The deformation and shortening in the Caucasus region are predominantly driven by the collision of Arabian and Eurasian plates with a possible contribution of the lithospheric deformation beneath the Caucasus.  The tectonic uplift/inversion, along with the formation of the Greater and Lesser Caucasus fold and thrust belts, is driven and maintained by the continental collision of the Arabian and Eurasian plates. However, the dominant factor for the regional variations of surface deformation and sub-crustal seismic activity, whether lithospheric delamination or slab detachment beneath the Caucasus region, is not well understood. Moreover, the variations in shortening along the Caucasus cannot be solely explained by plate boundary forces without constraints from lithospheric dynamics. The large uncertainties of the models lead to limited understanding of the formation and active deformation of this fold and thrust belt. The main reason for this shortcoming is the limited access to the seismic and geodetic data in the region. In this study, we merged seismic and geodetic data from Russia and surrounding countries.  We constructed a joint database for the period between 2007 and 2010 and updated 1D crustal velocity models for four sub-regions. We obtained the relocated seismicity within each region using the local velocity models. In addition, we updated the earthquake source mechanisms catalog in the Caucasus region.  A new Pn tomography model is computed using the new catalog. The crustal thickness variations are recomputed from receiver function analysis using the broad-band stations of Russia. We also update block boundaries and corresponding slip rates in the study region using both seismicity and geodetic data.

How to cite: Karabulut, H., Milyukov, V., Guvercin, S. E., Ozarpaci, S., Pavlovich, M. A., Ergintav, S., Özbey, V., Zabci, C., Konca, A. O., Diyagilev, R., and Mikhailovich, S. G.: Investigation of the Active Deformation in the Caucasus Region from Seismic and Geodetic Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12188, https://doi.org/10.5194/egusphere-egu24-12188, 2024.

6 February 2023 Mw 7.8 Pazarcık (Kahramanmaraş) Earthquake generated about a 300 km-long surface rupture between the Antakya airport to the south and the Karaköse and Yarpuzlu villages (Sincik, Adıyaman) to the north and strong ground motions, resulting in extensive property damage and loss of lives. We rapidly started to document the deformation structures on the surface by the second day of the event, spreading into smaller mapping teams and covering nearly the entire rupture zone. In addition to walking the rupture and recording locations with GPS waypoints, we made surface offset measurements with a standard tape measure. We used several sUAS’ to acquire high-resolution Digital Orthophoto Maps and Digital Surface Models (between 3 to 5 cm pixel resolution) to map the coseismic slip and surface rupture zone details. We utilized high resolution stereo aerial images with 10 or 30 cm ground pixel resolution, collected by the General Directorate of Mapping, in areas where we could not collect high-quality sUAS imagery.

This poster presentation aims to show the full extent of our field and sUAS-based rupture map and horizontal slip measurements of the Pazarcık Earthquake. At the most southern section, the rupture along the Hatay Rift is ~115 km long with a maximum sinistral offset of about 4.5 m between Nurdağ and Şekeroba towns. Between Türkoğlu and Gölbaşı, the rupture is 85 km long and the maximum slip reaches up to ~7m to the north of the Pazarcık town, close to the junction of the East Anatolian and Narlı faults. Farther to the NE, between Gölbaşı and Çelikhan, the slip first decreases to a mean value of ~2.5 m, but then it increases again to ~6.5 m at Kurucaova village. This section of the fault zone is nearly one km wide and is characterized by numerous sub-parallel surface breaks. To the north east of Çelikhan, the slip drops to less than one meter. It diminishes to the north of the Karaköse village (Sincik, Adıyaman), leaving of about 20 km-long unbroken fault section at the surface until the southwest termination of the 2020 Mw 6.8 Sivrice Earthquake rupture.

How to cite: Zabcı, C., Kıray, H., Akyüz, H. S., Sançar, T., Akçiz, S. O., Uçarkuş, G., Kırkan, E., Sunal, G., Aksoy, M. E., Battogtokh, D., Yakupoğlu, N., Köküm, M., Balkaya, M., and Sabuncu, A.: 6 February 2023 Mw 7.8 Pazarcık (Kahramanmaraş) Earthquake: the rupture geometry and slip distribution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18328, https://doi.org/10.5194/egusphere-egu24-18328, 2024.

The February 06, 2023, Kahramanmaraş earthquake sequence started with an earthquake with magnitude Mw 7.0 on the Narlı Fault and continued on the tectonic boundary between the Anatolian and Arabian plates. The main event, the Mw 7.8 Pazarcik earthquake, ruptured the East Anatolian Fault (EAF) bilaterally for over 300 km. This main event was followed nine hours later by the Mw 7.6 Elbistan earthquake, with the epicenter near the town of Ekinözü, about 100 kilometers away from the epicenter of the Pazarcik earthquake. The Elbistan earthquake also ruptured bilaterally, resulting in approximately 140 km of co-seismic surface rupture along a set of faults that form a major splay of the East Anatolian Fault Zone. Field investigations supplemented with interpretations of high-resolution photographs from small unmanned aircraft systems and helicopters show that the surface rupture associated with the Elbistan earthquake occurred on two different left-lateral strike faults: The first, known as the Çardak fault, extends from the town of Göksun in the west to Bıçakçı village in the east. The second is the newly identified Yeşilyurt Fault, an NE-SW-striking left-lateral fault with a subtle topographic expression that strikes parallel to the EAF.

The surface trace of the Çardak Fault can be divided into two geometric sections: The arc-shaped western section extends nearly 80 km between Göksun and Nurhak where the rupture was continuous and focused within a narrow zone. Horizontal slip along the eastern half of this section was typically over 6 meters, reaching over 8 meters at the maximum slip location just east of the epicenter. The average lateral slip drops to approximately 4 meters west of Ericek before decreasing uniformly to the west from Fındık until the surface rupture ends in Göksun. The second fault section extends nearly E-W between Nurhak and Bıçakçı for almost 20 km, including the structurally complex region associated with the Nurhak restraining bend, where only a handful of field slip measurements were made in this broadly deformed section. The average minimum horizontal slip measurements in this section of the Çardak fault is around 2.5 m. Our field investigations indicate that the rupture established a new trend parallel to the East Anatolian Fault instead of using the E-W-oriented Sürgü Fault to connect with it. The average slip along this new 40 km-long fault zone, here named Yeşilyurt Fault, is about 1m, with maximum left-lateral slip reaching  ~2.5m. Unlike the nearly continuous rupture along the Çardak fault, the rupture zone of the Yeşilyurt Fault generally consists of a series of right-stepping en-echelon arrays of discontinuous sinistral fault traces of various lengths and stepovers that range between tens of meters to several hundred meters.

How to cite: Akciz, S. O., Sançar, T., Kıray, H. N., Zabcı, C., Köküm, M., Balkaya, M., Battogtokh, D., and Akyüz, H. S.: Primary Surface Rupture and Slip Distribution Associated with the Mw 7.6 06 February 2023 Elbistan Earthquake, Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13350, https://doi.org/10.5194/egusphere-egu24-13350, 2024.

The south-southeastern Türkiye was struck by a series of earthquakes in February 2023 causing the death of more than 50,000 people and billions of USD of economical loss. The largest of these events, the February 6th Mw 7.8 Pazarcık and Mw 7.5 Ekinözü earthquakes occurred only 9 hours apart of each other generating surface ruptures of about 450 km and the majority of the destruction. All these events took place in a complex tectonic system where the boundary structures of the Anatolian Block, the Arabian Plate and the Adana-Cilicia-Hatay Basin merge together. The Pazarcık earthquake was initiated along a subsidiary splay, the Narlı Fault (NF), and continued with the bilateral rupturing of faults over a length of 300 km.

In this study, our aim is to document the surface deformation along the NF in order to have a better understanding of the initiation mechanism of the ‘multi-segment’ Pazarcık earthquake. In addition to our field observations, we operated a sUAS to map the rupture and measure offsets. We used a tape measure to determine the magnitude of slip across the well-established offset markers in the field, while the ultra-precise rupture mapping and a vast number of displacement measurements were made by using sUAS-based digital surface models (DSM) and orthophotos with a ground pixel resolution of ~3–5 cm.

We mapped two sets of continuous surface ruptures, the 14 km-long southern and the 10 km-long northern parts, separated by a ‘gap’ of 8 km. The average sinistral offset along the ~N20-30°–striking southern rupture is about 2 m, whereas the maximum value reaches up to 3.7 ± 0.7 meters. On the other hand, the horizontal slip along the N25-35°–striking northern rupture barely exceeds 1.2 m. In this section, it is highly probable that a large portion of the total horizontal deformation is shared by widely distributed surface shears within the wedge between the East Anatolian Fault and the NF, which can be an analogue to a variant of a Prandtl Cell Model. In addition, we identified semi-circular/elliptical surface cracks at more than 10 locations to the south of the NF rupture. These are interpreted as seismically induced sink-holes, given the widely distributed Eocene limestones in the region. The preliminary analysis of the time series of interferograms between 2015–2022 suggests a long-term systematic subsidence, supporting our hypothesis.

How to cite: Kıray Canik, H. N., Zabcı, C., Akyüz, H. S., Kırkan, E., Sunal, G., Yakupoğlu, N., Sabuncu, A., and Akoğlu, A. M.: The Narlı Fault: the characteristics of the surface rupture that initiated the 6 February 2023 Kahramanmaraş Earthquake Sequence (Türkiye), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-950, https://doi.org/10.5194/egusphere-egu24-950, 2024.

The research conducted on the 6th of February 2023 Mw7.8 Kahramanmaraş earthquake represents
a comprehensive study aimed at understanding the distribution of seismic intensity in the affected
areas and developing a novel intensity calculation formula for Eastern-Southeastern Turkey. This
seismic event, the most catastrophic in Turkey's last century, was initiated on the Narli splay fault
and propagated bilaterally along the East Anatolian Fault (EAF). The rupture extended over a
significant seismic gap of the EAF and the Amanos Fault, affecting 11 provinces in Turkey's Southeast
region and bordering areas of Syria, resulting in a total rupture length exceeding 300 km and causing
over 50,000 fatalities.
The study evaluates seismic intensity distribution across seven cities: Hatay, Gaziantep,
Kahramanmaraş, Adıyaman, Malatya, Osmaniye, and Şanlıurfa. An online intensity questionnaire
survey was distributed to educational institutions in these provinces. In October 2023, a Turkish-
Japanese reconnaissance team collaborated with the National Education Directorate of the seven
provinces to disseminate the questionnaire format and URL link to all public high schools, middle
schools, and elementary schools, garnering responses from 14,739 participants. Geocoordinate
inputs were accurately assigned using the ArcGIS survey123 system, contributing to the preliminary
survey results which included damage observations.
Microtremor observations were conducted in Hatay, Gaziantep, Kahramanmaraş, and Adıyaman
using the Kinkei seismic measuring device developed in Japan. The research involved single-point
microtremor measurements at 20 locations within the earthquake zone, fault-fracture zones,
damaged residential areas, particularly near the AFAD seismic stations. Additionally, array
microtremor measurements were made at 31 AFAD station locations with strong motion records.
The analysis of 39 microtremor measurements revealed preliminary results indicating a correlation
between heavily damaged buildings and areas where the Vs30 values are less than 180 m/s. The
finding suggests that areas with lower Vs30 values may be more susceptible to damage during
earthquakes.

These observations, combined with the result of the online intensity questionnaire surveys and local
soil amplifications, are utilized to assess the correlation between microtremor amplification and
seismic damage. The objective is to formulate a new intensity calculation formula tailored to the
Eastern-Southeastern part of Turkey. This research's findings are anticipated to offer significant
contributions to earthquake intensity assessment methodologies, particularly in regions with distinct
geological and seismic profiles. The collaboration between Turkish and Japanese experts adds an
international dimension to the study, potentially leading to improved seismic risk assessment,
preparedness strategies, and recovery measures on a broader scale in the future.

How to cite: Meral Ozel, N., Mori, S., Murakami, H., Koyama, M., Kepekçi, D., Polat, G., Korkusuz Ozturk, Y., Yotsui, S., Goto, H., Osato, S., Chiba, T., Hada, K., Yamada, M., Hayashida, T., and Sakamoto, M.: 6 February 2023 Kahramanmaras, Turkey Earthquakes: Microtremor Measurement, Extensive Field Survey On Seismic Intensity  And Structural Damage Correlations To Develop The New Intensity Formula For The Region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18974, https://doi.org/10.5194/egusphere-egu24-18974, 2024.

The eastern Mediterranean hosts complex tectonic units with multiple strike-slip and collision plate boundaries. The Anatolian plate is being pushed away from the Eurasian plate and Arabian plate via two left-lateral transform faults with uncoupled crust and upper mantle inferred from anisotropy studies. The rheological structure is thus important to better understand the plate dynamics of the Anatolian and its surrounding plates. The 2023 Mw7.8 and Mw7.6 earthquake doublet in the East Anatolian Fault zone provides a unique opportunity to study viscoelastic relaxation of the upper mantle and time-dependent afterslip over the crustal faults. Here we have derived the first 3-month postseismic displacements from GNSS time series of 94 stations after the events to investigate the early postseismic deformation processes through a three-dimensional viscoelastic finite element model. Afterslip in the model is simulated through a 2-km thick weak shear zone attached to the fault. Viscoelastic relaxation is represented by the bi-viscous Burgers rheology. We find that the observed long-wavelength displacements is dominated by the viscoelastic relaxation even in this early postseismic stage, and the contribution from the afterslip is spatially limited. The viscosity of the Anatolian upper mantle should be lower than 10¹⁹ Pa s to better fit the observed horizontal and vertical displacements. This inferred weak upper mantle may result from the upwelling mantle due to the tearing African slab.

How to cite: Wang, K. and Hu, Y.: Weak Anatolian upper mantle inferred from postseismic deformation of the 2023 Türkiye earthquake doublet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4865, https://doi.org/10.5194/egusphere-egu24-4865, 2024.

Understanding the evolution of the crustal kinematic/dynamic response of the Kahramanmaraş triple junction after the occurrence of the destructive earthquake doublet on 6 February 2023 is of great interest to seismologists and geodesists. Along with the near-field postseismic effects such as the afterslip, it is also essential to study relatively far-field effects where the interaction of the brittle upper crust with the lower crust and upper mantle can be relevant in how the stress is redistirbuted during the months/years following the earthquake. The latter seems to be a particularly interesting problem for this case because the earthquake perturbation to the interseismic velocity field is very significant and extends approximately 400 km to the west of the rupture zone.  The affected region seemingly comprises a large part of the Central Anatolian Block where the interseismic internal deformation was less than 10 nanostrain/yr prior to the large event. Most tomographic studies show that the lithospheric mantle beneath Central Anatolia is either very thin or absent. This indicates a necessity to test various upper mantle and lower crust viscosity scenarios for the far-field effects.

We conducted a GNSS (Global Navigation Satellite System) campaign in July 2023, reoccupying 18 sites around the triple junction area to monitor the intermediate and far-field post-seismic effects caused by the ruptures and the subsequent loading behavior of the faults therein. Our primary aim was to characterize: (1) the postseismic effect on the relatively far-field, which likely includes viscoelastic responses in central Anatolia where the lower crust and mantle are presumably weak; (2) variations of the strain field stemming from aftershocks of the large earthquakes; and (3) the response of secondary faults such as the Ecemiş, Deliler, and Sariz faults in Adana and Kayseri provinces. 1-year GNSS time series of continuous stations broadly reveal the postseismic field behavior. The occurence of a postseismic signal is clear northwest of the rupture zone however, the signal is weak for the stations southwest of the earthquake area. The preliminary analysis of the survey mode sites is in agreement with continuous stations. Here we present the resulting post-seismic velocity, the strain rate field and its contrast from the pre-event strain rate field and a preliminary viscoelastic model to shed light onto the underlying physical processes.

How to cite: Özbey, V., Henry, P., Özeren, M. S., Klein, E. C., Haines, A. J., Wang, L., Friedrich, A. M., and Şengör, A. M. C.: Post-seismic analysis of the Kahramanmaraş triple junction using GNSS data acquired following the 2023 Kahramanmaraş earthquakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12525, https://doi.org/10.5194/egusphere-egu24-12525, 2024.

On January 24, 2020 the Mw 6.8 Sivrice (Elazığ) earthquake was arrested by the ~80 km long Pütürge segment. On February 6, 2023, the first earthquake of the Kahramanmaras Earthquake Sequence, also ended at the southwest end of this segment. Is it creep also that arrest 2023 Pazarcik rupture? We analyzed InSAR data over the Pütürge segment to answer this question. We used over 5000 ARIA standard product interferograms from two ascending and two descending tracks of the Sentinel-1 satellites and the MintPy software to produce InSAR time series and velocity maps for the area. Also we processed both survey and continuous GNSS data with GAMIT/GLOBK GNSS software (v10.7) from 2014. We analysed the results in three time periods – before, between, and after the two earthquakes. InSAR shows that before both earthquakes the segment was creeping and GNSS data is confirming that outcome. We also are searching for any unbroken part of this segment and if this could be another danger in the future.

This work is supported by TUBITAK project numbers 114Y250, 118Y435 and 121Y400.

How to cite: Özarpacı, S., Hofstetter, C., Funning, G., Dogan, U., Ergintav, S., Çakır, Z., Zabcı, C., Özdemir, A., Ayruk, E. T., and Farımaz, İ.: Creeping Pütürge Segment with Geodetic Evidence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19720, https://doi.org/10.5194/egusphere-egu24-19720, 2024.

Geodetic GNSS (Global Navigation Satellite Systems) measurement systems play a crucial role in studies aimed at monitoring crustal movements. From the past to the present, GNSS measurement systems have served as active measurement tools within the scope of these studies. In these studies, geodetic GNSS measurement systems can be used as continuous reference stations and are primarily employed in campaign-type measurements. However, the setup and operation of continuous reference stations require a significantly high financial budget. On the other hand, campaign-type measurements necessitate simultaneous data collection using multiple GNSS measurement systems, depending on criteria such as the size of the field and the number of points. This, in turn, increases the overall measurement costs. Today, due to the high expenses associated with geodetic GNSS measurement systems, research is being conducted on the use of low-cost GNSS systems in structural health monitoring, displacement determination, and other applications. Since the studies conducted so far have generally been limited to short-term observations at short baselines, there remain questions about the performance of low-cost GNSS measurement systems in monitoring crustal movements. In this study, the objective is to determine the performance of GNSS measurement systems, whose unit costs are considerably lower compared to geodetic GNSS systems, in monitoring crustal movements. For this purpose, two low-cost GNSS measurement systems will be deployed on the northeastern edge of the surface rupture caused by the earthquakes of Mw7.8 and Mw7.6 that occurred in Kahramanmaraş on 06.02.2023. This will enable the continuous monitoring of the post-earthquake effects in the Çelikhan segment on the East Anatolian Fault (DAF). Furthermore, the performance of low-cost GNSS measurement systems will be assessed. In addition to the measurements taken at permanent stations, campaign-type GNSS measurements will be conducted at four different points using both geodetic and two low-cost GNSS measurement systems throughout the project. By processing the data obtained from geodetic GNSS measurement systems and the data acquired from low-cost GNSS measurement systems in the same region, the results will be analyzed. This analysis aims to determine the performance of low-cost systems in monitoring tectonic structures through continuous measurements and campaign-type measurements. This is work is supported by TUBITAK project number 123Y147.

How to cite: Akpinar, B., Özarpacı, S., Aydın, C., Aykut, N. O., Özdemir, A., Oku Topal, G., Güneş, Ö., Karabulut, F., and Doğan, U.: Monitoring Tectonic Movements with Low Cost GNSS Measurement Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18829, https://doi.org/10.5194/egusphere-egu24-18829, 2024.

The East Anatolian Fault Zone (EAFZ) is a major tectonic feature in Anatolia, moving westward relative to the Eurasian plate, primarily due to the compressional behavior of the African, Sinai, and Arabian plates. The EAFZ has been historically significant as the epicenter of several major seismic events, including the recent devastating earthquakes in Kahramanmaraş on February 06, 2023. In this study, we provide a comprehensive tectonic analysis of the EAFZ, focusing specifically on the Hatay Triple Junction (HTJ), where the EAFZ meets with the continuation of the Dead Sea Fault Zone and the Cyprus Arc. Through the synthesis of pre-seismic evaluations and co-seismic data derived from our comprehensive geodetic network, we aim to extend the understanding of the seismic cycle and fault behavior in this tectonically complex region.

In the pre-seismic phase, we employed a dense GNSS network, including the Turkish National Fundamental GPS Network (TUTGA) and various campaign sites, to analyze the strain accumulation and fault kinematics at the HTJ. Analyses revealed that the EAFZ and Karataş-Osmaniye fault exhibit complete locking at depths of 15 km and 7 km, respectively, while the Karasu Fault (KF) demonstrates locking up to a depth of 7 km. Our kinematic models indicated significant slip rates, suggesting a high potential for large earthquakes. Remarkably, during the revision of our manuscript in “Tectonophysics”, two major earthquakes (Mw 7.7 and Mw 7.6) occurred near the KF and EAFZ in Pazarcık and Elbistan, Kahramanmaraş, respectively. These earthquakes, happening in close succession, dramatically corroborated our predictions for seismic activity near the HTJ. 

In the co-seismic phase, following the Kahramanmaraş earthquakes, we utilized a high-resolution GNSS network with 73 permanent and 40 campaign stations to assess surface displacements and fault slip distributions. Significant displacements were recorded, with the largest being 466 cm, and substantial fault ruptures were observed along the EAFZ and Çardak fault segment, including the left-lateral slips of 494 cm and 391 cm in the first and second earthquakes, respectively.  

Our ongoing projects will integrate pre-earthquakes geodetic data with new GNSS measurements to analyze the postseismic deformation following the Kahramanmaraş earthquakes, including afterslip and its relation with aftershocks, as well as stress perturbations on the neighboring faults. This integrated approach is expected to further refine our ability to understand the behavior of the fault in the post-seismic phase and delineate the complete seismic cycle along the EAFZ.    

How to cite: Özkan, A., Tiryakioğlu, İ., Solak, H. İ., Uslular, G., Rousset, B., Masson, F., and Yavaşoğlu, H. H.: The seismic cycle of the Hatay Triple Junction from GNSS analysis: interseismic, coseismic and postseismic deformations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22128, https://doi.org/10.5194/egusphere-egu24-22128, 2024.

The recent M 7.5 earthquake that struck Japan on January 1st, 2024, marked a significant event due to its substantial magnitude and surprisingly minimal damage. This occurrence serves as a stark contrast to Türkiye's experience, notably the devastating Kahramanmaraş earthquake of February 2023. Japan's impressive success in earthquake resilience, achieved through strict building code enforcement and effective public awareness campaigns, stands in sharp contrast to Türkiye's ongoing struggle with seismic vulnerability. This discrepancy underscores the urgent need to bridge the gap between scientific knowledge and societal preparedness in Türkiye.

To address this pressing issue, we propose a set of actionable guidelines. Firstly, there is a need to integrate geoscience into Türkiye's educational system, thereby enhancing public understanding of earthquake risks. Simultaneously, opportunities for geoscientists should be expanded to facilitate expertise growth. Establishing local earthquake centers is paramount to improving seismic monitoring, research, and outreach efforts, bolstering the nation's preparedness for seismic events. Furthermore, geoscientists should prioritize science communication training to effectively engage the public and combat misinformation, thereby fostering a more informed and proactive society. In addition to these measures, implementing earthquake scenario modeling and regular preparedness exercises are instrumental in enhancing nationwide earthquake readiness and preparing Türkiye for future seismic events. Lastly, we emphasize the importance of fostering an earthquake culture through memory and awareness initiatives. This approach will instill a collective consciousness about seismic risks and responses, creating a more resilient society.

It is essential to recognize that the successful implementation of these guidelines will require active participation from scientists, institutions, and the public. By following these recommendations, Türkiye can build resilience and mitigate the impact of future earthquakes, ultimately ensuring a safer future for its citizens.

How to cite: Ertuncay, D., Karasözen, E., Büyükakpınar, P., Oral, E., and Havazlı, E.: Fostering an Earthquake Culture: Towards Enhancing Seismic Resilience in Türkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18563, https://doi.org/10.5194/egusphere-egu24-18563, 2024.

The Aegean region is under the influence of tectonic extension due to subduction zone along the Hellenic Arc. This extension leads to many earthquakes of magnitude 6 and above in the region. The earthquake that occurred on July 21, 2017, in Bodrum Mw 6.7 increased curiosity about the region due to the seismic activities in the Gulf of Gökova and the absence of an active fault in the area according to the active fault map published by the General Directorate of Mineral Research and Exploration (MTA). In the nearby region of the 2017 earthquake, there are the Gökova Fault Zone and the Fethiye-Burdur Fault Zone. Morphological linearity and the seismicity are observed between these two fault zones, and some recent studies indicate the existence of active faults. The aim of this study is to determine whether there are active faults in the Akyaka-Ula region with geodetic measurements. For this purpose we started to observe the area with GNSS campaigns and continuous data since 2021.

For this purpose, the data of Turkish National Permanent GNSS Network (CORS-TR) continuous stations, Turkish National Fundamental GNSS sites campaign measurements and survey data of a GNSS network established by our research group were processed together. The GNSS network stations were strategically placed in both near field and far field to the potential fault. GNSS data processed by using Bernese 5.2 software. According to the calculations based on the data from TNPGN-Active and TNFGN stations, the region exhibits an southwestward movement at a rate of approximately 3cm/year.

This work is supported by TUBITAK Project Number 121Y300

How to cite: Turgut, M., Özarpacı, S., Özdemir, A., Ayruk, E. T., Farımaz, İ., Doğan, U., and Dikbaş, A.: Akyaka-Ula Region Tectonics based on Geodetic Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19513, https://doi.org/10.5194/egusphere-egu24-19513, 2024.

In this study we explore the seismicity along the Eastern Marmara Sea using machine learning techniques to improve the detection threshold and improve the earthquake locations. The Sea of Marmara comprises network of faults including the northern strand of the North Anatolian Fault, the Main Marmara Fault (MMF). MMF features a ~150 km seismic gap that did not rupture in the last 250 years. In addition to the MMF, other normal and strike-slip faults generate seismicity in the vicinity especially to the south of the Princes’ Islands.  It is therefore crucial to understand whether this seismicity is related to the MMF or other faults.

Here by employing a convolutional neural network detection and phase picking algorithm (Mousavi et al., 2020) and using a phase associator based on a grid search of locations (Zhang et al., 2019) we show that we can increase the detected number of earthquakes significantly and obtain a catalog with very low travel time residuals. Our primary objective is to acquire an improved earthquake catalog to facilitate subsequent clustering and focal mechanism analysis, thereby illuminating the underlying fault system responsible for these seismic events.

(This study is funded by TÜBİTAK Project No 121Y407).

How to cite: Konca, A. Ö., Can, B., Özakın, A., and Aktar, M.: Investigating the Seismicity of Eastern Marmara Using Machine Learning Algorithms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13021, https://doi.org/10.5194/egusphere-egu24-13021, 2024.

The Cycladic Archipelago in Greece preserves widespread evidence for high-pressure (HP) metamorphism and subduction and extension tectonics, during the evolution of a NE dipping subduction zone. How and at what rates various HP rocks were subducted and exhumed and how the associated complex deformation patterns originated remains controversial. We collected 26 samples from the Cycladic Blueschist Unit (CBU), the overlying Makrotantalon Unit (MU) and their contact zone on Andros for white mica single grain ⁴⁰Ar/³⁹Ar dating and combined the results with field and petrological observations to constrain the tectonic evolution of the NW Cyclades. To investigate the thermal state during tectonic evolution and the duration of deformation, we conducted ⁴⁰Ar/³⁹Ar multiple single crystal dating on different grain size fractions of white mica from the same sample.

Our results show three distinct episodes of deformation:

• D0 is only locally preserved within the MU and the underlying contact zone and derives from the Early Cretaceous (128-119 Ma) Vardar ophiolite obduction above the Pelagonian margin, driving metamorphism and deformation of the passive margin. The white mica grains from the MU present Early Cretaceous ages of ~128 Ma (500-1000 mm) and ~117 Ma (120-250 mm). We suggest that the 11 Ma difference indicates a slower cooling rate.
• D1 recorded in the contact zone and in the CBU, indicating that the CBU was exhumed along this contact zone from subduction depths during the Eocene (52-48 Ma). The white mica grains from the CBU present Eocene ages of ~52 Ma (500-1000 mm) and ~48 Ma (120-250 mm), with a gap of 4 Ma suggesting a faster cooling rate.
• D2 is characterized by ductile-to-brittle deformation preserved in the contact zone and within the CBU, indicating they accommodated extension from around 28 Ma, with the initiation of slab rollback in the eastern Mediterranean. The contact zone between the MU and CBU exhumed greenschist-facies rocks of the CBU as a detachment until 21 Ma, when the rocks crossed the brittle-ductile transition and initiated brittle deformation, characterized by top-to-NE normal faulting.

We further redefine the structure of North Andros. In our study, we merge the MU and the ophiolites of the upper unit exposed in North Andros, previously thought to be separate units, in one unit equivalent of the Pelagonian unit. The contact between the MU and CBU, previously thought to be a thrust, is remapped as a brittle-ductile detachment fault between this one Pelagonian unit and the lower CBU and represents the NW extension of the Tinos, Mykonos detachments. This contact has accommodated syn-orogenic exhumation the CBU below the Pelagonian unit during Eocene HP metamorphism, and accommodated regional extension as part of the North Cycladic Detachment System during the Miocene.

How to cite: Shang, S., Uunk, B., Kuiper, K., Brouwer, F., and Wijbrans, J.: The Early Cretaceous to Miocene tectonic evolution of NW Cyclades based on 40Ar/39Ar multiple single crystal dating from Andros, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17400, https://doi.org/10.5194/egusphere-egu24-17400, 2024.

The 6 February 2023 sequence that was initiated by the failure of the <40 km-long Narlı fault turned out to be the biggest seismic event to occur in and around Türkiye during the modern times. While reaching a total rupture length of almost 450 km, the two separate sinistral events of Mw 7.7 and Mw 7.6 that took place 9 hours apart on the very same day also gave rise to an extremely heavy aftermath: loss of >50.000 lives and > USD 100 billion in economic damages.

We have analysed the first 12 months of postseismic movements following the February 2023 sequence using both Sentinel-1 and ALOS2 radar imagery. Movement along both the East Anatolian and Çardak fault zones are evident with the latter being more pronounced owing (probably) to the line-of-sight N-S insensitivity of the satellites. The time series analysis also shows movement along the westernmost part of the Sürgü fault and a ~20 km N-S oriented fault towards the western end of the Çardak rupture. The continuation of the dominantly E-W oriented Çardak rupture to northeast towards the city of Malatya is also evident in the postseismic data emphasizing once again the elevated seismic risk posed on the city.

Apart from the postseismic activity associated with the 2023 sequence another prominent feature observable in the radar data is the continuing aseismic movement along the Pütürge segment of the East Anatolian Fault Zone which was reported earlier by Çakır et al. (2023). Taking into account moderate earthquakes like the August 4^th, 2020 Mw 5.6 earthquake that took place in between the 2020 Mw 6.8 Sivrice-Elazığ earthquake rupture zone and the Yarpuzlu restraining bend where the Mw 7.7 event of the 2023 sequence has terminated; we propose that at least 20 km of the segment could still be unbroken.

How to cite: Akoğlu, A. M., Zabcı, C., and Çakır, Z.: Analysis of the First Year of Postseismic Movements Following the 2023 Kahramanmaraş (Türkiye) Earthquake Sequence Using InSAR Measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18791, https://doi.org/10.5194/egusphere-egu24-18791, 2024.

On 6 February 2023, the Eastern Anatolia experienced significant devastation due to two major seismic events, leading to the collapse of hundreds of thousands of structures and causing tens of thousands of human casualties, injuries, and homeless people. The substantial magnitude of these impacts is attributed to the extensive occurrence of heavy and very heavy structural damage, categorized as damage grades 4 and 5 according to the European Macroseismic Scale EMS-98, within the earthquake-affected area.

The discernible factors contributing to the disaster encompassed the substantial magnitude of the earthquakes, the occurrence of the initial seismic event during nighttime, thereby locating a considerable portion of the population within their residences, and the demographic attributes of the region characterized by densely constructed and populated zones, coupled with the close proximity of numerous residential areas to the ruptured faults. Additionally, the confluence of significant factors, closely associated with the seismotectonic context of the region, the effects of earthquake environmental effects, and the characteristics of the impacted structures, culminated in one of the most extensive earthquake disasters in the recent history of Turkey.

This study aims to highlight the factors controlling associated with building properties and the manifestation of earthquake environmental effects that govern the severity and spatial dispersion of structural damage within the earthquake-affected regions under study in the southeastern Turkey. The findings presented herein derive from field surveys undertaken by the authors in the immediate aftermath of the seismic events (7th to 11th February) and subsequently, almost two months later (31st March to 6th April). The field surveys included conventional techniques of geological mapping alongside innovative methodologies, including the deployment of Unmanned Aerial Systems (UAS).

With regard to building construction characteristics, insufficient adherence to building codes, arbitrary urban planning solutions, and substandard construction practices constitute primary deficiencies contributed to the disaster. Concerning geological factors, the generation of both primary and secondary earthquake environmental effects significantly influenced the intensity and distribution of damage. Locations where coseismic surface ruptures intersected with built-up areas exhibited heavy to very heavy structural damage, as evidenced along the ruptured segments of the East Anatolian Fault Zone. Liquefaction proximal to water bodies resulted in damage indicative of building foundation load-bearing capacity. Earthquake-triggered landslides predominantly impacted mountainous and semi-mountainous villages and areas characterized by pre-existing susceptibility. The substantial susceptibility to EEEs generation was extensively corroborated in numerous cases, leading to widespread damage. The presented information highlights the pivotal role of such studies in informing hazard mitigation and facilitating disaster risk reduction measures.

How to cite: Mavroulis, S., Vassilakis, E., Argyropoulos, I., Carydis, P., and Lekkas, E.: Geological Effects and Constructional Properties Controlling Structural Damage triggered by the 6 February 2023 Kahramanmaraş Earthquakes in Southeastern Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8446, https://doi.org/10.5194/egusphere-egu24-8446, 2024.

The East Anatolian Fault (EAF) is an approximately 420 km long sinistral strike-slip fault extending between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş) in the southwest. The earthquake in Sivrice (Elazığ) on January 24, 2020, with a magnitude of Mw 6.8, along with the earthquakes in Pazarcık (Kahramanmaraş) on February 6, 2023, with a magnitude of Mw 7.8, and Elbistan (Kahramanmaraş) with a magnitude of Mw 7.6, has increased the seismic potential of the left-lateral strike-slip East Anatolian Fault.

This study involved a total of 12 campaign measurements conducted at a GNSS network consisting of six sites in Palu (Elâzığ) segment of EAF  between the years 2015 and 2023. The distance of the survey GNSS sites and continuous GNSS stations from the fault varies between approximately tens of meters to hundred of kilometers. Before and after the earthquakes on February 6, 2023, near field GNSS data were utilized in the analysis of crustal movements related with  the earthquakes in 2020-2023. The estimated deformation in the GNSS network campaign results between September 2021 and September 2023, varies from approximately 10 ± 2.6 mm to 40 ± 2.9 mm in Palu segment. These estimations include not only the postseismic effects of the 2020 Sivrice (Elaz) earthquake, but also the coseismic and early postseismic effects of the 2023 Kahramanmaraş earthquake sequence, along with ongoing shallow creep observations.

How to cite: Hoşses, M. İ., Özarpacı, S., Özdemir, A., Ayruk, E. T., Turğut, M., Farımaz, İ., Doğan, U., and Ergintav, S.: Effects of the 2023 Kahramanmaraş Earthquake Sequence on the Palu Segment of the East Anatolian Fault, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15112, https://doi.org/10.5194/egusphere-egu24-15112, 2024.