seafloor spreading initiation remain debated (supra-subduction convection/extension, slab-pull). This problem is further compounded by the fact that our understanding of continental breakup used to be derived from the evolution of magma-poor and magma-rich Continent-Ocean Transitions (COT) of Atlantic margins.

Here, we describe and discuss the rifting style and the mode of continental breakup of three main Marginal Seas located in the Western Pacific, namely the South China Sea, the Coral Sea and the Woodlark Basin. All three examples formed under rapid extension rates and propagation of seafloor spreading.

In these three examples, continental extension is accommodated by a succession of hyper-extended basins controlled by low-angle normal faults that may form and be active at 30° (or less). These hyper-extended basins are filled by polyphase syn-rift sequences showing atypical geometries. These complex stratigraphic architectures result from the development of the low-angle normal faults interacting with antithetic faults, controlling the formation of extensional fishtails for example. The formation of such low-angle normal fault systems is enhanced by basement inheritance of the previous orogenic system.

Continental breakup and final extension are contemporaneous with an important magmatic activity emplaced in the distalmost part of these margins including volcanoes, dykes and sills. Continent-Ocean transitions (COTs) are characterized by a sharp juxtaposition of the continental crust against igneous oceanic crust suggesting that a rapid shift from rifting to spreading occurred. High extension rate prevents conductive cooling allowing the focusing of volcanic activity in sharp COTs, quickly evolving to magmatic accretion.

In conclusion, the rifting style and mode continental breakup are most likely associated with initial rheological conditions with hot geotherm combined with fast extensions rates likely directed by kinematic boundary conditions directly or indirectly controlled by nearby subduction zones.

How to cite: Mohn, G., Ringenbach, J.-C., Legeay, E., Tugend, J., Vetel, W., and Sapin, F.: Rifting style and continental breakup of Marginal Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11854, https://doi.org/10.5194/egusphere-egu24-11854, 2024.

EGU24-11873 | Posters on site | TS2.1

Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications 

Julie Tugend, Geoffroy Mohn, Nick Kusznir, Sverre Planke, Christian Berndt, Ben Manton, Dmitrii Zastrozhnov, and John, M. Millet

The Mid-Norwegian volcanic rifted margin and its NE-Greenland conjugate formed in relation to continental breakup in the latest Palaeocene to earliest Eocene during the emplacement of the North Atlantic Igneous Province (NAIP). The development of the NAIP and opening of the North Atlantic occurred contemporaneous to the Paleocene Eocene Thermal Maximum (PETM) which corresponded to a rapid 5-6 °C global warming episode.

The cause of this rapid global warming, explored as part of IODP Expedition 396, is thought to relate to the thermogenic gases released to the atmosphere via thousands of hydrothermal vents. The thermogenic gases were produced by contact metamorphism of carbon-rich sediments during widespread sill emplacement from the NAIP. The potential of hydrothermally-released greenhouse gases to influence climate depends strongly on the water depth at which they get released. Unless it is released in a shallow marine environment most methane will be oxidized before it reaches the atmosphere.

Early results from IODP Expedition 396 have documented that at least one of the Mid-Norwegian hydrothermal vents was emplaced in shallow marine to potentially sub-aerial conditions. The aim of this contribution is to constrain further the paleo-water depth at which hydrothermal vents formed along the other parts of the mid-Norwegian volcanic rifted margin. This study focuses on an integrated workflow of quantitative geophysical and geodynamic analyses calibrated by new IODP drilling results and structural and stratigraphic observations. We use a 3D flexural-backstripping, decompaction and reverse thermal subsidence modelling to predict the palaeobathymetry and palaeostructure at keys stages of the syn- to post-breakup evolution that can be compared with palaeo-water depths estimated from biostratigraphic data.

Results provide new constraints on the paleobathymetry of hydrothermal vent complexes required to confirm whether the global warming recorded by the PETM was triggered by the magma-rich continental breakup leading to the opening of the northeast Atlantic Ocean. 

How to cite: Tugend, J., Mohn, G., Kusznir, N., Planke, S., Berndt, C., Manton, B., Zastrozhnov, D., and Millet, J. M.: Palaeobathymetry of the Mid-Norwegian volcanic margin during continental breakup and paleoclimate implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11873, https://doi.org/10.5194/egusphere-egu24-11873, 2024.

EGU24-11877 | Orals | TS2.1

Along-strike magma-poor/magma-rich spreading transitions 

Michal Nemcok and Brian Frost

1D/2D data-based studies of active spreading centres brought the knowledge of extension ratedependent stretching-dominated v. buoyancy-dominated spreading. 3D reflection seismic data from the extinct centre of an initial oceanic corridor in the Caribbean allow us to see an along-strike transition between stretching- and buoyancy-dominated spreading where the spreading through detachment faulting is a precursor to the magma-assisted spreading. Studying progressively more evolved portions of the spreading centre, going from its end towards its centre, we see a progressively higher ascent of the asthenosphere, which heats the developing

core complex in the exhuming footwall of the initial stretching-dominated system. The asthenospheric ascent is associated with thermal weakening of the core complex, which eventually results in ductile deformation reaching the upper portion of the complex. Subsequently, the core complex is penetrated by the dyke located at the top of the asthenospheric body. The dyke, which subsequently evolves to a diapir-shaped body, reaches the sea floor

and establishes a magma-assisted steady-state seafloor spreading. These observations lead to a model explaining the initiation of the magma-assisted spreading in the initial oceanic corridor. Furthermore, they also improve our knowledge of multiple interacting mechanisms involved in the breakup of the last continental lithospheric layer, subsequent disorganized spreading and younger organized spreading.

How to cite: Nemcok, M. and Frost, B.: Along-strike magma-poor/magma-rich spreading transitions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11877, https://doi.org/10.5194/egusphere-egu24-11877, 2024.

EGU24-12130 | ECS | Posters on site | TS2.1

Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data 

Ibrahim Yusuf, Stephen M Jones, Tim Reston, Thomas Funck, Brian M O'Reilly, and John R Hopper

The Porcupine Basin, situated in the North Atlantic, serves as a unique natural laboratory for investigating the temporal evolution of magma-poor rifts. Notably, the basin exhibits a progressive increase in the total degree of stretching from north to south, offering a valuable opportunity to interpret its structure in terms of the temporal evolution of magma-poor rifted margins. This study, as part of the broader PORO-CLIM project, focuses on Profile 2 to construct a whole-crustal seismic velocity model and integrate it with existing data to unravel the complete rifting history of the Porcupine Basin.

In the northern region, Reston et al. (2004) identified a detachment fault, the P-reflector, indicating substantial rifting  [1]. Recent analyses by Prada et al. (2017) extended this understanding to the central basin, revealing progressive crustal thinning and mantle serpentinization [2]. However, the southern sector remains largely unexplored. This project aims to capitalise on newly acquired Ocean Bottom Seismometer (OBS) data from PORO-CLIM Profile 2 to image the deep crustal structure and complement this with basement mapping of the southern Porcupine Basin using industry 2D seismic data.

Seismic refraction data from 20 OBS along a 226 km transect form the basis for constructing a comprehensive crustal velocity model. Utilising the RAYINV modelling package, a layer-by-layer forward modelling approach is employed to correlate calculated and observed travel times. Concurrently, structural mapping using long-offset 2D seismic reflection data assists in delineating major faults and regions of mantle unroofing, contributing to the understanding of the Porcupine Basin's subsurface. Preliminary findings reveal extreme crustal thinning and asymmetry, highlighting north-to-south crustal thinning and the emergence of the P-reflector in the southern region of the Porcupine Basin.

[1] Reston, T.J., Gaw, V., Pennell, J., Klaeschen, D., Stubenrauch, A. and Walker, I. (2004). Extreme crustal thinning in the south Porcupine Basin and the nature of the Porcupine Median High: implications for the formation of non-volcanic rifted margins. Journal of the Geological Society, [online] 161, pp.783–798.

[2] Prada, M., Watremez, L., Chen, C., O’Reilly, B.M., Minshull, T.A., Reston, T.J., Shannon, P.M., Klaeschen, D., Wagner, G. and Gaw, V. (2017). Crustal strain dependent serpentinisation in the Porcupine Basin, offshore Ireland. Earth and Planetary Science Letters, [online] 474, pp.148–159.

How to cite: Yusuf, I., M Jones, S., Reston, T., Funck, T., M O'Reilly, B., and R Hopper, J.: Structure and Dynamics of the Porcupine Magma-Poor Continental Margin from new Ocean Bottom Seismometer Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12130, https://doi.org/10.5194/egusphere-egu24-12130, 2024.

EGU24-12991 | ECS | Orals | TS2.1

Tectonic structure and evolution of Brazilian Equatorial Margin  

Julia Fonseca, César Ranero, Paola Vannucchi, David Iacopini, and Helenice Vital

The Brazilian Equatorial Margin (BEM) is classically interpreted as a transform margin formed during the last phases of the Atlantic rifting of Gondwana. However, rift kinematics and subsequent continental break up has not been constrained.

We present a new model based on the interpretation of a 2D seismic grid acquired along the BEM. The datasets, provided by the Brazilian National Agency for Petroleum (ANP), expand for ~600 km of the margin and consist of approximately 10.000 km of crustal scale 2D seismic reflection profiles which have been calibrated with industry drillholes. The integration of crustal-scale tectonic structures and age and distribution of synrift sediment deposits allowed to determine the style and the timing of the different tectonic phases and to define the crustal thinning evolution of the entire rift system along the Potiguar and East Ceará Basins (NE Brazil).

Our findings indicate that: 1. rifting started ~140-136 My, 2. extension stopped earlier (late Aptian) in the shallow sector of the basin than in the deep-water (early Albian) domains. The shallow basin domains presents minor crustal thinning (~35 thick crust over ~100 km wide), whereas in the deep-water domains, about ~60 km wide, the crust is 4-8 km thick and it extended into the early Albian (116-110 My).

The distribution of deformation structures supports a model of rift evolution where: deformation is initially distributed while forming a shallow basin; it evolves by focusing the extension; finally, extension migrates toward the basin centre to form the deep-water domain. Constraints from seismic reflection data and drillholes help define an abrupt continent to ocean transition (COT), and breakup occurred during the early Albian. Basin sedimentation from its onset to the late Aptian is terrigenous, indicating an isolated environment disconnected from the Northern and Southern Atlantic oceans. Sedimentation changed during the late-most Aptian to the early Albian when marine facies deposited during a rapid ocean water infill of a previously endorheic basin.

The seismic images document that rifting across the margin is not dominated by transcurrent deformation, with strike-slip faulting limited to a relatively small sector, whereas most of the margin extended through normal faulting deformation during opening.

From the interpretation of the 2D seismic reflection grid it was possible to distinguish abrupt lateral changes in the architecture of the basement. These changes defined three distinct, first order segments along the margin named Southern, Central, and Northern segments. The different evolution of the three segments throughout the rifting process is defined by thickness map of the basement. The Northern segment is the only region that shows evidence of potential late synrift magmatism, likely formed during the COT emplacement, which defines second order segmentation. Our interpretation suggests a spatial correlation between first-order tectonic segmentation and second-order magmatic segmentation during the embryonic formation of the spreading center with the definition of fracture zone/transform faults. These findings suggest that most transform faults formed on the spreading centers may have originated from the pattern of continental segmentation during rifting.

How to cite: Fonseca, J., Ranero, C., Vannucchi, P., Iacopini, D., and Vital, H.: Tectonic structure and evolution of Brazilian Equatorial Margin , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12991, https://doi.org/10.5194/egusphere-egu24-12991, 2024.

EGU24-13269 | ECS | Posters on site | TS2.1

Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin 

Wei Wang, Satish Singh, Zhikai Wang, Aiguo Ruan, Yong Tang, Jérôme Dyment, Sylvie Leroy, Louise Watremez, Zhaocai Wu, He Li, and Chongzhi Dong

During the Jurassic period, the Gondwana Continent progressively rifted from north to south along three huge transform faults (Davie Fracture Zone (DFZ), Mozambique Fracture Zone (MFZ) and Agulhas-Falkland Fracture Zone (AFFZ)), forming the northern, central and southern continental margins along Mozambique, producing a series of divergent and strike-slip margins. These margins are crucial areas for understanding the evolution of Gondwana as their crustal nature and geometry have strongly impacted the kinematic reconstruction of Gondwana. Especially, the debate about continental or oceanic crust for the Mozambique Coastal Plain (MCP) and North Natal Valley (NNV) at the southern Mozambique margin led to tens of kinematic reconstruction models of Gondwana. Based on the OBS and MCS data results of PAMELA MOZ3/5 Cruises, MCP and NNV were identified as continental crust. This has led the scientific community to reconsider the issue, for example, the opening time of the oceanic basin, the movement direction of rifting, and the intense magmatism during the rifting and break-up of Gondwana.

In June 2021, the Second China-Mozambique Joint Cruise was conducted onboard the R/V “Dayang hao”. Three wide-angle seismic OBS profiles were acquired where 70 four-component OBSs were deployed along profiles DZ02 and DZ04 oriented nearly W-E and DZ01 oriented nearly N-S. Four Bolt air guns with a total volume of 8000 in3 in total were towed at ~100 m behind the R/V “Dayang hao” at ~10 m below the sea surface. The shot interval was 200 m.

Here, we present the tomographic results of P-wave velocity along 442 km long profile DZ02, where 21 OBSs were deployed. It traverses through the Continent Ocean Transition (COT) and extends into the Mozambique ocean basin. Approximately 19,000 P-wave arrivals were manually picked, using the travel-time tomography inversion to get the velocity model. The tomographic result shows an apparent decrease in crust thickness from COT to the ocean basin, and the thickness of the oceanic crust is about 8 km. We also observe high-velocity anomalies up to 7.4 km/s in the lower crust above Moho, suggestive of more primitive melt. We will also present the S-wave velocity model for DZ02.  

How to cite: Wang, W., Singh, S., Wang, Z., Ruan, A., Tang, Y., Dyment, J., Leroy, S., Watremez, L., Wu, Z., Li, H., and Dong, C.: Crustal Structure of Continental Margin and Oceanic Basin at the Southern Mozambique Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13269, https://doi.org/10.5194/egusphere-egu24-13269, 2024.

EGU24-13432 | Orals | TS2.1

Structural Evolution of the Black Sea Basin Using Sectioned Computational Models 

Armagan Kaykun and Russell Pysklywec

The tectonic formation of the Black Sea Basin (BSB) has been an ongoing debate: primarily, there is still not a consensus on whether the basin was rifted as one east-west oriented basin, or as two separate basins named Eastern and Western Black Sea Basins. These interpretations are based largely on deep-sea drilling projects and a growing dataset of seismic information (of variable access for academic use). Supporting the two-basin idea is the semi-parallel ridge and depression geometry of the BSB with NW-SE orientation in the Eastern portion of the Black Sea Basin; and W-E orientation in the Western portion of the Black Sea Basin. On the other hand, interpretations for a single basin are supported by the regional structure of the BSB being aligned with the geodynamic models of the basins rifted as a result of slab roll-back. Complicating the understanding of the basin extension and development is the inferred tectonic inversion to shortening in the region starting in the Late Eocene.

To propose a model to answer ongoing debates, we interpreted 24 long-offset 2D seismic lines acquired by GWL in 2011 in a structural geology context. We focused on the structural elements such as big scale normal faults, reverse faults, and tectonic inversion features to create a basis for our 2D computational models for both east and west portions of the BSB. One important finding was to determine the null points on basin bounding faults where the extensional tectonic movements stopped, and the compressional tectonic movements started. Utilizing the ASPECT geodynamic code, we built 2D computational models parallel to the selected two 2D seismic profiles. We compared our findings in our seismic interpretations with the results to understand the timing and basin-wide distribution of structural highs and the compressional tectonic features that shaped the BSB.

How to cite: Kaykun, A. and Pysklywec, R.: Structural Evolution of the Black Sea Basin Using Sectioned Computational Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13432, https://doi.org/10.5194/egusphere-egu24-13432, 2024.

Many orogenic belts today preserve evidence of past crustal rifting. During the syn-rifting, the crust undergoes thinning, forming rift basins with thick sedimentary deposits. The upwelling of the mantle during this extensional phase increases the geothermal gradient within the basin, affecting the crust and sedimentary rocks.

In this study, we used numerical models to simulate the temperature changes in sedimentary rocks within rift basins during both the active rifting phase and the passive continental margin phase after rifting cessation. We found that under a stretching rate of 0.7 cm per year, after 20 million years of continuous stretching, the geothermal gradient within the basin can reach 50-60°C per kilometer, with sedimentary rocks reaching temperatures as high as 450-500°C. After 20 million years of cooling following the end of stretching, the temperatures of the sedimentary rocks decrease by nearly 100°C, and the geothermal gradient reduces to approximately 30°C per kilometer.

We believe that these phenomena can be correlated with the evolution of the Hsuehshan Range in Taiwan, which experienced a transition from rifting to a passive continental margin. During the rifting phase, the temperatures of the sedimentary rocks within the basin reached high metamorphic temperatures of 450-500°C, as indicated by carbonaceous material Raman spectroscopy (RSCM). As the region entered the passive continental margin phase, the rocks gradually cooled, with a temperature decrease of nearly 100°C prior to the onset of mountain building in Taiwan. Similar high-temperature metamorphic temperatures were obtained through RSCM analysis along the Central Cross-Island Highway and Northern Cross-Island Highway, exceeding the closure temperatures of zircon core tracks. However, some zircon core tracks in certain areas did not yield closure ages, suggesting that the high metamorphic temperatures obtained from RSCM analysis were inherited from previous stretching events rather than occurring during the Penglai orogeny.

How to cite: zheng, M., Lee, Y.-H., and Tan, E.: Numerical modelling of continental margin of the Eurasian Plate Rifting and Tectonic evolution.Causes of the highest metamorphic temperature in the Hsuehshan Range and Backbone Range , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14297, https://doi.org/10.5194/egusphere-egu24-14297, 2024.

EGU24-14808 | Orals | TS2.1

Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup 

Egidio Armadillo, Daniele Rizzello, Pietro Balbi, Alessandro Ghirotto, Davide Scafidi, Guy Paxman, Andrea Zunino, Fausto Ferraccioli, Laura Crispini, Andreas Läufer, Frank Lisker, Antonia Ruppel, Danilo Morelli, and Martin Siegert

Recent sub-ice topography compilations of East Antarctica have imaged a wide sector, spanning from 100° E to 160° E in longitude and from the Oates, George V and Adelie coastlines to 85° S in latitude, which contains numerous low-lying basins of variable size and uncertain origin. The sector shows a Basin and Range style tectonics comprising two major basins of continental proportions, the Wilkes Basin and the Aurora Basin complex, and many smaller basins such as the Adventure, Concordia, Aurora and Vostok trenches. The main longitudinal axes of the basins consistently point towards the South Pole and many exhibit intriguing distinct triangular shapes, sitting within an approximately 2000 x 2000 km fan-shaped physiographic region limited by a semi-circular coast line. We name this region as the East Antarctic Fan shaped Basin Province (EAFBP). To the West, this sector is limited by the intraplate Gamburtsev Mountains (GM) and to the East by the Transantarctic Mountains (TAM) constituting the uplifted shoulder of the Cenozoic West Antarctic Rift System (WARS).

Origins and inter-relationships between these four fundamental Antarctic tectonic units (WARS, TAM, EAFBP, GM) are still poorly understood and strongly debated. Very little is known about the mechanism generating the basins in the EAFBP, their formation time, whether they are all coeval and if and how they relate to Australia basins before Antarctica-Australia rifting. Present genetic hypotheses for some of the basins span from continental rifting to a purely flexural origin or a combination of the two. Also, post-tectonic erosional and depositional processes may have had a significant impact on the present-day topographic configuration.

Here we interpret the EAFBP as the result of a single genetic mechanism: a wide fan-shaped intra-continental extension around a near pivot point at about 135° E, 85° S that likely occurred at the Mesozoic-Cenozoic transition. We discuss evidence from the sub-ice topography and potential field airborne and satellite data. We have applied image segmentation techniques to the rebounded sub-ice topography to semi-automatically trace the first order shape of the sub-ice basins, that we assume to be fault controlled. Then we have fitted the edges of the basins by maximum circles and estimated the best Euler pole identified by their intersection. Potential field anomalies have been taken into account in order to enlighten major discontinuities not revealed by the sub-ice topography.

The reconnaissance of this large sector of East Antarctica as the result of rotational extension may have major implications on global and regional tectonics plate reconstructions, plate deformation assumptions and new tectonic evolutionary models of WARS, TAM, and GM.

How to cite: Armadillo, E., Rizzello, D., Balbi, P., Ghirotto, A., Scafidi, D., Paxman, G., Zunino, A., Ferraccioli, F., Crispini, L., Läufer, A., Lisker, F., Ruppel, A., Morelli, D., and Siegert, M.: Some evidence of a wide rotational extension in East Antarctica preceding Gondwana breakup, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14808, https://doi.org/10.5194/egusphere-egu24-14808, 2024.

EGU24-14829 | Orals | TS2.1 | Highlight

The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms 

Freysteinn Sigmundsson, Michelle Parks, Halldór Geirsson, Andrew Hooper, Vincent Drouin, Kristín Vogfjörð, Benedikt Ófeigsson, Sonja H. M. Greiner, Yilin Yang, Chiara Lanzi, Gregory Paul De Pascale, Kristín Jónsdóttir, Sigrún Hreinsdóttir, Valentyn Tolpekin, Hildur María Friðriksdóttir, Páll Einarsson, and Sara Barsotti

A 15 km long dike formed rapidly in the Reykjanes Peninsula oblique rift on 10 November 2023 and propagated under the town of Grindavík.  From just before noon on 10 November until midnight, around 25 MW≥4 earthquakes occurred, two of which were of MW~5.2. Three-dimensional ground deformation is well resolved both temporally and spatially with dense Global Navigation Satellite System (GNSS) geodetic observations, which record cumulative displacements up to about 80 cm occurring mostly over 6 hours in the evening of 10 November and continuing at much reduced rates in the following days. Interferometric analysis of synthetic aperture radar images using Sentinel-1, COSMO-SkyMed, and ICEYE satellites records also well the dike deformation, which occurred simultaneously with deflation over the nearby central part of the Svartsengi volcanic system. Geodetic modelling, assuming uniform elastic host rock behavior, infers a dike volume of (130-139)×106 m3, with up to ~8 m dike opening, as well as some strike-slip shear motion. Deflation at Svartsengi in our model is best fit using a spherical point source with a volume decrease of (76-82)×106 m3up until 12 November. The temporal evolution of the dike opening was further modelled using hourly GNSS displacements, allowing better derivation of the temporal evolution of the flow rate into the dike and the contraction volume of the subsidence source. The maximum flow rate into the dike is inferred to be ~9500 m3/s, between 18:00 and 19:00 on November 10. We infer that the massive magma flow into the dike was established with only modest overpressure in the feeding magma body, a sufficiently large pathway opening at the boundary of the magma body, and pre-failure lowering of pressure along the pathway that had occurred through gradual build-up of high tensile stress over the previous eight centuries. This explains the unprecedented fast maximum magma flow rates that we infer. Such high flow rates provide insight into the formation of giant dike swarms under conditions of high tensile stress, and imply a high hazard potential for dike intrusions, considering their potential to transition into eruptions.

 

How to cite: Sigmundsson, F., Parks, M., Geirsson, H., Hooper, A., Drouin, V., Vogfjörð, K., Ófeigsson, B., Greiner, S. H. M., Yang, Y., Lanzi, C., De Pascale, G. P., Jónsdóttir, K., Hreinsdóttir, S., Tolpekin, V., Friðriksdóttir, H. M., Einarsson, P., and Barsotti, S.: The November 2023 Grindavik dike injection in Iceland:  Implications for continental rifting, dike formation in extensional tectonic settings, and giant dike swarms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14829, https://doi.org/10.5194/egusphere-egu24-14829, 2024.

EGU24-14830 | Posters on site | TS2.1

High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif) 

Prokop Závada, Vladimír Cajz, Andrew Kylander-Clark, and David Uličný

A new set of high-precision U-Pb data was acquired for two groups of phonolite bodies emplaced in the volcano-sedimentary sequence of the Cenozoic Eger Rift in Bohemian Massif. The phonolites are located in the western (5 bodies) and eastern (3 bodies) edge of this monogenetic volcanic field, stretched along the central part of the Eger Rift system. The selected phonolite bodies represent lava flows, cryptodomes or extrusive domes emplaced in phreatomagmatic maar-diatremes, remnants of dykes, and a laccolith. The U-Pb dates were acquired using the Laser Ablation Split Stream system at Santa Barbara University geochronology lab, which provides the coupled geochronology and also REE and selected major element geochemistry. Despite the great variety of internal zircon textures from oscillatory zoning to complex patchy patterns with a large range of cathodoluminescence intensity, the groups of spots gained coherent and surprisingly precise ages for each sample. The western group of phonolite bodies, namely the Bořeň, Želenický vrch, Špičák, Hněvín, and Ryzelský vrch display clusters of ages ranging between 33Ma and 36Ma, while zircons of the eastern group of the phonolites, Krompach, Mariánská hora and Luž (Lausche) indicate ages between 30Ma and 32Ma. Terra-Wasserburg diagrams for individual samples revealed remarkable precision marked by errors of only 90-180 thousand years (5 samples) and 300-650 thousand years (2 samples). The U-Pb zircon ages are interpreted to reflect primarily the high-temperature overprint of inherited (and possibly newly crystallized) zircons before emplacement of the phonolite bodies in the upper crust. In addition, titanite grains measured alongside the zircon grains (in another run) either overlap (Bořeň) with the zircon age error on Terra-Wasserburg diagrams (geochrone) or are 2 Ma years younger than corresponding zircon ages (Špičák phonolite body). REE binary diagrams revealed separate clusters of Sm/Nd and also Hf content of the zircons, which can be attributed to different degrees of partial melting of parental magma in the source upper mantle or the lower crust for both groups of sampled phonolites. In summary, the results suggest that U-Pb geochronology using the LASS system is a powerful tool with a great potential for deciphering the evolution of phonolites in the Cenozoic Rift system in Bohemian Massif and possibly other rift systems in the foreland of the Alpine orogeny.

This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Závada, P., Cajz, V., Kylander-Clark, A., and Uličný, D.: High precision U-Pb geochronology of Cenozoic phonolite volcanic bodies in Cenozoic Eger rift basin (Bohemian Massif), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14830, https://doi.org/10.5194/egusphere-egu24-14830, 2024.

EGU24-15107 | ECS | Posters on site | TS2.1

The evolution of fault networks during multiphase deformation: An analogue modeling approach 

Jun Liu, Matthias Rosenau, Ehsan Kosari, Sascha Brune, Frank Zwaan, and Onno Oncken

It is well known that triaxial deformation is a common feature of continental tectonics, and is accommodated by complex polymodal fault networks. Field investigations confirm that multiple phases involving time-dependent three-dimensional strain conditions (e.g. constriction, plane, and flattening strain) affect the spatial and temporal interaction of polymodal fault systems. However, a key question remains: How do changing strain conditions affect the reactivation of fault systems that formed during a previous deformation phase? Here, we conduct scaled analogue models with time-dependent boundary conditions to investigate how fault networks evolve under changing boundary conditions, including  reactivation and formation of new faults.

We have developed a setup in which a basal rubber sheet is stretched in one direction, so that longitudinal extension and layer thinning are accompanied by lateral shortening, hence producing triaxial deformation (Liu et al. in revision). According to previous brittle-viscous experiments with this set-up, an increase in longitudinal extension velocity results in a higher coupling between the rubber base and brittle layer, generating increasing transmission of lateral shortening from the base into the brittle layer. We thus induce constriction-to-plane strain conditions in the brittle layer as a function of longitudinal extension velocity by varying the magnitude of lateral contraction. In a new set of experiments, by varying extension velocity either stepwise or continuously, we realize time-dependent kinematic boundary conditions including deformation phases and secular changes, respectively. Digital image correlation (DIC) and photogrammetry (structure from motion, SFM) are employed to track the 3D kinematic surface and topography evolution, respectively.

Preliminary observations show both the formation of new faults and the reactivation of early phase faults through a change from plane to constriction strain. Conversely, a change from constriction to plane strain conditions results in the abandonment of the early phase fault network as it becomes overprinted by fault systems of the subsequent phase. Moreover, early-phase fault systems influence the propagation and linkage of fault populations in subsequent phases. Our analogue models highlight the impact of strain conditions on the overall plan-view geometry of fault populations, providing alternative explanations for complex fault patterns and interactions (e.g. the Jeanne d’Arc basin, the North Træna Basin, and the Beagle Platform).

How to cite: Liu, J., Rosenau, M., Kosari, E., Brune, S., Zwaan, F., and Oncken, O.: The evolution of fault networks during multiphase deformation: An analogue modeling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15107, https://doi.org/10.5194/egusphere-egu24-15107, 2024.

EGU24-15188 | Posters on site | TS2.1

Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia 

Radomír Grygar, Karel Mach, Roman Gramblička, and Tomáš Novotný

The Most Basin is the largest and best-preserved of sedimentary basins formed within the Eger Rift, the easternmost part of the European Cenozoic Rift System. Previous work on the tectono-sedimentary history of the basin and its surroundings has led to an interpretation of two main extensional phases that governed the Oligo-Miocene rift initiation and subsequent evolution. That interpretation has been derived mainly from large-scale considerations of main fault geometries, while a satisfactory support by a large mesoscopic dataset from the basin infill was lacking.

 

Systematic acquisition of mesoscopic structural data in some of the open-cast coal mines operating in the Most Basin has been motivated by prevention of accidents of bucket wheel excavators, threatened by sliding of blocks of mainly clayey sediments. As a result, over 5 thousand mesoscopic measurements were acquired in the Bílina Mine alone and hundreds in other mines over the past 13 years. In the Most Basin, the main coal seam is located close to the base of the basin fill. Open-case mines thus expose a thick overburden and, locally, also the underlying basement. The structural measurements involved the superposition and evolution of mesoscopic structural features in geological time, from Variscan metamorphic rocks through Cretaceous sediments and Oligocene volcanics through the Miocene coals and clastics of the basin fill.

 

Structural analysis of the dataset and statistical comparison of specific regions focused on

spatial and stratigraphic distribution of fault directions and inclination arrays, resulting in interpretation of spatial and stratigraphic distribution of local paleostress. The principal results are as follows:

  • the number of detected mesoscopic fault populations, as well as of interpreted deformation phases decreases upward through the stratigraphic column;
  • orientation of faults generally changes from a dominant E-W and NW-SE strike of population in the pre-Miocene formations into dominant SW-NE up to WSW-ENE strike within the youngest Libkovice Member (Early Miocene);
  • a trend of decreasing fault inclination from older, more consolidated formations to younger ones, most probably linked to rheological (stage of lithification) on brittle deformations;
  • generally, data evaluation of inclination and direction of faults gave generally similar results for the Bílina and Libouš mines, in spite of the 60 km distance between them and their proximity to different leading fault systems (Bílina and Victoria faults in the former case and the Ahníkov and Kralupy faults in the latter);
  • the large dataset of mesoscopic fault-slip data shows a generally more complex picture of possible paleostress evolution than the one derived from the geometries of the main bounding fault systems, due to the influence of local stress fields of normal and transtensional faults. The general picture, however, implies a plausible gradual evolution of extension vector from NNE-SSW to NW-SE orientations. throughout the early Miocene.

 

The Severočeské doly, a.s., supported the long-term acquisition of the structural dataset and its utilization for basic research purposes. This research has been supported by the Czech Science Foundation (GAČR) project 22-13980S.

How to cite: Grygar, R., Mach, K., Gramblička, R., and Novotný, T.: Insights into Miocene paleostress history of the Eger Rift from mining-related structural datasets: the Most Basin, Bohemia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15188, https://doi.org/10.5194/egusphere-egu24-15188, 2024.

EGU24-15268 | Orals | TS2.1

Shallow sources of upper mantle seismic anisotropy in East Africa  

Cynthia Ebinger, Miriam Reiss, Ian Bastow, and Mary Karanja

The East African rift overlies one or more mantle upwellings and it traverses heterogeneous Archaean-Paleozoic lithosphere rifted in Mesozoic and Cenozoic time. We re-analyze XKS shear wave splitting at publicly available stations to evaluate models for rifting above mantle plumes. We use consistent criteria to compare and contrast both splitting direction and strength, infilling critical gaps with new data from the Turkana Depression and North Tanzania Divergence sectors of the East African rift system. Our results show large spatial variations in the amount of splitting (0.1–2.5 s) but consistent orientations of the fast axes within rift zones: they are predominantly sub-parallel to the orientation of Cenozoic rifts underlain by thinned lithosphere with and without surface magmatism. The amount of splitting increases with lithospheric thinning and magmatic modification. Nowhere are fast axes perpendicular to the rift, arguing against the development of extensional strain fabrics. Thick cratons are characterized by small amounts of splitting (≤0.5 s) with a variety of orientations that may characterize mantle plume flow. Splitting rotates to rift parallel and increases in strength over short distances into rift zones, implying a shallow depth range for the anisotropy in some places. The shallow source and correlation between splitting direction and the shape of upper mantle thin zones suggests that the combination of channel flow and oriented melt pockets contribute > 1 s to the observed splitting delays. Enhanced flow, metasomatism, and melt intrusion at the lithosphere-asthenosphere boundary suggest that fluid infiltration to the base of the lithosphere may facilitate rifting of cratonic lithosphere. 

How to cite: Ebinger, C., Reiss, M., Bastow, I., and Karanja, M.: Shallow sources of upper mantle seismic anisotropy in East Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15268, https://doi.org/10.5194/egusphere-egu24-15268, 2024.

EGU24-16081 | Orals | TS2.1

Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport 

Adina E. Pusok, Yuan Li, Richard F. Katz, Tim Davis, and Dave A. May

Geophysical studies along the Main Ethiopian Rift and Eastern Rift in Kenya indicate that strain accommodation is dominated by magmatic intrusion rather than tectonic extension (e.g., Ebinger and Casey, 2001). However, it remains unclear how magmatic extension developed in the Turkana Depression, the low-lying, broadly rifted region separating the Ethiopian and East African plateaus. We investigate the rifting dynamics of the Turkana Depression with two-phase flow numerical models of melt transport through the ductile–brittle lithosphere. These models suggest that the pre-rift rheological structure of the lithosphere exerts a counter-intuitive control on melt extraction, which can explain the character of the Turkana region.

Recent seismic imaging shows that both the Turkana Depression and the uplifted plateaus are underlain by deep-seated, hot, partially-molten, buoyant mantle that ponds below a thinned plate (Kounoudis et al., 2021). Yet, Ogden et al. (2023) estimated the Moho is 10–20 km shallower throughout the Turkana Depression (~20–25 km) than surrounding regions (~35–40 km). Here, we hypothesise that variations in lithospheric strength across the Turkana Depression and the Ethiopian Plateau have influenced magma transport across the lithosphere and rift development (Morley, 1994). 

Our models of melt extraction through the ductile–brittle lithosphere incorporate a new poro-viscoelastic–viscoplastic theory with a free surface (Li et al., 2023), designed and validated as a consistent means to model dykes. We initialise models with a source of partial melt in the asthenosphere and investigate how rheology of the overlying lithosphere impacts melt migration to the surface. Experiments are performed for buoyancy-driven magma transport under no tectonic extension, and for low background tectonic extension rates typical to the Turkana Depression (4 mm/yr; e.g., Knappe et al., 2020). Results indicate that both the rheology of lithosphere and extension rate control the efficiency of magma extraction. Magma transport across a thick, elastic lithosphere is more efficient than across a thin, more ductile lithosphere, and increases with extension. Our results suggest that surface volcanism in the Ethiopian Plateau is more likely to occur compared with the Turkana Depression, and at earlier times. 

References

Ebinger and Casey (2001), Geology, DOI: 10.1130/0091-7613(2001)029<0527:cbimpa>2.0.co;2

Kounoudis et al. (2021), G-cubed, DOI: 10.1029/2021GC009782

Ogden et al. (2023), EPSL, DOI: 10.1016/j.epsl.2023.118088

Morley (1994), Tectonophys., DOI: 10.1016/0040- 1951(94)90170-8

Knappe et al. (2020), JGR: Solid Earth, DOI: 10.1029/2019JB018469

Li et al. (2023), GJI, DOI: 10.1093/gji/ggad173

How to cite: Pusok, A. E., Li, Y., Katz, R. F., Davis, T., and May, D. A.: Reduced magmatism in the Turkana Depression: a consequence of inefficient melt transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16081, https://doi.org/10.5194/egusphere-egu24-16081, 2024.

EGU24-16240 | ECS | Posters on site | TS2.1

Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years. 

Amber Distelbrink, Grace E. Shephard, Jean-Baptiste P. Koehl, Steffen G. Bergh, and Anouk Beniest

Constraining the evolution of the opening of the northernmost region of the Northeast Atlantic Ocean is of particular importance for understanding the diversity of ocean basin opening dynamics, including the development of oblique margins and shear zones. Accurately determining the timing and kinematics of the motion along the Senja Shear Zone and opening of the Fram Strait is of particular importance for climate research as this region forms the only deep-water gateway between the Northeast Atlantic Ocean and Arctic Ocean. This study combines new and legacy data and presents an analysis of the tectonic evolution of the northern Norwegian passive margin over the past 200 Ma, including integrating structural field observations and plate tectonics models.

Fieldwork took place on the islands of Senja and Kvaløya in Troms County of northern Norway. The field observations reveal four dominant brittle fault groups corresponding to four normal-oblique extension directions: E-W, NNW-SSE, NW-SE, NE-SW. In the Senja Shear Zone, the strike-slip faults are predominantly oriented NNW-SSE to NW-SE. Analysis of existing plate motion models for the region for 200 Ma to present day includes three prominent extension phases in chronological order: E-W, NNW-SSE, and NW-SE.

This study suggests that during the E-W oriented crustal thinning phase, normal faulting and minor strike-slip faulting dominated and gave way to basement-seated strike-slip faults during the NNW-SSE oriented extension phase. The presence of mid-upper crust faulting is argued by fault mineral striation assemblages and hydrothermal alteration. In the NW-SE oriented extensional phase, both normal faults and strike-slip faults were active. Comparisons to existing rigid plate tectonic models for the region suggest a revised deformable plate framework is required, and offers insights into the original thickness of the North-American and European plates and the role of mid-crustal tectonics in the breakup. The role of inheritance, including earlier shear zones and extensional phases will also be discussed. In addition, the present research encourages scientists to digitize analogue maps and data, preventing loss of knowledge during the analogue to digital transition.

How to cite: Distelbrink, A., Shephard, G. E., Koehl, J.-B. P., Bergh, S. G., and Beniest, A.: Insights into the tectonic evolution of the northern Norwegian passive margin: Integrating field observations and plate modeling over 200 million years., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16240, https://doi.org/10.5194/egusphere-egu24-16240, 2024.

EGU24-17089 | Posters on site | TS2.1

The ANR project “FirstMove”: first movements of divergence between future tectonic plates 

Julia Autin, Roxane Mathey, Harmony Suire, Mélanie Ballay, Marc Ulrich, Gianreto Manatschal, Daniel Sauter, Benoît Petri, Marc Schaming, and Luis Somoza Losada

As two tectonic plates drift away, the earlier movements, prior to oceanic crust formation, are ill-constrained. We are convinced that the kinematic models of plate movements could be significantly enhanced by focusing on the divergence before final lithospheric breakup. During this phase of transition several problems arise. Firstly, the classical interpretations of magnetic anomalies are not trustworthy (debated geometry and/or origin of anomalies). Secondly, the movements are more complex than in oceanic domain (polyphase deformation, obliquity, asymmetry). Those particularities occur especially if plate breakup happens in magma-poor conditions where mantle is exhumed at the surface (in about 50% of instances).

We focus on two pairs of conjugate magma-poor rifted margins: the Bay of Biscay and the Australia-Antarctica margins. In these areas, magnetic anomalies are controversial and seafloor formation started with large domains of hyperextended continental crust and exhumed mantle. Thus, the location and age of the LaLOC (landward limit of the oceanic crust) are uncertain. We aim to better define these domains in space, divergence direction and time through geophysical data and localized petrological observations and dating. This project is in its starting phase, it includes 2 PhD thesis. This presentation focuses on the general framework of the project and the preliminary results.

How to cite: Autin, J., Mathey, R., Suire, H., Ballay, M., Ulrich, M., Manatschal, G., Sauter, D., Petri, B., Schaming, M., and Somoza Losada, L.: The ANR project “FirstMove”: first movements of divergence between future tectonic plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17089, https://doi.org/10.5194/egusphere-egu24-17089, 2024.

EGU24-17201 | ECS | Posters on site | TS2.1

Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea 

Chao-Hsun Wang, Ping-Rong Wu, Kenn-Ming Yang, Chih-Cheng Yang, and Bieng-Zih Hsieh

Jieyang Depression is located between the Southern Depression of the Taixinan Basin and the Chaoshan Depression of the Pearl River Mouth Basin in northern South China Sea. A series of NE-SW striking half graben developed in this area from late Mesozoic to early Paleogene, and then another two stages of normal faulting happened during Neogene. The development of these stages of normal faults are separated by the breakup unconformity and a post-rift truncation. The main purposes of this study are to investigate the evolutionary sequences of the multi-stages of normal faults and the truncations during the multi-stages of extension, the spatial distribution of each phase of normal faults, and how the younger normal faults were affected by the pre-existing ones.

The normal faults in the Jieyang Depression can be divided into three types. Type 1 faults are related to the Paleogene half graben formation and only cut through the pre-rift and syn-rift strata. Type 2 normal faults only developed and cut through the post-rift strata. Type 3 normal faults cut through the syn-rift and post-rift strata. In this study, we further divide the Type 2 normal faults into two different kinds. Type 2-1 faults developed above the Paleogene half graben and cut off by the post-rift truncation. Type 2-2 faults developed after the truncation. Type 3 normal faults can be divided into two different kinds as well. Type 3-1 faults developed in the syn-rift stage and yet were reactivated and linked with the faults developing in the later extension. Type 3-2 faults are the Type 2 faults that developed continuously cutting downward into the syn-rift strata.

In terms of spatial distribution, Type 1 normal faults strike NE-SW, forming the half grabens. Most of the Type 2 normal faults are located far away from continental shelf. Type 3 normal faults mostly distribute on the northeast and northwest sides of the study area, close to the continental shelf, and most of them are cut by the post-rift truncation.

As a result, from the late Mesozoic to the early Paleogene, the northern slope of the South China Sea experienced a NW-SE extension. At the end of the Paleogene, the extension ceased, forming the breakup unconformity. In the Neogene, the Jieyang Depression experienced second extension. In this time the extension orientation was NNW-SSE, developing Type 2-1 and Type 3 faults before the post-rift truncation. The subsequent truncation cuts Type 2-1 faults and the upper part of the Type 3 faults. After accumulating new strata above truncation, the third stage of extension happened and Type 2-2 faults developed after the post-rift truncation.

Key words: South China Sea, Jieyang Depression, normal fault, multi-stage extension, truncation

How to cite: Wang, C.-H., Wu, P.-R., Yang, K.-M., Yang, C.-C., and Hsieh, B.-Z.: Structural Mode and Evolution of Multi-stage Normal Fault Development in Jieyang Depression, NE South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17201, https://doi.org/10.5194/egusphere-egu24-17201, 2024.

EGU24-17395 | ECS | Orals | TS2.1

Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin 

Valentin Rime, Anneleen Foubert, Derek Keir, and Tesfaye Kidane

The Danakil Depression is situated in the northern part of the Afar Depression in Ethiopia and Eritrea and is in an advanced phase of rifting close to continental breakup. It forms the equivalent of a magma-rich margin. As it is currently active and emerged, it offers a unique opportunity to study the processes of formation of these types of passive margins.

We combine seismic reflection data, field data, and remote sensing to constrain the structure and kinematics of this basin. Seismic data reveal the formation of Seaward Dipping Reflectors (SDRs). Surprisingly, field data show that these SDRs are dominated by clastic sediments and only contain relatively minor amount of magmatic material. Paleoshorelines and other proxies allow to quantify uplift and subsidence rates across the basin. These data highlight high spatial variability and allow to better understand the structure and evolution of older, deeply buried passive margins.

How to cite: Rime, V., Foubert, A., Keir, D., and Kidane, T.: Structure and kinematics of the Danakil Depression, Afar, Ethiopia: insights into the formation of a magma-rich margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17395, https://doi.org/10.5194/egusphere-egu24-17395, 2024.

EGU24-17937 | ECS | Posters on site | TS2.1

Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin. 

Alexandra Tamas, Robert E. Holdsworth, Dan M. Tamas, Edward D. Dempsey, Kit Hardman, Anna Bird, John R. Underhill, Dave McCarthy, Ken J.W. McCaffrey, and David Selby

Constraining the age of formation and movement along fault arrays in superimposed basins helps us to better unravel their kinematic history as well as the role of bounding faults or inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) comprises a series of superimposed basins overlying rocks of the Caledonian basement, the pre-existing Devonian-Carboniferous Orcadian Basin and a regionally developed Permo-Triassic North Sea basin system. The IMFB rifting occurred mainly in the Upper Jurassic – Lower Cretaceous after a long period of subsidence followed by localised uplift in its eastern parts due to thermal doming in the central North Sea (in the middle Jurassic). The rift basin later experienced further episodes of regional tilting, uplift and fault reactivation during Cenozoic.

New detailed field observations augmented by drone photography and creation of 3D digital outcrops, coupled with U-Pb geochronology of syn-faulting calcite-mineralised veins are used to constrain the absolute timing of fault movements and decipher the kinematic history of basin opening. It also helps to identify those deformation structures associated with earlier basin-forming events.

Five regional deformation events emerge: Devonian rifting associated with the older Orcadian Basin; Late Carboniferous inversion related to dextral Great Glen fault movements; Permian thermal subsidence with some evidence of minor fracturing; Late Jurassic – Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to many of these events.

How to cite: Tamas, A., Holdsworth, R. E., Tamas, D. M., Dempsey, E. D., Hardman, K., Bird, A., Underhill, J. R., McCarthy, D., McCaffrey, K. J. W., and Selby, D.: Using U-Pb geochronology of syn-faulting calcite-mineralised veins to track the evolution of superimposed rifting events: the Inner Moray Firth Basin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17937, https://doi.org/10.5194/egusphere-egu24-17937, 2024.

The presentation is based on the results of the research work of the Arktic-2011, Arktic-2014 and Arktic-2022 expeditions and contains the results of analysis of the structure of the sedimentary cover of the Eurasian basin of the Arctic Ocean. For the first time, the entire array of seismic data, including Russian and foreign seismic profiles, was used for tectonic constructions. The results obtained make it possible to reconstruct extensive areas of continental lithosphere development in the Eurasian basin. Based on the analysis of the structure of the sedimentary cover of the Amundsen Basin, four stages of the geological history of the formation of the sedimentary system of the Eurasian basin of the Arctic Ocean are substantiated. During the first (Cretaceous-Paleocene) stage, extensive axis-symmetric epicontinental paleo-basins of the Amundsen and Nansen Basins were formed on the shoulders of the continental rift, which were subsequently separated by seafloor spreading. Evidence of similar riftogenic settings in the second half of the Cretaceous is recorded along the entire periphery of the Arctic basin from Greenland to the Chukchi Rise. The second (Eocene)-spreading stage was characterised by stage accretion of the oceanic crust in the Gakkel Ridge and was accompanied by a gradual expansion of the sedimentary basin up to the present-day boundaries of the Eurasian basin. The third stage (Oligocene-Miocene) of sedimentary flexure corresponded to the accumulation of a thick undisturbed sedimentary cover over the entire Eurasian basin, indicating the temporary cessation of spreading in the Gakkel Ridge and the establishment of a tectonic quiescence regime. Similar conditions at this stage are recorded throughout the periphery of the Arctic basin. The resumption of spreading processes occurred at the fourth (Pliocene-Quaternary) neotectonic stage. As the result of the intensification of spreading processes in the Norwegian-Greenland Basin, tectonic stresses penetrated intothe Eurasian Basin along the axis of the Gakkel Ridge. The distinct morphological division of the Gakkel Ridge into Siberian-Marine and Atlantic segments is explained by the jump-like transmission of tectonic stresses of the North Atlantic, which is also confirmed by the anomalously high tectonic, volcanic and hydrothermal activity of the Gakkel Ridge.

How to cite: Neevin, I., Rekant, P., and Budanov, L.: MODEL OF THE FORMATION OF THE SEDIMENTATION SYSTEM OF THE EURASIAN BASIN OF THE ARCTIC OCEAN AS A BASIS FOR RECONSTRUCTING Its TECTONIC HISTORY, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18255, https://doi.org/10.5194/egusphere-egu24-18255, 2024.

EGU24-19671 | Orals | TS2.1

A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins 

Christian Heine, Ken McDermott, James Eldrett, Colin Grant, and Philip Thompson

The spatio-temporal analysis of rifts and passive margin evolution is often done based on regional case studies, using non-standardized terminology and classification models to characterize crustal boundaries and basin infill. As example, the use of “continent-ocean boundary” to delineate crustal types or “syn-rift” as basin infill characterization has proven to be no longer adequate, given our evolved understanding of passive margins. In general, such local approaches do not lean themselves to aggregate data for global and large-scale comparative analysis and often struggle to reconcile the spatially varying magmatic/weakly magmatic margin architecture in a rift system context. They also do not allow efficient deployment of spatio-temporal data analytic models due to a lack of standardized data classification.

To overcome these limitations, we have designed a novel “data science-ready” data model for crustal architecture that is based on commonly accepted terminologies, can be used independent of input data heterogeneity and can be deployed globally across the whole spectrum of margin types and complex 3D margin geometries/microplate settings. We classify two key crustal boundaries, the oceanward limit of continental crust ("OLCC") and the landward limit of oceanic crust ("LaLOC"), along with several key crustal interfaces, such as the top basement and base crust which are further subdivided into sub-categories. This approach allows us to easily generate standardized data products on rift system scale, which quantitatively describe key parameters relevant to understand lithosphere extension dynamics, such as volumes, ratio, and distribution of continental and magmatic crust, crustal stretching factors, and amount of crustal embrittlement. Coupled with plate kinematic models, these data products allow to build reproducible, extensible, and quantitative models of rift and margin evolution through time and highlight the dynamics of stretching, localization of deformation, the basin infill response, and spatio-temporally varying patterns and types of magmatism.

Applying this data model, we have characterized the crustal architecture of the conjugate South Atlantic passive margins, interpreting more than 100k line-kilometers of 2D and 3D seismic reflection data. Our findings highlight substantial shortcomings of current plate models to reconcile the crustal type distributions in the southern South Atlantic with a tight pre-breakup fit, the temporal emplacement dynamics of SDRs and plume-related magmatism along the whole South Atlantic rift, as well as the localization of deformation and dynamics of basin infill.

How to cite: Heine, C., McDermott, K., Eldrett, J., Grant, C., and Thompson, P.: A generic crustal architecture data model for rift and passive margin analysis: Application to the conjugate South Atlantic margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19671, https://doi.org/10.5194/egusphere-egu24-19671, 2024.

EGU24-19853 | Posters on site | TS2.1

Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting 

Marta Pérez-Gussinyé, Yangfan Xin, Tiago Cunha, Raghu Ram, Miguel Andres-Martinez, Dongdong Dong, and Javier Garcia-Pintado

The thermal history of margins controls the development of hydrothermal systems during rifting, diagenetic processes in the sediments and the generation and preservation of hydrocarbons. It also affects the depth of the oceanic gateways formed during continental break-up, thereby influencing ocean circulation and ultimately climate (Brune et al., 2023, Pérez-Gussinyé et al., 2023, Peron-Pinvidic et al., 2019). Observed heat-flow values however, do not always comply with classic rifting models. Here, we use 2D numerical models to investigate the relationship between rifting, sedimentation and thermal history of margins. We find that during the synrift, the basement heat flow and temperature are not only controlled by extension factor, but also by synrift sediment thickness and the evolution of deformation. As this progressively focuses oceanward, the proximal sectors thermally relax, while the distal sectors experience peak temperatures. This time lag is important for wide rifted margins. In the postrift, the lithosphere under the hyperextended margins does not return to its original state, at least for ~100 Myrs after breakup. Instead, it mimics that of the adjacent oceanic plate, which is thinner than that of the original continental plate. This results in heat flow values increasing oceanward at postrift stages where classic rifting theory predicts complete thermal relaxation. Our increased heat-flow estimations, may extend hydrocarbon plays into distal margin sectors and adjacent oceanic crust, previously discarded as immature. Finally, our models indicate that commonly used temperature approximations in basin analysis may strongly differ from those occurring in nature (Pérez-Gussinyé et al., 2024).

 

Brune, S., Kolawole, F., Olive, JA. et al. Geodynamics of continental rift initiation and evolution. Nat Rev Earth Environ 4, 235–253 (2023). https://doi.org/10.1038/s43017-023-00391-3

Pérez-Gussinyé, M., Collier, J., Armitage, J., Hopper, J. R., Sun, Z., and Ranero, C. R., Towards a process-based understanding of rifted continental margins, in Nature Reviews Earth and Environment, 2023, doi: 10.1038/s43017-022-00380-y

Marta Pérez-Gussinyé, Yanfang Xin, Tiago Cunha,  Raghu Ram, Miguel Andrés-Martínez, Dongdong Dong, Javier García-Pintado,Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension, in press, Geol. Soc Spec. Publ., 2024

Peron-Pinvidic, G., Manatschal, G., eta al. Rifted Margins: State of the Art and Future Challenges, Front. Earth Sci., 22 August 2019, Sec. Structural Geology and Tectonics, Volume 7 - 2, https://doi.org/10.3389/feart.2019.00218.

How to cite: Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andres-Martinez, M., Dong, D., and Garcia-Pintado, J.: Synrift and postrift thermal evolution of margins: a re-evaluation of classic models of rifting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19853, https://doi.org/10.5194/egusphere-egu24-19853, 2024.

EGU24-19947 | ECS | Posters on site | TS2.1

Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling 

Yaoyao Zou, Daniele Maestrelli, Giacomo Corti, Chiara Del Ventisette, Liang Wang, Xiaofan Wan, Yanjie Gao, and Chuanbo Shen

 

Multiple fault populations with different orientations and complex fault patterns can be observed during oblique rifting, conditions which result from a complex rift kinematics which combines dip-slip and strike-slip motion. Although analysis of different natural cases and analog or numerical modeling have shed light on the relations between rift obliquity and the related fault architecture, many aspects of the process remain poorly understood. One of these aspects is related to the existence of pre-existing fabrics in the upper crust, which may further complicate the fault pattern by forcing the development of faults with atypical geometries and orientation.

Here, we performed enhanced-gravity analog models of oblique narrow rifting to characterize the evolution and architecture of rift-related faults developing in a brittle upper crust characterized by inherited fabrics. The models reproduce a rift obliquity of 30° (angle between the rift trend and the orthogonal to the direction of extension), kept constant in all the experiments, and pre-existing vertical fabrics with variable orientation (from 0°, i.e. orthogonal to extension, to 90°, i.e. extension-parallel). Modeling results suggest that inherited fabrics have an important influence on rift-related faulting, with a significant correlation between the intensity of reactivation and their trend with respect to the extension direction. When the pre-existing fabrics trend perpendicular to the extension direction (obliquity 0°), they are strongly reactivated, localizing deformation and promoting the rapid development of faults and grabens perpendicular to the extensional direction. When the pre-existing fabrics trend at moderate obliquity (15°-45°), they are still reactivated and localize deformation causing the development of atypical fault trends and patterns. The degree of reactivation tends to gradually decrease with increasing obliquity; similarly, the influence of pre-existing structures decreases with progressive extension, and the fault pattern and evolution are progressively dominated by extension kinematics and crustal thinning. When the pre-existing fabrics trend at high obliquity (≥ 60°), they have almost no influence on the fault geometry and architecture.

This study has significant implications for explaining the fault geometry and evolution of some natural rift basins worldwide, such as basins of the East African Rift system, the North Sea Rift, and some offshore rift basins in eastern China.

How to cite: Zou, Y., Maestrelli, D., Corti, G., Del Ventisette, C., Wang, L., Wan, X., Gao, Y., and Shen, C.: Interactions between pre-existing fabrics and fault patterns during oblique rifting revealed by enhanced-gravity analog modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19947, https://doi.org/10.5194/egusphere-egu24-19947, 2024.

EGU24-20162 | ECS | Posters on site | TS2.1 | Highlight

 The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages 

Yafet Gebrewold Birhane, Raphael Pik, Nicolas Bellahsen, Irene Schimmelpfennig, Lydéric France, Jessica Flahaut, Dereje Ayalew, and Gezahegn Yirgu

The Afar depression at the northern end of the East African Rift system is presently experiencing the final stage of continental break-up and progressive onset of steady magmatic spreading. The Magmatic Rift Segments in Afar broadly analogous to those observed within the mid oceanic ridges, offer the opportunity to study both mantle and crustal processes. Investigating the crustal architecture of those magmatic segments represents a key aspect to decipher fundamental parameters that control focussing of magmatic and tectonic activity during the generation of magmatic crust. Here, we present the typical organization of a 32 km long subsegment of the Manda Hararo magmatic rift system, with fissural activities symmetrical to an apparent mid segment magmatic reservoir and establish geochronology of the last eruptive history. We combine field investigations, precise mapping of volcanological and tectonic features, cosmogenic 36Cl exposure dating and geochemical analysis of lavas to constrain the temporal frame and the dynamics of magmatic processes. Our results show that the recent historical volcanic events (~ 500 to 2000 years) are sourced from calderas and fissures representing an alternating sequence of effusive and explosive (block fields) activities related to a coherent rifting episode along a single self-consistent magmatic sub-segment. Those recent fissural flows resurfaced a large portion of the segment and emplaced on older thick pahoehoe flows with a rather long lag-time of about 75 kyr separating the two episodes. Strongly contrasted geochemical signatures are also observed between those two volcanic episodes, with more differentiated and trace elements enriched basalts for the recent one, compared to the older one which are characterized by a unusual depleted signature. These new results for the Central Afar Manda Hararo rift have important implications for: (i) the local hazards along the segments, and (ii) the volcano-tectonic organization of the segment with coexistence of contrasted melt reservoirs on the underlying transcrustal plumbing system.

How to cite: Birhane, Y. G., Pik, R., Bellahsen, N., Schimmelpfennig, I., France, L., Flahaut, J., Ayalew, D., and Yirgu, G.:  The Last Fissural Eruptions of the Manda Hararo Magmatic Segment, Central Afar (Ethiopia), Constrained from New cosmogenic Ages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20162, https://doi.org/10.5194/egusphere-egu24-20162, 2024.

EGU24-20218 | ECS | Posters on site | TS2.1

Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data. 

Louis Gaudaré, Cécile Doubre, Marc Jolivet, Olivier Dauteuil, Samuel Corgne, Raphaël Grandin, Marie-Pierre Doin, and Philippe Durand

Located at the southwestern terminus of the East African Rift System, the Okavango Rift System represents an opportunity to study the propagation of an active rift at its early stages (Gaudaré et al., in review). The Okavango Graben (northern Botswana) is an active half-graben of the Okavango Rift System, which shows normal to dextral strike-slip tectonic displacements of the order of 1 mm per year (Pastier et al., 2017). In addition to the impact of tectonics, large volumes of water (~10 km3 per year) brought in by the annual flood of the Okavango River generate seasonal subsidence of over 2 cm in the graben (Dauteuil et al., 2023). The prevalence of the hydrologic signal over the tectonic signal makes it challenging to provide clear interpretations of the Rift dynamics within the Okavango Graben. The previous studies are based on a network of GNSS stations, providing punctual data on displacements. To quantify the deformation field over the Okavango Graben, we analyze interferometric synthetic aperture radar (InSAR) data produced by the ForM@Ter LArge-scale multi-Temporal Sentinel-1 InterferoMetry service (FLATSIM, Thollard et al., 2021). FLATSIM automatically computes interferograms from Sentinel-1 synthetic aperture radar data and inverts them into displacement time series. The products span from April 2016 to April 2021 with a temporal resolution of 12 days, a spatial resolution of 115 x 115 m and cover the entire Okavango Rift System. We analyze and compare the seasonality of both the interferometric coherences and the InSAR displacement time series. Change detection in the interferometric coherence allows us to delineate flooded surfaces through time in the Okavango Graben, from which we deduce water loadings on the lithosphere and model the corresponding flexural response of the lithosphere. We then compare this response to the spatial distribution of annual vertical oscillations extracted from the displacement time series. Taking these seasonal signals into account, our objective is to estimate the rates of the tectonic subsidence in the Okavango Graben to better constrain the propagation of the East African Rift System at its southwestern end.

Dauteuil, O., Jolivet, M., Gaudaré, L., & Pastier, A.-M. (2023). Rainfall-induced ground deformation in southern Africa. Terra Nova, 00, 1–7. https://doi.org/10.1111/ter.12650

Gaudaré, L., Dauteuil, O., & Jolivet, M. Geomorphology of the Makgadikgadi Basin (Botswana): insight into the propagation of the East African Rift System. Tectonics, in review.

Pastier, A.-M., Dauteuil, O., Murray-Hudson, M., Moreau, F., Walpersdorf, A., & Makati, K. (2017). Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review. Tectonophysics 712–713, 469–481. https://doi.org/10.1016/j.tecto.2017.05.035

Thollard, F., Clesse, D., Doin, M.-P., Donadieu, J., Durand, P., Grandin, R., Lasserre, C., Laurent, C., Deschamps-Ostanciaux, E., Pathier, E., Pointal, E., Proy, C., & Specht, B. (2021). FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service. Remote Sensing, 13(18), 3734. https://doi.org/10.3390/rs13183734

How to cite: Gaudaré, L., Doubre, C., Jolivet, M., Dauteuil, O., Corgne, S., Grandin, R., Doin, M.-P., and Durand, P.: Unraveling Tectonic From Hydrological Subsidence Of The Okavango Graben (Botswana) Using FLATSIM InSAR Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20218, https://doi.org/10.5194/egusphere-egu24-20218, 2024.

EGU24-20223 | Posters on site | TS2.1

Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling. 

Thomas Theunissen, Ritske S. Huismans, Delphine Rouby, Sebastian Wolf, and Dave A. May

The magma-poor passive rifted conjugate margins in the Southern Equatorial Atlantic, North Atlantic/Arctic oceans, and Northern Mozambique Channel display en-echelon extensional segments separated by long transform faults (>300 km), influenced by inherited weaknesses. Using advanced 3-D forward geodynamic modeling coupled with surface processes, we investigate the formation of oblique rifts and passive margins. Our focus is on pre-existing weaknesses parallel to the extension direction, exploring the system's sensitivity to various erodibility factors. Key findings include: (1) erodibility within a low to moderate range has limited influence on the morpho-structural evolution of the oblique continental rift, (2) pure-strike slip faults reactivating transform weaknesses result in reduced topography, (3) major catchments sink in the inner corner at the tip of each extensional segments, and (4) hinterland drainage network capture along extensional segments is absent, controlled by isostatic rebound during rift flank drainage divide migration. This study enhances our understanding of the complex interplay between inherited weaknesses, erodibility, and the evolving morphology of oblique rifted margins.

How to cite: Theunissen, T., Huismans, R. S., Rouby, D., Wolf, S., and May, D. A.: Interaction of tectonics and surface process during oblique rifted margin formation. Insights from 3-D forward coupled geodynamic-surface process modelling., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20223, https://doi.org/10.5194/egusphere-egu24-20223, 2024.

EGU24-20850 | Posters on site | TS2.1

The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search 

Martina Busetti, Alberto Pastorutti, Magdala Tesauro, Carla Braitenberg, Florence Colleoni, and Laura De Santis

The basins composing the 1000-km wide West Antarctica Rift System (WARS), derived from extensional dynamics lasting from the Cretaceous to the Middle Neogene, bear evidence of a peculiar evolution through time: a transition from a diffuse to a localized thinning style and a migration of the focus of deformation, which likely progressed towards the cratonic domains of West Antarctica. Using the current observations, we aim at identifying which inherited starting conditions [1] result in outcomes compatible with the present-time structures and which do not allow so, unless other factors are accounted for.

To this aim, we turn to an extensive grid search in the parameter space, running a large number of forward numerical models to cover the possible permutations of parameters under test. We use the open source Underworld2 code [2] with a simplified scheme of starting conditions and kinematics boundaries, for lithospheric-scale 2-D thermomechanical models. We analyse the results obtained by changing a great number of parameters, including initial geometries of the crust and lithosphere, different rheologies, inherited structures, such as strain-weakening scars and thermal remnants of slabs.

We identify that a high crustal thickness (more than 45 km) is required to accommodate the first rifting phase (170 km ca. of cumulated extension, [3]) without producing crustal necking and eventual ocean formation. Parameters that favour a weaker strength profile, chiefly temperature (due to a thicker crust and/or a shallow lithosphere-asthenosphere boundary), are also required to avoid an early transition to localized deformation, in agreement with previous studies [4]. Smaller scale features, such as partition in multiple sub-basins, require additional factors, such as inherited weak-zone seeds (“scars”) in the crust and mantle, which are likely remnants of previous compressive phases [5].

[1] Perron, P., Le Pourhiet, L., Guiraud, M., Vennin, E., Moretti, I., Portier, É., & Konaté, M. (2021). Control of inherited accreted lithospheric heterogeneity on the architecture and the low, long-term subsidence rate of intracratonic basins. BSGF - Earth Sciences Bulletin, 192. https://doi.org/10.1051/bsgf/2020038

[2] Mansour, J., Giordani, J., Moresi, L., Beucher, R., Kaluza, O., Velic, M., Farrington, R., Quenette, S., & Beall, A. (2020). Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud. Journal of Open Source Software, 5(47), 1797. https://doi.org/10.21105/joss.01797

[3] Brancolini, G., Busetti, M., Coren, F., De Cillia, C., Marchetti, M., De Santis, L., Zanolla, C., Cooper, A.K., Cochrane, G.R., Zayatz, I., Belyaev, V., Knyazev, M., Vinnikovskaya, O., Davey, F.J., Hinz, K., 1995. ANTOSTRAT Project, seismic stratigraphic atlas of the Ross Sea, Antarctica. In: Cooper, A.K., Barker, P.F., Brancolini, G., (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin. Antarctic Research Series, vol. 68, https://doi.org/10.1029/AR068

[4] Huerta, A. D., & Harry, D. L. (2007). The transition from diffuse to focused extension: Modeled evolution of the West Antarctic Rift system. Earth and Planetary Science Letters, 255(1–2), 133–147. https://doi.org/10.1016/j.epsl.2006.12.011

[5] Talarico, F., Ghezzo, C., & Kleinschmidt, G. (2022). The Antarctic Continent in Gondwana: a perspective from the Ross Embayment and Potential Research Targets for Future Investigations. In Antarctic Climate Evolution (pp. 219–296). Elsevier. https://doi.org/10.1016/B978-0-12-819109-5.00004-9

How to cite: Busetti, M., Pastorutti, A., Tesauro, M., Braitenberg, C., Colleoni, F., and De Santis, L.: The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20850, https://doi.org/10.5194/egusphere-egu24-20850, 2024.

EGU24-1801 | Posters on site | TS3.1

Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling 

Eleftheria Papadimitriou and Vassilios Karakostas

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, exhibits the fastest rates of relative plate motion in the Mediterranean. It constitutes an active boundary and comprises five manor fault segments with a total length of nearly 120km, and are characterized by fast long–term rates of displacements of about ~25mm/yr for Kefalonia segments and ~15 mm/yr for Lefkada segments. Strike slip faulting with moment magnitudes Mw up to 7.0 characterizes the largest earthquakes, whereas the five almost along strike faults have been the sites of numerous earthquakes of moment magnitude, Mw, 5.0–7.0 during the past 50 years. The KTFZ in its entire length is much more active at the Mw>6.0 level than a comparable length of either the North Aegean Trough or Corinth rift, which are the most fastly deforming areas in the area of Greece. Alteration of active periods comprising multiple earthquakes with much longer quiescent periods is the mode of strong earthquake occurrence, with prevailing clustering over the period when historical information is available. The fast rate of plate motion, maximum size of earthquakes and relatively short repeat times make these fault segments suitable to seek for recurrence behavior that approaches quasi–periodic and its potential implications to the cyclic mode of seismogenesis. Recurrence of M6.0 earthquakes along nearly the same fault segment is attempted after evaluating the location of the historical events, based on all available macroseismic descriptions. These estimations are then compared with computed simulated catalogs.

The computed depths of earthquakes along the KTFZ are accurate enough to ascertain centroid depths as indicators of the downdip width of seismic faulting. With aftershock relocation we constrained the seismogenic layer in Kefalonia and Lefkada segments equal to 14 km (between depths of 3 and 17 km) and 10 km (between depths of 5 and 15 km) respectively, corresponding to downdip widths of 19 and 12 km, respectively. We compared these constraints with the calculated downdip width from a segment’s length along strike, moment release and relative plate motion ‘assuming’ full seismic coupling. The good correlation between the two support the high degree of coupling along the KTFZ.

Acknowledgments: Funded by the European Union. Views and opions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

 

 

How to cite: Papadimitriou, E. and Karakostas, V.: Strong (Mw>6.0) earthquakes along the KTFZ: implications for recurrence pattern and seismic coupling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1801, https://doi.org/10.5194/egusphere-egu24-1801, 2024.

EGU24-2188 | ECS | Posters on site | TS3.1

Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model 

Weilun Qin, Rob Govers, Mario D’Acquisto, Natasha Barlow, and Riccardo Riva

Subduction earthquake cycles are known to produce distinctive patterns of crustal motion, providing critical insights into the details of plate interface coupling and rupture behavior. Retrieving these patterns in the Cascadia subduction zone poses a significant challenge, particularly because the 1700 great Cascadia earthquake (Mw>=9.0) occurred more than three centuries ago.

Previous studies of the megathrust earthquake cycle along the Cascadia margin focused on either the geologically constrained coseismic rupture, or on the present-day interseismic coupling patterns based on geodetic observations. There thus is a gap in the comprehensive understanding of the earthquake cycle, particularly in the integration of available geological and geodetic evidence.

Our study aims to bridge this gap and unify the insights preserved in both records. To do so, we develop a three-dimensional viscoelastic earthquake cycle model with realistic slab geometry, crustal thickness, and topography. We simulate the coseismic, postseismic, and interseismic stages of the earthquake cycle by alternately locking and releasing asperities, which are derived from geodetic coupling (Li et al., 2018) and geological rupture (Wang et al., 2013) studies.

Our results show a good match to convergence-parallel interseismic velocities from the geodetic observations of McKenzie and Furlong (2021). Considering the subsidence signal in the geological record, a good fit can be obtained by a combination of coseismic slip and early afterslip. We find that our results are largely determined by the slab geometry, although factors like asperity configurations, downdip limits of the slab-crust interface, and mantle viscosity structure influence the model predictions.

How to cite: Qin, W., Govers, R., D’Acquisto, M., Barlow, N., and Riva, R.: Bridging geological and geodetic observations for the 1700 Cascadia earthquake with an earthquake cycle model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2188, https://doi.org/10.5194/egusphere-egu24-2188, 2024.

The 2021 Maduo MS7.4 earthquake occurred in the Jiangcuo fault with left-lateral strike-slip movement. In order to study the movement and deformation characteristics of the Jiangcuo fault before the Maduo earthquake and further analyze the seismogenesis process of the continental strong earthquake, the large-scale strain rate field distribution in western China, the locking degree and the evolution of slip deficit rate of the Jiangcuo fault, and the rupture mechanism of seismogenic fault are analyzed and discussed in this paper using the GPS velocity field on a long time scale and InSAR dynamic velocity field. The results show that: (1) The strain rate field in EW direction shows that the Maduo earthquake is located at the edge of the EW direction strong compression zone of Bayanhar block. The eastern part of the Maduo earthquake is a compression strain accumulation zone, and the western part is a gradual transition from weak compression to tension strain. The results of the maximum shear strain rate field show that the Maduo earthquake is located at the edge and high gradient zone of the high value area of the maximum shear strain rate field. (2) The inversion results of the locking degree show that deep unlocking occurs in some regions in the east and west of the epicenter of the fault during 2015-2021, gradually transitioned to a completely locked state in the middle of the fault, and the focal point of Maduo earthquake is at the edge of the completely locked region in the transition region. The dynamic results from 2015 to 2017 and 2017 to 2019 were basically stable. The whole fracture plane was basically in a state of strong locking, and only partial unlocking with a depth below 15km existed in local areas. From 2019 to 2021, some faults in the east and west of the epicenter have deep and shallow unlocking phenomena, including the overall unlocking of most areas of the western section and the local deep unlocking of the East section of the ruptured fault, while the rapid unlocking of the two sides of the epicenter may contribute to the occurrence of the main earthquake. This work was supported by Science for earthquake resilience (XH23047A).

How to cite: Zhao, J., Yuan, Z., and Wang, Y.: The movement and deformation of the Jiangcuo fault before the 2021 MS7.4 Maduo earthquake reflected by GPS and InSAR data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2226, https://doi.org/10.5194/egusphere-egu24-2226, 2024.

EGU24-2385 | ECS | Posters on site | TS3.1

Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data. 

Chris Milliner, Jean-Philippe Avouac, Saif Aati, James Dolan, and James Hollingsworth

As faults accumulate displacement, they are thought to mature from disorganized and distributed fracture networks to more simplified throughgoing fault structures with a more localized zone of inelastic strain. Understanding the degree of inelastic strain localization holds importance for seismic hazard, as smoother faults are thought to host faster rupture velocities and have different seismic shaking intensities from ruptures along rougher, less mature faults. However, quantifying this evolutionary process of strain localization along major fault systems has been difficult due to a lack of near-field coseismic measurements. Here we test if such an evolutionary process exists by measuring the near-field surface deformation pattern of 17 large (6.0 < Mw < 7.9) continental strike-slip surface ruptures. To do this we use a range of geodetic imaging techniques including, a new 3D optical pixel tracking method, and pixel tracking of radar amplitude data acquired by satellite and UAVSAR platforms. With these geodetic imaging data we measure the total coseismic offset across the surface rupture and difference them from the displacements recorded by field surveys, which we assume captures the on-fault, discrete component of deformation. This differencing allows us to obtain an average magnitude of off-fault deformation for each surface rupturing event, which we compare to a number of known source parameters to test the notion of progressive fault localization. Our results show that progressively smaller amounts of off-fault strain occur along fault systems with higher cumulative displacements, supporting the notion that faults systems localize as they mature. We also find strong correlations of off-fault deformation with the long-term fault slip-rate and the geometrical complexity of the mapped surface rupture, and a moderate correlation with rupture velocity. However, we find a weak-no correlation of off-fault deformation with the fault initiation age and the moment-scaled radiated energy. We also present comparisons of off-fault strain with other known seismic source parameters.

How to cite: Milliner, C., Avouac, J.-P., Aati, S., Dolan, J., and Hollingsworth, J.: Do Faults Localize as They Mature? Insight From 17 Continental Strike-slip Surface Rupturing Earthquakes (Mw > 6.1) Measured by Optical and Radar Pixel Tracking Data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2385, https://doi.org/10.5194/egusphere-egu24-2385, 2024.

EGU24-2389 | ECS | Orals | TS3.1

Decoding inter-seismic deformation: Insights from viscoelastic modeling 

Hugo Boulze, Luce Fleitout, Emilie Klein, and Christophe Vigny

GPS positioning offers millimetric precision in measuring deformation of the lithosphere during the seismic cycle. In particular, during the post-seismic phase, long-lasting and large-scale deformation are measured. They result from the viscoelastic relaxation in the asthenosphere. Consequently, the post-seismic phase is currently modeled using viscoelastic rheologies (e.g., Maxwell or Burgers viscous models). On the other hand, the inter-seismic phase is mainly modeled using purely elastic models. In particular, coupling models, widely used to quantify the accumulation of deformation on the subduction fault, are therefore used to evaluate earthquake hazard. However, such elastic models fail to explain mid-field deformation without the use of an external hypothesis (e.g., a third plate called sliver).

The study of post-seismic deformation has provided important insights into the rheological properties of the asthenosphere during the post-seismic phase. For example, viscous creep has been found Newtonian since the cumulative post-seismic displacements normalized by the co-seismic offset, as a function of distance to the trench, superimpose very well for earthquakes of different magnitudes [Boulze et al. 2022].

By incorporating these different results and using the backslip theory [Savage 1983], we model the inter-seismic phase using viscoelastic models. We explore the impact on coupling distribution along the Chilean subduction zone, in particular discussing differences with the elastic model in terms of depth and lateral extension. We also examine the impact of viscoelastic models in a region of Chile (Taltal region, 25.2°S) where elastic models currently fail to reproduce deformation in the near-field [Klein et al. 2018]. Finally, we show that a 2-Burgers viscous model is necessary to reproduce deformation in Argentina in 2010, before the Maule earthquake.

How to cite: Boulze, H., Fleitout, L., Klein, E., and Vigny, C.: Decoding inter-seismic deformation: Insights from viscoelastic modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2389, https://doi.org/10.5194/egusphere-egu24-2389, 2024.

We have developed a 3D viscoelastic finite element model to study processes that control the postseismic deformation due to the 2021 M8.2 Chignik, Alaska earthquake. Our model employs a bi-viscous Burgers rheology to represent the viscoelastic relaxation of the upper mantle and the first two years GPS data after Chignik event as constraints.

Initially, we investigated the viscoelastic relaxation mechanism and stress-driven afterslip mechanisms individually. We then attempted to reconcile their contributions by assessing the misfit between observed and simulated displacements. And, it is assumed that the afterslip evolution is governed by rate-strengthening friction. The results show that there exists a substantial misfit between the simulated and the observed value of the optimal model under the viscoelastic relaxation mechanism. Notably, at one observation site in the near-field, the observed displacement exceeds 200 mm, whereas the simulated value only less than 5 mm. Similarly, the optimal solution of simulated value under the afterslip mechanism does not align well with the observed value. Furthermore, we also utilized different frictional properties on updip (0-40 km) and downdip (40-100 km) regions of the coseismic rupture. The preferred misfit in this model is lower than that obtained using the model with a uniform friction parameter, but there is still a discrepancy between the simulated and observed values. These results indicate that neither the afterslip nor viscoelastic relaxation mechanisms alone can fully explain the total postseismic deformation.

Subsequently, we utilized an integrated model to simultaneously extract the contributions from both mechanisms. The combined modeling results indicate that the near-field postseismic displacements are dominated by both mechanisms together. However, in the far-field, deformation is primarily controlled by afterslip, with minimal influence from the viscoelastic relaxation mechanism. The inferred frictional properties on the updip and downdip regions of the coseismic rupture exhibit significant differences, which likely reflect variations in fault zone materials at different depths. And the optimal model supports a viscoelastic rheology for the continent mantle, with a steady-state viscosity is 1×1019Pa•s and the transient viscosity is 1×1018Pa•s. 

How to cite: Dong, P. and Zhao, B.: Afterslip and viscous relaxation on the postseismic deformation following the M8.2 Chignik, Alaska earthquake , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2967, https://doi.org/10.5194/egusphere-egu24-2967, 2024.

EGU24-6640 | ECS | Orals | TS3.1

Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake 

Wenqian Yao, Jing Liu_Zeng, Yann Klinger, Guiming Hu, Yanxiu Shao, Xiaoli Liu, Kexin Qin, Zhijun Liu, Zijun Wang, Yunpeng Gao, and Longfei Han

Faults grow through fault lengthening and slip accumulation, which are episodic processes related to the repetition of earthquakes. It is most often recorded in geomorphology. Meanwhile, the activity and seismic hazard of the ‘slow-moving’ faults are often overlooked due to their weak imprints in landforms, especially at their initial formation stage. The 2021 Mw 7.4 Maduo earthquake triggered a ~158-km long surface rupture along the poorly-known and geomorphically subtle Jiangcuo fault, which is one of the distributed faults in the Bayan Har block and splays that merge with the Kunlun Pass fault. The slip rate of the Jiangcuo fault is thus crucial for comprehending how the strain is distributed between the major and subsidy faults in the complete fault system of the Bayan Har block, as well as the broader deformation process at a large scale. In this study, we present three sites where the Jiangcuo fault left-laterally displaces Holocene geomorphic features (e.g., terraces, fans, and channels). Through the detailed interpretations of high-resolution Digital Elevation Models (DEMs), field investigations, and credible Optically Stimulated Luminescence (OSL) dating of displaced geomorphic features, we document an average left-lateral slip rate of 2.1 ± 0.2 mm/yr since ~12 ka of the Jiangcuo fault. Furthermore, we conservatively updated existing slip rates of the large strike-slip faults (East Kunlun fault, Ganzi-Yushu-Xianshuihe fault) bounding the Bayan Har block. Synthesizing the slip rate of the Jiangcuo fault with the updated rates of the bounding faults, our findings suggest that the Jiangcuo fault accommodates ∼10% of the total deformation in the Bayan Har block. This study provides valuable insights into the impact of younger faults on regional deformation processes.

How to cite: Yao, W., Liu_Zeng, J., Klinger, Y., Hu, G., Shao, Y., Liu, X., Qin, K., Liu, Z., Wang, Z., Gao, Y., and Han, L.: Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6640, https://doi.org/10.5194/egusphere-egu24-6640, 2024.

Strike-slip faults of considerable scale play a pivotal role in accommodating crustal deformation resulting from the Cenozoic India-Eurasia collision. The manner in which strike-slip motion is transferred along faults remains a topic of ongoing debate. In this study, we have meticulously compiled millennial strike-slip rates and GPS-derived strike-slip data along the extensive ~1800 km East Kunlun Fault (EKF). Our objective is to discern the slip distribution pattern and evaluate the mode of strike-slip transfer. The findings reveal a segmented pattern of strike-slip activity, characterized by a consistently high strike-slip rate exceeding 10 mm/yr along the central segments. In contrast, the eastern segment exhibits a reduced slip rate, measuring less than 5 mm/yr, and further diminishes to approximately 1 mm/yr along its eastern fault tip zone. Notably, strike-slip drop events occur within the fault bending zone, or in areas where the fault bifurcates, forming a horsetail structure. To complement our observational insights, numerical modeling has been employed to validate that the fault geometry may serve as a crucial controlling factor in the observed variation of strike-slip rates, Additionally, it influences the local stress situation along the fault, further contributing to the earthquake risk along the fault and the associated hazards impacting the local area.

How to cite: Zhang, Y. and Jiao, L.: Mechanism of Strike-slip Transfer along the East Kunlun Fault in Northern Tibet, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7062, https://doi.org/10.5194/egusphere-egu24-7062, 2024.

EGU24-7436 | ECS | Orals | TS3.1

Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data  

Yingfeng Zhang, Sam Wimpenny, Luca Dal Zilio, and Xinjian Shan

Strain partitioning between strike-slip faults within mountain ranges and thrust faults along their margins is a common process that accommodates oblique plate convergence in continental collision zones. In these settings accumulated strain is periodically released by earthquakes on the strain-partitioned fault systems, which threatens the densely populated foreland areas. An extreme earthquake rupture scenario in these settings is that multiple faults rupture simultaneously releasing the built up strain – an example being the 2016 Mw 7.8 Kaikoura earthquake where a cascading rupture occurred on many separate faults with different kinematics. Recent work suggests that such cascading ruptures may occur in fault systems that are coupled in the shallow crust that are being loaded by a deeper, creeping fault.

 

This study focuses on understanding earthquake risks in the northern Qilian strain-partitioned fault system, which is important due to the populated areas nearby. We investigate its 2-D kinematic models using available geodetic measurements under a Bayesian inversion frame. Our results prove that the kinematic models of the northern Qilian strain-partitioned fault system can be well determined, and compatible of the geological measurement and seismicity distribution. In contrast to the frequent thrust earthquakes, any thrust faults are not required to explain the available geodetic data indicating that the short-term geodetic measurements cannot reflect the thrust fault kinematics of the northern Qilian Shan in the geological time-scale. The non-thrust fault involved model also present a highly locked wedge beneath the foreland area, reconciling the supposed historical cascading earthquake ruptures in north Qilian Shan.

How to cite: Zhang, Y., Wimpenny, S., Dal Zilio, L., and Shan, X.: Strain partitioning and fault kinematics in the Northern Qilian Shan (NE Tibet) determined from Bayesian inference of geodetic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7436, https://doi.org/10.5194/egusphere-egu24-7436, 2024.

Geometric complexity plays an important role for a fault’s seismotectonic behavior as it affects the initiation, propagation and termination of an earthquake and influences stress-slip relationships, fault-segment size, and the probability of multi-segment rupture. Consequently, geometric fault complexity is studied intensively and increasingly incorporated into computational earthquake rupture simulations. These efforts reveal a problem: While a natural fault’s geometry may be well quantifiable at the surface (i.e., the fault trace), its down-dip buried portion cannot be well constrained. At this point, it is not clear how this epistemic uncertainty affects the propagation of individual ruptures and a fault’s seismotectonic behavior (e.g., large-earthquake recurrence).

We address this issue computationally with a physics-based multi-cycle earthquake rupture simulator (MCQsim), enabling us to investigate various aspects of rupture propagation and earthquake cycle in a controlled environment (e.g., with well constrained fault geometry). We approximate fault geometric complexity as a 2-D random field using the “random midpoint displacement” method which allows us to represent fault roughness (i.e., incorporate its epistemic uncertainty) while keeping the fault surface trace unchanged. 

Using MCQsim, we create 20kyr-long synthetic earthquake catalogs for strike-slip faults that share the same complex fault surface trace but have different sub-surface fault geometries. We analyze the resulting variations in single-event rupture propagation (i.e., the kinematic source model) and long-term seismotectonic behavior. We find that kinematic source models of individual events differ substantially between different realizations of sub-surface geometry. However, the long-term seismotectonic behavior (e.g., large-earthquake recurrence) does not differ as much and is less sensitive to the epistemic uncertainties of sub-surface fault geometry.

How to cite: Zielke, O. and Mai, P. M.: Exploring the effects of sub-surface fault geometry on rupture propagation and long-term fault behavior, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7556, https://doi.org/10.5194/egusphere-egu24-7556, 2024.

EGU24-7990 | ECS | Orals | TS3.1

Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data 

Guoguang Wei, Kejie Chen, and Luca Dal Zilio

The geometry of faults regulates the spatial patterns of interseismic, coseismic, and post-seismic surface deformation. Geodetic techniques can measure these deformation patterns during a seismic cycle and are expected to constrain the geometry of  seismogenic faults. However, the conventional linear inversion of geodetic data is unable to simultaneously estimate the fault slip distribution and the fault geometry. In this study, we propose a Bayesian framework that treats fault geometry as a time-invariant parameter. It can individually use coseismic deformation data or simultaneously utilize interseismic, coseismic, and post-seismic deformation data to invert for both fault slip distribution and non-planar fault geometry. Within this framework, geometry evidence informed by geophysical imaging, geological surveys, and microseismicity forms the basis for establishing the prior probability density function, while geodetic observations constitute the likelihood function. Our methodology provides an ensemble of plausible geometry parameters by sampling the posterior probability distributions of the parameters using Markov Chain Monte Carlo simulation. The performance of the developed method is tested and demonstrated through inversions for synthetic oblique-slip faulting models. Results demonstrate that assuming constant rake can significantly bias fault geometry estimates and data weighting. Additionally, considering the variability of slip orientations allows for plausible estimates of non-planar fault geometry with objective data weighting.We applied the method to the 2013 Mw 6.5 Lushan earthquake in Sichuan province, China. The results reveal dominant thrust slips with left-lateral components and a curved fault geometry, with the confidence interval of the dip angles ranging between 20° and 25° and 56° and 58°. Furthermore, the application of this method to the 2015 Gorkha earthquake in Nepal sheds light on the Main Himalayan Thrust, which serves as the interface between the Indian Plate and Eurasia. This may provide new insights into future seismic potential and topographic growth in the Nepal Himalaya.

How to cite: Wei, G., Chen, K., and Dal Zilio, L.: Development of a Bayesian non-planar fault geometry inversion using geodetic seismic cycle deformation data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7990, https://doi.org/10.5194/egusphere-egu24-7990, 2024.

EGU24-8280 | ECS | Orals | TS3.1

Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis 

Jin Fang, Tim Wright, Kaj Johnson, Qi Ou, Richard Styron, Tim Craig, John Elliott, and Andy Hooper

Earthquakes release strain energy that has accumulated between seismic events. Measuring strain accumulation rates is critical for understanding earthquake cycle and assessing earthquake potential, with fault slip rates serving as essential inputs for seismic hazard models. However, the Tibetan Plateau has been lacking comprehensive estimates of geologic slip rates on numerous faults. To address this gap, geodetic data have been invoked to derive fault slip (or slip deficit) rates using various methodologies. These include the commonly adopted classic and deformable block modelling approaches (Meade & Loveless, 2009) and the newly developed direct inversion of geodetic strain rates (Johnson et al., 2022), which has the advantage of not requiring blocks to be defined.  A comprehensive comparison of slip rates obtained from these different geodetic methods has been notably absent.

In this study, we focus on the southeastern Tibetan Plateau, utilising Sentinel-1 satellite data from 35 ascending and 32 descending frames spanning the period between 2014 and 2023, along with published GNSS velocities. We constructed high-resolution (1 km) maps of velocity and strain rate fields covering 1.3 million km2. Using these maps, we derived slip rates on newly mapped faults (Styron, 2022) using classic block modelling, “deformable block” modelling, and by the direct inversion of strain rates. Our strain rate fields reveal a partition through focused shear on the Kunlun fault, the Xianshuihe-Xiaojiang fault system, the Longriba fault, the Longmenshan fault possibly influenced by the ongoing postseismic deformation of the 2008 Mw 7.9 Wenchuan earthquake, and the Lijiang-Xiaojinhe fault. On the deforming plateau there is diffuse deformation away from the major faults, with average shear strain and dilatation rates of 14.3 and 13.1 nanostrain/year, compared to 9.4 and 11.1 nanostrain/year in the Sichuan basin (which likely reflects the noise floor in the data). The geodetically-determined slip rates from the three methods generally align with available geologic rates, particularly along-strike variations on the Kunlun fault and the Xianshuihe-Xiaojiang fault system. Our block model consists of 103 blocks bounded by 326 fault sections in the southeastern Tibetan Plateau. The model is constrained by the combined geodetic horizontal velocities from 6617 observation points. Classic block modelling without considering internal strain tends to overestimate slip rates on faults that slip faster than 5 mm/yr, compared to deformable block model that accounts for homogeneous intrablock strain, constituting 5% of the total. The two block models explain approximately 45-50% of the geodetic strain, predicting focused strain on block boundaries even in the absence of observed strain concentrations. By directly inverting strain rates, we suggest that 40-50% of the geodetic strain is attributable to elastic coupling (back slip) on faults, while the remaining can be explained by off-fault distributed moment sources (body forces) in a thin elastic plate. We discuss limitations of different geodetic approaches in modelling deformation (velocities or strain rates) and implications for seismic hazard by comparing the seismic moment release rate from earthquakes and the geodetic moment accumulation rate from our geodetic models.

How to cite: Fang, J., Wright, T., Johnson, K., Ou, Q., Styron, R., Craig, T., Elliott, J., and Hooper, A.: Kinematics of the Southeastern Tibetan Plateau from Sentinel-1 InSAR and GNSS: Implications for Seismic Hazard Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8280, https://doi.org/10.5194/egusphere-egu24-8280, 2024.

EGU24-9097 | ECS | Posters on site | TS3.1

Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey 

Nicolas Harrichhausen, Julia de Sigoyer, Yann Klinger, Cengiz Yildirim, Melike Karakaş, and Baptiste Camus

We present preliminary results from a paleoseismic study of the middle branch of the Northern Anatolian Fault (MNAF) in Turkey. Despite low instrumental seismicity and geodetic slip rates (~2.5 mm/yr) relative to the northern branch, historical, archeological, and paleoseismic studies indicate the MNAF has hosted several damaging earthquakes in the last two millennia. Recent geomorphic and bathymetric analyses reveal segmentation of the MNAF that may indicate strain partitioning of normal and strike slip along parallel fault strands. However, it remains uncertain whether these fault segments have ruptured simultaneously. Geologic studies have constrained right-lateral slip rates to between 2 and 5.3 mm/yr, with most results contrasting against the present-day geodetic slip rate of ~2.5 mm/yr. Whether this represents a reduction in strain rate along this branch of the Northern Anatolian fault is not clear. Our study has two main objectives: first, to delineate the earthquake history along the newly identified segment of the MNAF beneath Lake Iznik and map its onshore extensions to the east and west of the lake; second, to determine the right-lateral slip rate of the MNAF across different temporal scales. We will present preliminary results from geomorphic mapping, electromagnetic conductivity and ground penetrating radar surveys, and paleoseismic trenching aimed at achieving these objectives. By further establishing the earthquake history and length of the new branch beneath Lake Iznik, we aim to ascertain whether this segment has ruptured concurrently with parallel and along-strike segments, allowing us to estimate paleo-earthquake magnitudes and maximum rupture lengths. Concurrently, by constraining the slip rate of the MNAF over time, we seek to understand whether slip along this branch has decreased and if this reduction is linked to a subsequent increase in slip rate on either the northern or southern branch of the Northern Anatolian Fault.

How to cite: Harrichhausen, N., de Sigoyer, J., Klinger, Y., Yildirim, C., Karakaş, M., and Camus, B.: Understanding strain partitioning, segmentation, and the slip-rate history of the Middle Branch of the Northern Anatolian fault, Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9097, https://doi.org/10.5194/egusphere-egu24-9097, 2024.

EGU24-9399 | ECS | Posters on site | TS3.1

A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures 

Tristan Montagnon, Sophie Giffard-Roisin, James Hollingsworth, Erwan Pathier, Mauro Dalla Mura, and Mathilde Marchandon

Precise estimation of ground displacement from correlation of optical satellite images is fundamental for the study of natural disasters. In the case of earthquakes, characterizing near-field displacements around surface ruptures provides valuable constraints on the physics of earthquake slip. Recently, image correlation has been used to investigate the degree of slip localization, and how it may vary as a function of geological parameters (such as fault structural maturity), raising the possibility that slip localization (vs distribution) may be predictable, with important implications for seismic hazard assessment.

Current sub-pixel correlation methods (frequency or spatial domain) all rely on the same general approach: they work at a local scale, with small sliding windows extracted from a pair of co-registered satellite images acquired at different times, and they assume a rigid uniform shift between the two correlation windows. However, in the near-field of fault ruptures, where the correlation window spans the fault discontinuity, this hypothesis breaks down, and may bias the displacements. Additional smoothing associated with the correlation window further complicates the interpretation of sharp features in the displacement field, artificially shifting displacement to the off-fault region.

We developed a U-net-based method to solve the sub-pixel displacement estimation problem at a global scale. Such architecture is able to retrieve full scale surface displacement maps, making use of both global and local features, and potentially tackling different noises of the input images. We trained our model with real satellite acquisitions, warped with ultra-realistic synthetic displacement maps representing realistic faults. The model exhibits promising preliminary results, showcasing its capability to retrieve full-scale surface displacement maps with high accuracy. While direct comparisons with other state-of-the-art approaches (COSI-Corr and MicMac) are pending, our findings suggest that our proposed U-net-based approach has the potential to compete or even outperform these correlators. 

How to cite: Montagnon, T., Giffard-Roisin, S., Hollingsworth, J., Pathier, E., Dalla Mura, M., and Marchandon, M.: A new deep-learning approach for the sub-pixel correlation of optical images in the near-field of earthquake ruptures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9399, https://doi.org/10.5194/egusphere-egu24-9399, 2024.

Geometrical irregularities of faults drive stress heterogeneities that strongly affect the seismic rupture. Here we analyze the effect of fault topography and remote stresses during the interseismic phase on the static stress pattern around faults and on the onset of failure. The analytical solution is derived using perturbation theory for a defined interface topography. We apply our solution for the static stress field near the East Anatolian Fault and we show that a large stress barrier is developed around the segment that ruptured during the Mw 7.8 Kahramanmaraş Earthquake. Considering stress field conditions that are associated with left-lateral strike slip on the fault, we show how the barrier location is affected by the fault geometry, while the amplitude of stress variations are sensitive to the background stress values and their directions. The solution predicts that the value of the accumulated elastic energy in the host rock around the fault is maximal in the barrier region suggesting that in this area the elastic energy available for potential slip is the largest. We therefore suggest that the length of the ruptured segment and magnitude of the strong Kahramanmaraş Earthquake were greatly influenced by the stress heterogeneity generated by the fault geometry during the long interseismic period. This example of the East Anatolian Fault shows that the geometry of the fault is crucial for the location and the extent of earthquakes along it. We further suggest that the presented analytical approach provides a simple yet powerful new tool for assessing seismic hazards before earthquakes occur.

How to cite: Sagy, A., Morad, D., and Lyakhovsky, V.: Stress, energy, and the onset of failure around geometrically irregular faults: Example from the East Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9615, https://doi.org/10.5194/egusphere-egu24-9615, 2024.

EGU24-9782 | Orals | TS3.1

Detection of slow slip events along the southern Peru - northern Chile subduction zone 

Jorge Jara, Romain Jolivet, Anne Socquet, Diana Comte, and Edmundo Norabuena

Detections of slow slip events (SSEs) are now common along most plate boundary fault systems at the global scale. However, no such event has been described in the south Peru - north Chile subduction zone so far, except for the early preparatory phase of the 2014 Iquique earthquake. We use geodetic template matching on GNSS-derived time series of surface motion in Southern Peru - Northern Chile to extract SSEs hidden within the geodetic noise. We detect 33 events with durations ranging from 9 to 40 days and magnitudes from $M_w$~5.6 to 6.2. The moment released by these aseismic events seems to scale with the cube of their duration, suggesting a dynamic comparable to that of earthquakes. We compare the distribution of SSEs with the distribution of coupling along the megathrust derived using Bayesian inference on GNSS- and InSAR-derived interseismic velocities. From this comparison, we obtain that most SSEs occur in regions of intermediate coupling where the megathrust transitions from locked to creeping or where geometrical complexities of the interplate region have been proposed. We finally discuss the potential role of fluids as a triggering mechanism for SSEs in the area. 

How to cite: Jara, J., Jolivet, R., Socquet, A., Comte, D., and Norabuena, E.: Detection of slow slip events along the southern Peru - northern Chile subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9782, https://doi.org/10.5194/egusphere-egu24-9782, 2024.

EGU24-11002 | ECS | Posters on site | TS3.1

Simulating normal fault interactions during complex seismic sequences in the southern Apennines 

Constanza Rodriguez Piceda, Zoë K. Mildon, Yifan Yin, Billy J. Andrews, Claudia Sgambato, Martijn van den Ende, and Jean Paul Ampuero

Active faults with low extension rates can generate large magnitude earthquakes with severe damages, as exemplified in the southern Apennines (Italy) by the Irpinia earthquake (Mw 6.8) in 1980 and the Val D’Agri earthquake (Mw 7.1) in 1857. These earthquakes occur within a network of faults, and geological evidence (e.g. paleoseismic trenching) suggest that earthquake activity varies from decennial to millennial time scales on such fault systems. Therefore, improving our understanding and forecasting capabilities of seismic sequences in these areas is crucial. However, studying fault behaviour in slowly deforming regions can often prove challenging due to the long recurrence intervals and low slip rates of these faults, which results in limited instrumental, historical and paleoseismological records.

To address this issue, we use physics-based numerical models, since they allow for controlled experiments that can span thousands of years with relatively low computational costs, thus they are valuable tools to investigate the causal dynamics between seismic events. Here, we model a system of NW-SE oriented normal faults in the southern Apennines, accounting for the variable slip rates and geometry of the faults. The study region is characterized by areas with variable number of across-strike faults, thus it is suitable to study the effects of fault network geometry (across-and along-strike interaction) on the seismic cycle and earthquake statistics (e.g. recurrence time, coefficient of variation) of a geologically realistic fault network. We use the boundary-element code QDYN which incorporates rate-and-state friction and elastic interactions to examine relevant inputs for seismic hazard assessment, including inter-event time within and between faults, magnitude-frequency distribution, and nucleation location. We are able to simulate spontaneous ruptures following power-law relationships of frequency-magnitude distribution. Differences in the recurrence time (periodic vs. aperiodic cycles) and rupture extent (characteristic vs. non-characteristic seismicity) in the fault planes seem to correlate with the number of faults that exist across strike. Our simulations demonstrate how quasi-dynamic earthquake simulators can provide insights into how fault network geometry impacts earthquake occurrence and seismic hazard assessment.

How to cite: Rodriguez Piceda, C., Mildon, Z. K., Yin, Y., Andrews, B. J., Sgambato, C., van den Ende, M., and Ampuero, J. P.: Simulating normal fault interactions during complex seismic sequences in the southern Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11002, https://doi.org/10.5194/egusphere-egu24-11002, 2024.

EGU24-12582 | ECS | Orals | TS3.1

Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating. 

Jenni Robertson, Claudia Sgambato, Gerald Roberts, Zoe Mildon, Joanna Faure Walker, Francesco Iezzi, Sam Mitchell, Athanassios Ganas, Ioannis Papanikolaou, Elias Rugen, Varvara Tsironi, Joakim Beck, Silke Mechernich, Georgios Deligiannakis, Steven Binnie, Tibor Dunai, and Klaus Reicherter

We report the first example where the timing of earthquake slip from in situ 36Cl cosmogenic exposure dating of an active normal fault scarp can be verified using independently 14C dated Holocene coastal notches which are deformed along the strike of the fault. We have remodelled 36Cl data from the active Pisia-Skinos normal fault, Greece, published by Mechernich et al. (2018), which indicates that the fault slip rate fluctuated through time. We model the expected coastal uplift and subsidence induced by slip on the fault using elastic half-space models and surface ruptures observed following the 1981 Pisia-Skinos earthquakes. Coastal uplift is constrained by elevation measurements of Holocene coastal notches that have previously been dated using 14C by Pirazzoli et al. (1994) and agree with time periods consistent with Holocene climate stability. We mapped the elevations and numbers of notches along the strike of the Pisia-Skinos fault, including measurements made underwater for locations where fault slip has submerged the notches below the present-day shoreline. We show that the spatial patterns and timing of uplift and subsidence from the notches agrees with the timing of periods of high slip associated with earthquake clusters and quiescence associated with anti-clusters from the slip histories derived from 36Cl data, and with the uplift and subsidence derived from elastic half-space modelling. In particular, where modelled subsidence is highest, Holocene notches that formed between 6-2 ka can be preserved but are submerged. Notches could form at this time because the 36Cl data show that the Pisia fault had entered a period of relative quiescence with a slip-rate of <0.1 mm/yr, accompanied by uplift from the offshore Strava fault. In contrast, rapid slip on the Pisia fault at 1.4 mm/yr between 2 ka and the present-day did not allow notches to form during this time period in the location of highest subsidence. Our example is the first that independently calibrates the timing of slip derived from 36Cl on a fault plane using 14C dates on a deformed coastline, and is consistent with the idea that slip-rate variations can be measured and should be incorporated into seismic hazard assessment.

How to cite: Robertson, J., Sgambato, C., Roberts, G., Mildon, Z., Faure Walker, J., Iezzi, F., Mitchell, S., Ganas, A., Papanikolaou, I., Rugen, E., Tsironi, V., Beck, J., Mechernich, S., Deligiannakis, G., Binnie, S., Dunai, T., and Reicherter, K.: Deformed Holocene coastal notches reinforce the validity of earthquake slip histories implied by in-situ 36Cl exposure fault scarp dating., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12582, https://doi.org/10.5194/egusphere-egu24-12582, 2024.

The seismic chronicle, derived from the analysis of 14 short sediment cores and three long cores from Lake Iznik (NW Turkey), along with the identification of a subaquatic fault segment belonging to the Middle Strand of the North Anatolian Fault (MNAF), provides insights into both local seismicity and the regional seismic activity over the last 6000 years.

The integration of this seismic chronicle with ground-motion estimations at the core locations for all historical earthquakes, together with the evolution of sedimentation rate through time, allow to discuss the epicentral region and epicentral intensity of each historical earthquake in the western NAF system. This analysis also helps us to discriminate which earthquake is likely to generate an event deposit in the case of several historical earthquake candidate, especially when chronological uncertainty are larges

This approach allows a discussion of the factors influencing the threshold (sedimentation rate, ground motions at different spectral frequencies ) for triggering an event deposit in the Lake Iznik and the type of slope destabilization that can be triggered .

Thanks to these finding and through the established scaling relationship it is then possible to infer a minimum intensity for prehistoric earthquakes recorded in Lake Iznik at a given period.

Combining these data with paleoseismological data from the region allows us to propose a scenario for the long-term seismic cycle of the western NAF system.

How to cite: de Sigoyer, J., Domenge, J., Céline, B., Gastineau, R., Sabatier, P., and Duarte, E.: Information on past seismicity of the western NAF system (Turkey) combining ground-motion models with historical earthquakes and event deposits recorded in the sediments of Lake Iznik (NAF system, Turkey), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12894, https://doi.org/10.5194/egusphere-egu24-12894, 2024.

EGU24-13043 | ECS | Posters on site | TS3.1

PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS) 

Maureen Llinares, Lucilla Benedetti, Ghislain Gassier, and Sophie Viseur

Markov Chain Monte Carlo (MCMC) algorithms are sampling approaches relying on Bayesian inference, theorized in the late 1940s and used in many applications (multi-dimensional integral computations, probability law explorations, inversion problems, etc.). MCMC methods are computationally expensive and many variants have been proposed to optimize them Today, MCMC algorithms are used as inversion tools in different contexts: from receiver functions in seismology . The success and efficiency of those methodologies depends on: the complexity of the forward function, the efficiency of the MCMC strategy and the implementation language. The last MCMC sampler is the No U-Turn Sampler or NUTS (Hoffman and Gelman, 2011), an evolution of the Metropolis Hastings (HMC).

Estimating seismic history along fault scarps from 36Cl profiles is a typical inversion problem. Thus, previous studies have proposed MCMC routines to the forward function described in (Schlagenhauf et al., 2011), to invert 36Cl data and to infer seismic histories on fault scarps  (Beck et al., 2018; Mechernich et al., 2023; Tesson and Benedetti, 2019). The complexity of the forward function implies the necessity of a powerful MCMC sampler such as NUTS (Liesenfeld and Richard, 2008).

Here, we discuss these different approaches and present a new approach, termed as PyMDS, which relies on the NUTS algorithm. We implemented the code in python and performed synthetic tests to evaluate the algorithm ability to retrieve seismic histories.The results for three earthquakes synthetics tests will be presented and show that the algorithm is capable of finding the seismic scenario (ages, slips and slip rate) with a precision of few hundred years on the ages, 10 to 30 cm on the slips and inferior 0.05 mm/yr on the slip rate with a runtime of 4 hours (faster than the previous Fortran code published by Tesson & Benedetti (2019) that required 3 days to complete). We will also present preliminary results obtained on the five sites located on the Velino-Magnola fault system and the implication on seismic cycle. Finally, we will discuss potential improvement and development perspectives, such as the optimization of the forward function, the necessity to invert slips and the parametrization of the NUTS algorithm.

How to cite: Llinares, M., Benedetti, L., Gassier, G., and Viseur, S.: PyMDS, a Bayesian inversion algorithm for chlorine 36 dating based on the last No-UTurn Sampler (NUTS), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13043, https://doi.org/10.5194/egusphere-egu24-13043, 2024.

EGU24-13133 | ECS | Orals | TS3.1

Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities. 

Francesco Iezzi, Marco Francescone, Alberto Pizzi, Anna Maria Blumetti, Paolo Boncio, Pio Di Manna, Bruno Pace, Tommaso Piacentini, Felicia Papasodaro, Francesco Morelli, Marco Caciagli, Massimo Chiappini, Francesca D’Ajello Caracciolo, Valerio Materni, Iacopo Nicolosi, Vincenzo Sapia, and Stefano Urbini

Features such as fault geometry and slip-rates are key inputs to assess the seismic hazard imposed by either ground motion or fault displacement. However, complexities in the geology of faults, such as relay zones and along-strike fault bends, could lead to settings characterized by high segmentation, with multiple splays arranged both along and across strike. In order to assess the seismic hazard associated with such fault sectors, it is necessary to establish whether the 3D shallow deformation is equally spread over the multiple fault splays or the activity tends to localise on specific splays. This problem is enhanced when these faults are located within urban areas, and therefore their surface expression is altered by intense anthropic activity.

Within the framework of a work on the mitigation of the fault displacement hazard associated with the Mt. Marine active normal fault (Central Italy), we have performed two paleoseismological surveys within the town of Pizzoli (about 10 km NW of L’Aquila), where the fault is expressed with several splays arranged both along and across-strike. The trenches were planned to explore (i) potential fault scarps altered by human activity, identified through aerial photographs, LiDAR and fieldwork analysis, and (ii) discontinuities in the stratigraphic record highlighted by geophysical investigations (ERT, GPR) and borehole data.

The paleoseismological surveys intercepted five fault splays arranged across-strike, three synthetic and two antithetic to the main Mt. Marine fault. The fault splays show evidence of multiple Late Pleistocene/Holocene surface-rupturing seismic events, marked by colluvial wedges and infilled fractures. Moreover, we constrained the Late Pleistocene slip-rate of the Mt. Marine fault splays by dating and correlating Late-Pleistocene paleosols found (1) outcropping in the footwall of one of the inner fault splay and (2) in a borehole located just at the hangingwall of the outermost splay.

Our results show that the fault splays exhibit different and variable activity rates, suggesting that fault activity is localized on specific fault splays through space and time with the potential to rupture simultaneously during large earthquakes. Our findings have strong implications on fault-based seismic hazard assessments, as they imply that data collected on one splay may not be representative of the behaviour of the entire fault.

How to cite: Iezzi, F., Francescone, M., Pizzi, A., Blumetti, A. M., Boncio, P., Di Manna, P., Pace, B., Piacentini, T., Papasodaro, F., Morelli, F., Caciagli, M., Chiappini, M., D’Ajello Caracciolo, F., Materni, V., Nicolosi, I., Sapia, V., and Urbini, S.: Slip localization on multiple fault splays accommodating distributed deformation across normal fault complexities., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13133, https://doi.org/10.5194/egusphere-egu24-13133, 2024.

Previous studies have constrained the fault slip rates and block geometries of the SoutheasternTibetan Plateau (SETP) with contradictory results due to complex deformation patterns, limited datasets, and subjective choices of block boundaries. In this work, we address the issue of uncertain block geometries by employing an unsupervised machine learning (Euler pole clustering) algorithm that automatically resolves regions that behave as rigid blocks (clusters) using ~1000 GNSS velocity vectors. The optimal clustering results, determined by F-test and Euler-vector overlap analyses, indicate 4 elongated blocks exist in the SETP that are approximately parallel and delineated by a set of arcuate sinistral-slip faults. Our clustering results redefine the kinematicsof the SETP region with new block definitions which elucidate the dominance of sinistral-slipfaults.

How to cite: Xu, R. and Liu, X.: Clustering of GNSS Velocities Using Unsupervised Machine Learning in the Southeastern Tibetan Plateau: Block Identification and the Dominance of Sinistral-slip Faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13534, https://doi.org/10.5194/egusphere-egu24-13534, 2024.

EGU24-14326 | Orals | TS3.1

Low-angle normal faulting triggered by fluids 

Carolina Pagli, Alessandro La Rosa, Derek Keir, Gareth Hurman, Hua Wang, Cecile Doubre, Renier Viltres, Martina Raggiunti, and Atalay Ayele

In extensional settings under Andersonian mechanics, low-angle normal faults should not form in favour of steeply dipping normal faults. However, InSAR shows that a seismic sequence including an earthquake with magnitude Mw 5.6 on August 1st, 2023 (NEIC - National Earthquake Information Center) at the northern end of the Afar rift was caused by normal faulting on a low-angle 35° dipping plane. Our best-fit InSAR model shows that the low-angle normal fault occurred on the west margin of the rift axis, it was relatively deep (6.7 km) and it slipped fully seismically, having a geodetic magnitude of Mw 5.66 in agreement with the global seismic recordings (NEIC). Temporally, the faulting occurred at the end of a one-year period (December 2022-December 2023) of increased seismicity in the northern sector of Afar, with swarms of seismicity migrating northward along the rift. The seismic characteristics, fault location and kinematics are consistent with the low-angle normal fault being triggered by fluids that locally could be released by a deep magmatic heat source along the rift axis under high extensional stresses. Our observations show that low-angle normal faults can form in rifting settings, are activated seismically and are likely fluid-induced.

How to cite: Pagli, C., La Rosa, A., Keir, D., Hurman, G., Wang, H., Doubre, C., Viltres, R., Raggiunti, M., and Ayele, A.: Low-angle normal faulting triggered by fluids, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14326, https://doi.org/10.5194/egusphere-egu24-14326, 2024.

EGU24-16153 | ECS | Posters on site | TS3.1

Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece) 

Zoe Mildon, Manuel Diercks, Gerald Roberts, Joanna Faure Walker, Athanassios Ganas, Ioannis Papanikolaou, Vassilis Sakas, Jennifer Robertson, Claudia Sgambato, and Sam Mitchell

Loading and deformation during the interseismic period of the earthquake cycle is often considered to be constant for continental faults, therefore assuming that the short-term (annual-decadal) deformation is representative of longer-term deformation. Based on this assumption, geodetically-derived deformation rates are sometimes used to infer the slip-rates and thus seismic hazard of faults. However geological observations indicate that deformation and slip rates are variable over a range of timescales, and we present an observation of variable deformation across an active normal fault occurring on an annual timescale. The Pisia-Skinos normal fault in the Gulf of Corinth, Greece, is a well-known fault which slipped most recently during a sequence of damaging earthquakes in 1981. Using vertical deformation data, available from the European Ground Motion Service (EGMS), we observe uplift/subsidence of the footwall/hangingwall of the Pisia fault between 2016-2021. Of particular interest is our observation that the deformation is not uniform over the 6 year time period, instead there is an up to 7-fold increase in the vertical deformation rate in mid-2019. We hypothesise that this deformation is aseismic as there is no temporally correlated increase in the earthquake activity (M>1). We explore four possible causative mechanisms  for observed deformation; shallow slip, post-seismic after-slip, deep slip on an underlying shear zone, and post-seismic visco-elastic rebound. Our preferred hypothesis is that the transient deformation is caused by centimetre-scale slip in the upper 5km of the Pisia fault zone, based on the magnitude and spatial extent of the deformation. Our results suggest that continental normal faults can exhibit variable deformation over shorter timescales than previously observed, implying that the interseismic period of the earthquake cycle on continental faults may be more variable than previously hypothesised. This also highlights potential pitfalls of using slip rates measured over short-timescales to infer seismic hazard.

How to cite: Mildon, Z., Diercks, M., Roberts, G., Faure Walker, J., Ganas, A., Papanikolaou, I., Sakas, V., Robertson, J., Sgambato, C., and Mitchell, S.: Transient aseismic vertical deformation during the interseismic cycle across the Pisia-Skinos normal fault (Gulf of Corinth, Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16153, https://doi.org/10.5194/egusphere-egu24-16153, 2024.

EGU24-16171 | Orals | TS3.1

Fast stress-loading and -unloading below the seismogenic zone 

Claudia Trepmann, Lisa Brückner, and Fabian Dellefant

At depth just below the seismogenic zone of the continental crust, i.e. at greenschist facies conditions, stresses increase during seismic rupturing within minutes from differential stresses on the order of a few tens of MPa to several hundreds of MPa. These fast stress-loading rates are manifested in characteristic microfabrics in fault rocks (cataclasites and pseudotachylytes) exhumed from these depths. The microfabrics indicate quasi-instantaneous cataclasis of almost all rock-forming minerals including garnet and quartz, as well as mechanical twinning of pyroxenes, amphiboles and titanite. In combination with experiments, the microfabrics can be used as paleo-stress gauges, i.e., paleopiezometers. The characteristic microstructures can occur distributed over the whole width of large-scale thrust faults, as the Silvretta basal thrust in the Central European Alps. There, twinned amphiboles record transient differential stresses of more than 400 MPa in a rock volume to about 300 m above the basal thrust exposed at the contact to the Penninic units of the Engadine window over several tens of km. Fast stress-unloading is indicated by growth of new undeformed quartz grains along cleavage cracks in host quartz generated coeval with seismic rupturing and missing evidence of quartz dislocation creep after pseudotachylyte formation. This fast stress-loading and unloading is recorded in pseudotachylytes, i.e., close to the seismic rupture, whereas at larger distance to the seismic rupture accelerated creep at hundreds of MPa occurs on a longer time scale. 

How to cite: Trepmann, C., Brückner, L., and Dellefant, F.: Fast stress-loading and -unloading below the seismogenic zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16171, https://doi.org/10.5194/egusphere-egu24-16171, 2024.

EGU24-16276 | ECS | Orals | TS3.1

Triggered and recurrent slow slip in North Sulawesi, Indonesia 

Nicolai Nijholt, Wim Simons, Taco Broerse, and Riccardo Riva

Nearby faults interact with each other through the exchange of stress. However, the extent of fault interaction is poorly understood. In particular, closely tied tectonic systems like crustal-scale faults that are right next to subduction zone interfaces are likely to express such interactions. Interactions may lead to slow-slip activity, resulting in episodes of transient surface motion.

Our study concentrates on Northwest Sulawesi (Indonesia), which hosts two fault zones with potential for major earthquakes and tsunamis: the strike-slip Palu-Koro fault and the Minahassa subduction zone. Both fault zones accommodate 4 cm/yr of interseismic relative motion. Thanks to a 20-year-long effort in geodetic monitoring, we are able to identify multiple periods during which surface velocities deviate from their interseismic trend. The most recent episode followed the 2018 Mw7.5 Palu earthquake.

We use a Bayesian methodology with forward predictions of slip on the two fault interfaces to match the observations following the 2018 Mw7.5 Palu earthquake, and infer that both deep afterslip on the Palu-Koro fault and slow slip on the Minahassa subduction interface have caused the observed transient surface motion. This finding represents the first recording of a slow slip event on the Minahassa subduction interface. We also speculate that the subduction interface and the strike-slip fault are likely interacting on a regular basis, affecting the seismogenic potential of both parts of this tectonic system.

How to cite: Nijholt, N., Simons, W., Broerse, T., and Riva, R.: Triggered and recurrent slow slip in North Sulawesi, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16276, https://doi.org/10.5194/egusphere-egu24-16276, 2024.

EGU24-16670 | Orals | TS3.1

Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake 

Rob Govers, Celine Marsman, Femke Vossepoel, Ylona van Dinther, and Mario D'Acquisto

Geodetic data covering different phases of the earthquake cycle provide a great opportunity to improve our understanding of the processes and parameters governing the dynamics at subduction margins. However, quantifying the individual contributions of physical processes such as viscoelastic relaxation, afterslip, and (re)locking throughout the earthquake cycle remains challenging. Moreover, it is relevant to account for these processes within a rheological framework that is consistent over the entire earthquake cycle. We address this using Bayesian inference in the form of an ensemble smoother, a Monte Carlo approach that represents the probability density distribution of model states with a finite number of realizations, to estimate geodynamic model parameters. Prior estimates of the imperfect physical model are combined with the likelihood of noisy observations to estimate the posterior probability density distribution of model parameters.

 

We construct a 2D finite element seismic cycle model with a power-law rheology in the mantle. A priori information, such as a realistic temperature field and a coseismic slip distribution, is integrated into the model. Model pre-stresses are initialized during repeated earthquake cycles wherein the accumulated slip deficit is released entirely. We tailor the last earthquake to match the observed co-seismic slip of the 2011 Tohoku earthquake. The heterogeneous rheology structure is derived from the temperature field and experimental flow laws. Additionally, we simulate afterslip using a thin, low-viscosity shear zone with a Newtonian rheology. We focus on constraining power-law flow parameters for the mantle, and the shear zone viscosity.

 

We assimilate 3D GEONET GNSS displacement time series acquired before and after the 2011 Tohoku earthquake. The data require separate viscoelastic domains in the mantle wedge above and below ~50 km depth, and in the sub-slab mantle. Power-law viscosity parameters are successfully retrieved for all three domains. The trade-off between the power-law activation energy and water fugacity hinders their individual estimation. The wedge viscosity is >1019 Pa·s during the interseismic phase. Postseismic afterslip and bulk viscoelastic relaxation can be individually resolved from the surface deformation data. Afterslip is substantial between 40-50 km depth and extends to 80 km depth. Bulk viscoelastic relaxation in the wedge concentrates above 150 km depth with viscosities <1018 Pa·s. Landward motion of the near-trench region occurs during the early postseismic period without the need for a separate low-viscosity channel below the slab.

How to cite: Govers, R., Marsman, C., Vossepoel, F., van Dinther, Y., and D'Acquisto, M.: Bayesian Inference of Rheological Parameters from Observations Before and After the Tohoku Earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16670, https://doi.org/10.5194/egusphere-egu24-16670, 2024.

Shallow creep, as a widespread phenomenon in the earthquake cycle, plays an important role in understanding the behavior of faults and seismic hazards. However, it is still under debate whether creeping is an inherent behavior of fault or is a form of afterslip following large earthquakes. The East Anatolian Fault was recently ruptured by the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, providing a unique opportunity to investigate the relation between shallow creep and earthquakes along strike-slip fault. Here, we show the spatial distribution and temporal evolution of creeping segments along the EAF using the InSAR phase-gradient stacking method. We derive the shear-strain rates in three periods – before the 2020 earthquake, between the 2020 and 2023 earthquakes, and after the 2023 earthquake sequence. By comparing the spatial distribution of the interseismic strain rates, the coseismic slip, and the post-seismic strain rates, we document a tight connection between creeping and coseismic slip on the two recent earthquakes. We also investigate the temporal behavior of faults following the two earthquakes using time-series shear strain analysis. The results reveal behaviors of shallow creep on different segments of the EAF with different statuses before the earthquakes. Our results shed new light on understanding the mechanism of creeping and its relation with large earthquakes during the earthquake cycle.

How to cite: Liu, Z. and Wang, T.: Shear-strain rates across the East Anatolian Fault (EAF) response to the 2020 Mw6.8 Elazig, and 2023 Mw7.8/Mw7.6 Kahramanmaras earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18092, https://doi.org/10.5194/egusphere-egu24-18092, 2024.

EGU24-18562 | Posters on site | TS3.1

Insights into the site-to-site correlation of paleoseismic data  

Nicolás Pinzon and Yann Klinger

Integration of paleoseismic data from multiple sites is important to assess the past fault rupture scenarios and determine an earthquake chronology for the entire fault system. However, the current methods used to combine paleoseismic data are diverse and lack theoretical foundations from a mathematical perspective. We present a method to evaluate and integrate paleoseismic event data from multiple sites into a single earthquake time history. We apply this method to the central-eastern fault sections of the Altyn Tagh Fault using data from ten fault trenches. Applying a Bayesian approach we constructed time-stratigraphic models that yield the probability density functions corresponding to the age of individual earthquakes at each site. Then, our method to integrate these data consists of two main steps: 1) we constructed a rupture pool with all the modeled event ages, and we evaluated the overlapping degree between the site PDFs; 2) For sufficiently contemporary PDFs we combine them by computing the weighted-mean method which emphasizes the overlap in the site earthquake times. The weighted-mean method yields smaller earthquake-time uncertainties compared to the rupture-mean approach and is consistent with the earthquake rupture assumptions behind the integration of paleoseismic data and the probability theory of density functions. This approach helps to clarify the timing and rupture extent of past earthquakes along central-eastern ATF and is essential to improve the earthquake probability assessment for the region.

How to cite: Pinzon, N. and Klinger, Y.: Insights into the site-to-site correlation of paleoseismic data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18562, https://doi.org/10.5194/egusphere-egu24-18562, 2024.

Following large earthquakes, postseismic crustal deformations are often observed. They include the afterslip and the viscoelastic deformation of the crust and the upper mantle, activated by the coseismic stress change. In order to predict the future deformations, and the stress change distributions, it is important to divide each deformation. The physical parameters; frictional properties of the fault and the rheological properties are the key to determining the slip behavior, but they are generally unknown.

Data assimilation (DA) studies have attempted to estimate the frictional properties directly from the observational data. DA incorporates the observed data into the physics-based model to construct a more plausible model. When DA works well, we can obtain the physics-based model, including the physical properties, that can quantitatively explain the observed data. The constructed physics-based model can be used to simulate the slip evolution beyond the data period, i.e., prediction of the deformation.

There are two types of DA technique applying to nonlinear system, the sequential method called as Ensemble Kalman filter method (EnKF) and the variational method called as 4DVAR. For the fault system, EnKF is applied to the deformation data to estimate the physical variables (van Dinther et al., 2019, Hirahara and Nishikiori, 2019). 4DVAR is also applied to the afterslip assuming elastic medium to estimate the fault frictional properties (Kano et al., 2015; 2020). If the physics-based model under consideration is linear, the sequential and the variational methods are consistent, but this is not the case for fault systems.

In this presentation, I construct a simple model that include the fault slip that follows the rate- an state- friction law and the viscoelastic deformation. Then I apply both EnKF and 4DVAR, and compare the results to discuss the characteristics of the methods.

How to cite: Ohtani, M.: Numerical experiments on estimating the fault frictional properties and the viscosity from the postseismic deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19405, https://doi.org/10.5194/egusphere-egu24-19405, 2024.

EGU24-20077 | ECS | Orals | TS3.1

Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations 

Floriane Provost, Volkan Karabacak, Jean-Philippe Malet, Jérôme Van Der Woerd, Mustapha Meghraoui, Frédéric Masson, Matthieu Ferry, David Michéa, and Elisabeth Pointal

On February 6, 2023, southern Türkiye was hit by two major earthquakes at 01:17 UTC (Mw 7.8, Pazarcık, Kahramanmaraş) and at 10:30 UTC (Mw 7.6, Elbistan, Kahramanmaraş) leading to severe damages at the complex junction of the Dead Sea Fault (DSF), the Cyprus arc and the East Anatolian fault zone (EAFZ). The ruptures propagated along several known strands of the southwestern termination of the EAFZ, the main Pazarcık and Karasu valley faults and the Çardac-Sürgü fault. The spatial extent of the impacted zone (300 x 300 km) supports the use of satellite images to map ruptures and damages and measure the co-seismic displacement over the whole region. Among the different satellite constellation available nowadays, Sentinel-2 presents the advantages of offering high-resolution images (10 m), global coverage with frequent revisit time and open access policy to the images. We here present the high-resolution mapping of the entire coseismic surface ruptures derived from image correlation of optical Sentinel-2 satellite acquisitions. We further estimated the rupture width, the total and on-fault offset, and of the diffuse deformation obtained a few days after the two mainshocks along the two main ruptures at 50 m resolution along the rupture. The mapping and the estimation of the offset are validated with the location of the rupture and the offset measurements collected on the ground. We found that the ruptures extend over lengths of 310 km and 140 km, with maximum offsets reaching 7.5±0.8 m and 8.7±0.8 m near the epicenters, for the Mw 7.8 and Mw 7.6 mainshocks, respectively. We propose a segmentation of the two ruptures based on these observations, and further discuss the location of potential supershear rupture. The use of optical image correlation complemented by field investigations along earthquake faults provides new insights into seismic hazard assessment.

How to cite: Provost, F., Karabacak, V., Malet, J.-P., Van Der Woerd, J., Meghraoui, M., Masson, F., Ferry, M., Michéa, D., and Pointal, E.: Co-seismic fault offsets of the 2023 Türkiye earthquake ruptures using Sentinel-2 satellite imagery and field observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20077, https://doi.org/10.5194/egusphere-egu24-20077, 2024.

EGU24-20361 | ECS | Posters on site | TS3.1

3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault 

Adélaïde Allemand, Liqing Jiao, and Yann Klinger

Knowing about the geometry of both (i) ruptured zones during seismic events, and (ii) faults throughout seismic cycles, as well as the evolution of this geometry, is important to understand what is controlling the start and the ending of large earthquakes. In this study, we use 3D Discrete Element Modeling (DEM) in order to simulate a strike-slip fault, formed from an initially homogeneous, intact medium representing brittle rock that is submitted to tectonic loading. Indeed, this numerical method models the crust as an assembly of rigid spheres which are linked by user-defined interactions and reconfigurate very naturally when subjected to loading. Therefore, such approach is adapted to study the evolution of fault geometry through earthquake cycles, since it permits to simulate large displacements of the particles, while avoiding prescribing fault location and geometry, and letting such geometry evolve freely.

A 3D parallelepipedic model is designed and then indefinitely sheared by assigning periodic boundary conditions. The particular feature of our model is the implementation of a healing phenomenon, a key process which allows fractured zones to restrengthen after a slip event. During the simulation, the position of particles and the state of their bonds are recorded at regular time intervals; consequently, the shape and dimension of deformation are evaluated, the evolution of fault geometry is monitored, and the stresses in the domain can be measured. Results show a stick-slip behaviour which can be identified as earthquakes separated by locking periods. In addition, the amount of displacement and the rupture surface can be estimated and enable the computation of a magnitude-like quantity. Thus, earthquake-like events seem to follow a magnitude-frequency relationship, and earthquake-like surface deformations are comparable to observations of ground deformation after real size earthquakes. Eventually, the evolution of the fault geometry during the simulation is also scrutinized.

How to cite: Allemand, A., Jiao, L., and Klinger, Y.: 3D discrete element modeling for the simulation of seismic cycles on a strike-slip fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20361, https://doi.org/10.5194/egusphere-egu24-20361, 2024.

EGU24-293 | ECS | Orals | TS3.3

Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya 

Jyoti Tiwari, Surendra S. Bhakuni, Pradeep Goswami, and Anil Tiwari

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.

How to cite: Tiwari, J., Bhakuni, S. S., Goswami, P., and Tiwari, A.: Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-293, https://doi.org/10.5194/egusphere-egu24-293, 2024.

There is a growing interest among seismologists on the nonlinearity of seismic processes, corresponding to the synergetic approach to the development of the Earth as a nonlinear, open, self-organizing system. In the analysis of very complex multi-component geological-geophysical systems, it is important to assess the degree of their nonlinearity based on a set of control parameters. For the analysis of the seismic process, we propose to use seismic-tectonic stress in the Earth's crust and lithosphere as a control parameter. Also, in the analysis of processes releasing tectonic stresses in the form of earthquakes, the synergetic of choosing the initial state becomes important.

To choose the initial state of the Earth's crust and lithosphere, we consider them as an oscillatory block-hierarchical system, interconnected and developing over time but differing in various layers of the Earth's crust – sedimentary, consolidated crust, lower crust, and mantle beneath the Moho boundary, as each layer has its lithological properties and is in different physical conditions, at least due to the change in pressure. Block sizes are determined based on the thickness of the layer, and vertical planes of the block are determined based on the morphology of the layer, as well as the presence of a fault inside the block. Changes in the seismic-tectonic deformation vector indicate a change in the initial state of seismic-tectonic deformation of each block. Thus, for the analysis of the nonlinear seismic process, we obtain a continuous series of changes in seismic-tectonic stresses in different layers and for each block of the layer. Thanks to the known time of deformation changes, as well as the known size of each block, we have an approximation of the nonlinear oscillatory process in the block-hierarchical system of the Earth's crust and lithosphere, manifested as seismicity. Within the designated time interval, the seismic-tectonic deformation process in each block follows a linear law. We have tested our methodological approaches to the analysis of the nonlinear seismic process in the example of the Crimean-Black Sea region. We have processed earthquakes contained in the new catalog of seismic events for the period 1970-2012, recalculated according to the Seismological Bulletins of the USSR and Ukraine. The method of Aki was used to determine the seismic-tectonic deformation regime by constructing averages foci by the signs of the first arrivals of P-waves taken from the bulletins. Time series of changes in seismic-tectonic deformation regimes in different layers of the Earth's crust and lithosphere show that each layer has its peculiarities of deformation but fits into the general context of tectonic processes in the region. One of the interesting features of the tectonic process in the region turned out to be the unexpected variability of regimes and their duration from 2 to 10 years in different areas of the Crimean-Black Sea region. An important consequence of our study is the definition of clear spatial-temporal frameworks for the analysis of the amounts of seismic energy release in each of the blocks, which will improve the quality of seismic risk assessment for individual regions.

How to cite: Shumlianska, L. and Vilarrasa, V.: Approximation of nonlinear seismic processes based on space-time series of changes in seismotectonic deformation regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-641, https://doi.org/10.5194/egusphere-egu24-641, 2024.

The faults and the fault zones are essential to determine the seismotectonic features and the regime of a region and to produce seismic hazard and risk maps. Many geophysical methods, such as seismic, magnetic and gravity are used to determine the location and direction of faults. This study aims to detect potential fault edges located in the south-southwest of Nisyros Island and west of Tilos Island in the southeastern Aegean Sea and to interpret the seismic activity and faulting characterization. To this end, the potential fault edges were initially detected using the total horizontal derivative method on the gravity dataset collected from the WGM2008 database. The obtained spatial locations were combined with the seismicity and the focal mechanisms of the earthquakes. The detected fault has a northeast-southwest orientation with normal faulting. It was proved that this obtained fault is not included in the active faults of the Eurasia database (AFEAD), European Fault - Source Model 2020 (EFSM20) database and the Mineral Research and Exploration General Directorate (MTA) active fault map. Moreover, this observed fault was detected as longer than the fault shown on the National Observatory of Athens (NOAFAULTs) in terms of length. Consequently, it is highly recommended that this potential fault, which produces earthquakes with a moment magnitude greater than 4.0 (on instrumental period) must be added to such fault databases to increase and spread the knowledge of seismological and seismotectonic research.

How to cite: Tamtaş, B. D. and Toktay, H. D.: Seismotectonic interpretation and edge detection of the potential fault on the SE Aegean Sea using the total horizontal derivative method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-785, https://doi.org/10.5194/egusphere-egu24-785, 2024.

EGU24-1278 | ECS | Posters on site | TS3.3

Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia 

Tamar Shikhashvili, Mariam Mariam Bekurashvili, Anzor Giorgadze, Aleksander Razmadze, Onise Enukidze, and Victor Alania

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region (e.g., Cavazza et al., 2023). 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 Kura foreland basin (Alania et al., 2023). Our study area is located within the LC-GC convergence zone in the western Kura foreland basin and is represented by the lenticular-shaped compressional basin formed by northward and southward-directed thrusting. 2D seismic reflection profiles revealed the presence of triangle zones at the frontal part of the LC retro-wedge and GC pro-wedge. According to analog, seismic, and sequential kinematic modeling results, the frontal part of the GC is represented by a double wedge-dominated triangle zone and is characterized by the presence of passive, active wedges and passive-forethrust. In the frontal part of the LC orogen, the syn-kinematic (Middle-late Miocene) strata have been deformed and uplifted by passive-back thrusting at the triangle zone. Seismic reflection profiles show north-vergent duplex and structural wedge at the triangle zone beneath the thrust front monocline and is represented by Cretaceous-Paleogene strata. Western part of the triangle zone of the Kavtiskhevi-Akhalkalaki area is introduced by south-vergent imbricated fan (passive-back thrusts). The imbricated fan is characterized by fault-propagation folding. The kinematic evolution of south-vergent fault-propagation folds is related to northward propagating duplex. Recent and historical earthquakes and paleoseismic data indicate that the frontal part of LC and GC is tectonically active (e.g., Stahl et al., 2022; Tsereteli et al., 2016).

 

Reference

Alania, V., et al. (2023). Interpretation and analysis of seismic and analog modeling data of triangle zone: a case study from the frontal part of western Kura foreland fold-and-thrust belt, Georgia. Frontiers in Earth Sciences 11, 1195767.

Cavazza, W., et al. (2023). Two-step exhumation of Caucasian intraplate rifts: a proxy of sequential plate-margin collisional orogenies, Geoscience Frontiers 15, 101737.

Stahl, T. A., et al. (2022). Recent Surface Rupturing Earthquakes along the South Flank of the Greater Caucasus near Tbilisi, Georgia. Bull. Seism. Soc. Am. XX, 1–19.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328-344.

How to cite: Shikhashvili, T., Mariam Bekurashvili, M., Giorgadze, A., Razmadze, A., Enukidze, O., and Alania, V.: Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1278, https://doi.org/10.5194/egusphere-egu24-1278, 2024.

EGU24-1557 | Posters on site | TS3.3

Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia 

Mariam Bekurashvili, Tamar Shikhashvili, and Victor Alania

Our study area, Tbilisi urban area is located in the eastern Achara-Trialeti fold-and-thrust belt. The Achara-Trialeti fold-and-thrust belt, which is one of the good examples of collision-driven far-field deformations, is located within the northernmost part of the Lesser Caucasus orogen and is associated with Arabia-Eurasia convergence. Our interpretation has integrated seismic reflection profiles, several oil wells, and surface geology data to reveal the deformation structural style of the eastern Achara-Trialeti fold-and-thrust belt. Fault-related folding theories were used for seismic interpretation. Seismic reflection data reveal the presence of south-vergent and north-vergent fault-propagation folds, duplexes, and structural wedge. Interpreted seismic reflection profiles, structural cross-section, and recent earthquakes reveal the presence of an active blind thrust fault and structural wedge(s) beneath Tbilisi and the surrounding area. The structural model shows that the 2002 Mw 4.5 Tbilisi earthquake was related to a north-vergent blind thrust and the Kumisi and Teleti earthquakes are related to a north-vergent blind wedge thrust system.

How to cite: Bekurashvili, M., Shikhashvili, T., and Alania, V.: Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1557, https://doi.org/10.5194/egusphere-egu24-1557, 2024.

EGU24-1713 | Posters on site | TS3.3

The Valsugana area (TN, Italy): a structural knot 

Silvana Martin, Laura Montresor, Pina Zambotti, Giovanni Monegato, Guido Roghi, Gianluca Piccin, Alessia Modesti, and Francesco Gosio

In the Valsugana area (Southern Italian Alps) a NE-SW trending pre-permian Southalpine phyllitic basement is intruded by an Early to Middle Permian granitoids (Cima d’Asta,190 km2) and includes volcanic calderas of the Athesian Volcanic Group (125 km2) of the same age, and is locally covered by Upper Permian to Miocene sedimentary sequences. A complex system of faults juxtaposes these different geological domains. In particular, the Permian tectonic structures have been repeatedly reactivated during Mesozoic and Tertiary. The phyllitic basement, which suffered Variscan metamorphism and deformation, and the granitoids were dismembered by NNW-SSW and N-S tectono-magmatic faults associated with the opening of permian calderas. The main tectonic system of this area is the ENE-WSW oriented Valsugana fault system of Middle-Late Miocene age (Heberer et al., 2017 ). The master fault separates the metamorphic basement from the sedimentary sequences (e.g., M. Armentera, M. Civerone and M. Lefre). At the footwall of the master fault, other faults deformed in a compressive to transpressive regime the sedimentary sequences. Some of these are extensional faults were reactivated many times from Triassic to Lower Jurassic. The Valsugana fault system ends against the Permian to Mesozoic Calisio fault to the SW, while it continues to the NE towards Brocon and Cereda Passes (Gianolla et al. 2022). The Valsugana fault system is cut across by the Val di Sella fault of Late Miocene-Pliocene age, oriented c.a. E-W which deformed the northern walls of the Asiago Plateau (Barbieri & Grandesso, 2007), transporting slices of metamorphic basement and Permo-Mesozoic sequences to the north, over the Middle Miocene sandstones and marls of Valsugana. The most recent tectonic system consists of a set of NNW-SSE to N-S faults which cut across the ENE-WSW Valsugana and E-W Val di Sella fault systems. The N-S Grigno-Tolvà fault cuts across the Cima d’Asta magmatic complex from Val Vanoi to the north to Asiago Plateau to the south over XX km, and dislocates the Belluno and Val di Sella thrust faults at the footwall of the Valsugana fault system. All these faults are still seismically active.

Barbieri G. & Grandesso P. (2007) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 082, Asiago.

Heberer B., Reverman R.L., Fellin M.G., Neubauer F., Dunkl I., Zattin M., Seward D., Genser J. & Brack P. (2017) - Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation. International Journal of Earth Sciences (Geologische Rundschau), 106:1557–1580.

Gianolla G., Caggiati M. & Riva A. (2022) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 046, Longarone.

How to cite: Martin, S., Montresor, L., Zambotti, P., Monegato, G., Roghi, G., Piccin, G., Modesti, A., and Gosio, F.: The Valsugana area (TN, Italy): a structural knot, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1713, https://doi.org/10.5194/egusphere-egu24-1713, 2024.

EGU24-1794 | Orals | TS3.3

Disaggregation bands as indicator for active blind faults 

Christian Brandes, David Tanner, Haakon Fossen, Matthias Halisch, and Katharina Müller

The identification of active faults is an important step in the seismic hazard evaluation process. However, this task is often difficult because many faults are unknown, buried below younger sediments. Especially in slowly-deforming intraplate areas with long recurrence intervals between individual seismic events, the detection of hidden blind faults is a major challenge. Furthermore, active faults can undergo long episodes of aseismic creep and thus do not produce typical earthquake-related, soft-sediment deformation structures, which also hinders the detection of these faults. Consequently, there is the demand for a robust universal geological indicator for active blind faults. Based on outcrop studies, we are able to show that disaggregation bands (near-surface deformation bands that develop in unconsolidated sediments due to reorganization of the grain fabric) are such an indicator. Disaggregation bands are developed at several locations in Central Europe and Scandinavia, in near-surface sandy sediments above the tip lines of blind faults. The strike of these bands is parallel to the strike of the underlying faults, which indicates that the disaggregation bands formed as a consequence of fault movement. The disaggregation bands internally show a pore-space reduction and in some cases a clear alignment of elongated grains. The thickness of the disaggregation bands increases with the amount of offset along the bands. Based on these observations, we infer that the bands formed in the process zone of propagating faults due to a shear-related reorganization of the grain fabric that leads to strain-hardening and a growth of the bands into centimetre-thick tabular structures. With analogue shearing experiments we show that disaggregation bands can form at a wide range of deformation speeds, even down to speeds several orders of magnitudes lower than seismogenic fault-slip velocities. Thus, disaggregation bands are key structures that record large parts of the seismic cycle and represent a very suitable indicator for active blind faults, even if the related fault creeps without emitting seismic waves. Disaggregation bands can easily be recognized in outcrops and artificial trenches, and previous studies showed that it is possible to even image them with ground-penetrating radar.

How to cite: Brandes, C., Tanner, D., Fossen, H., Halisch, M., and Müller, K.: Disaggregation bands as indicator for active blind faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1794, https://doi.org/10.5194/egusphere-egu24-1794, 2024.

EGU24-1802 | Posters on site | TS3.3

The shear deformation zone along the KTFZ: implications for faulting properties 

Vasileios Karakostas and Eleftheria Papadimitriou

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, a dextral strike slip transform zone, exhibits the fastest rates of relative plate motion in the Mediterranean. Strong (Mw>6.0) earthquakes associated with the fault segments comprised in KTFZ are frequent as historical information and instrumental record reveals. Four main shocks of this order magnitude, among other earthquakes of Mw>5.0 occurred since 2003 on almost along strike adjacent fault segments, with high aftershock productivity extended far beyond the fault tips forming aftershocks zones remarkably wider than expected of strike slip faulting. This enhanced aftershock seismicity is associated with the shear deformation zone surrounding the mainshock rupture plane. It has been suggested that it results from the reactivation of secondary faults, its width decreases as a power law with cumulative fault displacement being narrower around mature faults than around immature faults. As the structural maturity may have a strong impact on earthquake behavior, such as magnitude, stress drop, distribution of slip, rupture velocity, ground motion amplitude, and number of ruptured segments, as prior studies have suggested, we aim at investigating the shear deformation zone along KTFZ. We used the relocated aftershock seismicity of the four recent (2003 – 2015) strong (Mw>6.0) main shocks that occurred on almost along strike positioned strike slip faults for defining the fault width in conjunction with the fault length, as we have already done in the case of the 2015 Lefkada main shock, and the activation of secondary faults, most probably triggered by stress changes and stress redistribution due to the main shock coseismic slip. Detailed slip models, when available, are engaged for this scope for investigating possible triggering of the secondary fault segments taking part in each seismic excitation, due to the stress transfer, taking also into account the stress sensitivity on the geometry and faulting properties of the minor faults, along with the accurately relocated aftershock seismicity. After the main fault width definition, we investigated the decrease of aftershock frequency and spatial density as a function of distance from the main fault.

Acknowledgments: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

How to cite: Karakostas, V. and Papadimitriou, E.: The shear deformation zone along the KTFZ: implications for faulting properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1802, https://doi.org/10.5194/egusphere-egu24-1802, 2024.

EGU24-2168 | Posters on site | TS3.3

Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review 

Federico Pasquaré Mariotto, Alessandro Tibaldi, Fabio Luca Bonali, Noemi Corti, Martina Pedicini, Babayev Gulam, and Tsereteli Nino

The convergence between the Arabian and the Eurasian plates resulted in the development of the Greater Caucasus (GC) and the Lesser Caucasus fold-and-thrust belts, separated across most of their length by the Transcaucasian depression. The whole sub-horizontal shortening of the Caucasus was quantified at hundreds of kilometers and, according to several studies, reached its maximum rate in the Miocene-Pliocene. At present, convergence between the Eurasian and African-Arabian plates is still active, producing widespread deformation within the mountain belt and in surrounding regions, as testified to by seismological, paleoseismological and GPS data.

Understanding the active tectonics of the Caucasus is of paramount importance for a better assessment of geohazards, especially seismic hazard. Moreover, there is a major concentration of residents in Tbilisi, the capital of Georgia, hosting 1.2 million citizens, and in Baku, the capital of the Azerbaijan Republic, with over 2.3 million citizens; both cities are located in active tectonic basins at the southern foothills of the GC. Hundreds of rural villages are scattered in the mountain regions, and all were built without taking into consideration antiseismic criteria. All the above shows that the Caucasus and Transcaucasus regions are subject to an extreme seismic hazard and risk.

Here, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, structural-geological and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, activeWNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, although swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus.

How to cite: Pasquaré Mariotto, F., Tibaldi, A., Bonali, F. L., Corti, N., Pedicini, M., Gulam, B., and Nino, T.: Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2168, https://doi.org/10.5194/egusphere-egu24-2168, 2024.

EGU24-3078 | Orals | TS3.3 | Highlight

Differences in earthquake size distributions for thrusts and normal faults: the case of Italy 

Michele M. C. Carafa and Matteo Taroni

The earthquake size distribution is characterized by an exponential function determined by the b-value parameter. Previous studies have demonstrated the dependence of the b-value on both the differential stress and tectonic settings. This study proposes a novel approach to categorize earthquakes based on the kinematics of interseismic geodetic strain rates and horizontal stress directions. When combined with other geological or geophysical information, incorporating stress directions and geodetic data enhances seismotectonic models, reducing arbitrariness in delineating seismic zones.

Using the Italian peninsula as a case study, we observe a significantly larger b-value for extensional faults than thrusts, albeit with smaller differences than previously reported. Additionally, our findings reveal that the spatial fragmentation of uniform tectonic regimes can lead to inaccurate b-value estimates for single faults due to the undersampling of earthquake size distribution.

How to cite: Carafa, M. M. C. and Taroni, M.: Differences in earthquake size distributions for thrusts and normal faults: the case of Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3078, https://doi.org/10.5194/egusphere-egu24-3078, 2024.

In this research, we combine seismic and tectonic approaches in an attempt to apply the empirical relationships between fault parameters and earthquake magnitudes aiming to assess the maximum possible magnitude for the prediction of intensity ground motion in the areas close to active faults. The case we study is the Talysh area in southern Azerbaijan with the total area of 3960 km². It stretches to 38054'N northern latitude and 48035'E eastern longitude and spreads to the north through the Alborz mountains of Iran. The earthquakes with a higher depth are concentrated mainly in the central part of the Talysh zone (up to 70 km) and in the southwestern part of the Caspian Sea (up to 55 km), with the local magnitude range of up to M5.5.

The earthquake magnitudes calculated on the basis of the surface fault length were compared with the catalogued magnitudes. As a procedure, (1) a comprehensive catalogue of all available known faults was compiled; (2) earthquake magnitude is then derived from fault length; (3) the resulting fault-length-earthquake-magnitudes were compared by the mathematical difference with catalogued earthquake magnitudes; and (4) as a final, intensity simulation of ground motion on near-fault areas was plotted. The results show the approximate consistence of the calculated fault-length-earthquake-magnitude with the catalogued seismicity. The map shows that the highest intensity areas of VII are observed in the central and western parts of the zone. An intensity VI covers majority of the Talysh zone. The results will contribute to the implementing more solid analyses for advancing seismic hazard analysis. Our research emphasizes the seismotectonic areas in southern Azerbaijan where further comprehensive studies on faults are required.

How to cite: Babayev, G., Aliyev, Y., and Aliyev, M.: Magnitude and intensity simulation of ground motion on near-fault areas: the case of Talysh (southern Azerbaijan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3646, https://doi.org/10.5194/egusphere-egu24-3646, 2024.

EGU24-5338 | ECS | Posters on site | TS3.3

A dynamic identification of continuous discontinuities in geodynamic numerical models 

Valeria Fedeli and Anna Maria Marotta

 Discontinuities affect the Earth’s dynamics, yet the Earth is often represented in geodynamical models as a continuous material. The challenge of representing discontinuities in numerical models has been addressed in several ways in literature. The split node method, originally introduced by Jungels (1973) and Jungels and Frazier (1973) for elastic rheology and then modified by Melosh and Raefsky (1981) to simplify its implementation, allows the introduction of discontinuity into a finite element model by imposing an a-priori slip at a designated node, where the displacement depends on the element which the node is referred to. Originally, this method requires that the discontinuity’s geometry and slip are pre-established.

More recently, Marotta et al. (2020) modify this approach by introducing a coupling factor that indicates the percentage difference between the velocities of the element to which the slip node belongs, while the velocity consistently derives from the dynamic evolution of the system. However, this method still requires the pre-establishment of the discontinuity’s geometry.

We here present a new technique that enables the dynamic identification of the discontinuity’s during the thermomechanical evolution of the system, based on physical parameters and without predefining the slip or the geometry.

We have implemented a new algorithm that identifies one or more discontinuities in a finite-element scheme operating through two phases: nucleation and propagation. Nucleation involves selecting a yield physical property and identifying the potential slip nodes, i.e., nodes on which the chosen physical property exceeds a yield value. The nucleus is then identified as the potential slip node where the chosen property most exceeds the yield. Propagation can be performed by choosing between three approaches of propagation: single simple fault, multiple simple fault and single double fault; and three schemes for the identification of neighboring nodes: grid-bounded, pseudo-free and free. The resulting discontinuity is the line connecting the nucleus and the propagation nodes.  Once the discontinuity has been identified, a coupling factor is introduced and the algorithm continues to operate following the Marotta et al., (2020)’s scheme.

The results of several benchmark tests, performed through both simple and complex finite-elements models, confirm the success of the algorithm in recognizing yield conditions and introducing a discontinuity into a finite-element model and demonstrate the correctness of the propagation’s geometry.

References

Jungels P.H.; 1973: Models of tectonic processes associated with earthquakes. PhD thesis.

Jungels P.H., Frazier G.A. Frazier; 1973: Finite element analysis of the residual displacements for an earthquake rupture: source parameters for the San Fernando earthquake. Journal of Geophysical Research.

Marotta A.M., Restelli F., Bollino A., Regorda A., Sabadini R.; 2020: The static and time-dependent signature of ocean-continent and ocean-ocean subduction: The case studies of Sumatra and Mariana complexes. Geophysical Journal International.

Melosh H.J., Raefsky A.; 1981: A simple and efficient method for introducing faults into finite element computations. Bulletin of the Seismological Society of America.

How to cite: Fedeli, V. and Marotta, A. M.: A dynamic identification of continuous discontinuities in geodynamic numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5338, https://doi.org/10.5194/egusphere-egu24-5338, 2024.

EGU24-6061 | Orals | TS3.3

Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China). 

Martine Simoes, Christelle Guilbaud, Jérôme Van der Woerd, Guillaume Baby, Laurie Barrier, Haibing Li, and Jiawei Pan

The Tibetan Plateau stands as a prominent topographic feature at the Earth’s surface, characterized by intense seismic activity, in particular along the mountain ranges that form its bounding edges. To the northwest, the Western Kunlun Range has received increasing attention since the 2015 Mw 6.4 Pishan earthquake but its kinematics of deformation remain to be properly documented. Here, we analyse the terrace record of active deformation along the Karakash River, where it crosses the Hotan anticline. We date terraces using in-situ produced cosmogenic isotopes, and show that terrace incision and uplift are spatially correlated with blind duplex ramps beneath the anticline. From there, we quantify the overall slip rate of the duplex to be 1.2-2.8 mm/yr over the last ~250 kyr. Our data are not able to resolve the detailed kinematics on each blind ramp and we cannot exclude that several of them are active at places along the anticline. By comparison to the data available west of our study area, we propose that the blind structures all along the foothills of the Western Kunlun range have an overall slip rate of ~2 mm/yr. However, the way this slip rate is to be partitioned on one or several blind ramps is expected to vary along strike, generating a certain structural and kinematic segmentation of active deformation, and from there possibly explaining the moderate recorded seismicity in this region. Because this slip is transmitted upward and forward onto the Mazar Tagh wide and geometrically simple frontal thrust sheet, we question the possibility of large – but rare – earthquakes rupturing this structure. From there, we propose the idea of a bimodal seismicity in the region, as a mirror of the structural segmentation of active faults.

How to cite: Simoes, M., Guilbaud, C., Van der Woerd, J., Baby, G., Barrier, L., Li, H., and Pan, J.: Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6061, https://doi.org/10.5194/egusphere-egu24-6061, 2024.

EGU24-6563 | Orals | TS3.3

Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines 

Deborah Di Naccio, Cinzia Di Lorenzo, Marco Battistelli, Simona Miccolis, Vanja Kastelic, and Michele MC Carafa

In the past decade, seismic hazard assessment has progressively relied on innovative approaches based on seismotectonic models for robust physical-based short-term and long-term estimations. For this reason, consistency and homogenization are crucial in collecting data for a scientifically sounding seismotectonic model, especially when dealing with large amounts of information at different temporal and spatial scales. Additionally, a solid probabilistic approach is needed to correctly explore the uncertainties of the seismotectonic model components (e.g., offset, age, long-term slip rate). In this contribution, we focus on the active tectonics of the central Apennines because they have been repeatedly investigated in past decades, and a significant amount of complementary data is available. In such a case, we can define an innovative fault database for seismic hazard assessment, exploring in a probabilistic sense the deformation data (age and offset) and rate (long-term slip rate). Our approach provides a substantial methodological upgrade to fault-based input for seismic hazard assessment. The proposed methodology can be easily exported to zones with scarce data availability.

How to cite: Di Naccio, D., Di Lorenzo, C., Battistelli, M., Miccolis, S., Kastelic, V., and Carafa, M. M.: Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6563, https://doi.org/10.5194/egusphere-egu24-6563, 2024.

EGU24-6771 | Posters on site | TS3.3

Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia 

Victor Alania, Onise Enukidze, Nino Kvavadze, Anzor Giorgadze, Demur Merkviladze, Alexander Razmadze, and Tornike Xevcuriani

The Greater Caucasus orogen is a typical active double wedge orogen that accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Our study area is a central part of the Greater Caucasus pro-wedge and represented by the Dzirula-Imereti Uplift zone and epicentral area of Racha 1991 (MW=7) and 2009 (MW=6) earthquakes - Southern Slope of Greater Caucasus. Here we present a new structural model based on interpreted seismic profiles and regional balanced cross-sections. Seismic reflection data reveals the presence of a basement structural wedge, fault-related folds, triangle zones, and active- and passive-roof duplexes. The most important observation from our study is that the Dzirula massif is a basement wedge and forms a triangle zone. The Dzirula structure is defined by mid-crustal detachment and a roof thrust, constituting a tectonic wedge with a passive back thrust. The regional balanced cross-sections show that the Racha earthquakes are related to crustal-scale duplexes.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Alania, V., Enukidze, O., Kvavadze, N., Giorgadze, A., Merkviladze, D., Razmadze, A., and Xevcuriani, T.: Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6771, https://doi.org/10.5194/egusphere-egu24-6771, 2024.

EGU24-7249 | Orals | TS3.3

Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt 

Daniele Cheloni, Nicola Angelo Famiglietti, Cristiano Tolomei, Riccardo Caputo, and Annamaria Vicari

On September 8, 2023, a magnitude 6.8 earthquake impacted the High Atlas Mountains in western Morocco, approximately 70 km southwest of Marrakesh, resulting in significant devastation and casualties. This study delves into a comprehensive geodetic dataset, utilizing interferometric synthetic aperture radar (InSAR) measurements to analyze the fault segment accountable for the seismic occurrence. Our findings propose two potential fault scenarios: a transpressive NNW-dipping high-angle fault (70°), associated with the Tizi n’Test alignment, or a transpressive SSW-dipping low-angle fault (22°) linked to the North Atlas Fault, where slip (up to 2.2 m) is observed predominantly in deeper sections of the fault. Although seismic catalogs were inconclusive regarding the dip direction of the fault, evidence from mainshock locations, gravity and heat-flow data, along with modeling, and the active shortening direction, collectively indicate the activation of a low-angle, southwesterly dipping oblique thrust of the North Atlas fault during the 2023 Moroccan earthquake. Integrating interferometric analyses with geological, tectonic, and seismological data could be crucial for resolving ambiguities in satellite-based models. This study therefore underscores the complexity of fault identification and the need for a multidisciplinary approach in understanding seismic events.

How to cite: Cheloni, D., Famiglietti, N. A., Tolomei, C., Caputo, R., and Vicari, A.: Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7249, https://doi.org/10.5194/egusphere-egu24-7249, 2024.

EGU24-7666 | ECS | Orals | TS3.3

Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians). 

Martin Šutjak, Rostislav Melichar, Ivo Baroň, Yi-Chin Chen, Jan Černý, Jia-Jiyun Dong, Václav Dušek, Filip Hartvich, Lenka Kociánová, Tung Nguyen, Matt Rowberry, and Chia-Han Tseng

The Outer Western Carpathians are fractured by several syn-thrust and post-thrust faults. One of them, the Mikulov Fault, has been studied using a combination of surface and subsurface methods. The former comprised the analysis of a LiDAR digital terrain model and aerial photographic interpretation while the latter comprised the analysis of ERT profiles and 2D seismic reflection profiles interpreted with the aid of borehole data. Paleostress analysis has also been used to understand the stress history and progressive development of the fault. By combining these methods it has been possible to define a distinct N-S directed fault zone that intersects or delineates the majority of the Jurassic limestone nappe outliers around the highlands of Pavlov Hills. This almost continuous fault zone runs for several kilometers on the Czech side of the border and extends further south into Austria. The thrusted Jurassic limestone bodies are cut by the fault zone, which tectonically crushed the limestone in its core and the cores of the secondary fault branches. The mapped pattern of the fault zone suggests branching and reattaching with the production of lenticular tectonic slices. Consequently, we interpret the fault as a prominent sinistral shear zone. This is indicated on the surface by block displacement on Svatý kopeček Hill and by the orientation of the accompanying subvertical Riedel shears with identified horizontal lineation. Subsurface kinematic indication derives from the interpretation of a prominent negative flower structure in the deep seismic profiles, just beneath the fault zone. The ERT profiles have revealed that the limestone bodies are tectonically bound by accompanying fault branches. Moreover, paleostress analysis suggest that fault zone activity can be divided into three main stages: (i) NE-SW thrust faults indicate thrusting of the Carpathian accretion wedge over the Bohemian Massif; (ii) NE-SW strike-slip faulting, during which the fault blocks moved along the faults in the direction of propagating wedge; (iii) N-S strike-slip faulting, marking the change in compression direction and transition from thrusting to a strike-slip regime. The main movement along the fault is probably of the late Miocene age and probably continues to the present day.

 

The research was funded by the Grant Agency of the Czech Republic (GC22-24206J).

How to cite: Šutjak, M., Melichar, R., Baroň, I., Chen, Y.-C., Černý, J., Dong, J.-J., Dušek, V., Hartvich, F., Kociánová, L., Nguyen, T., Rowberry, M., and Tseng, C.-H.: Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7666, https://doi.org/10.5194/egusphere-egu24-7666, 2024.

EGU24-7731 | ECS | Posters on site | TS3.3

Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations 

Xianwei Zeng, Chunquan Yu, and Gongheng Zhang

The 2021 MS 6.4 Yangbi earthquake occurred near the southwestern boundary of the Chuandian block in the SE Tibetan Plateau. Previous studies found that the mainshock occurred to the west of the main boundary fault – the Weixi-Qiaohou-Weishan fault, but the detailed seismogenic structure of the Yangbi earthquake sequence remains unclear. Accurate spatiotemporal characteristics of aftershocks and precise fault-zone structure are crucial for a more thorough understanding of the seismogenic structure and nucleation mechanisms of the Yangbi earthquake. Five days after the mainshock, we deployed a dense array with 200 short-period nodal seismometers spaced approximately 2 to 3 km in the vicinity of the Yangbi earthquake source region. In this study, we use the three-month-long continuous recordings of the dense array to study aftershock source parameters and fault-zone structures. We first obtained an earthquake catalog containing 88934 high-resolution event locations and 625 high-quality focal mechanisms. The entire aftershock sequence has a complete magnitude of -0.2, and a b-value of 0.97, with earthquake depths concentrated between 1 and 7 km below sea level. Combining precise aftershock locations and focal mechanisms, we constructed a detailed three-dimensional fault-zone structure model for the Yangbi earthquake sequence. The results reveal significant geometric variations in both strike and dip directions of the main fault. Along the dip direction, a conspicuous flower-like structure is present in the shallow part, transitioning to a listric structure inclined to the southwest at deeper levels. Along the strike direction, a noticeable bend exists in the central part. Several conjugate or intersecting faults are also present around the main fault. One of these faults, intersecting the main fault at a depth of about 4 km and dipping to the northeast, is likely the seismogenic fault of the largest foreshock. Additionally, below the main fault, there is another listric fault which appears to connect to the known Weixi-Qiaohou-Weishan fault at the surface. Our study provides new insight into the mechanism of the 2021 Yangbi earthquake sequence. The 3D fault-zone geometry can potentially be used for dynamic source modeling to better understand the initiation and rupture process of the mainshock.

How to cite: Zeng, X., Yu, C., and Zhang, G.: Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7731, https://doi.org/10.5194/egusphere-egu24-7731, 2024.

EGU24-7828 | Orals | TS3.3

3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia  

Onise Enukidze, Victor Alania, Nino Kvavadze, Alexandre Razmadze, Anzor Giorgadze, and Demur Merkviladze

The Rioni foreland basin system is located between the Lesser Caucasus (LC) and the Greater Caucasus (GC) orogens. Deformation of the Rioni double flexural foreland basin was controlled by the action of two opposing orogenic fronts, the LC retro-wedge to the south and the GC pro-wedge to the north (Alania et al., 2022). The Rioni foreland fold-and-thrust belt (RFFTB) is part of the Greater Caucasus pro-wedge.  Here we show the deformation structural style of the RFFTB based on seismic reflection profiles and serial structural cross-sections. On the basis of serial structural cross-sections, 3-D structural models. 2-3D structural models show that the Rioni foreland is a thin-skinned fold-and-thrust belt and the main style of deformation within the RFFTB is represented by a set of fault-propagation folds, duplexes, and triangle zones. The presence of two detachment levels in the RFFTB raises important questions about the deformation sequence. The serial structural cross-sections show that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. The formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. Recent earthquake data indicate that the RFFTB is still tectonically active and earthquake focal mechanisms within the RFFTB are thrust faults (Tsereteli et al., 2016), and active structures are mainly represented by thrust faults, blind thrusts, and blind wedges. 

Acknowledgments. This work was funded by the Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

References

Alania, V., et al. (2022). Deformation structural style of the Rioni foreland fold-and-thrust belt, western Greater Caucasus: Insight from the balanced cross-section. Frontiers in Earth Science 10, 10968386.

Tsereteli, N., et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328–344.

How to cite: Enukidze, O., Alania, V., Kvavadze, N., Razmadze, A., Giorgadze, A., and Merkviladze, D.: 3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7828, https://doi.org/10.5194/egusphere-egu24-7828, 2024.

EGU24-8289 | ECS | Orals | TS3.3

Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy) 

Tiziano Volatili, Veronica Gironelli, Lucia Luzi, Paolo Galli, Michele Carafa, and Emanuele Tondi

The Inner Abruzzi region ranks among Italy's highest seismic hazard areas, hosting a system of SW-dipping normal faults historically active with moderate-to-large earthquakes (Mw ≥ 5.5). The L’Aquila earthquake in April 2009 (Mw = 6.3) intensified interest in assessing active fault seismogenic potential. Despite extensive studies, the Maiella Massif's historical seismicity, notably the 1706 and 1933 earthquakes (Mw ~6.8 and 5.9, respectively), causing severe damage, remains elusive. The investigation of historical seismic events, such as the 1706 earthquake within the Maiella area, aligns with the pressing need to identify and characterize potential seismogenic sources of future seismic activity. This task is often hindered by the scarcity of unambiguous evidence or quantitative data at both near-surface and seismogenic depths. Many source hypotheses, possibly related to the 1706 earthquake, are present in the literature. These structures, with different geometrical parameters, depths, and kinematics, characterized the tectonic setting of this region.

This study offers a comprehensive overview of these hypotheses in assessing the 1706 earthquake’s source. Their 3D geometrical representation was modelled, considering the available geological and geophysical information. The resultant seismic scenarios were estimated in terms of macroseismic intensity by calculating peak ground motion values (i.e., PGV, PGA) for each point within the 1706 macroseismic field. This procedure incorporates site amplification effects into the synthetic ground motion calculations at each site within the macroseismic field, coupling a Vs,30 map of the Italian territory. Finally, the determination of the best source model involves assessing the misfit (residuals) between the simulated macroseismic intensities and the observed ones. The accuracy of the simulated macroseismic field in reproducing the real field is evaluated by calculating the residual mean and the root-mean-square error (RMSE).

The study outcomes highlight the complexities in determining the exact source of the 1706 earthquake. Despite detailed modelling efforts, discrepancies in intensity distributions and the absence of recent seismic activity on specific faults pose uncertainties in understanding seismicity in the Inner Abruzzi area. While contributing to the ongoing debate, the research underscores the need for further investigations to better constrain the seismic hazard of this region.

How to cite: Volatili, T., Gironelli, V., Luzi, L., Galli, P., Carafa, M., and Tondi, E.: Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8289, https://doi.org/10.5194/egusphere-egu24-8289, 2024.

EGU24-9839 | ECS | Posters virtual | TS3.3

Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China 

Nianfa Yang and Zonghu Liao

Characterizing the structures of buried faults is inherently challenging due to a lack of data. However, the seismic survey has demonstrated the potential to reveal geometrical features of faults in the subsurface. In this study, we utilized three-dimensional seismic data and its associated attributes of variance, edge detection, and azimuth for investigating the distribution and structural characteristics of the buried faults in the Bohai Basin, eastern China. The results indicate: (1) there are two 7-km NNE strike-slip carbonate faults (F1, F2, in the Figure) dominated in this region, with fault sub-systems of horst and graben, stepped combinations, and "Y"-shaped; (2) F1 fault is approximately 6.5km with a fault damage zone of about 0.75km in width, and F2 fault is about 7.5km with a fault damage zone of 1.0km in width; (3) The width of fault damage zones increases from south to north, with increasing fault displacement. The maximum fault displacements of F1 and F2 are estimated at 420m and 700m, respectively. We argue that fault displacement leads to the growth of fault damage zones, which potentially controls the evolution of fault architecture. The geometrical information from the subsurface may provide crucial insights for understanding the fault mechanisms and associated earthquakes.

Figure 1. (A) Seismic attribute map of edge detection and time structure showing the two carbonate faults (F1, F2); (B) Measured fault displacement and damage zone width along the fault striking direction of F1 and (C) F2.

How to cite: Yang, N. and Liao, Z.: Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9839, https://doi.org/10.5194/egusphere-egu24-9839, 2024.

EGU24-10101 | Posters on site | TS3.3

Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan  

Alessandro Tibaldi, Fabio Bonali, Federico Pasquaré Mariotto, Paolo Oppizzi, Nino Tsereteli, Hans Havenith, Gulam Babayev, and Tomáš Pánek

We present the main features of the frontal structure, known as Kur Fault, of the Plio-Quaternary Kura fold-and-thrust belt in the Greater Caucasus (Azerbaijan). The Kur Fault has been analysed thanks to geological-structural and geomorphological surveys of its whole length, integrated by a relocation of instrumental seismicity, data on historical seismicity, new focal mechanism solutions, and ambient vibration measurements across the fault trace. The in-depth study of the frontal structure can: i) provide insights into the shallow propagation of a regional reverse fault, ii) contribute to a better understanding of the earlier stage of development of a young continent-continent collision, and iii) have implications for seismic hazard assessment because the area is seismically active and hosts the most important infrastructure for energy production in the country. The results show that the fault deforms the surface for a total length of 123 km. The shallow expression is given by four main scarp segments, with a right-stepping arrangement, which have different structural significance; they are represented by an alternation of fault-propagation folds, folds with offset frontal limbs, and shallow faulting. Analyses of the age of deformed deposits and landforms suggest activity from Mid-Late Miocene times to the Holocene. The fault attitude and its reverse kinematics are coherent with the Holocene and present-day state of stress, characterised by a N-S to NNE-SSW horizontal s1, suggesting the capability for seismic reactivation. Earthquake focal mechanism solutions indicate from pure reverse motions to transpressional kinematics in the area. Calculation of potential Mw indicates values in the range 7.5-7.9 if we consider its entire fault length, 6.1-7.2 if we consider the single segments.     

How to cite: Tibaldi, A., Bonali, F., Pasquaré Mariotto, F., Oppizzi, P., Tsereteli, N., Havenith, H., Babayev, G., and Pánek, T.: Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10101, https://doi.org/10.5194/egusphere-egu24-10101, 2024.

EGU24-10669 | Posters on site | TS3.3

Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy) 

Cinzia Di Lorenzo, Michele Carafa, Deborah Di Naccio, and Vanja Kastelic

The large amount of long-term fault slip rate measurements allows for determining the long-term tectonic moment rate for the central Apennines (Italy). Converting the long-term moment rate in seismicity rates requires a correct estimation of the long-term seismic coupling due to aseismic creep, possibly responsible for some of the observed dislocations. Ignoring this issue could induce a gross overestimation of the regional seismic hazard. Consequently, we must quantify the fraction of tectonic deformation released as earthquakes to correctly use the fault-based approach for forecasting long-term seismicity and assessing the seismic hazard of a region. To this aim, we introduce the seismic coupling in the calculation and treat it as a statistical variable. The probabilistic approach also considers the uncertainties in each parameter of active faults (depth of seismicity cutoff, length, and slip rate). The parameters of a regional Tapered Gutenberg-Richter distribution are determined to reproduce the observed earthquake size distribution. We found that about three-quarters of the long-term tectonic moment rate goes into earthquake activity, suggesting a non-marginal role of aseismic deformation for active faults in the central Apennines.

How to cite: Di Lorenzo, C., Carafa, M., Di Naccio, D., and Kastelic, V.: Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10669, https://doi.org/10.5194/egusphere-egu24-10669, 2024.

EGU24-11665 | Posters on site | TS3.3

Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy) 

Rita de Nardis, Alessandro Vuan, Luca Carbone, Donato Talone, Maria Adelaide Romano, and Giusy Lavecchia

Our study extensively explores the analysis of successive swarms and seismic sequences that followed the 2009 L'Aquila mainshock (Mw 6.3) in the southern-central Apennines of Italy—a region historically recognized for seismic events, some reaching ~M7.

The study area is characterized by active fault alignments well-documented in the geological literature. Bounded eastward by the Fucino-Marsicano-Barrea SW-dipping faults and westward by the southern termination of the Ernici NE NNE-dipping fault systems, it is also crosscut by the Villavallelonga-Pescasseroli–San Donato-Val Comino and the innermost right-stepping en-echelon Balsorano-Posta Fibreno sets, as well as the Sora fault.

Despite its active fault systems, the study area exhibits a low level of seismicity, prompting extensive investigation in previous experiments conducted by temporary seismic networks (Bagh et al., 2007; Romano et al., 2013) and more recent contributions by Frepoli et al. (2017). Notwithstanding, the paucity of seismicity, coupled with the deep geometry of faults and their association with historical earthquakes, remains a topic of ongoing debate in the literature.

Through the application of template matching techniques (Vuan et al., 2018) to enhance the available seismic catalog, we unveil previously undetected low-level seismicity with a completeness magnitude ML ~ 0.0. The space-time evolution of the intense seismicity, along with the characterization of each seismic episode, migration velocity, and Vp/Vs ratios, combined with the 3D distribution of seismicity and geological data, revealed both a clear tectonic influence and the role of fluids in seismic processes. This exploration illuminated previously unknown geometric aspects and provided the first evidence of the WNW-ESE deformation zone in the southernmost segment of the Villavallelonga fault at depths ranging from 11 to 15 km. Our results indicate that deeper seismicity (>16 km) suggests an ascending trend of possible mantle-derived CO2.

These findings significantly contribute: (1) to the understanding of tectonic seismic swarms in extensional domains, (2) to provide insights into fluid involvement in seismic processes, and (3) to the discussion of the seismotectonic setting in high seismic-risk areas. The acknowledgment of the value of microseismicity for regional seismotectonic studies serves as a compelling conclusion, underscoring the broader significance of these findings.

 

Bagh, S., Chiaraluce, L. et al. 2007. Background seismicity in the Central Apennines of Italy: The Abruzzo region case study. Tectonophysics, 444,80–92.

Frepoli, A, Cimini, G.B et al., 2017. Seismic sequences and swarms in the Latium-Abruzzo-Molise Apennines (central Italy): New observations and analysis from a dense monitoring of the recent activity, Tectonophysics, 312-329.

Vuan, A., Sugan, M., et al., 2018. Improving the Detection of Low‐Magnitude Seismicity Preceding the Mw 6.3 L’Aquila Earthquake: Development of a Scalable Code Based on the Cross Correlation of Template Earthquakes. BSSA 108, 471–480.

Latorre, D., Di Stefano, R., et al., 2023. An updated view of the Italian seismicity from probabilistic location in 3D velocity models: The 1981–2018 Italian catalog of absolute earthquake locations (CLASS): Tectonophysics, 846, 229664.

Romano, M. A., de Nardis, et al., 2013. Temporary seismic monitoring of the Sulmona area (Abruzzo, Italy): A quality study of microearthquake locations. NHESS, 13, 2727–2744.

How to cite: de Nardis, R., Vuan, A., Carbone, L., Talone, D., Romano, M. A., and Lavecchia, G.: Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11665, https://doi.org/10.5194/egusphere-egu24-11665, 2024.

EGU24-12862 | ECS | Posters on site | TS3.3

Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series 

Renier Viltres, Cécile Doubre, Marie-Pierre Doin, and Frédéric Masson

The present-day tectonics of the northernmost Africa region is dominated by the oblique convergence
between the Nubia and Eurasia plates initiated 35 Ma ago. GNSS-derived velocities indicate that the
relative plate motion of only ~5 mm/yr is accommodated within a wide region involving inland
and offshore tectonic structures, from Morocco to Tunisia and from the Mediterranean Sea to the Sahara
platform. Due to limited and sparse geodetic measurements, the main zones of strain accommodation as
well as the strain partitioning between thrust and strike-slip faults remain unresolved. However, despite
the low strain budget, significant seismicity and destroying earthquakes have been recorded in the region
with five M>6 events nucleated on both inland and offshore faults during the last decade.

To better identify the active inland faults and constrain their interseismic behavior for a better seismic
hazard assessment in northernmost Africa, we used multi-temporal InSAR analysis to produce the first
regional-scale interseismic velocity map of the region. The primary data consists of up to ~8 years of
SAR imagery from the Sentinel-1 satellite constellation for 6 tracks in both the ascending and descending
orbits. The data processing and the generation of InSAR-based time series describing the spatio-temporal
evolution of surface deformation were performed using the New Small Baselines Subset processing chain
(NSBAS, Doin et al. 2011). We followed a three-blocks processing strategy leading to (1) interferograms
generation, (2) phase unwrapping, and (3) time series estimation. Within the first block, interferometric
networks combining image pairs with short and long temporal baselines were defined to mitigate potential
bias introduced by changes in soil properties (e.g., snow, vegetation growth, dunes). Before unwrapping,
interferograms flattening, multi-looking, and atmospheric phase screen (APS) corrections based on the
ECMWF ERA-5 atmospheric model were implemented. The resulting time series of surface displacement
along the line-of-sight direction (LOS) for the 2014-2022 period were decomposed into the near-vertical
and horizontal (E-W) components and expressed into a Eurasia-fixed reference frame using the GNSS
velocities in Billi et al. (2023).

Our estimated deformation maps reveal multi-scale present-day motions, with large- and small-scale
signals suggesting tectonic origin and ground response to anthropogenic activity or landslides, respectively.
The oblique plate convergence involves the interseismic loading of a series of E-W oriented right-lateral
strike-slip inland faults. Between the longitudes ~3°W and ~9°E, this inland deformation is localized
within a 25-75 km wide zone consistent with a unique linear strike-slip fault without any clear uplift related
to thrusting on already mapped transfer structures. The rates and directions of surface displacements
suggest that the shortening component of the Nubia-Eurasia relative plate motion is almost entirely
accommodated by offshore tectonic structures which has an important impact on the assessment of
seismic and tsunamigenic hazards.

 

 

How to cite: Viltres, R., Doubre, C., Doin, M.-P., and Masson, F.: Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12862, https://doi.org/10.5194/egusphere-egu24-12862, 2024.

EGU24-13778 | Orals | TS3.3

Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array 

Wei-Hau Wang, Yi-Shen Lin, Wei-Cheng Huang, and Strong Wen

We employed dense seismic arrays to reveal the seismogenic zones beneath the foreland basin and the foothills in southwestern Taiwan. We used EqTransformer to pick earthquakes and P and S wave arrival time, GaMMA to associate earthquakes, and NonLinLoc to locate the earthquakes. Our results show that the thin-skinned thrust belts were mostly locked above a shallow decollement at a depth of ca. 6 km. Below it, a foreland-dipping seismogenic belt extends from the base of the shallow decollement to a depth of about 15 km, the deep decollement, beneath the coastal plain. We interpret this westward-dipping seismogenic belt as a passive roof duplex by inversion of the pre-existing graben-and-horst structure sliding along a ductile shear zone at a depth of 15 km during the ongoing orogeny.

How to cite: Wang, W.-H., Lin, Y.-S., Huang, W.-C., and Wen, S.: Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13778, https://doi.org/10.5194/egusphere-egu24-13778, 2024.

EGU24-13981 | Posters on site | TS3.3

Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence 

Chung-Hsiang Mu, Ching-Chou Fu, Hao Kuochen, Kuo-Hang Chen, and Kuo-Wei Chen

Our goal is to comprehend fluid circulation within fault zones and its impact by monitoring hydrochemical and hydrophysical aspects across multiple dimensions. We also monitor nearby micro-seismicity and surface deformation. MAGIC (Multidimensional Active fault of Geo-Inclusive observation Center) is located at the Chihshang creeping fault, situated at the boundary of tectonic plates in eastern Taiwan. This fault exhibits aseismic creep at a rate of 2 cm per year, alongside high seismic activity.

The earthquake sequence of 2022 began with a magnitude 6.4 event on September 17 (local time), followed by a magnitude 6.8 earthquake the next day. The epicenters were within the Central Range fault system, positioned to the west of our monitoring network. This presents a significant opportunity to observe co-seismic changes in pore pressure within the footwall and fault zone.

The findings revealed that after the initial earthquake in the adjacent fault system, the pore pressure within the footwall swiftly decreased by nearly 100 cm within 15 hours. Simultaneously, the pore pressure within the fault zone increased by approximately 25 cm during the same period. Subsequently, the footwall's pore pressure continued to decrease with the second earthquake and then slowly recovered. These alterations in pore pressure suggest that fractures underwent both opening and closure during stress migration.

How to cite: Mu, C.-H., Fu, C.-C., Kuochen, H., Chen, K.-H., and Chen, K.-W.: Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13981, https://doi.org/10.5194/egusphere-egu24-13981, 2024.

EGU24-14319 | Posters on site | TS3.3

Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea 

Seongjun Lee, Youngbeom Cheon, Jong-won Han, Sangmin Ha, Jeong-Heon Choi, Yeong Bae Seong, Hee-Cheol Kang, and Moon Son

The 2017 Pohang earthquake (ML 5.4) ranked as the second-largest instrumental earthquake in Korea and the most destructive seismic event. Before this event, the absence of documented instrumental seismic activity and no mapped Quaternary faults near the epicenter raised questions about the paleoseismic history of the region. This study aims to gather and trace evidences of the paleoseismic ruptures along the surface projection of seismogenic fault, reported by previous study, and interpret their implications. To achieve it, we conducted comprehensive paleoseismological investigations, including geomorphic analysis, fieldwork, drilling survey, trench excavation and numerical age dating. Through geomorphic analysis and drilling survey, we identified two lineaments: NNE–SSW-striking Fault-1 and NE–SW to NNE–SSW-striking Fault-2. In the excavation site of fault-1, stratigraphic features and numerical ages indicate that the PE event occurred between 11±1 ka and 2.6±0.1 ka, and then the MRE event activated after 0.17±0.01 ka.  On the other hand, the combined results of two outcrops of Fault-2 show that the MRE and PE of Fault-2 could be constrained to have occurred between 148±7 ka and ca. 40 ka and around 200 ka, respectively. Our findings present that even before the 2017 Pohang earthquake, seismic events causing surface ruptures of moderate to large magnitude have occurred at least three times in this area during the late Quaternary.

This work was supported by a grant (2022-MOIS62-001) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, South Korea).

How to cite: Lee, S., Cheon, Y., Han, J., Ha, S., Choi, J.-H., Seong, Y. B., Kang, H.-C., and Son, M.: Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14319, https://doi.org/10.5194/egusphere-egu24-14319, 2024.

Kvarner area belongs to the External Dinarides fold-and-thrust belt that is characterized by intensive tectonic deformations of a few kilometers thick sedimentary cover of the central part of the Adriatic microplate. The main deformations occurred predominantly during Eocene to Oligocene thin-skinned tectonics, while late-orogenic thick-skinned deformations and wrenching resulted in the exhumation of the orogenic belt. The latter tectonic mechanism is supposed to be still active, but there is no reported evidence of active faults on the surface of predominantly karstic terrain. Nevertheless, seismological data reveal subsurface activity along various fault plane solutions, and crucial evidence of possible active deformations on the surface is expected within stratified superficial deposits in the area. However, stratified Quaternary sediments are rare onshore and on the Kvarner islands but are widespread on the bottom of the surrounding Adriatic Sea. During the targeted high-resolution sub-bottom geoacoustic seismic survey we focused on the zones that are characterized by earthquakes and on the previously arbitrarily recognized regional seismogenic sources. However, only shallow seismic profiles along and across the Vinodol and the NW part of the Velebit channel revealed clear evidence of fault-related deformations of the youngest Quaternary sediments. The fault zone is up to hundreds of meters wide, limited by parallel sub-vertical fault planes, and characterized by deformations of the strata between the planes either in a positive (uplifted) or a negative (downthrown) manner along the strike, which are typical for strike-slip faults. Besides, the disturbed layering of the uppermost well-stratified unit (Late Pleistocene) resembles fluid/sediment escape structures that could be related to strong shaking during prehistorical earthquakes. The fault zone is also tentatively recognized in the onshore bedrock along the strike of the submerged fault, where it appears as an indistinct fractured zone that is more corroded than surrounding bedrock carbonates. Therefore, sub-bottom profiling has been proven to be a useful tool for identifying active faults and should be used as a key method in future seismotectonic research of submerged seismogenic zones.

How to cite: Korbar, T., Hasan, O., Brunović, D., and Markušić, S.: High-resolution seismic imaging of the sub-bottom Quaternary deposits revealed an active fault in the Vinodol-Velebit channel (Kvarner, Croatia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14660, https://doi.org/10.5194/egusphere-egu24-14660, 2024.

To better understand seismotectonic processes and the associated seismic hazards within a region, it is imperative to explore the causality between earthquakes, active tectonics, and individual fault structures. Hypocenter locations represent a well-established method to identify active faults, their spatial geometry and temporal evolution. First motion focal mechanisms provide insights into source processes and fault kinematics, aiding in the reconstruction of seismic strain and seismogenic stress regimes. Waveform modelling is key to refine earth structure models and constrain source process parameters.

Here, we present the challenging case of the seismic sequence of Saint-Ursanne of March and April 2000 in Switzerland, where we applied advanced seismological analyses to reduce uncertainties in hypocenter locations and focal mechanisms, commonly encountered in shallow seismicity. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which has been approved as a site for the development of a deep geothermal project. Our results, combined with geological data, suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the sequence. These new findings provide new insights into the present-day seismotectonic processes of the Jura fold-and-thrust belt (FTB) of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely <0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement. This transpressive regime is confirmed by the ongoing Réclère earthquake sequence, ca. 20 kilometres west of St. Ursanne, which initiated with a reverse event of ML 4.1 on December 24, 2021, and was followed by few aftershocks in January 2022. Seismic activity started again in March 2023 with another ML4.3 reverse event, which activated a left-lateral strike-slip secondary fault just west of the reverse fault. This fault seems to be more active in terms of microseismicity and is responsible for the increased activity over the last years.  

How to cite: Lanza, F. and Diehl, T.: Deciphering seismic sequences with high-precision hypocenter locations, focal mechanisms, and waveform modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14739, https://doi.org/10.5194/egusphere-egu24-14739, 2024.

EGU24-14973 | Orals | TS3.3

Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area 

Barreca Giovanni, Pepe Fabrizio, Sulli Attilio, Morreale Gabriele, Gambino Salvatore, Gasparo Morticelli Maurizio, Grassi Sabrina, Monaco Carmelo, and Imposa Sebastiano

Archaeoseismic analysis performed in Western Sicily point to deformed archeological remains at Lilybaeum, a Punic coastal city founded in 397 B.C. at the Island’s westernmost edge. Starting from the direct observation of deformed ruins, an interdisciplinary work-strategy, which has included field-structural analysis, drone-shot high-resolution aerial photogrammetry, and geophysical prospecting, was employed to investigate whether the identified deformations may represent the ground effects of a previously unknown large earthquake in the area. Among the unearthed remains, some mosaics and a stone-paved monumental avenue show evidence of tectonic deformation being fractured, folded, and uplifted. Trend of folding and fracturing is consistent with the NNW-SSE oriented tectonic max stress axis to which western Sicily is currently undergoing. Displacement along a fracture deforming the Decumanus Maximus together with the finding of a domino-type directional collapse, enable us to interpret the observed deformation as the ground signature of a coseismic slip. Seismic rupture occurred along a previously unmapped deformation front that well fits in the seismotectonic context of Western Sicily. Measured offset, geophysical prospecting, and age-constraints all point to the possibility that a highly-energetic earthquake nucleated in the area following a coseismic rupture along a NE-SW trending back-verging reverse fault towards the end of the IV century A.D. Since seismic catalogs do not provide evidence of such a large earthquake, the latter might represent a missed event in the historical seismic record. This finding provides constraints to redefine the seismic hazard of Western Sicily, a region where recurrence-time intervals for large earthquakes are still unknown.

How to cite: Giovanni, B., Fabrizio, P., Attilio, S., Gabriele, M., Salvatore, G., Maurizio, G. M., Sabrina, G., Carmelo, M., and Sebastiano, I.: Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14973, https://doi.org/10.5194/egusphere-egu24-14973, 2024.

EGU24-15305 | Posters on site | TS3.3

Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy) 

Mara Monica Tiberti, Francesco Emanuele Maesano, Mauro Buttinelli, Pasquale De Gori, Fernando Ferri, Liliana Minelli, Maria Di Nezza, and Chiara D'Ambrogi

In the Central Apennines (Italy), the project RETRACE-3D provided a reliable 3D model of the crust in the area affected by the 2016-17 Amatrice-Visso-Norcia seismic sequence, highlighting that the coseismic rupture at the surface can involve old inherited normal faults while the seismogenic sources lay at depth, possibly reactivating and inverting previous thrust faults, as in the case of the Mw 6.5 Norcia earthquake (30 october 2016). Here we present a 2D gravity model across the Central Apennines, spanning from the Tyrrhenian coast to the Adriatic Sea, aimed at completing and verifying the crustal geometries resulting from the 3D model itself. The cross-section was built integrating different types of data, such as surface geology, hydrocarbon wells, seismic lines, and results from receiver function analysis. It was then checked against gravity anomalies and the velocity distribution from Local Earthquake Tomography (LET), adding further details, and, finally, against seismicity recorded during the 2016-2017 sequence. The results substantiate the reliability of the geometries proposed in the RETRACE 3D model, as they fit well, except for some local misfits, with the other independent data, such as the Bouguer anomalies and the velocity distribution from LET. Furthermore, the integration of different types of data allowed us to describe in detail the structural setting of the Apennine chain also in the surroundings of the RETRACE study area, where the cross-section length exceeds the 3D model, and to add some new elements at seismogenic depths, that exceed those typical of hydrocarbon exploration. In particular, we were able to investigate the nature of the basement top and its relationship with seismotectonics.

How to cite: Tiberti, M. M., Maesano, F. E., Buttinelli, M., De Gori, P., Ferri, F., Minelli, L., Di Nezza, M., and D'Ambrogi, C.: Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15305, https://doi.org/10.5194/egusphere-egu24-15305, 2024.

Outer Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, followed by an Mw 5.1 aftershock 10 minutes later considered as foreshocks, and culminated with the main shock Mw 6.38 on 26 November 2019, preceded by several immediate foreshocks (Mw 2.0-4.4), followed by numerous aftershocks (Mw > 5.0). We model the co-seismic slip distribution using InSAR, permanent and campaign GNSS measurements. Two hypotheses are tested: an earthquake on a thrust plane with direction N160°, and an earthquake on a backthrust. Varying the depth and dip angle for the first hypothesis and only the dip angle for the second, it is concluded that the optimal solution is a blind thrust at a depth of 15 km with an eastward dip of 40°, a maximum slip of 1.4 m and a Mw of 6.38. The GNSS time series obtained after 2020 shows two slow slip events (SSE): the first 200 days after the main shock up to about 26 days, and the second 300 days after the main shock up to about 28 days. We tested three hypotheses: SSE occurred along the basement thrust where the main shock was localised, SSE occurred along the flat formed by the detachment layer of the cover, and SSE occurred along these two faults. It has therefore been concluded that SSE has occurred along the detachment layer or along both the detachment layer and the basement thrust activated during the Mw 6.38 Durres earthquake.

How to cite: Matraku, K., Jouanne, F., and Dushi, E.: The 26 November 2019 Durres earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15944, https://doi.org/10.5194/egusphere-egu24-15944, 2024.

EGU24-16075 | ECS | Posters on site | TS3.3

Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults 

Nino Kvavadze, Victor Alania, and Onise Enukidze

The Caucasus region, which is one of the good examples of collision-driven far-field deformations, is located in the northernmost part of the Arabia/Eurasia collision zone and is classified with moderate seismic activity. Racha region, a part of Greater Caucasus orogen, in particular is characterized with the highest activity. In recent year several moderate earthquakes were observed in the region, notably 2009 September 7 (Mw = 6.0), 2011 August 18 (Mw = 4.8), and also 2024 January, 2 (Mb = 4.4), with depths varying from 10 to 15 km. The strongest event during the instrumental period recorded in Racha was observed in 1991 April 29, with magnitude Mw=7.0 and Depth = 17.2 km. Which was the largest earthquake recorded in the region, causing casualties. This event caused a number of fore- and aftershocks. Following the Racha 1991 earthquake temporary, dense seismic network was installed around the area to study aftershock activity, around 2000 aftershocks of different magnitudes were recorded by this network in total. This data was analyzed in several papers (for example Triep, et al., 1995, Fuenzalida, et al., 1997), including hypocenters and focal mechanisms. Depths of the aftershocks were observed ranging from 0 to 15 km. The mechanism of Racha 1991 main shock was shown to be reverse faulting on a gently sloping (35°) plane. Also, strong earthquake mechanisms show reverse faulting with strike-slip components. This work was oriented to analyze existing earthquake data and see its correlation to a 2-3D structural model created for the area.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Kvavadze, N., Alania, V., and Enukidze, O.: Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16075, https://doi.org/10.5194/egusphere-egu24-16075, 2024.

EGU24-16527 | ECS | Posters on site | TS3.3

First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses 

Giulia Patricelli, Maria Eliana Poli, Emanuela Falcucci, Stefano Gori, Giovanni Paiero, Enzo Rizzo, Andrea Marchesini, and Riccardo Caputo

We present the findings of a multimethodological study made on the Budoia-Aviano Thrust System conducted as part of the NASA4SHA PRIN Project “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy”.

The NW dipping, SW-NE striking Budoia-Aviano Thrust System represents the southeast-verging external front of the Plio-Quaternary Eastern Southalpine Chain, occurring at the front of the western Carnic Pre-Alps, between Polcenigo and Montereale (PN).

The recent activity of the Budoia-Aviano thrust is evidenced by numerous geological and morphostructural features, including the exposure of Mio-Pliocene reliefs emerging from the Last Glacial Maximum alluvial plain, the upwarping of the LGM fan of the Artugna stream, and geomorphic anomalies of the surface hydrographic network (Poli et al., 2014).

Moreover, to identify sites to perform excavation aimed at exploring the Holocene movements of the thrust system, we performed multiscale geophysical investigations, such as Deep Electric Resistivity Tomography, Electric Resistivity Tomography and Ground Penetrating Radar across the entire thrust system. They revealed the presence of a series of possible north-verging shear planes, whose trace seemed to correspond to the more pronounced up-ward convex profile of the Artugna alluvial fan.

Based on geophysical results, two NNW-SSE paleoseismological trenches were excavated along selected GPR profiles. The trenches exposed late LGM-to-Holocene alluvial fan deposition of the Artugna stream. Notably, a paleosoil embedded in alluvial sequence yielded a 14C age interval between 16 Ky and 5 ky BCE.

In both trenches, the entire excavated late Quaternary succession was affected by a set of north-verging reverse planes, coinciding with the discontinuities identified in GPR profiles. In each trench, the total vertical displacement measured across all thrust planes is of about 4.5 meters, resulting from at least three displacement events occurred in the last 7,000 years. Moreover, the involvement of the bottom of the ploughed soil supports the hypothesis of the backthrust being activated during the MW 6.3 Alpago-Cansiglio earthquake (Rovida et al., 2022) as suggested by Galadini et al. (2005).

The integration of paleoseismology, photogrammetry, and high-resolution geophysics enabled the construction of a detailed 3D model of the Budoia-Aviano Thrust System, revealing a 20-meter-wide deformation zone on the hanging wall of the main south-verging Budoia-Aviano Thrust. In the perspective of seismic hazard assessment and regional planning, it is worth to consider the proximity of this active and capable fault to industrial complexes, urban centres, and vulnerable structures characterizing the Budoia and Aviano area.

REFERENCES

  • Galadini, M.E. Poli, Zanferrari, A. (2005). Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy). Geophysical Journal International161(3).
  • M.E. Poli, G. Monegato, A. Zanferrari, E. Falcucci, A. Marchesini, S. Grimaz, P. Malisan, E. Del Pin (2014). Seismotectonic characterization of the western Carnic pre-alpine area between Caneva and Meduno (Ne Italy, Friuli). DPC-INGV-S1 Project.
  • Rovida, M. Locati, R. Camassi, B. Lolli, P. Gasperini, A. Antonucci (2022). Catalogo Parametrico dei Terremoti Italiani (CPTI15), versione 4.0. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/CPTI/CPTI15.4

How to cite: Patricelli, G., Poli, M. E., Falcucci, E., Gori, S., Paiero, G., Rizzo, E., Marchesini, A., and Caputo, R.: First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16527, https://doi.org/10.5194/egusphere-egu24-16527, 2024.

EGU24-17289 | ECS | Orals | TS3.3

Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images 

Jihong Liu, Sigurjón Jónsson, Xing Li, and Yann Klinger

Large strike-slip earthquakes are usually modeled as slip on localized planar fault planes within a homogeneous or layered elastic half-space. However, geodetic fault-slip inversions often show a shallow slip deficit, where the maximum slip is found at a depth of several kilometers with gradually decreasing slip towards the surface. High-resolution satellite images of earthquake surface ruptures also suggest a reduction in on-fault slip, often termed as off-fault damage or distributed deformation. In this study, we refer to this reduction in near-fault deformation as surface absent deformation (SAD). The presence of coseismic SAD, due to off-fault damange and/or compensated for by shallow interseismic fault creep and afterslip, holds significance for earthquake rupture processes, paleoseismology, and earthquake hazard assessments.

In our study, we quantify the SAD along the main ruptures of the magnitude 7.8 and 7.6 Kahramanmaraş earthquakes, which occurred on 6 February 2023 near the Türkiye-Syria border, by mapping coseismic three-dimensional (3D) surface displacements using differential interferometry and pixel tracking of satellite synthetic aperture radar (SAR) images. The two earthquakes had a combined rupture length of approximately 500 km, exhibiting multi-meter surface fault offsets and diverse fault geometries, necessitating high-resolution deformation mapping near and away from the fault. We obtained the SAD distribution by analyzing fault-perpendicular profiles of fault-parallel displacement from the SAR-derived 3D displacements. For each profile, an arctan function was used to predict the near-fault (e.g., 0-5 km) elastic displacement based on the far-field (e.g., 5-50 km) observations, yielding an estimate of the lack of deformation close to the fault (i.e., the SAD). The results reveal a clear correlation between SAD and geometrical complexities along the two co-seismic ruptures. Using this strategy to determine the SAD, we find that about 35% of the surface fault slip is “missing” and expressed as SAD within a distance of 5-7 km from the coseismic surface ruptures. By comprehensively analyzing the interseismic, coseismic, and postseismic deformation in this area, we find that shallow interseismic fault creep and afterslip cannot explain the coseismic SAD and that it appears to be dominated by off-fault damage. Notably, existing research on off-fault damage has been concentrated within a range of only 1-2 km. Our results therefore underscore the significance of extending investigations of off-fault damage to 5-10 km from fault ruptures, and suggest that relying solely on on-fault offset measurements may lead to an underestimation of fault slip rate estimations by as much as one third.

How to cite: Liu, J., Jónsson, S., Li, X., and Klinger, Y.: Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17289, https://doi.org/10.5194/egusphere-egu24-17289, 2024.

EGU24-19541 | Orals | TS3.3

Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy) 

Pierfrancesco Burrato, Andrea Brogi, Paola Vannoli, Martina Zucchi, Umberto Fracassi, Gianluca Valensise, Hsun-Ming Hu, and Chuan-Chou Shen

We explored the behaviour and earthquake potential of an active fault system in the slowly deforming part of southern Tuscany. This region corresponds to the eastern margin of the Siena Basin, a Neogene structural depression that developed during the extensional tectonics that affected the inner northern Apennines. Here, N-, NE- and WNW-trending faults were active during the Zanclean-Latest Quaternary. Clear evidence of the activity of these faults, particularly the most recent WNW-striking ones, is represented by faulted Late Pleistocene-Holocene travertine deposits that preserve also evidence of active seismogenic faulting. Indeed, this area in recent times was mostly interested by low-magnitude seismic sequences that occurred in the uppermost 10 km of the crust, mainly characterized by transcurrent and transtensive faulting mechanisms. However, the historical record includes also damaging earthquakes in the 5.0-6.0 Mw range, such as the 7 August 1414, Mw 5.7, Colline Metallifere, 13 April 1558, Mw 6.0, Valdarno Superiore, and 25 August 1909, Mw 5.3, Crete Senesi events, but, to date, very little is known about the geometry, maximum earthquake potential and slip rate of their causative faults.
In this study, we characterize an active, capable, and seismogenic fault system identified in the saw-cut walls of an active travertine quarry near Serre di Rapolano, a few kilometres south-east of the city of Siena. To document the geometric and kinematic features of the active faults, we carried out a detailed geological and structural field survey of the quarry outcrop, collected samples for U-Th dating and constructed a virtual outcrop model. We found compelling evidence for nearly SW-NE surface-breaking faulting, perpendicular to the main structural fabric of the central and northern Apennines, whose activity extends at least into the Upper Pleistocene. The peculiar geology of the area also suggests that these faults have generated earthquakes associated with surface faulting, namely the occurrence of clastic dykes injected within the fault zones during earthquake-induced liquefaction.
Our results may help to address the current lack of understanding concerning earthquake activity in the slowly deforming region, and improve the current knowledge of the seismotectonic setting of the Siena Basin and the corresponding part of the inner northern Apennines. Our findings hint to a still unexplored tectonic mechanism, which suggests that the earthquakes affecting this part of southern Tuscany may be caused by segments of rather elusive, very long, SW-NE and WNW-ESE lineaments crossing the entire Apennine stack.

How to cite: Burrato, P., Brogi, A., Vannoli, P., Zucchi, M., Fracassi, U., Valensise, G., Hu, H.-M., and Shen, C.-C.: Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19541, https://doi.org/10.5194/egusphere-egu24-19541, 2024.

EGU24-20372 | Orals | TS3.3

FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023) 

Martin Zeckra, Lahcen El Moudnib, Abderrahime Nouyati, and Sebastián Carrasco

The 2023 Mw 6.9 Al Haouz Earthquake in the Moroccan High Atlas mountains is the most recent example of a destructive event in an intraplate setting under the absence of a causative plate boundary. Their large inter-event times in such seismotectonic regimes hinders the study of single focus regions and apparently underestimates their larger seismic hazard potential, leaving local communities unaware of the scale of their exposure to these risks. One major shortcoming in the immediate scientific analysis of this unprecedented earthquake is the lack of (publicly) available seismic waveform recordings in the source area.

An immediate impact is displayed in the source location uncertainty, including a high variability in focal depth estimations. Associating the earthquake origin to a causative fault remains puzzling, bearing in mind the deeper-than-average focal depth of around 32 km. The complex tectonic history of the Atlas mountain chains is depicted in a plethora of active, reactivated and abandoned faults. In addition, prior studies noticed a lithospheric anomaly underneath the High Atlas mountain range, that lacks a classical mountain root. Thus, this event raise questions on the thermo-elastic parameters at depth in order to support a large seismogenic thickness of the crust.

In the immediate aftermath of the Al Haouz, we initiated a rapid-response task force for setting up a temporal seismic network in the High Atlas. Within two weeks, six autonomous seismological stations have been installed between 20 and 80 km from the estimated epicenter. Due to the large degree of destruction, problematic access and absence of major infrastructure in the epicentral region, we relied on autarkic and robust sensors. As a novelty, the stations consisted of SmartSolo® three component 5 Hz geophone sensors. These industrial-level instruments are light-weight and easy to deploy in any terrain. In a compact casing, the passive sensors host digitizer, data storage, GPS and battery life-time of up to 30 days.

Here, we present the first data of this 2 months temporary network. Based on preliminary analysis, we could obtain more than 1000 events recorded on all stations of the network during the 54 recording days. The largest recorded events had an assigned magnitude of ML 4.5. Considering single stations detections as well, we estimate more than 10,000 earthquake detections overall. This catalog will greatly expand the scientific insight into the mechanisms of this exceptional earthquake in the near-future.

Further, through the use of simple geophone sensors this study presents a proof of concept for rapid response installations of temporary aftershock network. These sensor types strongly outperform the fully elaborated counterparts in installation speed, transportability and external requirements for potential installation sites without large drawbacks in data quality.

How to cite: Zeckra, M., El Moudnib, L., Nouyati, A., and Carrasco, S.: FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20372, https://doi.org/10.5194/egusphere-egu24-20372, 2024.

EGU24-20764 | Orals | TS3.3

POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain 

César R. Ranero, Paraskevi Nomikou, Filomena Loreto, Irene Merino, Valentina Ferrante, Danai Lampidou, Elisavet Nikoli, and Serafeim Poulos

The cruise POSEIDON from 10-22 June 2023, mapped the tectonic structure of the region extending from the western Peloponnese across the Ionian Islands. This is one of the most complex and comparatively little evaluated regions, with demonstrated seismic hazard, in the Mediterranean.

The region contains a complex fault system with numerous strands controlling much of the submarine and subaerial relief and with dramatic lateral changes in deformation rates. The fault system has produced large earthquakes, mostly offshore, recorded during the past few decades in the Greek national seismological network. However, the largest recent Mw~6.8-7.0 Kephalonia 1953 event was recorded in few stations available then. This earthquake - possibly the most destructive in recent Greek history - cause the collapse of ~85% of all buildings on Kephalonia Island, ~1k deaths, and ~145k people homeless. However, the 1953 earthquake is poorly understood compared with more recent, albeit less destructive events. The epicentre of the 1953 event is not well constrained, and the location and dimensions of the causative fault are unknown. Likewise, the hypocenter depth of the 1953 event thrust-fault focal mechanism, that occurred E or SE of Kefalonia, is defined from <50 km to <20 km, depending on the analysis. Studies in the islands interpret active shallow thrusting to propose that the 1953 event ruptured the upper 5 km of several shallow faults, but such a rupture cannot explain a Mw~6.8-7.0 even.

The goal of POSEIDON is to define the regional fault system structure and kinematics and to place it in the proper geodynamic context that helps understand hazards and eventually evaluate associated risks. The DEM displays a rugged terrain from the Ionian Islands to the Peloponnese Peninsula, with numerous features that indicate active deformation across the entire region. Major submarine tectonic structures around the islands trend from NE-SW to NNW-SSE, similar to the basins and ranges on the islands. Elongated shallow troughs offshore laterally project to the relief trends on the islands, supporting widespread active faulting.

A further complication in the research area is that the upper-crust fault system, might be located above, or sole into, a mega-thrust plate boundary fault of the Hellenic subduction zone, inferred -in publications- to dip in a NE direction at ~25-40 km depth under the surface. However, the location of a mega-thrust seismogenic zone is yet not well constrained. POSEIDON seismic data image the tectonic features in the crust and integrated with the high-resolution bathymetry allow to define the main faults across the offshore region in unprecedented detail.

Acknowledgements

We acknowledge the professional and dedicated work of the National Institute of Oceanography and Applied Geophysics (OGS-Trieste) technical party and the technical party of the Marine Technology Unit (UTM) from the Spanish National Research Council (CSIC) to make the experiment a success. We also acknowledge the professional and dedicated work of the master, officers and crew of the R/V Laura Bassi during the POSEIDON experiment.

How to cite: Ranero, C. R., Nomikou, P., Loreto, F., Merino, I., Ferrante, V., Lampidou, D., Nikoli, E., and Poulos, S.: POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20764, https://doi.org/10.5194/egusphere-egu24-20764, 2024.

EGU24-63 | ECS | PICO | TS5.2

Harmonic Dynamic of the Earth 

Xianwu Xin

The Harmonic Motion Phenomenon of the Earth is introduced through Experiments: Under the Combined Action of Tidal Force and the Earth's Rotation, Continental Unit Body Segments, like Caterpillars, actively crawl westward on the Mantle. Based on the Force Analysis of the Earth Motion Process and the Generalized Hooke's Law, the Harmonic Motion Equation and the Crustal Motion Equation of the Earth are derived, also the Conversion Equation of Continental Drift Datum has been derived. The Velocity Field of Continent Latitudinal Movement is calculated, and compared with the Measured Value of ITRF2000 station. From the Perspective of Kinematics, it is proved that the Harmonic Motion of the Earth is the Basic Dynamic Mechanism of the crust and inside of the Earth Movement. The Degree of Dominance which this Dynamic Process to Continental Drift is 72% to 97.4%. It's Energy comes from the Rotation Energy of the Earth. Using the results of Motion Calculation to was reconstructed the Proto Ancient Continent, that was it moment of started cracked at before 250 million years. In addition, the Driving Force Equation of the Earth’s Harmonic Motion is derived. Discussed the Driving Force accumulation process and the formation mechanism of Earthquake: The Thrust of the Rock Stratum to the Hindered Portion slowly increases with the Creep between stratus and the Successive Compression each time it from Peak Point to Valley Point. Continuously increase the Elevation and Area of the Compression Zone. When the Driving Forces Accumulation reaches the Limit of the Strength of the Hindered Rock Stratum, sudden movement or Fracture Occurs, and an Earthquake formation. Earthquakes are a Process of Concentrated Energy Release. In High-Temperature and High-Pressure Areas within 700km underground, when Earthquakes, some Rocks melt to form Magma, and driven by Harmonic Motion, enriches westward along Rock Fractures and enters the Ocean Ridges Bottoms and the Below of the Volcano. The Magma of Below the Volcano erupts from the Earth's Surface after increasing Pressure. The Magma at the Bottom of the Ocean Ridge is driven by the Footpath Board Effect and moves upwards along the Cracks, and Condensed on the Surface of the Sidewall, when change the Gaps of the Cracks along with the Ocean Floor Undulating, the Ocean Floor on Both sides of the Ocean Ridge is pushed apart from each other. This kind of process of Ocean Floor Fluctuate Spreading leads to Gradual wear and tear of the Ocean Floor, Ultimately Subducting beneath Land or trenches and returning to the Mantle. In Passive Mantle Convection and Ocean Floor Fluctuate Spreading, the Driven Force of Magma flow is provide by the Earth's Rotation through Fluctuate Processes, magma does not output Power. At last, according to the Driving Force Equation of Earth‘s Harmonic Motion, the Energy Conversion Equation is given. The Total Power of Earth‘s Harmonic Motion is calculated, and compared with the Relevant Measured Values. It is further proved from the Perspective of Dynamics and Energy Conversion: The Harmonic Dynamic Proces of the Earth is the Basic Dynamical Proces of Tectonic Movement.

How to cite: Xin, X.: Harmonic Dynamic of the Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-63, https://doi.org/10.5194/egusphere-egu24-63, 2024.

Fold-and-thrust belts (FTBs) evolve over a mechanically weak basal décollement that separates overlying intensely deformed rocks from the underlying less deformed or undeformed rocks. Although fold-and-thrust belts are often considered laterally cylindrical in nature, a closer inspection reveals remarkable variations in structural style (e.g., fold geometry) both along and across the strike of mountain belts. Using crustal scale thin-sheet laboratory experiments, this study focuses on the role of laterally varying coupling strength of the basal décollement on the evolution of structural styles in natural FTBs. In this study, we used a rectangular slab of silicon putty, a linear viscous material, of uniform thickness in all experiments to simulate the crustal section and the models were deformed at a uniform convergence velocity of ~7.649 × 10-5 ms-1. Analyses of experimental results show remarkable changes in the wedge growth with the introduction of along strike variations in décollement strength. The segment of the deforming wedge over weakly coupled décollement propagates at a faster rate towards the frontal direction compared to the laterally continuous segment over a strongly coupled décollement, leading to an overall sinuous geometry of the deformation front. In contrast, an approximately linear deformation front represents a condition of uniform along-strike coupling strength at the basal décollement. Based on our experimental results, we argue that the broad arcuation of the mountain front along the eastern margin of the Zagros fold-thrust belt (i.e., Fars arc region) might have resulted due to along strike variations in the décollement strength, while the occurrence of a linear deformation front from the central to western margin of the fold-and-thrust belt represents a segment of the wedge with a uniform coupling strength at the basal décollement. Our experimental results can be carefully used to explain the cause of strike-wise segmentation of tectonic processes in orogenic belts, variations in topography and earthquake activities.   

How to cite: Roy, S., Willingshofer, E., and Bose, S.: Influence of lateral variations of décollement strength on the structure of orogenic wedges: insights from experimental viscous wedge models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3310, https://doi.org/10.5194/egusphere-egu24-3310, 2024.

With the wide application of high-quality three-dimensional (3-D) seismic volumes in hydrocarbon exploration, it has been found that a special type of fault system, i.e., conjugate strike-slip fault system, is often developed in the Cratonic basins (e.g., Tarim Basin, Sichuan Basin, and Ordos Basin in China). They not only can directly indicate the principal stress direction, but also play a crucial role in controlling the transport and formation of hydrocarbons in the basin. Analysis of 3-D seismic data revealed that the Tarim Basin exhibited typical X-shaped (symmetrical) and asymmetrical (two sets of faults differing greatly in number) conjugate strike-slip fault systems. However, there is a lack of analogue models on the geometries and progressive evolution of conjugate strike-slip faults, as well as a poor understanding of the mechanisms of asymmetric conjugate strike-slip fault systems. Additionally, previous experiments have not been compared with such natural examples.

Based on the structural analysis of strike-slip faults in the Tarim Basin using seismic reflection data, we used three sets of symmetric (rectangular shape) and two sets of asymmetric (parallelogram shape) rubber basement models to investigate the geometries and progressive evolution of conjugate strike-slip faults. In this study, our research successfully modelled the kinematic and geometric evolution of different types of conjugate strike-slip fault systems, and found that they have the same acute angle and that the direction of their angular bisectors is parallel to the direction of contraction. In symmetric models, we observed the development of numerous typical X-shaped conjugate strike-slip faults were developed. Conversely, the development of two sets of faults in the asymmetric models showed an asymmetry, i.e., one set of faults was more obviously developed than the other, and with the degree of asymmetry increased, the asymmetry was even more obvious. Furthermore, we analysed the stress state of the models using the Mohr space and inferred that the stress state of the model changed from the strike-slip in the early stages to the extension in the later stages.

We proposed two synoptic models, namely, the symmetric conjugate strike-slip fault system (SCSFS) model and the asymmetric conjugate strike-slip fault system (ACSFS) model, for conjugate strike-slip fault systems based on the results of the different models. The models and experimental results were compared with natural examples of the two sets of strike-slip fault systems in the Tabei uplift in China’s Tarim Basin, which exhibited many strong similarities in their structural geometries, and they also provided further insight into the mechanisms of strike-slip faults in the Tabei uplift. These synoptic models proposed based on the analogue models may provide useful templates for the seismic interpretation and mechanism of different types of conjugate strike-slip fault systems in nature and for inferring the orientation of the maximum principal stress.

How to cite: Xiao, K. and Tong, H.: Analogue modelling of conjugate strike-slip faults in the Cratonic basin: A case from the Tarim Basin, NW China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3751, https://doi.org/10.5194/egusphere-egu24-3751, 2024.

Fault evolution is influenced by multiple factors, including the reactivation of pre-existing structures, stress transmission within ductile detachment layers, and the growth, interaction, and connection of newly formed fault segments. In the same stress field, displacement vectors of fault strikes, dip-slip vectors, and subtle fractures accommodate strain distributed everywhere. This study employs PIV analysis and model reconstruction to simulate oblique extensional fault systems formed at four different angles. Simulation modelling indicates that oblique extensional reactivation of pre-existing structures controls the linear arrangement of fault segments in the overlying strata. Arcuate faults can be classified into linear master fault segments controlled by pre-existing structures, curved splay faults in termination zones, and normal fault segments responding to regional stress fields. Along-strike displacement is regulated by linear segments within the master strike-slip fault, while progressive bending of splay faults, relay ramps' dislocation, and inclined displacements are regulated by relay ramps within the overlap zone. Small-angle (15°) oblique extension favours the formation of fault segments with distinct step-like features, leading to additional relay ramps. In contrast, high-angle (60°) oblique extension often results in the development of more continuous fault segments. As faults continuously evolve, new fault segments tend to deviate from the control of pre-existing structures, concentrating more on the development of planar and continuous master faults. Finally, we compared the established model with the transtensional fault system within the intraplate rift system in eastern China, demonstrating that the oblique extension angle controls the composite characteristics of the overlying strata faults.

How to cite: Wang, Y. and Yu, F.: The Linkage Evolution of Strike-Slip Faults with Normal Faults—Insights from Analogue Modelling at Various Oblique Extension., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4813, https://doi.org/10.5194/egusphere-egu24-4813, 2024.

EGU24-6667 | ECS | PICO | TS5.2

Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting:  

Mouad Ankach, Mohamed Gouiza, and Khalid Amrouch

The Atlas fold and thrust belt extend from the Atlantic rifted margin of Morocco to Tunisia over a distance of 2500km. Before its inversion in the Cenozoic to the present, the Atlas system evolved initially as a rift basin that opened simultaneously with the Atlantic rift in the west and the Tethys in the north, during the upper Triassic-Jurassic period.

The Western High Atlas is believed to be influenced by the Atlantic Ocean (also known as the Atlantic domain), where the Triassic to Early Jurassic strata are considered to be syn-rift, while the Middle Jurassic to Cretaceous deposits are labelled as post-rift. In contrast, the Marrakech High Atlas (MHA), Central High Atlas (CHA), Middle Atlas (MA), and the Eastern High Atlas (EHA) are assumed to be influenced by the Tethys Ocean (also known as Tethyan domain), where the Triassic to Jurassic sediments are considered to be syn-rift. This implies that the Mesozoic rifting along the Atlas was diachronous, making it difficult to determine the exact timing and kinematic of crustal stretching. Constraining the extensional phases in the Atlas system is crucial for understanding how the Atlas crust was stretched and thinned. Our work aims to quantify the magnitude and regional kinematic of stretching in the Atlas system using various methods, namely, thickness variation method, subsidence analysis and palinspatic reconstruction of 2D cross-sections.

Our preliminary results indicate that the maximum stretching factor (beta factor) in the Atlas is β = 1.25; and that crustal thinning did not exceed 20%, based on tectonic subsidence analysis. While the palinspatic restoration suggest that the Moroccan Atlas system underwent approximately a uniform stretching with β = 1.11 in EHA (Midelt-Errachidia area), β = 1.08 in CHA (Imilchil area), and β = 1.12 in the East Marrakech High Atlas (EMHA: Demnat area). These values indicate that the Moroccan Atlas crustal thickness has been thinned by 9% in EHA, 8% in CHA, and 11% in EMHA. In addition, the geological context of the High and Middle Atlas regions, where the estimated shortening is reported to be less than 20%, the stretching factor (β) was calculated based on the crust thickness. The initial crustal thickness (IC) of the Meseta block, which constitutes one of the Atlasic rift shoulders, considered an undeformed area, served as a reference. Accounting for the observed shortening, the final crustal thickness was deduced by subtracting the reported shortening value representing 7.8 km from the observed crustal thickness (39 km), resulting in a β value of 1.25, which is consistent with the result obtained from the subsidence analysis.

Keywords: Atlas system, extension, stretching factor, Thinning factor,

 

 

 

How to cite: Ankach, M., Gouiza, M., and Amrouch, K.: Decoding the extensional phase of the Atlas system: Unraveling Crustal Stretching during rifting: , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6667, https://doi.org/10.5194/egusphere-egu24-6667, 2024.

EGU24-6869 | ECS | PICO | TS5.2 | Highlight

Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning 

Giacomo Mastella, Fabio Corbi, Jonathan Bedford, Elvira Latypova, Federico Pignalberi, Marco Scuderi, and Francesca Funiciello

Despite considerable progress in monitoring natural subduction zones, key aspects of megathrust seismicity remain puzzling, mainly due to the temporally incomplete and spatially fragmented available record. Scaled seismotectonic models yield valuable insights by spontaneously creating multiple stick-slip cycles in controlled, downscaled three-dimensional laboratory replicas. Here we report recent progress in analog modeling of the megathrust seismicity, particularly focusing on a meters-scale elasto-plastic model featuring a frictionally segmented, granular fault that mimics the subduction channel at natural subduction zones. We showcase how by employing analog materials under low-stress conditions, the potentialities of monitoring can be maximized using three diverse techniques: 1)  Precise monitoring of surface spatial deformation over time is achieved through digital image correlation techniques, mirroring a uniformly distributed dense geodetic network spanning land to trench in real subduction zones. 2) A Micro-Electro-Mechanical (MEMS) accelerometric network, emulating a seismic network, captures seismic wave propagation at the model surface. 3) Embedded piezoelectric sensors within the granular analog fault capture near-field acoustic signatures of frictional instabilities. These diverse monitoring techniques allow for investigating the consistency between continuous seismic activity and surface deformation data, offering insight into both micro and macroscopic features of analog seismic cycles. At the macroscopic level, the models' frictional behavior can be numerically reproduced via rate and state numerical simulations, considering earthquake fault slip as a nonlinear dynamical process dominated by a single slip plane. At smaller scales, the model accounts for complexities in fault slip emerging from grain interactions, reflecting nonlinearities that arise when considering faults as distributed three-dimensional volumes. These fundamental attributes, coupled with their capacity to create extensive catalogs of small labquakes, make scaled seismotectonic models exceptional apparati for employing Machine Learning (ML) in comprehending multi-scale spatiotemporal seismic processes. Cutting-edge Deep Learning methods are employed to predict the spatiotemporal evolution of surface deformation, where regression algorithms not only forecast timing but also the propagation and magnitude of analog earthquakes across diverse spatiotemporal scales. Given that one of the monitoring systems used in seismotectonic analog models mimics a geodetic-like network in nature (GNSS data-Global Navigation Satellite Systems), an attempt to generalize the promising outcomes achieved in the laboratory to natural subduction faults is proposed.  Such promising avenues emphasize the potential for ML to bridge the gap between laboratory experiments and real-world seismic events. These initial findings, combined with advancements in the instrumentation of fault laboratories in nature and expanding data reservoirs, reinforce the belief that ML can significantly augment our understanding of the multiscale behaviors of natural faults.

How to cite: Mastella, G., Corbi, F., Bedford, J., Latypova, E., Pignalberi, F., Scuderi, M., and Funiciello, F.: Multiscale, multisensor analysis of scaled seismotectonic models: Bridging the Gap Between Laboratory and Nature through Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6869, https://doi.org/10.5194/egusphere-egu24-6869, 2024.

EGU24-7785 | ECS | PICO | TS5.2

Haromonic Curvature and Bedding Uncertainty Across Scales 

David Nathan, Mario Zelic, Eun-Jung Holden, Daniel Wedge, and Christopher Gonzalez

Observations of geological structures are often made at different scales and often can cross multple orders of magnitude. This attribute of scale though is often not explicitly incorporated into the workflow of geological modeling and is usually treated as data preparation or sampling bias. The spectral properties of the discrete Laplacian operator, when applied to reconstructed surfaces from implicit modeling though offer a potential means of bridging this gap, when also combined with appropriate directional statistical anaysis. We present an example of how bedding orientation measurements from a 1:5000 scale surface map and drillhole bedding orientation picks from borehole televiewer images can be integrated using the manifold harmonics of the Laplacian operator and a mixture of von-Mises Fisher probability distributions. This provides automated insights for sampling for modeling and also possible kinematic and tectonics processes.

How to cite: Nathan, D., Zelic, M., Holden, E.-J., Wedge, D., and Gonzalez, C.: Haromonic Curvature and Bedding Uncertainty Across Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7785, https://doi.org/10.5194/egusphere-egu24-7785, 2024.

This study investigates a fold-and-thrust belt (FTB) beneath the South Yellow Sea Basin, a noteworthy petroleum exploration target, featuring a basement high and a detachment layer. In the central basin, magnetic anomalies reveal the development of the basement high. Seismic reflection data, in conjunction with drilling information, disclose the presence of the Lower Silurian Gaojiabian Formation, exceeding ~500 m, acting as a low-cohesion detachment layer. However, the impact of these features on regional structures and the resulting hydrocarbon preservation conditions remains uncertain. This study explores the kinematic characteristics and deformation localization associated with the basement high and intermediate detachment using four sandbox models and particle velocity analysis within the FTB framework. Model 1, the reference, utilized pure quartz sand without either feature. Model 2 examined the role of the intermediate detachment using glass microbeads, revealing a limited effect in generating typical thin-skinned FTB. Model 3 considered the basement high and found that it strongly influenced the deformation regime of the wedge. Model 4 examined both features and suggested their combined influence on FTB deformation processes. In Model 2, lacking a pre-existing basement high, the intermediate detachment did not contribute to FTB deformation. In Model 3, lacking an intermediate detachment, deformation propagated along the surface of the basement high upon reaching its edge. In Model 4, shortening propagated upward along the edge of the basement high and then into the intermediate detachment, producing comparable structural geometry to the prototype, including both thick- and thin-skinned FTBs in nature. The results indicate that in the central South Yellow Sea Basin, structural layers between the basement high and detachment are likely to experience weak deformation; thus, favorable hydrocarbon preservation conditions can be anticipated in this region. This study holds significant importance in guiding future petroleum exploration efforts in the central South Yellow Sea Basin.

How to cite: Zhang, P., Fu, Y., and Yan, B.:  Influence of Basement High and Detachment on the Kinematics of a Fold-and-Thrust Belt in the Central South Yellow Sea Basin with Implications for Hydrocarbon Preservation: Insights from Analog Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8859, https://doi.org/10.5194/egusphere-egu24-8859, 2024.

EGU24-10540 | ECS | PICO | TS5.2

Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models  

Afonso Gomes, Filipe Rosas, Nicolas Riel, João Duarte, Wouter P. Schellart, and Jaime Almeida

Ophiolites are exposed remnants of oceanic lithosphere that are critical to our understanding of the structure, composition, and evolution of oceanic plates.

Some ophiolites (e.g., some Tethyan-type ophiolites) originate in the oceanic forearc of an intra-oceanic subduction system (i.e., in the overriding plate). If the trailing edge of the subducting oceanic lithosphere is connected to a continental passive margin, then that passive margin may also be subducted (beneath the forearc and proto-ophiolite) once all the oceanic lithosphere is “consumed” at the trench. The subduction of the continental passive margin means that a buoyant continental crust will underthrust the oceanic forearc (i.e., proto-ophiolite). This crust goes through a burial-exhumation cycle, and as it exhumes it can drag and detach the tip of the overlaying oceanic forearc, creating an ophiolite klippe. The exhumation-emplacement process is, however, still not fully understood, particularly regarding the constraints imposed by the forearc itself. For example, the detachment of the tip of the forearc (ophiolite) from the remainder of the plate should, at least in part, be controlled by the mechanical properties of the forearc (i.e., presumably the tip of a “weak” forearc will detach more easily than the tip of a “strong” forearc).

Present-day intra-oceanic subduction forearcs (i.e., present-day model-types for Tethyan-type ophiolites) experience significant chemical alteration induced by the circulation of metamorphic fluids originating from the dehydration of the underlying subducting plate. This chemical alteration occurs mostly in the form of serpentinization of forearc peridotites, leading to a substantial weakening of the forearc lithospheric mantle. The circulation of these fluids, and hence the serpentinization process, is thought to occur primarily along preexisting deeply rooted fault systems, further weakening these strain-localizing structures, although some diffuse alteration probably also occurs. It is then reasonable to assume that the paleo forearcs that originated Tethyan-type ophiolites were also subject to these chemical and mechanical alterations, which are then expected to have affected the ophiolite emplacement process.  

Here we present novel 2D and 3D dynamic numerical models that investigate the role of forearc weakening on ophiolite emplacement processes. Specifically, we test different mechanical weakening patterns, i.e., localized (serpentinized faults) vs homogeneous (diffuse serpentinization) weakening.

Preliminary results suggest that prior serpentinization of the forearc has a critical control on ophiolite emplacement. Furthermore, differing degrees of forearc serpentinization, as well as serpentinization distribution patterns, result in different tectonic regimes of ophiolite emplacement.

 

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and through scholarship SFRH/BD/146726/2019.

How to cite: Gomes, A., Rosas, F., Riel, N., Duarte, J., P. Schellart, W., and Almeida, J.: Proto-ophiolite serpentinization may influence ophiolite emplacement: Insights from numerical models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10540, https://doi.org/10.5194/egusphere-egu24-10540, 2024.

EGU24-12208 | PICO | TS5.2

Numerical and analogue modelling of boudinage under non-coaxial shear strain 

Filipe Rosas, Afonso Gomes, Jaime Almeida, João Duarte, Nicolas Riel, and Wouter Schellart

The recognition of different boudinage patterns is of key importance to the unravelling of the tectono-metamorphic evolution of different domains in different tectonic contexts and at different considered spatio-temporal scales.

The main reason for this is twofold: (1) Boudins tend to preserve the relic metamorphic conditions that characterize deformation prior to the one recorded by matrix fabrics and associated mineral associations. (2) Specially under shear deformation regimes, quarter-structure geometric patterns comprising rotated boudins and folded matrix planar fabrics, can be used to determine the shear sense of the later (sin-boudinage) deformation.

In the present work, we present preliminary numerical and analogue modelling results of boudinage, under non-coaxial (shear strain) deformation. We specifically investigate the potential influence of three main parameters on the genesis of different (boudins-folds) quarter structures patterns: i) the viscosity contrast between the boudin and the matrix; ii) the original position of the non-equidimensional boudin; and ii) the assumed (bulk) shear strain rate.

We proceed by presenting a preliminary comparison of our results with archetypical natural examples of boudinage, in different tectonic-structural contexts and at different scales, further illustrating the potential value of these type of structures in the unravelling of the deformation history in different situations.

Acknowledgements

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

How to cite: Rosas, F., Gomes, A., Almeida, J., Duarte, J., Riel, N., and Schellart, W.: Numerical and analogue modelling of boudinage under non-coaxial shear strain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12208, https://doi.org/10.5194/egusphere-egu24-12208, 2024.

EGU24-12468 | ECS | PICO | TS5.2

Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems  

Nemanja Krstekanic, Ernst Willingshofer, Antoine Auzemery, Liviu Matenco, and Jasper Smits

In subduction systems, asthenospheric flow, generated by subducting slabs, is considered as one of the key forces contributing to the deformation of the overlying lithosphere. Previous analogue modelling studies predominantly focused on understanding the kinematics and dynamics of subduction roll-back-driven asthenospheric flow, without looking at the influence of that flow on upper-plate deformation due to the modelling setups or methodological limitations. We developed a novel analogue modelling approach where gravity-driven asthenospheric flow represents the main driver for upper plate deformation. Volume-constant flow within the deformation box is achieved by an inlet-outlet system. In the models, we gradually increase the setup complexity from single-layer asthenosphere-only models to 4-layer asthenosphere-lithosphere models to test flow velocity distribution and its sensitivity to the outlet size, model thickness and rheological stratification of the model, as well as the transfer of deformation from the asthenosphere to the overlying lithosphere. Furthermore, we study the effects of the inherited lithospheric structures, such as weak zones representing old sutures, on deformation transfer. The results are compared with the Pannonian-Carpathians system of south-eastern Europe, where the large Pannonian back-arc basin formed during the Miocene retreat of the Carpathians slab.

For the methodological approach, the results show that asthenospheric flow can be fully controlled by the inlet-outlet system by adjusting the outlet size, which provides an efficient mechanism for the deformation of the overlying mechanically stratified lithosphere. The models also demonstrate that the back-arc extension is initiated farther away from the asthenospheric flow origin (i.e., the outlet in the models or slab-roll back in nature). The subsequent deformation propagates in two directions, towards the flow origin, and farther away from it, both directions controlled by the shape of an indenter located laterally to the subduction zone. Most of the back-arc extension and the lithospheric thinning are accommodated in the area farther to the “slab” due to the strain shadow effect of the indenter. The indenter also contributes significantly to the strain partitioning in its closer proximity where a complex pattern of bi-directional extension, transtensional, strike-slip and transpressional deformation forms. The weak zones accommodate the onset of back-arc extension or act as transfer zones between areas with different extension rates, depending on their orientation relative to the asthenospheric flow. These models show several similarities with the Pannonian-Carpathians system, where most of the Pannonian lithospheric thinning is located at a significant distance from the subducting Carpathians slab, bypassing the Transylvanian-Apuseni area. This extension started by reactivation of the Neotethys suture zone, while the Mid-Hungarian Fault zone transferred the deformation between areas of higher extension to the south and lower extension to the north. Furthermore, several triangular-shaped sub-basins within and at the margin of the Pannonian Basin are radially located around the Moesian NW corner, similar to our modelling results. The complex pattern of the bi-directional extension and strike-slip observed in the models were recorded by the Carpathians-Balkanides orocline in the vicinity of the Moesian indenter.

How to cite: Krstekanic, N., Willingshofer, E., Auzemery, A., Matenco, L., and Smits, J.: Asthenospheric flow-driven lithospheric deformation in analogue models – a novel methodological approach and implications for natural systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12468, https://doi.org/10.5194/egusphere-egu24-12468, 2024.

EGU24-13464 | ECS | PICO | TS5.2

A new geodynamic model of the Azores archipelago: preliminary results 

Jaime Almeida, João Duarte, Filipe Rosas, Rui Fernandes, Fernando Geraldes, Luis Carvalho, and Ricardo Ramalho

The Azores archipelago is an integral part of the Macaronesian geographic region (which also includes the volcanic archipelagos of Madeira, Selvagens, Canaries and Cape Verde). This region, located in the centre of Atlantic Ocean, has its individual islands spread around a triple junction, which has been suggested to affected by a plume-ridge interaction (Storch et al., 2020; Beier et al., 2022). One of the major questions surrounding its history concern the why/how the Terceira Rift (i.e., the NW-SE oriented connection between the mid-ocean ridge and the Gloria Fault Zone) was formed.

To explore this issue, we have run sets of 3D viscoelastoplastic models for the region using the state-of-the-art modelling code LaMEM (Kaus et al., 2016). As our objective was to evaluate how the geological data and the suggested evolution for the region fit geodynamic constraints. We based our numerical models on previously established evolutionary models for the region, such as the leaky transform model (Madeira and Ribeiro, 1990).

Preliminary results hint that the formation of the Terceira Rift could be formed as the result of a shift in the regional tectonic forcing, which we attribute to the collision between the Iberian and Eurasian plates. Furthermore, our results suggest that a strong rheological contrast in the region was required to ensure the localization of deformation. Models without this feature tended to maintain a simple E-W connection between the Gloria Fault Zone and the southern part of the mid-ocean ridge.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through projects GEMMA (https://doi.org/10.54499/PTDC/CTA-GEO/2083/2021) and national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

 

References

Beier, C. et al. (2022) ‘The submarine Azores Plateau: Evidence for a waning mantle plume?’, Marine Geology, 451, p. 106858. Available at: https://doi.org/10.1016/j.margeo.2022.106858.

Kaus, B.J.P. et al. (2016) ‘Forward and Inverse Modelling of Lithospheric Deformation on Geological Timescales’, NIC Series, 48, pp. 978–3.

Luis, J.F. and Miranda, J.M. (2008) ‘Reevaluation of magnetic chrons in the North Atlantic between 35°N and 47°N: Implications for the formation of the Azores Triple Junction and associated plateau’, Journal of Geophysical Research: Solid Earth, 113(B10). Available at: https://doi.org/10.1029/2007JB005573.

Madeira, J. and Ribeiro, A. (1990) ‘Geodynamic models for the Azores triple junction: A contribution from tectonics’, Tectonophysics, 184(3–4), pp. 405–415. Available at: https://doi.org/10.1016/0040-1951(90)90452-E.

Storch, B. et al. (2020) ‘Rifting of the oceanic Azores Plateau with episodic volcanic activity’, Scientific Reports, 10(1), p. 19718. Available at: https://doi.org/10.1038/s41598-020-76691-1.

How to cite: Almeida, J., Duarte, J., Rosas, F., Fernandes, R., Geraldes, F., Carvalho, L., and Ramalho, R.: A new geodynamic model of the Azores archipelago: preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13464, https://doi.org/10.5194/egusphere-egu24-13464, 2024.

Eastern Sichuan fold belt, a prolific hydrocarbon province in China, shows the similar fold styles to the Swiss Jura Mountain fold belt, which’s therefore called as Jura-type fold by Chinese geologists. However, it’s still a matter of geologist’s debate on the formation mechanism of the eastern Sichuan fold belt.

To unravel how this type of fold trains form, a systematic scaled 2D contractional analogue experiments with composite materials were conducted. Silica-sand represents the overburden with added mica-flakes, and a stiff plasticine interlayer introducing different mechanical anisotropies. Viscous silicone rubber represents the salt detachment. The following 3 main issues have been investigated: 1) what type mechanical stratigraphy can form the fold train during lateral contraction; 2) what are the mutual interaction between faulting and folding during the formation process of detachment fold; 3)what are kinematics and its related strain distribution patterns for a detachment fold system.

The modelling results indicate that the presence of a stiff plasticine layer is the key perquisite for the formation of a concentric fold train for the following reasons: 1) it encourages the shortening to be periodically accommodated by sinusoidal-symmetric buckle folds at the inceptive folding stage; 2) it can keep the break-thrust ramps from being activated with further shorting delaying the development of faulted detachment folds at the later folding stage. As for silicone detachment, it mainly plays a role in the amplification of detachment folds via the redistribution of ductile material between the syncline and anticline domain.

DIC strain data show that the main sections of detachment fold-the limbs, especially in the forelimb, and the hinge are easily strained. More specifically, the normal faults and breakthrusts can form in the anticlinal hinge and limbs, respectively, when the detachment fold cannot be tightened any more. However, the strain is not easily accumulated in the syncline domain.

Our modelling result together with the latest interpretation of seismic reflection suggest that the eastern Sichuan fold belt is a result of faulted detachment folds, mainly controlled by the competence contrast within the overburden and the thickness of both the weak viscous detachment and strong brittle overburden.

Keywords: Eastern Sichuan Basin; Analogue modelling; DIC; Fold-thrust belt; Detachment fold

How to cite: Feng, G., Adam, J., Chen, S., and Wang, X.: Key controlling factors on the formation of Jura-type fold in eastern Sichuan Basin, South China: insights from analogue modelling with optical strain monitoring (Digital Image Correlation), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13637, https://doi.org/10.5194/egusphere-egu24-13637, 2024.

EGU24-13652 | ECS | PICO | TS5.2

Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling 

Nuno Rodrigues, Filipe Rosas, Nicolas Riel, Jaime Almeida, Afonso Gomes, and João Duarte

Continental collision occurs when two continents are dragged towards each other by the pull of the attached subducting oceanic lithosphere. Previous geodynamic modeling studies of collisional systems focused on first-order processes (such as coupled/decoupled regimes, continental delamination, slab break-off dynamics) and regional or even local scale dynamics (e.g., exhumation of HP/UHP rocks, surface topography). However, continuous subduction of continental lithospheric mantle after the onset of collision and long-term dynamics of continental subduction remains poorly constrained. Long-term continental subduction bears major geodynamic implications for the evolution of past and present collision zones.

To this aim, we use the geodynamic code LaMEM to perform high-resolution (2048 × 512) 2D buoyancy-driven numerical models, coupled with phase diagrams to account for density changes, of continued continental subduction with conditions that favor flake tectonics. We investigate the role of lower crust rheology to assess which rheological scenarios allow continental flaking and, thus, continued subduction of continental lithospheric mantle.

Our preliminary results exhibit long-term continental subduction, due to decoupling of the lower crust from the subducting continental mantle and/or density changes. This separation allows the deformation to be transmitted onto the overriding plate, with the emplacement of the subducting plate crust onto the overriding plate spanning more than 350 km and lasting over 100 Myr.

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 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and through scholarship UI/BD/154679/2023.

How to cite: Rodrigues, N., Rosas, F., Riel, N., Almeida, J., Gomes, A., and Duarte, J.: Crust-mantle delamination enables continental subduction and flake tectonics: insights from numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13652, https://doi.org/10.5194/egusphere-egu24-13652, 2024.

The deformation associated with the evolution of fold-thrust tectonic (FTT) wedge has been in the focus of research due to their association with hydrocarbons resources. Analogue sandbox modelling has been proven to be useful in characterizing FTT wedge. However, it is less convenient to interpret the influence of complex boundary conditions and material rheological parameters and to derive the stress distribution pattern from the analogue models. Nonetheless, these challenges can be accomplished competently by means of an exact numerical equivalence of those analogue models. Therefore, we undertook a numerical replication of the analogue sand-box with an absolute identical set up. This makes the attempt unique from earlier approaches, where lengths, rheology, and/or cohesive strengths were likely varied for converging the solutions in codes. Here, propagation parallel profile of sandbox experiments is numerically modelled in a 2-dimensional (2D) space with a plain strain assumption. For simplicity, the models are devoid of complex geological phenomena such as isostasy, pore fluid pressure and surficial processes. The present model enforces an elastoplastic constitutive relationship having exactly same rheology as our sand-box model. The model comprises cover material resting over a rigid decollement with frictional interaction. The cover material is subjected to asymmetrical push from one end as in physical experiment. With the identical rheology, dimensions, and geometry our numerical model successfully produced comparable results with our physical sandbox models. The measured kinematic attributes of the wedge such as taper angle, wedge width, thrust spacing, displacement along thrust from our numerical model are found in good agreement both qualitatively and quantitively with their analogue counterparts. The dynamics of deformation has also been investigated by extracting the magnitudes of stresses from each node of the numerical mesh of the present models.  From the dynamic analysis, the spatial distribution of stresses revealed that within a deforming wedge all the stress parameters are maxed periodically at a certain distance away from the pushing end boundary. The position of maximum stress is found consistent with the zone localized failure. Monitoring the periodic peaks of stress approximate the location of failure, in return leading to measure the thrust spacing. Furthermore, empirical relationships for stress distribution within a collisional wedge have been successfully developed from the observed stress distribution patterns. With the help of these relationships, mathematical expressions were developed for predicting 2D curvature of a thrust plane within a tectonic wedge. 

How to cite: Behera, A. and Bhattacharjee, D.: The dynamics of fold-thrust tectonic wedge: An insight from impeccable simulation of Physical Sandbox Experiment with Finite Element Model., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14388, https://doi.org/10.5194/egusphere-egu24-14388, 2024.

EGU24-14511 | PICO | TS5.2

Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China 

Jingbo Zhang, Sixian Chen, and Zonghu Liao

Abstract

Accurate understanding and identification of faults architecture is crucial in seismic data interpretation and earthquake analysis, where fault slip surfaces may interact with damage rocks, forming damage zones with a width larger than hundred meters. We use machine learning (ML) to show 10 kinds of seismic attributes from a seismic survey could be applied in identification and quantification of fault damage zone in northeast Sichuan Basin, China. The results indicate: (1) Six seismic attributes provide highest contribution to the fault characterization, including root mean square amplitude attributes, azimuth angle attributes, reverse attributes, original attributes, chaotic body attributes and ant body attributes; (2) The application of SHAP (SHapley Additive exPlanations) algorithm improves the model's accuracy, as the loss value (Mean Square Error , MSE) of the test data is restored from 17.86% to 16.03%; (3) Width estimation from the kernel density estimation algorithm (KDE) show the fault damage zone ranges from 0.3 to 1.2 km. Our work provides new insights into the interpretation of fault architecture in the subsurface, and we argue the geometrical parameters of the fault damage zone is significant for understanding the evolution of fault and earthquake simulations.

Keywords:  Fault damage zone; Seismic interpretation; Machine learning (ML); Geometrical parameters

Figure1.The seismic attributes of the actual work area entered into the model and the model calculation results: (A) Original attributes of the work area. (B) Variance attribute of the work area. (C) Results calculated by the ML model

Figure2. Thermal diagram presents the structure of the fault damage zone: (A) A vertical line perpendicular to the fault orientation correction; (B) indicates the fault range with a thermal index greater than 1.572; (C) indicates a fault range with a thermal index greater than 2.065; (D) indicates a thermal index greater than 2.401 fault range. The width of the damage zone could be estimated by these figures.

 

Figure3. Descriptive diagram of fault damage zone width. Fault_1 represents the direction of fault width with thermal index greater than 1.572; Fault_2 represents the direction of fault width with thermal index greater than 2.065; Fault_3 represents the fault width trend map with thermal index greater than 2.401

How to cite: Zhang, J., Chen, S., and Liao, Z.: Machine learning reveals the width of fault damage zones in northeast Sichuan Basin, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14511, https://doi.org/10.5194/egusphere-egu24-14511, 2024.

EGU24-16472 | PICO | TS5.2

How the rigidity of the subducting plate affects the geometry of accretionary prisms? 

Laetitia Le Pourhiet, Alexis Gauthier, Nadaya Cubas, Julie Tugend, and Geoffroy Mohn

Simulations of accretionary prisms are most of the time realized either using a simplified set up that cannot account for the evolution of temperature with the growth of the prism nor deformable basement or using a very large size simulation of the complete subduction zone using a larger resolution locally. The first method is over-simplified and discards the possibility to study crustal scale accretionary prism, the second method is very costly numerically.  

Here, we present simulations of accretionary prisms that use 1/ heatflux as boundary condition allowing the temperature at the base of the model to evolve as the accretionary prism grows and 2/ flexural deformation of the basement in response to the growth of the accretionary prism. This new boundary condition is very cheap to compute as we implemented it by solving analytically the flexure equation using sinus decomposition and image method.  

We then present a set of numerical simulations of crustal scale accretionary prism with particular focus on the geometry of the subducting basement in order to better understand how the alternation between period of subduction erosion and accretion affects the geometry of the accretionary prism and its thermal history as a function of the rigidity of the subducting plate. We compare our simulations with a set of east-west trending seismic profiles located southwest of Taiwan showing along strike structural variations of the accretionary prism.    

How to cite: Le Pourhiet, L., Gauthier, A., Cubas, N., Tugend, J., and Mohn, G.: How the rigidity of the subducting plate affects the geometry of accretionary prisms?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16472, https://doi.org/10.5194/egusphere-egu24-16472, 2024.

EGU24-17730 | ECS | PICO | TS5.2

Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India 

Uma Narayan M, Surendra Kumar Sahu, Rishikesh Bharti, and Archana M Nair

The continual modification of the topography due to varied processes results in diverse and dynamic terrain. Landscape evolution studies can link the effect of small-scale topographic quantities on long-term landscape evolution. In this study, the evolutionary pattern of the Dibang basin, located at the limb of the Eastern Himalayan Syntaxis stretch along the active tectonic region of northeast India is analysed using the stream power incision model (SPIM). SPIM is an empirical power law equation linking erosion with channel area and bed slope.  With constant tectonic forcing and homogeneous physical properties, river profiles deviate from linearity and exhibit convexity (indicating uplift) and concavity (indicating erosion) in their longitudinal profiles. These deviations indicate the transient responses of the river profile due to tectonics. Here, the landscape is modelled assuming that the Dibang River lying close to the mountain front shows bedrock properties. The evolved topography is seen to exhibit an erosion-dominated landscape with a rapid decrease in the mean elevation. The profile of the Dibang River exhibits a concave-convex-concave shape, indicating that the river channel is in a state of disequilibrium. The steepness index is observed to be varying across the Dibang basin with higher values in the middle and upper right parts of the basin. The χ plot also reveals the transient nature of the river profile.

How to cite: Narayan M, U., Sahu, S. K., Bharti, R., and Nair, A. M.: Numerical simulation of Landscape Evolution using Landlab: A case study of Dibang Basin, North-East India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17730, https://doi.org/10.5194/egusphere-egu24-17730, 2024.

EGU24-18656 | PICO | TS5.2

Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting 

Martin Staněk, Prokop Závada, and Ondřej Krýza

The Reykjanes Peninsula (RP) in southwestern Iceland represents a zone of oblique rifting where the divergent boundary of the Mid-Atlantic ridge is offset to the eastern Iceland along a left-lateral transform fault - the South Iceland Seismic Zone (SISZ). RP and the SISZ represent regions of the most abundant earthquake activity on Iceland, development of fissure arrays and occasional lava eruptions. A series of earthquake swarms at RP in the 2021-2023 period indicates development of distributed fracture networks along ENE direction of the transform fault and two new fissure arrays trending NE divided by a gap in seismicity. In the last 3 years, the volcanic activity culminated two times in volcanic eruptions, bringing magmas from Moho depth at 15 km.

Inspired by the recent tectonic activity at RP, we conducted a series of analogue experiments consisting of a silicone magma chamber embedded in a photoelastic gelatine crust. The aim of our study is to constrain the links between the depth level of the magma chamber, the crustal scale fracture arrays, faults, magma pathways, superficial fractures and the location of related potential volcanic activity in a transform setting. Inducing strike slip deformation of the system, we explored the influence of shape and orientation of the magmatic chamber on the evolution and pattern of progressively developed fractures along the central shear domain. During the experiment, we captured the stress fringe patterns in the fractured gelatine. The surface deformation was traced by a stereoscopic digital image correlation (DIC) system employing two high-speed LaVision cameras. Analog magma spreading was traced using fluorescent dye mixed to the silicone or into the gelatine interlayer.

Modelling results show that decoupling of the crust above the magma reservoir in strike-slip setting produces a domain with higher vorticity bounded by a conjugate set of tensional fractures. The largest open fractures initiate at and propagate from the intersection of the principal strike-slip fault plane with the vertical contact of the magma chamber and the surrounding crust. Including other open fractures, the orientation of the fracture set is oblique (~ 60°) to the fault plane. With formation approximately coeval to those of the fractures, fine wrinkles at the crust surface are observed with orientation of ~ 120° with respect to the fault plane.

How to cite: Staněk, M., Závada, P., and Krýza, O.: Fracture and magma pathways development above sill like magmatic chambers in strike-slip setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18656, https://doi.org/10.5194/egusphere-egu24-18656, 2024.

Abstract: The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U‒Pb‒Hf isotope, whole-rock geochemistry, Sr‒Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U‒Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr‒Nd, and Lu‒Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to −5.1) and εHf(t) (−6.7 to −1.2) values, high Rb/Y and Th/La ratios, slight Nd‒Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic‒intermediate rocks from the western margin of the Yangtze Block commonly show high K2O/Na2O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area.

Keywords: Potassium-enriched intrusive rocks; Southwestern Yangtze Block; Fractional crystallization; Lithospheric mantle; Sediment melt

How to cite: Jiang, X. and Lai, S.: Petrogenesis of Neoproterozoic high-K intrusion in the southwestern Yangtze Block, South China: Implication for the recycled subducted-sediment in the mantle source, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-253, https://doi.org/10.5194/egusphere-egu24-253, 2024.

EGU24-330 | Orals | GD4.1

The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau 

Ebru Şengül Uluocak, Russell N. Pysklywec, Andrea Sembroni, Sascha Brune, and Claudio Faccenna

Post-subduction tectonics can involve a wide range of spatiotemporal processes associated with regional and large-scale upper mantle forces. To better understand the interaction between these forces in collisional settings, we focus on active mantle dynamics beneath the East Anatolian Plateau, a well-documented segment of the Arabian-Eurasian continental collision zone. In detail, we use state-of-the-art instantaneous thermomechanical models by combining the advantages of 3D numerical modeling with high-resolution imaging techniques. We analyze the model’s outputs, such as 3D stress-strain and temperature variations of upper mantle convection and reconcile them with numerous geological and geophysical observations. Our results show prominent northward-directed channel flow in the mantle that cuts across the plateau and surroundings, from the Arabian foreland to the Greater Caucasus domain. This result reproduces and elucidates the proposed ~SW-NE-oriented Anatolian Background Splitting pattern and recent seismic low-ultra low-velocity anomalies. We argue that this large-scale upper mantle flow constitutes the engine for the long-wavelength dynamic topography (~400 m) in the region and promotes the relatively small-scale convection pattern by supporting intraplate rift tectonics in the extensional Van Lake zone.

How to cite: Şengül Uluocak, E., Pysklywec, R. N., Sembroni, A., Brune, S., and Faccenna, C.: The Role of Upper Mantle Forces in Post-subduction Tectonics: Insights from 3D Thermo-mechanical Models in the East Anatolian Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-330, https://doi.org/10.5194/egusphere-egu24-330, 2024.

  Yanshanian magmatic rocks are widely distributed in the northern margin of the South China Sea and the continental margin of South China. These magmatic rocks are generally believed to have been formed by the subduction of the Paleo-Pacific plate to the South China Plate from Late Jurassic to Early Cretaceous. Due to the small number of wells drilled to the basement, most predecessors have studied on the distribution range, origin and tectonic setting of Yanshanian magmatic rocks by geophysical means(magnetic anomalies and seismic data). At present, The reported ages of basement magmatic rocks in the Pearl River Mouth Basin are mainly concentrated in Zhu 1 Depression and Panyu Low Uplift, and there is no petrological evidence in other regions.Baiyun Depression, as the largest hydrocarbon generating depression in the Pearl River Mouth Basin, has important oil and gas significance. In order to better define the spatial and temporal distribution of Yanshanian magmatic rocks, nearly 30 basement drilling samples in the periphery of Baiyun Depression and 8 onshore outcrop samples were collected. The genesis and tectonic significance of Yanshanian magmatic rocks are discussed through 76 thin sections, 7 U-Pb zircons dating, 26 major elements analysis, 16 trace elements analysis and 4 Sr-Nd-Pb isotope analysis.The results show that the magmatic rocks in the study area are concentrated in the J3-K1 and mainly developed S-type granite. These magmatic rocks are basically derived from the crust, and a few magmatic rocks or a small amount of mantle-derived materials are mixed in. The trace element discrimination diagram indicates that all samples belong to volcanic island arc type granite. The distribution curve of rare earth elements shows that light rare earth elements are enriched and heavy rare earth elements are low and stable.According to the above results, these magmatic rocks are part of the NE-trending continental margin magmatic arc formed by subduction and accretion of the paleo-Pacific plate to the South China Plate during the Yanshanian.Combined with the previous research results, it is believed that the extensional action caused by subduction and retreat of the Paleo-Pacific plate migrated to the ocean direction in the late stage of tensile rupture, and magmatism also migrated to the ocean, so the intrusion time of the magmatic rocks from continental to marine along the NW-SE direction gradually became late.This study adds important petrological evidence to clarify the genesis and tectonic setting of Yanshanian magmatic rocks in the northern margin of the South China Sea and the South China continent, and also has important application value for oil and gas exploration of buried hills in the Pearl River Mouth Basin.

How to cite: lu, F. and zhao, J.: Genesis and Tectonic Setting of Yanshanian Magmatic Rocks in the Northern Margin of South China Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-339, https://doi.org/10.5194/egusphere-egu24-339, 2024.

EGU24-568 | ECS | Posters on site | GD4.1

Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement? 

Nikola Stanković, Taras Gerya, Vladica Cvetković, and Vesna Cvetkov

Oceanic obduction and ophiolite emplacement are processes which result in positioning of more dense oceanic lithosphere on top of less dense continental crust. It is known that obduction is related to the closure of oceanic realms, however exact mechanisms that lead to the obduction of these ophiolite rocks, and more importantly, their permanent emplacement onto the continental crust is still controversial.

Although many mechanisms for ophiolite emplacement have been proposed, there have been substantial difficulties in modelling the ophiolite emplacement by means of numerical simulations. Creating physically viable simulations of the ophiolite emplacement is of paramount importance for better understanding of the process itself. There have been some notable successful attempts. For example, [1] succeeded in emplacing ophiolites by artificially reversing the velocity conditions once the ophiolite block is already obducted. More recently, [2] have shown that continental extrusion mechanism, which is a result of the activation of subducted continental crust at higher P-T conditions, can account for the emplacement of far-travelled ophiolites.

In this communication, we report interim results of our attempt to explain spontaneous emplacement of large ophiolite blocks by means of trans-lithospheric diapirism of continental crust. This phenomenon has recently been modelled [3] in the context of continental collision and the formation of the European Variscides. However, in this study, we produce a spontaneously induced intra-oceanic subduction. This model involves a retreating subduction with trench reaching the passive continental margin, leading to the continental subduction under very young oceanic lithosphere. Consequently, subducted crust is activated in deeper regions and forms a diapiric upward flow. This trans-lithospheric diapirism reaches the surface, thus separating the already obducted parts of the oceanic lithosphere from the rest of the oceanic domain, resulting in permanent ophiolite emplacement.

The presence of crustal rocks in such deep environments of ultra-high pressure certainly leads to their metamorphism. In the scope of our simulations we are monitoring the P-T paths of relevant crustal markers and propose rough estimates of the P-T conditions of metamorphic peak. For the calculations of the numerical simulations we utilize marker-in-cell method with conservative finite differences [4].

 

[1] T. Duretz, P. Agard, P. Yamato, C. Ducassou, E. B. Burov, and T. V. Gerya, “Thermo-mechanical modeling of the obduction process based on the oman ophiolite case,” Gondwana Research, vol. 32, pp. 1-10, 2016.

[2] K. Porkoláb, T. Duretz, P. Yamato, A. Auzemery, and E. Willingshofer, “Extrusion of subducted crust explains the emplacement of far-travelled ophiolites,” Nature Communications, vol. 12, no. 1, p. 1499, 2021.

[3] P. Maierová, K. Schulmann, P. ’Štípská, T. Gerya, and O. Lexa, “Trans-lithospheric diapirism explains the presence of ultra-high pressure rocks in the european variscides,” Communications Earth & Environment, vol. 2, no. 1, p. 56, 2021.

[4] T. V. Gerya and D. A. Yuen, “Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties,” Physics of the Earth and Planetary Interiors, vol. 140, no. 4, pp. 293-318, 2003.

How to cite: Stanković, N., Gerya, T., Cvetković, V., and Cvetkov, V.: Trans-Lithospheric Diapirism as a Possible Mechanism for Ophiolite Emplacement?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-568, https://doi.org/10.5194/egusphere-egu24-568, 2024.

EGU24-700 | ECS | Posters on site | GD4.1

The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints 

Noémie Bosc, Delphine Bosch, Mélody Philippon, Mélanie Noury, Olivier Bruguier, Lény Montheil, Douwe van Hinsbergen, and Jean Jacques Cornée

The British Virgin Islands (BVI) is a NE-SW trending archipelago located in the northeastern corner of the Caribbean plate. Exposing volcanic arc rocks, it is located at the junction between the old arc of the Greater Antilles to the Northwest and the active arc of the Lesser Antilles to the South. The BVI are a key location to study the geodynamical evolution of the northeastern boundary of the Caribbean plate. In order to understand its significance into the overall Caribbean evolution, a set of 16 igneous samples from seven islands was studied for petrology, geochemistry (major and trace elements, and Pb-Sr-Nd-Hf isotopes), thermobarometry (Al-in-hornblende) and U-Pb geochronology on accessory minerals (zircon, titanite and apatite). The studied rocks show a typical volcanic arc signature and correspond to a calc-alkaline series, differentiated along a NE/SW gradient. Trace elements patterns show strong negative HFSE anomalies and LILE enrichments. ɛHfi are homogeneous ranging from +11.4 to +14.1 typical of a MORB-type mantle. Magmas were thus originated from a homogeneous mantle corresponding to the mantle wedge, with participation of a slab component. The slab component contribution is estimated to be less than 2% and is dominated by aqueous fluids, except for Peter and Norman Islands. U-Pb ages emphasize an active magmatic period spanning between ~43 Ma and ~30 Ma along a NE-SW younging gradient. This age range and strong geochemical similarities with arc lavas exposed in St Martin and St Barthélémy suggest that the BVI represent the northern continuity of the Eo-Oligocene extinct branch of the Lesser Antilles arc. Crystallization depth of the studied plutonic bodies, estimated by thermobarometric constraints, supports a NE-SW increasing emplacement depth from ~7km to ~13km. The oldest plutonic bodies at NE thus experienced less total exhumation than the youngest plutonic bodies at SW (maximum rate of ~2.2 mm/yr at SW and minimum rate of ~0.2 mm/yr at NE). From Eocene to Oligocene it has been recently demonstrated that the block from Puerto Rico-Virgin Islands (PRVI) rotated 45° counter clockwise (Montheil et al., 2023). Previous thermochronological data shows that the BVI exhumation occurred synchronously along the archipelago between ~25 and ~21 Ma (Román et al., 2021). Together these observations suggest a regional tilt of the BVI block that occurred between plutons crystallisation and their exhumation at ~2 km depth. We propose that the tilting and the fast exhumation of the BVI, that are synchronous with counterclockwise rotation of the PRVI block, are the consequence of subduction locking generated by the Bahamas bank accretion to the northeastern Caribbean plate.

How to cite: Bosc, N., Bosch, D., Philippon, M., Noury, M., Bruguier, O., Montheil, L., van Hinsbergen, D., and Cornée, J. J.: The British Virgin Islands in the Caribbean Evolution: Petrogeochemical and geochronological constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-700, https://doi.org/10.5194/egusphere-egu24-700, 2024.

EGU24-1044 | ECS | Orals | GD4.1

The role of hydration-induced processes in the deformation of the North China craton 

Açelya Ballı Çetiner, Oğuz Göğüş, Jeroen van Hunen, and Ebru Şengül Uluocak

Numerous previous studies have been conducted in the North China Craton to investigate its anomalously thin lithosphere, high magmatism, and extensional tectonics along its eastern margin. Based on petrological analyses it has been suggested that the cratonic mantle lost its root (~100 km) with multiple tectonic processes during the late Jurassic – Early Cretaceous. The weakening and erosion of the North China craton is often attributed to its high water content and lower viscosity of the lithosphere associated with the movement and position of the Paleo-Pacific plate. However, other mechanisms and control parameters for the craton destruction have been proposed, and the thinning of the North China craton remains an enigmatic process.

To have a better understanding of the dynamics of the lithospheric deformations beneath the North China Craton that changes over time, we conducted a series of 2D geodynamic models. Specifically, we investigate the impact of hydration-induced processes on the lithosphere and the overriding plate and focus on parameters such as external tectonic forcing, the rheology and the strength of the overriding plate. Moreover, the effect of the angular position of the oceanic plate, and the existence of the mid-lithosphere discontinuities was also examined. Our results reveal that the destruction of North China Craton is more complex and heterogeneous than is often assumed in modelling studies. Furthermore, we find that without significant weakening, the mantle lithosphere is unlikely to delaminate. Extensive hydrous weakening may account for this, but external tectonic forcing in combination with non-linear rheology and eclogitization of the lower crust may have played an important role too.  

How to cite: Ballı Çetiner, A., Göğüş, O., van Hunen, J., and Şengül Uluocak, E.: The role of hydration-induced processes in the deformation of the North China craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1044, https://doi.org/10.5194/egusphere-egu24-1044, 2024.

EGU24-3010 | ECS | Posters on site | GD4.1

Thermo-mechanical models on the missing forearc basement in Taiwan 

Chih-Hsin Chen, Eh Tan, Shu-Huei Hung, and Yuan-Hsi Lee

Taiwan is located at the edge of the Eurasian plate and borders the Philippine Sea plate. The Philippine Sea plate is moving northwestward at a speed of 70 to 80 mm/yr and is converging with the Eurasian plate, forming the Luzon arc and the Taiwan orogenic belt. However, in the middle section of the Taiwan orogenic belt, the Luzon arc is directly adjacent to the edge of the Eurasian continental margin, and the forearc basement is missing. This phenomenon of missing forearc basement is also widely observed in similar plate convergence zones. Previous studies have suggested that this forearc basement has subducted between the Philippine Sea plate and the Eurasian plate. In order to explore the mechanism of forearc basement subduction, we used thermal-mechanical coupled numerical simulations combined with geological data to simulate the dynamic mechanism of forearc basement subduction in the middle section of the Taiwan orogenic belt.

 

The simulation results show that when the subducting plate transitions from oceanic crust to continental crust, the continental crust has a lower density and is not easily subducted. The huge mass formed by the orogeny blocks the Philippine Sea plate from moving northwestward, causing the forearc crust to bend concavely and form a forearc basin. The basin begins to accumulate a large amount of sedimentary material. Later, the center of the basin breaks to form the Longitudinal Valley fault, the island arc to the east of the basin thrusts over the forearc basement, pushing the basin sediment to uplift rapidly, and finally the forearc basement subducts below the Philippine Sea plate.

 

This model explains the mechanism for the missing forearc basement, the timing of the formation of the Longitudinal Valley fault, and the dramatic up and down movements recorded in the sedimentary rocks of the Coastal Mountains. It also explains the spatial pattern of the surface heatflow.

How to cite: Chen, C.-H., Tan, E., Hung, S.-H., and Lee, Y.-H.: Thermo-mechanical models on the missing forearc basement in Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3010, https://doi.org/10.5194/egusphere-egu24-3010, 2024.

EGU24-4122 | ECS | Orals | GD4.1

Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective 

Xin Zhou, Nicolas Coltice, and Paul Tackley

Subduction initiation (SI) creates new subduction zones and provides driving forces for plate tectonics, being a key process of theplate tectonic regime on Earth. Although SI has been extensively studied in 2D regional numerical models, obtaining a global perspective on SI remains elusive. Geological observations and plate reconstructions both suggest that SI is coeval with the global or local plate reorganizations. The tectonic plate reorganizations are marked by rapid changes of plate motions occurring over a few million years and are recurrent throughout Earth’s history.  One of the most well-known plate reorganization events occurred at approximately 53-47 Ma ago, characterized by the bending of Hawaii-Emperor Seamount Chain. Simultaneously, several SI events occurred in the Pacific Plate, such as Izu-Bonin-Mariana (~52 Ma) and Tonga-Kermadec (~50 Ma). The relationship between SI and plate reorganizations, as well as their collective impacts on continental evolution, is poorly understood. It is also unclear whether these processes are dominated  by a “top-down” or “bottom-up” mechanism. This study is committed to exploring the interaction between SI and plate reorganizations using 3D global mantle convection models. We reproduce SI coeval with plate reorganizations in these numerical models. We analyze the changes of stress distribution in the lithosphere during the plate reorganizations and their effects on SI. A variety of different interplays between SI and tectonic plates reorganizations have been identified based on their chronology and driving mechanisms. We also investigate their influences on the supercontinental breakup and assembly. Two major plate reorganization events, occurring at 100 Ma and 50 Ma ago respectively, are used to compare with the numerical modeling results. The effects of key parameters, such as lithosphere thickness and strength, will be examined. Plate reconstruction models will also be included to study the interaction between SI and plate reorganizations in the future.

How to cite: Zhou, X., Coltice, N., and Tackley, P.: Investigating Interactions between Subduction Initiation and Plate Reorganizations From A Global Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4122, https://doi.org/10.5194/egusphere-egu24-4122, 2024.

Subduction initiation remains one of the least understood global processes of plate tectonics.  Prominent models have been cast in terms of two broad classes: “spontaneous” cases due to lithospheric gravitational instabilities and “induced” cases due to forced plate convergence. Yet gravitationally unstable lithosphere is old, strong, and difficult to begin to bend into a subduction zone and convergent forces necessary to begin subduction are often too large given the plates involved. These models also consider the asthenospheric mantle as passive, even though relative motion between slabs and the asthenosphere has long been regarded as a strong control on subduction dynamics. Here I propose that subduction-transform edge propagator (STEP) faults can initiate subduction depending on the absolute motion of the STEP fault with respect to the asthenosphere. STEP faults form where subduction zones end and the subducting plate tears forming a down flexed transcurrent plate boundary at the surface shearing against the adjacent rear arc lithospheric plate. However, STEP faults are not simple transcurrent boundaries. Absolute motion of the down flexed STEP fault edge with respect to the surrounding asthenosphere can produce a strong “sea anchor” force that either continues to bend the edge downward, initiating subduction, or opposes slab bending, inhibiting subduction. In the south Pacific, the southern end of the New Hebrides Trench and the northern end of the Tonga Trench are type-example STEP faults with opposite senses of dip but both moving northward with respect to the asthenosphere. The northward dipping New Hebrides STEP fault moves northward in a mantle reference frame creating a strong asthenospheric flow against the STEP fault edge, inducing active subduction at the Matthew-Hunter trench. In contrast, the Tonga STEP fault dips southward but also has a northward component of motion with respect to the mantle. Asthenosphere thus flows southward beneath the down flexed Tonga STEP fault edge opposing further bending.  Subduction does not initiate at the Tonga STEP fault despite a ~100 Myr age contrast between the Pacific and north Fiji and Lau basin lithospheres. Since absolute plate motions reflect the sum of all forces acting on the entire lithospheric plate, a strong sea anchor mantle force may be generated at a STEP fault edge, initiating subduction (or inhibiting it), even where lithosphere is old, strong, and resists bending and without requiring large convergent forces between plates, overcoming these objections to previous models.

How to cite: Martinez, F.: Subduction initiation (or not) due to absolute plate motion at STEP faults: The New Hebrides vs. the Tonga examples, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4189, https://doi.org/10.5194/egusphere-egu24-4189, 2024.

The migration and character of magmatism over time can provide important insights into the tectonic evolution of an orogen. We present evidence for three separate episodes of compositionally distinct granitoid magmatism associated with the Acadian orogenic cycle in the eastern and southern Newfoundland Appalachians. The interpretations are based on new zircon U-Pb ages, geochemical data, and Sr-Nd-Hf-O isotopic data for 18 samples from 15 Silurian and Devonian granitoid plutons, combined with previously published data. The three episodes outline hinterland and foreland-directed migration trends and represent subduction (435-420 Ma), syn-collision (415-405 Ma), and post-collision (395-370 Ma) settings in the Acadian orogenic cycle. The Silurian plutons (435-420 Ma) consist mainly of quartz diorite, tonalite, granodiorite, monzogranite, and syenogranite, with high-K calc-alkaline and enriched Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -5 to -2; εHf[t] = -3 to -1; δ18O = +6 to +8). They are interpreted to record the subduction of oceanic lithosphere of the Acadian seaway that separated the leading edge of composite Laurentia represented by the Gander margin and Avalonia. The Early Devonian plutons (415-405 Ma), containing more voluminous monzogranite and syenogranite, have calc-alkaline to high-K calc-alkaline features, adakite-like compositions, and more-depleted Sr-Nd-Hf-O isotopic compositions (e.g., εNd[t] = -6 to 0; εHf[t] = +1 to +3; δ18O = +5 to +6). This stage occurs mostly to the northwest of the Silurian, indicating a regional scale northwestward (hinterland-directed) migration of magmatism with a rate of > 9 km/Ma. The migration is interpreted to be related to the progressive shallow underthrusting of Avalonia beneath the Gander margin (composite Laurentia) at least as far as 90 km inboard. The Middle to Late Devonian plutons (395-370 Ma) consists mainly of monzogranite, syenogranite, and alkali-feldspar granite, which are silica- and alkali-rich with large negative Eu anomalies. These rocks are concentrated along both sides of the Dover - Hermitage Bay fault zone, which represents the boundary between Avalonia and composite Laurentia, to the southeast of the Silurian-Early Devonian igneous rocks. This stage of magmatism represents a foreland-directed (retreating) migration. The Early Devonian and Middle to Late Devonian magmatism were separated by a gap between 405 and 395 Ma, and recorded an evolution from (high-K) calc-alkaline to alkaline compositions, which is ascribed to partial delamination of Avalonian lithospheric mantle in a post-collisional setting.

How to cite: Wang, C., Wang, T., Cees, V. S., Hou, Z., and Lin, S.: Evolution of Silurian to Devonian magmatism associated with the Acadian orogenic cycle in Newfoundland Appalachians: Evidence for a three-stage evolution characterized by episodic hinterland- and foreland-directed migration of granitoid magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4216, https://doi.org/10.5194/egusphere-egu24-4216, 2024.

Convergent continental margins are the major sites for the formation, differentiation, preservation, and destruction of continental crust. This article focuses on the Mesozoic crustal modification history of northeastern China from a magmatic perspective. During Mesozoic times, NE China was influenced by three convergent systems, namely the Paleo-Asian Ocean (PAO) regime to the south, the Mongol-Okhotsk Ocean (MOO) regime to the northwest, and the Paleo-Pacific Ocean (PPO) regime to the east. This study comprehensively synthesizes information on Early Triassic to Early Cretaceous magmatic rocks. We unravel the spatiotemporal effects of the above-mentioned convergent regimes by evaluating the migration of major magmatic belts and other geological and geophysical evidence. The PAO regime is confined to the southernmost part of NE China and exerted influence during pre-late Late Triassic times. The MOO regime-related magmatism lasted until the early Early Cretaceous and occurred throughout the Great Xing’an Range and adjacent regions. The spatial effect of the PPO did not exceed the eastern margin of the Songliao Basin until the Early Jurassic; low-angle to flat subduction of the PPO slab led to the westward migration of continental arc front in the Middle Jurassic and the waning of PPO regime-related magmatism in the Late Jurassic. Since the earliest Cretaceous, the rollback and retreat of the PPO slab became the predominant geodynamic control in NE China, but the superposition of the MOO regime played a role during the early Early Cretaceous. Employing whole-rock Nd and zircon Hf isotope spatial imaging, this study elucidates that, although the pre-Mesozoic lithospheric heterogeneity provides first-order control, the Mesozoic crustal architecture of NE China was further carved by Mesozoic tectonics. Retreating subduction (slab rollback) and post-collisional lithospheric delamination resulted in the prolonged extensional background and crustal growth (rejuvenation); on the contrary, low-angle subduction and syn-collisional compression could cause transient periods of ancient crust reworking. Our results also estimate the high altitude of the Great Xing’an Range and adjacent regions in the Early Cretaceous. This study opens new possibilities to explicitly document crustal modification processes in fossil orogens from a magmatic perspective.

How to cite: Huang, H., Wang, T., and Guo, L.: Crustal modification influenced by multiple convergent systems: Insights from Mesozoic magmatism in northeastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4240, https://doi.org/10.5194/egusphere-egu24-4240, 2024.

EGU24-4319 | Posters virtual | GD4.1

Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians 

Uros Stojadinovic, Marinko Toljić, Branislav Trivić, Radoje Pantović, Danica Srećković-Batoćanin, Nemanja Krstekanić, Bojan Kostić, Miloš Velojić, Jelena Stefanović, Nikola Randjelović, and Maja Maleš

Among the many examples observed worldwide, the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians represents an excellent area for a process-oriented study on the interplay between tectonics, sedimentation, and magmatism in continental back-arc basins above evolving subducted slabs. The TMC is a segment of the larger Late Cretaceous Apuseni-Banat-Timok-Srednogorie (ABTS) magmatic belt, formed in response to the subduction of the Mesozoic Neotethys oceanic lithosphere beneath the Carpatho-Balkanides of south-eastern Europe. However, despite many qualitative studies, the quantitative link between the subducted slab's mechanics and the overlying basins' evolution is less understood. Within the scope of the newly funded TMCmod project, supported by the Science Fund of the Republic of Serbia (GRANT No TF C1389-YF/PROJECT No 7461), coupled field and laboratory kinematic and petrological investigations will be focused on creating a conceptual definition of the TMC geodynamic evolution, by combining near-surface observations with the known evolution of the subduction system. This definition will be subsequently validated through analogue modelling and integrated into a coherent geodynamic model of tectonic switching in basins driven by the evolution of subducted slabs. The new geodynamic model coupling the TMC basin with its Neotethys subduction driver will quantitatively advance the strategy of prospecting and exploration of world-class porphyry copper-gold deposits, which have been actively exploited in this region for more than a century. Furthermore, reconstructed regional kinematic evolution will improve seismic hazard assessment during industrial and societal infrastructure planning and construction.

How to cite: Stojadinovic, U., Toljić, M., Trivić, B., Pantović, R., Srećković-Batoćanin, D., Krstekanić, N., Kostić, B., Velojić, M., Stefanović, J., Randjelović, N., and Maleš, M.: Towards understanding the interplay between tectonics, magmatism, and sedimentation in the Timok Magmatic Complex (TMC) basin of the Serbian Carpathians, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4319, https://doi.org/10.5194/egusphere-egu24-4319, 2024.

Previous subduction thermal models are inconsistent with the values of forearc heat flow (50-140 mW/m2) and global P‒T conditions of exhumed rocks, both suggesting a shallow environment 200~300°C warmer than model predictions. Here, we revaluate these problems in Kuril-Kamchatka using 3-D thermomechanical modeling that satisfies the observed subduction history and slab geometry, while our refined 3-D slab thermal state is warmer than that predicted by previous 2-D models and better matches the observations involving exhumed rock records. We show that warmer slabs create hierarchical slab dehydration fronts at various forearc depths, causing fast and slow subduction earthquakes. The multilayered subduction regime and a large downdip thermal gradient of > 5°C/km beneath Kuril-Kamchatka indicate a stratified characteristic effect on slab dehydration efficiency. We conclude that fast-to-slow subduction earthquakes all play a key role in balancing plate coupling energy release on megathrusts trenchward of high P‒T volcanism.

How to cite: Zhu, W. and Ji, Y.: Reestimated slab dehydration fronts in Kuril-Kamchatka using updated three-dimensional slab thermal structure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4972, https://doi.org/10.5194/egusphere-egu24-4972, 2024.

Oceanic Core Complexes (OCCs) are peridotite and serpentinite rich geological features, commonly located at the external intersections of slow-spreading mid-oceanic accreting ridges (MORs) with transform faults (TFs). The peridotites of these complexes are commonly considered to derive from the upper mantle while the serpentinites are attributed to chemical weathering that affected rock-mass during its ascent through the lithosphere. Description of cores drilled into OCCs commonly describes in detail the various peridotites but ignores the serpentinites, which are considered secondary additions. However, this presumption seems flawed due to the absence of high-pressure rocks such as eclogites, therefore it seems that the origin of the various peridotite minerals were formed concurrently with the serpentinites from pyroxenes under constrains of moderate geological pressures and temperatures, and various availabilities of H2O.

The intersections between slow MORs and TFs, where most OCCs occur, are characterized by steep thermal gradients and by distinct density contrasts. The thermal gradients in the upper crust of the MOR axial rift are nearly 1300/km, due to the shallow depth of the upper mantle there. The density of the fresh basaltic lava at the MOR is ca. 2700 kg/m3, because the temperature of the fresh basalt is some 1100oC. However, the density of the older basalt that builds the older plate across the transform fault is 2900 kg/m3. It is plausible that at fast-spreading MORs the plate juxtaposed against the active spreading rift would still be warm and its density would too light to initiate the spontaneous subduction. Tectonic experiments showed that at least 200 kg/m3 density contrast between lighter and denser crustal slabs would be sufficient to initiate spontaneous subduction. Furthermore, geochemical experimentation shows that under 500oC temperatures, namely at depths of ca. 4 km under the MOR, minerals of the pyroxene group in the oceanic basalts, are likely to be altered either into peridotites under dry conditions or into serpentinites under wet constraints at such temperature. These constraints suggest that the serpentinites in OCCs are generic and not erosional features, and their light densities and plasticity could have generated the diapiric ascent of the OCCs. The density contrast between the fresh and the old basalts, juxtaposed at the ridge – transform junctions, could take place if the spreading rate of the MOR is slow and the older slab has the time required to cool and reach the density of 2900 kg/m3.

 Keywords: Ridge-transform intersection, oceanic core complexes, spontaneous subduction, peridotites, serpentinites, diapirs.

How to cite: Mart, Y.: Oceanic core complexes: Serpentinite diapirs at slow ridge - transform fault intersections?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5261, https://doi.org/10.5194/egusphere-egu24-5261, 2024.

EGU24-5274 | ECS | Orals | GD4.1

Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling 

Christian Schuler, Boris Kaus, Eline Le Breton, and Nicolas Riel

The geodynamic evolution of the Alpine-Mediterranean area is complex and still subject to ongoing debate. The Adriatic microplate motion is of particular interest as it is influenced by three distinct subduction systems: the Alpine subduction in the north, the Dinaric-Hellenic subduction in the east, and the Calabrian-Apenninic subduction in the west. Additionally the system is influenced by the northward movement of the African continent, which further contributes to the geodynamic complexity of the region.

In this study, 3D thermomechanical simulations of the Alpine-Mediterranean region are performed using the code LaMEM (Kaus et al., 2016). The simulations employ a viscoelastoplastic rheology and an internal free surface to investigate the internal dynamics of the mantle. The initial plate configuration for the simulations is based on the kinematic reconstructions of Le Breton et al. (2021) at 35 Ma. The objective is to identify the controlling factors that drive the motion of the Adriatic microplate. This is achieved by investigating the role of various model parameters, such as the thermal structure of the lithosphere, the geometry and strength of the continental margin, the mantle viscosity, brittle parameters of the crust and the location of crustal heterogeneities.

Results show that Adria undergoes two distinct phases of plate motion over the past 35 million years. Between 35 Ma and 20 Ma, the African plate moves northward, pushing Adria in the same direction. However, once the Hellenic slab rolls back from the east and the Calabrian and Apenninic slabs roll back from the west, the Adriatic microplate decouples from the African plate, resulting in an anticlockwise rotation of Adria. Overall, this study provides valuable insights into the parameters that affect subduction dynamics in the Mediterranean and the independent motion of the Adriatic microplate.

Kaus, B. J. P., A. A. Popov, T. S. Baumann, A. E. Pusok, A. Bauville, N. Fernandez, and M. Collignon, 2016: Forward and inverse modelling of lithospheric deformation on geological timescales. Proceedings of NIC Symposium.

Le Breton, E., Brune, S., Ustaszewski, K., Zahirovic, S., Seton, M., & Müller, R. D. (2021). Kinematics and extent of the Piemont–Liguria Basin–implications for subduction processes in the Alps. Solid Earth, 12(4), 885-913.

How to cite: Schuler, C., Kaus, B., Le Breton, E., and Riel, N.: Investigating the plate motion of the Adriatic microplate by 3D thermomechanical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5274, https://doi.org/10.5194/egusphere-egu24-5274, 2024.

Fluid release from dehydration reactions and subsequent fluid migration in the subducting slab control the distribution of fluids in subduction zones, impacting many subduction processes, such as intraslab earthquakes, megathrust earthquakes, episodic slip and tremor, mantle wedge metasomatism, and arc-magma genesis.  Previous numerical models of two-phase flow indicate that compaction-pressure gradients induced by the dehydration reactions could drive updip intraslab fluid flow near the slab surface (Wilson et al., 2014). However, how the initial hydration in the incoming oceanic mantle prior to subduction impacts the updip fluid flow has not been investigated. Here, we use a 2-D two-phase flow model to investigate this effect under various initial slab-mantle hydration states and slab thermal conditions, the latter of which impact the depth extent of the stability of hydrous minerals. We especially focus on quantifying the lateral shift between the site of dehydration reactions and the location at which the fluids reach the slab surface due to their updip migration within the slab. The modeling results show that the most favourable path for updip flow is the antigorite dehydration front, the spatial extent of which depends on the slab-temperature and the thickness of the hydrated slab mantle. Our models predict that slab-derived fluids can travel over tens of km updip within the slab before reaching the slab surface. Such updip migration is more likely in warm(ish)-slabs, in which the formation of the antigorite dehydration front in the slab mantle does not require deep hydration of the incoming oceanic mantle prior to subduction.

How to cite: Cerpa, N. and Wada, I.: Role of degree and depth extent of slab-mantle hydration in controlling the intraslab fluid flow upon dehydration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6007, https://doi.org/10.5194/egusphere-egu24-6007, 2024.

EGU24-6290 | Orals | GD4.1

Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography? 

Jifei Han, Nick Rawlinson, Hrvoje Tkalčić, Caroline Eakin, Mike Coffin, and Joann Stock

Subduction is a key process in both the recycling and creation of new oceanic crust, the exchange of water between the Earth, oceans and atmosphere, and the distribution of earthquakes and volcanoes. However, the formation of new subduction zones - or subduction initiation - remains a poorly understood process. Macquarie Island, which lies along the Macquarie Ridge Complex (MRC) that forms the transpressional boundary between the Australian and Pacific plates in the southwest Pacific, is one location on Earth where subduction initiation is thought to be taking place. Several studies have suggested that the northern and southern segments of the MRC may be experiencing incipient subduction, but it is unclear what is happening in the central section, which includes Macquarie Island.


Indirect evidence for at least incipient subduction beneath Macquarie Island includes (i) ophiolite (oceanic crust) being exposed above sea level; (2) extreme topography, with Macquarie Island lying  ~5 km above the surrounding ocean basin; (3) thrust faults on either side of the island. To help investigate whether subduction may have been initiated in the neighborhood of Macquarie Island, we analyze teleseismic body wave data recorded by a network consisting of land stations and oceanic bottom seismometers deployed between October 2021 and November 2022. We extract teleseismic P-wave arrival time residuals across the combined array from ~20 events with epicentral distances between 30 and 90 degrees and invert them using FMTOMO to obtain 3-D P-wave velocity anomalies in the upper mantle. Preliminary results indicate that higher velocities are present to the east of the MRC in the vicinity of Macquarie Island, although further refinement is required before a detailed interpretation is possible.

How to cite: Han, J., Rawlinson, N., Tkalčić, H., Eakin, C., Coffin, M., and Stock, J.: Can we identify evidence of subduction initiation beneath the Macquarie Ridge Complex from teleseismic tomography?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6290, https://doi.org/10.5194/egusphere-egu24-6290, 2024.

The spinel phase (wadsleyite, ringwoodite) in the mantle transition zone (MTZ), can contain up to 1–2 wt% of water. However, whether these water reservoirs in the MTZ are filled is debated and, as the result, water content estimates in the MTZ range from less than 1 to up to 11 surface oceans (Ohtani, 2021 and references therein). I test water stability in the MTZ numerically by using 2D hydro-thermomechanical-chemical upper-mantle scale models with phase transitions and water diffusion and percolation in the mantle. Initial conditions correspond to a hydrated stagnant slab segment placed on top of 660 km discontinuity. Numerical model predicts that water diffusion from thermally relaxing slab triggers development of cold hydrous plumes from the slab surface, which are driven by the water-induced buoyancy (Richard and Bercovici, 2009). These plumes rise to and interact with olivine-spinel transition at 410 km. Positive Clapeyron slope of this transition causes cold plume upwellings to spread under it until their temperature rises enough to allow hydrated material to cross the transition. This crossing triggers aqueous fluid release, which rapidly rises upward in form of porosity waives. Relatively low water content and cold temperature of the wet plumes rising from stagnant slabs in the mantle transition zones may suppress hydrous melting above the 410 km discontinuity, thereby disabling the transition-zone water filter effect (Bercovici and Karato, 2002) at this boundary. Based on the results of experiments, we conclude that, due to the intrinsic positive buoyancy of hydrated mantle compared to dry rocks, mantle transition zone can only serve as a transient water reservoir. The duration of water residence mainly depends on the characteristic thermal-chemical relaxation time of subducting slabs in the mantle transition zone. Therefore, average water content in this zone should mainly depend on the average amount of water brought into it by subducting slabs globally during the characteristic relaxation time.

 

References

Bercovici, D., Karato, S., 2003. Whole-mantle convection and the transition zone water filter. Nature, 425, 39–44.

Ohtani, E., 2021. Hydration and Dehydration in Earth's Interior. Annual Review of Earth and Planetary Sciences, 49, 253-278.

Richard, G.C., Bercovici, D., 2009. Water-induced convection in the Earth’s mantle transition zone. J. Geophys. Res. 114, B01205.

How to cite: Gerya, T.: Is mantle transition zone a water reservoir? Yes, but only transient, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6602, https://doi.org/10.5194/egusphere-egu24-6602, 2024.

EGU24-6689 | Orals | GD4.1

Hoop Stresses in Free Subduction on a Sphere 

Neil Ribe, Stephanie Chaillat, Gianluca Gerardi, Alexander Chamolly, and Zhonghai Li

Because Earth's tectonic plates are doubly curved shells, their mechanical behavior during subduction can differ significantly from that of flat plates. We use the boundary-element method to study free (gravity-driven) subduction in 3-D spherical geometry. The model comprises a shell with thickness h and viscosity η1 subducting in a viscous planet with radius R0. Our focus is on the magnitude of the longitudinal normal membrane stress (`hoop stress'), which has no analog in Cartesian geometry. Scaling analysis based on thin-shell theory shows that the resultant (integral across the shell) of the hoop stress obeys the scaling law Tφ ∼ (η1h W/R0) max(1, cotθ) where θ is the colatitude and W is the velocity of the shell normal to its midsurface that is associated with bending. We find that the state of stress in the slab is dominated by the hoop stress, which is 3-7 times larger than the downdip stress. Because the hoop stress is compressive, it can drive longitudinal buckling instabilities. We perform a linear stability analysis of a subducting spherical shell to determine a scaling law for the most unstable wavelength, which we compare with observed shapes of trenches in the Pacific ocean. 

How to cite: Ribe, N., Chaillat, S., Gerardi, G., Chamolly, A., and Li, Z.: Hoop Stresses in Free Subduction on a Sphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6689, https://doi.org/10.5194/egusphere-egu24-6689, 2024.

The dynamics of subducting lithosphere with an embedded continental fragment is complex, with rapid changes in plate kinematics, mantle flow and uplift of the overriding plate as the fragment impacts the trench. However, the sequence and timing of the effects is often difficult to constrain, leading to uncertainties in the exact causes for particular subduction zones. We conducted 2D and 3D numerical modelling of subduction with Underworld2.0 to investigate the interactions between the subducting lithosphere and an embedded continental fragment, the Eratosthenes Seamount in the Cyprus subduction zone. Due to the uncertainty in the size of the continental crust around the Eratosthenes Seamount, we varied the size of the fragment from 200 km to 400 km (trench perpendicular) and compared to 3D model with a fixed seamount. The 3D model matches the regional seismic tomography models that show the absence of lithosphere on the subducting slab ahead of the continental fragment. In all the models, the subduction zone first develops as expected as the continental fragment approaches the trench. As the fragment contacts the trench at 6.5 Ma, the first uplift in Anatolia is experienced. However, the pace of uplift increases dramatically at 450 ka as the slab tear develops and the mantle flow pattern changes. The observed uplift rate before 450 ka is 0.07 mm/yr while after 450 ka, the uplift rate increases to 3.21 – 3.42 mm/yr. The model that best matches the size of the fragment is 200 km with a rate of 0.04 mm/yr before 450 ka and 1.76 mm/yr after 450 ka. The reference uplift rate from the model without the slab break-off from 450 ka is only 0.02 mm/yr.  The models demonstrate that the slab tear and break-off caused by the impact of the Eratosthenes Seamount causes the uplift observed and in particular is responsible for the more rapid uplift rates observed since 450 ka in the Central Taurides. 

How to cite: Clark, S. and Lou, P.: The Acceleration of Uplift in the Central Taurides due to Continental Fragment Collision in the Subduction Zone of the Eastern Anatolian Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7174, https://doi.org/10.5194/egusphere-egu24-7174, 2024.

EGU24-7864 | Orals | GD4.1

Folding of subducting slabs controls their deep thermal structures in the mantle transition zone  

Fanny Garel, Nestor Cerpa, Hana Čížková, Xavier Vergeron, Diane Arcay, Serge Lallemand, and Cécilia Cadio

The thermal structure of slabs is thought to be a key parameter for deep-focus earthquakes in subduction zones, since most proposed mechanisms, such as transformational faulting, dehydration reactions or shear instabilities, are controlled by temperature. However, the classical (shallow) thermal parameter "phi", associated to the downward advection of isotherms and approximated as slab age x sinking velocity (Kirby et al., 1996), does not explain deep-focus seismicity occurring in relativelty “hot” subduction zones, e.g. under Bolivia.

 

On the other hand, the various morphologies if subducting slabs imaged by seismic tomography reveal reveal the diversity of slab deformation histories in the transition zone as they reach the high-viscosity lower mantle, e.g. folding, deflection, vertical piling.

 

Using numerical models of subduction dynamics, we propose here to characterize the spatio-temporal evolution of deep thermal structures of subducted slab