SM – Seismology

EGU22-2052 | Presentations | MAL10 | Beno Gutenberg Medal Lecture

Space-time variations of crustal, fault zone, and seismicity structures 

Yehuda Ben-Zion

Beno Gutenberg made fundamental contributions to knowledge about large-scale earth structures and properties of moderate to large earthquakes using the seismic data available at the time. Data recorded in the last few decades by improved regional networks and dense seismic arrays provide opportunities for resolving fine details of subsurface rocks and seismicity in 4D. I review such results based primarily on recent data from Southern California. The discussed topics include multi-scale seismic imaging of the crust and fault zones, monitoring temporal changes of seismic velocities, and tracking localization of rock damage and low magnitude seismicity before large earthquakes.

The seismic imaging results reveal hierarchical rock damage structures around large fault zones with intense core damage zones and bimaterial interfaces. The fault damage zones follow overall a flower-shape structure, with significant damage in the top few km that decreases in amplitude and width with depth, and they tend to be offset from the surface trace to the side with higher seismic velocity at depth. The top 100-300 m section has generally extreme seismic properties (very low Vp, Vs, Q values; very high Vp/Vs ratios), which make it highly susceptible to failure and temporal changes. Large earthquakes produce changes of seismic velocities that decay with distance from the rupture zones, but remain significant on a regional scale in the shallow crust. The co-seismic velocity changes are followed by log(t) recovery, and can be very large (e.g. >30%) in the top 100-300 m. Appreciable changes of shallow materials are also generated by atmospheric and other non-tectonic loadings on various timescales.

The results on localization processes are based on (i) estimated production of rock damage by background seismicity, (ii) spatial localization of background events within damaged areas, and (iii) progressive coalescence of individual earthquakes into clusters. The analyses reveal generation of earthquake-induced rock damage on a decadal timescale around eventual rupture zones of large earthquakes, and progressive localization of background seismicity 2-3 yrs before M > 7 earthquakes in Southern and Baja California and M > 7.5 events in Alaska. This localization phase is followed by coalescence of earthquakes into growing clusters that precede the mainshocks. Corresponding analyses around the 2004 M6 Parkfield earthquake in the creeping section of the San Andreas fault, which is essentially always localized, show opposite tendencies to those involving faults that are locked in the interseismic periods.

Continuing efforts in these topics include merging local high-resolution imaging results within regional models, monitoring temporal changes of properties at seismogenic depth, and including geodetic data and insights from laboratory experiments in the localization analyses.

How to cite: Ben-Zion, Y.: Space-time variations of crustal, fault zone, and seismicity structures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2052, https://doi.org/10.5194/egusphere-egu22-2052, 2022.

EGU22-2108 | Presentations | MAL10 | SM Division Outstanding ECS Award Lecture

The Deep Roots of Geology: Tectonic History of Australia as expressed by Mantle Anisotropy 

Caroline Eakin

Australia is an old stable continent with a rich geological history. Limitations in sub-surface seismic imaging below the Moho, however, mean that is unclear to what extent, and to what depth, this rich geological history is expressed in the mantle. Studies of seismic anisotropy, which reflect past/present mantle deformation, can offer potential insights. One commonly employed technique is shear wave splitting, in which the wave polarisation is measured. New such results from seismic arrays deployed across central Australia, reveal a pattern of anisotropy that is consistent with past deformation of the Australian lithosphere that has been preserved for over 300 million years. Another informative technique is to use scattered surface waves, called Quasi-Love waves, that can detect lateral gradients in seismic anisotropy. The first such study for the region finds that scatterers are preferentially located near (1) the passive continental margins, and (2) the boundaries of major geological provinces within Australia. Such lateral anisotropic gradients within the continental interior imply pervasive fossilized lithospheric anisotropy, on a scale that mirrors the crustal geology at the surface. Beneath the continental margins, lateral anisotropic gradients may indicate small-scale dynamic processes in the asthenosphere, such as edge-drive convection, that are tied to the margins.

How to cite: Eakin, C.: The Deep Roots of Geology: Tectonic History of Australia as expressed by Mantle Anisotropy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2108, https://doi.org/10.5194/egusphere-egu22-2108, 2022.

SM1 – General Seismology

EGU22-2498 | Presentations | SM1.1

Crustal structure and mantle anisotropy beneath Klyuchevskoy Volcano and surrounding regions in Kamchatka 

Ayoub Kaviani, Georg Rümpker, Ivan Koulakov, Christoph Sens‐Schönfelder, and Nikolay Shapiro

We use seismological data collected from a recently deployed seismic network around the Klyuchevskoy Volcanic Group (KVG) in Kamchatka to study the crustal structure and mantle anisotropy beneath the region. In order to improve and extend the data coverage, we combined this data set with data from previous temporary deployments and permanent stations to reach a total number of 145 stations covering a region defined in the geographic coordinates 150°-167°E and 50°-61°N.

We use receiver function (RF) analysis to study the crustal structure beneath the study area. P-RFs are migrated to depth and stacked to image seismic interfaces beneath the network of seismic stations. We used a recently published three-D seismic tomography model to migrate the RFs from time to space domain. The RF amplitudes are stacked in the space domain using the Common Conversion Point (CCP) approach. The stacked RF amplitudes provide a 3-D image of seismic interfaces. The use of the 3-D velocity model helps migrate the RF amplitude to correct depths so that the depth and geometry of subsurface interfaces are constrained more correctly.  Furthermore, we are able to better compare the 3-D CCP images with the 3-D tomography model. In addition, at stations with a sufficient number of RFs, we also tried to calculate Moho depth and mean Vp/Vs ratio using the single-station H-k stacking approach. This analysis provides a way to better identify the interfaces beneath different locations and verify and adjust the depths obtained using the CCP stacking. We found a relatively complex crustal structure in the entire region of the KVG that laterally merges to a simpler structure to the west. Seismic tomography images provide better lateral resolution of velocity anomalies while RF analysis provides better vertical resolution of vertical velocity constants. Our RF-CCP images reveal two main interfaces beneath the active volcanic region. The shallow interfaces with a limited lateral extent have depths varying between 20 and 30 km. The deeper interface occurs at depths 50-60 km with an east-to-west dipping direction. In comparison with the seismic tomography model, we infer that the shallow interface is related to a velocity increase from <6 km/s to >7 km/s, implying the presence of a shallow low-velocity zone beneath the volcanic group. The deeper interface that correlates with a velocity increase from <7 km/s to around 8 km/s might be related to the top of the subducting plate. 

In addition to the RF analysis for the crustal structure, we also perform splitting analysis of core-refracted shear waves (SKS) to study mantle seismic anisotropy as a proxy for the pattern of the mantle flow field. Our SKS-splitting analysis indicates a trench-normal mantle flow beneath the eastern edge of the Kamchatka peninsula that converts to a more complex pattern beneath the KVG region. We argue that this pattern of fast polarization direction suggests the rotational mantle flow that may be related to a slab gap at the junction between the Kuril-Kamchatka and Aleutian arcs.

How to cite: Kaviani, A., Rümpker, G., Koulakov, I., Sens‐Schönfelder, C., and Shapiro, N.: Crustal structure and mantle anisotropy beneath Klyuchevskoy Volcano and surrounding regions in Kamchatka, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2498, https://doi.org/10.5194/egusphere-egu22-2498, 2022.

EGU22-2839 | Presentations | SM1.1

A decade of short-period earthquake rupture histories from multi-array back-projection 

Felipe Vera, Frederik Tilmann, and Joachim Saul

Teleseismic back-projection has emerged as a widely-used tool for understanding the rupture histories of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry, notably the `swimming' artifact. We present a teleseismic back-projection method with multiple arrays and combined P and pP waveforms. The method is suitable for defining arrays ad-hoc in order to achieve a good azimuthal distribution for most earthquakes.

We present a catalog of short-period rupture histories (0.5-2.0 Hz) containing 54 events from 2010 to 2021 (Mw  7.5), including recent and significant earthquake ruptures, e.g., 2021 Mw 8.3 South of Sandwich Islands, 2021 Mw 8.2 Chignik, 2021 Mw 8.1 Kermadec Islands, and 2020 Mw 7.8 Simeonof Island.

The method provides semi-automatic estimates of rupture length, directivity, speed, and aspect ratio, which are related to the complexity of large ruptures. We determined short-period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub-Rayleigh regime for thrust and normal earthquakes, whereas strike-slip events propagated in the unstable supershear range. Many of the rupture histories exhibited complex behaviors such as rupture on conjugate faults (e.g., 2018 Mw 7.9 Gulf of Alaska), bilateral ruptures (e.g., 2017 Mw 7.8 Komandorsky Islands), and dynamic triggering by a P wave (e.g., 2016 Mw 7.9 Solomon Islands). For megathrust earthquakes, ruptures encircling asperities were frequently observed, with down-dip (e.g., 2021 Mw 8.1 Kermadec Islands), up-dip (e.g., 2016 Mw 7.8 Pedernales), double encircling (e.g., 2015 Mw 8.3 Illapel), and segmented (e.g., 2020 Mw 7.8 Simeonof Island) patterns. Although there is a preference for short-period emissions to emanate from central and down-dip parts of the megathrust, emissions up-dip of the main asperities are more frequent than suggested by earlier results.

How to cite: Vera, F., Tilmann, F., and Saul, J.: A decade of short-period earthquake rupture histories from multi-array back-projection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2839, https://doi.org/10.5194/egusphere-egu22-2839, 2022.

EGU22-3017 | Presentations | SM1.1

An Improved shear velocity model beneath the Iranian plateau using adjoint noise tomography 

Abolfazl komeazi, Ayoub Kaviani, Farzam Yaminifard, and Georg Rümpker

We perform an adjoint waveform tomography using Rayleigh-wave empirical Green‘s functions (EGFs) at periods 10-50 s to improve a pre-existing 3-D velocity model of the crust and uppermost mantle beneath the Iranian plateau. The starting model was derived from a conventional surface-wave dispersion tomography based on high-frequency ray-theory assumption to invert of a quasi-3-D shear-wave velocity model. We use the EGFs from the same study that were derived from cross correlation of continuous seismic noise. Adjoint tomography refines the initial model by iteratively minimizing the frequency-dependent travel-time misfits between synthetic and observed EGFs measured in different period bands. Our new model covers the known tectonic units such as the Central Iranian Block, Zagros fold-and-thrust belt, Sanandaj-Sirjan metamorphic zone and Urumieh-Dokhtar magmatic arc.

Overall, the adjoint tomography provides images with better lateral resolution and depth sensitivity and more realistic absolute velocity values due to the inclusion of finite-frequency waveforms. The use the numerical spectral-element solver in adjoint tomography provides accurate structural sensitivity kernels, which helps to obtain more robust images rather than those generated by ray-theory tomography. The final model adjusts the shapes of velocity anomalies at crustal depth more specifically for the eastern Zagros. The final model significantly improves the initial model at the upper mantle depths and provides a higher resolution for the shape of velocity anomalies.

How to cite: komeazi, A., Kaviani, A., Yaminifard, F., and Rümpker, G.: An Improved shear velocity model beneath the Iranian plateau using adjoint noise tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3017, https://doi.org/10.5194/egusphere-egu22-3017, 2022.

EGU22-3794 | Presentations | SM1.1

Preliminary results of investigation of “unidentified fault” associated with the Mw 7.3 Flores Sea earthquake 

Pepen Supendi, Nicholas Rawlinson, Bambang Setiyo Prayitno, Sri Widiyantoro, Kadek Hendrawan Palgunadi, Andrean Simanjuntak, Andri Kurniawan, Gayatri Indah Marliyani, Andri Dian Nugraha, Daryono Daryono, Iman Fatchurochman, Muhammad Sadly, Suko Prayitno Adi, Dwikorita Karnawati, Mohammad Taufik Gunawan, and Abraham Arimuko

On December 14, 2021, the Mw 7.3 Flores Sea earthquake occurred approximately 100 km to the north of Flores Island, one of the most complex tectonic settings in Indonesia. The existence of the causative fault that generated this earthquake was not been previously known, therefore making further analysis crucial for assessing future seismic hazard in the region. In this study, we relocated the hypocenter of the mainshock and aftershocks using a double-difference method, determine focal mechanisms using waveform inversion, and then analyse stress changes to estimate the fault type and stress transfer caused by this earthquake. Our relocated hypocenters show that this earthquake sequence ruptured on at least three segments: the source mechanism of the mainshock exhibits dextral strike-slip motion (strike N288oW and dip 78o) that occurred on a West-East trending fault which we call the Kalaotoa Fault, while rupture of the other two segments located to the west and east of the mainshock (WSW-ESE directions, respectively) may have been triggered by this earthquake. The Coulomb stress change of the mainshock shows that areas to the northwest and southeast experienced an increase in stress, which is consistent with the observed aftershock pattern.

How to cite: Supendi, P., Rawlinson, N., Prayitno, B. S., Widiyantoro, S., Palgunadi, K. H., Simanjuntak, A., Kurniawan, A., Marliyani, G. I., Nugraha, A. D., Daryono, D., Fatchurochman, I., Sadly, M., Adi, S. P., Karnawati, D., Gunawan, M. T., and Arimuko, A.: Preliminary results of investigation of “unidentified fault” associated with the Mw 7.3 Flores Sea earthquake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3794, https://doi.org/10.5194/egusphere-egu22-3794, 2022.

EGU22-4071 | Presentations | SM1.1

Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers 

Jannes Münchmeyer, Jack Woollam, Andreas Rietbrock, Frederik Tilmann, Dietrich Lange, Thomas Bornstein, Tobias Diehl, Carlo Giunchi, Florian Haslinger, Dario Jozinović, Alberto Michelini, Joachim Saul, and Hugo Soto

Seismic event detection and phase picking are the base of many seismological workflows. In recent years, several publications demonstrated that deep learning approaches significantly outperform classical approaches, achieving human-like performance under certain circumstances. However, as studies differ in the datasets and evaluation tasks, it is yet unclear how the different approaches compare to each other. Furthermore, there are no systematic studies about model performance in cross-domain scenarios, i.e., when applied to data with different characteristics.

Here, we present the results from a large-scale benchmark to address these questions. We compare six previously published deep learning models on eight datasets covering local to teleseismic distances and on three tasks: event detection, phase identification and onset time picking. Furthermore, we compare the results to a classical Baer-Kradolfer picker.

Overall, we observe the best performance for EQTransformer, GPD and PhaseNet, with a small advantage for EQTransformer on teleseismic data. Furthermore, we conduct a cross-domain study, analyzing model performance on datasets they were not trained on. We show that trained models can be transferred between regions with only mild performance degradation, but models trained on regional data do not transfer well to teleseismic data.

As deep learning for detection and picking is a rapidly evolving field, we ensured extensibility of our benchmark by building our code on standardized frameworks and making it openly accessible. This allows model developers to easily evaluate new models or performance on new datasets. Furthermore, we make all trained models available through the SeisBench framework, giving end-users an easy way to apply these models.

 

Published as Münchmeyer, J., Woollam, J., Tilmann, F., Rietbrock, A., Lange, D., Bornstein, T., Diehl, T., Giunchi, C., Haslinger, F., Jozinović, D., Michelini, A., Saul, J. & Soto, H. (2021). Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers. Journal of Geophysical Research: Solid Earth. doi.org/10.1029/2021JB023499

How to cite: Münchmeyer, J., Woollam, J., Rietbrock, A., Tilmann, F., Lange, D., Bornstein, T., Diehl, T., Giunchi, C., Haslinger, F., Jozinović, D., Michelini, A., Saul, J., and Soto, H.: Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4071, https://doi.org/10.5194/egusphere-egu22-4071, 2022.

EGU22-4238 | Presentations | SM1.1

MERMAIDs in the South Pacific Ocean: Observations, Measurements, Modeling, Data Availability, and First Hints at Mantle Structure 

Jessica Irving, Joel Simon, Sirawich Pipatprathanporn, Frederik Simons, and The EarthScope-Oceans Consortium


MERMAIDs (Mobile Earthquake Recording in Marine Areas by Independent Divers) are seismic instruments which record local, regional and teleseismic earthquakes, and other signals, in the oceans. In the Southern Pacific Ocean, some fifty MERMAIDs are collecting acoustic pressure time series as part of the South Pacific Plume Imaging and Modeling (SPPIM) project. Deployed in 2018 and 2019 by members of the EarthScope-Oceans consortium, these instruments record continuous time series data on a one-year buffer and autonomously report a wealth of waveforms, selectively triggered mostly by teleseismic events, suitable for mantle tomography. 

Listening for signals while roughly 1.5 km below the ocean surface, MERMAIDs' primary mission is to detect and deliver records of P-waves generated by distant earthquakes, and collectively they have returned many thousands of seismograms corresponding to such signals. We present highlights from our earthquake catalog and discuss the changing character and causes of the background noise. Whilst the South Pacific fleet is programmed to only send short seismic records, corresponding to confident identifications of teleseismic first arrivals, some records contain later-arriving phases. In addition to P-waves, we present a miscellany of observations of other signals, including core phases, converted S- and surface waves, and T-phases. Furthermore, we illustrate that we are able to obtain other recorded data segments through buffer requests via satellite. 

Data from the MERMAIDs owned by Geoazur and Princeton University that we report on here are being archived by IRIS—those from three instruments is available without embargo. We highlight MERMAID waveform availability and its utility to the scientific community via examples of their modeling and preliminary interpretations that can be made regarding wavespeed heterogeneity in the dynamic mantle below the Pacific Ocean. 

How to cite: Irving, J., Simon, J., Pipatprathanporn, S., Simons, F., and EarthScope-Oceans Consortium, T.: MERMAIDs in the South Pacific Ocean: Observations, Measurements, Modeling, Data Availability, and First Hints at Mantle Structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4238, https://doi.org/10.5194/egusphere-egu22-4238, 2022.

EGU22-5570 | Presentations | SM1.1

Seismicity analysis of Southern Ghana II: Updated crustal velocity model and hypocentral parameters 

Susana Custódio, Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, Luis Matias, and Graça Silveira

A small network of six broadband seismic sensors operated in southern Ghana between October 2012 and April 2014 (GHDSN). During this period, no seismicity was reported by the global data centers, however application of the Deep Learning algorithm EQTransformer resulted in the detection and subsequent location of 73 earthquakes. Preliminary constant crustal velocity models with  vp=5.55 km/s and vs=3.36 km/s have been utilized since 2002 to locate the local earthquakes in southern Ghana. Using this crude velocity model resulted in scattered seismicity, hinting into a likely inadequacy of these preliminary velocity parameters to represent the elastic properties of the area. In this study, we perform a joint-inversion for estimating an updated 1D crustal velocity model and the hypocentral parameters of the 73 recently detected local earthquakes. A grid search method is implemented and a 6-layer velocity model is defined, down to 45 km crustal depth. The space of velocity model parameters is searched by altering the upper depth of the layers (ud), P-wave velocity in each layer (vp), and the ratio of vp/vs. The optimized velocity model and hypocenteral parameters are evaluated by minimizing the RMS error function between the observed (533 picked phases consisting of 282 P and 251 S phases) and calculated arrival times. A two-step implementation is devised to increase the computational efficiency of the inversion process. Initially, the optimum  vp/vs is estimated by implementing a coarse grid search on vp and ud values. Then, incorporating the optimum vp/vs a fine grid search on vp and ud is applied.
The results yields layers with 1, 13, 8, 13 and 10 km thickness, with vp = 5.9, 6.1, 6.3, 6.5, 6.9 and 7.2 km/s, respectively. The updated velocities for the first and last layers are 6% and 26% percent higher than the previously reported constant velocity models. Furthermore, the updated vp/vs=1.70 is 0.03% higher than the corresponding value vp/vs=1.65 of the constant velocity model. The updated hypocentral locations of the 73 earthquakes with  2.5<ML<3.9 are concentrated on five major clusters. Two clusters are located on the AFZ, indicative of the active role of this structure in the seismicity of the region. Two other clusters, which have the highest rate of activity,  are positioned in the intersection between the AFZ and CBF. The last cluster consists of scattered earthquakes that coincide with mapped segments of the AFZ. Incorporating the updated velocity model for estimating the hypocentral parameters resulted in enhanced seismogenic source delineation in southern Ghana.  This research contributes to the FCT-funded projects SHAZAM (PTDC/CTA-GEO/31475/2017), RESTLESS (PTDC/CTA-GEF/6674/2020), SIGHT (PTDC/CTA-
GEF/30264/2017) and IDL (UIDB/50019/2020).

How to cite: Custódio, S., Mohammadigheymasi, H., Tavakolizadeh, N., Matias, L., and Silveira, G.: Seismicity analysis of Southern Ghana II: Updated crustal velocity model and hypocentral parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5570, https://doi.org/10.5194/egusphere-egu22-5570, 2022.

EGU22-5860 | Presentations | SM1.1

Seismicity analysis in southern Ghana- I: Detecting local earthquakes by Deep Learning 

Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, S. Mostafa Mousavi, Graça Silveira, and Rui Fernandes

A large volume of digital seismic data was recorded by six broadband seismic sensors equipped with GPS-clock timing in the Ghana Digital Seismic Network (GHDSN) between October 2012 and April 2014. For this period, no public seismicity catalog was reported by the global data centers, International Seismological Center (ISC), and United States Geological Survey (USGS) for southern Ghana. In this study, this database is processed to detect local earthquakes. To facilitate the challenging and time-consuming process of detecting the earthquakes and picking the arrival times of P and S phases, we utilize EQTransformer, a Deep Learning (DL) model deploying Hierarchical Attention Mechanism (HAM) for simultaneous earthquake detection and phase picking. This model utilizes global and local levels of attention mechanism for identifying earthquake and seismic phases deriving benefits from deep neural networks, including convolutional and recurrent neurons. The thresholding values of 0.2, 0.07, and 0.07 are set for earthquake detection, P-picking, and S-picking, respectively. As a result, a list of events for each station of the network with the associated time of detection, as well as P and S phase arrivals are obtained. Taking these arrival times into account, we have devised a so-called ”conservative strategy” to optimally extract all possible earthquakes in the data set, amenable to locate. Initially, a list of preliminary events recorded by at least two stations is created by comparing the earthquake occurrence and arrival times of the P and S phases for all stations regarding a 100 sec time threshold. The list in this step includes 317 events recorded by at least two stations. Eventually, an analyst controls the obtained waveforms in other stations assesses whether EQTranasformer misses the preliminary list of events in those stations. Consequently, a number of 533 picked phases (282 P and 251 S) recorded by a minimum of 3 stations are finalized. Incorporating these phases and removing the instrument response from the waveforms, the hypocentral parameters for 73 earthquakes with 2.5 ≤ M L ≤ 4.0 are estimated. The main concentration of events is on the intersection of the Akwapim fault zone and the coastal boundary fault, with some scattered seismicity along the Akwapim fault zone. The corresponding set of seismic phases is utilized to estimate an updated 1D crustal velocity model for the study area. This research contributes to the FCT-funded projects SHAZAM (Ref. PTDC/CTA-GEO/31475/2017), RESTLESS (Ref. PTDC/CTA-GEF/6674/2020), SIGHT (Ref. PTDC/CTA-GEF/30264/2017), and IDL (Ref. UIDB/50019/2020).

How to cite: Mohammadigheymasi, H., Tavakolizadeh, N., Mousavi, S. M., Silveira, G., and Fernandes, R.: Seismicity analysis in southern Ghana- I: Detecting local earthquakes by Deep Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5860, https://doi.org/10.5194/egusphere-egu22-5860, 2022.

The Eifel region is a large volcanic system in the middle of European continent. From the Eifel teleseismic tomography experiment (8 months in 1997-1998), a mantle plume beneath the volcanic fields (down to 400 km depth) has been identified and further confirmed by receiver function and teleseismic surface wave dispersion analyses. A study in 2020 using dense geodetic observations leads to the conclusion that the Eifel region experiences a pronounced uplift encompassing the neighbouring countries Netherlands, Belgium, Luxembourg and France, which is attributed to the same buoyant mantle plume.

A detailed focus on the uppermost 30 km above the Moho has been missing until recently. However, a noteworthy recent seismological investigation showed the evidence of a deep magmatic recharge beneath the Laacher See Volcano in East Eifel between 2013 and 2018. Located at depth roughly between 40 and 10 km, low-frequency seismic swarms, which are typical of volcanic environment, convey the presence of magma movements and potential storage zones in the crust.  

The present study aims to bring additional information on this shallow active magmatic system using an Ambient Noise Tomography (ANT). Thanks to theoretical and technical developments over the two last decades, this approach has been increasingly popular for imaging Earth structure worldwide at different scales. We use here ambient noise data from archives of the 1997-1998 Eifel experiment and more recent (2019-2020) continuous seismic record. The group velocity dispersion of Rayleigh waves are estimated between station pairs from Noise Cross-correlation Functions (NCF) covering the secondary microseismic frequency band, which allows to sample the uppermost 10-20 km of the crust. Our contribution includes a complete description of the ANT/NCF processing (e.g., directivity of the noise sources, sensitivity tests) in order to better constrain the velocity anomalies observed in the Eifel region and around.

How to cite: Barrière, J. and Oth, A.: Imaging the uppermost layers of the Eifel volcanic system (Germany) using ambient microseismic noise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7268, https://doi.org/10.5194/egusphere-egu22-7268, 2022.

EGU22-7994 | Presentations | SM1.1

The impact of the September 27, 2021, Mw=6.0 Arkalochori (Central Crete, Greece) earthquake on the natural environment and the building stock 

Spyridon Mavroulis, Haralambos Kranis, Stylianos Lozios, Ioannis Argyropoulos, Emmanuel Vassilakis, Konstantinos Soukis, Emmanuel Skourtsos, Efthymis Lekkas, and Panayotis Carydis

On September 27, 2021, an Mw=6.0 earthquake struck the central part of Crete Island (southern Greece) and in particular the Heraklion Region. This event was preceded by an extended foreshock sequence started on early July 2021 and it was followed by an Mw=5.3 aftershock on the following day.

Taking into account the spatial distribution of foreshocks and aftershocks and the focal mechanism of mainshock as well as the active faults of the earthquake-affected area, it is evident that the seismic activity is strongly related to the NNE-SSW striking W-dipping faults of the Kasteli fault zone located along the eastern margin of the Neogene to Quaternary Heraklion Basin. The latter has been filled with Miocene to Holocene post-alpine deposits.

A field reconnaissance conducted by the authors in the earthquake-affected area shortly after the mainshock revealed that the earthquake-triggered effects comprised mainly rockfalls and slides, as well as ground cracks within or close to landslide zones. These effects were located within the hanging-wall of the KFZ. The affected sites are mainly composed of Miocene deposits and they are characterized by pre-existing instability conditions and high susceptibility to landslides. Far field effects were also observed south of the earthquake-affected area and in particular in the southern coastal part of Heraklion Region.

In regards to the spatial distribution of the earthquake-induced building damage, the vast majority was caused in villages and towns founded on Miocene and Holocene deposits of the hanging-wall. Damage was not reported in settlements located in the footwall, which is composed of alpine formations.

The dominant building types of the earthquake-affected area comprise: (i) buildings with load-bearing masonry walls made of stones and bricks with clay or lime mortar, mainly constructed without any anti-seismic provisions and (ii) buildings with reinforced-concrete frame and infill walls constructed according to the applicable seismic codes. The former suffered the most severe structural damage including partial or total collapse in many villages founded on post-alpine deposits of the hanging-wall of KFZ. The latter responded satisfactory during the mainshock and were less affected with only non-structural damage including cracking, detachment of infill walls from the surrounding reinforced concrete frame, peeling of concrete and short-column failures.

From the abovementioned, it is concluded that the impact of the 2021 Arkalochori earthquake was limited to the hanging-wall of the causative fault zone and in particular to residential areas founded on post-alpine deposits and to slopes highly susceptible to failure within the Heraklion Basin.

How to cite: Mavroulis, S., Kranis, H., Lozios, S., Argyropoulos, I., Vassilakis, E., Soukis, K., Skourtsos, E., Lekkas, E., and Carydis, P.: The impact of the September 27, 2021, Mw=6.0 Arkalochori (Central Crete, Greece) earthquake on the natural environment and the building stock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7994, https://doi.org/10.5194/egusphere-egu22-7994, 2022.

EGU22-8366 | Presentations | SM1.1

The 14 December 2021, Mw 7.4 Flores Earthquake: Review of the hypocenter relocation, slip distribution, coulomb stress, and seismic hazard 

Supriyanto Rohadi, Tio Azhar Prakoso, Tatok Yatimantoro, Aditya Rahman, Bambang Sunardi, Agustya Adimarta, Nelly Florida Riama, Suko Prayitno Adi, Bagus Adi Wibowo, and Dwikorita Karnawati

A major earthquakes struck the north of Flores island, in Nusa Tenggara Timur, Indonesia, on 14  December 2021 at 10:20:22 local time, the hypocenter is 7.59°S, 122.26°E, depth 12.0 km, with moment magnitude Mw 7.4. The faulting orientation of the mainshock, fault plane was strike = 290°, dip = 89°, and rake = 177°, and the auxiliary plane was strike = 21°, dip = 87°, and rake = 1°, respectively, is possibly related to thrust fault in the sea. Focal mechanism solutions for the earthquakes indicate rupture occurred thrust fault with large dip angle. The mainshock was followed by low aftershocks productivity may due to homogeneous faulting systems and relatively uniform stress state in that region. We analyze aftershock hypocenter relocation and gravity anomaly, slip distribution, coulomb stress and seismic hazard (PSHA) to investigate the earthquake characteristics and seismic hazard analysis. The distribution of hypocenter relocations show that aftershock ruptured distribute between two block of high gravity anomaly, its indicate that it was not the new fault. The inversion of the source model shows several time periods of energy release with three main peaks. These temporal rupture suggest repetition of a large scale slip on the large asperity. The models of coulomb stress indicate that static stress transfer due to the Mw 7.4 earthquake is suitable with aftershock spatial distribution. We compute the probabilistic seismic hazard assessment in the Flores region for Earthquake mitigation

How to cite: Rohadi, S., Prakoso, T. A., Yatimantoro, T., Rahman, A., Sunardi, B., Adimarta, A., Riama, N. F., Adi, S. P., Adi Wibowo, B., and Karnawati, D.: The 14 December 2021, Mw 7.4 Flores Earthquake: Review of the hypocenter relocation, slip distribution, coulomb stress, and seismic hazard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8366, https://doi.org/10.5194/egusphere-egu22-8366, 2022.

EGU22-8492 | Presentations | SM1.1

Boundary and elastic parameter sensitivity kernels for a receiver function waveform misfit in a global earth. 

Janneke de Jong, Hanneke Paulssen, and Jeannot Trampert

The receiver function method is widely used in seismology to study the characteristics of Earth’s major discontinuities. Ray theory and an assumed planar incoming wave are often used to estimate which regions of the mantle, crust and discontinuity contribute to the receiver function. To test the validity of these simplifying assumptions, we derived the adjoint source of a receiver function waveform misfit and applied the adjoint method on synthetic teleseismic receiver functions to calculate their sensitivity kernels of both subsurface velocity parameters in the mantle and boundary topography on the discontinuity. Here we focused on the P660s-phase and the 660-discontinuity. We observe a strong sensitivity to the wavefield far away from the discontinuity, particularly for the Vp sensitivity kernel. It has a strong sensitivity to the Fresnel zone of the P660s-phase before conversion, but also to the scatterers of the direct P-wave and other phases that arrive within the considered time window. This implies that mapping the observations solely to the P660s ray paths and ray-theoretical conversion points might be too simplistic and lead to inaccuracies in the conclusions. In general, a receiver function has a strong dependance on the background velocity models everywhere in the mantle. The boundary topography kernels have a sensitivity predominantly to the area near the conversion point. The diameter of the high-sensitivity area is roughly 300 km for an event with a source halftime of 5 s. Relatively weak sensitivity to the source region and the scatterers of the direct P-wave are observed in the boundary kernels as well. Our results show that using the adjoint method on receiver function waveforms to invert for mantle structure and boundary topography is possible and advisable. It allows for an automatic consideration of all contributing phases and scatterers arriving within the chosen time window, which is important for correctly dealing with velocity perturbations. The boundary kernels demonstrate that the receiver functions’ sensitivity to topography is concentrated to the region around the ray theoretical conversion point.

How to cite: de Jong, J., Paulssen, H., and Trampert, J.: Boundary and elastic parameter sensitivity kernels for a receiver function waveform misfit in a global earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8492, https://doi.org/10.5194/egusphere-egu22-8492, 2022.

EGU22-8496 | Presentations | SM1.1

Characteristic of Source and Seismic Hazard Analysis of Majene Earthquake Mw 6.2, January 15, 2021 

Retno Agung Prasetyo, Supriyanto Rohadi, Rahmat Setyo Yuliatmoko, Aditya Rahman, Yusuf Hadi Perdana, Nelly Florida Riama, Suko Prayitno Adi, Dwikorita Karnawati, and Bambang Setiyo Prayitno

A major earthquakes struck the Majene Regency, in West Sulawesi province, Indonesia, on 15 January 2021 at 02.28 local time, the hypocenter is 2.97°S, 118.99°E, depth 38.0 km, with moment magnitude Mw 6.2 with an epicenter located about 6 km Northeast Majene, West Sulawesi. This large event causing extensive damage, great economic loss and casualties in the Majene city and surrounding region. The mainshock preceded by significant foreshock on 14 January 2021 at 14.35 local time, 3°S, 118.94°E, depth 10.0 km Mw 5.9, epicenter was located at about 4 km Northwest of Majene. The faulting orientation of the mainshock, and foreshock was strike = 330°, dip = 17°, and slip = 59°, and strike = 353°, dip = 29°, and slip = 61°, respectively, is possibly related to Mamuju-Majene thrust fault. Focal mechanism solutions for the earthquakes indicate rupture occurred thrust fault with low dip angle. The mainshock was followed by low aftershocks productivity may due to homogeneous faulting systems and relatively uniform stress state in that region. We use hypocenter relocation, stress drop, coulomb stress and seismic hazard (PSHA) to investigate the earthquake characteristics and seismic hazard analysis. The distribution of hypocenter relocations indicate aftershock ruptured northern extension of the mainshock. This result supports that the highest of acceleration is the north component of the three component recorded acceleration, this detect the components of directivity toward the north for the foreshock distribution.

How to cite: Prasetyo, R. A., Rohadi, S., Yuliatmoko, R. S., Rahman, A., Perdana, Y. H., Riama, N. F., Adi, S. P., Karnawati, D., and Prayitno, B. S.: Characteristic of Source and Seismic Hazard Analysis of Majene Earthquake Mw 6.2, January 15, 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8496, https://doi.org/10.5194/egusphere-egu22-8496, 2022.

EGU22-8536 | Presentations | SM1.1

The DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging (DETECT) experiment, a new paradigm for near-fault observations 

Matteo Picozzi, Antonio Giovanni Iaccarino, Dino Bindi, Fabrice Cotton, Gaetano Festa, Angelo Strollo, Aldo Zollo, Tony Alfredo Stabile, Guido Maria Adinolfi, Claudio Martino, Ortensia Amoroso, Raffaella De Matteis, Vincenzo Convertito, and Daniele Spallarossa and the DETECT team

Near-fault observations can provide insights into the physical process interaction between fault slip activation, fluid presence/migration and seismicity production, processes acting at different timescales that generate large earthquakes.

The DETECT experiment aims at exploiting very dense seismic networks deployed across a segmented faults system to foster the development of scientific integrated methodologies for monitoring and imaging the faults behavior during the inter-seismic phase. Target of the monitoring is to: detect and track space-time trends of different source parameters that could be related to a preparation process leading to a larger earthquake; investigate the frictional and stress states of the fault segments to anticipate the characteristics of the future large earthquake (e.g., hypocenter but also future large seismic energy release locations); analyze the interactions between the different fault segments to model/anticipate potential cascade effects.

The DETECT experiment is carried out in the Irpinia area (southern Italy), one of the regions in Italy and Europe showing the highest seismic hazard. Since august 2021, a constellation of 20 seismic arrays, for a total of 200 seismic stations (20 broad-band sensors and 180 short-periods), has been installed over the fault segments responsible for the Ms 6.9, 1980 Irpinia earthquake, the strongest and most destructive seismic event of the last half-century in southern Italy.

DETECT results from a joint effort of local Universities, National and International Research Institutes. A novel and crucial aspect is that, differently from most studies concerning intra-plate earthquakes which are usually carried out after that large magnitude earthquakes have occurred, DETECT aims to put us in advantageous position and to unveil the preparatory process that generate large earthquakes and anticipate the role of the segmentation by studying at one time different fault segments, some of which are in rather late stage of their seismic cycle.

With this contribution, we aim to present the DETECT experiment, the preliminary results and foster additional cooperation including complementary expertise to further enrich the partnership.

How to cite: Picozzi, M., Iaccarino, A. G., Bindi, D., Cotton, F., Festa, G., Strollo, A., Zollo, A., Stabile, T. A., Adinolfi, G. M., Martino, C., Amoroso, O., De Matteis, R., Convertito, V., and Spallarossa, D. and the DETECT team: The DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging (DETECT) experiment, a new paradigm for near-fault observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8536, https://doi.org/10.5194/egusphere-egu22-8536, 2022.

EGU22-8652 | Presentations | SM1.1

Testing seismic velocity models with quarry blast data 

Pierre Arroucau, Jessie Mayor, Marc Grunberg, Emmanuelle Nayman, and Guillaume Daniel

Seismic event locations are usually performed by means of iterative, linearized arrival time inversion considering 1D velocity models with fixed data errors. Both the use of inaccurate velocity structure or data error estimates may however affect the quality of event location and uncertainty evaluation. Here, we test a 3D P- and S-wave velocity model built in a previous work for Metropolitan France (the part of France located in Europe) and we compare it with the “Auvergne” 1D velocity model used by BCSF-RéNaSS (Bureau Central Sismologique Français - Réseau National de Surveillance Sismique) using quarry blast data. The reason for using quarry blast data is that, to some extent, their epicentral location and depth are known, which is not the case for earthquakes. We first identify potential active quarries over the territory of Metropolitan France by comparing catalog quarry blast locations with those from quarries visible from satellite images. Relocation is achieved by means of a Hierarchical Bayesian inversion procedure in which not only the hypocentral parameters (longitude, latitude, depth, origin time) are inverted for, but also P- and S-wave arrival time errors. The area of interest is a 1° by 1° zone located between 4°E and 5°E in longitude and 44°N and 45°N in latitude, the region where the Le Teil earthquake occurred (Mw 4.9, 2019/11/11). We first demonstrate the ability of the algorithm to properly determine hypocentral parameters and data noise using two simple synthetic experiments. Then we apply it to real data and relocate 147 quarry blasts that occurred in the region between 1980 and 2020 and that were located wit the “Auvergne” 1D velocity model. Relocations obtained with the 1D and 3D model are rather similar. Estimated data errors are larger, in both cases, than the amplitude of picking uncertainties, meaning that both models could be improved, by seismic arrival time tomography for instance. They are larger in the 3D case, suggesting that, from that point of view, the 1D model is in better agreement with the data. Distances between relocated hypocenters and the closest known quarry are comparable but relocations with the 3D model are characterized by shallower hypocenters than those obtained with the 1D model, so they appear more consistent with the fact that events are quarry blasts. In both cases, some events are quite far away from the closest quarry, suggesting that some of them might be natural events.

How to cite: Arroucau, P., Mayor, J., Grunberg, M., Nayman, E., and Daniel, G.: Testing seismic velocity models with quarry blast data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8652, https://doi.org/10.5194/egusphere-egu22-8652, 2022.

EGU22-8833 | Presentations | SM1.1

Searching for Mid-Mantle Water with Multitaper-Correlation SS Precursors 

William Frazer and Jeffrey Park

Earth’s mantle transition zone (MTZ) is a possible global water reservoir and may be responsible for long-term (~100 Ma) ocean-mass regulation, driven by plate tectonics and mantle convection. Estimates of MTZ mineral water capacity exceed 1 wt%, far greater than that of rocks of either the upper- or lower-mantle. When water-rich material from the transition zone penetrates the upper or lower mantle, partial melting occurs due to the decrease in water capacity after phase transition, generating a reduction in seismic velocities. This process can add an additional low-velocity zone (LVZ) that can be imaged above(below) the 410(660)-km discontinuities, if melt is present. Depending on the melt fraction and wetting angle at mineral-grain boundaries, decreases in shear velocity of 0.5-2.6% can be generated. Seismic receiver functions have detected velocity reductions both above and below the MTZ, interpreted to be partial melting induced by high water content under the Alpine orogeny, in the deep Japan-slab subduction zone, and across the western United States. Since much of Earth lacks seismic stations, we apply SS precursors to conduct a global survey for such LVZs. The precursors to the SS phase reflect off interfaces near the source-receiver midpoint, so seismic stations are not required to be located above the target region. Detection and interpretation of LVZs surrounding sharp positive-velocity gradients, such as the 410- or 660-km discontinuity, is often complicated by side lobes, an artifact of common signal-processing routines. To address this challenge, we develop an SS precursor method based on the multitaper-correlation (MTC) technique. MTC allows for analysis at higher frequency, leading to finer depth resolution, and can increase the number of useful data records. We conduct MTC SS-precursor analysis for seismic waveforms recorded on the ~125 stations of the Global Seismographic Network to benchmark our new method and search for LVZs. Results will be compared to LVZs interpreted from previous seismic analysis.

How to cite: Frazer, W. and Park, J.: Searching for Mid-Mantle Water with Multitaper-Correlation SS Precursors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8833, https://doi.org/10.5194/egusphere-egu22-8833, 2022.

EGU22-9062 | Presentations | SM1.1

Investigating Vrancea intermediate depth seismic activity in Romania using automatic waveform processing methods 

Natalia Poiata, Bogdan Grecu, Raluca Dinescu, Felix Borleanu, and Dragos Tataru

Seismic activity in Romania is dominated by the intermediate-depth earthquakes generated inside the seismogenic body of the Vrancea seismic zone extending to the depth of 180 km. This earthquakes represent the main source of seismic hazard for Romania and neighbouring countries, with the most recent largest events of M 7.7 and 7.4 in 1940 and 1977 that caused significant and widespread destruction. Space distribution of the intermediate-depth earthquakes from Vrancea is constrained to a compact volume (60-180 km in depth and 20x50 km areal extent) falling into the category of, so called, “seismic nests”, which have peculiar and not well understood seismogenic mechanisms.

We present first results obtained by applying the automated waveform analysis schemes to the detection, location and characterization of seismicity from the Vrancea zone to the continuous data recorded at seismic stations of the Romanian seismic network. We evaluate the performance of the methods like network-based full-waveform coherency earthquake detection and location and the template-based waveform similarity analysis for building a detailed view of seismic activity in space and time and to provide a fully automated workflow for continuous seismic data analysis. We use case-specific, for Vrancea seismic region, synthetic example to test the detection and location scheme setup and resolution. The real dataset of continuous seismic data focuses on the two month time period around the recent, moderate (M 5.6) December 27, 2016 earthquake.

The preliminary results of the automated detection and location analysis indicate reduced foreshock and aftershock activity for this event. According to the Romanian earthquake catalog, this appears to be a common pattern for moderate (M ~5.0-6.0) magnitude events. We also discuss the results of the template-based waveform similarity analysis for the detected and located events, as well as how the combination of the two methods can contribute to the enhanced seismic monitoring and hazard assessment.

How to cite: Poiata, N., Grecu, B., Dinescu, R., Borleanu, F., and Tataru, D.: Investigating Vrancea intermediate depth seismic activity in Romania using automatic waveform processing methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9062, https://doi.org/10.5194/egusphere-egu22-9062, 2022.

EGU22-9192 | Presentations | SM1.1

Recalculating the local magnitude of events in the Hungarian National Seismological Bulletin 

Marietta Csatlós and Bálint Süle

Local magnitude is one of the oldest and widely used term for characterizing the size of seismic events. Mostly based on the maximum amplitude measured on the components of the seismograms associated with the seismic event. The events in the Hungarian National Seismological Bulletin were relocated by Bondar et al. (2018). Before 2015 the bulletin did not contain amplitudes therefore it was not possible to calculate new local magnitudes for the new hypocenters. Moreover, the magnitudes were calculated by different methodology before 2015.

In this study, all three components of all available waveforms were collected for the events occurred between 1996 and 2016, and the local magnitudes were recalculated. Thus, we present a consistent data set for the whole period. Magnitude values based on both horizontal and vertical components are presented.

Amplitudes were measured on all three components, thus it was possible to compare the maximum amplitudes of the horizontal and vertical components recorded at stations in different geological conditions. For stations located on sediment, generally higher amplitude values were obtained on the horizontal components. The horizontal amplitude was 2.5 or 3 times larger for the Great Hungarian Plain stations on thick sediments. The differences between stations on firm bed rock were smaller.

The collected waveforms and amplitude measurements provide the opportunity to perform the calibration of the local magnitude scale to the geological conditions of Hungary.

 

 

Bondár, I., Mónus, P., Czanik, Cs., Kiszely, M., Gráczer, Z., Wéber, Z., the AlpArrayWorking Group. 2018: Relocation of Seismicity in the Pannonian Basin Using a Global 3D Velocity Model. Seismological Research Letters. pp.2284-2293.

How to cite: Csatlós, M. and Süle, B.: Recalculating the local magnitude of events in the Hungarian National Seismological Bulletin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9192, https://doi.org/10.5194/egusphere-egu22-9192, 2022.

EGU22-10192 | Presentations | SM1.1

Remote Reconnaissance Mission to the 14th August 2021 Haiti Earthquake; remote sensing and building damage assessments 

Michael Whitworth, Giorgia Giardina, Camilla Penney, Luigi Di Sarno, Keith Adams, Tracy Kijewski-Correa, Josh Macabuag, Fatemeh Foroughnia, Valentina Macchiarulo, Mobin Ojaghi, Alessandra Orfeo, Francesco Pugliese, Kökcan Dönmez, Jacob Black, and Yasemin d Aktas

Post-earthquake reconnaissance missions are critical to understand the event characteristics, identify building and infrastructure vulnerabilities, and improve future construction practice. However, in-field missions can present logistic and safety challenges that do not make them viable in every post-disaster scenario. Remote sensing technique can be used to rapidly collect a large amount information that can be used to enrich the post-event learning process. While the possibility to deploy teams in the field remain a valuable asset for an integrated understanding of technical and socio-economic factors, a mix of remote and in-field reconnaissance activities can be a way forward in post-disaster management.

This work presents the results of a hybrid mission mobilised by the Earthquake Engineering Field Investigation Team (EEFIT) after the 2021 Haiti earthquake. On 14 August 2021, a 7.2 magnitude earthquake struck the Tiburon Peninsula in the Caribbean nation of Haiti, approximately 150km east of the capital Port au Prince. The event was followed by numerous aftershocks up to magnitude 5.7, and tiggered over 1000 landslides. Over 2000 people lost their lives, with over 15,000 injured and over 137,000 houses damaged or destroyed. The estimated economic impact is of the order of US$1.6 billion. Due the complex political and security situation in Haiti, coupled with the global pandemic, a full in field mission was not considered feasible, so a hybrid mission was designed instead.

First, open-source information was collected and used to characterise the seismic event, analyse the strong ground motion and compare to established national and international earthquake codes and standard. Second, remote sensing techniques including Interferometric Synthetic Aperture Radar (InSAR) and Optical/Multispectral imagery were used to understand the earthquake mechanism, the ground displacement distribution and the possibility to detect landslide on a regional scale. The general applicability of remote sensing technique in the context of post disaster assessment was also evaluated. Finally, the earthquake impact on different building typologies in Haiti was investigated through the damage assessment of over 2000 buildings comprising schools, hospitals, churches and housing. This was done in collaboration with the Structural Extreme Events Reconnaissance (StEER) team, who mobilised a team of local non-experts to rapidly record building damage.

This talk summarises the mission setup and findings, and discusses the benefits of and difficulties encountered during this hybrid reconnaissance.

How to cite: Whitworth, M., Giardina, G., Penney, C., Di Sarno, L., Adams, K., Kijewski-Correa, T., Macabuag, J., Foroughnia, F., Macchiarulo, V., Ojaghi, M., Orfeo, A., Pugliese, F., Dönmez, K., Black, J., and d Aktas, Y.: Remote Reconnaissance Mission to the 14th August 2021 Haiti Earthquake; remote sensing and building damage assessments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10192, https://doi.org/10.5194/egusphere-egu22-10192, 2022.

EGU22-10613 | Presentations | SM1.1

Meeting the challenging performance requirements of Global Seismic Observatory Networks with the new Trillium 360 GSN 

Geoffrey Bainbridge, Bruce Townsend, Sarvesh Upadhyaya, and Valarie Hamilton

Nanometrics new Trillium 360 GSN seismometer embodies the culmination of many years of research and technology innovation as well as extensive collaboration with and input from the scientific community interested in very broadband seismometry.  Several generations of seismometers with 240 or 360 second corner frequency have demonstrated successive improvements in self-noise at both very low and high frequencies.  The most recent development has produced the lowest self-noise of any vault seismometer, and is the only seismometer currently being manufactured that meets the performance requirements of a primary seismometer for the Global Seismographic Network and Geoscope. 

Posthole, Borehole and Vault form factors are available and being manufactured and delivered to the GSN.  Performance testing of several units of each model type has been carried out at the facilities of GSN participating member institutions.  The results of the performance testing are reviewed and interpreted, and compared with other co-located instrument types including the venerable STS-1.  Field deployment is now proceeding, to upgrade networks with the Trillium 360 GSN seismometer.  We will show results from new deployments as available at the time of the 2022 SSA conference.  

We will also present the Trillium 360 roadmap, with a smaller low-power version for ocean bottom and portable land deployments in development for 2022, and early test results as available.  The goal of this next phase is to bring very broadband performance to any location and environment at reduced logistical cost.

How to cite: Bainbridge, G., Townsend, B., Upadhyaya, S., and Hamilton, V.: Meeting the challenging performance requirements of Global Seismic Observatory Networks with the new Trillium 360 GSN, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10613, https://doi.org/10.5194/egusphere-egu22-10613, 2022.

EGU22-11076 | Presentations | SM1.1

Preliminary results of the two seismic sequences in the Vienna Basin in March and April 2021 

María del Puy Papí Isaba, Wolfgang Lenhardt, Rita Meurers, Maria Theresia Apoloner, Helmut Hausmann, Maurizio Mattesini, and Elisa Buforn

We present a preliminary analysis of two seismic sequences between March and April 2021, near Neunkirchen and Gloggnitz, about 50 km from Vienna, Austria, and around 15 km apart from each other. Despite the moderate magnitudes, the recent earthquakes in the epicentral region, in the southern part of the Vienna Basin, were felt in the epicentral region and up to a distance of 300 km away. 

The Neunkirchen sequence started on March 11th, 2021. According to the Austrian Seismological Service at ZAMG, the last recorded earthquake occurred on May 12th, 2021. Over 245 earthquakes, with local magnitudes ranging from 0.5 to 4.6, were recorded until mid of May 2021. Out of the 245 earthquakes, 21 were felt by the population (1.8 ≤ ML ≤ 4.6), and two of them (ML4.6 and ML4.4) caused minor damage in the epicentral region. According to the Austrian Seismological Service, the depths of this sequence ranged from 7 to 12 km. 

The Gloggnitz sequence started on April 1st, 2021, and continued until May 8th, 2021. The epicenters of 65 detected earthquakes were located. Four earthquakes were felt, from which two (ML3.6 on April 20th and ML3.8 on April 23rd) caused slight damage. The local magnitudes of this seismic sequence ranged from -0.3 to 3.8; depths varied between 4 and 7 km. 

The relocation of the earthquakes of both sequences was carried out using the NonLinLoc by Lomax et al. (2019). We obtained the ellipse error for all relocated earthquakes. The focal mechanisms of the largest earthquakes were calculated using Seismic Moment-Tensor-Inversion. For the remaining events, a joint fault-plane solution was investigated. Furthermore, we compiled and analyzed the macro-seismic questionnaires of all felt earthquakes in the series and produced intensity maps (EMS-98). We compared the intensity attenuation as a function of distance with the newly available data and derived an Intensity Prediction Equation (IPE) for the region.

How to cite: Papí Isaba, M. P., Lenhardt, W., Meurers, R., Apoloner, M. T., Hausmann, H., Mattesini, M., and Buforn, E.: Preliminary results of the two seismic sequences in the Vienna Basin in March and April 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11076, https://doi.org/10.5194/egusphere-egu22-11076, 2022.

EGU22-11974 | Presentations | SM1.1

Covariance Matrix Analysis and Classification of Low-Frequency Tectonic Seismic Activity in Shikoku, Japan 

Andres Barajas, Cyril Journeau, and Nikolai Shapiro

Low-frequency seismic tremors and earthquakes play an important role in the understanding of the seismic processes occurring in seismogenic fault zones and volcanic systems. The covariance matrix, a method that analyses the spatial coherence of continuous seismic noise records on the surface, has proven to be an efficient tool to detect and localize seismovolcanic processes, allowing the classification between local earthquakes, tremors, and low-frequency earthquakes. We use this method in the analysis of tectonic seismic activity in the region of Shikoku, Japan, where a high rate of tremors and low-frequency earthquakes have been previously reported. The classification of the seismic activity over the spectral width and the network response function, shows distinct characteristic distributions from studies done in volcanic systems. We perform a series of synthetic tests that reproduce the classification patterns and spectral widths observed in volcanic and tectonic systems, allowing us to recognize fundamental differences in the duration, frequency and distribution patterns of volcanic and tectonic tremors and low-frequency earthquakes. 

How to cite: Barajas, A., Journeau, C., and Shapiro, N.: Covariance Matrix Analysis and Classification of Low-Frequency Tectonic Seismic Activity in Shikoku, Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11974, https://doi.org/10.5194/egusphere-egu22-11974, 2022.

Most of the largest volcanic activity in the world occurs in remote places as deep oceans or poorly monitored oceanic islands. Thus, our capacity of monitoring volcanoes is limited to remote sensing and global geophysical observations. However, the rapid estimation of volcanic eruption parameters is needed for scientific understanding of the eruptive process and rapid hazard estimation. We first a method to rapidly identify large volcanic explosions, based on analysis of seismic data. The method automatically detects and locate long period (0.01-0.03Hz) signals associated with physical processes close to the Earth surface, by analyzing surface waves recorded at global seismic stations. With this methodology, we promptly detect the January 15, 2022 Hunga Tonga eruption, among many other signals associated with known and unknown processes. We further use the waves generate by the Hunga Tonga volcanic explosion and estimate important first-order parameters of the eruption (Force spectrum, impulse). We then relate the estimated parameters with the volcanic explosivity index (VEI). Our estimate of VEI~6, indicate how the Hunga Tonga eruption is among the largest volcanic activity ever recorded with modern geophysical instrumentation, and can provide new insights about the physics of large volcanoes.

How to cite: Poli, P. and Shapiro, N.: Seismological characterization of dynamics parameter of the Hunga Tonga explosion from teleseismic waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13572, https://doi.org/10.5194/egusphere-egu22-13572, 2022.

EGU22-13576 | Presentations | ITS3.6/SM1.2

The 2022 Tonga tsunami in the marginal seas of the northwestern Pacific Ocean 

Elizaveta Tsukanova, Alisa Medvedeva, Igor Medvedev, and Tatiana Ivelskaya

The Hunga Tonga volcanic eruption on 15 January 2022 created a tsunami affecting the entire Pacific Ocean. The observed tsunami was found to have a dual mechanism and was caused both by the wave incoming from the source area and by an atmospheric wave propagating with the speed of sound. The tsunami was clearly recorded in the marginal seas of the northwestern Pacific, including the Sea of Japan, the Sea of Okhotsk and the Bering Sea, in particular on the coasts of Kamchatka, the Kuril Islands and the Aleutian Islands. We examined high-resolution records (1-min sampling) of about 50 tide gauges and 15 air pressure stations in these seas for the period of 14-17 January 2022. On the Russian coast, the highest wave with a trough-to-crest wave height of 1.4 m was recorded at Vodopadnaya, on the southeastern Kamchatka Peninsula; on the coasts of the Aleutian Islands the tsunami waves were even higher, up to 2 m. Based on numerical modelling we estimated the arrival time of the gravitational tsunami waves from the source. We revealed that the character of sea level oscillations for most of the stations evidently changed before these waves arrived. A comparative analysis of sea level and atmospheric data indicated that these changes were probably caused by the atmospheric waves generated by the volcanic eruption.

How to cite: Tsukanova, E., Medvedeva, A., Medvedev, I., and Ivelskaya, T.: The 2022 Tonga tsunami in the marginal seas of the northwestern Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13576, https://doi.org/10.5194/egusphere-egu22-13576, 2022.

EGU22-13578 | Presentations | ITS3.6/SM1.2

Global ionospheric signature of the tsunami triggered by the 2022 Hunga Tonga volcanic eruption 

Edhah Munaibari, Lucie Rolland, Anthony Sladen, and Bertrand Delouis

The Hunga Tonga volcanic eruption on Jan. 15, 2022 released a highly energetic atmospheric pressure wave that was observed all around the globe in different types of measurements (e.g., barometers and infrasound sensors, satellites images, ionospheric measurements, etc.). In addition, the eruption triggered a meteo-tsunami followed by a series of tsunami waves. Tide gauges across the Pacific Ocean, the Atlantic and the Indian oceans recorded significant sea-level changes related to the primary eruption.

We focus our presentation on the imprint of tsunami waves on the ionosphere. We make use of an extensive collection of Global Navigation Satellites Systems (GNSS) data recorded by multi-constellation GNSS receivers across the Pacific Ocean and beyond. The observation of tsunami-induced ionospheric signatures is made possible by the efficient coupling of tsunami waves with the surrounding atmosphere and the generation of internal gravity waves (IGWs). With the help of GNSS systems (Beidou, GPS, Galileo, GLONASS, QZSS), ionospheric disturbances can be monitored and observed by utilizing the Total Electron Content (TEC) derived from the delay that the ionosphere imposes in the electromagnetic signals transmitted by the GNSS satellites. We identify and characterize the ionospheric TEC signatures following the passage of the Tonga tsunami. We investigate the influence of known key ambient parameters such as the local geomagnetic field, the tsunami propagation direction, and the distance to the tsunami source on the amplitude of the observed signatures. Moreover, we correlate the detected tsunami-induced TEC signatures with sea level measurements to assess their tsunami origins. And we contrast the identified TEC signatures in the Pacific Ocean with their analogs induced by the tsunami triggered by the Mar. 4, 2021 8.1 Mw Kermadec Islands earthquake. Both events took place relatively in the same geographical region, with the former being less complex (no meteo-tsunami, shorter duration, and about one order of magnitude smaller in amplitude). Finally, we provide estimations of the tsunami amplitude at the ocean level in the areas crossed by GNSS radio signals, some of them not covered by open ocean sea-level sensors (DART buoys).

How to cite: Munaibari, E., Rolland, L., Sladen, A., and Delouis, B.: Global ionospheric signature of the tsunami triggered by the 2022 Hunga Tonga volcanic eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13578, https://doi.org/10.5194/egusphere-egu22-13578, 2022.

EGU22-13579 | Presentations | ITS3.6/SM1.2

Modeling low-frequency Rayleigh waves excited by the Jan. 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano 

Shenjian Zhang, Rongjiang Wang, and Torsten Dahm

Low-frequency seismic energy whose spectrum is centered at certain narrow bands has been detected after violent volcano eruptions. Normal-mode analysis related this signal to the resonances between the atmosphere and the solid earth.
After the powerful eruption of Hunga Tonga-Hunga Ha’apai volcano on Jan. 15, 2022, this low-frequency signal is found on long period and very long period seismometers worldwide. The amplitude spectrum of the signal for this eruption consists of three clear peaks locating at 3.72, 4.61 and 6.07 mHz, instead of two distinct bands for previous cases. The spectrogram analysis shows that this low-frequency energy lasts for several hour and is independent of air wave arrival, while the cross-correlation result confirms that the signal travels as Rayleigh waves with a speed of 3.68 km/s. In this study, we summarize our findings on the observation, and show our synthetic waveforms to provide a possible explanation for the source of this signal. We suggest that the atmospheric oscillations near the volcano excited by the eruption act as an enduring external force on the surface of the solid earth, and produce Rayleigh waves propagating all over the world.

How to cite: Zhang, S., Wang, R., and Dahm, T.: Modeling low-frequency Rayleigh waves excited by the Jan. 15, 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13579, https://doi.org/10.5194/egusphere-egu22-13579, 2022.

The population and built infrastructure of the Kingdom of Tonga are highly exposed to ocean- and climate-related coastal hazards. The archipelago was impacted on January 15, 2022, by a destructive tsunami caused by the Hunga Tonga-Hunga Ha'apai submarine volcanic eruption. Weeks later, several islands were still cut off from the world, this situation was made worse by covid-19-related international lockdowns and no precise idea of the magnitude and pattern of destruction. Like in most Pacific islands, the Kingdom of Tonga lacks an accurate population and infrastructure database. The occurrence of events such as this in remote island communities highlights the need for (1) precisely knowing the distribution of residential and public buildings, (2) evaluating what proportion of those would be vulnerable to a tsunami depending on various run-up scenarios, (3) providing tools to the local authorities for elaborating efficient evacuation plans and securing essential services outside the hazard zones. Using a GIS-based dasymetric mapping method previously tested in New Caledonia for assessing, calibrating, and mapping population distribution at high resolution, we produce maps that combine population clusters, critical elevation contours, and the precise location of essential services (hospitals, airports, shopping centers, etc.), backed up by before–after imagery accessible online. Results show that 62% of the population on the main island of Tonga lives in well-defined clusters between sea level and the 15 m elevation contour, which is also the value of the maximum tsunami run-up reported on this occasion. The patterns of vulnerability thus obtained for each island in the archipelago, are further compared to the destruction patterns recorded after the earthquake-related 2009 tsunami in Tonga, thereby also allowing us to rank exposure and potential for cumulative damage as a function of tsunami cause and source-area. By relying on low-cost tools and incomplete datasets for rapid implementation in the context of natural disasters, this approach can assist in (1) guiding emergency rescue targets, and (2) elaborating future land-use planning priorities for disaster risk-reduction purposes. By involving an interactive mapping tool to be shared with the resident population, the approach aims to enhance disaster-preparedness and resilience. It works for all types of natural hazards and is easily transferable to other insular settings.

How to cite: Thomas, B. E. O., Roger, J., and Gunnell, Y.: A rapid, low-cost, high-resolution, map-based assessment of the January 15, 2022 tsunami impact on population and buildings in the Kingdom of Tonga, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13580, https://doi.org/10.5194/egusphere-egu22-13580, 2022.

The phreatic eruption of Hunga-Tonga on January 15, 2022 was so energetic that it excited globe circling air-waves. These wave packets with a dominant period of 30 minutes have been observed in single barograms even after completing at least  four orbits or 6 days after the eruption. Constructive and destructive interference between waves that have left the source region in opposite direction lead to the emergence of standing pressure waves: normal modes of the atmosphere.

 

We report on individual modes of spherical harmonic degree between 30 and 80 covering the frequency bend from 0.2 mHz to 0.8 mHz. These modes belong to the Lamb wave equivalent modes with a phase velocity of 313 m/s.  They are trapped to the Earth’s surface, decay exponentially with altitude and their particle motion is longitudinal and horizontal. The restoring force is dominated by incompressibility. 

 

In the frequency band where we observe these modes the mode branches do not cross with mode branches of the solid Earth. Hence we do not expect any significant coupling with seismic normal modes of the solid Earth. Such a crossing occurs at 3.7mHz and aboce.

 

How to cite: Widmer-Schnidrig, R.: Observation of acoustic normal modes of the atmosphere after the 2022 Hunga-Tonga eruption., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13581, https://doi.org/10.5194/egusphere-egu22-13581, 2022.

The explosive eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15th of January 2022 impacted the Earth, its oceans and atmosphere on a global scale. Witnesses report an audible “bang” as a result of the event in distances of up to several thousand kilometers. With infrasound sensors this sound wave can be detected where the frequency content or the amplitude of the signal renders the event inaudible to the human ear. Infrasound sensors are distributed globally, a selection of these stations upload their data in real time to publicly available servers. In combination with Open Source libraries such as obspy or scipy it is possible to use these data sources to observe the atmospheric disturbances caused by the eruption on a global scale in near real time. With a minimum of data processing not only the first arrival peak of the atmospheric lamb wave can be identified at most stations but also further passes of the wave as it propagates around the planet several times. Having large amounts of publicly available data is crucial in that process. New data chunks can be analyzed and displayed immediately while the signal is still ongoing because data access requests are not required. Additionally, having immediate access to a large dataset allows for big data analysis and reduces the necessity to consider outliers at individual stations and increases the chance to identify the signal after multiple days when overall signal to noise ratios have decreased.

How to cite: Eckel, F., Garcés, M., and Colet, M.: The 15 January 2022 Hunga Tonga event: Using Open Source to observe a volcanic eruption on a global scale in near real time, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13582, https://doi.org/10.5194/egusphere-egu22-13582, 2022.

EGU22-13583 | Presentations | ITS3.6/SM1.2 | Highlight

Satellite observations and modeling of the 2022 Hunga Tonga-Hunga Ha'apai eruption 

Simon Carn, Benjamin Andrews, Valentina Aquila, Christina Cauley, Peter Colarco, Josef Dufek, Tobias Fischer, Lexi Kenis, Nickolay Krotkov, Can Li, Larry Mastin, Paul Newman, and Paul Wallace

The 15 January 2022 eruption of the submarine Hunga Tonga-Hunga Ha'apai (HTHH) volcano (Tonga) ranks among the largest volcanic explosions of the satellite remote sensing era, and perhaps the last century. It shares many characteristics with the 1883 Krakatau eruption (Indonesia), including atmospheric pressure waves and tsunamis, and the phreatomagmatic interaction of magma and seawater likely played a major role in the dynamics of both events. A portion of the HTHH eruption column rose to lower mesospheric altitudes (~55 km) and the umbrella cloud extent (~500 km diameter at ~30-35 km altitude) rivalled that of the 1991 Pinatubo eruption, indicative of very high mass eruption rates. However, sulfur dioxide (SO2) emissions measured in the HTHH volcanic cloud (~0.4 Tg) were significantly lower than the post-Pinatubo SO2 loading (~10–15 Tg SO2), and on this basis we would expect minimal climate impacts from the HTHH event. Yet, in the aftermath of the eruption satellite observations show a persistent stratospheric aerosol layer with the characteristics of sulfate aerosol, along with a large stratospheric water vapor anomaly. At the time of writing, the origin, composition and eventual impacts of this stratospheric gas and aerosol veil are unclear. We present the preliminary results of a multi-disciplinary approach to understanding the HTHH eruption, including 1D- and 3D-modeling of the eruption column coupled to a 3D atmospheric general circulation model (NASA’s GEOS-5 model), volatile mass balance considerations involving potential magmatic, seawater and atmospheric volatile and aerosol sources, and an extensive suite of satellite observations. Analysis of the HTHH eruption will provide new insight into the dynamics and atmospheric impacts of large, shallow submarine eruptions. Such eruptions have likely occurred throughout Earth’s history but have never been observed with modern instrumentation.

How to cite: Carn, S., Andrews, B., Aquila, V., Cauley, C., Colarco, P., Dufek, J., Fischer, T., Kenis, L., Krotkov, N., Li, C., Mastin, L., Newman, P., and Wallace, P.: Satellite observations and modeling of the 2022 Hunga Tonga-Hunga Ha'apai eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13583, https://doi.org/10.5194/egusphere-egu22-13583, 2022.

EGU22-13584 | Presentations | ITS3.6/SM1.2 | Highlight

The 15 January 2022 Hunga eruption, Tonga – first petrographic and geochemical results 

Shane Cronin, Marco Brenna, Taaniela Kula, Ingrid Ukstins, David Adams, Jie Wu, Joa Paredes Marino, Geoff Kilgour, Graham Leonard, James White, Simon Barker, and Darren Gravley

The phreatoplinan eruption of the shallow submarine Hunga Volcano Tonga formed global air-pressure waves, regional tsunami and an up to 55 km-high eruption column. Despite its large explosive magnitude, the magma erupted were similar to past compositions, and comprised crystal poor (<8 wt% total; plag>cpx>opx) andesite with ~57-63 wt% silica glass. Low magnitude Surtseyan eruptions in 2009-2015 formed from small pockets of andesite that ascended slowly, resulting in high microphenocryst and microlite contents. Large eruptions, including events in ~AD200 and AD1100 and the 2022 event drew magma rapidly from a ~5-7 km deep mid-crustal reservoir. Rapid decompression and quenching (augmented by magma-water interaction) records the heterogeneity of the reservoir, with mingled glass textures and cryptic mixing of subtly different melts. The 2022 feldspar phenocrysts show more mafic melt inclusion compositions than host glass, clear uniform cores and thin rims evidencing ~1 month-long changes caused by decompression, rise and internal mingling of subtlety different melts. CPX phenocrysts show uniform cores a variety of more mafic and similar melt inclusions to the bulk glass, and thin overgrowth rims reflecting only decompression and mingling. Lithic fragments (<8wt%) include common hydrothermal minerals (sulphides, quartz etc). Without evidence of a mafic trigger, or crystalisation induced overpressures, this extremely violent eruption was triggered by top-down processes that led to rapid exhumation/decompression of magma and very efficient explosive magma-water interaction. This could include any, or all of: flank collapse; hydrothermal seal fracturing and ingress of water into the upper magma system and caldera collapse. Subsequent earthquakes suggest that the crustal magma system was rapidly recharged in the days following the eruption.

How to cite: Cronin, S., Brenna, M., Kula, T., Ukstins, I., Adams, D., Wu, J., Paredes Marino, J., Kilgour, G., Leonard, G., White, J., Barker, S., and Gravley, D.: The 15 January 2022 Hunga eruption, Tonga – first petrographic and geochemical results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13584, https://doi.org/10.5194/egusphere-egu22-13584, 2022.

EGU22-13585 | Presentations | ITS3.6/SM1.2

Hunga-Tonga-Hunga-Ha’apai Jan 15, 2022 eruption: Assembly of heterogeneous magma sources recorded in melt inclusions from plagioclase, clinopyroxene and orthopyroxene. 

Ingrid Ukstins, Shane Cronin, David Adams, Jie Wu, Joali Paredes Marino, Marco Brenna, Ian Smith, and Isabelle Brooks-Clarke

The 15 Jan 2022 eruption of Hunga-Tonga-Hunga-Ha’apai was the largest explosive volcanic event in the last 30 years. These islands represent the subaerially exposed summit of the Hunga Volcano, merged into a single land mass during the most recent eruption in 2014-2015. The 2022 eruption likely represents a 1-in-1000-year event for the Hunga Volcano, with the previous large-magnitude eruption occurring in ~1100 CE during a series of caldera-forming events. The 2022 erupted magma is plagioclase-, orthopyroxene- and clinopyroxene-bearing basaltic andesite to andesite dominated by blocky, poorly vesicular glassy ash with lesser amounts of vesicular pumiceous ash and fine lapilli. Melt Inclusions (MIs) hosted in plagioclase, clinopyroxene and orthopyroxene are abundant and glassy, some displaying shrinkage bubbles, with no evidence of secondary crystallization along the walls or within the MI glass. The groundmass glass and MI in the three main phenocryst phases were analysed for major, trace and volatile element concentrations to enable identification of magmatic sources and to better constrain processes happening at depth. Preliminary data indicate that plagioclase phenocrysts range from An93 to An78, and MI range from 54.1 to 58.7 wt % SiO2, with MgO from 2.5 to 5.3 wt %. Clinopyroxene phenocrysts range from En42 to En50, and MI range from 51.6 to 65.1 wt % SiO2, with MgO from 1.1 to 5.7 wt %. Orthopyroxene phenocrysts range from En68 to En77, and MI range from 55.7 to 59.6 wt % SiO2, with MgO from 2.5 to 5.3 wt %. Clinopyroxene MI span the full range of SiO2 compositions observed from the Hunga Volcano, from the host 2022 event (SiO2: ~57.5 wt %), the 1100 CE event (SiO2: ~60 wt %), the 2014-2015 event (SiO2: ~60.5 wt %), and the most evolved 2009 event (SiO2: ~63 wt %) and extend an additional ~4 wt % SiO2 to more mafic compositions. Orthopyroxene MI most closely resemble the 1100 CE event and the average groundmass glass compositions of the 2022 event. Plagioclase MI overlap the least silicic compositions observed in the 2022 groundmass glass (58.6 wt% SiO2) and extend down to 54 wt % SiO2, overlapping the main field of clinopyroxene MI. Both plagioclase and clinopyroxene MI tend to show higher MgO as compared to the 2022 groundmass glass at the same SiO2 concentration, whereas orthopyroxene shows lower MgO than the groundmass glass. SO3 in MI ranges up to 1600 ppm, significantly higher than the 2022 groundmass glass which averages 200 ppm, with both plagioclase and clinopyroxene MI preserving the highest observed concentrations. In contrast, Cl concentrations in MI extend to 2000 ppm, with the highest values in orthopyroxene and clinopyroxene, and plagioclase MI are lower and generally overlie the main groundmass glass concentrations (~1300 ppm). F was below detection limits. We postulate that clinopyroxene crystals reflect a more primitive basaltic andesite magma, whereas orthopyroxene crystals were likely derived from the magmatic remnants of the 2009 and 2014/2015 events in the upper magma system, and plagioclase crystals were sourced from the full range of magma sources.

How to cite: Ukstins, I., Cronin, S., Adams, D., Wu, J., Paredes Marino, J., Brenna, M., Smith, I., and Brooks-Clarke, I.: Hunga-Tonga-Hunga-Ha’apai Jan 15, 2022 eruption: Assembly of heterogeneous magma sources recorded in melt inclusions from plagioclase, clinopyroxene and orthopyroxene., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13585, https://doi.org/10.5194/egusphere-egu22-13585, 2022.

EGU22-13586 | Presentations | ITS3.6/SM1.2 | Highlight

Post-2015 caldera morphology of the Hunga Tonga-Hunga Ha’apai caldera, Tonga, through drone photogrammetry and summit area bathymetry 

Sönke Stern, Shane Cronin, Marta Ribo, Simon Barker, Marco Brenna, Ian E. M. Smith, Murray Ford, Taaniela Kula, and Rennie Vaiomounga

In December 2014, eruptions began from a submarine vent between the islands of Hunga Tonga and Hunga Ha’apai, 65 km north of Tongatapu, Tonga. The “Hungas” represent small NW and NE remnants of the flanks of a larger edifice, with a ~5 km-diameter collapse caldera south of them. The 2014/15 Surtseyan explosive eruptions lasted for 5 weeks, building a 140 m-high tuff ring.

Deposits on Hunga Ha’apai and tephra fall on Tongatapu record two very large magnitude eruptions producing local pyroclastic density currents and tephra falls of >10 cm-thick >65 km away. These likely derive from the central edifice/caldera. The 2022 eruption produced slightly less tephra fall, but an extremely large explosive event, with regional tsunami indicating substantive topographic change.

Here we report the bathymetric details of the caldera as of November 2015. A multibeam sounder (WASSP) was used to mapping the shallow (<250 m) seafloor concentrating on the edges of the Hunga caldera. These results were combined with an aerial survey of the 2015 tuff cone, using a combination of drone photogrammetry and real-time kinematic GPS surveys. The bathymetry reveals that previous historical eruptions, including 1988 and 2009, and likely many other recent unknown produced a series of well-preserved cones around the rim of the caldera. Aside from the raised ground in the northern caldera produced by the 2009 and 2014/15 eruptions, the southern portion is also elevated to within a few m below sea level, with reefs present. During the 2015 visit, uplifted fresh coral showed that inflation was ongoing and that the caldera was likely in the process of resurgence.

Much of Hunga Tonga and the 2014/2015 cone was destroyed in the 2022 eruptions, with Hunga Ha’apai intact, but dropping vertically by ~10-15 m. The violence of the 2022 eruption was likely augmented by either caldera collapse or flank collapse from the upper edifice, rapidly unroofing the andesitic magma system and enabling efficient water ingress.

This data provides an essential base layer for assessing changes on the ocean floor, especially to determine any caldera or upper-flank changes. Understanding these changes is crucial for future forecasting future volcanic hazards at Hunga and other nearby large submarine volcanoes.

How to cite: Stern, S., Cronin, S., Ribo, M., Barker, S., Brenna, M., Smith, I. E. M., Ford, M., Kula, T., and Vaiomounga, R.: Post-2015 caldera morphology of the Hunga Tonga-Hunga Ha’apai caldera, Tonga, through drone photogrammetry and summit area bathymetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13586, https://doi.org/10.5194/egusphere-egu22-13586, 2022.

EGU22-13587 | Presentations | ITS3.6/SM1.2

Understanding fragmentation mechanism(s) during the 15 January 2022 Hunga Volcano (Tonga) eruption through particle characteristics 

Joali Paredes-Mariño, James White, Tobias Dürig, Rachel Baxter, Taaniela Kula, Shane Cronin, Ingrid Ukstins, Jie Wu, David Adams, Marco Brenna, and Isabelle Brooks-Clarke

The January 2022 eruption of Hunga Volcano, Tonga is likely the most explosive mafic eruption yet documented. It exhibited dynamics of ash plume expansion and atmospheric pressure waves unlike anything seen before. This is remarkable considering that it erupted crystal-poor and microlite-poor andesitic magma (57-63 wt% silica glass). The climactic phase produced an eruptive column of at least 39 km in height, however, the ash volume appears anomalously small for the explosive magnitude. Ash from nine different sites across the Kingdom of Tonga were analyzed for textural and morphological properties and grain size distribution. The tephra comprises light pumice (16%), dark pumice (44%), glassy microlite-rich grains (25%), lithics (7%) and free-crystals (Pl, Cpx, Opx) (8%). Specific gravity of particles range from 0.4 to ~2.5. Secondary electron images show that pumices have a variable vesicularity, from dense glassy blocky particles; glassy particles with isolated vesicles and weakly deformed, thick vesicle walls; and a smaller percentage of microvesicular pumices, coated in finer particles. The general characteristics imply a rapid decompression, fragmentation and chilling. This implies some form of phreatomagmatism but with high-efficiency to generate such a large blast – e.g., via propagation of stress waves and thermal contraction rapidly increasing a magma surface area for interaction. The ash is fine-grained and poorly sorted overall. Less than 20 wt.% of ash particles are >1 mm at 80 km SE of the volcano on the main island of Tongatapu, while 70 km NE of the volcano (Nomuka Island) has finer ash, with only 2% of particles >1 mm. It appears that the dispersion axis for the event was directed toward the E or ESE, across the main population centre of Nuku’alofa on Tongatapu. Of the fine fraction 20 wt.% is < 30 micron, 8 wt.% <10 micron but unusually few particles of very fine range (<0.05 wt.% finer than 1 micron). Variations in the mode and sorting of ash fall at different locations and angles from the vent show that there was potentially complex dispersal of ash from different phases of the 11-hour long eruption, and or different plume heights and fragmentation processes involved. Plume observations suggest at least two different plume levels during main phases of the eruption and the fragmentation mechanisms likely varied from the blast-generating phase and the lesser-explosive phases leading up to and following this.

How to cite: Paredes-Mariño, J., White, J., Dürig, T., Baxter, R., Kula, T., Cronin, S., Ukstins, I., Wu, J., Adams, D., Brenna, M., and Brooks-Clarke, I.: Understanding fragmentation mechanism(s) during the 15 January 2022 Hunga Volcano (Tonga) eruption through particle characteristics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13587, https://doi.org/10.5194/egusphere-egu22-13587, 2022.

EGU22-13588 | Presentations | ITS3.6/SM1.2

The global reach of the 2022 Tonga volcanic eruption 

Jadranka Sepic, Igor Medvedev, Isaac Fine, Richard Thomson, and Alexander Rabinovich

The Tonga volcanic eruption of 15 January 2022 generated tsunami waves that impacted the entire Global Ocean as far away as 18,000 km from the source in the tropical Pacific Ocean. A defining characteristic of the tsunami was the dual forcing mechanism that sent oceanic waves radiating outward from the source at the longwave speed and atmospheric pressure Lamb waves radiating around the globe at the speed of sound (i.e. roughly 1.5 times faster than the longwave phase speed). Based on time series from several hundred high-resolution observational sites, we constructed global maps of the oceanic tsunami waves and the atmospheric Lamb waves. In some areas of the Pacific Ocean, we were able to distinguish between the two types of motions and estimate their relative contribution. A global numerical model of tsunami waves was constructed and results from the model compared with the observations. The modeled and observed tsunami wave heights were in good agreement. The global maps also enabled us to identify regional “hot spots” where the tsunami heights were highest. In addition to areas in the Pacific Ocean (Chile, New Zealand, Japan, the U.S. West Coast, and the Alaska/Aleutian Islands), “hot regions” included the Western Mediterranean and the Atlantic coasts of Europe and northern Africa.

How to cite: Sepic, J., Medvedev, I., Fine, I., Thomson, R., and Rabinovich, A.: The global reach of the 2022 Tonga volcanic eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13588, https://doi.org/10.5194/egusphere-egu22-13588, 2022.

EGU22-13589 | Presentations | ITS3.6/SM1.2 | Highlight

Numerical investigations on different possible generating mechanisms for the tsunami following the January 15 2022 Hunga Tonga-Hunga Ha’apai eruption 

Alberto Armigliato, Cesare Angeli, Glauco Gallotti, Stefano Tinti, Martina Zanetti, and Filippo Zaniboni

The Hunga Tonga-Hunga Ha’apai eruption of January 15 2022 was the culminating event of a sequence of seismic and volcanic events starting back in December 2021. The January 15 eruption manifested itself above the sea level with a number of phenomena, including the generation of a convective column ascending well into the stratosphere, pyroclastic flows travelling over the sea surface, an atmospheric pressure wave recorded by several instruments around the globe, and a tsunami, that represents the main focus of this study.

The tsunami that followed the eruption was observed both in the near-field and in the far-field, propagating across the entire Pacific Ocean and causing damage and loss of lives as far as Peru. In the near-field (Tonga archipelago) it is trickier to distinguish the damage induced by the impact of the eruption and the tsunami waves.

It is still not clear what the main generating mechanism for the ensuing tsunami was. In this contribution, several different hypotheses are investigated, adopting simplified models ranging from the submerged volcanic edifice collapse to the phreatomagmatic explosion and to the atmospheric pressure wave that was recorded across the entire globe. The propagation of the tsunami is simulated numerically with both non-dispersive and dispersive codes. Different spatial scales and resolutions are adopted to check the relative weight of the different generating mechanisms in the near- and in the far-field. Tentative conclusions are drawn by comparing the simulated results with the available experimental data in terms of tide-gauge records and near-field coastal impact.

How to cite: Armigliato, A., Angeli, C., Gallotti, G., Tinti, S., Zanetti, M., and Zaniboni, F.: Numerical investigations on different possible generating mechanisms for the tsunami following the January 15 2022 Hunga Tonga-Hunga Ha’apai eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13589, https://doi.org/10.5194/egusphere-egu22-13589, 2022.

EGU22-13590 | Presentations | ITS3.6/SM1.2 | Highlight

Caldera subsidence during the Hunga-Tonga explosive eruption? 

Thomas R. Walter and Simone Cesca and the GFZ-DLR-Geomar Task Force Team

The Hunga-Tonga eruption culminated on January 15, 2022, with a high-intensity Plinian eruption exceeding 20 km height, tsunamis affecting local islands and the circumpacific region, locally air-coupled seismic surface waves recorded at teleseismic distances, and explosive shock waves that repeatedly travelled around the world. Hunga-Tonga is a flat-topped volcano that rises about 1700 m above the seafloor, hosting a submarine 3-4 km diameter caldera floor that lies at less than 200 m water depth and is surrounded by an elevated, approx. 100-200 m high caldera wall. Only small parts of the volcano are rising at the caldera wall above the sea level, such as the islands Hunga Tonga Hunga Ha'apai in the north and small unnamed rocks in the south. Satellite imagery acquired by Pleiades and Sentinel 1A suggests that during the January 15, 2022 eruption, the central part of the Hunga Tonga Hunga Ha'apai as well as the small rocks in the south disappeared. By analysing satellite radar and imagery, we constrain island perimeters and morphologies before and after the eruption, to find evidence for island subsidence and erosion. In addition, seismic data recorded during the January 15, 2022 eruption was analysed in the time and frequency domains, revealing high amplitude activity over ~1 hr. The comparison of seismic, GNSS and local tsunami recordings gives insights into the time-succession of the eruption. For instance, moment tensor inversion suggests that the largest amplitude seismic signal was produced by a dominant tensile non-double component, characteristic of volcanic explosions. Furthermore, we also found evidence for reverse polarity mechanisms in agreement with subsidence of a caldera, possibly indicating incremental activity of a ring fault. We discuss the possible contribution of a caldera to the evolving eruption dynamics and the need to improve geophysical monitoring of this island arc in general and acquire high-resolution submarine data Hunga Tonga Hunga Ha'apai in specific.

How to cite: Walter, T. R. and Cesca, S. and the GFZ-DLR-Geomar Task Force Team: Caldera subsidence during the Hunga-Tonga explosive eruption?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13590, https://doi.org/10.5194/egusphere-egu22-13590, 2022.

EGU22-13591 | Presentations | ITS3.6/SM1.2

Volcanogenic tsunami on January 15, 2022: insights from deep-ocean measurements 

Mikhail Nosov, Kirill Sementsov, Sergey Kolesov, and Vasilisa Pryadun

The explosive eruption of the Hunga Tonga-Hunga Ha'apai volcano on January 15, 2022 triggered tsunami waves that were observed throughout the Pacific Ocean. In particular, the waves were recorded by several dozen deep-ocean DART stations located at source distances from hundreds to more than 10 thousand kilometers. Our study is aimed at analyzing tsunami waveforms recorded by DART stations in order to identify the formation mechanisms of this volcanogenic tsunami. Waveforms are processed using wavelet analysis. The arrival times of signals of different genesis are estimated making use robust physical assumptions, numerical modeling and satellite images. It has been found that in all records the tsunami signal is clearly observed long before the calculated moment of arrival of gravity surface waves caused by sources localized in the immediate vicinity of the volcano. On the records obtained by distant stations (~10000 km) dispersive gravity waves arrive with a delay of several hours after the signals following the passage of acoustic wave in the atmosphere. In addition to the analysis of waveforms, theoretical estimates of the amplitude of gravity waves in the ocean, caused by an acoustic wave in the atmosphere, will be presented. We also provide a theoretical estimate on how acoustic waves in the atmosphere manifest in pressure variations recorded by an ocean-bottom sensor.

This study was funded by a grant of the Russian Science Foundation № 22-27-00415, https://rscf.ru/en/project/22-27-00415/.

How to cite: Nosov, M., Sementsov, K., Kolesov, S., and Pryadun, V.: Volcanogenic tsunami on January 15, 2022: insights from deep-ocean measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13591, https://doi.org/10.5194/egusphere-egu22-13591, 2022.

EGU22-13592 | Presentations | ITS3.6/SM1.2 | Highlight

The Near Real time analysis of Hunga Tonga-Hunga Ha’apai eruption in the ionosphere by GNSS 

Boris Maletckii and Elvira Astafyeva

The 15th January 2022 Hunga Tonga- Hunga Ha’apai (HTHH) volcano explosion is one of the most powerful eruptive events over the last 30 years. Based on early computations, its VEI was at least 5. The explosion caused atmospheric air shock waves that propagated around the globe, and also generated a tsunami. All these effects seemed to have produced quite a significant response in the ionosphere.

In this contribution, we analyze the ionospheric disturbances generated by the HTHH volcano eruption by using ground-based 8 GNSS receivers located in the near-field of the volcano (i.e., less than 2000 km). We test our previously developed methods to detect and locate the explosive event and its ionospheric signatures in a near-real-time (NRT) scenario. 

To detect co-volcanic ionospheric disturbances (co-VID), we use the TEC time derivative approach that was previously used for detection of ionospheric disturbances generated by large earthquakes. For this event, we modified the previously developed method to proceed not only 1-second but also 30 sec data. This approach detects the first perturbations ~12-15 minutes after the eruption onset. Further, it estimates the instantaneous velocities in a near field to be about ~500-800 m/s. Finally, from the obtained velocity vectors and the azimuths of co-VID propagation we calculate the position of the source in the ionosphere. 

Besides, we used the same TEC time derivative approach to produce NRT Travel Time Diagrams. The NRT TTD additionally verify the correlation with the source and velocities’ values.

How to cite: Maletckii, B. and Astafyeva, E.: The Near Real time analysis of Hunga Tonga-Hunga Ha’apai eruption in the ionosphere by GNSS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13592, https://doi.org/10.5194/egusphere-egu22-13592, 2022.

EGU22-13593 | Presentations | ITS3.6/SM1.2

Stratospheric observations of acoustic-gravity waves from the Hunga-Tonga eruption 

Aurélien Podglajen, Raphaël Garcia, Solene Gerier, Alain Hauchecorne, Albert Hertzog, Alexis Le Pichon, Francois Lott, and Christophe Millet

In the frame of the Strateole 2 balloon project, 17 long-duration stratospheric balloons were launched from Seychelles in fall 2021. At the time of the main eruption of Hunga-Tonga on January 15 2022, two balloons were still in flight over the tropical Pacific, respectively at altitudes of 20 and 18.5 km, and distances of 2,200 and 7,600 km from the volcano. The balloon measurements include wind, temperature and pressure at a sampling rate of 1 Hz. Those observations of this extreme event at that altitude are unique.

In this presentation, we will describe the observations of multiple wave trains by the balloons. The signature of the Lamb wave and infrasounds are particularly striking. The characteristics of the eruption and its scenario will be examined using a synergy of stratospheric in situ observations, ground observations and geostationary satellite images. Finally, we will discuss the complementarity of balloon observations with respect to the ground network due to their altitude and geographic location with respect to the source.

How to cite: Podglajen, A., Garcia, R., Gerier, S., Hauchecorne, A., Hertzog, A., Le Pichon, A., Lott, F., and Millet, C.: Stratospheric observations of acoustic-gravity waves from the Hunga-Tonga eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13593, https://doi.org/10.5194/egusphere-egu22-13593, 2022.

EGU22-13594 | Presentations | ITS3.6/SM1.2 | Highlight

Observation and simulation of the meteotsunami generated in the Mediterranean Sea by the Tonga eruption on 15 January 2022 

Audrey Gailler, Philippe Heinrich, Vincent Rey, Hélène Hébert, Aurélien Dupont, Constantino Listowski, Edouard Forestier, and Stavros Ntafis

Meteotsunamis are long ocean waves generated by atmospheric disturbances. The Tonga volcano eruption on 15 January 2022 generated a Lamb pressure wave propagating all over the globe and generating a tsunami observed at most tide gauges in the world. A first atmospheric wave arrived 20 hours after the eruption on the French Mediterranean coasts and propagated southward. This abrupt atmospheric pressure change was recorded by hundreds of barometers of weather stations around Europe. A second one originating from Africa was observed four hours later with an attenuated amplitude. The first wave can be roughly defined by a sinusoid signal with a period close to one hour and an amplitude of 150 Pa. The associated tsunami was observed by the French stations of the HTM-NET network (https://htmnet.mio.osupytheas.fr/) [1]. Amplitudes range from a few cm to 15 cm and periods range from 20 min to 1 hour.

 

Numerical simulation of the tsunami is performed by the operational code Taitoko developed at CEA [2]. The nested multigrid approach is used to simulate the water waves propagating in the bay of Toulon. The meteotsunami is generated by calculating analytically the atmospheric pressure gradient in the momentum equation. Comparisons of time series between numerical solutions and records are very satisfactory in regions defined by a high resolution topo-bathymetry. A second tsunami simulation is performed by introducing a second pressure wave propagating in the North direction and reaching the HTM-NET stations 4 hours after the first arrival. This second pressure wave results in additional and higher tsunami water waves in agreement with records.

 

 

[1] Rey, V., Dufresne, C., Fuda, J. L., Mallarino, D., Missamou, T., Paugam, C., Rougier, G., Taupier-Letage, I., On the use of long term observation of water level and temperature along the shore for a better understanding of the dynamics: Example of Toulon area, France Ocean Dyn., 2020, https://doi.org/10.1007/s10236-020-01363-7.

[2] Heinrich, P, Jamelot, A., Cauquis, A., Gailler A., 2021. Taitoko, an advanced code for tsunami propagation, developed at the French Tsunami Warning Centers. European Journal of Mechanics - B/Fluids 88(84) . DOI: 10.1016/j.euromechflu.2021.03.001.

How to cite: Gailler, A., Heinrich, P., Rey, V., Hébert, H., Dupont, A., Listowski, C., Forestier, E., and Ntafis, S.: Observation and simulation of the meteotsunami generated in the Mediterranean Sea by the Tonga eruption on 15 January 2022, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13594, https://doi.org/10.5194/egusphere-egu22-13594, 2022.

EGU22-13595 | Presentations | ITS3.6/SM1.2

Persistence Hunga Tonga plume in the stratosphere and its journey around the Earth. 

Bernard Legras, Sergey Khaykin, Aurélien Podglajen, and Pasquale Sellitto and the ASTuS

The Hunga Tonga eruption has generated an atmospheric plume rising above 40 km,  establishing an observational record. Due to the explosive nature of the eruption with a lot of water, the plume carried an unprecedented amount of water and a cloud of sulfated aerosols and possibly ultra-thin ashes was released. The aerosols have already persisted for four weeks with peak scatterring ratio initially above 200 that are still above 30 on many patches, as seen from CALIOP. These high values combined with low depolarization suggest a large amount of small sub-micronic spherical particles, confirmed by in situ balloon measurements. This is compatible with dominance of sulfated aerosols.

As the stratospheric flow has been mostly zonal with no breaking wave during the period and region of interest, and the horizontal shear dominates, the plume has been mostly dispersed in longitude keeping a similar latitudinal vertical pattern from the early days. A part has migrated to the tropical band reaching 10°N. Several concentrated patches have been preserved in particular a "mushroom" like pattern at 20S which has already circulated once around the Earth. . We will discuss the stability of this pattern in relation with vortical and thermal structures that are detected from several instruments and the meteorological analysis.

We will also discuss the likely impact on the stratospheric composition and the radiative effect on the yearly basis.  

How to cite: Legras, B., Khaykin, S., Podglajen, A., and Sellitto, P. and the ASTuS: Persistence Hunga Tonga plume in the stratosphere and its journey around the Earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13595, https://doi.org/10.5194/egusphere-egu22-13595, 2022.

EGU22-13598 | Presentations | ITS3.6/SM1.2

A global analysis of deep infrasound produced by the January 2022 eruption of Hunga volcano 

Julien Vergoz, Alexis Le Pichon, Constantino Listowski, Patrick Hupe, Christopher Pilger, Peter Gaebler, Lars Ceranna, Milton Garcés, Emanuele Marchetti, Philippe Labazuy, Pierrick Mialle, Quentin Brissaud, Peter Näsholm, Nikolai Shapiro, and Piero Poli

The eruption of Hunga volcano, Tonga is the most energetic event recorded by the infrasound component of the global International Monitoring System (IMS). Infrasound, acoustic-gravity and Lamb waves were recorded by all 53 operational stations after circling four times the globe. The atmospheric waves recorded globally exhibit amplitude and period comparable to the ones observed following the 1883 Krakatoa eruptions. In the context of the future verification of the Comprehensive Nuclear-Test-Ban Treaty, this event provides a prominent milestone for studying in detail infrasound propagation around the globe for almost one week as well as for calibrating the performance of the IMS network in a broad frequency band.

How to cite: Vergoz, J., Le Pichon, A., Listowski, C., Hupe, P., Pilger, C., Gaebler, P., Ceranna, L., Garcés, M., Marchetti, E., Labazuy, P., Mialle, P., Brissaud, Q., Näsholm, P., Shapiro, N., and Poli, P.: A global analysis of deep infrasound produced by the January 2022 eruption of Hunga volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13598, https://doi.org/10.5194/egusphere-egu22-13598, 2022.

EGU22-13599 | Presentations | ITS3.6/SM1.2

Early evolution of the Hunga – Tonga Volcanic Plume from Lidar Observations at Reunion Island (Indian Ocean, 21°S, 55°E) 

Alexandre Baron, Guillaume Payen, Valentin Duflot, Patrick Chazette, Sergey Khaykin, Yann Hello, Nicolas Marquestaut, Marion Ranaivombola, Nelson Bègue, Thierry Portafaix, and Jean-Pierre Cammas

Explosive volcanism periodically induces disturbances of the upper troposphere and low stratosphere. These injections of massive amount of aerosols, ash and gases perturb locally the physico-chemical balance of the impacted atmospheric layers, in particular the ozone concentration via heterogeneous chemistry on particles. On a larger scale some exceptional eruption can have a significant influence on the Earth radiative budget as it was the case following eruptions of El Chichon in 1982 and Mount Pinatubo in 1991.

On January 15, 2022, the Hunga-Tonga volcano erupted in the Tonga archipelago (20.5°S, 175.4°W). The Plinian eruption was of a rare intensity, especially because of the depth of the underwater caldera. The first estimates indicate a power between 10 and 15 Mt TNT, probably the most powerful since the eruption of Krakatoa in 1883. This short (~ 8min) but intense explosion whose pressure wave was observed all around the globe injected about 400 kt of material into the atmosphere (to be compared to the 20 Mt injected during the Mount Pinatubo eruption). The Volcano Stratospheric Plume (VSP) quickly moved westwards and then overflew the island of La Réunion (21°S, 55°E), located at ~12000 km away from Tonga.

In order to monitor the evolution of the VSP, lidar observations were performed at the Observatoire de Physique de l’Atmosphère de La Réunion (OPAR). This observatory is equipped with three lidars capable of stratospheric aerosols measurements at two wavelengths (355 nm and 532 nm). First observations were performed every night from 19 to 27 January 2022 when the first passage of the VSP occurred. The plume structures appeared to be highly variable along time, with altitudes ranging from 19 km to 36 km above the mean sea level while plume thicknesses were ranging from ~1 km to more than 3 km. Remarkable aerosol optical depth were associated with these stratospheric aerosol layers, up to 0.8 at 532 nm on January 21.

The temporal evolution of the VSP structure and optical properties will be presented and discussed.

How to cite: Baron, A., Payen, G., Duflot, V., Chazette, P., Khaykin, S., Hello, Y., Marquestaut, N., Ranaivombola, M., Bègue, N., Portafaix, T., and Cammas, J.-P.: Early evolution of the Hunga – Tonga Volcanic Plume from Lidar Observations at Reunion Island (Indian Ocean, 21°S, 55°E), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13599, https://doi.org/10.5194/egusphere-egu22-13599, 2022.

EGU22-13601 | Presentations | ITS3.6/SM1.2

The Hunga Tonga-Hunga Haʻapai hydration of the stratosphere 

Luis Millán, Lucien Froidevaux, Gloria Manney, Alyn Lambert, Nathaniel Livesey, Hugh Pumphrey, William Read, Michelle Santee, Michael Schwartz, Hui Su, Frank Werner, and Longtao Wu

Hunga Tonga-Hunga Haʻapai, a submarine volcano in the South Pacific, reached an eruption climax on 15 January 2022. The blast sent a plume of ash well into the stratosphere, triggered tsunami alerts across the world, and caused ionospheric disturbances. A few hours after the violent eruption, the Microwave Limb Sounder (MLS) measured enhanced values of water vapor at altitudes as high as 50 km - near the stratopause.
On the following days, as the plume dispersed, several MLS chemical species, including H2O and SO2, displayed elevated values, far exceeding any previous values in the 18-year record. In this presentation we discuss the validity of these measurements, the stratospheric evolution of the SO2 and H2O plumes, and, lastly, the implications of the large-scale hydration of the stratosphere by the eruption.

How to cite: Millán, L., Froidevaux, L., Manney, G., Lambert, A., Livesey, N., Pumphrey, H., Read, W., Santee, M., Schwartz, M., Su, H., Werner, F., and Wu, L.: The Hunga Tonga-Hunga Haʻapai hydration of the stratosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13601, https://doi.org/10.5194/egusphere-egu22-13601, 2022.

EGU22-3569 | Presentations | GMPV9.3

Volcanically-triggered changes in glacier surface velocity 

Michael Martin, Iestyn Barr, Benjamin Edwards, Elias Symeonakis, and Matteo Spagnolo

Many (~250) volcanoes worldwide are occupied by glaciers. This can be problematic for volcano monitoring, since glacier ice potentially masks evidence of volcanic activity. However, some of the most devastating and costly volcanic eruptions of the last 100 years involved volcano-glacier interactions (e.g. Nevado del Ruiz 1985, Eyjafjallajökull 2010). Therefore, improving methods for monitoring glacier-covered volcanoes is of clear societal benefit. Optical satellite remote sensing datasets and techniques are perhaps most promising, since they frequently have a relatively high temporal and spatial resolution and are often freely available. These sources often show the effects of volcanic activity on glaciers, including ice cauldron formation, ice fracturing, and glacier terminus changes. In this study, we use satellite sources to investigate possible links between volcanic activity and changes in glacier velocity. Despite some studies reporting periods of glacier acceleration triggered by volcanic unrest, the potential of using the former to monitor the latter has yet to be investigated. Our approach is to observe how glacier surface velocity responded to past volcanic events in Alaska and Chile by applying feature-tracking, mostly using optical satellite imagery. The overall aim is to systematically track changes in the glacier velocity, with hope of improving volcano monitoring and eruption prediction. 

How to cite: Martin, M., Barr, I., Edwards, B., Symeonakis, E., and Spagnolo, M.: Volcanically-triggered changes in glacier surface velocity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3569, https://doi.org/10.5194/egusphere-egu22-3569, 2022.

As loci of the fresh formation of alkaline rock, volcanic islands are hotspots of geochemical activity. Collectively volcanic islands are responsible for approximately one third of the global long term CO2 drawdown from chemical weathering. Glaciers also form environments with substantial chemical weathering activity. Despite zero-degree temperatures, subglacial environments provide both freshly ground down mineral surfaces and highly dilute meltwaters, allowing chemical processes to occur at faster rates than in warmer settings where reactions occur near chemical saturation. Yet, the degree to which glaciation enhances weathering on volcanic islands has received relatively little study.

Beerenberg, Jan Mayen, Norway, is the world´s northernmost active stratovolcano. It is mostly glacierized, with 23 distinctly named glaciers descending from the top of the volcanic cone to the sea. Many of the Beerenberg glaciers release sediment-laden subglacial water, indicative of water-rock interaction in subglacial environments. In August 2021, we did a preliminary survey of the aqueous geochemistry and sediment composition of several subglacial outlets at Beerenberg’s largest glacier, Sørbreen. We also surveyed glacial surface streams, glacial ice and snow, non-glacial melt streams, springs, and proglacial lakes.

The subglacial waters of Sørbreen are strongly enriched in bicarbonate, with little chloride despite the marine location and only trace amounts of other anions. Cation composition is ~60% Na and K and 40% Ca and Mg by mole, suggesting a balance between divalent and monovalent cations reflective of local bedrock. Together this strongly suggests carbonation weathering of silicate minerals as the source of the vast majority of dissolved load in the subglacial waters. Non-glacial waters are more dilute and enriched in sea water derived ions (Cl, SO4, and Na) compared to subglacial waters.  

While a complete geochemical budget is not possible from our initial observations, these results imply that Beerenberg is a hot spot of chemical weathering. If our dissolved CO2 fluxes are representative of long-term averages, then atmospheric CO2 drawdown at Sørbreen is comparable to other glacierized mafic volcanic rock regions, such as those on Iceland and Disko Island. These atmospheric CO2 drawdown rates are approximately double the world average and a factor of five higher than the drawdown in non-glacierized high latitude regions.

How to cite: Graly, J., Engen, S., and Yde, J.: Preliminary Geochemical Assessment of the Subglacial Environment of Beerenberg, the World’s Northernmost Active Stratovolcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4743, https://doi.org/10.5194/egusphere-egu22-4743, 2022.

EGU22-6528 | Presentations | GMPV9.3

Pre-Holocene glaciovolcanism in the Katla area, south Iceland 

Rosie Cole, Magnús Gudmundsson, Birgir Óskarsson, Catherine Gallagher, Guðrun Larsen, and James White

The Katla volcanic system is one of the most productive in Iceland. Frequent basaltic and occasional silicic phreatomagmatic eruptions through the ice cap Mýrdalsjökull have provided a rich Holocene tephra record. Understanding of pre-Holocene eruptions and the thickness and extent of ice cover during glacial periods is much more limited.

We present eruption and emplacement models for three formations exposed on the flanks of the Katla volcano. Two are rhyolitic nunataks and one is an alkali basaltic sequence. These formations rise above the surrounding ice and topography, respectively, and show evidence for ice-confined emplacement, indicating their formation at a time when ice cover was thicker and more extensive.

Our models of each formation are based on field study, a photogrammetry survey, and major element geochemical analyses. The basaltic formation of Morinsheiði is an intercalated sequence of volcaniclastic rocks, pillow lavas and pillow breccias, entablature-jointed and lobate lavas, and more massive pahoehoe lava sheets, intruded by several dykes. The top of the sequence is a glacially eroded surface and it is bounded on all sides by deep valleys. The Enta nunatak is a kinked ridge or possibly two en-echelon ridges. A silicic volcaniclastic unit is intercalated with and intruded by fluidal and heavily jointed rhyolite lobes, spines and sheets. This formation is capped by a segment of crater wall composed of scoria. The Kötlujökull nunatak is tabular in shape, has a clastic base and is capped by jointed lava with lobate margins and breakout lobes descending the steep slopes.

Each formation exhibits evidence of multiple eruption styles in varying hydrological conditions, and at least for Morinsheiði a fluctuating water level. These are the preliminary results from the project “SURGE: Uncapping subglacial eruption dynamics and glacier response”, which aims to better understand the relative influences of magma chemistry, eruption style and glacial conditions on meltwater production and retention, glacial response, and the feedback effects for continued eruptions. These models, combined with new 40Ar-39Ar dating of the lavas, will also provide greater insight into the form of Katla and the glacial conditions that prevailed during the late Pleistocene.

How to cite: Cole, R., Gudmundsson, M., Óskarsson, B., Gallagher, C., Larsen, G., and White, J.: Pre-Holocene glaciovolcanism in the Katla area, south Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6528, https://doi.org/10.5194/egusphere-egu22-6528, 2022.

EGU22-8641 | Presentations | GMPV9.3

The Bláfjall tuya in North Iceland, morphological characteristics and effect of ice flow and icesheet slope on edifice form  

Anna Margrét Sigurbergsdóttir and Magnús Tumi Gudmundsson

Tuyas are basaltic to intermediate glaciovolcanic edifices, formed in a body of meltwater within an ice sheet, in an ocean or a lake. The most common tuya stratigraphy consist of a lowermost layer or a mound of pillow lava, overlain by hyaloclastite tuffs and capped by a layer of subaerially-formed, horizontally bedded, lava flows. The parts of the lava flows more distant from the vent are built on flow-foot breccias, with the transition from subaerially-formed lava flows and breccias being a distinct stratigraphic boundary: the passage zone. The elevation of the passage zone marks the water level in the englacial lake into which the evolving tuya was built. At many locations the elevation of the passage zone appears to vary considerably from one location on a tuya to another. Some tuyas are elongated. One idea is that the elongation is predominantly in the direction of ice flow at the time of eruption.

By studying tuyas through aerial photography, satellite imagery and ground observations, the edifices variations in the elevation of the passage zone can be studied. This provides information on the eruption processes and environmental conditions at the time of formation.  We have analyzed the variation of passage zone elevation with distance along strike of a selected set of tuyas in Iceland. These include Bláfjall, located in Northern Iceland. It was formed within a Pleistocene ice sheet a continuous, prolonged eruption, or in a series of eruptions, closely spaced in time. The lava cap reaches a maximum thickness of approximately 100 m but is only a few meters to a few tens of meters thick on average, showing clear signs of influence from the ice sheet. Apparently, both the thickness of the ice sheet and the direction of ice flow direction exerted major control on the height and elongation of the Bláfjall tuya. The eruption took place well to the north of the ice divide at the time, and the flow of ice was predominantly from south to north, with the elongated structure of the tuya oriented parallel to the flow of the ancient glacier. The thickness of the lava cap is greatest in the north part and generally decreases towards south. This is despite the fact that the elevation of the mountain increases southwards. This indicates that the northern part is mostly formed by an advancing lava delta, propagating in the direction of ice flow and that the level of the water body present at the end of the advancing lava delta become progressively lower towards north. This suggests a sloping ice sheet at the time of formation, or possibly a receding ice sheet, leading to gradual thinning with time as the eruption progressed.   

How to cite: Sigurbergsdóttir, A. M. and Gudmundsson, M. T.: The Bláfjall tuya in North Iceland, morphological characteristics and effect of ice flow and icesheet slope on edifice form , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8641, https://doi.org/10.5194/egusphere-egu22-8641, 2022.

EGU22-8667 | Presentations | GMPV9.3

Tephra layer formed in the 1996 eruption of Gjálp, Iceland 

Irma Gná Jóngeirsdóttir, Magnús Tumi Gudmundsson, and Gudrún Larsen

Gjálp is a hyaloclastite ridge situated beneath the western part of the ~8000 km2 Vatnajökull ice cap, located midway between the subglacial calderas of Grímsvötn and Bárdabunga volcanoes. The tephra erupted at Gjálp has affinities fitting with the Grímsvötn volcanic system while the associated seismicity and unrest preceding the eruption suggest that the eruption was caused by lateral magma flow from Bárdarbunga.  Eruptions occurred at Gjálp in 1938 and 1996 but only the 1996 eruption is thought to have broken through the ice. The 1996 eruption was first detected on the 30th of September at about 22:00 GMT by the onset of seismic tremor; the following day heavily crevassed ice cauldrons were noticed. Around 30 hours after detection of the tremor the eruption broke through the ice sheet. The eruption lasted for 13 days, during which a 6-7 km long subglacial, hyaloclastite ridge was formed. The subglacial eruption melted large volumes of ice that accumulated within the Grímsvötn caldera until early November, when it was released in a major jökulhlaup, destroying bridges and damaging roads. In comparison with the subglacial eruption the subaerial part was relatively modest. The style of activity was mostly Surtseyan and the tephra erupted is mildly intermediate in composition.

The tephra fall began on October 2 and continued intermittently until October 13. The first tephra was seen at 05:18 on October 2. By 08:50 the largest explosions threw tephra about 1 km above the ice surface and the plume rose to 4-4.5 km above sea level. This tephra was carried north and north-northeast across North and Central Iceland and was detected as far as 250 km from source. On October 3 the plume was reported to have reached 8-9 km a.s.l. Tephra was also dispersed to the east and south and most of the tephra accumulated on the Vatnajökull glacier. During the eruption, repeated snow fall caused layering within the tephra deposit. In the following year samples were collected from the tephra fall area on the glacier. These consist mostly of snow cores with tephra thickness ranging from dm to mm. The samples were processed to estimate the tephra volume and to create a dispersal and isopach map. The tephra layer deposited on the glacier is volumetrically only a few percent of the bulk volume (~0.7 km3) of the subglacial ridge formed in the 1996 eruption.

How to cite: Jóngeirsdóttir, I. G., Gudmundsson, M. T., and Larsen, G.: Tephra layer formed in the 1996 eruption of Gjálp, Iceland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8667, https://doi.org/10.5194/egusphere-egu22-8667, 2022.

EGU22-8751 | Presentations | GMPV9.3 | Highlight

The causes of unexpected jökulhlaups, studied using geothermal reservoir modelling 

Hannah Iona Reynolds, Magnús T. Gudmundsson, and Thórdís Högnadóttir

Jökulhlaups (glacier outburst floods) are considered the most common type of volcanic hazard in Iceland, and result from the accumulation of meltwater during long-term geothermal activity beneath glaciers, or very rapid melting over a short period of time. Jökulhlaups may occur without visible precursors or prior warning, varying in size from being persistent leakage to floods that have caused considerable damage like the jökulhlaups in Múlakvísl and Kaldakvísl in July 2011. Little has been known about the onset time of water accumulation/melting, whether water accumulated before it was released, and how these events are related to intrusion of magma. This study categorises known ice cauldrons within Icelandic glaciers based on their volume, rate of formation, and longevity. Geothermal reservoir modelling was then used to explore possible heat sources which generate the cauldrons. Five scenarios were simulated: (1) Subglacial eruption – freshly erupted magma in direct contact with the ice at the glacier base; (2) Intrusion into homogeneous bedrock - magma intrudes into a bedrock of homogeneous properties; (3) Intrusion into high permeability channel – similar to scenario (2) but a high permeability channel extends from the intrusion to the glacier-bedrock boundary, e.g. zone of high permeability at a caldera fault; (4) Sudden release of pressure – a hot reservoir is topped by caprock, with a high permeability pathway from depth up to the glacier-bedrock boundary, representing a sudden breach of a pressurised reservoir; and (5) Intrusion into a very hot reservoir – similar to scenario (3) but the reservoir is near boiling point, from previous repeated intrusive activity. This work improves our understanding of sudden and unexpected jökulhlaups, which is helpful for hazard assessments and response plans for unrest in glaciers near inhabited areas, tourist spots, and power plants. 

How to cite: Reynolds, H. I., Gudmundsson, M. T., and Högnadóttir, T.: The causes of unexpected jökulhlaups, studied using geothermal reservoir modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8751, https://doi.org/10.5194/egusphere-egu22-8751, 2022.

EGU22-8774 | Presentations | GMPV9.3

The role of volcanic particle thermal conductivity, density, and porosity in influencing ice melt. 

Katie Reeves, Jennie Gilbert, Stephen Lane, and Amber Leeson

Volcanoes can generate pyroclastic material that is deposited on ice and snow surfaces. However, a range of particle properties and spatial distribution of layer thicknesses are associated with deposition of volcanic material1. This can modify the thermodynamic behaviour and optical properties of clean ice. Typically, thin layers of particles (i.e. in ‘dirty’ ice conditions) can increase ice ablation, whilst thick layers of particles (i.e. in ‘debris-covered’ conditions) can hinder ablation2. Therefore, the state of ice is an important control on the energy balance of an ice system. 20.4% of Earth’s known Holocene volcanoes are associated with glacier or permanent snow cover3, and so it is crucial to understand how volcanic material interacts with ice systems to (1) better understand the evolution of debris-covered and dirty ice in general and (2) forecast future ice-melt scenarios at individual ice-covered volcanoes.

We present laboratory experiments that systematically reviewed the impact of volcanic particles of a range of compositions and properties (e.g. thermal conductivity, diameter, density, and albedo) on ice. Experiments assessed single particles and a scattering of particles on optically transparent and opaque ice, subjected to visible light illumination from a light emitting diode in a system analogous to dirty ice. Automated time-lapse images and in-person observations captured the response of particles and ice to radiation. Particles investigated included trachy-andesitic cemented ash particles from Eyjafjallajökull (Iceland), basaltic-andesitic scoria from Volcán Sollipulli (Chile), and rhyolitic pumice from Mount St. Helens (USA).

The experiments provided insight into some of the processes associated with volcanic particle interaction with ice. Results demonstrated that all volcanic particles with varying albedos induced ice melt and drove convection systems within the meltwater. This convection resulted in indirect heating beyond the immediate margins of the particles. The particles additionally lost finer grained fragments to meltwater, further driving ice melt through the addition of multiple absorbing surfaces within the ice system. This demonstrated that volcanic particles have the capability to melt ice very effectively in dirty ice conditions. In all experiments, the particles had a low thermal conductivity (relative to ice), although the density differed between particle types. Our experiments showed that the porosity and density of a volcanic particle can dictate the behaviour of particle-ice interaction; a dense particle can melt downwards through the ice (in similarity with the behaviour of iron-based meteorites4), whilst a less dense particle can become buoyant in meltwater, resulting in an extensive area of surface melt.

1. Möller et al. (2018), Earth Syst. Sci. Data, https://doi.org/10.5194/essd-10-53-2018

2. Fyffe et al. (2020), Earth Surf. Process. Landforms, DOI: 10.1002/esp.4879

3. Curtis and Kyle (2017), Journal of Volc. And Geo. Research http://dx.doi.org/10.1016/j.jvolgeores.2017.01.017

4. Evatt et al. (2016), Nature Comms., DOI: 10.1038/ncomms10679

How to cite: Reeves, K., Gilbert, J., Lane, S., and Leeson, A.: The role of volcanic particle thermal conductivity, density, and porosity in influencing ice melt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8774, https://doi.org/10.5194/egusphere-egu22-8774, 2022.

EGU22-10002 | Presentations | GMPV9.3

Characterization of alteration minerals in Deception Island (Antarctica): implications for the dynamics of the current hydrothermal system 

Raquel Arasanz, Oriol Vilanova, Adelina Geyer, Meritxell Aulinas, Jordi Ibañez-Insa, Antonio M. Álvarez-Valero, Helena Albert, and Olga Prieto-Ballesteros

Hydrothermal systems, commonly developed in volcanic calderas, play an important role on the type and location of the post-caldera volcanic activity. The hydrothermal alteration and mineral precipitation can modify the physical properties and mechanical behaviour of the affected rocks, with the progressive alteration facilitating the occurrence of phreatic or hydrothermal explosive eruptions. Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 eruptions and three documented unrest periods over the past two centuries. The island consists of a composite volcano with an 8.5 x 10 km centrally located caldera dated at c. 8,300 years, according to paleomagnetic data, and 3,980 ± 125 calibrated years before the present (cal yr BP) based on tephrochronology, sedimentological studies and 14C dating. After the caldera-forming event, volcanic activity has been characterized by monogenetic magmatic and phreatomagmatic eruptions located around the caldera rim. Also, a hydrothermal system developed in the Port Foster area, although no detailed study has been done so far. The aim of this work is to shed further light in the dynamics of Deception Island hydrothermal system by studying several representative samples of magmatic rocks. A detailed petrographic study and a characterization of primary and secondary minerals have been carried out. The presence of secondary minerals and the palagonite alteration in the Fumarole Bay Formation suggest that the alteration of the samples took place under conditions of low water/rock ratios, basic pH and temperatures below 200 °C. The secondary minerals from the Basaltic Shield Formation samples may be indicative of fluids with temperatures higher than 200 °C and richer in CO2. Finally, the physical changes observed in the samples of this study lead to the conclusion that the investigated areas of the Fumarole Bay Formation are more likely to host hydrothermal or phreatic explosive eruptions, compared to the Basaltic Shield Formation zones.

This research is part of POLARCSIC research initiatives and was partially funded by the MINECO grants POSVOLDEC(CTM2016-79617-P)(AEI/FEDER-UE) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE) and the grant PID2020-114876GB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and, as appropriate, by “ERDF A way of making Europe”, by the “European Union” or by the “European Union NextGenerationEU/PRTR”. This research is also supported by the PREDOCS-UB grant.

How to cite: Arasanz, R., Vilanova, O., Geyer, A., Aulinas, M., Ibañez-Insa, J., Álvarez-Valero, A. M., Albert, H., and Prieto-Ballesteros, O.: Characterization of alteration minerals in Deception Island (Antarctica): implications for the dynamics of the current hydrothermal system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10002, https://doi.org/10.5194/egusphere-egu22-10002, 2022.

EGU22-10267 | Presentations | GMPV9.3

Pyroclastic Density Currents Over Ice: An Experimental Investigation of Microphysical Heat Transfer Processes 

Amelia Vale, Jeremy Phillips, Alison Rust, and Geoff Kilgour

Pyroclastic density current (PDC) interactions with ice are common at high altitude and latitude stratovolcanoes. When PDCs propagate over ice, melt and steam are generated. The incorporation of melt and steam into PDCs can alter the flow dynamics by reducing friction at the particle-ice interface and between individual particles. Melt incorporation can also transform a PDC into an ice-melt lahar. The hazardous and temporally unpredictable nature of these flows limits field observations. Conceptual models of PDC-ice interactions for hazard assessment and modelling exist, but quantifications of the microscale physical processes that underpin these interactions are limited. We use experiments to characterise the melting and friction reduction that occur when PDCs are emplaced onto ice.

In experiment set one, a heated particle layer was rapidly emplaced onto a horizontal ice layer contained within an insulated beaker 7.3 cm in diameter. The particle types used were glass ballotini, crushed pumice, and Ruapehu PDC samples, covering a diverse range of grain characteristics. The particle layer was varied in thickness up to 45 mm and across temperatures up to 700 °C. In each experiment, the mass of melt and steam were quantified, and the time evolution of temperature through the particle layer was measured.

Across all particle types, increasing particle layer mass (therefore layer thickness) and temperature increased melt and steam production. However, Ruapehu and pumice melt masses showed greater sensitivity than ballotini to particle temperature for any given layer thickness. Conversely, steam production was greater for the ballotini for any given layer thickness and was more sensitive to ballotini particle temperature.

Localised steam escape, fluidisation, capillary action, and particle sinking, were observed to varying extents in the experiments. These phenomena caused melt to be incorporated into the particle layer. The rate of increase in melt generation decreases with increasing particle layer thickness. This is due to increasing steam production, the increasing temperature of incorporated meltwater, energy losses to the atmosphere, and alterations to the bulk particle diffusivity.

Experiment set two characterised the mobility of particles over frozen and non-frozen substrates. Pumice and Ruapehu particles of varying temperature and layer thickness were poured into a 4.5 cm diameter alumina tube, which was rapidly lifted, allowing the particles to radially spread over the substrate. This configuration has been widely studied in experiments on granular flow mobility. The initial and final aspect ratios of the particle layer were measured, and conform to a power-law form previously interpreted as showing that frictional interactions are only important in the final stages of flow emplacement. Enhanced particle layer mobility over ice was only observed for Ruapehu particles above 400 °C, which we interpret to be due to fluidisation of the particles by rising steam. This is consistent with experiment set one, where Ruapehu particles produced more steam than pumice, and were often fluidised above 400 °C.

Experimental data will be used to calibrate surface flow hazard models for PDC runout and lahar generation, enabling prediction of PDC-ice interaction hazards. These models will be tested at Mt. Ruapehu, New Zealand. 

How to cite: Vale, A., Phillips, J., Rust, A., and Kilgour, G.: Pyroclastic Density Currents Over Ice: An Experimental Investigation of Microphysical Heat Transfer Processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10267, https://doi.org/10.5194/egusphere-egu22-10267, 2022.

EGU22-12210 | Presentations | GMPV9.3

Characterising ice-magma interactions during a shallow subglacial fissure eruption: northern Laki, Iceland, a case study 

Catherine (Kate) Gallagher, Magnús Tumi Gudmundsson, Thorvaldur Thordarson, Bruce Houghton, Birgir Óskarsson, Robert Askew, Rosie Cole, William Moreland, Valentin Troll, and Guðrún Þorgerður Larsen

Iceland has the largest variety of subglacially formed volcanic edifices worldwide, given the extensive glacial cover during the Pleistocene and its frequent volcanic activity. As substantial parts of the volcanic zones are presently ice-covered, eruptions beneath glaciers are common.

 

Phreatomagmatic activity and flood deposits have been hypothesised for shallow subglacial fissure eruptions, at or within a glacial margin. However, to date, no historical examples that did not immediately break through the ice, resulting in dry magmatic activity, have been directly observed. Also, at dynamic ice-margin settings, no extensive resultant formations from shallow subglacial fissure eruptions formed in older historic eruptions have been studied until now. 

 

The final fissure from the 1783–84 CE Laki basaltic flood lava event in the Síða highlands of Iceland, fissure 10, provides a perfect natural laboratory to understand the eruptive dynamics of a shallow subglacial or intraglacial fissure eruption. Fissure 10 is a 2.5 km long formation, which constitutes the final phase of activity on the 29 km long Laki crater row, formed as eruptive activity from the Laki eruption propagated under Síðujökull, an outlet glacier from the Vatnajökull ice-cap. The resultant eruptive sequences display evidence of the increasing influence of ice when traced along strike from SW to NE, with the eruption transitioning to a predominantly phreatomagmatic phase with increasing degrees of lateral confinement. The sequence is dominated by volcanoclastic units, formed by multiple phreatomagmatic and magmatic phases suggestive of fluctuating water levels, intercalated with hackly jointed intrusions, hackly jointed lobate lava flows and debris flows. Repeating units of agglutinated spatter and spatter-fed lava flows cap the sequence, suggesting decreasing influence of external water with stratigraphic height and towards the end of the fissure’s eruptive activity. A thin layer of glacial till coats the top of the fissure 10 sequences. The margin of Síðujökull has since fully receded from the formation.

 

Our model for the eruptive dynamics of the northern Laki fissure 10 formation is based on field mapping, a drone photogrammetry survey, petrological observations and EMP analysis of glassy tephra and lava selvages to gain a full understanding of the activity and how eruptive activity progressed. The Laki eruption benefits from a wealth of previous studies on the magmatic phases from the other 9 subaerially eruptive fissures, to the SW of fissure 10, allowing for the effects of the glacier on this fissure’s activity to be isolated and defined.

 

Fissure 10 allows for an approximate reconstruction of the ice margin and glacier slope at the time of eruption, adding valuable information on the extent of the glaciers in SW-Vatnajökull in the late 18th century, and during the Little Ice Age. These shallow subglacially erupted deposits are the only fully accessible intraglacial eruptive vents, from a known historical eruption, on Earth. Detailed mapping and petrological analysis of deposits like these is important for interpreting landforms in paleo-ice margins, where transitional activity occurs.

How to cite: Gallagher, C. (., Gudmundsson, M. T., Thordarson, T., Houghton, B., Óskarsson, B., Askew, R., Cole, R., Moreland, W., Troll, V., and Larsen, G. Þ.: Characterising ice-magma interactions during a shallow subglacial fissure eruption: northern Laki, Iceland, a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12210, https://doi.org/10.5194/egusphere-egu22-12210, 2022.

EGU22-12717 | Presentations | GMPV9.3

Volcano-ice interaction:  The empirical constraints derived from eruptions in Iceland in the period 1918-2015 

Magnus Tumi Gudmundsson, Thórdís Högnadóttir, Eyjólfur Magnússon, Hannah I Reynolds, Guðrún Larsen, and Finnur Pálsson

Eruptions where glacier ice has a significant effect on the style of activity occur in some parts of the world, notably the Andes, Alaska, parts of Antarctica and Iceland.  Due to its northerly latitude and considerable ice cover within the volcanically active zones, about 50% of all eruptions in Iceland occur within glaciers, which is about 15 such eruptions per century.  In the last 25 years, six such confirmed eruptions have taken place while only one minor confirmed eruption occurred in the period 1938-1996.  This is due to the episodic nature of activity in the volcanoes covered by the 7900 km2 Vatnajökull ice cap, with a new period of high activity starting with the Gjálp eruption of 1996.   Contemporary observations have therefore provided considerable empirical data on these events.  These data include glacier thickness prior to eruptions, ice cauldron development, glacier flow perturbations, melting rates and transitions from fully subglacial to explosive/partly subaerial eruptions.  In addition, some data exist that constrains the volcano-ice interaction in the eruptions of Katla in 1918, Grímsvötn in 1934 and 1983, Gjálp in 1938 and Hekla in 1947.  The majority of these events were basaltic.  However, at least two eruptions that had an initial fully subglacial phase (Gjálp 1996, Eyjafjallajökull 2010) were of intermediate composition.  The volume of subglacially-erupted magma ranged from a few million m3 to 0.45 km3 (DRE), initial ice thicknesses ranging from 50 to 750 m, and melted ice volumes between 0.01 km3 to 4 km3.  Combined, the data from the eruptions of the last 100+ years, provides important constraints on heat transfer rates, the rate of penetration of eruptions through ice, glacier response to eruption, and the potential for generation of jökulhlaups and lahars.  Post-eruption observations in Grímsvötn have revealed that craters formed in eruptions that break through the glacial cover can be partly built on ice.  These tend to be highly transient features due subsequent melting and ice movement.  Surface melting of ice by pyroclastic density currents has occurred in Iceland, but this type of activity has in the recent past mostly been confined to the occasional sub-Plinian to Plinian eruptions in e.g. Hekla volcano.   However, there are indications that such activity has played an important role in some relatively rare large Plinian eruptions at ice covered volcanoes in Iceland, as observed in e.g. Alaska and the Andes.

How to cite: Gudmundsson, M. T., Högnadóttir, T., Magnússon, E., Reynolds, H. I., Larsen, G., and Pálsson, F.: Volcano-ice interaction:  The empirical constraints derived from eruptions in Iceland in the period 1918-2015, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12717, https://doi.org/10.5194/egusphere-egu22-12717, 2022.

EGU22-65 | Presentations | TS7.4

Middle Permian calc-alkaline basalts and ferroan rhyolites in the Istanbul Zone, NW Turkey: Evidence for Permo-Triassic subduction 

Cumhur Babaoğlu, Gültekin Topuz, Aral Okay, Serhat Köksal, Jia-Min Wang, and Fatma Köksal

Middle Permian bimodal volcanic rocks exposed in the Kocaeli Peninsula represent the first igneous event in the entire Paleozoic record of the Istanbul Zone together with coeval acidic intrusions reported from other parts of the zone. These volcanic rocks crop out as intercalations at the lower horizons of Permian-Earliest Triassic fluvial sedimentary rocks and mainly include basalts and rhyolites with subordinate andesites and rhyolitic tuffs. The basalts were derived from 1-3% partial melting of spinel peridotite in the lithospheric mantle; their high Mg-numbers (Mg# = 63-68) along with Ni (85-136 ppm) and Cr (198-240 ppm) concentrations point to derivation from near-primary mantle melts with minor fractionation. These rocks did not undergo low-pressure plagioclase crystallization based on the lack of a Eu anomaly (Eu/Eu* = 0.95-0.99). Their vesicles are filled by secondary calcite, epidote, pumpellyite, albite and chlorite due to hydrothermal alteration under subgreenschist facies conditions whereby temperatures ranged between 250-300°C. The rhyolites are ferroan [FeO*/(FeO*+MgO) = 0.87-0.96], characterized by high Zr concentrations (279-464 ppm) and compositionally similar to A2-type granitic magmas. Incompatible trace element ratios, rare earth element patterns, initial εNd isotopic data along with temperatures of the rhyolitic melts and absence of inherited zircons in the rhyolites collectively suggest that the rhyolites were derived from fractional crystallization of some basaltic melts in a crustal magma chamber with plagioclase fractionation and minor crustal contamination while the basalts were directly derived from the lithospheric mantle and reached the surface with negligible fractionation. Both volcanic rocks display diagnostic features of subduction-zone melts such as (i) medium- and high-K calc-alkaline affinity and (ii) enrichment in large-ion lithophile elements (LILE) but depletion in high-field strength elements (HFSE) (e.g., Nb-Ta troughs). U-Pb dating of zircon grains extracted from one rhyolite sample yielded a concordia age of 262.7 ± 0.7 Ma (2σ) (Capitanian). The observation that the rhyolites occur near the base of the associated sedimentary rocks places a tight constraint on the age of deposition of these deposits. The bimodal nature of the volcanic rocks, A2-type signature of the rhyolites, local stratigraphic record and data from regional geology (e.g., possible correlation with Late Permian-Early Triassic A-type rift-related granites in Carpathians and Balkans) all indicate an extensional event in the region which started in Middle Permian and resulted in the deposition of Early Triassic quartz sandstones. This extension seems to have taken place above a subduction zone developed in response to a Late Paleozoic-Triassic ocean floor (Paleo-Tethys) dipping northward beneath Laurasia, as evidenced by Permo-Triassic accretionary melanges restricted to Sakarya Zone. In conclusion, geochronological, geochemical and regional data provide additional evidence that the Paleo-Tethys Ocean was subducting northward beneath Laurasia during Permian time.

How to cite: Babaoğlu, C., Topuz, G., Okay, A., Köksal, S., Wang, J.-M., and Köksal, F.: Middle Permian calc-alkaline basalts and ferroan rhyolites in the Istanbul Zone, NW Turkey: Evidence for Permo-Triassic subduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-65, https://doi.org/10.5194/egusphere-egu22-65, 2022.

EGU22-322 | Presentations | TS7.4

Paleozoic development of OIB and see-mounts in the Turkestan Ocean within the Khaidarkan and Ulug-Too deposits, South Tianshan (STS) 

Baiansuluu Terbishalieva, Oleh Hnylko, Larysa Heneralova, and Johanne Rembe

The study area is situated in the Ulug-Tau and Khaidarkan gold-antimony-mercury deposits in the South Tienshan (STS). Together with Khadamzhai, Chauvai, and Abshyr deposits, they can be grouped into one ore province. The STS consists mainly of middle and late Paleozoic marine sedimentary rocks, which were deposited in the Turkestan Ocean and on the adjacent continental margins. They crop out along with subordinate metamorphic rocks, arc-related and intraplate volcanic suites, and ophiolites. Various lithologies were juxtaposed together in an accretionary prism during the late Carboniferous - early Permian closure of the Turkestan Ocean.

In the investigated area, Late Silurian to Devonian limestones of the Aktur carbonate platform cover both the shales of the Pulgon Formation (Fm.) (Zarhar-Say) and the basalts with gabbro bodies. Gabbro specimens were sampled for absolute age determination by amphibole 40Ar/39Ar geochronology. Volcanic rocks related to the basement of the Silurian-Carboniferous Akturian carbonate platform, part of the regional nappes of Osh-Uratyube, have been studied by Biske et al., (2019) and our group. The nappe sits on top of basaltic rocks of the Chonkoy Fm. and andesites, tuffs, and carbonate rocks of the Dedebulak Fm. In the latter unit, the volcanic suite forms the lower member which is overlain by Cambrian limestone and dolomite with intercalations of radiolarite (upper member). The volcanic rocks at the base of the Aktur carbonate platform succession indicate the Early Paleozoic geodynamic situation in the Turkestan Ocean as well as about the structure of the Khaidarkan and Ulug-Too gold-antimony-mercury deposits. The Ulug-Tau orefield is situated along the mélange zone at the base of the Aktur nappe.

Results of geochemical and geochronologic analyses (in progress) show that the basalts and basaltic andesites of the lower member of the Dedebulak Fm. formed in an island-arc setting. These volcanic rocks confirm the existence of Early Paleozoic island arcs in the Turkestan Ocean. In a later stage, those arcs possibly died out and were overlapped by carbonate platforms. For the Aktur carbonate platform, it can be assumed that it was detached from the Cambrian island arc basement during the Late Carboniferous and was added to the accretionary prism as the Aktur Nappe. The Cambrian island arc basement (Dedebulak Fm.) formed another thrust-sheet unit as part of the accretionary prism. Plastic Silurian shales and other sediments, primarily located between the Aktur carbonate platform sediments and the Cambrian island arc volcanic rocks, were incorporated into the polymictic mélange.

 

How to cite: Terbishalieva, B., Hnylko, O., Heneralova, L., and Rembe, J.: Paleozoic development of OIB and see-mounts in the Turkestan Ocean within the Khaidarkan and Ulug-Too deposits, South Tianshan (STS), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-322, https://doi.org/10.5194/egusphere-egu22-322, 2022.

EGU22-394 | Presentations | TS7.4

Origin of the metamorphic flysch sequence of the Strandja Massif (NW Turkey) in the Tethyan Realm: insights from new age and structural data 

Ali Akın, Gürsel Sunal, Boris Alexeevich Natal'in, and Namık Aysal

The Strandja Massif is a key location for understanding the Paleozoic and Mesozoic tectonic evolution of the Tethyan Realm in the NW Turkey. Some researchers have suggested that the Strandja Massif is a part of the Cimmerian continent, but others consider it as a section of the southern passive continental margin of the Eurasia. Traditionally the massif is divided into two tectono-stratigraphic units: 1) Pre-Permian crystalline basement and 2) Mesozoic sedimentary cover. However, the ages of the lithostratigraphic units have been significantly revised following the recent geochronological studies. Structural relations between these units are not simple and should be re-examined carefully. Our previous studies have shown that the crystallization time of the magmatic rocks and sedimentation ages of the rocks range from late Proterozoic to Permian especially at the east of the Strandja Massif. In this study, the Serves metagreywacke sporadically containing metabasic rocks and Kumlukoy quartz-rich metasandstones are investigated at the north of the Kıyıköy town, in order to check the first studies that assigned them to the Jurassic and Cretaceous cover deposits. These units stretch along the Black Sea coast and reveal significant differences with units that are exposed to the south. Particularly the Serves unit consists of alternation of lithic metasandstones, schists, and phyllites whereas metaconglomerate layers, marble and dolomite bodies are common among Jurassic rocks exposed in the south. Detrital zircon studies carried on the metasandstone reveal that the sedimentation should be younger than Visean-Serpukhovian, because the youngest U-Pb zircon age population obtained are between ~338 and 327 Ma. Considering widespread late Carboniferous magmatism (~312-306 Ma) in the Strandja Massif and bereft of such magmatics constrain deposition of this unit between ~327 and 312 Ma (early-middle Pennsylvanian). In contrast, the Kumlukoy Unit has quartz-rich metasandstones and it has lower metamorphic degree than the Serves Unit. The detrital zircons of these metasandstones, which were considered as Cretaceous in the previous studies, indicate that the sedimentation interval of the unit is younger than latest Permian (~256 Ma). According to the detrital ages obtained the Kumlukoy metasandstone represent a higher stratigraphical position than the Serves metagreywacke. The Kumlukoy metasandstone is most probably the equivalent of the Triassic metaclastics reported in the cover units of the NW Strandja Massif. Whereas the age and petrography of the Serves metagraywacke are similar to the Mahya Complex and Yavuzdere Arc which was interpreted as a paired magmatic arc-accretionary prism unit. Another interpretation is that the Serves Unit predates the Mahya Complex and Yavuzdere Arc and all of them represents a long-lasting subduction and accompanying accretion events in the late Paleozoic history of the Strandja Massif, namely the Silk-road Arc.

How to cite: Akın, A., Sunal, G., Natal'in, B. A., and Aysal, N.: Origin of the metamorphic flysch sequence of the Strandja Massif (NW Turkey) in the Tethyan Realm: insights from new age and structural data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-394, https://doi.org/10.5194/egusphere-egu22-394, 2022.

EGU22-452 | Presentations | TS7.4

A new set of overprinting slip-data along Manisa Fault in Aegean Extensional Province, Western Anatolia 

Taner Tekin, Taylan Sançar, and Bora Rojay

Interplay between the dynamic effects of the northward subduction of the African plate beneath the Aegean continental fragment and the North Anatolian dextral strike slip fault to the north caused a complex large-scale extensional crustal deformational domain, named Aegean extensional province.

The Gediz-Alaşehir Graben (GAG), being in that large scale extensional terrain, is a NW-SE trending extensional basin developed to the north of K. Menderes Graben (KMG). NW-SE trending Manisa fault is one of the important elements of the GAG, displaying active fault geomorphology.

The slip data were collected from the high angle normal faults, Manisa fault, controlling the Quaternary configuration and faults that are cutting through the Miocene sequences. Angelier’s reverse inversion method (WinTensor) was carried out to differentiate the deformational phases acting on the Manisa fault, based on σ1 - σ3 relation and θ ratio.

The Manisa fault is a high angle normal and dipping towards NE where the final dip-slip motion overprinted onto strike-slip motion. The analysis of the fault slip data simply implies an almost NNW-SSE and NE-SW, two extensional periods acted in the region possibly following Early Miocene contractional period since post-Oligocene. The Plio-Quaternary NNW-SSE extension overprinted onto almost ENE-WSW compression (dextral strike-slip data) which is finally overprinted by the NE-SW to NW-SE multi-directional extension in Aegean region.

To sum up; final phase of the intermittent extensional deformation, NE-SW to NW-SE multi-directional extension, superimposed on the older contractional systems, evolved under the control of North Anatolian strike-slip shear in north and southern Aegean subduction in the south with a cumulative regionwide 30° counterclockwise rotation of western Anatolia since latest Miocene or the contractional data might be possibly inherited from a strike slip structure at depth (“İzmir-Balıkesir transfer zone or Tear”) or else might be evolved along the edges of block boundaries of rotated fault domains.

Key words: Aegean extensional province, Manisa fault, normal faulting, strike-slip faulting.

How to cite: Tekin, T., Sançar, T., and Rojay, B.: A new set of overprinting slip-data along Manisa Fault in Aegean Extensional Province, Western Anatolia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-452, https://doi.org/10.5194/egusphere-egu22-452, 2022.

EGU22-568 | Presentations | TS7.4

Arabia-Eurasia Collision and The Geodynamic Models for Plateau Uplift in Turkish-Iranian Plateau 

Uğurcan Çetiner, Jeroen van Hunen, Oğuz Göğüş, Mark Allen, and Andrew Valentine

Orogenic plateaux, the broad high elevation regions of Earth, are mainly formed by plate convergence/shortening and in some cases, there is (hot) mantle support for their formation. Two major examples at present are the Tibetan and Turkish-Iranian plateaux. For instance, Turkish-Iranian plateau, is a consequence of the continental plate collision between Arabia and Eurasia, which began at ~34-25 Ma and continues to the present day. The plateau can be regarded as two distinct entities, with a boundary at roughly the political border between Turkey and Iran. While there have been studies to explain the uplift history, lithospheric/crustal structure and associated magmatism, currently, the mechanisms behind the plateau growth are not well understood. The western region, also known as the East Anatolian Plateau, has a tectonic plate structure with a near-normal crustal thickness (~35-40 km) and a markedly thinned mantle lithosphere (a few 10s of km in thickness). This suggests that, to achieve its regional elevation of ~2 km there is likely considerable support from the underlying hot asthenospheric mantle. In the east, the crust of most of Iran is thicker, up to ~65 km, and it is underlain by a variable but thicker mantle lithosphere (commonly >100 km thick). It is intriguing why these two regions have similar surface elevations (2-3 km on average) and regional geomorphology, despite predicted lithospheric structures. This study will apply new class of geodynamic models to understand how such plateaux form in response to plate collision/convergence and possible mantle upwelling/support. By comparing models with different setups (varying lithospheric thicknesses, strength profiles etc.) suggested by the natural case studies, this study will provide a more general assessment of controls on plateau growth with 2-D and 3-D perspectives in the context of Arabia-Eurasia collision. Further, the study will also help to explain the role of the forces that generate dynamic topography in the evolution of such geologic structures.

How to cite: Çetiner, U., van Hunen, J., Göğüş, O., Allen, M., and Valentine, A.: Arabia-Eurasia Collision and The Geodynamic Models for Plateau Uplift in Turkish-Iranian Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-568, https://doi.org/10.5194/egusphere-egu22-568, 2022.

EGU22-765 | Presentations | TS7.4

Fracture networks in a Late Jurassic Arab-D reservoir outcrop analogue, Upper Jubaila Formation, Saudi Arabia. 

Yuri Panara, Pankaj Khanna, Viswasanthi Chandra, Thomas Finkbeiner, and Volker Vahrenkamp

Fracture networks are responsible for channeling flow in subsurface reservoirs (hydrocarbon or geothermal) and markedly impact well productivity and ultimate recovery. Yet, methods to provide fracture (network) distribution at sufficiently high resolution are still lacking – mainly because subsurface data do not adequately capture natural fractures at the mesoscale (cm to m in size) beyond the well bore. In this study we utilize an outcrop analogue to bridge this scale gap.  Over the last decades 3D digital photogrammetry drastically improved in terms of measurement amount and quality enabling the collection of large data sets over wide outcrops. Such data provide critical insights on depositional and structural heterogeneities that may then be utilized for reservoir analogue simulations. Subject of this study is an outcrop in Wadi Laban located in SW Riyadh, Saudi Arabia, along the Mecca-Riyadh highway. We constructed a reliable 3D Digital Outcrop Model (DOMs) at high resolution of the Late Jurassic (Kimmeridgian) Upper Jubaila Formation following a ~800m long escarpment without any occlusion or bias. In particular we reconstruct a colorized dense point cloud using the high-quality setting of Agisoft Metashape© software. We investigated DOMs with CloudCompare© software (CloudCompare, 2021) to map the visible fractures 3D exposure and infer general fractures pattern. Four fracture sets are evident in the data: the predominant sets 1 and 2 are roughly E-W oriented, while sets 3 and 4 are roughly NNE-SSW oriented. Most fractures are strata bound and sub-vertical in nature. Fracture intensity (P21) analysis along the entire outcrop enables us to describe and quantify lateral and vertical variability. Laterally natural fractures are concentrated in corridors with a spacing of few tens of meters. Vertically, fracture intensity is heterogeneous. Furthermore, we found a strong correspondence between fracture intensity on the outcrop and a porosity log acquired on core samples from a well drilled only a few meters behind the outcrop. The outcome of this study provides a step forward for the comparison of outcrop and subsurface fractures, and expand the application of outcrop data to generate high resolution and fidelity reservoir analogue models.

How to cite: Panara, Y., Khanna, P., Chandra, V., Finkbeiner, T., and Vahrenkamp, V.: Fracture networks in a Late Jurassic Arab-D reservoir outcrop analogue, Upper Jubaila Formation, Saudi Arabia., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-765, https://doi.org/10.5194/egusphere-egu22-765, 2022.

EGU22-1162 | Presentations | TS7.4

Subsidence and Sedimentation Rates of the Beni Suef Basin, Egypt: Insights From the Burial and Thermal History Modeling 

Ahmed Yousef Tawfik, Robert Ondrak, Gerd Winterleitner, and Maria Mutti

The Beni Suef Basin, a rift basin in north-central Egypt, was formed in response to the NeoTethys and Atlantic oceans opening and the associated tectonic motion between Africa and Eurasia during the Early Cretaceous. It is bisected by the Nile Valley into the East and West of the Nile Provinces (EON and WON) and comprises a mixed siliciclastic-carbonate succession ranging from the Albian to the Oligocene.

Burial and thermal history modeling was performed to investigate the subsidence and sedimentation rates in the context of the tectonic evolution of the basin. Tareef-1x well from the EON and Fayoum-1x well from the WON were selected for this study, where the input data and the boundary conditions were incorporated based on the available well reports and literature.

The results show that during the Albian syn-rift phase, sedimentation was initiated slightly later with low burial rates of about 33 m/My in the EON compared with high sedimentation rates of about 210 m/My in the WON. The post-rift phase was characterized by rapid thermal subsidence accompanied by relatively moderate sedimentation rates of around 117 m/My in the EON and 97 m/My in the WON. By the Late Cretaceous, an erosional uplift occurred and culminated through the entire Paleocene resulting in the removal of some parts of the Late Cretaceous Khoman Formation from both sides of the basin. Subsidence had resumed during the Eocene due to extensional tectonics with elevated average sedimentation rates of approximately 145 m/My in the EON compared with relatively low sedimentation rates of approximately 74 m/My in the WON. These phases are interrupted by a hiatus period during the Late Eocene-Oligocene in the EON, while the WON has continued subsiding and resulted in the deposition of the Oligocene Dabaa Formation. The Miocene thermal uplift represents the last tectonic phase, which led to significant erosion from the Eocene Apollonia Formation in the EON and the Oligocene Dabaa Formation in the WON.

The implications on the hydrocarbons potentiality were also investigated through the thermal history modeling, where we found that the Turonian Abu Roash “F” source rock exists in the early oil window with a transformation ratio of about 20 % across the entire basin. While the Lower Kharita shale source rock, which is only deposited in the WON, has reached the late oil window with a transformation ratio of approximately 70 %.

In summary, sedimentation began slightly later in the EON (Middle to Late Albian) compared with the WON (Early Albian), where the paleo basement high has hindered the deposition of the Early Albian Lower Kharita shale in the EON compared with the WON, thus caused a delay at the beginning of the deposition. The different sedimentation rates across the basin could be attributed to various factors such as the amount of sediment supply, climate conditions, different slopes across the basin, and /or lithology, which need to be addressed in further research.

How to cite: Tawfik, A. Y., Ondrak, R., Winterleitner, G., and Mutti, M.: Subsidence and Sedimentation Rates of the Beni Suef Basin, Egypt: Insights From the Burial and Thermal History Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1162, https://doi.org/10.5194/egusphere-egu22-1162, 2022.

EGU22-1319 | Presentations | TS7.4

Assessing the geometry of the Main Himalayan thrust in central Nepal: Insights from thermokinematic modelling 

Suryodoy Ghoshal, Nadine McQuarrie, Delores M. Robinson, Katherine Huntington, and Todd A. Ehlers

The 2015 Gorkha earthquake reignited an existing debate about whether geometric barriers on faults play a role in containing the propagation of ruptures. Models suggest that the extent of the Gorkha earthquake rupture, and of other historical earthquakes were controlled by the locations of ramps in the Main Himalayan thrust (MHT), notably on the western edge of the rupture. The existence of such a pronounced lateral boundary to the west of the Gorkha epicenter is supported by an offset in the surface trace of the Main Central thrust (MCT), closely followed by an offset in the distribution of young (<5 Ma) muscovite 40Ar/39Ar (MAr) ages. However, the zircon (U-Th)/He (ZHe) and apatite fission track ages show more linear east-west distributions over the same region, as does Physiographic Transition 2 (PT2). We explore the formation of these relationships by combining forward-modeled balanced cross-sections through the Marsyangdi, Daraundi, and Budhi Gandaki valleys in central Nepal, and investigate the continuity of active structures across the western portion of the Gorkha rupture. The sequential kinematics of each of these sections are combined with a thermokinematic model (PECUBE) to evaluate the exhumation and cooling histories of the rocks exposed at the surface. We gauge the validity of these models by comparing their predicted cooling ages to measured ages, discarding those that do not match the measured distribution of cooling ages.

Our 3D models show that the offset in the surface geology along the Daraundi is due to a shorter (by 1/3) Trishuli thrust sheet, that has been completely translated to the south of the modern ramp and folded by the Lesser Himalayan duplex. Similarly, the southern extent of the reset MAr ages is also controlled by these relationships requiring observed surface offsets to be the result of changes in the hanging wall rocks translated over the ramp, rather than changes in the geometry of the modern ramp. Notably, the continuity and location of the modern MHT ramp is evidenced by the linear distribution of the youngest ZHe and AFT ages, which are most sensitive to the location of the active ramp. Additionally, the out-of-sequence thrust responsible for PT2 soles directly into the modern ramp during its proposed period of activity at ~1.2 Ma, resulting in the highly linear trace of PT2, running parallel to the location of the ramp. These linear relationships and their reproducibility in thermo-kinematic models argue strongly against any geometric offsets in the modern MHT ramp that have been proposed to limit rupture propagation in central Nepal.

How to cite: Ghoshal, S., McQuarrie, N., Robinson, D. M., Huntington, K., and Ehlers, T. A.: Assessing the geometry of the Main Himalayan thrust in central Nepal: Insights from thermokinematic modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1319, https://doi.org/10.5194/egusphere-egu22-1319, 2022.

EGU22-1665 | Presentations | TS7.4

Coeval volcanism and rotation of Neotethyan oceanic crust in the Oman ophiolite – fact or fiction? 

Antony Morris, Anita Di Chiara, Mark Anderson, Chris MacLeod, Louise Koornneef, James Hepworth, and Michelle Harris

The upper crustal volcanic section of the Oman suprasubduction zone ophiolite is divided into an older V1 sequence, overlain by slightly younger V2 lavas and (in places) a final V3 sequence. Paleomagnetic data from the V1 and V2 sequences of the northern massifs of the ophiolite have been used previously to infer that clockwise rotation of the Oman lithosphere began while the upper crust was actively accreting, with V1 lavas apparently more rotated than the overlying V2 units. This inference has been largely accepted by the geological community and has influenced models for the spreading history and geodynamic evolution of the Oman ophiolite.

Here we present new paleomagnetic data from well-exposed and structurally well-constrained volcanic sequences in the Salahi and Fizh massifs of the ophiolite that discredit this interpretation. In contrast to previous studies that employed standard structural tilt corrections, we use a net tectonic rotation approach to determine rotation parameters, taking confidence limits on input variables into account using Monte Carlo modelling. Importantly, we correct the magnetization direction and structural orientation of the older V1 lavas for the effects of the net tectonic rotation of the younger V2 lavas prior to calculating rotation parameters for the older units. Results demonstrate that both massifs rotated ~120° clockwise around steeply-plunging rotation axes after eruption of the V2 lavas. This rotation occurred during roll-back of the Neotethyan subduction zone in response to impingement of the Arabian margin with the trench. Early rotation of the Salahi V1 lavas around shallowly-plunging, broadly ridge-parallel axes indicates only simple tilting between eruption of the V1 and V2 sequences, and no early rotation of the Fizh V1 lavas is required at all. These new constraints on the evolution of the ophiolite therefore provide no evidence of vertical axis rotation during accretion of the Oman volcanic sequences.

How to cite: Morris, A., Di Chiara, A., Anderson, M., MacLeod, C., Koornneef, L., Hepworth, J., and Harris, M.: Coeval volcanism and rotation of Neotethyan oceanic crust in the Oman ophiolite – fact or fiction?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1665, https://doi.org/10.5194/egusphere-egu22-1665, 2022.

The northern extent of the supercontinent Gondwana in the late Neoproterozoic-Cambrian is not well defined. In most localities the continental margin is covered by thick sedimentary successions, formed following the successive rifting of Tethyan Oceans that episodically detached continental terranes from the edge of the supercontinent. East of the Mediterranean, despite the continental continuity between the Arabian-Nubian-Shield (ANS) and the Tauride block (a Cadomian terrane), the original transition between the two crustal domains is inaccessible and remains obscured. In Israel, investigations of Late Ediacaran, late-stage igneous intrusions of the ANS in the South, together with granulite xenoliths from the lower crust in the North, allow us to probe into the North-Gondwana edge in the late Neoproterozoic and envisage its transition towards the peri-Gondwana Cadomian realm, as well as the evolution of the North Gondwana crust subsequently to the Neoproterozoic. Geochronology and isotopic geochemistry of alkaline intrusions in the Amram massif (southern Israel) as well as doleritic intrusions in the late Neoproterozoic Zenifim Formation (subsurface of south-central Israel) has revealed an igneous and thermal imprint at ca. 550 Ma recorded by the reset of apatite U-Pb ages, together with additional apatite U-Pb dates taken to represent crystallization. Nd and Hf isotopes in apatite, zircon and whole rock also show the ca. 550 Ma intrusions are isotopically distinct from the ANS and resemble Cadomian magmatism in the Taurides. Granulite xenoliths from the lower crust under the lower Galilee (North Israel) contain abundant zircons of distinct U-Pb-Hf properties. These include detrital grains remnant of Neoproterozoic sediment that was subducted and relaminated to the lower crust, late Carboniferous zircons (peaking at 300 Ma) with contrasting εHf(t) signatures, some of which represent syn-Variscan magmatism, and zircons with the age of the host Pliocene basalt. We demonstrate that the Cadomian (ca. 550 Ma) igneous and thermal imprint on the North ANS may have been driven by proto-Tethys subduction that brought about sediment relamination to the North Gondwana lower crust in the latest Neoproterozoic. The late Carboniferous ages recorded in the xenoliths involve both the reworking of depleted ANS basement as well as the relaminated sediment in the means of metamorphism and minor magmatism. Carboniferous thermal disturbance was associated with the formation of continental scale basin and swell architecture across present-day N Africa, Arabia and Iran, and the development of ‘Hercynian unconformities’ in these areas, that were located at the time south of the passive(?) margin of Paleo-Tethys.

How to cite: Abbo, A., Avigad, D., Gerdes, A., and Morag, N.: The Cadomian and Variscan record of the Gondwana margin in Israel: Protracted Crustal Evolution between the Arabian-Nubian Shield and multiple Tethyan Oceans, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1777, https://doi.org/10.5194/egusphere-egu22-1777, 2022.

The Tethys-derived Semail Ophiolite had formed during the Cenomanien-Turonian. Along with deep-sea sediments, it was obducted onto the Arabian Plate as it was still young, hot and buoyant. Thrusting and loading triggered the formation of the Aruma Foreland system consisting of a foredeep, a forebulge and a backbulge basin.

The studied succession represents the uppermost part of the Permo-Mesozoic shallow marine shelf sequence of the Arabian Platform, which is blanketed at an angular unconformity by shales of the Late Cretaceous Muti Formation of the Aruma (foreland) Group. The structural position of the succession is on the forebulge which is characterized by eroded Cretaceous and Jurassic shelf formations of the Arabian Platform (Wasia-Aruma Break).    

We identified two forebulge successions. Both display repetitive lithofacies, beginning with (1) shallow subtidal massive/poorly bedded bioclastic wackestones to floatstones, followed by (2) peloidal grainstones, (3) ferruginous crusts and (4) shallow marine ferruginous oolites. From base to top, both successions record an overall shallowing-up trend. At the same time, the relative sedimentation rate decreases in the same direction. The coarse-grained massive facies may have been deposited on a regular slope which was well-supplied with bioclasts. The finer grained grainstone facies and their peloids indicate a lower sedimentation rate, reflecting the transition form a regular slope to a forebulge on which in the next step sediment condensation occurred (crusts) and chemical precipitation of ferruginous material (crusts and oolites). Each forebulge succession is capped by clayey material.

The similar facies development of the two successions suggests repetitively similar depositional and tectonic conditions. As both sequences occur at the same site, two vertical forebulge developments are concluded.

The ferruginous crusts formed under at least slightly reducing conditions, associated with minor water-deepening events. Both oolites contain chlorite, hematite, quartz, calcite and apatite. The nuclei of the ooids are often chlorite or hematite fragments, having most-likely derived from preexisting ferruginous crusts. Iron oxyhydroxides and clinochlore of the oolites reflect bathymetric changes to more oxidizing aqueous conditions, associated minor water-shallowing events.

Fe-rich anoxic to sub-oxic sea water of the marine foredeep was the Fe source for the crusts and oolites, coinciding with (1) a high rate of global Cretaceous oceanic crust production, (2) related hydrothermalism and (3) the regional proximity of an active spreading axis. Fe was likely stabilized in ocean water as Fe colloids and organic Fe complexes.

How to cite: Mattern, F., Pracejus, B., Scharf, A., Frijia, G., and Al-Salmani, M.: Two Cretaceous forebulge successions in the Oman Mountains, triggered by the obducted Semail Ophiolite, identified by the facies analysis of limestones, ferruginous crusts and ferruginous oolites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2123, https://doi.org/10.5194/egusphere-egu22-2123, 2022.

EGU22-2493 | Presentations | TS7.4

Seismic structure of a Tethyan back-arc: transdimensional ambient noise tomography of the Black Sea lithosphere 

Laura Petrescu, Felix Borleanu, and Anica Placinta

The Black Sea is the largest European back-arc basin connected to the subduction and final closure of the Tethys ocean. Its origin and type of crust are widely debated, with contrasting views suggesting it is either a relic of Paleotethys or a rifted back-arc basin formed within the thick and cold Precambrian lithosphere. To investigate the structure of this atypical intra-continental basin, we constructed the highest resolution seismic tomography of the region using the latest techniques of probabilistic inversion of ambient noise data recorded at seismic stations around the sea. Our results indicate the presence of thinned continental crust beneath the basin, likely of Precambrian lithospheric origin, thus invalidating the existence of either a relic Paleotethys fragment or younger oceanic crust. Extension and rifting probably exploited pre-existing sutures, but the rheologically strong lithosphere resisted transition to seafloor spreading. Seismic anisotropy shows complex paleo-deformational imprints within the crust and upper mantle related to the closure of Tethys. Extension caused by subduction roll-back generated anisotropic lithospheric fabric parallel to the rifting axis within the thinnest sections of the crust in the western basin. The eastern part developed on a distinct lithospheric domain that preserves paleo-extension anisotropy signatures in the form of lower crustal viscous deformation. Further south, anisotropy orients along the Balkanide-Pontide collisional system that records the final stages of Neotethys closure. Our results place key constraints on the type of deformations that occurred throughout the Tethyan realm, with fundamental implications for the development and evolution of back-arc basins and continental break-up. 

How to cite: Petrescu, L., Borleanu, F., and Placinta, A.: Seismic structure of a Tethyan back-arc: transdimensional ambient noise tomography of the Black Sea lithosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2493, https://doi.org/10.5194/egusphere-egu22-2493, 2022.

EGU22-3985 | Presentations | TS7.4

Thermal overprinting of Mesozoic shelfal limestones on Jabal Akhdar, Oman 

Bernhard Pracejus, Andreas Scharf, and Frank Mattern

The Jabal Akhdar Dome of the Hajar Mountains (northern Oman) has long been considered to have had no significant thermal overprinting since the start of its doming (Eocene, ~40 to 30 Ma). Only the Semail Ophiolite, obducted during the Late Cretaceous, metamorphosed the overridden sedimentary rocks at its base. However, this is stratigraphically well above the positions of the rocks discussed here. Our findings describe the first evidence for an increased metamorphic alteration of Late Permian, Jurassic and Lower Cretaceous shelfal limestones. Two independent sites were identified, where calcite was either replaced by wollastonite or sulfides. 

 

The calc-silicates, which occur southeast of the Saiq Plateau (stratigraphically above the plateau), contain up to centimeter-sized wollastonite crystals. The conversion into marble has been interrupted, as indicated by relict fossils and ooliths of Jurassic and Lower Cretaceous limestones. So far, the outcrop has been mapped over a length of ~1.2 km. It is dissected by several NW-striking dextral faults in a difficult terrain and, thus, the occurrence may be significantly wider. Wollastonite concentrates in sub-horizontal to gently SE-dipping limestone layers, neighbouring strata may be almost void of it. In places, strong and coarse-grained dolomitisation coincides with decreased wollastonite content. The area is cross-cut by irregular quartz-wollastonite-rich veins.

 

Adjacent to the outcrops are younger quartz-siderite veins, which have almost completely replaced limestone layers (encased wollastonite-carrying limestone relicts). Distal to the mineralisations, the limestones contain decimeter-sized chert nodules. This entire silica-dominated system must have reached 450 ºC in order to form the well crystallised wollastonite. The mostly oxidising character of the environment during overprinting is reflected by fine euhedral hematite grains throughout the examined profile. However, slightly reducing settings promoted the formation of very rare and tiny crystals of erdite (NaFeS2·2H2O) in two places.

 

Sulfides in finely laminated Permian carbonates, which contain fine as well as very coarse-grained black carbonates, occur on the northwestern side of the Saiq Plateau in no longer accessible excavation materials. So far, the search for another outcrop failed, due to the sub-vertical wadi walls near-by. The strongly dominating pyrite is accompanied by trace amounts of sphalerite and less galena. Collectively, sulfides replaced carbonate laminae with fine crystalline impregnations and concentrated in up to decimeter-large lensoid concretionary shapes. Dark carbonaceous laminae and recrystallised coarse-grained materials contain finest graphite flakes. This again indicates temperatures of ~450 ºC, at which the graphite formation started during decarbonisation, also promoting a reducing regime (the sulfides show no signs of oxidation).

 

Our working hypothesis is that the thermal overprint (>450 ºC) coincided with the late Eocene to Oligocene doming event, leading to multiple mafic intrusions. Similar intrusions are known from the Muscat and Batain area and have the same age.

How to cite: Pracejus, B., Scharf, A., and Mattern, F.: Thermal overprinting of Mesozoic shelfal limestones on Jabal Akhdar, Oman, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3985, https://doi.org/10.5194/egusphere-egu22-3985, 2022.

EGU22-4246 | Presentations | TS7.4

Implications for the pre-Alpine evolution of the Eastern Alps – a U/Pb zircon study on the Austroalpine Schladming Nappe 

Isabella Haas, Walter Kurz, Daniela Gallhofer, and Christoph Hauzenberger

The Schladming Nappe, as a part of the Silvretta-Seckau Nappe System of the Eastern Alps, comprises pre-Alpine remnants of crystalline basement rocks which give important information for reconstructing the Variscan and even pre-Variscan history of the Alps.

The Schladming Nappe mainly consists of paragneisses being intruded by subsequently overprinted granitoids. U-Pb zircon ages were acquired through LA-MC-ICPMS to determine the magmatic emplacement of the metagranitoids and constrain the tectono-metamorphic history of the Schladming Nappe.

Within these meta-granitoids, several intrusive events can be distinguished: (1) a Cambrian event with 206Pb/238U zircon mean ages between 496±6.5 and 501±7 Ma, (2) a Late Devonian/Early Carboniferous event with zircon mean ages between 350±5 Ma and 371±5 Ma and (3) a Permian event with zircon mean ages between 261±3 Ma and 263±3.5 Ma. The youngest age group is only found in metagranitoids from the southeastern part of the Schladming Nappe. The tectonic contact to the metapelites of the Wölz Nappe system and therefore the affiliation of these Permian granitoids to the Schladming Nappe, however, is still enigmatic.

The various age groups can also be differentiated by their whole rock geochemistry. While all of the metagranitoids are peraluminous, the Cambrian age group exhibits higher SiO2 values compared to the Late Devonian age group. The Late Devonian age group shows higher contents of CaO, MgO, FeO, Al2O3, as well Sr and Ba and can be further divided into two subgroups, with one depicting a distinct negative Eu-anomaly (EuN/Eu*=0.44-0.69) and the other subgroup lacking one (EuN/Eu*=0.82-1.08). The Permian age group often displays high contents of K2O, Nb and Y.

The Late Cambrian to Early Ordovician metagranitoids can be classified as part of a magmatic arc system, probably belonging to the northern Gondwana margin. The early Variscan granitoids can also be interpreted as part of an active margin. The Permian granitoids show a within plate granite affiliation and can further be interpreted as A-type granitoids, probably related to post-Variscan lithospheric extension.

How to cite: Haas, I., Kurz, W., Gallhofer, D., and Hauzenberger, C.: Implications for the pre-Alpine evolution of the Eastern Alps – a U/Pb zircon study on the Austroalpine Schladming Nappe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4246, https://doi.org/10.5194/egusphere-egu22-4246, 2022.

Situated between Africa and Eurasia in the eastern Mediterranean, the island of Cyprus has developed on the northern margin of the southern Neotethys by the accretion of three terrains, the Mamonia complex, the Troodos ophiolite, and the Kyrenia terrane. The Kyrenia terrane comprises a tectonic stack of Triassic to Eocene rock units interleaved with basic and acid volcanics and minor metamorphic inliers, alongside an Oligocene-Miocene flysch. Our U-Pb-Hf detrital zircon investigation in the Kyrenia Triassic to Eocene section reveals a large amount of Neoproterozoic zircons (950-600 Ma), alongside Silurian (∼430 Ma), Carboniferous (∼300 Ma), Triassic (∼240 Ma), and Upper Cretaceous (∼85 Ma) zircons. The Precambrian age profile of all three studied units resembles that of Paleozoic sandstones of the Tauride Block, as well as that of Paleozoic and Mesozoic sandstones found across North Africa. It is interpreted as reflecting the reworking of Paleozoic sandstone units from the Taurides or other peri-Gondwanan source. The presence of a substantial proportion of ~300 Ma zircons, as early as in Triassic sediments of the Kyrenia, is of significant interest because Carboniferous magmatism is confined to the Paleotethyan realm which is traced north of the Taurides. Deposition of the Kyrenia sequence closer to a Northern Tethyan province would better fit its detrital zircon signal. The detrital signal of the Kyrenia, indicative for Eurasian terranes north of the Mediterranean, also differs significantly from that of the Mamonia Complex (SW Cyprus) in which only Afro-Arabian sources are distinguished. Thus, in view of its unusual detrital zircon content, the Kyrenia sequence stands out in the Eastern Mediterranean as an exotic rock pile that cannot be straightforwardly correlated with its neighboring geologic environment.

How to cite: Glazer, A., Avigad, D., Morag, N., Güngör, T., and Gerdes, A.: Detrital zircon evidence for exotic elements in the southern Neotethys: A provenance study of Triassic-Eocene rock units in the Kyrenia terrane, Northern Cyprus, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5391, https://doi.org/10.5194/egusphere-egu22-5391, 2022.

EGU22-6471 | Presentations | TS7.4

Formation and contractional reactivation of the NW Sulu Sea (SE Asia) 

Patricia Cadenas and César R. Ranero

Located in SE Asia in between the Palawan and the Philippine islands, the lozenge-shaped Sulu Sea corresponds to a marginal sea that displays a complex seafloor morphology. The NE-SW trending Cagayan Ridge separates a southeastern deep-water domain, which is bounded by the Sulu Trench towards the east, from a shallower and narrower northwestern domain. Interpretations of low-resolution 2D streamer datasets, ODP Leg 124 drilling results, magnetic, geochemical, and geochronological studies, and gravity inversion results led to distinctive tectonic models, with contrasting basin formation mechanisms, and ages of opening and subsequent contractional reactivation. The debates remain because the structure of most of the Sulu Sea and its along-strike structural variability remain underexplored to date.

We focus on this work on the first detailed analysis of the structure and seismo-stratigraphy of the NW Sulu Sea. Based on the reprocessing, calibration of the Silangan-1 exploration borehole, and interpretation of > 5384 km of 2D seismic data along 19 regional profiles of an irregular grid that covers the whole NW Sulu Sea, we identify, map and interpret the seismo-stratigraphic horizons and units, major structures, and rift-related and syn-orogenic depocenters and structural domains. We define six seismo-stratigraphic units in the NW Sulu Sea, consisting of Quaternary to Paleogene sediments, which developed during an early phase of Paleogene to early Miocene extension, a following early to Middle Miocene phase of contraction, and a late Miocene to Quaternary stage of relative tectonic quiescence. While transpressional faults core uplifted basement areas, strike-slip, high-angle and low-angle oblique extensional faults crosscut continental crystalline basement of variable thickness and bound pull-apart basins, half-grabens and sags respectively. The distribution and trend of rift-related depocenters describe a strong structural segmentation and vary along NW-SE and NE-SW oriented zones. Thrust-cored anticlines, inverted transtensional and transpressional faults and mud diapirs deform the sediment pile and control the geometry of syn-orogenic depocenters distinctively across the NW Sulu Sea.

Normal and oblique trending sets of faults controlled the extension and compartmentalized the NW Sulu Sea. Subsequent contractional reactivation differentiated NE and SW basement and sedimentary domains, separated by the NW Sulu Break Elevation. These domains show a contrasting overall architecture, basement thickness, contractional structures and distribution of rift-related and syn-orogenic depocenters. Rift segmentation, and particularly, basement thickness variations, may have conditioned the type and distribution of contractional deformation.

How to cite: Cadenas, P. and R. Ranero, C.: Formation and contractional reactivation of the NW Sulu Sea (SE Asia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6471, https://doi.org/10.5194/egusphere-egu22-6471, 2022.

EGU22-7096 | Presentations | TS7.4

Geodynamics of long-term continental subduction and Indian indentation at the India-Eurasia collision zone 

Kai Xue, Wouter P. Schellart, and Vincent Strak

India-Eurasia convergence velocities have dropped significantly from ~18 cm/yr in the Late Cretaceous-earliest Eocene to ~4-5 cm/yr since ~50 Ma. The mechanisms of convergence deceleration, continued convergence since ~50 Ma, long-term continental subduction and long-term Indian indentation into Eurasia still remain controversial. Many previous studies consider an external driving force for the long-term convergence, continental subduction and Indian indentation, and the initial India-Eurasia collision as the trigger for the deceleration. In this study, we investigate the mechanism(s) of the abrupt deceleration, the continued convergence, the long-term continental subduction and long-term Indian indentation using buoyancy-driven analog experiments. We conduct three large-scale experiments to simulate the subduction and collision process at the convergent boundary with different boundary conditions at the 660-km discontinuity, including an infinite viscosity step (the lower-upper-mantle viscosity ratio (ηLMUM) is infinitely high), no viscosity step (ηMUM =1) and an intermediate viscosity step. The experiment with infinite ηLMUM shows a deceleration when the slab tip reaches the 660-km discontinuity, while the other two experiments show a deceleration at the onset of continental subduction. Our experiments show that a higher ηLMUM favors a lower velocity drop at the onset of continental subduction, lower convergence velocities, reduced continental subduction and a higher indentation amount, and vice versa. Furthermore, our models suggest that in nature, with an intermediate-high ηLMUM, the negative buoyancy force of both upper and lower mantle slab segments is the main driver of long-term convergence, continental subduction and Indian indentation.

How to cite: Xue, K., Schellart, W. P., and Strak, V.: Geodynamics of long-term continental subduction and Indian indentation at the India-Eurasia collision zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7096, https://doi.org/10.5194/egusphere-egu22-7096, 2022.

EGU22-7993 | Presentations | TS7.4

Petrology and Geochemistry of intrusive igneous rock from the Inthanon zone, Northwestern Thailand 

Srett Santitharangkun, Christoph Hauzenberger, Daniela Gallhofer, and Etienne Skrzypek

Large plutons are common within the Inthanon Zone in Northwestern Thailand. These igneous rocks are also known as Central Granitoids Belt in mainland Southeast Asia. They are interpreted to be part of the suture zone between Sibumasu and Indochina and were emplaced mainly in the Upper Triassic.

Here, we present new petrological and geochemical data for the Central Granitoids Belt.  A geochronological study on selected samples will follow.  The sampled granitoids can be separated into three groups: (1) biotite granite, (2) hornblende granite, (3) syenite/monzonite. The samples consist of various light colored to dark grey granitoids due to the type and amount of mafic minerals (biotite or hornblende) present. The general mineral assemblage of all the intrusive igneous rocks is quartz + plagioclase + K-feldspar + biotite + apatite + zircon ± allanite ± titanite ± ilmenite. The biotite granites are mostly composed of biotite aggregates associated with accessory minerals: zircon, ilmenite, and apatite. The syenite/monzonite group usually contains additional clinopyroxene and hornblende. Plagioclase and hornblende of the syenite/monzonite group commonly exhibit a sieve texture.

The biotite granite group is typically peraluminous and belongs to the high-K calk-alkaline to shoshonitic series. The hornblende granite group is mostly peraluminous and of predominantly shoshonitic affinity. The syenite/monzonites are typically metaluminous but also belong to the shoshonitic series. The chondrite normalized rare earth element (REE) patterns are quite similar for all igneous rocks with elevated LREE, pronounced negative Eu anomaly and a flat HREE segment. The granite tectonic discrimination plots after Pearce et al. (1984) classify most samples as syn-collision granites (syn-COLG) and when using the Batchelor and Bowden (1985) discrimination diagram as syn-, late, and post-collisional.

The intrusive igneous rocks from Northwestern Thailand were presumably emplaced in a syn- to post-collisional setting when the Sibumasu block collided with the Sukhothai terrane and was eventually amalgamated to the Indochina block. This led to the closure of the Palaeotethys along the eastern area of the Sibumasu block.

Batchelor, R.A. and Bowden, P. (1985) Petrogenetic Interpretation of Granitoid Rock Series Using Multicationic Parameters. Chemical Geology, 48, 43-55.

Julian A Pearce, Nigel BW Harris, Andrew G Tindle (1984). Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, 956-983.

 

How to cite: Santitharangkun, S., Hauzenberger, C., Gallhofer, D., and Skrzypek, E.: Petrology and Geochemistry of intrusive igneous rock from the Inthanon zone, Northwestern Thailand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7993, https://doi.org/10.5194/egusphere-egu22-7993, 2022.

EGU22-9219 | Presentations | TS7.4 | Highlight

Mapping the extent of seismoturbidites near the southern Dead Sea Fault in the Gulf of Aqaba 

Matthieu Ribot, Sigurjón Jónsson, Yann Klinger, Ulaş Avsar, and Zeynep Bektaş

Despite multiple research efforts since the late 1950’s, many questions regarding the earthquake activity of the Dead Sea Fault (DSF) remain, in particular for its southernmost portion in the Gulf of Aqaba. This is due to its offshore location and little-known interactions with the Red Sea rift system. The emergence of the NEOM city-project in northern Saudi Arabia and the planned King Salman road crossing across the Gulf of Aqaba have made it important to find answers for these questions related to the earthquake hazard of the region. The last major earthquake in the Gulf of Aqaba occurred in 1995 along one of the main strike-slip fault segments in the gulf, bringing both extremities of the fault rupture closer to failure. Studies of the DSF have found that large events along the entire DSF cluster during relatively short active seismic periods lasting about 100-200 years, separated by longer quiescent periods of about 350-400 years. From a tectonic point of view, the time gap between 1995 and the previous major earthquake in AD1588 conforms to this scheme and suggests that the DSF might be ripe for a new earthquake sequence, with the 1995 earthquake as the starter. That said, new results from GPS and InSAR observations have pointed to possible fault creep in the southern part of the gulf, which would significantly decrease the seismic hazard in the area. To explore this possible creep and to test the clustering model, we investigate new sub-bottom profiling data acquired in December 2019 in the Gulf of Aqaba. We aim to map the extent of sand layers present in the different sub-basins of the gulf and to correlate them with seismoturbidite layers found in sediment cores collected in 2018. By looking at the geographic extent of these sand layers, we also aim to define the source of the coarse deposits, or at least, to determine whether they are related to the regular sediment influx or linked to turbidites generated by slope failures during large earthquakes. Our preliminary results indicate that the sub-bottom profiling data allow us to map sand layers up to a depth of about 8 meters. Considering a sedimentation rate in the gulf between 0.2 - 0.4 mm/year, we could be able to gain an overview of the sediment infill of the Gulf of Aqaba over the last 20 ky or more. Even if the resolution of the sub-bottom profiling data is lower than that of the sediment cores, and the assumptions made for the correlation of the sand layers, due to the scattered grid, do not help to constrain properly the source of the deposits, we can still propose a longer-term overview of the earthquake activity and discuss the temporal organization of the large events in the area.

How to cite: Ribot, M., Jónsson, S., Klinger, Y., Avsar, U., and Bektaş, Z.: Mapping the extent of seismoturbidites near the southern Dead Sea Fault in the Gulf of Aqaba, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9219, https://doi.org/10.5194/egusphere-egu22-9219, 2022.

EGU22-9365 | Presentations | TS7.4

Asymmetrical lithospheric necking of Red Sea rift 

Thamer Aldaajani, Hany Khalil, Philip Ball, Fabio Capitanio, and Khalid Almalki

The Red Sea rift exhibits two distinct rifting styles: in the north, the rifting is magma-poor, the crust is hyperextended and the lithospheric necking is asymmetric, in the south, rifting rapidly localized atop a symmetric lithospheric necking. One of the long-standing questions is what drives such different lithospheric necking style? We ran 2D high-resolution thermomechanical numerical simulations of lithospheric rifting to address the northern and southern Red Sea extensional end members and validate the models’ deformation patterns by comparing them against 2D data-driven structural models. The modelling investigates (a) the effect of rotational extension by varying extension velocities along the Red Sea, and (b) the thermal structure of the southern Red Sea due to plume impingement, while the analysis of the outcomes focuses on the early rifting stage, which involves normal rifting and dike intrusion. We find that asymmetrical lithospheric necking in the central and northern Red Sea is potentially driven by the velocity boundary conditions and inherited structures, mainly the Sirhan rift. The decoupling between the upper portion of the lithosphere and the asymmetrical lithospheric necking, which plays an essential role in the observed deformation patterns in the Arabian margin, is likely controlled by the lower crustal rheology and thickness. Furthermore, we find that the Afar plume near the southern Red Sea, which introduced in our models in form of thermal anomaly, promotes rifting localization.

How to cite: Aldaajani, T., Khalil, H., Ball, P., Capitanio, F., and Almalki, K.: Asymmetrical lithospheric necking of Red Sea rift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9365, https://doi.org/10.5194/egusphere-egu22-9365, 2022.

The eastern Mediterranean Sea preserves crust that was trapped during the collision of Africa with Eurasia and the closure of the Neo-Tethyan Ocean. Thick sedimentary blanketing (10 to 15 km) complicates our ability to assess the nature of the crust, and therefore it has remained one of the least understood regions of the collision belt. In this presentation, I review recent marine geophysical observations (surface and deep-tow magnetics, high-resolution bathymetry and seismic reflection data) and discuss their geodynamic implications. The surface total field and vector magnetic anomalies from the Herodotus Basin reveal a sequence of long-wavelength NE-SW lineated anomalies that straddle the entire basin suggesting a deep two-dimensional magnetic source layer. The magnetic vector data indicate an abrupt transition from a 2D to a 3D magnetic structure along the eastern edge of the Herodotus Basin and west of the Eratosthenes Seamount, where a prominent gravity feature is found. These findings indicate that the Herodotus Basin preserves remnants of oceanic crust accreted along a mid-ocean ridge system that spread in an NW-SE direction. The African Plate's continuous northward and counterclockwise motion during the Paleozoic and Mesozoic allow predicting the crustal remanent magnetization directions, which dictate the shape of the present-day magnetic anomalies. The shape of the Herodotus anomalies best fit Carboniferous magnetization directions. The combination of surface and deep-tow magnetic data, as well as thermal and magnetic forward modeling, suggest that spreading was slow (~25 km/myr half spreading rates) and that the upper oceanic crust has been entirely demagnetized, probably due to the heating effect induced by the thick sedimentary coverage.

 

The stretched continental crust of the Levant Basin, found east of the Herodotus Basin, preserves a series of horsts and grabens that generally orient in an orthogonal direction relative to the spreading direction, suggesting that they may have formed concurrently with the initial opening of the Herodotus Basin. Earthquake data and long NW-SE bathymetric scars found within the northern edge of the Nile deep-sea fan suggest that an active fault belt transfers the motion from the Gulf of Suez toward the northern convergence boundaries. This fault belt is directed toward, and merges with, the continental-ocean boundary that straddles the eastern Herodotus Basin. This observation may indicate that the mechanical transition from the rather weak and stretched continental crust of the Levant to the relatively strong oceanic Herodotus crust has guided the location of the western boundary of the Sinai Microplate, formed during the Oligocene by the fragmentation of the African Plate.

How to cite: Granot, R.: Trapped remnant of the Tethyan realm: the influence of ancient tectonics on the present-day geodynamics of the eastern Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9408, https://doi.org/10.5194/egusphere-egu22-9408, 2022.

EGU22-11305 | Presentations | TS7.4

The Neotethyan Arabian necking zone exposed at the SE Oman mountains: field evidence and consequences 

Maxime Ducoux, Emmanuel Masini, Andreas Scharf, and Sylvain Calassou

The Late Cretaceous Oman Mountains are generally assumed to result from obduction followed by the inversion of the mid-Permian- to Triassic Neotethyan rifted margin. However, the key rift-related crustal features, such as a necking zone or hyper-extended rift domains remain inferred and poorly described so far. In this study, we investigate the tectono-stratigraphic record of the eastern part of the Oman Mountains where the exposed Tonian (Neoproterozoic) crystalline basement outcrops together with the pre- to syn-obduction sedimentary record in the Ja’alan massif area. The description of these units together with subsurface data enables to describe the former Arabian necking zone. The Ja’alan massif itself and the Arabian platform to the southwest represent the former proximal margin domain. It is characterized by the eroded basement sealed by post-obduction continental to shallow marine sediments. In contrast, the north-eastern side of the massif is flanked by Permian-Mesozoic deep marine post-rift sediments (Batain Group) equivalent to the Hawasina thrust sheet in the Oman Mountains. These two endmember paleogeographic units are separated by a major N20 dipping top-to-the-NE normal fault with dip-slip kinematics (slikensides with striae, S/C-fabric). The damage zone of this fault is characterized by a cataclastic and a gouges fault zone, overlain by slope facies with syn-kinematic polymictic mega-breccias reworking the adjacent basement. The breccias are grading finer upwards, contain conglomerate and sandstone interbeds interpreted as to slope-environment turbiditic channel deposits. This exhumation and rift-related record is unconformably covered by the post-obduction sequence affected by a late Cenozoic E/W-directed low-amplitude shortening. The intensity of shortening is increasing toward the NW leading to reactivate the Arabian Necking zone as a ramp for the Hawasina thrust system. Based on these observations, we propose a new geodynamic model showing that the final stage of the obduction result from the inversion of the former Arabian necking zone with significant impacts on the evaluation of (1) the shortening rates accommodated and (2) the former architecture of the Arabian Tethyan rifted margin. As the belt never recorded a mature continent-continent collision, we think that the Oman study case could significantly help to investigate the dynamics of hyper-extended rifted margins inversion at an early orogenic stage.

How to cite: Ducoux, M., Masini, E., Scharf, A., and Calassou, S.: The Neotethyan Arabian necking zone exposed at the SE Oman mountains: field evidence and consequences, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11305, https://doi.org/10.5194/egusphere-egu22-11305, 2022.

EGU22-11791 | Presentations | TS7.4

Geomorphology of the Mabahiss Deep area, Northern Red Sea: New insights from high-resolution multibeam bathymetric mapping 

Margherita Fittipaldi, Daniele Trippanera, Nico Augustin, Froukje M. van der Zwan, Alexander Petrovic, Dirk Metz, and Sigurjon Jónsson

The Red Sea is a unique place to study a young oceanic rift basin and the interplay between magma and tectonics at a young divergent plate boundary. The spreading rate of the Red Sea rift changes from ~17 mm/yr in the south to ~7 mm/yr in the north, and so does the morphology. The southern Red Sea is a continuous and well-developed oceanic rift, whereas the so-called deeps characterize the central portion with oceanic crust separated by shallower inter-trough zones, and the northern part contains more widely spaced deeps with extensive areas covered by sediments in between. While the central Red Sea morphology has been extensively studied, the structure of the northern Red Sea and its link to the central Red Sea are less clear. Indeed, the northern Red Sea rift, marked at its southern end by Mabahiss Deep, is offset by about 60 km to the central Red Sea axis by the still poorly understood Zabargad Fracture Zone.

Here we aim to improve the understanding of the volcano-tectonic setting of the Mabahiss Deep area with new high-resolution bathymetric data from multiple multibeam surveys with R/V Thuwal and R/V Pelagia. Our results show that the 15 km long, 9 km wide, and 2250 m deep Mabahiss Deep, and the 800 m high and 5 km wide central volcano, are the most prominent structures of the area. The deep is bordered by a series of Red Sea parallel normal faults on both sides, forming a graben-like structure and thus suggesting a rift-like morphology. The central volcano has a 2 km wide summit caldera containing several volcanic cones. Several normal faults cut its southern flank, and radial fractures are present on its summit. In the multibeam backscatter data, several recent lava flows (<10 kyrs) are visible on the northern and southern flanks of the volcano. Even if the ocean floor outside the deep is mainly covered by salt flows, limiting structural analysis of the surrounding areas, the Mabahiss Deep area and the central Red Sea have similar rift-like structures with stable axial MORB-volcanism, showing typical features found at other (ultra-)slow-spreading ridges, such as magma focusing on the segment centers. This suggests that although the Mabahiss Deep appears to be offset from the central Red Sea rift, the same processes are probably taking place in this area.

Our new high-resolution bathymetric mapping allows a more precise structural and geomorphological analysis of the Mabahiss Deep area that represents a starting point for understanding the overall structure of the poorly studied northern Red Sea.

How to cite: Fittipaldi, M., Trippanera, D., Augustin, N., van der Zwan, F. M., Petrovic, A., Metz, D., and Jónsson, S.: Geomorphology of the Mabahiss Deep area, Northern Red Sea: New insights from high-resolution multibeam bathymetric mapping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11791, https://doi.org/10.5194/egusphere-egu22-11791, 2022.

EGU22-11825 | Presentations | TS7.4

The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the evolution of Triassic magmatism in the Adria Plate 

Matteo Velicogna, Marko Kudurna Prasek, Luca Ziberna, Angelo De Min, Valentina Brombin, Fred Jourdan, Paul R. Renne, and Andrea Marzoli

The magmatic bodies of Jabuka, Brusnik, and Vis Islands of the Adriatic Sea are located in the easternmost part of the Adria Plate (Adriatic Unit according to Slovenec & Šegvić, 2021), close to the External Dinarides (Pamić and Balen, 2005). The magmatic rocks on the islands are, from West to East, intrusive bodies on Jabuka, sub-intrusive on Brusnik, and effusive rocks on Vis.

Feldspar separates from Jabuka and Brusnik Islands yielded mini-plateau 40Ar/39Ar ages of 229.0 ± 5.4 Ma and 221.5 ± 2.5 Ma indicating that this magmatism is Carnian-Norian in age. The whole-rock geochemical compositions (major and trace elements, Sr-Nd isotopes) indicate that the magmatic rocks of the Croatian Islands range from tholeiitic to calc-alkaline, yielding a subduction signature. This signature is also shared by coeval magmas from the Adria Plate and may be related to crustal components subducted during the Hercynian orogeny and recycled within the mantle source(s) of this anorogenic magmatism.

How to cite: Velicogna, M., Prasek, M. K., Ziberna, L., De Min, A., Brombin, V., Jourdan, F., Renne, P. R., and Marzoli, A.: The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the evolution of Triassic magmatism in the Adria Plate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11825, https://doi.org/10.5194/egusphere-egu22-11825, 2022.

Continental collision succeeds long term subduction of oceanic lithosphere into the earth's mantle whereby the negative buoyancy of the downgoing oceanic lithosphere (slab) provides the principal driving force for plate motions. Previous studies have shown that subduction-induced mantle flow could drive overriding plate shortening and orogenesis, and the arrival of the positively buoyant lithosphere at the trench affects the dynamics of the overriding plate and plate motions. The subsequent slab detachment at the subducted continent-ocean margin removes the driving force in the system and eventuates in cessation of subduction (Cloos, 1993)  and plate convergence. The India-Eurasia subduction-collision system has multiple inferred slab break-off episodes (Replumaz et al., 2010), yet convergence is still ongoing. Here, we present 2D-cartesian buoyancy-driven numerical models of continental collision after subduction of a long oceanic plate (~6000 km) in a whole mantle reservoir (2880km), investigating the dynamics of such systems in the presence of detached slabs. These models’ wide aspect ratio (6:1) allows for exploring deep subduction of oceanic slabs and detached slab(s), approximately at the centre of the domain, thereby minimising the effect of free slip sidewalls on obtained slab morphology in the mantle and associated mantle flow. Our results indicate that poloidal mantle flow induced by the sinking of the detached slab sustain long term convergence in collisional settings. Although 2D models lack the 3D components of mantle flow, these models can be used to understand the dynamics of the centre of >4000km wide subductions zones and facilitate interpretation in light of tomographic and plate reconstruction studies.

 

References:

Cloos, M. (1993). Lithospheric buoyancy and collisional orogenesis: Subduction of oceanic plateaus, continental margins, island arcs, spreading ridges, and seamounts. Geological Society of America Bulletin, 105(6), 715-737.

Replumaz, A., Negredo, A. M., Guillot, S., & Villaseñor, A. (2010). Multiple episodes of continental subduction during India/Asia convergence: Insight from seismic tomography and tectonic reconstruction. Tectonophysics, 483(1-2), 125-134.

How to cite: Laik, A., Schellart, W., and Strak, V.: Convergence at continental collision zones: Insights from long-term 2D geodynamic models buoyancy-driven subduction and collision., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12441, https://doi.org/10.5194/egusphere-egu22-12441, 2022.

The Eocene Lower and Middle members of Rus Formation are exposed at the King Fahd University of Petroleum and Minerals (KFUPM) campus and contain 'odd' structural features. Previously, such structures were overlooked or misinterpreted by other researchers. In this study, we interpret these structures as hydroplastic kinematic indicators in the basal part of the Middle Rus Member. Their occurrence is related to the Rus soft-sediment detachment, a major displacement zone at the boundary/interface between the Lower and Middle Rus. The structures are fist-sized vugs coupled with carrot- or comet-trail imprints (VCT structures), previously translated calcite geodes. VCT structures demonstrate NNW (345°) transport/slip and are found on flat to low-dipping surfaces characterized as Y, R, and P shears according to the Rus detachment orientation. The Andersonian transtension stress regime is indicated by palaeostress analysis, but it was not enough to activate the Rus soft-sediment detachment. The negative effective principal stress σ3' and the exceptionally low frictional coefficient generated by fluid pressure resulted in detachment activity. Because it reveals the Arabian platform's instability in the larger area of the Dammam Dome during the Late Eocene, the soft-sediment Rus detachment can be considered a 'sensitive stress sensor' for the Zagros collision. The beginning of the Zagros collision, which was previously thought to occur during the Oligocene based on the well-known pre-Neogene unconformity, is credited with this instability.

How to cite: Osman, M. and Tranos, M.: New hydroplastic structures of the Eocene Rus Soft-sediment Detachment (Eastern Saudi Arabia) and their contribution to the dating of the Zagros Collision, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13058, https://doi.org/10.5194/egusphere-egu22-13058, 2022.

EGU22-13597 | Presentations | TS7.4

Mineralogy, structure and tectonic significance of quartz veins from the northern Saih Hatat Dome (eastern Oman Mountains) 

Andreas Scharf, Frank Mattern, Bernhard Pracejus, Ivan Callegari, Robert Bolhar, Sobhi Nasir, Saja Al-Wahaibi, Laila Al-Battashi, Marwa Al-Hadhrami, Thuraiya Al-Harthi, and Safiya Al-Suqri

The rocks of the Saih Hatat Dome (SHD) formed during and after two major geological events shaping Arabia: 1) Subduction of continental rocks in the course of the Late Cretaceous Semail Ophiolite obduction onto the Arabian Plate and 2) Exhumation of >16 km and high deformation/folding in the northeastern part of the SHD. The latter resulted in a ~20 km wide recumbent fold (Saih Hatat Fold Nappe). The sub-horizontal fold axis of this fold trends NNE in the northern SHD. The core of the SHD and the recumbent fold consist of dark Neoproterozoic meta-shales and meta-sandstones, while its margin (and upper/lower limbs of the recumbent fold) consist of Permian cliff-forming carbonates.

Within the northern SHD, numerous milky quartz veins occur. We structurally and mineralogical analyzed >500 of these veins, covering an area of ~200 km2. The veins vary in width from one centimeter to a few meters, while the length ranges between several decimeters to several decameters. Associated with the predominant milky quartz, are calcite, siderite, chlorite, albite, anorthite, actinolite, rutile, hematite, goethite, and pyrrhotite. Rare molybdenite aggregates seem to replace carbonate, in which it occurs exclusively. Quartz microstructures include bulging (BLG) recrystallization, sub-grain rotation (SGR) recrystallization, and undulose extinction. Sub-grains and triple junctions in quartz are common. The mineralogy and quartz microstructures indicate maximum peak temperature conditions of ~400-500°C.

At least two sets of veins can be distinguished. Both vein sets occur mostly in clusters and partly form vein swarms. The mineralogy and quartz microstructure of both vein sets is similar. The older set 1 has been folded by the Saih Hatat Fold Nappe. Thus, vein formation predates 76-70 Ma. Furthermore, veins of set 1 are often sub-parallelly oriented to the main foliation of the host rocks, and they may be boudinaged. They may form complicated vein structures. We assume that this vein set initially formed during the Permian Pangean/Tethys rifting. The second vein set is abundant, sub-vertically and strikes consistently E/W to ESE/WNW. These veins cut the overall moderately NW-dipping bedding surfaces of the ambient rocks. Set 2 veins either formed during exhumation of the dome (Late Cretaceous to early Eocene and late Eocene to Oligocene) or they are part of the NW-striking sinistral Hajar Shear Zone, which affected the entire eastern Oman Mountains during the Oligocene to early Miocene. Ongoing U-Pb dating of carbonates and further field survey will further contribute to the understanding of their age and tectonic setting.

How to cite: Scharf, A., Mattern, F., Pracejus, B., Callegari, I., Bolhar, R., Nasir, S., Al-Wahaibi, S., Al-Battashi, L., Al-Hadhrami, M., Al-Harthi, T., and Al-Suqri, S.: Mineralogy, structure and tectonic significance of quartz veins from the northern Saih Hatat Dome (eastern Oman Mountains), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13597, https://doi.org/10.5194/egusphere-egu22-13597, 2022.

EGU22-164 | Presentations | TS4.1

Speleothem deformation due to the 2017 Mw 6.6 Bodrum–Kos earthquake in a cave on Pserimos (Dodecanese, Greece) 

Bernhard Grasemann, Lukas Plan, Ivo Baron, and Denis Scholz

Although damaged speleothems have been widely investigated to study paleo-earthquake records in caves, only few reports could directly link damages to specific recent earthquakes. We mapped before the 2017 Mw 6.6 Bodrum–Kos earthquake the so-far unexplored Korakia Cave on Pserimos island in the Dodecanese (Greece), which is located at the transition between the Aegean and Anatolian region and is known for its strong seismicity. The cave formed along an active normal fault and records numerous broken columns and flowstones sealed by younger speleothems. New 230Th/U-ages show that paleoseismic events occurred since the formation of the cave, which is older than the limit of the dating method. During a cave visit 2 months after the 2017 Mw 6.6 Bodrum–Kos earthquake we noted that c. 10 cm small stalactites, which were actively growing along fractures in the cave ceiling, have been chipped off by movements along the fractures and were lying on flowstones covered by greenish biofilms. Removal of the broken fragments demonstrated that the chlorophyll pigment below the position of the fragments did not show a colour difference to the surrounding area, which is exposed to the daylight of the cave entrance. The preservation of the photoautotrophic biofilm, which can survive only a few months without daylight, suggests that the stalactites have been broken by the 2017 Mw 6.6 Bodrum–Kos earthquake, which also caused the collapse of several buildings on the island of Kos only 4 km S of Pserimos. We conclude that earthquake capable of causing small shear displacements on fractures can damage speleothems. However, other delicate speleothems including long and slim stalactites remained undamaged.

How to cite: Grasemann, B., Plan, L., Baron, I., and Scholz, D.: Speleothem deformation due to the 2017 Mw 6.6 Bodrum–Kos earthquake in a cave on Pserimos (Dodecanese, Greece), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-164, https://doi.org/10.5194/egusphere-egu22-164, 2022.

Continental transform faults are generally known to have widely distributed structures and sparse seismicity, in opposite to their oceanic counterparts. The North Anatolian Shear Zone (NASZ) is an ideal example, where the total deformation is shared between multiple structures especially during its evolutionary stages. The North Anatolian Fault (NAF), the most prominent member of the NASZ, started to form of about 11 Ma in the east and propagated to the west, reaching to the Marmara Sea only a few hundred thousand years ago. This principal displacement zone generally extends as a single strand from its easternmost tip to the west until Bolu for about 900 km. To the west of Bolu, it bifurcates into two branches, Düzce and Mudurnu Valley segments, delimiting the Almacık Flake (AF) respectively to the north and south. Although there is a considerable number of multi-disciplinary studies on the kinematics and history of active faulting within and around the AF, we still have gaps in our knowledge on (a) the ratio of strain distribution, (b) time of formation of bounding fault segments and (c) their evolutionary stages.

In order to fulfil some parts of this gap, we studied the major morphometric indices, including hypsometric curve and integral (HI), asymmetry factor (Af), channel concavity (θ), chi (χ) and knickpoint analyses on drainage basins across the whole AF and all surrounding fault segments. Our goal is not only to document the comparative tectonic effect of the bounding fault segments on the topography, but also to test any potential cumulative morphological response to pre- and post-peak structures, especially along the Düzce Segment. Almost all of 83 extracted drainage basins yield high HI values, usually ranging between 0.4 and 0.72, and suggest a rejuvenating morphology compatible with the general ‘uplift hypothesis’ for the AF. In more details, θ and χ values point out the strong and confined effect of the active bounding faults. Moreover, knickpoints do not show evidence for any pre-peak structures rather than recent active faulting. This may be result of limited size, thus ages, of drainage basins, which are cut by bounding faults at both sides of the AF. Alternatively, these fault segments may be older than previous assumptions, whereas the effect of pre- and post-peak shear structures on topography has already been erased mainly by external processes. On the other hand, χ values, based on 0.45 reference θ, suggest a high incision along the western sections of the Mudurnu Valley Segment, which may indicate a strain transfer from north to south. Nevertheless, the breach of a landslide dam of about 5750 years ago and the strong incision of the Mudurnu River following this event to the south of the AF, as suggested by previous studies, can be another reason for this anomaly. Briefly, our preliminary results suggest a strong tectonic control on the AF’s topography mainly due to the activity of the bounding structures. We do not see any morphometric evidence for the secondary (pre- and post-peak) faults in the near past of the NASZ around the AF.

How to cite: Kiray, H. N., Sançar, T., and Zabcı, C.: Spatial strain distribution along continental transform faults: insights from morphometric analyses of the Düzce and Mudurnu Valley segments (North Anatolian Fault, NW Turkey), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-459, https://doi.org/10.5194/egusphere-egu22-459, 2022.

EGU22-1477 | Presentations | TS4.1

Incipient lithospheric collision throughout the East Mediterranean 

David Fernández-Blanco and César R. Ranero


We propose that lithospheric collision of Africa and Eurasia is incipient throughout the entire East Mediterranean. Our evidence confirms the incipient continent-continent collision that has been recently proposed for the Cyprus Arc and showcases how collision is expressed at depth and across the Hellenic Arc. We provide evidence of basin-wide lithospheric-scale collision by coupling, at tectonic scale (1.5M km2), quantitative joint analysis of submarine and terrestrial relief, and the interpretation of a compilation of regional vintage multichannel seismic data (>46.000 km), reprocessed with modern techniques. No megathrust surface marking a subduction interplate contact is imaged in any seismic line, and the relief across sedimentary piles is not shaped as mechanically-accreted wedges. Instead, continent-continent collision is expressed across plates in two modes along longitude. In the offshore regions south of Cyprus and Crete, submarine thrust systems with no frontal structure nor imbrication, and lacking latitudinal continuation, record collision stacking basin sediments vertically. Onshore, concurrent uplift and extension are recorded by uplifting strandlines, hanging valleys, and normal faulting, in both continents, and neatly so in the African margin in front of Crete. Joint plate deformation at lithospheric scale is further inferred as wavelengths of relief coherent across both plates. Regions located latitudinally to these collisional sites extrude away obliquely, either rigidly along transpressional systems, as immediately east of Cyprus and Crete, or through flow and halokinesis of Messinian salts, as on the eastern and western sectors of the Mediterranean Ridge. Our evidence typifies incipient lithospheric collision as expressed throughout the East Mediterranean.

How to cite: Fernández-Blanco, D. and R. Ranero, C.: Incipient lithospheric collision throughout the East Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1477, https://doi.org/10.5194/egusphere-egu22-1477, 2022.

EGU22-1692 | Presentations | TS4.1

Slow-slip events destabilize upper-plate and trigger large-magnitude earthquake at the western-end of the Hellenic Subduction System 

Vasiliki Mouslopoulou, Vasso Saltogianni, Gian Maria Bocchini, Simone Cesca, Jonathan Bedford, Armin Dielforder, Onno Oncken, Michael Gianniou, and Gesa Petersen

Slow slip events (SSEs) in subduction zones can precede large-magnitude earthquakes and may therefore serve as precursor indicators, but the triggering of earthquakes by slow slip remains poorly understood. Here we report on a multidisciplinary dataset that captures a synergy of slow slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 Mw 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). We find that this long-lasting preparatory phase was initiated by a slow-slip event that released, over a period of 4-months, aseismic slip equivalent to a ~Mw 6.4 earthquake on the Hellenic plate-interface. This SSE, which is the first to be reported in the HSS, was associated with mild Coulomb failure stress changes (≤3 kPa) that were nevertheless sufficient to destabilize faults in the overriding plate. Tectonic instability was evidenced by a prolonged (~4 years) period of suppressed b-values (<1), an associated increase in upper-plate seismicity rates on discrete thrust, normal and strike-slip faults, including an earthquake swarm in the epicentral area of the Mw 6.9 earthquake, and another episode of slow-slip immediately preceding the Zakynthos mainshock. We show that this second SSE in 2018 caused stress changes up to 25 kPa in the epicentral area immediately prior to the mainshock, affecting a highly overpressured and mechanically weak forearc, whose state of stress fluctuated between horizontal deviatoric compression and tension during the years preceding the Zakynthos Earthquake. We conclude that this configuration facilitated episodes of aseismic and seismic deformation that ultimately triggered the Zakynthos Earthquake and may characterise other subduction zones globally.

How to cite: Mouslopoulou, V., Saltogianni, V., Bocchini, G. M., Cesca, S., Bedford, J., Dielforder, A., Oncken, O., Gianniou, M., and Petersen, G.: Slow-slip events destabilize upper-plate and trigger large-magnitude earthquake at the western-end of the Hellenic Subduction System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1692, https://doi.org/10.5194/egusphere-egu22-1692, 2022.

EGU22-1972 | Presentations | TS4.1

​Studying the active tectonic in the northern flank of the Bozqush Mountains, NW Iran 

Ali Nasiri and Mahtab Aflaki

The NW-striking North Tabriz Fault is one of the most important basement faults in the northwest of the Iranian ‎plateau. This fault defines the boundary between the two tectonic ‎blocks with different stress regimes in its northern and southern parts as characterized with NW-SE and NE-SW direction of maximum horizontal compression, respectively. In the southern ‎termination of the North Tabriz fault, part of deformation is concentrated along its EW-striking splay faults extending along northern and southern boundaries of the Bozqush Mountains. The occurrence of medium-magnitude earthquakes, as ‎well as morphotectonic evidence reveal that modern deformation is dominantly concentrated along ~EW-striking dextral/reverse dextral and NNE-striking sinistral faults in the southern flank of the Bozqush Mountains. It is still not known to what extent the deformation is also accomodated in the northern flank of the Bozqush Mountain. The approach of this research is to ‎answer the question by studying the state of stress along the northern border of the Bozqush Mountains by applying the inversion method on the fault slip data measured during the field studies, studying their related ‎morphotectonic evidence, and comparing the results with ‎the state of stress and the morphotectonic evidence reported throughout the southern flank of the Bozqush Mountains. Fault kinematic data were collected at 35 sites ‎along the northern boundary of the Bozqush Mountains. Evidence of the modern NW-SE stress regime is found at five sites measured within the Quaternary detrital deposits in the western part of the study area. At the other ‎sites, evidence of the older stress regime, with NE-SW direction of maximum horizontal ‎compression is obtained. Also, the systematic deflection of the stream channels, especially in the eastern part of the region, ‎indicates the sinistral displacement along the EW-striking faults, consistent with the old ‎stress regime in the region. Evidence of dextral deflection was observed along few EW-striking faults cutting the Quaternary deposits only in the western parts of the region. Therefore, ‎by comparing these kinematic data and morphotectonic evidences with those reported from the southern flank of the Bozqush Mountains, it can be concluded that the modern deformation is dominantly absorbed along the splay faults in the southern flank of the Bozqush.‎

 

​Key Words: North Tabriz fault, Modern stress state, NW Iran, Northern flank of Bozqush Mountains, Stress inversion

How to cite: Nasiri, A. and Aflaki, M.: ​Studying the active tectonic in the northern flank of the Bozqush Mountains, NW Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1972, https://doi.org/10.5194/egusphere-egu22-1972, 2022.

EGU22-2092 | Presentations | TS4.1

Rapid large-amplitude vertical motions generated by 3D subduction slab roll-back in the Valencia Trough, Western Mediterranean 

Penggao Fang, Julie Tugend, Geoffroy Mohn, Nick Kusznir, and WeiWei Ding

        The Cenozoic geodynamic evolution of the Western Mediterranean is complex comprising subduction, slab roll-back, back-arc extension, collision, and lithosphere delamination. We investigate the subsidence of a regionally observed unconformity in the Valencia Trough of the Western Mediterranean, here referred to as the Miocene Unconformity, which separates Mesozoic from latest Palaeogene to Neogene sediments. The mechanisms controlling its subsidence are poorly understood.

        We show, using a dense grid of seismic reflection data, well data and 3D flexural backstripping, that the Miocene Unconformity in the SW Valencia Trough subsided by more than 1.5 km to the present day at an average rate of 90 m/Myr. The absence of Cenozoic extensional faults affecting the basement shown by seismic data indicates that this rapid subsidence is not caused by Cenozoic rifting or remaining Mesozoic post-rift thermal subsidence. Neither can this subsidence be explained by subduction dynamic subsidence or flexural loading related to the thin-skin Betic fold and thrust belt which only affects subsidence observed near the deformation front.

        We interpret the 1.5 km subsidence of the Miocene Unconformity as the collapse of a back-arc transient uplift event. Erosion during this uplift, resulting in the formation of the Miocene Unconformity, is estimated to exceed 4 km. Transient uplift was likely caused by heating of back-arc lithosphere and asthenosphere, combined with mantle dynamic uplift, both caused by segmentation of Tethyan subduction resulting in slab tear. Subsidence resulted from thermal equilibration and the removal of mantle flow dynamic support Tethyan subduction slab roll-back. We propose that our observations and interpretation of rapid back-arc km-scale uplift and collapse have global applicability for other back-arc regions experiencing subduction segmentation and slab tear during subduction slab roll-back.

How to cite: Fang, P., Tugend, J., Mohn, G., Kusznir, N., and Ding, W.: Rapid large-amplitude vertical motions generated by 3D subduction slab roll-back in the Valencia Trough, Western Mediterranean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2092, https://doi.org/10.5194/egusphere-egu22-2092, 2022.

EGU22-2986 | Presentations | TS4.1

This Rift is on Fire: Volcano-Tectonic Evolution of the Christiana-Santorini-Kolumbo volcanic field, Aegean Sea 

Jonas Preine, Christian Hübscher, Jens Karstens, Emilie Hooft, and Paraskevi Nomikou

Many of the most hazardous volcanoes lie in rift systems, where tectonics often seems to exert control on magma emplacement. However, our current knowledge of the interplay between volcanism and tectonics is immature due to the lack of observations on geological time scales. Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo (CSK) volcanic field lies in a prominent continental rift zone caused by back-arc extension along the Hellenic Arc. Covered by numerous geophysical surveys, this area offers the unique possibility to reconstruct a volcanic rift in time and space. Previous studies have revealed that the CSK volcanic field developed during four distinct volcanic phases, which initiated in the Pliocene and only recently matured to form the vast Santorini edifice. Here, we combine P-wave velocity tomography models and high-resolution reflection seismic data to reveal the internal architecture and the spatio-temporal evolution of the rift basins as well as their relation to the evolution of the CSK volcanoes. Our joint analysis reveals a distinct NE-SW-directed horst-structure separating the volcanic rift into a volcanically active northwestern zone and a volcanically inactive southeastern zone. Using a refined seismo-stratigraphic framework of the internal architecture of the rift basins, we identify four distinct phases of the rift system that correspond to the volcanic phases of the CSK field. These phases reflect the gradual development of a Pliocene-Pleistocene NE-SW oriented fault system overprinting an older Miocene-Pliocene ESE-WNW oriented fault system. The latest volcanic phase, during which volcanism focussed on Santorini and became highly explosive, corresponds to a distinct shift in the tectonic behavior of the rift system after which enhanced subsidence at the Santorini-Anafi and Amorgos faults occurred that was rapidly filled up by thick volcano-sedimentary deposits. We conclude that the volcanism of the CSK field is fundamentally controlled by NE-SW-directed rifting, which lies parallel to the Pliny and Strabo trends of the southeastern Hellenic Arc. This volcanic system is bounded to the southeast by the Akrotiri-Anhydros horst, which seems to be a deep-rooted structural boundary for the volcanic plumbing system. The shift from ESE-WNW directed faulting to NE-SW directed faulting is an indication that the dominant direction of slab-rollback driving the extension of the CSK rift shifted from the southwestern to the southeastern Hellenic Arc with Santorini lying at the hinge of these trends.

How to cite: Preine, J., Hübscher, C., Karstens, J., Hooft, E., and Nomikou, P.: This Rift is on Fire: Volcano-Tectonic Evolution of the Christiana-Santorini-Kolumbo volcanic field, Aegean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2986, https://doi.org/10.5194/egusphere-egu22-2986, 2022.

Crustal deformation and seismic activity in the Levant is mainly related to the interplate Dead Sea Fault (DSF) and the intraplate Carmel-Gilboa Fault System (CGFS). In this study we analyze the interseismic deformation along these fault systems using 23 years of GPS measurements obtained from 209 campaign and 60 continuous stations. This GPS dataset is the longest record and the densest dataset for the DSF and the Levant region. We use this dataset to investigate the spatial variations of slip and creep rates along the southern and central sections of the DSF and the CGFS. Our inversion model results indicate that part of the tectonic motion is transferred from the DSF to the CGFS. We find that the left-lateral strike-slip motion along the DSF decreases in a rate of 0.9±0.4 mm/yr, from 4.8±0.3 mm/yr south to the intersection with the CGFS, to 3.9±0.4 mm/yr north to this intersection. Along the CGFS the left-lateral strike-slip motion ranges between ~0.3-0.5 mm/yr and the extension rate between ~0.6-0.7 mm/yr, indicating a total slip rate vector of 0.8±0.4 mm/yr in the DSF direction, in agreement with the reduction of slip rate along the DSF near the intersection with the CGFS. Shallow creep is found along the southern and central sections of the Dead Sea basin and the northern Jordan Valley section of the DSF, with creep rates of 3.4±0.4 and 2.3±0.4 mm/yr, respectively. These creeping sections were identified as areas with thick salt layers at the shallow subsurface. We suggest that shallow creep behavior along the DSF is govern by the presence and mechanical properties of the salt layers, which probably allows plastic deformation and the transition to velocity strengthening at the shallow subsurface and promotes creep.

How to cite: Hamiel, Y. and Piatibratova, O.: Spatial variations of slip and creep rates along the Dead Sea Fault and the Carmel-Gilboa Fault System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3591, https://doi.org/10.5194/egusphere-egu22-3591, 2022.

EGU22-3939 | Presentations | TS4.1

Timing of rock-uplift and of the North Anatolian Fault development in the Central Pontides 

Simone Racano, Taylor Schildgen, and Paolo Ballato

The Central Pontide orogenic belt marks the northern margin of the Central Anatolian Plateau and is the result of several geodynamic processes, including the subduction of the Neo-Tethys crust, the opening of the Black Sea, the continental collision between the southern Eurasian margin and the Anatolide-Tauride block, and the development of the North Anatolian Fault (NAF). Transpressional deformation and crustal thickening along the North Anatolian fault zone are thought to have generated rock-uplift rates of 0.2 – 0.3 km/Myr since ca. 400 ka within the Central Pontides based on Quaternary marine and river terraces. Moreover, data from low-temperature thermochronology suggest that an enhanced exhumation phase in the Central Pontides occurred within the last 11 Mya. However, the precise onset of this faster uplift phase, which likely reflects the timing of the development of the NAF in the Central Pontides, is poorly constrained.

In this work we define the spatiotemporal pattern of rock-uplift rates within the Central Pontides over the last ca. 10 Myr by performing linear inversions of river profiles that drain the northern, external margin of the Central Pontides. We analyze 19 different catchments that drain from the Sinop Range to the Black Sea, first applying a non-dimensional inversion on the chi-plots of the selected stream channels. We then use 21 new basin-averaged denudation rates derived from 10Be concentrations in river sands to calibrate an erodibility parameter, which we use in turn to scale our chi-transformed river profiles. Our results document an increase in rock-uplift rates after 8 Ma, with peak uplift rates of around 0.15 – 0.25 km/Myr occurring between 4 and 2 Ma. Moreover, the spatiotemporal pattern of uplift suggests that faster rock uplift started first in the eastern part of the Sinop Range and migrated westward over a period of ca. 2 to 2.5 Myr. Overall, these results provide important new constraints on the timing of topographic development in the Central Pontides and the westward migration of the NAF from eastern Turkey.

How to cite: Racano, S., Schildgen, T., and Ballato, P.: Timing of rock-uplift and of the North Anatolian Fault development in the Central Pontides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3939, https://doi.org/10.5194/egusphere-egu22-3939, 2022.

The origin and tectonic evolution of the Western Mediterranean region, specifically the Gibraltar Arc system, is the result of a complex geodynamic evolution involving the convergence of the Eurasia and Africa plates and the dynamic impact of the Gibraltar slab observed in tomographic studies. Although geologic and geophysical data collected in the last few years have greatly increased our knowledge of the Gibraltar Arc region, it is still unclear the mechanical links between the Gibraltar slab and the past deformation of the overriding Alboran lithosphere as well as present-day motion shown in detailed GPS observations. In this work, we use the code ASPECT to model the geodynamic evolution of the Alboran slab in 2D over the last 20 million years. The initial model setup simulates a vertical WE section at a latitude of about 36oN and represents the situation at 20 Ma, when the trench had already fully rotated to the southwest and the predominantly westward rollback of the Gibraltar slab started taking place. We conduct a parametric study varying the rheological parameters and the initial slab properties (dip angle and length) to properly fit the robust current slab features, particularly, its position and its curved morphology extending eastward. We show how after 20 Myr of model evolution, i.e. at present time, the slab pull appears to have a still significant influence on surface velocities. We find a westward surface motion in the Gibraltar arc caused by the negative buoyancy of the slab. These velocities increase westwards from 1 to 4 mm/yr consistently with geodetic observations. Our models roughly reproduce the Alboran basin evolution, initially developing the West Alboran Basin and then the East Alboran Basin. Finally, preliminary 3D models further support these results and properly the main trends of the coupled dynamics of the Gibraltar slab and Alboran basin evolution during the last 20 Myr.

How to cite: Gea, P. J., Negredo, A., and Mancilla, F. D. L.: The Gibraltar slab dynamics and its influence on past and present-day Alboran domain deformation: Insights from thermo-mechanical numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4234, https://doi.org/10.5194/egusphere-egu22-4234, 2022.

EGU22-5227 | Presentations | TS4.1

Present strain partitioning in SE Spain. Insights from CGNSS data 

Ivan Martin-Rojas, Alberto Sánchez-Alzola, Ivan Medina-Cascales, María Jesús Borque, Pedro Alfaro, and Antonio Gil

SE Iberia Tectonics is presently dominated by the NNW-SSE convergence between the Eurasian and Nubian plates. Farther east, the eastern Spanish coast and the Valencia Trough are dominated by ENE-WSW extension related to thermal subsidence. This extension has been interpreted as the final stage of abort rift responsible for the ENE motion of the Balearic promontory. Our data from 11 CGNSS stations permit us to discuss the deformation partitioning in SE Iberia related to the two abovementioned processes.

We identify three kinematic domains: a relatively stable domain, a domain moving towards NNW and undergoing NNW-SSE shortening, and a third domain relatively moving towards ENE and experiencing ENE-WSW extension. Our results indicate that plate convergence-related NNW-SSE shortening is mainly absorbed by the Eastern Betic Shear Zone (EBSZ), in agreement with previous studies, but also show that a significant fraction of this shortening is accommodated south of the EBSZ.

We also identify and quantify for the first time ENE-WSW extension northeast of the EBSZ. We propose that this extension could be absorbed by basement normal faults whose surface expression is obscured due to decoupling of deformation between the basement and the cover. Our results shed light on the tectonic puzzle of SE Spain.

How to cite: Martin-Rojas, I., Sánchez-Alzola, A., Medina-Cascales, I., Borque, M. J., Alfaro, P., and Gil, A.: Present strain partitioning in SE Spain. Insights from CGNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5227, https://doi.org/10.5194/egusphere-egu22-5227, 2022.

EGU22-5335 | Presentations | TS4.1

Delayed lithosphere tearing along STEP Faults 

Taco Broerse, Rob Govers, and Ernst Willingshofer

Tearing of the lithosphere at the lateral end of a subduction zone is a consequence of ongoing subduction. The location of active lithospheric tearing is known as a Subduction-Transform-Edge-Propagator (STEP). The transcurrent plate boundary system lengthens with time and is referred to as the STEP Fault. Lithospheric tearing was taken to start at the trench in the classical STEP model of Govers and Wortel (2005). They show that active STEPs and STEP Faults can be found alongside many subduction zones. However, recent seismicity studies show results near the active STEPs that are difficult to reconcile with the classical STEP model: there is significant and deep seismicity along the STEP Fault near to the west of Trinidad in the southeast Caribbean; a Wadati-Benioff zone perpendicular to the Pliny-Strabo trenches (the STEP Fault) in the eastern Mediterranean reaches 180 km depth; STEP Fault perpendicular earthquake slip vectors are observed along the northern termination of the South Sandwich trench. We seek to understand these discrepancies by studying the tearing process.  

We show results of new physical analog lab models that aim to elucidate what controls lithospheric tearing and the resulting geometry of the lithospheric STEP. We study the ductile tearing in the process of STEP evolution, which is dynamically driven by the buoyancy of the subducting slab. In our experiments, the lithosphere as well as asthenosphere are viscoelastic media in a free subduction setup. A stress-dependent rheology plays a major role in localization of strain in tearing processes of lithosphere such as slab break-off. 

We find that complete tearing of the lithosphere typically occurs later than in the classical model, at 100-150 km depth. The slab is consequently highly curved near the lateral end of the trench. However, not all STEPs show evidence for such delay, e.g., the north end of the Tonga trench. In our model experiments we therefore investigate the influence of age and integrated strength of the lithosphere and its contrasts across the passive margin, on the timing, depth, and the degree of localization of the tearing process. Furthermore, we relate the tearing at depth to deformation at the surface along and across the STEP fault and we discuss potential consequences for STEP evolution for a number of subduction zones worldwide. Delayed lithospheric tearing explains the observations qualitatively. 

How to cite: Broerse, T., Govers, R., and Willingshofer, E.: Delayed lithosphere tearing along STEP Faults, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5335, https://doi.org/10.5194/egusphere-egu22-5335, 2022.

EGU22-5475 | Presentations | TS4.1

Insights into the 3D lithospheric structure below the Sea of Marmara region from seismic tomography and forward gravity modeling 

Naiara Fernandez, Magdalena Scheck-Wenderoth, Judith Bott, Mauro Cacace, and Ershad Gholamrezaie

The North Anatolian Fault Zone (NAFZ) extends for about 1500 km in the Eastern Mediterranean region, from eastern Anatolia to the northern Aegean. The NAFZ is characterized by strong and frequent seismic activity, increasing the seismic hazard in the region. In the Sea of Marmara area (NW Turkey), the North Anatolian Fault splits into three main branches. The northern branch of the fault, the Main Marmara Fault (MMF), has produced several major earthquakes (M7+) in the past, with a recurrence time of about 250 years. At present, there is a 150 km seismic gap along the MMF which has not ruptured since 1766. The observed fault segmentation, with creeping and locked segments, is indicative of along-strike variability in the fault strength along the seismic gap.

Previous modeling studies in the Sea of Marmara have revealed how crustal heterogeneities effectively affect the thermal and mechanical states of the lithosphere and can likely explain the observed fault segmentation in the area. Therefore, constraining the 3D structure of the deeper crust and upper mantle below the Sea of Marmara is crucial to better assess the mechanical stability of the fault and the possible seismic hazards in the area. In this study, we make use of seismic tomography models and forward gravity modelling to gain insights into the 3D lithospheric structure below the Sea of Marmara. Two tomographic models are used to compute a 3D density model of the area relying on two distinct approaches for the crust and the lithospheric mantle. The results showcase a heterogeneous and rather complex crustal density distribution in the study area[m1] . The 3D density distributions are used in a second step to forward model the gravity response. The results from this new tomography-constrained 3D gravity modelling are then compared to published gravity data and iteratively corrected to fit the overall gravity signals. The final 3D lithospheric-scale density model of the study area will be the basis for thermo-mechanical modeling experiments aimed at improving our current understanding of the present-day geomechanical state of the Sea of Marmara and the MMF and its implications for the seismic hazard of the region.

How to cite: Fernandez, N., Scheck-Wenderoth, M., Bott, J., Cacace, M., and Gholamrezaie, E.: Insights into the 3D lithospheric structure below the Sea of Marmara region from seismic tomography and forward gravity modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5475, https://doi.org/10.5194/egusphere-egu22-5475, 2022.

EGU22-5479 | Presentations | TS4.1

Kinematic and tectonic analysis of the Baza and Galera Fault (S Spain). Insights from GNSS data 

Frank García-Tortosa, Pedro Alfaro, Alberto Sánchez-Alzola, Ivan Martin-Rojas, Jesus Galindo-Zaldívar, Manuel Avilés, Angel Carlos López Garrido, Carlos Sanz de Galdeano, Patricia Ruano, Francisco Jose Martínez-Moreno, Antonio Pedrera, Maria Clara de Lacy, Maria Jesus Borque, Ivan Medina-Cascales, and Antonio Jose Gil

We here discuss the results of a local GNSS episodic network from the Baza sub-Basin (S Spain). This network including six sites, was established in 2008 and has been measured seven times since then. Our data permit us to present the first short-term slip rates for the two active faults in this area. The main active structure is the normal Baza Fault. We estimate slip rates for this fault ranging between 0.3±0.3 mm/yr and 1.3±0.4 mm/yr. For the strike-slip Galera Fault, we quantify the slip rate as 0.5±0.3 mm/yr. These values are higher than previously reported long-term slip rates. We postulate that the discrepancy for the Baza Fault between short-term and long-term slip rates could indicate that the fault is presently in a period with a displacement rate higher than the mean of the magnitude 6 seismic cycle. Moreover, the velocity vectors that we obtained also show the regional tectonic significance of the Baza Fault, as this structure accommodates one-third of the regional extension of the Central Betic Cordillera.

Our results also show that the Baza and Galera Faults are kinematically coherent and they divide the Baza sub-Basin into two tectonic blocks. This points to a likely physical link between the Baza and Galera Faults; hence, a potential complex rupture involving both faults should be considered in future seismic hazard assessment studies.

How to cite: García-Tortosa, F., Alfaro, P., Sánchez-Alzola, A., Martin-Rojas, I., Galindo-Zaldívar, J., Avilés, M., López Garrido, A. C., Sanz de Galdeano, C., Ruano, P., Martínez-Moreno, F. J., Pedrera, A., de Lacy, M. C., Borque, M. J., Medina-Cascales, I., and Gil, A. J.: Kinematic and tectonic analysis of the Baza and Galera Fault (S Spain). Insights from GNSS data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5479, https://doi.org/10.5194/egusphere-egu22-5479, 2022.

EGU22-5691 | Presentations | TS4.1

Reconstruction of tectonically driven Quaternary fluvial dynamics of the Western Kura Fold-Thrust Belt (Eastern Caucasus, Georgia) 

Lasha Sukhishvili, Giorgi Boichenko, Giorgi Merebashvili, Zurab Javakhishvili, Adam Forte, and Tea Godoladze

Since the Plio-Pleistocene, southward migration of shortening in the Eastern part of the Greater Caucasus (GC) into the Kura foreland basin has formed the Kura fold–thrust belt (KFTB) and Alazani piggyback basin between the GC and KFTB, modifying the drainage network within the southern foreland. The northern, eastern and south-eastern flanks of the Western KFTB (Gombori range) expose the predominantly alluvial Alazani series, while the central (highest) part of the range is covered by Tsivi suite. The base of the Alazani series is estimated to be 2.7-2.5 Ma and deposition spanned the Akchagyl and Apsheronian regional stages. The KFTB likely initiated during the Akchagyl-Apsheronian period, and thus the paleocurrents of the alluvial Alazani series sediments represent potential archives for tracking resulting drainage reorganization within the foreland. Previous measurements of paleocurrents from the Alazani series revealed a reversal from south to north flow directions, but the measurements were limited to the northern flank of the Gombori range. Here we present new observations from the central and southern flanks of the Gombori. Results from the eastern and southeastern regions are consistent with the currents from the northern flank, but paleocurrents from the Tsivi suite are more complex and raises additional questions regarding its depositional context and age. The new results help to build a more complete picture of fluvial dynamics driven by Quaternary tectonic deformations within the GC foreland.

How to cite: Sukhishvili, L., Boichenko, G., Merebashvili, G., Javakhishvili, Z., Forte, A., and Godoladze, T.: Reconstruction of tectonically driven Quaternary fluvial dynamics of the Western Kura Fold-Thrust Belt (Eastern Caucasus, Georgia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5691, https://doi.org/10.5194/egusphere-egu22-5691, 2022.

EGU22-6407 | Presentations | TS4.1

Morphological and paleoseismic evidence of surface faulting in the coastal Zagros, southwestern Iran 

Aram Fathian, Hamid Nazari, Mohammad Ali Shokri, Morteza Talebian, Manouchehr Ghorashi, and Klaus Reicherter

The Zagros Mountains accommodate intense seismicity due to the ongoing deformation; however, surface faulting has been rarely observed and/or documented. The earthquakes of Furg (November 6th, 1990) and Qir-Karzin (April 10th, 1972) are unique events in the Zagros associated with a surface rupture. We use tectonic geomorphology and paleoseismology to document a previously unknown outcropped fault within the Zagros. This ~ 20 km fault zone lies between the Khormuj and Khaki anticlines, where the Simply Folded Belt (SFB) of the Zagros is physiographically known as the coastal Zagros as well. The Khormuj anticline, located in the northeast of the city of Khormuj, was previously linked to the Main Front Fault (MFF) on the southern limb of the anticline. Further to the south, the oblique-slip Khormuj fault zone with a strike of N120°–N125° cut the Quaternary sediments and displaced the streams and ridges laterally and vertically. Opposite to the dip of the MFF, the Khormuj fault dip is inclined to the southwest—approximately 75°—where the southern block is uplifted and marks an obvious trace on the ground. We carried out a kinematic GPS survey along the deflected ridges to measure the horizontal and vertical components. Our observations indicate significant dextral strike-slip displacements compared to the dip-slip offset. We observed a sequence of fluvial risers in three different levels along the Khormuj fault. We additionally studied a paleoseismological trench perpendicular to the Khormuj fault scarp evidencing at least two paleoearthquakes. The OSL age of the bottom of the colluvium wedge correlated with the older event indicates the latest event is younger than 25±8 ka considering the fault cuts these deposits up to the ground surface.

How to cite: Fathian, A., Nazari, H., Shokri, M. A., Talebian, M., Ghorashi, M., and Reicherter, K.: Morphological and paleoseismic evidence of surface faulting in the coastal Zagros, southwestern Iran, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6407, https://doi.org/10.5194/egusphere-egu22-6407, 2022.

EGU22-7451 | Presentations | TS4.1

A revision of the main active fault systems of the Alboran Basin: their significance in plate tectonics and a first appraisal of its seismogenic and tsunamigenic potential. 

Laura Gómez de la Peña, César R. Ranero, Guillermo Booth-Rea, José Miguel Azañón, Eulàlia Gràcia, Francesco Maesano, Roberto Basili, and Fabrizio Romano

The Alboran Basin is located in the westernmost Mediterranean Sea. This basin was formed during the Miocene, and since the late Miocene, has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. Thus, the Alboran Basin is a seismically active area, which hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which several small faults are accommodating the deformation.

Based on a modern set of active seismic data, we were able for the first time to quantify the total slip accommodated by the most prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin.

These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. Using the most complete dataset until the date, we performed a revision of the geometry and characteristics of the main fault systems offshore. Based on this data, we perform a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.

How to cite: Gómez de la Peña, L., R. Ranero, C., Booth-Rea, G., Azañón, J. M., Gràcia, E., Maesano, F., Basili, R., and Romano, F.: A revision of the main active fault systems of the Alboran Basin: their significance in plate tectonics and a first appraisal of its seismogenic and tsunamigenic potential., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7451, https://doi.org/10.5194/egusphere-egu22-7451, 2022.

EGU22-7780 | Presentations | TS4.1

The vertical movement of Karpathos: Competing hypotheses  

Violeta veliz borel, Onno Oncken, Vasiliki Mouslopoulou, John Begg, and Johannes Glodny

Karpathos is a roughly north-south oriented island that emerges between Crete and Rhodes in the forearc of the eastern Hellenic subduction system. It extends for ~60 km to the north of the 40 km contour of the plate interface depth. Further, the northern part of the island is confined to a N-S trending Horst bounded by two large normal faults that shape the seafloor off both, the eastern and western shore.  Furthermore, many normal faults, mainly in the north, strike parallel to the Horst and shape the topography onshore. Given the location and the structural configuration of the island, we expect that multiple processes are reflected in both the sedimentary and morphological record of vertical movement. Marine terraces and paleo-cliffs are observed all around the island recording its vertical movements over the last ~1 Ma. Moreover, sedimentary basins in the southern and central parts of the island are excellent archives of long-term uplift interrupted by subsidence over the last ~4.5 Ma. Twenty-five samples were collected at elevations between 1 and ~310 masl. We have gathered six (n=6) age/elevation data-points obtained by Sr-isotope dating, and nineteen (n=19) age/elevation data-points by radiocarbon dating. We explored the likelihood of different hypotheses on what drives the uplift:  whether it is driven by upper-crust normal faults, megathrust earthquakes, underplating, or a combination of these phenomena. We present preliminary results on both the temporal and spatial fluctuations of the vertical movement of Karpathos.

How to cite: veliz borel, V., Oncken, O., Mouslopoulou, V., Begg, J., and Glodny, J.: The vertical movement of Karpathos: Competing hypotheses , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7780, https://doi.org/10.5194/egusphere-egu22-7780, 2022.

EGU22-7890 | Presentations | TS4.1

Knickpoints and faulted alluvial fans: evidence of orogen parallel active extension related to delamination in the Western Betics 

Marcos Moreno-Sanchez, Daniel Ballesteros, Guillermo Booth-Rea, José Vicente Pérez-Peña, Carlos Pérez-Mejías, Cristina Reyes-Carmona, José Miguel Azañón, Jorge P. Galve, and Patricia Ruano

We present the first results of the MORPHOMED project, in order to deepen the chronology, uplifting rate, and tectonic forcing of different sectors of the Betic Cordillera since the Pliocene. Our initial morphotectonic analysis in the Western Betics, at the active termination of the Betic dextral STEP fault, highlights the location of active orogen-parallel normal faults cutting Pliocene marine sediments, uplifted above 600 masl, and Quaternary alluvial fans. The morphometric study we carried out includes normalized river steepness (ksn) and other geomorphic indices calculated in GIS using our own code designed in python. The fieldwork developed comprises the identification of uplifted Pliocene marine deposits, faulted alluvial fans and remnants of uplifted planation surfaces. The alluvial fans are related to travertine deposits older than 350 ka, which would be associated with hot springs. Geochronological studies involve previous and new U-Th dating on travertines and speleothems from caves in the high areas. The preliminary morphometric analyses reveal the occurrence of knickpoints that coincide with normal faults affecting marine Pliocene deposits and alluvial fans. These fans show vertical displacement of more than 20 m and their age remains unknown albeit the associated travertines are being dated. These results support previous works concerning of active tectonics in the Central and Western Betic Cordillera and they will serve to define new active faults, driving tectonic uplift of the Western Betics, which are the key to understand the landscape evolution forced probably by deep mantle rooted tectonics like slab tearing and edge delamination.

How to cite: Moreno-Sanchez, M., Ballesteros, D., Booth-Rea, G., Pérez-Peña, J. V., Pérez-Mejías, C., Reyes-Carmona, C., Azañón, J. M., Galve, J. P., and Ruano, P.: Knickpoints and faulted alluvial fans: evidence of orogen parallel active extension related to delamination in the Western Betics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7890, https://doi.org/10.5194/egusphere-egu22-7890, 2022.

The occurrence of earthquake-repeaters, i.e. co-located seismic events of comparable magnitude with highly similar waveforms breaking the same fault patch with an almost identical mechanism, is generally regarded as an indication that the fault surrounding the earthquake asperity is (aseismically) creeping. Earthquake repeaters can either occur during transient loading, e.g. within the afterslip of large earthquakes, or during the constant tectonic loading of tectonic faults. In this study we consider the latter.

The Main Marmara Fault (MMF) belongs to the western part of the North Anatolian Fault Zone (NAFZ) between the Anatolian and Eurasian plates and runs close to the population centre of Istanbul below the Marmara Sea. While the main NAFZ branches to the east and west of the MMF ruptured in M>7 earthquakes in the last century, the MMF itself is regarded as a seismic gap with the potential to host an M>7 event in the near future. Knowledge about the amount of aseismic creep of the off-shore MMF strand is important for a better seismic hazard assessment for the city of Istanbul and is heavily debated.

Building on earlier studies that identified repeating earthquakes in the western part of the MMF, we investigate a newly compiled seismicity catalogue of the Sea of Marmara for repeating events along the complete MMF. The catalogue spans the time period 2006-2020, comprises almost 14,000 events in the magnitude range M0.3-M5.7 and was compiled from regional permanent stations operated by AFAD and KOERI. Phase onset times were automatically picked with a two-step procedure using higher-order statistics and an AIC-representation of the waveforms for crude and fine-tuned estimation of the P- and S-onsets. The resulting onset-times were used in the Oct-tree location algorithm of the probabilistic NLLoc software using a regional velocity model and station corrections to obtain the final hypocentres.

To search for earthquake repeaters, we divide the MMF into overlapping segments and perform a station-wise cross-correlation analysis for all available event waveforms in each segment. Correlated waveforms start 1 s before the P-wave arrival and include the complete waveform including the S-wave coda. Waveforms were bandpass filtered between 2 and 20Hz to retain a rather wide frequency spectrum. We apply strict selection criteria and identify repeating events only as those with a normalized cross-correlation coefficient larger than 0.9 at at least 3 stations and a temporal separation of more than 30 days to exclude bursts of highly similar events in aftershock sequences or earthquake swarms.

The highest density of repeating earthquakes is found below the western Marmara Sea (Central Basin and Western High) with a systematic decrease of repeaters towards the east (Kumburgaz Basin) and none at all in the presumably locked Princess Islands section of the MMF immediately south of Istanbul. These results for the first time provide a consistent image of the amount of creep along the entire overdue Marmara section of the NAFZ derived from permanent onshore stations refining earlier results obtained from individual spots using local seafloor deployments.

How to cite: Becker, D., Martínez-Garzón, P., Wollin, C., and Bohnhoff, M.: Systematic variations of fault creep along the Marmara seismic gap, north-western Turkey, based on the observation of earthquake repeaters obtained from a high-resolution regional earthquake catalogue, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8142, https://doi.org/10.5194/egusphere-egu22-8142, 2022.

EGU22-8675 | Presentations | TS4.1

Subduction hints from the northeastern Mediterranean Sea 

Nicolò Bertone, Lorenzo Bonini, Eugenia Colin, Anna Del Ben, Giuseppe Brancatelli, Angelo Camerlenghi, Edy Forlin, and Gian Andrea Pini

The eastern Mediterranean is shaped by the interaction between the African, Arabian, and Eurasian plates resulting in a complex tectonic framework. The Hellenic subduction is well documented and studied but, the northeast corner of the eastern Mediterranean Sea remains enigmatic. It is a tectonically active region where different plate boundary conditions coexist (i.e., oceanic subduction, continental collision, extension, and strike-slip movements). An active and tsunamigenic system has been interpreted west and east of Cyprus by using deep seismic reflection lines. Vintage deep-penetrating seismic reflection profiles of the Mediterranean Sea project (MS project) - acquired during the ’70 - were re-analyzed and merged with a synthesis of available subsurface data from the scientific literature. This study focuses on two transects (MS53 and MS56) that cross the major offshore structures (i.e., Florence Rise, Latakia Ridge, and Kyrenia Ridge) from north to south. The western transect (MS53) shows the Herodotus oceanic crust subducting northward beneath the Eurasian plate. The Florence Rise is the leading edge of the system, and the Antalya Basin is its forearc basin. Close to the Turkish coast, a buried block seems to act as a backstop for the offshore system, and north of it, some out-of-sequence thrusts have been interpreted. The strain is partitioned between the Florence Rise and the Taurides front. The eastern transect (MS56) crosses the Latakia Ridge, i.e., the northern boundary of the Levant Basin, where shortening is greater than in the western area. The seismic line continues northward into the Cyprus – Latakia Basin, crossing the Kyrenia Ridge, and reaching the Turkish coast. On the seismic section, we interpreted the Mesozoic subduction front now hindered by strike-slip movements on the Latakia Ridge. Another prominent transpressive structure is the Kyrenia Ridge, which is interpreted as an active structure with a well-imaged thrust system in front of it. The seismic sections were depth converted to provide a regional geologic model for the northeastern Mediterranean Sea. Active subduction fronts, which are only partially imaged, were structurally modeled and then crosschecked with previous studies to better constrain their geometry. In the northeastern Mediterranean Sea, a plate boundary is buried offshore with active subduction west of Cyprus and mainly transpressional tectonics to the east. A better understanding of its nature and kinematics would be useful to assess the tsunami hazard in this area.

How to cite: Bertone, N., Bonini, L., Colin, E., Del Ben, A., Brancatelli, G., Camerlenghi, A., Forlin, E., and Pini, G. A.: Subduction hints from the northeastern Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8675, https://doi.org/10.5194/egusphere-egu22-8675, 2022.

EGU22-9537 | Presentations | TS4.1

New constraints on the kinematics of the western Sinai Microplate: geodynamic implications 

Roi Granot, Oded Katz, Mor Kanari, Orit Hyams, and Yariv Hamiel

The tectonic nature of the Sinai Microplate's western boundary is clouded with uncertainties. Early studies suggested that the western edge of Sinai is fully connected to the African Plate, thus concluding that Sinai is a sub-plate. Later, bathymetric analyses of prominent lineated faults straddling across the western edge of the Levant Basin have suggested that, in fact, this area is a plate boundary that accommodates dextral motion between the African Plate and the Sinai Microplate. However, this inference contradicts geological and geophysical observations across the Gulf of Suez, the southern continuation of the same plate boundary. Here we present preliminary results from a recent geophysical cruise aboard the R/V Bat Galim. We focused our investigation on one of the major faults, oriented in an NW-SE direction (located ~80 km southwest of the Eratosthenes Seamount), creating the plate boundary. We collected high-resolution shallow multichannel seismic reflection data complemented with multibeam bathymetry data. We also acquired two piston cores near the trace of the fault. These observations unravel the shallow three-dimensional structure of the fault system whereby several curved and steeply dipping normal fault segments are splayed from the main fault trace in a westerly direction. These secondary faults display a back-tilted and step-like morphology. This structure is best explained by a sinistral motion acting along the master fault. Independently, we present an updated Africa-Sinai Euler pole based on the motion of GPS stations recorded between 1996 and 2019. The results suggest that Sinai is moving in a northwesterly direction with respect to Africa (1.7-1.9±0.9 mm/yr). Focal mechanism solutions calculated for recent earthquakes occurring in this region (Mw>4.5) agree with the geodetic constraints of a sinistral relative motion.

Overall, these observations suggest that the western boundary of Sinai has been, and still is, accommodated sinistral motion relative to Africa. This conclusion implies that the Sinai Microplate is moving faster with respect to Eurasia relative to the motion of Africa with respect to Eurasia. This, in turn, seems to be in conflict with the notion that subduction of the oceanic lithosphere north of the Sinai Microplate (i.e., east of Cyprus) has recently ceased. We speculate that the downgoing slab might still promote the relatively fast northward motion of Sinai and/or a northward drag force induced by large-scale mantle flow related to the Afar plume could also contribute to the motion of the Sinai Microplate.

How to cite: Granot, R., Katz, O., Kanari, M., Hyams, O., and Hamiel, Y.: New constraints on the kinematics of the western Sinai Microplate: geodynamic implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9537, https://doi.org/10.5194/egusphere-egu22-9537, 2022.

EGU22-9541 | Presentations | TS4.1

Slow slip events captured by GNSS  along the Central Section of the North Anatolian Fault 

Jorge Jara, Alpay Ozdemir, Ugur Dogan, Romain Jolivet, Ziyadin Çakir, and Semih Ergintav

Recent observations suggest that seismogenic faults release elastic energy not only during sudden earthquakes but also aseismically. Slow slip can be persistent, lasting for years, or episodic. Aseismic slip is thought to be influenced by the presence/migration of fluids, stress interactions through fault geometrical complexities, or fault material heterogeneities. However, slow slip events have mostly been captured by regional GNSS networks in subduction zones, and the finest details of the nucleation, propagation, and arrest of such events have not been observed yet. Therefore, continental creeping faults are ideal targets for tackling such observational gaps and focusing on the sub-daily behavior of such slow slip events.

 

The central segment of the North Anatolian Fault is known to be creeping at least since the 1950s. This region was struck by the Mw 7.3 Bolu/Gerede earthquake in 1944, and since then, no earthquake of magnitude greater than 6 has been recorded. During the 1960s, aseismic slip was discovered as a wall built across the fault in 1957 was being slowly offset. Geodetic studies (InSAR, GNSS, and creepmeters) focused on capturing and analyzing aseismic slip around the village of Ismetpasa. Creepmeter measurements during the 1980s and 2010s, along with InSAR time series analysis, suggest that aseismic slip occurs episodically rather than persistently. However, no permanent GNSS stations were available close enough to the fault to study the details of such slow slip events.

 

Within the scope of a French-Turkish collaboration, we installed 17 GNSS stations (ISMENET) in 2019 to survey the spatio-temporal evolution of aseismic slip rate and characterize the physical properties of the fault zone. A creepmeter array located in the Ismetpasa village reported the occurrence of a significant slow slip event between December 2019 - January 2020. We analyze the GNSS record to search for small aseismic slip episodes and describe their behavior. We use a combination of Multivariate Singular Spectrum Analysis (MSSA) and Geodetic Template Matching (GTM) to extract the signature of aseismic slip and characterize its source. Results are compared to creepmeter measurements, as well as the historical earthquakes, fault geometrical complexities, and kinematic coupling. Our results confirm that aseismic slip in the region is not permanent. Therefore, even though the aseismic slip rate in the long-term seems to be constant, such a rate might result from the contribution of many aseismic slip episodes as the one detected in this work.

How to cite: Jara, J., Ozdemir, A., Dogan, U., Jolivet, R., Çakir, Z., and Ergintav, S.: Slow slip events captured by GNSS  along the Central Section of the North Anatolian Fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9541, https://doi.org/10.5194/egusphere-egu22-9541, 2022.

The Apennine Tyrrhenian margin records the evolutionary steps of the back-arc basin developed at the rear of a E-ward migrating fold-and-thrust belt. As well-documented in literature, the counterclockwise rotation of the Apennines is related to the southward increase of the roll back-related subduction of the Adria slab. This led first to the progressive incorporation of thrust sheets within the Apennine prism in the upper plate and later to its subsequent back-arc extension that is contemporaneous with the continuate inarching of the Apennine front towards the Adriatic and Ionian seas. Uncertainties arise on the structural style and timing in the internal Apennines between the orogenic and post-orogenic stages, that are respectively represented by thrust-sheet implacement, and crustal thinning.

We hereby propose a combined 2D seismic and field data review that allows identifying the geodynamic processes preceding the crustal stretching of the Apennine Tyrrhenian margin with new insights from on- and off-shore seismic lines. In particular, the construction of a new geotraverse across the margin, which is stretched over 100 km between the internal Central Apennines belts and the Pontian escarpment, allows to roughly estimate: i) the Late Miocene - Earliest Pliocene shortening with its change of the basal decollement depth through time; in particular, subsurface data highlighted stacked thrust sheets that were involved in an initial in-sequence propagation with top-to-the-ENE, synchronous to late Tortonian foredeep to wedge-top sedimentation. We also distinguish late backthrusts related to the formation of triangle zones that are more deeply rooted moving to the western chain interior. ii) The amount of crustal stretching and subsidence; Back arc-related orogenic collapse is preceded by initial orogen uplift and erosion in the internal sectors. iii) The onset of at least two magmatic cycles; in this frame, the lateral slab tearing and retreat is tracked by E-rejuvenated volcanic activity in the upper plate along the Volsci Volcanic Field and the Palmarola-Vesuvius lineaments. Those volcano-tectonic trends are favoured by a series of transtensive structures that progressively reflect the arc expansion in the rear. In this frame, the NE-dipping crustal detachment(s) may have played into crustal thinning during the Pliocene, driving and occasionally hampering magma emplacement, while high-angle faults have locally driven monogenetic eruptions. Finally, we report on field and seismic evidence of neo-tectonics, supporting ongoing extension occurring on the margin.

How to cite: Vico, G. and Cardello, G. L.: From thrusting to back-arc extension: seismic structure and field evidence of the Apennine Tyrrhenian margin (Central Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9955, https://doi.org/10.5194/egusphere-egu22-9955, 2022.

EGU22-10062 | Presentations | TS4.1

A re-evaluation of the 5th October 1948 M7.3 Ashgabat earthquake (Turkmenistan) 

Neill Marshall, Richard Walker, Qi Ou, and Christoph Gruetzner

The 1948 M 7.3 Ashgabat earthquake, killing over 38,000 people, occurred in the dextral strike-slip Kopeh Dagh fault zone in the Iran-Turkmenistan border region. Previously, it has been debated which fault(s) it occurred on and whether this earthquake was a thrust/reverse, strike-slip, or multi-fault earthquake, as published focal mechanisms suggest it had a reverse mechanism. We relocated the hypocentre using historical seismograms and present a new strike-slip focal mechanism. We used Pleiades satellite stereo imagery to produce Digital Elevation Models of part of the ruptured area. These data reveal clear strike-slip faults where surface ruptures were mapped in 1948. The earthquake did not rupture the Main Kopeh Dagh fault, but instead these subsidiary faults, highlighting the importance of considering lesser faults in seismic hazard models.

How to cite: Marshall, N., Walker, R., Ou, Q., and Gruetzner, C.: A re-evaluation of the 5th October 1948 M7.3 Ashgabat earthquake (Turkmenistan), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10062, https://doi.org/10.5194/egusphere-egu22-10062, 2022.

EGU22-10145 | Presentations | TS4.1

Coseismic and Postseismic Deformation of the January 24, 2020 Sivrice (Elazig) Earthquake Under the Constrain of Geodetic Observations 

İlay Farımaz, Seda Özarpacı, Alpay Özdemir, M. Hilmi Erkoç, Efe Turan Ayruk, Semih Ergintav, Uğur Doğan, and Ziyadin Çakır

January 24, 2020 Sivrice earthquake (Mw 6.8), which is the largest along the East Anatolian Fault (EAF) over the last century, is providing a wealth of information on the mechanics of transform faulting and for monitoring the different phases of the last seismic cycle. In this study, we aim to estimate coseismic and postseismic surface deformation along the Sivrice earthquake rupture and determine the strain accumulations on Pütürge segment by combining InSAR and GNSS measurements. The area was described one of the major seismic gaps along the EAF and we have started to study from Palu to Sivrice segments of the EAF, since 2015. Near field survey GNSS network has been established since 2015 and measured two times in a year, until 2021. Besides, after the earthquake, we surveyed 60% of near field sites to contain the coseismic field within 2-3 days. This dataset analyzed with continuous GNSS stations around the region to control the far field of the deformation field. Additionally, this dataset is densified by InSAR deformation field. For this purpose, the stack of interferograms have been interpreted from descending orbit Sentinel-1 dataset, composed of 6 days interval SAR acquisitions that starts from January 2020 to June 2020 which covers the earthquake time. As a result, significant differences between the pattern of strain accumulation before and after earthquake are documented with both GNSS and InSAR data. Moreover, the signature of the postseismic deformations is presented for 6 months.  

This study was supported by TUBITAK 1001 project no. 114Y250 and 118Y435.

Keywords: Sivrice earthquake, EAF, coseismic, postseismic, InSAR, GNSS

How to cite: Farımaz, İ., Özarpacı, S., Özdemir, A., Erkoç, M. H., Ayruk, E. T., Ergintav, S., Doğan, U., and Çakır, Z.: Coseismic and Postseismic Deformation of the January 24, 2020 Sivrice (Elazig) Earthquake Under the Constrain of Geodetic Observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10145, https://doi.org/10.5194/egusphere-egu22-10145, 2022.

EGU22-10193 | Presentations | TS4.1

Determining Strain Accumulation Along NAF with Block Modelling 

Efe Turan Ayruk, Seda Özarpacı, Alpay Özdemir, Volkan Özbey, Semih Ergintav, and Uğur Doğan

The North Anatolian Fault (NAF) is a one of the major dextral strike-slip faults of Turkey which forming the boundary between the Eurasian - Anatolian plates. From 1939 to 1999, significant earthquakes occurred as showing a westward migration. Several studies are being conducted due to this seismic activity along the NAF. However, none of these are sufficiently dense to understand the behaviour of the fault. Here we present our block modelling results obtained from combine that published GNSS velocity datasets to determine strain accumulation along the NAF with TDEFNODE software (McCaffrey,1995). Our study area separates to 3 blocks, starts from east of the Sapanca Lake and includes the Karliova Triple Junction on the east, extends over the Black Sea on the north and 130 kilometers from the fault on the south. Checkerboard method is used to test the resolution of the dataset, then node distribution on the NAF is optimized and Wang’s model is used for inversion solution (Wang,2003). Euler Pole and block strain are estimated with inversion solution for Eurasia/Anatolia plates and the slip deficit variations are estimated for NAF. Under the constrain of the dense GNSS networks, we displayed that some segments of NAF are creeping up to shallow part of the crust and some other segments are locked at deeper region. Herein to better understand latest circumstance of complex slip deficit pattern of the NAF, estimated by our model, we evaluated our results under the complementary present and paleo-seismological datasets.

Keywords: NAF, block modelling, GNSS

How to cite: Ayruk, E. T., Özarpacı, S., Özdemir, A., Özbey, V., Ergintav, S., and Doğan, U.: Determining Strain Accumulation Along NAF with Block Modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10193, https://doi.org/10.5194/egusphere-egu22-10193, 2022.

EGU22-10619 | Presentations | TS4.1

Neogene to recent geodynamic evolution of Northern Tunisia foreland thrust belt. 

Seifeddine Gaidi, Fetheddine Melki, Guillermo Booth-Rea, Wissem Marzougui, Jose Vicente Pérez-Peña, Patricia Ruano, Jorge Pedro Galve, Haifa Chouaieb, Jose Miguel Azañón, and Fouad Zargouni

This work analyses the tectonic evolution of Northern Tunisia from the Late Miocene to Present. Two orthogonal extensional systems with ENE- and SE-directed transport produced the extensional collapse of the Tell and Atlas Foreland Thrust Belts (FTBs) in northern Tunisia during the Late Miocene to Pliocene in a context of NW-SE plate convergence between Africa and Eurasia. These systems produced the extensional denudation of the Tunisian Atlas and Tell foreland thrust belts, which we related to deep mantle tectonic mechanisms, known as a common feature in other FTB´s in the western Mediterranean, i.e. Betics, Rif, Calabria and Apennines. Low-angle normal faults have extended and reworked the Tunisian Tell external foreland thrust belt, exhuming midcrustal lower-greenschist metapelites and marbles with Triassic protholiths, and forming Late Miocene basins. This extension was followed by later Pliocene to Present tectonic inversion, developing the active shortening structures in Northern Tunisia. The main shortening structure is formed by different reverse and strike-slip fault segments, linked forming the 130 km long Alia-Thibar fault zone. Restored Plio-Quaternary deformation observed on reflection seismic lines indicates deformation rates around 0.6-0.8 mm/yr in the studied segments and larger amounts of shortening to the West of Northern Tunisia (16%) than to the East (7%), which suggests that tectonic inversion started earlier to the West and later propagated eastwards, reaching Northeastern Tunisia in the Late Pliocene. Due to the young age of this tectonic inversion, the present relief of Northern Tunisia is characteristic of a young thrust and fold belt, with dominating axial valleys along synforms and an incipient transverse drainage development propagating from West to East.

How to cite: Gaidi, S., Melki, F., Booth-Rea, G., Marzougui, W., Pérez-Peña, J. V., Ruano, P., Galve, J. P., Chouaieb, H., Azañón, J. M., and Zargouni, F.: Neogene to recent geodynamic evolution of Northern Tunisia foreland thrust belt., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10619, https://doi.org/10.5194/egusphere-egu22-10619, 2022.

EGU22-11846 | Presentations | TS4.1

Mantle origins of topography, volcanism and the North Anatolian Fault in Anatolia: constraints from seismic tomography, seismic anisotropy and crustal structure 

Ian Bastow, Thomas Merry, Rita Kounoudis, Christopher Ogden, Rebecca Bell, Saskia Goes, Jennifer Jenkins, Laurence Jones, Beth Grant, and Charles Braham

The eastern Mediterranean hosts, within the span of a few hundred kilometres, extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this complex region using a variety of broadband seismological techniques, with new P- and S-wave tomographic images in Kounoudis et al. (2020), seismic anisotropy constrained via an updated dataset of SKS shear-wave splitting observations in Merry et al. (2021), and crustal structure imaged by quality-controlled H-κ stacking of receiver functions in Ogden & Bastow (2021). Overall, seismic anisotropy and crustal structure are more spatially variable than previously recognised, and such variations correspond well with variations in mantle structure shown by the tomography. In general, Moho depth is poorly correlated with elevation, suggesting crustal thickness variations do not fully explain topographic differences, and residual topography calculations indicate the requirement for a mantle contribution to Anatolian Plateau uplift. Evidence for such a contribution exists in central Anatolia, where an imaged horizontal tear in the Cyprus slab spatially corresponds with volcanism, a residual topographic high, and a region of reduced splitting delay times and nulls, all consistent with upwelling of asthenospheric material through the tear. Anisotropic fast directions are consistent with flow through the imaged gap between the Cyprus and Aegean slabs, again correlating roughly with both volcanism and high residual topography. Slow uppermost‐mantle wave speeds below active volcanoes in eastern Anatolia, and ratios of P-to-S wave relative traveltimes, indicate a thin lithosphere and melt contributions. Elsewhere, there is more evidence for slab processes controlling mantle flow, with anisotropic fast directions diverted at the edges of imaged slabs and consistent with flow towards the retreating Hellenic trench in the Aegean. The North Anatolian Fault is revealed to be a deep, plate-scale structure: whilst there are no clear changes in Moho depth across the fault, deep velocity contrasts suggest a 40­-60km decrease in lithospheric thickness from the Precambrian lithosphere north of the fault to a thinned Anatolian lithosphere in the south. Moreover, short-length-scale variations in anisotropy and backazimuthal variations in splitting parameters at the fault indicate fault-related lithospheric deformation, with seismic fast directions either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone. Upper mantle structure thus exerts a strong influence on uplift, volcanism and deformation in Anatolia.

References

Kounoudis, R., I.D. Bastow, C.S. Ogden, S. Goes, J. Jenkins, et al.,  (2020), Seismic Tomographic Imaging of the Eastern Mediterranean Mantle..., G3, 21(7), doi:10.1029/2020GC009009.

Merry, T.A.J., I.D. Bastow, R. Kounoudis, C.S. Ogden, R.E. Bell, & L. Jones (2021), The influence of the North Anatolian Fault and a fragmenting slab architecture on upper mantle seismic anisotropy... ,G3, 22, doi:10.1029/2021GC009896.

Ogden, C.S., & I.D. Bastow (2021), The Crustal Structure of the Anatolian Plate from Receiver Functions..., GJI, doi:10.1093/gji/ggab513.

How to cite: Bastow, I., Merry, T., Kounoudis, R., Ogden, C., Bell, R., Goes, S., Jenkins, J., Jones, L., Grant, B., and Braham, C.: Mantle origins of topography, volcanism and the North Anatolian Fault in Anatolia: constraints from seismic tomography, seismic anisotropy and crustal structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11846, https://doi.org/10.5194/egusphere-egu22-11846, 2022.

EGU22-12611 | Presentations | TS4.1

New insights on the relationship between inherited structures of the opening of the Algero-Balearic basin and recent inversion of its southern margin 

Shaza Haidar, Pierre Leffondré, Jacques Déverchère, David Graindorge, Frauke Klingelhoefer, Mohamed Arab, Mourad Medaouri, and Marie-Odile Beslier

The Algero-Balearic Basin (ABB) is an Oligo-Miocene back-arc basin resulting from a polyphase tectonic evolution involving Tethyan subduction retreat and bilateral slab tear propagation. The ABB was fully opened by the Tortonian, while the Gibraltar and Calabria arcs formed by the narrowing of retreating slab fragments. Since then, the Algerian margin has undergone a tectonic inversion, potentially preceding an incipient subduction as shown by the analysis of the on-offshore deformation distribution. In this work, we aim to shed light on the relationships between the large-scale structures inherited from the ABB opening and the recent margin inversion. For this purpose, we rely on two recent analyses, one addressing the ABB opening (Haidar et al., 2021) and the other mapping the inversion-related structures off-Algeria (Leffondré et al., 2021), both being constrained by a set of deep penetration multi-resolution seismic profiles cross-correlated with magnetic, gravimetric and bathymetric data. 

The deep ABB has been subdivided into 4 zones with relatively distinct geodynamic evolutions, as demonstrated by variations in pre-Messinian sedimentary infill thickness and basement depth : (1) the oldest, fan-shaped oceanic basin to the east (off-Jijel), formed during the Langhian-Serravallian after collision of the Kabylian blocks with the stretched African margin; (2) the shallower and younger Hannibal thinned continental domain (HD), intruded by intense post-collisional magmatic activity during the Upper Serravallian - Lower Tortonian; and ever-younger to the west, (3) the central-western (off-Algiers-Tipaza) and (4) westernmost zones, formed from the Tortonian to the Lower Messinian in response to the westward retreat of the Gibraltar slab and the concomitant migration of the Alboran block by propagation of vertical tears along a STEP (Subduction Transform Edge Propagator) type margins.

The tectonic inversion is characterised by long-wavelength of flexure (>100km) of the ABB towards the Algerian margin and/or buckling of shorter wavelengths (≈30km). The central (HD) and central-eastern (off-Jijel) zones are dominated by flexure, whereas buckling is dominant in the central-western zone. Further, the easternmost (off-Annaba) and westernmost zones exhibit a combination of flexure and buckling. Except in the westernmost zone, characterized by low deformation on a single fault, the margin toe consistently displays inversion-related faults systems consisting of 3 to 4 south-dipping and sub-parallel thrust faults.

By comparing the zonation of the deep ABB and the zones with different responses to inversion, we evidence a similar zonation of the margin, with only slight differences likely resulting from data density variations. To the east, the old and wide fan-shaped basin has favored the development of a significant flexural response, whereas the young westernmost zones, narrower and bordered by STEP-faults, evidence a combination of buckling and short-wavelength of flexure. The HD is a complex zone with a shorter wavelength of flexure compared to the eastern zone, probably related to magmatic activities affecting the potentially continental crust. Our results suggest that if initial zonation persists, several parameters may be involved in the control of the inversion mode. These parameters may include the opening-related structural inheritance, the oceanic lithosphere composition, as well as the age and former structures of the margin.

How to cite: Haidar, S., Leffondré, P., Déverchère, J., Graindorge, D., Klingelhoefer, F., Arab, M., Medaouri, M., and Beslier, M.-O.: New insights on the relationship between inherited structures of the opening of the Algero-Balearic basin and recent inversion of its southern margin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12611, https://doi.org/10.5194/egusphere-egu22-12611, 2022.

EGU22-13052 | Presentations | TS4.1

Connecting subduction, extension, and shear localization across the Aegean Sea and Anatolia 

Sylvain Barbot and Jonathan Weiss

The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African, and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction, but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geologic structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north-south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts, including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa-Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm/yr in a largely trench-normal direction, except near eastern Crete where variably-oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy-Pliny-Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback, and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea, and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.

How to cite: Barbot, S. and Weiss, J.: Connecting subduction, extension, and shear localization across the Aegean Sea and Anatolia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13052, https://doi.org/10.5194/egusphere-egu22-13052, 2022.

EGU22-2908 | Presentations | GD8.4

New insights in the lithospheric configuration of the Ligurian-Provençal Basin derived from gravity field interpretation 

Hans-Jürgen Götze, Judith Bott, Boris Kaus, Magdalena Scheck-Wenderoth, and Christian Schuler

The area of the western Mediterranean between the French and Italian coasts and Corsica-Sardinia is still of great interest in terms of its structural development, which remains incompletely understood. The resolution of geophysical data was not always high enough to explore detailed structures in the lithosphere. After completion of the new AlpArray gravity maps, a high-resolution gravity field is available. The intended 3D modelling of the lithosphere requires the search for reliable constraints for the density/susceptibility models (seismic, bathymetry, gravity fields, gradients). The calculation of residual gravity fields is difficult due to uncertainties in the calculation of regional fields which are characterized by pronounced gravity highs and lows in a very limited spatial area. The residual fields calculated here provide new insights into the lithospheric structure and suggest that the mass distribution in the Ligurian-Provençal Basin does not monotonously follow the known major geological units. A broad belt of local gravity highs (25 - 40 x 10-5 m/s2) extends off the French coast to the northwest of the basin where it merges with NW-SE directed gravity highs (up to 45 x 10-5 m/s2) near the Italian coast. Hitherto unknown is the residual field anomaly south of Marseille with max. 100 x 10-5 m/s2. Euler deconvolution and correlations with maps of focal depths of earthquakes resulted in source depths that lie in the mantle. The results of further processing techniques (curvature calculations, third derivative of potential, terracing and cluster analysis) were superimposed on geological maps to make visual correlations clear. Results of dynamic modelling of the surrounding subduction zones, as well as newly inferred Moho and LAB depths, are also available for interpreting gravity field components of deeper regions of the Earth's mantle in the study area. Previously performed investigations (magnetic field modelling and recent seismic campaigns, e.g., LOBSTER and AlpArray seismic tomography models) were also added to the research.

How to cite: Götze, H.-J., Bott, J., Kaus, B., Scheck-Wenderoth, M., and Schuler, C.: New insights in the lithospheric configuration of the Ligurian-Provençal Basin derived from gravity field interpretation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2908, https://doi.org/10.5194/egusphere-egu22-2908, 2022.

EGU22-3243 | Presentations | GD8.4

Seismic discontinuities from the Moho to 410 km depth between the Alps and Scandinavia from Sp converted waves 

Rainer Kind, Stefan Schmid, Felix Schneider, Thomas Meier, and Xiaohui Yuan

We use teleseismic data from all available broadband stations, permanent and mobile, in the entire area. Our processing method applies distance moveout correction, amplitude normalization, sign equalization and summation of traces with piercing points in 1° latitude times 1° longitude cells. The traces are stacked along the picked SV onset times. We obtain very clear signals from the Moho, less strong signals from velocity reductions below the Moho and again clear signals from the 410 km discontinuity. We also see locally velocity reductions just above the 410 km discontinuity. We show a number of profiles through the study area and hope to show maps of all seismic discontinuities. We compare our results with earlier observation.

How to cite: Kind, R., Schmid, S., Schneider, F., Meier, T., and Yuan, X.: Seismic discontinuities from the Moho to 410 km depth between the Alps and Scandinavia from Sp converted waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3243, https://doi.org/10.5194/egusphere-egu22-3243, 2022.

EGU22-3790 | Presentations | GD8.4

Quaternary paleostress regimes in the Eastern Alps inferred from ruptures in karst caves 

Ivo Baroň, Jacek Szczygieł, Rostislav Melichar, Lukas Plan, Bernhard Grasemann, Eva Kaminsky, and Denis Scholz

In the Alps, the Adriatic plate convergence provoked eastward lateral extrusion compensated by strike-slip faulting and N-directed thrusting. Since the Miocene, these complex processes have led to several paleostress phases. Since the Quaternary phase is the least recognized, we used karst cave passages as the geomorphic displacement indicators. This study presents an overview of 190 Quaternary fault ruptures in totally 27 caves in the Eastern Alps, some radiometrically dated, and the paleostress analysis based on cave passages offset. Reactivated faults have been registered with their orientation, slip vector and offset, in caves adjacent to major fault systems of the Eastern Alps. The paleostress was computed using the multiple inversion method for heterogeneous fault-slip data.

Most active faults in caves along the southern part of the sinistral Vienna Basin Transfer Fault were NW-SE, and NNE-SSW oriented and revealed mostly normal to sinistral kinematics and cumulative offsets of a few mm to a couple of cms. The associated extensional paleostress state comprised the E-W σ3 in agreement with the opening mode of the Vienna Basin. At sinistral Mur-Mürz Fault, the active faults striking NNE-SSE and ENE-WSW operated under a strike-slip regime with σ1 NE-SW. In the eastern segment of sinistral Salzach-Ennstal-Mariazell-Puchberg fault associated strike-slip paleostress regime with horizontal SE-NE σ1, and subhorizontal SE-trending σ3. This stress regime was computed from reverse, oblique reverse, oblique normal, and sinistral strike-slip reactivated faults documented in the Hochschwab massif. The central segment of Salzach-Ennstal-Mariazell-Puchberg fault is adjoin to Totes Gebirge and Dachstein massifs. In the western part of Totes Gebirge, three stress regimes were recorded. N-S and NW-SE striking oblique normal strike-slip faults revealed an extensional regime with NE σ3. Two strike-slip regimes with NE-SW σ1 and subhorizontal σ3 gently inclined to SE and NW were calculated from mostly steep oblique reverse NNE to NW striking faults with offsets up to a few decimetres. In the Dachstein massif, two paleostress phases were identified: the extensional regime with σ3 subhorizontally tilted to NE and the strike-slip regime with N-S σ1. Tens of active, mostly oblique normal strike-slip faults were documented in massifs adjacent to sinistral Königsee-Lammertal-Traunsee Fault: Hoher Göll, Tennengebirge and Hagengebirge. The dominating associated paleostress is an extensional regime with NE-SW σ3. The polyphase sinistral and reverse-dextral NE-SW faults with Late Pleistocene to Early Holocene reactivations and up to 40 cm offsets, identified at the sinistral Obir Fault attributed to the dextral Periadriatic Line. Neither the strike-slip regime with ENE-plunging σ1 nor the other strike-slip regime with σ1 WNW oriented to fit the regional stress setting. It probably resulted from large-scale complex Karawanken Mts. transpressive shear zone deformation.

In conclusion, the paleostress multiple inversions from the Quaternary cave passage ruptures kinematic data brought original information on the paleostress regime over a significant portion of the Eastern Alps in their latest deformational period.

How to cite: Baroň, I., Szczygieł, J., Melichar, R., Plan, L., Grasemann, B., Kaminsky, E., and Scholz, D.: Quaternary paleostress regimes in the Eastern Alps inferred from ruptures in karst caves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3790, https://doi.org/10.5194/egusphere-egu22-3790, 2022.

EGU22-3979 | Presentations | GD8.4

Initial results of modelling 3D plate dynamics in the Alpine-Mediterranean area 

Christian Schuler, Boris Kaus, Eline Le Breton, and Nicolas Riel

Tectonic reconstructions of lithospheric plate motion can be approached by different geological methods. However hypotheses derived from these findings are often not validated in a physically consistent manner. Therefore we employ 3D geodynamic modelling in order to test geological reconstructions.

In this work, 3D thermomechanical forward simulations of the Alpine-Mediterranean area are conducted using the software LaMEM (Kaus et al. (2016)). A viscoelastoplastic rheology and an internal free surface are applied, which means that apart from the internal dynamics also the surface response can be investigated. Kinematic reconstructions of Le Breton et al. (2021) at 35 Ma serve as an initial setup for the simulations. The goal of these simulations is to determine the main driving forces of plate dynamics in this area. This is done by evaluating effects of different model parameters such as the thermal structure and the geometry of the slabs, the viscosity of the mantle and brittle parameters of the crust.

The geodynamic behaviour of the Alpine-Mediterranean area is dominated by various subducting plates which makes it particularly difficult to distinguish the unique influence of different geodynamic processes. The Adriatic microplate plays a key role in the development of the Alpine Orogeny and its plate motion and therefore serves as a marker as it is possible to compare the current position of this plate with the simulation itself. Even though these forward simulations are not capable of exactly reconstructing the current tectonic setting, they provide insights into parameters which influence the subduction dynamics.

First results suggest that the plate motion of Adria is primarily driven by the interaction of the Calabria slab and the Hellenic slab and that the propagation of these slabs strongly depends on the slab geometry and the initial trench location. Furthermore the spreading rate of rifting in the Liguro-Provençal Basin massively affects the timing of Adria’s plate motion.

 

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 deformationon geological timescales. Proceedings of NIC Symposium.

Le Breton, E., S. Brune, K. Ustaszewski, S. Zahirovic, M. Seton, R. D. Müller, 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.: Initial results of modelling 3D plate dynamics in the Alpine-Mediterranean area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3979, https://doi.org/10.5194/egusphere-egu22-3979, 2022.

EGU22-4420 | Presentations | GD8.4

Seismotectonics in the Central Alps: An attempt to link fault structures, seismic activity and recent crustal movements 

Marco Herwegh, Samuel Mock, Tobias Diehl, Elmar Brockmann, Sandro Truttmann, Edi Kissling, Eva Kurmann-Matzenauer, Stefan Wiemer, and Andreas Möri

Owing to still ongoing convergence within the Europe-Adria collision zone, Switzerland is affected by heterogeneously distributed moderate seismic activity. The project SeismoTeCH aims to improve the understanding of the links between the seismic activity, existing fault structures and geodynamics in Switzerland and its close vicinity. We started with compiling existing databases on faults (fault densities, lengths and orientations), seismic activity (spatial hypocenter and magnitude distributions, detection of seismic lineaments, focal mechanisms), orientations of mean principal stress axes and recent crustal movements (GNSS, high precision levelling) in order to establish potential correspondences as well as regional variations.

Due to the long-lasting Alpine deformation, fault-orientation patterns as well as fault-densities vary between specific tectonic domains (Jura/North-Alpine foreland, Alpine frontal sediment nappe systems, External Crystalline Massifs, inner-Alpine domains and Southern Alps). Despite this variability, the fault patterns show first order correlations with the spatial arrangement of newly mapped seismic lineaments, earthquake focal planes and associated focal mechanisms. This correlation indicates a regional geodynamics-controlled reactivation of the specific fault networks during current crustal movements. In terms of recent surface movements, variations in (i) horizontal GNSS movements with respect to stable Europe and (ii) vertical uplift (from levelling and GNSS data) have to be discriminated. (i) From E to W in southern Switzerland (S-Grisons–Ticino–Valais, S of Rhone-Simplon line), horizontal movements change from NW to SW directions (velocities >0.5-0.8mm/yr). The southern Adria crustal block shows minimal to no lateral motions in the W-part and a clear NE-directed motion that is progressively increasing towards the E. This motion can be correlated with the so-called counter-clockwise rotation of the Adriatic plate. North of aforementioned domain, N- to NW-directed movements dominate but velocities decrease progressively from the central Alpine domains (<0.3-0.5mm/yr) towards southern Germany, where they are generally small (<0.3-0.4mm NE-CH). This variability between southern and central/northern Switzerland as well as that from E to W, respectively, is accommodated by NE-SW (Rhone-Simplon system) and N-S oriented strike-slip systems. (ii) Most substantial vertical uplift occurs in a WSW-ENE oriented central Alpine belt ranging from the Valais to the Grisons. Note that absolute values of this vertical uplift are 2-3 times larger compared to horizontal movements in the corresponding domains. Focal mechanisms in this high uplift belt indicate orogen-parallel NE-SW extension mainly in the S-Valais and Grisons accommodated by active normal faulting S of the Penninic front. Uplift rates gradually decrease towards the N- and S-Alpine foreland as well as towards Austria and France. Data even suggest tendencies of subsidence at very low rates in the Bresse graben, Upper Rhine graben as well as somewhat more pronounced ones in the eastern Po-plane but not in the CH-Molasse basin. Parts of the northern Alpine foreland exhibit upper to lower crustal seismic activity, while in the thick-crustal-root-enhanced high uplift domains upper crustal seismicity dominates and earthquakes below 20km depth do not occur.

Overall recent surface movements and seismicity in and along Central Alpine crustal blocks are affected by buoyancy-driven vertical combined with transpressional/-tensional horizontal movements indicating a lithosphere-scale geodynamic forcing. 

How to cite: Herwegh, M., Mock, S., Diehl, T., Brockmann, E., Truttmann, S., Kissling, E., Kurmann-Matzenauer, E., Wiemer, S., and Möri, A.: Seismotectonics in the Central Alps: An attempt to link fault structures, seismic activity and recent crustal movements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4420, https://doi.org/10.5194/egusphere-egu22-4420, 2022.

EGU22-4500 | Presentations | GD8.4

Controls on along-strike variations of basin development: a case study of the Northern Alpine Foreland Basin 

Lucas Eskens, Nevena Andrić-Tomašević, Peter M. Süss, Todd A. Ehlers, Rolf Herrmann, and Matthias Müller

The Northern Alpine Foreland Basin developed in response to the collision between the European and Adriatic plates. During the Oligocene-Early Miocene coeval along-strike deposition of terrestrial and deep marine conditions are recorded in the western and eastern parts of the basin respectively. However, the mechanisms driving the observed variability in along-strike development of the basin are still poorly understood.

To study the causes of the observed along-strike variability we review published geological data and (re)interpret available 2D and 3D seismic data, constrained by well data. We interpret (1) seismic facies, (2) stratigraphic surfaces and (3) tectonic structures. Our current focus area covers the transitional zone between the western and eastern parts of the basin.

In our study we distinguish 6 stratigraphic surfaces from the Base Tertiary to the Top Aquitanian. From Upper Swabia to the German-Austrian border (along the basin strike) we observe that the top of the crystalline basement is tilted towards the east with an angle of 2-3°. Furthermore, the base of the Tertiary deposits is also tilted towards the east with an angle of 0.3°. The main structural features are E-W and NW-SE striking normal faults. In the western part of our study area the normal faults cut the crystalline basement, Mesozoic and Oligocene deposits. The faults are sealed by Rupelian deposits. Thickness changes (~20 m) occur in Rupelian and overlying Chattian deposits. Maximum offsets of up to 60 m are observed for Mesozoic reflectors. In the eastern part of our study area the normal faults cut the crystalline basement, Mesozoic, Oligocene and Early Miocene deposits. Thickness changes across these faults indicate fault activity during the Rupelian, Chattian and Aquitanian. Maximum offsets (>150 m) are observed for Chattian reflectors. Upper Aquitanian deposits seal these faults, which is younger than observed in the western part of the study area. The NW-SE striking faults confine Paleozoic grabens within the crystalline basement.

We relate the observed normal faulting of the Oligocene and Early Miocene deposits to flexural downbending of the European plate, assumed to have been caused by tectonic loading of the Alps and/or European slab pull. Furthermore, we suggest that the observed temporal variation in termination of fault activity is related to temporal and spatial variations in tectonic loading of the Alps and/or European slab pull. Finally, based on the observed eastward tilt of the top crystalline basement and Base Tertiary along the basin strike, variations in pre-existing crustal architecture must be considered.

How to cite: Eskens, L., Andrić-Tomašević, N., Süss, P. M., Ehlers, T. A., Herrmann, R., and Müller, M.: Controls on along-strike variations of basin development: a case study of the Northern Alpine Foreland Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4500, https://doi.org/10.5194/egusphere-egu22-4500, 2022.

EGU22-4501 | Presentations | GD8.4

High-resolution deformation maps from the Southern-Eastern Alps compiled from 5-yr-long radar interferometric time-series 

Sabrina Metzger, Milan Lacecký, and Najibullah Kakar

Entering the terminal phase of continental collision, the European Alps exhibit surface deformation rates at the mm-level. Uplift peaks in the Central Alps at 2-3 mm/yr as a result of the post-glacial isostatic rebound, slab tearing, and erosion. Horizontal rate changes of <2 mm/yr are observed in the Southern-Eastern Alps due to the anticlockwise rotation of the Adriatic lithosphere. Here, N–S shortening is primarily accommodated at the densely-populated foothills of the Southern Alps, where seismicity is abundant and includes M6+ earthquakes like the devastating Mw6.5 Friuli earthquake in 1975. Further north and beyond the ESE-trending, dextral Periadriatic fault, the Eastern Alps extrude into the Pannonian basin. Today’s fault slip rates are constrained by Global Navigation Satellite System (GNSS) data with an inter-station distance too sparse to provide a detailed insight into plate locking—a vital component of estimating the fault’s seismic potential.

We present 4D-deformation data of the SE-Alps in unprecedented resolution (~400 m, 6 days). The rate maps were derived from radar-interferometric time-series collected since 2017 by the European Sentinel-1 satellites. Each of the assembled 240-km-wide radar tiles consists of 300+ images. The interferograms were automatically generated, phase-unwrapped, and corrected for atmospheric and topographic signal contributions. We estimated the deformation rates using the LiCSBAS time-series analysis software that involves a small-baseline approach and accounts for spatio-temporal coherence and seasonality. By tying the individual, relative InSAR rates—observed in two look directions—into a Eurasian reference frame based on by published GNSS rates we decompose them into east and vertical rates.

Our results illuminate the extreme, to which we can push the InSAR signal-detection threshold if the signal-backscatter properties are as challenging as in the vegetated SE-Alps: The predominant, vertical rates result from a mixture of isostatic, tectonic and anthropogenic processes, overlaid by a soil-moisture bias; the horizontal shortening rates align northwards, to which the radar satellites is least sensitive. Nevertheless, our rates provide new, dense deformation data and highlight processes yet undetected by the GNSS monitoring network.

How to cite: Metzger, S., Lacecký, M., and Kakar, N.: High-resolution deformation maps from the Southern-Eastern Alps compiled from 5-yr-long radar interferometric time-series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4501, https://doi.org/10.5194/egusphere-egu22-4501, 2022.

EGU22-6582 | Presentations | GD8.4

The AlpArray Seismicity Catalog 

Matteo Bagagli, Irene Molinari, Tobias Diehl, Edi Kissling, and Domenico Giardini

Exploiting the new large seismic data set provided by the AlpArray Seismic Network (AASN) as part of the AlpArray research initiative (www.alparray.ethz.ch), we provide a highly consistent seismicity catalog with precise hypocenter locations and uniform magnitude calculations across the greater Alpine region (GAR) covering the period from 1st January 2016 to 31st December 2019.

With a backbone of 715 broadband seismic stations (415 permanent, 300 temporary) and a uniform interstation distance of ~50 km, the AASN provides a unique opportunity to assess the laterally heterogeneous GAR seismicity distribution. Regularly, the GAR seismicity is monitored and reported by a dozen national and international observatories, requiring a challenging effort to create a uniform and reliable catalog to document and investigate the complex seismicity and tectonics of the GAR.

To establish the highly consistent AlpArray Seismicity Catalog (AASC), we developed a new multi-step, semi-automated method. We applied the SeisComP3 (SC3) seismic-monitoring software and run it in playback mode to analyze the ~50 Tb of continuous data collected in 4 years for initial events detection and to calculate their hypocenter locations. We cleaned this preliminary, automatic seismic catalog from fake events and from events with an initial magnitude less than 2.0 MLv. We then made use of two additional software packages to refine phase picks and locations: the new ADAptive Picking Toolbox (ADAPT) Python library and the VELEST algorithm. The former was used to develop a new multi-picking algorithm for phase identification and precise arrival time determination. The latter was used to obtain the most reliable earthquakes locations, their quantitative error estimation and to reliably predict phase arrivals by solving the coupled hypocenter-velocity problem using the powerful joint-hypocenter determination technique (JHD). The JHD approach was also implemented as a filtering tool for outlier observations and to detect problematic events.

We eventually recalculate the local magnitude (MLv) in a consistent and uniform way, obtaining a statistical magnitude of completeness of 2.4 MLv with different catalog-based techniques. The AASC is also regionally consistent up to 3.0 M+  with seismic bulletins provided by national and international agencies.

Our final 4-year catalog contains 3293 precisely located earthquakes with magnitudes ranging between 0.4 - 4.9 MLv and it clearly delineates the major seismically active fault systems within the GAR. We additionally provide a new minimum 1D P-velocity model for the GAR and appropriate station delays, for both temporary and all permanent stations. These station delays for the permanent seismic station arrays, together with the velocity model, are key to consistently link the GAR past and future seismicity with our current catalog. This would allow the compilation of a broader consistent seismic catalog suitable for other seismological studies including, but not limited to, seismic hazard and a regional 3D local earthquake tomography.

How to cite: Bagagli, M., Molinari, I., Diehl, T., Kissling, E., and Giardini, D.: The AlpArray Seismicity Catalog, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6582, https://doi.org/10.5194/egusphere-egu22-6582, 2022.

EGU22-7246 | Presentations | GD8.4

Status and Implementation of the AdriaArray Seismic Network 

Petr Kolínský, Thomas Meier, and the AdriaArray Seismic Network Working Group

With the advent of plate tectonics in the last century, our understanding of the geological evolution of the Earth system improved essentially. The internal deformation and evolution of tectonic plates remain however poorly understood. This holds in particular for the Central Mediterranean: The formerly much larger Adriatic plate is recently consumed in tectonically active belts spanning at its western margin from Sicily, over the Apennines to the Alps and at its eastern margin from the Hellenides, Dinarides towards the Alps. High seismicity along these belts indicates ongoing lithospheric deformation. It has been shown that data acquired by dense, regional networks like AlpArray provide crucial information on seismically active faults as well as on the structure and deformation of the lithosphere. The Adriatic Plate and in particular its eastern margin have however not been covered by a homogeneous seismic network yet.

Here we report on the status and preparation of AdriaArray – a seismic experiment to cover the Adriatic Plate and its actively deforming margins by a dense broad-band seismic network. Within the AdriaArray region, currently about 950 permanent broad-band stations are operated by more than 40 institutions. Data of 90% of these stations are currently available via EIDA. In addition to the existing stations, 385 temporary stations from 18 mobile pools are to be deployed in the region to achieve a coverage with an average station distance of about 50 – 55 km. The experiment will be based on intense cooperation between network operators, ORFEUS, and interested research groups. Altogether, more than 50 institutions will participate in the AdriaArray experiment. We will introduce the time schedule, participating institutions, mobile station pools, maps of suggested temporary station distribution with station coverage and main points of the agreed Memorandum of Collaboration. The AdriaArray experiment will lead to a significant improvement of our understanding of the geodynamic causes of plate deformation and associated geohazards.

How to cite: Kolínský, P., Meier, T., and Seismic Network Working Group, T. A.: Status and Implementation of the AdriaArray Seismic Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7246, https://doi.org/10.5194/egusphere-egu22-7246, 2022.

EGU22-7333 | Presentations | GD8.4

Towards a high-resolution vS crustal velocity model for the Ivrea Geophysical Body: constraints from seismic ambient noise tomography 

Matteo Scarponi, Jiri Kvapil, Ludek Vecsey, Jaroslava Plomerová, IvreaArray Working Group, and AlpArray Working Group

The arc of the Western Alps is characterized by a complex crustal structure. Lower-to-middle crustal composition outcrops are exposed in the Ivrea-Verbano Zone (IVZ) and a major crustal anomaly, known as Ivrea Geophysical Body (IGB), presents dense and seismically fast rocks right below the surface. Understanding better their relation provides a key to refine our understanding of orogeny formation mechanisms.

We performed seismic ambient noise tomography using data from the IvreaArray and the AlpArray Seismic Network, selected within a radius of ca. 100 km around the study area. Previous seismic investigations provided knowledge on the crustal structure in the Western Alps, by means of active refraction seismics and of more recent local earthquake and ambient noise tomography at regional scales (e.g. Solarino et al. 2018 Lithos, Lu et al. 2018 GJI). Recently, gravity data and receiver function analysis imaged the IGB as a dense and fast seismic anomaly, related to upper mantle material, reaching up to few km depth below sea level (Scarponi et al. 2021 Frontiers). However, local high-resolution constraints on the absolute vS distribution remain unknown.

We used raw summer seismic data (June to September) across 3 years of recording, and computed daily ambient noise cross-correlation traces, for all the available station pairs (61 stations in total) in the 2-20s period range. Daily cross-correlations were stacked and processed to extract Green’s functions. Subsequently, we performed frequency-time analysis to get group velocity dispersions for the fundamental mode of surface Rayleigh waves. We computed 2D surface group velocity maps at each period, which clearly show the slow sediment area of the Po Plain, and the fast IGB structure within the crust.

We are going to use the 2D group velocity maps to derive local dispersions curves and invert for 1D vS-depth profiles with the use of the Neighborhood Algorithm, to produce a 3D vS velocity model for the IVZ at high-resolution. This will also provide new geophysical constraints in the target area of the scientific drilling project DIVE (www.dive2ivrea.org) and reliable information for crustal corrections, which are necessary for upper mantle studies in such a complex area.

How to cite: Scarponi, M., Kvapil, J., Vecsey, L., Plomerová, J., Working Group, I., and Working Group, A.: Towards a high-resolution vS crustal velocity model for the Ivrea Geophysical Body: constraints from seismic ambient noise tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7333, https://doi.org/10.5194/egusphere-egu22-7333, 2022.

EGU22-7433 | Presentations | GD8.4

Thermo-kinematic evolution of the Eastern Alps along TRANSALP: Exploring the transient tectonic state towards slab reversal 

Paul Eizenhöfer, Christoph Glotzbach, Jonas Kley, and Todd Ehlers

The Eastern Alps are shaped by the indentation of Adria into Europe and exhibit a doubly-vergent lithospheric wedge geometry. Immediately after the subduction of the Penninic ocean, pro- and retro-wedges have been established in the European and Adriatic plates, respectively. Recent tomographic studies, depicting several detached slab fragments beneath the Alps, have been interpreted as evidence of continuous southward subduction, contrary to an often-invoked subduction polarity reversal. Systematic changes in orogen-scale exhumation, driven by rock displacement along active faults, should reflect such change in subduction polarity. Low temperature thermochronology can evaluate upper lithospheric cooling as a response to changes in tectonic and/or erosional boundary conditions. This study investigates whether a potential change in locations of the pro- and retro-wedges is reconcilable with observed crustal re-organisations, exhumation patterns and mantle tomography. A suite of thermo-kinematic forward models driven by a new 2D structural-kinematic reconstruction of continental collision along the TRANSALP profile in the Eastern Alps has been subject to systematic sensitivity analyses encompassing variations in shortening rates, thermophysical parameters and topographic evolution, supplemented by new apatite and zircon fission-track data. Results from the thermo-kinematic modelling reproduce: (i) the orogen-scale structural geometry, (ii) the distribution of low-temperature thermochronometer ages, (iii) independently determined time-temperature paths, and (vi) the present-day surface heat flux. We suggest that the observed thermochronologic record along the TRANSALP profile is primarily driven by cooling through rock displacement along active faults. Our thermo-kinematic reconstruction emphasises a systematic southward shift of deformation, in particular in the Southern Alps, since onset of motion along the Tauern Ramp. Interpreting both, the Tauern Ramp as a mega retro-thrust and the southward shift of deformation in the Southern Alps, as a response to new Coulomb-wedge criterions, then our results are consistent with a Mid-Miocene reversal of continental subduction polarity. This time frame is compatible with a detachment of the European slab and a tectonic re-organisation of the Eastern Alps since ~10-25 Ma.   

How to cite: Eizenhöfer, P., Glotzbach, C., Kley, J., and Ehlers, T.: Thermo-kinematic evolution of the Eastern Alps along TRANSALP: Exploring the transient tectonic state towards slab reversal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7433, https://doi.org/10.5194/egusphere-egu22-7433, 2022.

EGU22-7455 | Presentations | GD8.4

Anisotropy of the Bohemian Massif lower crust from ANT - VTI model or additional azimuthal variations? 

Jiří Kvapil, Jaroslava Plomerová, Hana Kampfová Exnerová, and the AlpArray Working Group

Transversely isotropic lower crust of the Bohemian Massif (BM) has been revealed by an ambient noise tomography (ANT) of the BM (Kvapil et al., Solid Earth 2021). The significant feature of this 3D vSV model is the low velocity layer in the lower part of the crust at depth between 18-30 km and the Moho. The upper interface is characterized by a velocity drop in the 1D velocity models retrieved by the ANT. The interface is interrupted around boundaries of major tectonic units of the BM. The lower interface (Moho) exhibits a sharp velocity increase at 26-40km depths through the massif.

In this work we test whether we are able to detect azimuthal anisotropy in the lower crust, approximated up to now by anisotropic VTI model. We use Rayleigh wave dispersion curves evaluated from station pairs sampling the BM in the period range sensitive to the lower crust. First, we analyze seasonal variations of noise sources and their effect on quality and repeatability of dispersion curve measurements. Then we remove the effect of local heterogeneities by subtraction of synthetic dispersion curves calculated for the 3D vSV model along each station-pair raypath. Retrieved variations of azimuthal anisotropy are period-dependent with the fast velocity directions around NE-SW. We interpret the lower crust anisotropy layer as an imprint of the Variscan orogenic processes such as the NW-SE shortening of the crust and the late-Variscan strike-slip movements along boundaries of the crustal unit recorded in the interruptions of velocity drop interface in zones where anisotropic fabric of the lower crust was modified or erased.

How to cite: Kvapil, J., Plomerová, J., Kampfová Exnerová, H., and Working Group, T. A.: Anisotropy of the Bohemian Massif lower crust from ANT - VTI model or additional azimuthal variations?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7455, https://doi.org/10.5194/egusphere-egu22-7455, 2022.

EGU22-7660 | Presentations | GD8.4

Identifying Seismic Anisotropy Patterns and Improving Tomographic Images in the Alps and Apennines Subduction Environments with Splitting Intensity 

Judith M. Confal, Silvia Pondrelli, Paola Baccheschi, Manuele Faccenda, Simone Salimbeni, and the AlpArray Working Group

Active and past subduction systems influence the interpretation and understanding of current tectonics and velocity structures of the upper mantle of the Alps and Apennines. Computational advances over the years made it possible to identify remnant and active slabs up to great depths. SKS splitting measurements revealed mostly clockwise rotation in the Alpine region and mostly splitting parameters parallel to the Apennines (with new measurements in Central Italy). More than 700 stations were used in this study to calculate splitting intensities and with those similar but more stable fast polarization directions were recovered compared to SKS measurements. Splitting intensity measurements support a possible mantle material flowing through a tear in the Central Apennines. In the Po Plain region as well as east of the Apennine mountains anisotropy seems to be weaker. Moreover the complexity of layered anisotropy, upper mantle flow through possible slab detachments, and subduction related anisotropy with a dipping axis of symmetry are difficult to recover. Due to directional dependency of splitting intensity measurements, they can be used in tomographic inversions to get depth dependent horizontal anisotropy. So far we are able to recover the most prominent splitting patterns and see some changes with depth, especially for anisotropic strength. In this study we intend to use our results to improve tomographic images of the upper mantle by mapping and comparing existing and new anisotropy measurements (e.g., SKS, Pn anisotropy, azimuthal anisotropy from surface waves tomography, and splitting intensities).

How to cite: Confal, J. M., Pondrelli, S., Baccheschi, P., Faccenda, M., Salimbeni, S., and AlpArray Working Group, T.: Identifying Seismic Anisotropy Patterns and Improving Tomographic Images in the Alps and Apennines Subduction Environments with Splitting Intensity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7660, https://doi.org/10.5194/egusphere-egu22-7660, 2022.

EGU22-7800 | Presentations | GD8.4

Towards a comprehensive High Resolution 3D P- and S-Wave Velocity Model for the Alpine Mountain Chain using Local Earthquake Data 

Benedikt Braszus, Andreas Rietbrock, and Christian Haberland

Seismic data availability and automated picking algorithms drastically improved in the European Alps since the last orogen wide crustal P-wave velocity model was compiled by Diehl et al. (2009). Especially, the abundant seismic data recorded by the AlpArray Seimic Network (AASN) which was in operation from 2015-2021 provides a unique high resolution seismic data set. The aim of our project therefore is to create a comprehensive 3D P- and S-wave crustal velocity model for the European Alpine region using Local Earthquake Tomography (LET). Such a model is not only needed to sharpen high resolution teleseismic tomography studies imaging subducted slabs but also to relate surface structures to mountain building processes in the mantle.
To achieve this aim precise onset times of seismic crustal phases are needed. Here we show our first results of automatic onset time determination obtained through the deep-neural-network PhaseNet. When compared to catalogues of manual travel time picks, we find its performance as accurate as a human analyst's. This confirms the transferability of machine learning approaches to our area and data set.
The large amount of evenly distributed seismic stations yields up to a total of 720 P and S arrival picks with epicentral distances up to 700km for events with ML > 3.5. Earthquakes with magnitudes of ML=2.5 are generally detectable for epicentral distances up to at least 200km and contribute approximately 200-300 arrivals per event.
As a first step towards a 3D model we present a thorough analysis of the consistency of the automatically determined arrival times, which facilitates a reliable removal of outliers. 
Furthermore, we show visualizations of our preliminary tomography model and its resolution.

How to cite: Braszus, B., Rietbrock, A., and Haberland, C.: Towards a comprehensive High Resolution 3D P- and S-Wave Velocity Model for the Alpine Mountain Chain using Local Earthquake Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7800, https://doi.org/10.5194/egusphere-egu22-7800, 2022.

EGU22-7892 | Presentations | GD8.4

Crustal and upper mantle 3D Vs structure of the Pannonian Region from joint earthquake and ambient noise Rayleigh wave tomography 

Máté Timkó, Amr El-Sharkawy, Lars Wiesenberg, László Fodor, Zoltán Wéber, Sergei Lebedev, and Thomas Meier and the AlpArray Working Group

The Pannonian basin is a continental back-arc basin in Central Europe, surrounded by the Alpine, Carpathian, and Dinaric mountain ranges. To better understand this area's tectonic affinity and evolution, a high-resolution model of the crust, the mantle lithosphere, and the asthenosphere is essential. The region's crustal structures are well documented, e.g., classical active seismic, receiver functions, and ambient noise surface wave studies, but consistent imaging of the entire lithosphere remains a challenge. Here we present a new high-resolution 3D shear wave velocity model of the crust and upper mantle of the broader Pannonian region using joint tomographic inversion of ambient noise and earthquake data.

For this purpose, we collected continuous waveform data from more than 1280 seismic stations for ambient noise cross-correlation measurements from a region centered to the Pannonian Basin and encompassing the rimming orogenic chains. This dataset embraces all the permanent and temporary stations operated in the time period from 2005 to 2018. We calculated Rayleigh wave ambient noise phase velocity dispersion curves using the phase of the noise cross-correlation functions of the vertical components in the period range from 5 to 80 s. Then we combined this dataset with existing measurements from earthquake data in the period range of 8-300 s.

At lower periods (< 50 s) and shorter interstation distances, there is a well-documented systematic discrepancy between the dispersion measurements collected by the two methods. The phase-velocity curves measured by the noise-based method are slower on average than the dispersion curves extracted by the earthquake-based method. A correction term is defined by comparing phase velocity curves from both data sets for the same station pairs. Phase velocity maps are then calculated from 5 s to 250 s periods using ambient noise and earthquake measurements.

Local dispersion curves extracted along each grid node of the 2D phase velocity maps are inverted for depth velocity models using a newly implemented Particle Swarm Optimization (PSO) algorithm to obtain the 3D distribution of the shear-wave velocities. The shear wave velocity structure reveals pronounced variations of the lithospheric thickness and physical properties related to deep tectonic mechanisms operated in the region.

How to cite: Timkó, M., El-Sharkawy, A., Wiesenberg, L., Fodor, L., Wéber, Z., Lebedev, S., and Meier, T. and the AlpArray Working Group: Crustal and upper mantle 3D Vs structure of the Pannonian Region from joint earthquake and ambient noise Rayleigh wave tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7892, https://doi.org/10.5194/egusphere-egu22-7892, 2022.

EGU22-7932 | Presentations | GD8.4

Seismic properties profiles of the alpine slab predicted by petrophysics versus ambient noise tomography lithospheric model 

Manon Sonnet, Loïc Labrousse, Jérôme Bascou, Alexis Plunder, Ahmed Nouibat, Laurent Stehly, and Anne Paul

The objective of the present study is to use potential lithologic analogues sampled in the European crust units exhumed in the Alps to predict the seismic properties of the buried continental crust panel. To this end, from the chemical compositions of representative rock samples, we calculate seismic velocities (Vp, Vs or Vp/Vs) at any P and T, under the assumption that the rocks have completely re-equilibrated during burial.

The sample catalog comprehend (1) the mafic intercalations, present in the Variscan basement series of the External Crystalline Massif; (2) the rocks involved in the Grand Paradis - Schistes Lustrés contact (metabasites and garnet bearing micaschists of the upper unit, mylonite and gneiss of the lower unit); (3) those along the Lanzo-Canavese contact (serpentinites, blue schist facies mylonites and biotite bearing gneiss); (4) lithologies of the Ivrea domain (peridotites, garnet bearing gabbros, textured mafic rocks, amphibolitic and mylonitic paragneiss), (5) those from the Gruf massif (biotite bearing orthogneiss, deformed leucogranites and charnockites from the Gruf complex and amphibolites and serpentinites from the Chiavenna unit); (6) lithologies from Alpine Corsica (pelitic gneisses of the granulite facies and more or less foliated metagabbros, from the San Petrone and Farinole unit).

In these diagrams, the main seismic contrasts appear to correspond to the early stages of jadeite crystallization (mainly in the Vp/Vs diagram), as well as to the boundaries of the garnet and clinopyroxene stability fields. Considering the selected rocks as relevant analogues, we then compare the evolution of seismic properties along the top of the Alpine dipping panel with profiles inferred from recent Vp and Vs tomography models (CIFALPS 1 and AlpARRAY), varying the effective thermal profile of the Alpine panel, its reaction degree and overall chemistry. Preliminary results suggest that the lower crust of the plunging panel has a seismic velocity too low to be eclogitized. Its velocity rates are closer to those of an underreacted quartzo-felspathic gneiss. At first sight, observed velocities are too low compared to values predicted for any lithology fully reacted during subduction. The best-fitting scenario turns out to be that of a lower crust thermally relaxed in the variscan without significant mineralogical footprint of subduction. If detected, the velocity rise due to eclogitization might offset of several tenth along the slab, implying a sensible impact of reaction kinetics.

How to cite: Sonnet, M., Labrousse, L., Bascou, J., Plunder, A., Nouibat, A., Stehly, L., and Paul, A.: Seismic properties profiles of the alpine slab predicted by petrophysics versus ambient noise tomography lithospheric model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7932, https://doi.org/10.5194/egusphere-egu22-7932, 2022.

EGU22-8102 | Presentations | GD8.4

3D anisotropic P-wave tomography of the Central Mediterranean: new insights into slab geometry and upper mantle flow patterns 

Francesco Rappisi, Brandon Paul VanderBeek, Manuele Faccenda, Andrea Morelli, and Irene Molinari

Characterized by the coexistence of different compressional and extensional phases associated with episodes of orogenesis, slab rollback, slab tearing and oceanic spreading, the Central Mediterranean represents one of the most interesting convergent margin on Earth. Since the late 1990s, several seismologists have studied this region aiming at imagining the isotropic and anisotropic structures below its surface. Although numerous researchers have demonstrated that performing P-wave tomography neglecting seismic anisotropy can introduce significant imaging artefacts, prior tomographic studies have largely assumed an isotropic Earth. Using the method proposed by VanderBeek & Faccenda (2021), here we discard the isotropic approximation and invert for both P-wave isotropic velocity anomalies and seismic anisotropy and present the first 3D anisotropic P-wave tomography of the upper mantle covering the entire Central Mediterranean. Our results show that inverting for seismic anisotropy strongly reduces the magnitude of the isotropic P-wave anomalies. This suggests that lateral variations in temperature and/or composition are smaller that what can be inferred from purely isotropic tomographies. P-wave fast azimuths orient mostly parallel to the trend of the Balcanic and the Alpine orogens in Eastern and Central Europe, respectively. In the Central Mediterranean the P-wave fast azimuths are sub-parallel to the Oligocene/Miocene-to-present retreating direction of the Ionian trench which led to the opening of the Liguro-Provençal and Thyrrenian basins and rotation of the Corsica-Sardinia block. We find that the pattern of the P-wave fast azimuths is largely consistent with the S-wave fast azimuths determined from the splitting of SKS waves and from Rayleigh waves. This poses further constraints on the interpretation of the regional geodynamic evolution and on the accuracy of the employed inverse method.

References:

VanderBeek, B. P., & Faccenda, M. 2021. Imaging upper mantle anisotropy with teleseismic P-wave delays: insights from tomographic reconstructions of subduction simulations. Geophysical Journal International,225(3), 2097–2119.

How to cite: Rappisi, F., VanderBeek, B. P., Faccenda, M., Morelli, A., and Molinari, I.: 3D anisotropic P-wave tomography of the Central Mediterranean: new insights into slab geometry and upper mantle flow patterns, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8102, https://doi.org/10.5194/egusphere-egu22-8102, 2022.

EGU22-8174 | Presentations | GD8.4

Moho depths beneath the European Alps from receiver functions of the AlpArray Seismic Network 

Konstantinos Michailos, Matteo Scarponi, Josip Stipčević, György Hetényi, Katrin Hannemann, Dániel Kalmár, Stefan Mroczek, Anne Paul,  Jaroslava Plomerová, Frederik Tilmann, Jerôme Vergne, and the AlpArray Receiver Function Research Group AlpArray Working Group

The European Alps, formed by the interactions between the European and Adriatic plates, is a unique geological structure that has been extensively studied over the past decades. Despite numerous active and passive seismic investigations in the past, the crustal structure across the whole Alpine domain is somehow limited - mainly due to the limited number of seismometers available. The deployment of the AlpArray Seismic Network provides, which consisted of around 600 broadband seismometers and was operational from early 2016 till mid-2019, offers a unique opportunity to further update the current knowledge of the crustal structure beneath the European Alps by employing Receiver function (RF) analysis. 

RF method can provide an efficient way to image the structures and the discontinuities within the uppermost part of the Earth. We use teleseismic earthquakes with M≥5.5 and M<8.5 and epicentral distances ranging between 30 and 90 degrees that occurred during the operational time of the AlpArray Seismic Network. We compute RFs using a time-domain iterative deconvolution method. We apply quality control steps to both the original three-component waveforms and the calculated RFs to ensure that we only use high-quality signals. 

As of abstract submission, we are in the process of calculating the RFs. We also intend to perform a time to depth migration, in a 3D spherical coordinate system, to the RFs. This methodology, together with unprecedented data coverage, will provide us with migrated profiles that will image the structure of the crust and map the Moho depths at a great level of detail. 

How to cite: Michailos, K., Scarponi, M., Stipčević, J., Hetényi, G., Hannemann, K., Kalmár, D., Mroczek, S., Paul, A., Plomerová,  ., Tilmann, F., Vergne, J., and AlpArray Working Group, T. A. R. F. R. G.: Moho depths beneath the European Alps from receiver functions of the AlpArray Seismic Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8174, https://doi.org/10.5194/egusphere-egu22-8174, 2022.

EGU22-8725 | Presentations | GD8.4

The DIVEnet: a local seismographic network monitoring the lower continental crust drillings for the ICDP-DIVE project 

Silvia Pondrelli, György Hetényi, Simone Salimbeni, Adriano Cavaliere, Stefania Danesi, Emanuela Ercolani, Irene Molinari, Carlo Giunchi, Konstantinos Michailos, Claudia Piromallo, Lucia Zaccarelli, Giovanna Cultrera, Rocco Cogliano, Gaetano Riccio, and Alberto Zanetti

The ICDP DIVE project (www.dive2ivrea.org) is aimed at addressing fundamental questions on the nature of the lower continental crust and its transition to the mantle, in a first phase through two drillings in the Ivrea Verbano zone (IVZ). The IVZ, considered the world's best outcrop of lower crustal continental rocks, is the exposed part of the Ivrea Geophysical Body (IGB), a major high gravity and high seismic velocity anomaly studied since the 1960s and strongly related to Western Alps structural and tectonic history. Beneath the IVZ the Moho possibly reaches very shallow depth (locally ~1±1 km b.s.l.), making this site unique all over the World.

The two proposed drillings will start in the 2022 in Val D’Ossola: the first in Ornavasso and the second in Megolo, 7 km apart from each other. The assemblage of the two will constitute the most complete record of lower continental crust. Physical and chemical data systematically collected downhole as well as along drill cores will be combined and compared with local/regional geophysical and geological surveys. Within this frame and scope, a dedicated seismographic network named DIVEnet has been planned to monitor local earthquakes and operation-related seismic activity.

Starting from summer 2021 the survey and seismic station deployment started to have all stations running by January 2022. So far 10 seismographic stations provided by INGV and University of Lausanne have been installed within a 15 km maximum distance from the mid-point between the two drilling sites and recording in continuous mode (100 sps). One of the seismometers will be housed in the first completed borehole while the second one is being drilled. Given that the area is characterized by low natural local seismicity and low seismic stations density, having a long time record of background activity and background noise, including the period before and after the drilling activities’ initiation, is of crucial importance. The acquisition and first elaboration of seismic data have been actively included in the routine work at INGV.

How to cite: Pondrelli, S., Hetényi, G., Salimbeni, S., Cavaliere, A., Danesi, S., Ercolani, E., Molinari, I., Giunchi, C., Michailos, K., Piromallo, C., Zaccarelli, L., Cultrera, G., Cogliano, R., Riccio, G., and Zanetti, A.: The DIVEnet: a local seismographic network monitoring the lower continental crust drillings for the ICDP-DIVE project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8725, https://doi.org/10.5194/egusphere-egu22-8725, 2022.

EGU22-8790 | Presentations | GD8.4

Establishing the eastern alpine-dinaric transition with teleseismic receiver functions: Evidence for subducted European Crust 

Stefan Mroczek, Frederik Tilmann, Jan Pleuger, Xiaohui Yuan, and Ben Heit and the SWATH-D and AlpArray Working Groups

The dense SWATH-D seismic network in the Central-Eastern Alps gives an unprecedented window into the collision of the Adriatic and European plates. We apply the receiver function method to the SWATH-D stations, covering approximately the area from 45-49°N and 10-15°E, supplemented by the AlpArray Seismic Network and the EASI data. A switch in the subduction polarity between the Central Alps (European subduction) and the Dinarides (Adriatic subduction) had been previously suggested to occur below the Eastern Alps but its location and nature are heavily debated. To probe this hypothesis we produce a high resolution Moho map of the Eastern Alps and derive Moho depths from joint analysis of receiver function images of direct conversions and multiple reflections, which enables us to map overlapping discontinuities. Contrary to the hypothesis suggesting the subduction of Adriatic lithosphere in the Eastern Alps, we observe the European Moho to be underlying the Adriatic Moho up to the eastern edge of the Tauern Window (~13.5°E). East of this longitude, a sharp transition from underthrusting European to a flat and thinned crust associated with Pannonian extension tectonics occurs, which is underthrust by both European crust in the north and by Adriatic crust in the south. The northeast-directed underthrusting of Adriatic lithosphere smoothly transitions to subduction below the northwestern Dinarides.

Teleseismic tomography and receiver functions show different aspects of the same system (velocity anomalies versus velocity gradients) making direct comparisons difficult. The common conversion point stacks and Moho picks show good agreement with the tomography however some key differences remain. In particular, teleseismic tomography indicates high velocity anomalies detached from the crust east of ~13°E while receiver functions, in particular the transverse component, show some evidence for connection with a continuous interface going to depth.

How to cite: Mroczek, S., Tilmann, F., Pleuger, J., Yuan, X., and Heit, B. and the SWATH-D and AlpArray Working Groups: Establishing the eastern alpine-dinaric transition with teleseismic receiver functions: Evidence for subducted European Crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8790, https://doi.org/10.5194/egusphere-egu22-8790, 2022.

EGU22-9206 | Presentations | GD8.4

Present-day upper mantle structure of the Alps: insights from data-driven dynamic modelling 

Ajay Kumar, Mauro Cacace, Magdalena Scheck-Wenderoth, Judith Bott, Hans-Jürgen Götze, and Boris Kaus

Present-day surface deformation in the Central Alps, that is, uplift and upper-crustal level seismicity in contrast to its northern and southern forelands, has been attributed to surface (i.e., climatic) and tectonic processes (i.e., subduction, slab detachment/break-off, mantle flow). Understanding the relative contribution of these processes is fundamental to understanding their coupling and role in mountain building. The present-day 3D architecture of the lithosphere (i.e., lateral variations of crustal layers and lithospheric mantle thickness) and asthenosphere (i.e., subducted slabs, attached or detached to the orogenic lithosphere) resulting from tectonic processes operating at geologic time scale serve as a boundary condition to test the contribution of surface processes. While the crustal structure in the Alps is well constrained by seismic and gravity data, the upper mantle (i.e., lithospheric mantle and asthenosphere) structure differs from that due to the diversity and subjective interpretation of seismic tomography models. We convert the results of regional shear-wave seismic tomography models to temperature models using the Gibbs-free energy minimization algorithm to define the base of the lithosphere and the position of slabs in the asthenosphere. Our results show that the shallow/attached slab in the Northern Apennines is a common feature in different tomography models, but there are differences in the Alps area. We statistically cluster tomography models into three end-members corresponding to the mean and 67% confidence intervals to address these differences objectively. These end-members represent scenarios ranging from shallow/attached slabs to almost no slabs in the Northern Apennines and Alps. The three end-member scenarios are then used as an input to model the topography and velocities by solving the buoyancy-forces driven instantaneous flow, subject to the first-order rheological structure of the lithosphere-asthenosphere system. Modelled topography and velocities are compared to the first-order patterns of observed topography and GPS derived vertical velocities to discern among the end-member scenarios. Our preliminary results suggest that the lithospheric slab subducting beneath the Northern Apennines should be connected to the overlying lithosphere, whereas it appears to be detached along most of the Alps. The sensitivity of results to the viscosity structure of the crust, lithosphere, and asthenosphere will be discussed.  

How to cite: Kumar, A., Cacace, M., Scheck-Wenderoth, M., Bott, J., Götze, H.-J., and Kaus, B.: Present-day upper mantle structure of the Alps: insights from data-driven dynamic modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9206, https://doi.org/10.5194/egusphere-egu22-9206, 2022.

EGU22-9314 | Presentations | GD8.4

The Saint-Ursanne earthquakes of 2000 revisited: Evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt 

Federica Lanza, Tobias Diehl, Nicholas Deichmann, Toni Kraft, Christophe Nussbaum, Senecio Schefer, and Stefan Wiemer

The interpretation of seismotectonic processes within the uppermost few kilometers of the Earth’s crust has proven challenging due to the often significant uncertainties in hypocenter locations and focal mechanisms of shallow seismicity. Here, we revisit the shallow seismic sequence of Saint-Ursanne of March and April 2000 and apply advanced seismological analyses to reduce these uncertainties. 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 is currently evaluated as a possible site for the development of a deep geothermal project. Template matching analysis for the period 2000-2021, including data from mini arrays installed in the region since 2014, suggests that the source of the 2000 sequence has not been persistently active ever since. Forward modelling of synthetic waveforms points to a very shallow source, between 0 and 1 km depth, and the focal mechanism analysis indicates a low-angle, NNW-dipping, thrust mechanism. These 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 Saint-Ursanne sequence. Together with two other more recent shallow thrust faulting earthquakes near Grenchen and Neuchâtel in the north-central portion of the Jura fold-and-thrust belt (FTB), these new findings provide new insights into the present-day seismotectonic processes of the Jura 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 trenspressive regime is confirmed by the ML4.1 Réclère earthquake of December 24. 2021, which occurred ~20 kilometres west of St. Ursanne in the uppermost crust.

How to cite: Lanza, F., Diehl, T., Deichmann, N., Kraft, T., Nussbaum, C., Schefer, S., and Wiemer, S.: The Saint-Ursanne earthquakes of 2000 revisited: Evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9314, https://doi.org/10.5194/egusphere-egu22-9314, 2022.

EGU22-9691 | Presentations | GD8.4

The three-dimensional stress field around the margins of the Adriatic Plate derived from source mechanisms 

Elisabeth Glück, Thomas Meier, and Josip Stipcevic

At present time, the formerly much larger Adriatic Microplate is still actively being subducted beneath the Apennines and the Dinarides-Hellenides zone with continental collision and related processes occurring under the Alps and the Dinarides. These tectonic processes along with the large-scale component of the northward moving African Plate resulted in a complex 3D stress field.

In the light of the complex tectonic processes accompanying the movement of the Adriatic Plate, we aim to investigate the three-dimensional stress field in that area by stress inversion using focal mechanism data from the available CMT and RCMT earthquake catalogues. The focal mechanisms are inverted to better understand the stress regime in that region and how the stress pattern is depending on the current tectonic setting. A staggered grid algorithm was used for binning the focal mechanisms before the inversion.

The calculated 3D stress field indicates that the direction of the large-scale convergence of Africa and Eurasia is similar to the dominating direction of the maximum horizontal stress axis in the western central Mediterranean, with the exception of the Apennines, where the subduction of the Adriatic Plate beneath the northern Apennines is the primary source of stress. On the eastern margin of the Adriatic Plate the lack of deeper seismicity and a back arc basin, as well as the orogen normal orientation of the maximum horizontal stress axis in the Dinarides is pointing towards a continental subduction zone with an aseismic delaminating slab of lower lithosphere without a significant slab pull component.
Changes of the stress pattern within the Adriatic Plate may result from intraplate deformation, which points towards a fragmentation of Adria along the Mid Adriatic Ridge into two subplates, Adria Sensu Strictu in the north and Apulia in the south. While Adria Sensu Strictu is moving independently from Africa, Apulia is depending on the larger plates movement.
The inversion of the focal mechanisms from the Hellenic Subduction Zone yields results about the rotation of the stress field with depth, as the maximum horizontal stress rotates from trench normal at shallow depths to trench parallel deeper down.

How to cite: Glück, E., Meier, T., and Stipcevic, J.: The three-dimensional stress field around the margins of the Adriatic Plate derived from source mechanisms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9691, https://doi.org/10.5194/egusphere-egu22-9691, 2022.

EGU22-11256 | Presentations | GD8.4

Revisiting moment tensors in Switzerland: Unraveling source characteristics in Central Alps and their foreland 

Maria Mesimeri, Tobias Diehl, John Clinton, Marco Herwegh, and Stefan Wiemer

Studies on moment tensors (MT) and focal mechanisms are of great importance for assessing regional and local seismotectonic processes, especially when a high-quality, dense network is in operation. However, common MT inversion methods are largely restricted to magnitudes > 3.5. In order to lower the completeness of MT catalogs, improved Green’s functions and/or hybrid inversion techniques are needed. In this study, we revisit small-to-moderate earthquakes, which occurred in Switzerland and surrounding regions by means of various MT inversion methods and assess the potential to improve completeness of MT catalogs in Central Alps region. To accomplish this, we implement state-of the art methods for MT inversion using either full waveform data or combinations of first-motion polarities with amplitudes and amplitude ratios. Methods based on full waveform inversion considered in this study are ISOLA (Sokos & Zahradnik 2013) and Grond (Heimann et al. 2018), as well as techniques based on amplitudes and/or polarities (HybridMT (Kwiatek et al. 2016), MTfit (Pugh & White 2018)), which can solve MTs for smaller magnitude earthquakes. Hence, the combination of multiple techniques allows to compute full or deviatoric MTs for a broader range of magnitudes and enrich the existing catalogs.

We first apply these methods to recent earthquake sequences occurred in the Central Alps between 2019 and 2021. During that period, several earthquake sequences, like the one associated with the 2021 M4.1 Arolla earthquake, occurred and show complexity on the waveforms, due to their shallow focal depths. In addition, several of the standard MT solutions calculated by the Swiss Seismological Service (SED) for these earthquakes indicate complex moment tensors with unusually high percentage of the CLVD component. To check whether such CLVD component is real and not an artifact caused, for instance, by unmodeled heterogeneities, we invert for full and deviatoric MTs using multiple 1D velocity models and algorithms. Additionally, we perform MT inversions for several earthquakes either within selected earthquake sequences or regional background seismicity. The resulting MT solutions are compared to existing high-quality focal mechanisms computed using first motion polarities as well as to high-precision double difference locations. Uncertainties of MT solutions are estimated using bootstrap-based methods. This work contributes towards an enriched high-quality focal mechanisms database for Switzerland, which could be used to revisit the regional to local stress field at unprecedented resolution and provides new insights into the complexities of active fault systems in the Central Alps region.

References:

Heimann, S., Isken, M., Kühnn, D., Sudhaus, H., Steinberg, A., Vasyura-Bathke, H., Daout, S., et al. (2018) Grond - A probabilistic earthquake source inversion framework., GFZ Data Services. doi:10.5880/GFZ.2.1.2018.003

Kwiatek, G., Martínez-Garzón, P. & Bohnhoff, M. (2016) HybridMT: A MATLAB/Shell Environment Package for Seismic Moment Tensor Inversion and Refinement. Seismol. Res. Lett., 87, 964–976. doi:10.1785/0220150251

Pugh, D.J. & White, R.S. (2018) MTfit: A Bayesian Approach to Seismic Moment Tensor Inversion. Seismol. Res. Lett., 89, 1507–1513. doi:10.1785/0220170273

Sokos, E.N. & Zahradnik, J. (2013) Evaluating Centroid-Moment-Tensor Uncertainty in the New Version of ISOLA Software. Seismol. Res. Lett., 84, 656–665. doi:10.1785/0220130002

How to cite: Mesimeri, M., Diehl, T., Clinton, J., Herwegh, M., and Wiemer, S.: Revisiting moment tensors in Switzerland: Unraveling source characteristics in Central Alps and their foreland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11256, https://doi.org/10.5194/egusphere-egu22-11256, 2022.

EGU22-11266 | Presentations | GD8.4

Internal deformation of the Dolomites Indenter, eastern Southern Alps: structural field data and low-temperature thermochronology 

Thomas Klotz, Hannah Pomella, Anna-Katharina Sieberer, Hugo Ortner, and István Dunkl

The Dolomites Indenter represents the front of the Neogene to ongoing N(W)-directed continental indentation of Adria into Europe. Deformation of the Dolomites Indenter is well studied along its rim, documented by important fault zones such as the Periadriatic fault system, the Giudicarie belt, and the Valsugana and Montello fault systems. With this study, we aim to investigate the internal deformation of the Dolomites Indenter, which has been much less studied so far but is important for understanding crustal-scale processes during the Alpine orogeny.

 

Our approach to unravel the indenters exhumation and deformation history comprises (i) the compilation and acquisition of detailed structural and sedimentological field data within the Dolomites Indenter, (ii) a collection of a new and comprehensive low-temperature thermochronological dataset (this contribution), and (iii) crustal- to lithospheric-scale physical analogue modelling experiments (see contribution of Sieberer et al. in session TS7.2 – Internal deformation of the Dolomites Indenter, eastern Southern Alps: Orthogonal to oblique basin inversion investigated in crustal scale analogue models).

 

New field data comprise evidence for four distinguishable shortening directions. Examined intersection criteria along N-S cross sections covering the indenters extend from Periadriatic to Bassano fault system support a succession of Top SW, Top (S)SE, Top S and Top E(SE) movement. However, preexisting geometry strongly seems to affect the regional expression of respective compression phases and along strike variation of lineation trends can be observed within coherent fault systems.

 

The limited amount of existing thermochronological data already indicates the presence of relative vertical displacements within the Dolomites Indenter after the onset of indentation, including mostly Miocene apatite fission track (AFT) cooling ages along the Periadriatic and the Valsugana fault and several age clusters of Triassic to Jurassic AFT data. In order to obtain a detailed picture of the indenters thermotectonic evolution, an extensive set of samples has been collected along three roughly N-S striking corridors between Bolzano in the west and Tolmezzo in the east. In this contribution we present the new apatite (U-Th)/He and fission track data along the westernmost corridor (Mauls - Brixen - Valsugana - Schio).

 

The results of field work, comprehensive modelling of time temperature paths, and physical analogue modelling substantially contribute to the understanding of internal deformation and thus enable conclusions to be drawn about the processes at lithospheric scale.

How to cite: Klotz, T., Pomella, H., Sieberer, A.-K., Ortner, H., and Dunkl, I.: Internal deformation of the Dolomites Indenter, eastern Southern Alps: structural field data and low-temperature thermochronology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11266, https://doi.org/10.5194/egusphere-egu22-11266, 2022.

EGU22-11358 | Presentations | GD8.4

Distribution of Active Seismic Deformation in the Eastern Alps from the Recent Swath-D Experiment 

Rens Hofman, Joern Kummerow, Simone Cesca, Joachim Wassermann, and Thomas Plenefisch and the AlpArray Working Group

The Swath-D network was a temporary seismic experiment nested within the AlpArray backbone network. Roughly 150 broadband stations were deployed across the Austrian-Italian border in the Eastern Alps during the second half of 2017, and were active to late 2019. This dense network provided an unprecedented resolution in a tectonically active region that is considered to play an important role in the evolution of the Alps. Extracting new information from this dataset turned out to be challenging due to the large volume of the dataset, low magnitude of the seismicity, and heterogeneity of the study area.

We applied waveform-based methods to detect, phase-pick, and relocate seismic events using data from the Swath-D network in the Eastern Alps. A GPU-accelerated template matching algorithm was developed in order to increase the number of detected earthquakes based on the previously known seismicity. Newly detected events were automatically picked using based on waveform similarity, and precisely relocated. This poster provides an overview of our results and the methods that we have applied.

How to cite: Hofman, R., Kummerow, J., Cesca, S., Wassermann, J., and Plenefisch, T. and the AlpArray Working Group: Distribution of Active Seismic Deformation in the Eastern Alps from the Recent Swath-D Experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11358, https://doi.org/10.5194/egusphere-egu22-11358, 2022.

EGU22-12266 | Presentations | GD8.4

SEismic imaging of the Ivrea ZonE (project SEIZE) reveals the 3D structure of the Ivrea body near Balmuccia, Italy 

Britta Wawerzinek, Trond Ryberg, Klaus Bauer, Manfred Stiller, Christian Haberland, Alberto Zanetti, Luca Ziberna, György Hetényi, Michael Weber, and Charlotte M. Krawczyk

The Ivrea-Verbano Zone (IVZ) located in the Italian Alps is known as one of most complete archetypes of continental crust–upper mantle section on Earth (e.g. Pistone et al., 2017). Because of its accessibility at the surface it can be used as natural laboratory to improve the understanding of the crust–mantle transition zone. Several geophysical observables indicate the presence of mantle rocks (high density, high seismic velocity) in the shallow sub-surface (~ 1 km), commonly known as the “Bird’s Head” or Ivrea body (Berckhemer, 1968; Diehl et al., 2009; Scarponi et al., 2021). 

The project SEIZE images and characterizes the shallow upper crust at the Balmuccia site (Italy) providing depth, extent and shape of the outcropping Ivrea body as well as its rock properties. Our tomographic study covers the crust down to about 3 km depth, while seismic reflection imaging is possible down to 6 km depth or deeper. With SEIZE we contribute to the comprehensive ICDP Drilling program in the Ivrea-Verbano ZonE (DIVE, www.dive2ivrea.org).

To tackle this task, a controlled source (vibroseis) seismic experiment was carried out in the region around Balmuccia in October 2020. The seismic survey comprised two crossing profiles with a total length of 28 km which ran along (NNE-SSW) and across (W-E) the Balmuccia peridotite. In total, 432 vibro points were acquired with a nominal distance of ~60 m which were recorded using a fix-spread (110 receivers, ~250 m spacing) and a roll-along setup (330 receivers, ~20 m spacing).

To obtain a structural image of the shallow upper crust various seismic techniques are applied: The fix-spread data set is used to recover the velocity structure down to 3 km depth. By using a 3D Markov chain Monte Carlo travel time tomography a shallow, distinct high velocity body is imaged in 3D near Balmuccia, at the proposed drill site. Reflection seismic processing is applied to the roll-along data set. However, the difficult terrain setting (deep mountain valleys) results in complex wave propagation that is challenging for conventional processing methods (e.g. static and dynamic corrections, CDP stacking). Therefore, pre-stack migration techniques are applied enabling the imaging of steeply dipping structures.

How to cite: Wawerzinek, B., Ryberg, T., Bauer, K., Stiller, M., Haberland, C., Zanetti, A., Ziberna, L., Hetényi, G., Weber, M., and Krawczyk, C. M.: SEismic imaging of the Ivrea ZonE (project SEIZE) reveals the 3D structure of the Ivrea body near Balmuccia, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12266, https://doi.org/10.5194/egusphere-egu22-12266, 2022.

EGU22-12668 | Presentations | GD8.4

Inside the fault core in the footwall of Simplon Fault Zone (Central Alps): ductile to brittle deformation history shown by fault gouge 

Valentina Argante, David Colin Tanner, Christian Brandes, Christoph Von Hagke, and Sumiko Tsukamoto

For thorough understanding of the dynamics of mountain building processes, it is crucial to reconstruct the youngest crustal deformation history over time. Low-angle normal faults are features caused by orogen-parallel extension, which occurs in the last stage of collision. Low-angle normal faults play a key role in the exhumation of the lower crust and they are the reason for most of the seismicity within the chain.

We carried out microstructural analyses on an outcrop in the footwall of one of the major normal faults of the Alpine chain, the Simplon Fault Zone. This low-angle normal fault extended the crust by tens kilometers and it caused exhumation of its footwall, the deeper lower crust of the Alps, i.e. the Penninic nappes. The Simplon Fault Zone itself consists of a thick mylonitic zone overprinted by a narrow cataclastic zone, with the same kinematics. Its timing evolution history from ductile to brittle deformation is still under discussion. This study shows a new microstructural analysis from a fault gouge within the footwall of the northern part of the Simplon Fault Zone, and how it can reconstruct the different stages of exhumation history of this shear zone.

Results from micro-structural analyses show grain boundary migration features on folded quartz veins. This suggests that the protolith of the fault zone was at high temperature conditions, T>600°C, during dynamic deformation. This folding belongs to extension-parallel folds that affect only the ductile shear zone. The presence of greenschist facies minerals suggests that the rock was exposed to low temperature and pressure conditions (T=300-400°C, P=0.2GPa). Pressure-solution mechanisms affect both quartz and greenschist paragenesis, indicating formation in a shallow position of the shear zone. The last deformation was purely brittle, as shown by vertical calcite veins or fractures in quartz. It suggests a near-surface position of the fault.

Altogether, these multiple deformation phases within the gouge samples indicate a continuous exhumation history from high to low temperatures, with clear cross-cutting relationships. However, the lack of cataclasite features can be related to an involvement of the rocks within the fault core in a subsequent stage of deformation. To explain this we suggest a model in which the footwall maintained a high temperature over a long time, which inhibited cataclastic processes.

How to cite: Argante, V., Tanner, D. C., Brandes, C., Von Hagke, C., and Tsukamoto, S.: Inside the fault core in the footwall of Simplon Fault Zone (Central Alps): ductile to brittle deformation history shown by fault gouge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12668, https://doi.org/10.5194/egusphere-egu22-12668, 2022.

EGU22-13245 | Presentations | GD8.4

3D geophysical and thermal modelling of the northeast Carpathian lithosphere: Implications for geothermal potential of the Baia Mare region 

Alexander Minakov, Carmen Gaina, Liviu Matenco, Maik Neukirch, and Ionelia Panea

The presented study is part of an international multidisciplinary project aiming to investigate the geothermal potential of the Baia Mare volcanic province in north-western Romania. We integrate existing geological, geochemical, hydrogeological, and geophysical data into a 3D lithospheric temperature model. In addition, new seismic reflection and broadband magnetotelluric data, acquired in the study region, provide additional constraints on the crustal-scale structures possibly controlling the transport of deep heat to the surface.

The study area is located within the Neogene Inner Carpathian volcanic arc and includes the area of the recent crustal uplift between the north-eastern part of the Pannonian Basin and the Transylvanian Basin. Borehole temperature measurements showed a geothermal gradient of 45-55 oC km-1 and temperatures higher than 150 oC at depths of 3000 m, the highest values of heat flow recorded to date in Romania. The region is known for surface hot springs and hydrothermal and epithermal volcanic ore deposits.

The heterogeneous pre-Neogene basement contains metamorphic and igneous rocks deformed or emplaced during Precambrian to Paleozoic orogenic cycles and a Triassic-Paleogene sedimentary cover with a variable radioactive heat production rate. The Miocene magmatic plumbing system within the Neogene sedimentary sequence includes intrusive bodies of 1-10s of km size. Crustal hydraulic properties and associated hydrothermal systems are possibly controlled by the regional Bogdan Voda – Dragos Voda strike-slip faults system, which provided pathways for the Miocene volcanic emplacement and sub-volcanic intrusions.

The knowledge of deep lithospheric structure is important for the characterisation of sedimentary basins with a geothermal exploration potential. In this contribution, we present geophysical and geological data and describe the construction of a regional 3D lithospheric temperature model. The structural model includes sedimentary successions, crystalline crustal layers and lithosphere-asthenosphere boundary constrained by gravity, seismic tomography and magnetotelluric data. The temperature modelling is performed by solving 3-D steady state heat conduction equation using a finite element method. We compare the model responses with available surface heat flow and borehole temperature measurements and discuss the role of local crustal heterogeneities, transient heat transfer and fluid circulation on the thermal state of the Baia Mare region.

How to cite: Minakov, A., Gaina, C., Matenco, L., Neukirch, M., and Panea, I.: 3D geophysical and thermal modelling of the northeast Carpathian lithosphere: Implications for geothermal potential of the Baia Mare region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13245, https://doi.org/10.5194/egusphere-egu22-13245, 2022.

Wholesale slab breakoff or detachment in the Alps has been invoked to explain Periadriatic
calc-alkaline magmatism (43-29 Ma), rapid exhumation of HP metamorphics, as well as
clastic infill of proximal parts of the Alpine Molasse basin (31-28 Ma). However, the 14 My
timespan of these events exceeds the duration of slab detachment estimated from
thermomechanical modelling (2-8 My) and from depocenter migration (~5 My) along
equivalent lengths of the Carpathians and Apennines. Moreover, wholesale slab
detachment does not explain major E-W differences in Alpine orogenic structure, basin
evolution, and kinematics of indentation in the Alps.
Recent V p tomography from AlpArray suggests that the slab segment beneath the
Central Alps comprises European lithosphere and remains attached down to the MTZ. The
~600km length of this segment suggests that it never ruptured and is still connected to
subducted lithosphere of Alpine Tethys. In contrast, the Alpine slab is detached beneath the
Eastern Alps and Pannonian Basin. The minimum time since detachment is bracketed at 25-
10 Ma based on a comparison of vertical detachment distance with global slab sink rates.
We propose a new model of slab detachment in the Alps that began with slab
steepening when the Adria-Europe convergence rate after collision at ~35 ma decreased to
<1 cm/yr. Periadriatic magmatism is no longer attributed to slab detachment and
asthenospheric upwelling, but to fluxing of the cold mantle wedge by fluids derived from
the devolatilizing Alpine slab (Müntener et al. 2021; doi: 10.2138/gselements.17.1.35). Slab
steepening and delamination were more pronounced in the Eastern Alps, possibly due to
the greater negative buoyancy of the slab in the absence of Brianconnais continental
lithosphere, which was never present in the eastern part of Alpine Tethys. Slab pull thus
drove subsidence and continued marine sedimentation in the E. Molasse basin from 29-19
Ma, while the western part of the basin filled with terrigeneous sediments already at 31-28
Ma.
Slab detachment was restricted to the part of the Alps east of the Giudicarie Fault in
Miocene time. Detachment coincided with a switch in the advancing orogenic front, from
the northern front in the Eastern Alps to the southern front in the eastern Southern Alps.
This also coincided with rapid exhumation in the Tauern Window and lateral eastward
escape of the orogenic crust toward the Pannonian Basin. Rapid W-to-E filling of the Eastern
Molasse basin between 19-16 Ma is interpreted to reflect eastward propagation of the slab
tear and the onset of rollback subduction in the Carpathians.
E-W differences in Alpine structure are thus attributed to the contrasting response of
the Alpine orogenic wedge to slab steepening, delamination and detachment. Whereas
steepening and delamination in the west in late Oligocene time induced horizontal
shortening and increased taper of the orogenic wedge with rapid exhumation and
denudation focused in the retro-wedge, Miocene detachment in the east triggered a
dramatic switch in the pro- and retro-wedges, such that rapid exhumation and denudation
was ultimately focused in the axis of the orogenic wedge.

How to cite: Handy, M. R.: A new model of slab detachment in the Alps and its geodynamic consequences, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13517, https://doi.org/10.5194/egusphere-egu22-13517, 2022.

EGU22-2024 | Presentations | ITS3.1/SSS1.2 | Highlight

Understanding natural hazards in a changing landscape: A citizen science approach in Kigezi highlands, southwestern Uganda 

Violet Kanyiginya, Ronald Twongyirwe, Grace Kagoro, David Mubiru, Matthieu Kervyn, and Olivier Dewitte

The Kigezi highlands, southwestern Uganda, is a mountainous tropical region with a high population density, intense rainfall, alternating wet and dry seasons and high weathering rates. As a result, the region is regularly affected by multiple natural hazards such as landslides, floods, heavy storms, and earthquakes. In addition, deforestation and land use changes are assumed to have an influence on the patterns of natural hazards and their impacts in the region. Landscape characteristics and dynamics controlling the occurrence and the spatio-temporal distribution of natural hazards in the region remain poorly understood. In this study, citizen science has been employed to document and understand the spatial and temporal occurrence of natural hazards that affect the Kigezi highlands in relation to the multi-decadal landscape change of the region. We present the methodological research framework involving three categories of participatory citizen scientists. First, a network of 15 geo-observers (i.e., citizens of local communities distributed across representative landscapes of the study area) was established in December 2019. The geo-observers were trained at using smartphones to collect information (processes and impacts) on eight different natural hazards occurring across their parishes. In a second phase, eight river watchers were selected at watershed level to monitor the stream flow characteristics. These watchers record stream water levels once daily and make flood observations. In both categories, validation and quality checks are done on the collected data for further analysis. Combining with high resolution rainfall monitoring using rain gauges installed in the watersheds, the data are expected to characterize catchment response to flash floods. Lastly, to reconstruct the historical landscape change and natural hazards occurrences in the region, 96 elderly citizens (>70 years of age) were engaged through interviews and focus group discussions to give an account of the evolution of their landscape over the past 60 years. We constructed a historical timeline for the region to complement the participatory mapping and in-depth interviews with the elderly citizens. During the first 24 months of the project, 240 natural hazard events with accurate timing information have been reported by the geo-observers. Conversion from natural tree species to exotic species, increased cultivation of hillslopes, road construction and abandonment of terraces and fallowing practices have accelerated natural hazards especially flash floods and landslides in the region. Complementing with the region’s historical photos of 1954 and satellite images, major landscape dynamics have been detected. The ongoing data collection involving detailed ground-based observations with citizens shows a promising trend in the generation of new knowledge about natural hazards in the region.

How to cite: Kanyiginya, V., Twongyirwe, R., Kagoro, G., Mubiru, D., Kervyn, M., and Dewitte, O.: Understanding natural hazards in a changing landscape: A citizen science approach in Kigezi highlands, southwestern Uganda, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2024, https://doi.org/10.5194/egusphere-egu22-2024, 2022.

EGU22-2929 | Presentations | ITS3.1/SSS1.2

Possible Contributions of Citizen Science in the Development of the Next Generation of City Climate Services 

Peter Dietrich, Uta Ködel, Sophia Schütze, Felix Schmidt, Fabian Schütze, Aletta Bonn, Thora Herrmann, and Claudia Schütze

Human life in cities is already affected by climate change. The effects will become even more pronounced in the coming years and decades. Next-generation of city climate services is necessary for adapting infrastructures and the management of services of cities to climate change. These services are based on advanced weather forecast models and the access to diverse data. It is essential to keep in mind that each citizen is a unique individual with their own peculiarities, preferences, and behaviors. The base for our approach is the individual specific exposure, which considers that people perceive the same conditions differently in terms of their well-being. Individual specific exposure can be defined as the sum of all environmental conditions that affect humans during a given period of time, in a specific location, and in a specific context. Thereby, measurable abiotic parameters such as temperature, humidity, wind speed, pollution and noise are used to characterize the environmental conditions. Additional information regarding green spaces, trees, parks, kinds of streets and buildings, as well as available infrastructures are included in the context. The recording and forecasting of environmental parameters while taking into account the context, as well as the presentation of this information in easy-to-understand and easy-to-use maps, are critical for influencing human behavior and implementing appropriate climate change adaptation measures.

We will adopt this approach within the frame of the recently started, EU-funded CityCLIM project. We aim to develop and implement approaches which will explore the potential of citizen science in terms of current and historical data collecting, data quality assessment and evaluation of data products.  In addition, our approach will also provide strategies for individual climate data use, and the derivation and evaluation of climate change adaptation actions in cities.

In a first step we need to define and to characterize the different potential stakeholder groups involved in citizen science data collection. Citizen science offers approaches that consider citizens as both  organized target groups (e.g., engaged companies, schools) and individual persons (e.g. hobby scientists). An important point to be investigated is the motivation of citizen science stakehoder groups to sustainably collect data and make it available to science and reward them accordingly. For that purpose, strategic tools, such as value proposition canvas analysis, will be applied to taylor the science-to-business and the science-to-customer communications and offers in terms of the individual needs.

How to cite: Dietrich, P., Ködel, U., Schütze, S., Schmidt, F., Schütze, F., Bonn, A., Herrmann, T., and Schütze, C.: Possible Contributions of Citizen Science in the Development of the Next Generation of City Climate Services, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2929, https://doi.org/10.5194/egusphere-egu22-2929, 2022.

EGU22-4168 | Presentations | ITS3.1/SSS1.2

Extending Rapid Image Classification with the Picture Pile Platform for Citizen Science 

Tobias Sturn, Linda See, Steffen Fritz, Santosh Karanam, and Ian McCallum

Picture Pile is a flexible web-based and mobile application for ingesting imagery from satellites, orthophotos, unmanned aerial vehicles and/or geotagged photographs for rapid classification by volunteers. Since 2014, there have been 16 different crowdsourcing campaigns run with Picture Pile, which has involved more than 4000 volunteers who have classified around 11.5 million images. Picture Pile is based on a simple mechanic in which users view an image and then answer a question, e.g., do you see oil palm, with a simple yes, no or maybe answer by swiping the image to the right, left or downwards, respectively. More recently, Picture Pile has been modified to classify data into categories (e.g., crop types) as well as continuous variables (e.g., degree of wealth) so that additional types of data can be collected.

The Picture Pile campaigns have covered a range of domains from classification of deforestation to building damage to different types of land cover, with crop type identification as the latest ongoing campaign through the Earth Challenge network. Hence, Picture Pile can be used for many different types of applications that need image classifications, e.g., as reference data for training remote sensing algorithms, validation of remotely sensed products or training data of computer vision algorithms. Picture Pile also has potential for monitoring some of the indicators of the United Nations Sustainable Development Goals (SDGs). The Picture Pile Platform is the next generation of the Picture Pile application, which will allow any user to create their own ‘piles’ of imagery and run their own campaigns using the system. In addition to providing an overview of Picture Pile, including some examples of relevance to SDG monitoring, this presentation will provide an overview of the current status of the Picture Pile Platform along with the data sharing model, the machine learning component and the vision for how the platform will function operationally to aid environmental monitoring.

How to cite: Sturn, T., See, L., Fritz, S., Karanam, S., and McCallum, I.: Extending Rapid Image Classification with the Picture Pile Platform for Citizen Science, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4168, https://doi.org/10.5194/egusphere-egu22-4168, 2022.

EGU22-5094 | Presentations | ITS3.1/SSS1.2

Life in undies – Preliminary results of a citizen science data collection targeting soil health assessement in Hungary 

Mátyás Árvai, Péter László, Tünde Takáts, Zsófia Adrienn Kovács, Kata Takács, János Mészaros, and László Pásztor

Last year, the Institute for Soil Sciences, Centre for Agricultural Research launched Hungary's first citizen science project with the aim to obtain information on the biological activity of soils using a simple estimation procedure. With the help of social media, the reactions on the call for applications were received from nearly 2000 locations. 

In the Hungarian version of the international Soil your Undies programme, standardized cotton underwear was posted to the participants with a step-by-step tutorial, who buried their underwear for about 60 days, from mid of May until July in 2021, at a depth of about 20-25 cm. After the excavation, the participants took one digital image of the underwear and recorded the geographical coordinates, which were  uploaded to a GoogleForms interface together with several basic information related to the location and the user (type of cultivation, demographic data etc.).

By analysing digital photos of the excavated undies made by volunteers, we obtained information on the level to which cotton material had decomposed in certain areas and under different types of cultivation. Around 40% of the participants buried the underwear in garden, 21% in grassland, 15% in orchard, 12% in arable land, 5% in vineyard and 4% in forest (for 3% no landuse data was provided).

The images were first processed using Fococlipping and Photoroom softwares for background removing and then percentage of cotton material remaining was estimated based on the pixels by using R Studio ‘raster package’.

The countrywide collected biological activity data from nearly 1200 sites were statistically evaluated by spatially aggregating the data both for physiographical and administrative units. The results have been published on various platforms (Facebook, Instagram, specific web site etc.), and a feedback is also given directly to the volunteers.

According to the experiments the first citizen science programme proved to be successful. 

 

Acknowledgment: Our research was supported by the Hungarian National Research, Development and Innovation Office (NKFIH; K-131820)

Keywords: citizen science; soil life; soil health; biological activity; soil properties

How to cite: Árvai, M., László, P., Takáts, T., Kovács, Z. A., Takács, K., Mészaros, J., and Pásztor, L.: Life in undies – Preliminary results of a citizen science data collection targeting soil health assessement in Hungary, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5094, https://doi.org/10.5194/egusphere-egu22-5094, 2022.

EGU22-5147 | Presentations | ITS3.1/SSS1.2

Distributed databases for citizen science 

Julien Malard-Adam, Joel Harms, and Wietske Medema

Citizen science is often heavily dependent on software tools that allow members of the general population to collect, view and submit environmental data to a common database. While several such software platforms exist, these often require expert knowledge to set up and maintain, and server and data hosting costs can become quite costly in the long term, especially if a project is successful in attracting many users and data submissions. In the context of time-limited project funding, these limitations can pose serious obstacles to the long-term sustainability of citizen science projects as well as their ownership by the community.

One the other hand, distributed database systems (such as Qri and Constellation) dispense with the need for a centralised server and instead rely on the devices (smartphone or computer) of the users themselves to store and transmit community-generated data. This new approach leads to the counterintuitive result that distributed systems, contrarily to centralised ones, become more robust and offer better availability and response times as the size of the user pool grows. In addition, since data is stored by users’ own devices, distributed systems offer interesting potential for strengthening communities’ ownership over their own environmental data (data sovereignty). This presentation will discuss the potential of distributed database systems to address the current technological limitations of centralised systems for open data and citizen science-led data collection efforts and will give examples of use cases with currently available distributed database software platforms.

How to cite: Malard-Adam, J., Harms, J., and Medema, W.: Distributed databases for citizen science, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5147, https://doi.org/10.5194/egusphere-egu22-5147, 2022.

EGU22-5571 | Presentations | ITS3.1/SSS1.2

RESECAN: citizen-driven seismology on an active volcano (Cumbre Vieja, La Palma Island, Canaries) 

Rubén García-Hernández, José Barrancos, Luca D'Auria, Vidal Domínguez, Arturo Montalvo, and Nemesio Pérez

During the last decades, countless seismic sensors have been deployed throughout the planet by different countries and institutions. In recent years, it has been possible to manufacture low-cost MEMS accelerometers thanks to nanotechnology and large-scale development. These devices can be easily configured and accurately synchronized by GPS. Customizable microcontrollers like Arduino or RaspBerryPI can be used to develop low-cost seismic stations capable of local data storage and real-time data transfer. Such stations have a sufficient signal quality to be used for complementing conventional seismic networks.

In recent years Instituto Volcanológico de Canarias (INVOLCAN) has developed a proprietary low-cost seismic station to implement the Canary Islands School Seismic Network (Red Sísmica Escolar Canaria - RESECAN) with multiple objectives:

  • supporting the teaching of geosciences.
  • promoting the scientific vocation.
  • strengthening the resilience of the local communities by improving awareness toward volcanism and the associated hazards.
  • Densifying the existing seismic networks.

On Sept. 19th 2021, a volcanic eruption started on the Cumbre Vieja volcano in La Palma. The eruption was proceeded and accompanied by thousands of earthquakes, many of them felt with intensities up to V MCS. Exploiting the attention drawn by the eruption, INVOLCAN started the deployment of low-cost seismic stations in La Palma in educational centres. In this preliminary phase, we selected five educational centres on the island.

The project's objective is to create and distribute low-cost stations in various educational institutions in La Palma and later on the whole Canary Islands Archipelago, supplementing them with educational material on the topics of seismology and volcanology. Each school will be able to access the data of its station, as well as those collected by other centres, being able to locate some of the recorded earthquakes. The data recorded by RESECAN will also be integrated into the broadband seismic network operated by INVOLCAN (Red Sísmica Canaria, C7). RESECAN will be an instrument of scientific utility capable of contributing effectively to the volcano monitoring of the Canary Islands, reinforcing its resilience with respect to future volcanic emergencies.

How to cite: García-Hernández, R., Barrancos, J., D'Auria, L., Domínguez, V., Montalvo, A., and Pérez, N.: RESECAN: citizen-driven seismology on an active volcano (Cumbre Vieja, La Palma Island, Canaries), EGU General A