TS4.4

Geodetic measurements of crustal deformation provide crucial constraints on a region’s tectonics, geodynamics and seismic hazard. However, such geodetic constraints have traditionally been hampered by poor spatial and/or temporal sampling, which can result in ambiguities about how the lithosphere accommodates strain in space and time, and therefore where and how often earthquakes might occur. High-resolution surface deformation maps address this limitation by imaging (rather than presuming or modelling) where and how deformation takes place. These maps are now within reach for the Alpine-Himalayan Belt thanks to the COMET-LiCSAR InSAR processing system, which performs large-scale automated processing and time-series analysis of Sentinel-1 InSAR data. Expanding from our work focused on Anatolia, we are combining LiCSAR products with GNSS data to generate high-resolution maps of tectonic strain rates across the central Alpine-Himalayan Belt. Then, assuming that the buildup rate of seismic moment (deficit) from this geodetically-derived strain is balanced over the long term by the rate of moment release in earthquakes, we pair these strain rate maps with seismic catalogs to estimate the recurrence intervals of large, moderate and small earthquakes throughout the region. We also use arguments from dislocation modeling to identify two key signatures of a locked fault in a strain rate field, allowing us to convert the strain maps to “effective fault maps” and assess the contribution of individual fault systems to crustal deformation and seismic hazard. Finally, we address how to expand these approaches to the Alpine-Himalaya Belt as a whole.

How to cite: Rollins, C., Wright, T., Weiss, J., Hooper, A., Walters, R., Lazecky, M., and Maghsoudi, Y.: Mapping tectonic strain in the central Alpine-Himalayan Belt with Sentinel-1 InSAR and GNSS observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-630, https://doi.org/10.5194/egusphere-egu21-630, 2021.

The North Anatolian Fault (NAF) has produced numerous major earthquakes. After decades of quiescence, the Mw 6.8 Elazı˘g earthquake (24 January 2020) has recently reminded us that the East Anatolian Fault (EAF) is also capable of producing significant earthquakes. To better estimate the seismic hazard associated with these two faults, we jointly invert interferometric synthetic aperture radar (InSAR) and GPS data to image the spatial distribution of interseismic coupling along the eastern part of both the NAF and EAF.We perform the inversion in a Bayesian framework, enabling to estimate uncertainties on both long-term relative plate motion and coupling. We find that coupling is high and deep (0–20 km) on the NAF and heterogeneous and superficial (0–5 km) on the EAF. Our model predicts that the Elazı˘g earthquake released between 200 and 250 years of accumulated moment, suggesting a bicentennial recurrence time.

How to cite: Bletery, Q., Cavalié, O., Nocquet, J.-M., and Ragon, T.: Distribution of Interseismic Coupling Along the North and East Anatolian Faults Inferred From InSAR and GPS Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1204, https://doi.org/10.5194/egusphere-egu21-1204, 2021.

Twenty six years after the Mw 7.3 Bolu/Gerede Earthquake of 1944, Ambraseys (1970) first recognized, in the offset of a manmade wall constructed across the fault in 1957, the signature of slow aseismic slip along the central segment of the North Anatolian Fault (NAF). Following this discovery, many studies have characterized the behaviour of this aseismic slip with land- and space-based geodetic techniques, and with creepmeters. It is now recognized that the rate of aseismic slip decreases logarithmically from more than 3 cm/yr in the years following the Gerede Earthquake to approximately 6±2 mm/yr today. Of this rate, approximately 1.2 mm/year is residual afterslip and the remainder appears to be linear creep interrupted by creep events. In the last two decades, InSAR allowed the derivation of maps of ground velocities that indicates aseismic slip extends along a 100-km-long section of the fault, with a spatially variable aseismic slip rate, reaching its peak value approximately 15-24 km east of the city of Ismetpasa. Furthermore, creepmeter measurements and InSAR time series indicate that surface aseismic slip in the region of Ismetpasa is largely episodic, alternating between quiescent periods and transient episodes of relatively rapid aseismic slip. These observations raise questions about how slip accommodates tectonic stress along the fault with significant implications in terms of hazard along the seismogenic zone.

In July 2016, we established ISMENET (Ismetpasa Continuous GNSS Network) to monitor spatial and temporal variations in the aseismic slip rate and detect slow slip events along the fault. ISMENET stations are distributed along 120 km long segment of the fault. In order to explore the shallow, fine spatio-temporal behavior of aseismic slip, 19 stations are located within 200 m to 10 km of the fault with 30 and 1 sec sampling rate. We analysed the GNSS time series to extract the signature of aseismic slip using a principal component analysis to reduce the influence of non-tectonic noise. We compared results with creep events quantified by creepmeters.

Keywords: Ismetpasa, Aseismic slip, GNSS, PCA, Time Series Analysis, NAFZ

How to cite: Özdemir, A., Doğan, U., Jara, J., Jolivet, R., Ergintav, S., Çakır, Z., Özarpacı, S., and Bilham, R.: Detecting Transient Creep Events on the Ismetpasa Segment of the North Anatolian Fault with Continuous GNSS Time Series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11185, https://doi.org/10.5194/egusphere-egu21-11185, 2021.

Seismological studies on the western part of the North Anatolian Fault (NAF) revealed the possibility that it may constitute a bimaterial interface at various locations. One evidence for this came from Karadere and Mudurnu segments where Fault Zone Head Waves (FZHW) and Fault Zone Reflected Waves (FZRW) indicated bimaterial interfaces and damage zones of various depth ranges. These were often interpreted as factors affecting various aspects of rupture propagation velocities and rupture lengths. In addition, the difference in crustal structure between the northern shore of the Sea of Marmara and the deep basins may results in an effective rigidity contrast across the Main Marmara Fault, at least in its Eastern part from Kumburgaz Basin, to the entrance of Izmit Gulf. This could result in reduced elastic loading of the northern block, leading to an underestimation of slip deficit in geodetic models. However, the problem was never looked at using multiple constraints at the same time such as the GPS, InSAR and underwater geodetic data. In this study we use the interseismic slip distribution on the westernmost section of the NAF (comprising largely the Main Marmara Fault and the bifurcation zone to the east of the Izmit Gulf) obtained using a block model as a reference model and use a finite element model to test the perturbations to this model as a function of the elastic moduli contrasts across the fault. We are testing the case where there is a bimaterial interface all the way from Izmit Gulf to Kumburgaz and then a lack of such a contrast in the Central Basin. We are also investigating a scenario where the Ganos region also has bimaterial interface (but reverse in its nature).

How to cite: Özbey, V., Özeren, M. S., Henry, P., Cavalié, O., Le Pichon, X., Klein, E., Tarı, E., and Galgana, G.: Kinematics of the Sea of Marmara using GPS, InSAR and underwater geodetic data: Possible Influence of Crustal Heterogeneity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13441, https://doi.org/10.5194/egusphere-egu21-13441, 2021.

The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 years have passed since the last major earthquake in the Central Marmara region. Here, an assessment on the location of possible asperities to host the expected next large earthquake is done based on the heterogeneities on the seismic velocity structure. Using long-term ocean bottom seismograph (OBS) observation data, seismic tomography and precise hypocenter estimations have been conducted. As a result, about five times more microearthquakes than the events in a land-based catalog has been detected. A comparison with previously published results suggests that the seismicity pattern has not changed during the three years period between Sep. 2014 and Jun. 2017. The obtained velocity model shows strong lateral contrast whose changing points locate at 28.10°E and 28.50°E. The western corner of the area (28.10°E) corresponds to a segmentation boundary where the dip angle of the NAF segments changed. The high velocity zones in the tomographic images are characterized by low seismicity eastward from the segment boundary at 28.10°E. Eastern 28.50°E, the high velocity zone becomes thicker in the depth direction. These zones are interpreted as asperities to be ruptured by the next large earthquake which are possibly accumulating strain since the mainshock rupture associated with the May 1766 Ms7.3 earthquake.

How to cite: Yamamoto, Y., Kalafat, D., Pinar, A., Takahashi, N., Polat, R., Kaneda, Y., and Ozener, H.: A robust seismic structure along the North Anatolian Fault beneath the Central Marmara Sea, and its implication for seismogenesis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-757, https://doi.org/10.5194/egusphere-egu21-757, 2021.

How to cite: Jenkins, J., Stephenson, S., Martinez-Garzon, P., Bohnhoff, M., and Nurlu, M.: Crustal Thickness Variation Across the Sea of Marmara Region, NW Turkey: A Reflection of Modern and Ancient Tectonic Processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6040, https://doi.org/10.5194/egusphere-egu21-6040, 2021.

            Since the Neogene, the Central Mediterranean geodynamics is controlled by the migration of narrow orogenic belts, driven by fast slabs retreat, and the slowly converging Nubian and Eurasian plates. Nowadays, the Calabrian Arc continues its southeast migration in response to the Ionian oceanic plate rollback but at a much slower rate. The Sicilian kinematics has reached a transient state between the ending subduction-collision phase that formed the island, and the steady-state convergence between Africa and Eurasia. This setting explains why Sicily is among the most seismically active region of the Mediterranean, gathering the most destructive historical events recorded in Italy, such as the Noto (1693, Mw ∼ 7.4) and Messina earthquakes (1908, Mw ∼ 7.1). Such tectonic activity has led to numerous studies aimed at evaluating current surface motions at a regional scale using GPS networks. To improve the spatial coverage, we built the first 3D geodetic velocity field over the whole Sicily Island by processing from the Sentinel-1 InSAR time-series.

            Averaged velocities along the ascending and descending satellite line-of-sight (LOS) were obtained using the Permanent-Scatterer approach (PS-InSAR) over the 2015-2020 period. We converted PS velocity fields into the Nubia reference frame, with the ITRF2014 vertical reference, by adjusting PS to 3D-GPS mean velocities. Reliable GPS velocities were retrieved from time-series of the MAGNET GPS network, leading to about 40selectedsitescoveringSicily and south-west Calabria. Onalltracks, theagreementbetweenPSandGPSLOSvelocitiesisexcellent (rms < 1mm/yr), and derived orbital corrections are robust, except for the western descending track that is only constrained by five GPS data. Since the projected north-south GPS velocity difference along the LOS is about 0.5 mm/yr, we assumed that thenorth-componentoftheground displacementisnegligible. By reducing the problem to a 2D estimation(East and Up component) and using both ascending and descending LOS velocities, we derived the East-andUp-component of the ground deformation within the Nubia-ITRF2014 reference frame. Uncertainties are estimated in the order of 1mm/yr.

            The results show that the Up-component is consistent with previous works indicating a significant uplift of the Peloritani range (~ 1±0.5 mm/yr) in north-eastern Sicily. Together with the East-component, the whole Peloritani block appears, however, as a coherent tectonic unit and does not show any dislocation along the Tindari line, as suggested by previous structural field observations. Interestingly, PS-InSAR data evidence an eastward tilting of the Hyblean Plateau, with about 1.5 mm/yr of subsidence of the Augusta bay relative to the Vittoria plain, and a 1 to 2 mm/yr of differential vertical motion along the southern coast, between Agrigento and the Licata and Sciacca locations. Although the reconstructed ground motion only captures a short time-window of the seismic cycle, these data represent a major milestone to evaluate the seismic hazard of Sicily.

How to cite: Henriquet, M., Peyret, M., Dominguez, S., Barreca, G., Malavieille, J., and Monaco, C.: Pseudo-3D ground deformation map of Sicily derived from Sentinel-1 InSAR time-series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7105, https://doi.org/10.5194/egusphere-egu21-7105, 2021.

The Republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and the Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of up to 20 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.

As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.

The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The main objective of the given work is to monitor a millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.

This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.

How to cite: Khazaradze Tsilosani, G., Sokhadze, G., Hahubia, G., and Kachakhidze, M.: Contemporary crustal deformation in Georgia (Caucasus), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2675, https://doi.org/10.5194/egusphere-egu21-2675, 2021.

Multi-spectral satellite imagery becomes a powerful tool in analyses of the earth’s surface in various aspects, including tectonic studies. There are many worldwide samples of such studies, documenting the distribution of faulting or deformation of lithological units especially in arid, semi-arid regions. The East Anatolian Shear Zone and its most prominent member, the East Anatolian Fault (EAF), is part of such a region, where the modern techniques of remote sensing can provide information on the history of this transform fault system. The EASZ and the EAF, together form the eastern boundary of the Anatolian Block, which in this study, we compare the efficiency of Advanced Space Borne Thermal Emission and Reflection Radiometer (ASTER) and Landsat-8 Operational Land Imager (OLI) images in the discrimination of lithological formations and the Pazarcik Segment of the EAF. First, we used the band combinations of 2/5/1 and 7/3/1, then 4/3-6/2-7/4 and 1/3-1/9-3/9 band ratios were independently selected in order to make an additional evaluation of the lithological discrimination for Landsat 8 OLI and ASTER T1 images, respectively. In the last stage, we used Principal Component Analysis (PCA), which provided a richer colour spectrum than the Band Combination and Band Ratio methods. The preliminary joint-analysis of these three methods allowed us to better understand the basin geometry along this part of the Pazarcik Segment. Accordingly the northern part of the Golbasi basin which hosts the Golbasi Lake, presents a rhomboidal geometry whereas the southern part is divided from the north with a wedge-shaped basin geometry. Towards southwest of the Pazarcik Segment, the Kisik River is left-laterally offset about ~4.8 km which is detectable on the band ratio images. Most critically, the image analysis highlight a geological offset along the Pazarcik Fault Segment at the Golbasi Lake side of the Hoya Formation. A left-lateral cumulative offset of ~11 km is measured along the displaced Hoya formation favouring the hypotheses of either a diachronic origin for the northern and eastern tectonic boundaries of Anatolia, among which the northern one highly exceeds the eastern boundary in terms of total slip, hence the age, or a wider shear zone where the total strain has been shared among parallel/sub-parallel segments.

How to cite: Kırkan, E., Uçarkuş, G., and Zabcı, C.: Preliminary results on the slip history of the Pazarcik Segment of the East Anatolian Fault (Turkey): Insights from the integrated analyses of ASTER T-1 and Landsat 8 OLI multi-spectral imagery-based lithological mapping, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14174, https://doi.org/10.5194/egusphere-egu21-14174, 2021.

The Arabia-Eurasia collision zone is an example of large-scale continental deformation. The collision started recently (25-15 Ma) and is characterized by a low shortening rate. The shortening caused by the collision is partly accommodated by vertical uplift, leading to large fold-and-thrust belts that give rise to the Zagros, Caucasus, and Alborz mountain ranges. The other part of the shortening is presently taken up by the lateral extrusion toward the west of the Anatolian block, a relatively rigid continental lithospheric block. This extrusion is accommodated by the conjugate North and East Anatolian Faults.

In this work we aim at understanding the dynamic of the crustal deformation processes resulting from the continental collision, including generation of positive topography and localization of major shear zones that evolve into lithospheric-scale strike-slip faults. Previous modeling attempt were mostly limited to the kinematic description of the strike-slip fault system and did not consider any topographic changes. In this earlier attempt fault geometry was usually assigned a-priori, and most often slab-pull along the Aegean subduction zone was partly needed to drive the extrusion.

Here, using a Discrete Element Modeling approach, we built a 3D model of the Arabia-Eurasia collision zone, including gravity forces, to study the temporal evolutions of the different tectonic structures, thrust and strike-slip faults, involved in accommodating the continental collision deformation processes.

On one hand, our modeling approach does not require to pre-set any fault geometry at the beginning of the collision. On the other hand, this approach allows us testing the impact of specific boundary conditions, such as the existence of two oceanic-crust relics forming respectively the Black Sea and the Caspian Sea, and which are considered 100% rigid.

Our preliminary models reproduce at first order the successive deformation steps of the Arabia-Eurasia collision that lead to the current configuration. The first phase of deformation is characterized by the formation of a wide fold-and-thrust belt in front of the Arabian plate indenter. Only in a second phase, the extrusion of an Anatolian block westward is taking place. This extrusion, however, happens only when rigid bodies (the Black Sea and the Caspian Sea) are present in the model. Conversely, extrusion in our models does not require the existence of slab-pull to occur. Eventually, the strike-slip faults generated in our models are showing good qualitative agreement with the current geometry of the North and East Anatolian faults. Faults generated in our models accommodate the rotation of the extruded block in a consistent way with the present-day pattern of the Anatolia block. Further work will allow quantifying the length of the different time steps in the collision process, and to explore the impact of the geometry of the indenter.

How to cite: Jiao, L., Hubert-Ferrari, A., and Klinger, Y.: 3D discrete element modeling of the Arabia-Eurasia collision zone and related extrusion of the Anatolian Block, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16315, https://doi.org/10.5194/egusphere-egu21-16315, 2021.

Çavdarhisar (Kütahya) province plays a very important role to understand geology and tectonics of the Western Anatolia. Active tectonics characteristics of the region give major information about the evolution of tectonics of the Çavdarhisar (Kütahya) and surrounding areas especially from Late Cenozoic to present day. In this study, kinematic analysis of observed faults in the field and focal mechanism solutions of earthquakes from this region and surroundings are used to reveal the Late Cenozoic stress states of Çavdarhisar (Kütahya). Kinematic analysis results of the faults give four different stress state (SS) regimes from Pre-Late Miocene to Quaternary. Firstly, a main strike-slip faulting (transpressional) (SS.1) has been developed under a NE-SW local compressional tectonic regime in Pre-Late Pliocene with 32°/31° (σ1) and 124°/10° (σ3) trends and Rm ratio was calculated as 0.616. Secondly and consistently with first regime, a NW-SE trending extensional regime (SS.2) produce a local normal faulting presents a minimum stress with 329°/6° (σ3) trend as in horizontal plane in the same period. Then, a NW-SE trending compressional tectonic regime has been efficient in Late Pliocene. This tectonic regime (SS.3) developed a strike-slip faulting (transtensional) has showing by a maximum stress axis by 325°/19° (σ1) and 60°/8° (σ3) trends and Rm ratio was calculated as 0.499. Finally, in the study area, a tectonic regime change has occurred during Quaternary time interval. This regime (SS.4) is oriented a minimum stress state trend as in horizontal plane by a NE-SW directed extensional regime produce a normal faulting in present day and shows a minimum stress with 58°/17° (σ3) trend and Rm ratio is calculated as 0.549. Focal mechanism solutions of the earthquakes that hit the study area show NNE–SSW extension direction which is consistent with present day extensional regime of Çavdarhisar (Kütahya) and surrounding areas. The reason for the regionally effective NNE–SSW trending extensional regime in western and south western Anatolia is related with complex subduction processes between African and Anatolian plates.

 Key words: Çavdarhisar, Kütahya, kinematic analysis, tectonic regime, active tectonics, stress state

How to cite: Tunç, G. and Özden, S.: Stress State Analysis and Active Tectonics of Çavdarhisar (Kütahya) Province, (NW Anatolia, Turkey) from Pre-Late Cenozoic to Quaternary, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-464, https://doi.org/10.5194/egusphere-egu21-464, 2021.

Characterized for the first time in 2013, the Island Akarnanian Block (IAB) is a micro-plate located in the western Greece. This micro-plate accommodates the deformation in between larger scale tectonic structures as the Gulf of Corinth (South-East), the Hellenic subduction (South) and the Apulian Collison (West).

We started a micro-seismic survey (MADAM) at the end of 2015 with a dense seismological network over the area, between the Gulf of Patras and the Gulf of Amvrakikos. In order to obtain precise locations of the recorded events, we better constrained the local velocity model. In fact, several velocity models (local or regional) have been proposed for this area. However, the velocity model generally used by the scientific community remains the Hasslinger 98 velocity model. This model, nevertheless, raises some questions about its physical meaning, mainly due to a low velocity layer between 4 and 7 km-depth.

Thanks to our seismological network and permanent networks of the Corinth Rift Laboratory and the Hellenic Unified Seismic Network, we collected and analysed a huge quantity of data acquired between October 2015 and December 2017. Those analyses of more than 10,000 events allowed us to develop a new and robust local velocity model, which is consistent with the seismic data and the geophysical observations.

The observed seismic activity is characterized by the presence of numerous clusters. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their possible implications in the fault activity to finally have a better understanding of the deformation mode(s) of the IAB micro-plate.

How to cite: Lefils, V., Rigo, A., and Sokos, E.: Micro-seismicity, seismic-wave velocity model and earthquake clustering in the Akarnanian region (western Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7672, https://doi.org/10.5194/egusphere-egu21-7672, 2021.

The NNE-SSW, right-lateral Kefalonia Transform Fault (KTF) marks the western termination of the subducting Hellenic slab, which is a part of the oceanic remnant of the African plate. The inception of the KTF, described as a STEP fault, is placed in the Pliocene. KTF is considered to be the most active earthquake source in the Eastern Mediterranean. During the last two decades, four significant earthquakes (M>6.0) have been associated with the KTF. These events are attributed to the reactivation of different segments of the KTF, which are (from North to South) the North Lefkada, South Lefkada, Fiskardo, Paliki and Zakynthos segments: the North Lefkada segment ruptured in the 2003 earthquake, the 2014 Kefalonia events are associated with the Paliki segment and the 2015 Lefkada earthquake with the South Lefkada (and possibly the Fiskardo) segments.

The upper plate structure in the islands of Lefkada and Kefalonia is characterized by the Ionian Unit, thrusted over the Paxi (or Pre-Apulian) Unit. The Ionian Thrust, which brings the Ionian over the Paxi Unit, is a main upper-plate NNW-SSE, NE-dipping structure. It runs through the island of Lefkada, to be mapped onshore again at the western coast of Ithaki and at SE Kefalonia. Two other major thrusts are mapped on this island: the Aenos thrust, which has a WNW-ESE strike at the southern part of the island and gradually curves towards NNW-SSE in the west and the Kalo Fault in the northern part. These Pliocene (and still active) structures developed during the late-most stages of thrusting in the Hellenides, strike obliquely to the KTF and appear to abut against it.

We suggest that these thrusts control not only the deformation within the upper plate, but also the earthquake segmentation of the KTF. This suggestion is corroborated by the spatio-temporal distribution and source parameters of the recent, well-documented earthquake events and by the macroseismic effects of these earthquakes. The abutment of the Ionian thrust against the KTF marks the southern termination of the Lefkada earthquake segment, which ruptured in the 2003 earthquake, while the Aenos, (or the Kalo) thrust mark the southern end of the Fiskardo segment. The spatial distribution of the Earthquake Environmental Effects related to the four significant events in the last 20 years displays a good correlation with our interpretation: most of the 2003 macroseismic effects are located in the northern part of Lefkada, which belongs to the upper block of the Ionian thrust; similarly, the effects of the 2014 earthquakes of Kefalonia are distributed mainly in the Paliki Peninsula and the southern part of the island that belong to the footwall of the Aenos thrust and the 2015 effects are found in SW Lefkada, which is part of the footwall of the Ionian thrust.

We suggest that correlation between upper-plate structure and plate boundary faulting can provide insights in the understanding of faulting pattern in convergent settings, therefore contributing to earthquake management plans.

How to cite: Skourtsos, E., Kranis, H., Mavroulis, S., and Lekkas, E.: Upper-plate structural controls on the segmentation of the Kefalonia Fault (Ionian Sea, Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15736, https://doi.org/10.5194/egusphere-egu21-15736, 2021.

The month-to-year-long deformation of the Earth’s crust where active subduction zones terminate is poorly explored. Here we report on a multidisciplinary dataset that captures the synergy of slow-slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 M_w 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). It appears that this long-lasting preparatory phase initiated due to a slow-slip event that lasted ~4 months and released strain equivalent to a ~M_w 6.3 earthquake. We propose that the slow-slip event, which is the first to be reported in the HSS, tectonically destabilised the upper 20-40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (M<4) on neighbouring faults, earthquake swarms in the epicentral area of the M_w 6.9 earthquake ~1.5 years before the main event, another episode of slow-slip immediately preceding the mainshock and, eventually, the large (M_w 6.9) Zakynthos Earthquake. Tectonic instability in the area is evidenced by a prolonged (~4 years) period of overall suppressed b-values (<1) and strong earthquake interactions on discrete strike-slip, thrust and normal faults. We propose that composite faulting patterns accompanied by alternating (seismic/aseismic) deformation styles may characterise multi-fault subduction-termination zones and may operate over a range of timescales (from individual earthquakes to millions of years).

How to cite: Mouslopoulou, V., Bocchini, G. M., Cesca, S., Saltogianni, V., Bedford, J., Petersen, G., Gianniou, M., and Oncken, O.: Slow-slip, earthquake-swarms and fault-interactions at the western-end of the Hellenic Subduction System precede the Mw 6.9 Zakynthos Earthquake, Greece, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8623, https://doi.org/10.5194/egusphere-egu21-8623, 2021.

The Samos-Izmir Earthquake (Mw=6.9) of October 30, 2020 is among the strongest earthquakes that occurred in recent years throughout the Eastern Aegean. The epicenter of this earthquake was 14 km away from Samos Island and 25 km away from Gümüldür-İzmir region. The local tsunami with the wave heights reaching ~2m was triggered by the mainshock. The most affected areas were Sigacik and Akarca in Tukey (Yalciner et. al.,2020) and Vathy Town (NE Samos Island) in Greece (Triantafyllou et. al.,2020).

In this study, we present an estimation of co-seismic deformations using an indirect approach based on GNSS, InSAR and Tide Gauge data. GNSS time series were used from 25 continuous GNSS stations data obtained from TUSAGA-Aktif in Turkey and NOANET in Greek, and the campaign GNSS measurement for 10 GNSS sites located at the western Turkey coast has been carried out after the earthquake. Moreover, InSAR deformation analyses have been performed using Sentinel-1 data. In addition, relative sea level changes have been analyzed in KOS, PLOMARI, and MENTES tide gauge stations.

The vertical components of GPS stations have shown 10 cm uplift in Samos Island and 10 cm subsidence in the coast of Turkey. The results of the geodetic (GNSS, InSAR) analysis are consistent with each other. The rise time estimated here may correspond to the time elapsed shortly before the generation of tsunami waves reached up to 6 meters that propagated rapidly and caused significant damage around the source region. Also, it has been seen that whereas relative sea level in KOS and PLOMARI tide gauge stations are affected by the local tsunami, but relative sea level changes could not be observed in the MENTES station.

How to cite: Erkoç, M. H., Özarpacı, S., Özdemir, A., Eskiköy, F., Ayruk, E. T., Farimaz, İ., Doğan, U., and Ergintav, S.: The Vertical Coseismic Deformation Field of the Samos-Izmir Earthquake (Mw6.9), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4767, https://doi.org/10.5194/egusphere-egu21-4767, 2021.

On November 30, 2020 11:51 UTC, a major earthquake (Mw7.0) struck the northern area offshore Samos island, Greece, causing serious damage to the island and nearby Turkish coast. This seismic event is an ideal opportunity to explore extensional seismicity in the back-arc area of the Hellenic subduction zone. To that end, first and foremost we study the behavior and characteristics of the main event source. Then, we examine the evolution of the aftershock in space and time and relate it to the main event. We implement the technique of local backprojection on strong-motion recordings  (e.g. Kao & Shan, 2007; Evangelidis, 2013) to infer the spatiotemporal distribution of the earthquake source. This method is performed at relatively short periods, making it possible to map in detail the high-frequency radiation of the source, without imposing any a priori constraints on the geometry or shape of the ruptured fault. Furthermore, and which is not often the case, the strong-motion recordings were carefully assessed prior to being used in backprojection, in order to avoid any significant influence of local site effects and amplification, which could in impact the robustness of the backprojection solution. Synthetic tests were also used to resolve the accuracy. Our results show evidence of multiple distinct sources of high-frequency radiation during the earthquake rupture. In addition, the first month of the aftershock sequence was located, clustered and relocated, ultimately highlighting the faults activated in the area. The quality of the resulting high-resolution catalogue was further assessed, and the moment tensors of the strongest events were estimated. Combining the backprojection results with the detailed picture of the aftershock seismic sequence leads to an interpretation of the short- and long-term fault rupture process and their associated secondary effects (tsunami, landslides) in the area. 

The research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (SIREN, Project Number: 910).

How to cite: Fountoulakis, I., Evangelidis, C. P., and Ktenidou, O.-J.: Imaging the Samos 2020 Mw7.0 earthquake rupture by backprojecting local strong-motion recordings and relocating the aftershock sequence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15291, https://doi.org/10.5194/egusphere-egu21-15291, 2021.

On 2020 October 30, an M_w6.9 earthquake struck offshore Samos Island. Severe structural damages were observed in Greek Islands and city of Izmir (Turkey). 114 people lost their lives and more than a thousand people were injured in Turkey. The earthquake triggered local tsunami. Significant seismic activity occurred in this region following the earthquake and ~1800 aftershocks (M>1) were recorded by KOERI within the first three days. In this study, we analyze the slip distribution and aftershocks of the 2020 earthquake.

For the aftershock relocations, the continuous waveforms were collected from NOA, Disaster and Emergency Management Authority of Turkey (AFAD) and KOERI networks. The database   was created based on merged catalogs from AFAD and KOERI. For estimating optimized aftershock location distribution, the P and S phases of the aftershocks are picked manually and relocated with double difference algorithm. In addition, source mechanisms of aftershocks M>4 are obtained from regional body and surface waveforms.

The surface deformation of the earthquake was obtained from both descending and ascending orbits of the Sentinel-1 A/B and ALOS2 satellites. Since the rupture zone is beneath the Gulf of Kusadası, earthquake related deformation in the interferograms can only be observed on the northern part of the Samos Island. We processed all possible pairs chose the image pairs with the lowest noise level.

In this study, we used 25 continuous GPS stations which are compiled from TUSAGA-Aktif in Turkey and NOANET in Greece. In addition to continuous GPS data, on 2020 November 1, GPS survey was initiated and the earthquake deformation was measured on 10 GNSS campaign sites (TUTGA), along onshore of Turkey.

The aim of this study is to estimate the spatial and temporal rupture evolution of the earthquake from geodetic data jointly with near field displacement waveforms. To do so, we use the Bayesian Earthquake Analysis Tool (BEAT).

As a first step of the study, rectangular source parameters were estimated by using GPS data. In order to estimate the slip distribution, we used both ascending and descending tracks of Sentinel-1 data, ALOS2 and GPS displacements. In our preliminary geodetic data based finite fault model, we used the results of focal mechanism and GPS data inversion solutions for the initial fault plane parameters. The slip distribution results indicate that earthquake rupture is ~35 km long and the maximum slip is ~2 m normal slip along a north dipping fault plane. This EW trending, ~45° north dipping normal faulting system consistent with this tectonic regime in the region. This seismically active area is part of a N-S extensional regime and controlled primarily by normal fault systems.

Acknowledgements

This work is supported by the Turkish Directorate of Strategy and Budget under the TAM Project number 2007K12-873.

How to cite: Eskikoy, F., Ergintav, S., Dogan, U., Özarpacı, S., Özdemir, A., Erkoç, M. H., Ayruk, E., Farimaz, İ., Vasyura-Bathke, H., and Konca, A. Ö.: Slip Distribution of the 2020 Mw6.9 Samos Earthquake Using a Bayesian Approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14970, https://doi.org/10.5194/egusphere-egu21-14970, 2021.