Polat, Orhan; Ozer, Caglar; Ozturk, Serkan

Two devastating earthquakes occurred on the Eastern Anatolian Fault Zone (EAFZ), measuring 7.8 and 7.6 moment magnitudes (Mw), struck Türkiye and Syria on February 6, 2023. The first earthquake Mw7.8 took place on the EAFZ in Pazarcik district of Kahramanmaras city and the second earthquake (Mw7.6) was on Cardak Fault (CF, an E-W aligned segment of the EAFZ) in Elbistan district of the same city. The first earthquake on EAFZ and the second earthquake on CF reveal dominant sinistral strike-slip character according to focal mechanisms solutions of aftershocks (e.g., Mw = 6.8, Mw = 6.4). Total number of aftershocks exceeds 58,000 as of November 2023. Destructive earthquakes have resulted significant impact on 11 cities in Türkiye and 5 provinces in Syria. Doublet earthquakes (compound earthquake) and aftershocks have caused remarkable surface rupture that exhibit horizontal and vertical slips along NE-SW oriented EAFZ (400 × 40 km2) and E-W aligned CF (250 × 40 km2). Based on the seismicity analysis, 88% (45 events over 51 of the aftershocks with magnitudes greater or equal to 5.0 occurred within the first three days following the Mw = 7.8 mainshock. The state of stress from 1977 to the Kahramanmaras doublet earthquakes (DEQ), was almost shear stress regime whereas it reveals between extension (normal) to strike-slip regime. The CF zone area exhibits a dominant shear stress regime. The Kahramanmaras earthquake has generated remarkable set of surface ruptures about ~ 500 km, in total (~ 350 km long for EAFZ and ~ 150 km for CF) with a dominant sinistral strike-slip character. These ruptures could be observed mainly from the south of Hatay city up to north of Celikhan district along the EAFZ, and between Goksun district and Kelhalil village along the CF. Seismic gaps with low geodetic strain rates and low background seismicity were observed between Islahiye (Hatay city) and Nurdagi (Gaziantep city) districts, and around Pazarcik district (Kahramanmaras city). The largest peak ground acceleration (PGA) was recorded by Pazarcik station (Code: 4614) with about 2 g (2039 gal) in the EW component. The next target location for destructive earthquake could be on the Cyprus arc towards Island with the potential to cause a tsunami, or could occur along the DSF by affecting Syria and Lebanon. The EAFZ is an important reminder that large faults can generate very large earthquakes on multiple segments as Türkiye and Syria have experienced during and after the Mw = 7.8 mainshock.

Ozturk, Serkan; Alkan, Hamdi

In this study, current earthquake hazard is tried to present and earthquake forecasting is made for Lake Van and its adjacent area for the next five years. For this purpose, a statistical analysis is achieved with the concomitant use of the b-value, Z-value, relative intensity (RI) and pattern informatics (PI) data. In addition, for the earthquake forecasting in the intermediate term and hazard, a comprehensive discussion is made with the studies analyzing the different seismological and geophysical variables in literature. The relations between these parameters reveal more accurate and reliable approaches. Consequently, at the beginning of 2022, particularly the areas having small b-value and large Z-value with the hotspots (possible earthquake areas) between 2022 and 2027 from the combined forecast map are determined in and around Muradiye, Çaldıran, Özalp, Van city centre and Gevaş including Çaldıran, Yeniköşk, Erciş and Malazgirt faults with Saray and Van Fault zones.

Ahadov, Bahruz; Ozturk, Serkan

In this study, a comprehensive statistical analysis was made for different parts of the world. For this purpose, fundamental seismotectonic earthquake parameters such as b-value, magnitude completeness, Mc-value stress distribution and moment release were analysed and their interrelationship was investigated. In this context, for the evaluation of earthquake hazard potential, spatial variations of these fundamental parameters were achieved for the Eastern Mediterranean and Caucasus since there do not exist detailed studies including these parameters for these regions of the world. The high-resolution maps of the b-value, Mc-value and stress variance were analysed in the different seismotectonic regions in the Eastern Mediterranean and Caucasus. This study considers the spatial anomalies and correlation models between the b-value, faulting styles, and stress regime and moment release. Lower b-values (b ≤ 1) were observed along with the Main Marmara Fault, eastern Turkey, western Alborz, northern Zagros, south-east Iran and the north-east Caucasus, and these small b-values indicate the active seismic region. Mc level in most of Turkey is in and around 2.8. However, Mc-value is about 3.0 in the Caucasus and about 3.5 level in Iran. This work also includes a stress inversion map in the region based on the focal mechanisms. The normal, strike-slip and a few thrust fault solutions were observed in the research areas. The results show that a combination of these parameters may supply preliminary tools for future researches. Consequently, the spatial pattern of the b-values, moment releases and stress regimes can be used as considerable promise for the predicting of forthcoming seismic hazard regions.