Şimşek, Ecenur Cansu; Alkan, Hamdi; Öztürk, Serkan

In this research, current and near-future potential earthquake zones in and around Muş basin (eastern Türkiye) are investigated using the instrumental period earthquake catalog and focal mechanism parameters of local earthquakes. For this purpose, the relationships between the b-value distributions and the Colulomb stress changes are interpreted with different depth ranges (5 to 25 km). Also, for a reliable prediction, the occurrence probabilities, recurrence periods of earthquakes, and the Z-value distribution (seismic quiescence areas) are taken into consideration. 15,722 earthquakes with moment magnitudes with 0.8≤Mw≤6.9 between the latitudes of 38.2°N-39.6°N and longitudes of 40.0°E-43.0°E, over a period of ~90.63 years between November 12, 1934, and June 30, 2025, are used for all statistical analyses. Completeness magnitude, Mc-value is accepted as 2.5±0.5. The b-value is determined to be 0.780 ± 0.04, which is smaller than the average (b = 1.0). Additionally, twenty local events with magnitudes greater than Mw≥4.8 are selected to image the Coulomb stress changes. The occurrence probabilities of earthquakes with Mw=5.5, 6.5, and 6.9 in 10 years are predicted as ~83%, ~27% and ~15%, respectively. Recurrence periods of events with these magnitudes are estimated as ~13, ~32, and ~63 years, respectively. Large Z-values are detected in the Kargapazarı segment, Bingöl province, and west of the Kulp and Kozluk segments. Additionally, the analyses of b-value and Coulomb stress change used for hazard prediction reveal a decreasing b-value and an increasing stress change around the Karlıova Triple Junction at a depth of approximately 10 km. Finally, these seismotectonic parameters can represent the possible locations for earthquake occurrences in the near future.

Salah, Mohamed K.; Alkan, Hamdi; Öztürk, Serkan; Güney, Recep

On February 6, 2023, two destructive earthquakes and many posterior aftershocks hit the Kahramanmaras,area in southern Anatolia. The Kahramanmaras, earthquake sequence (KMES) caused extensive damage and economic losses in T & uuml;rkiye and Syria. In this study, the 3-D crustal seismic velocities surrounding the hypocentral region of the KMES are determined using a large dataset of body wave arrival times obtained from local earthquakes. To better constrain the physical properties and seismogenic behavior of the KMES source region, the Vp/Vs ratio is calculated and correlated with Poisson's ratio using the obtained velocity models. To gain a better understanding of the stress conditions and regional earthquake activity in the study area, the depth variation of the b-value is also examined. The velocity structure is generally heterogeneous with both low and high velocities at upper crustal depths. Along the East Anatolian Fault Zone and its environs, low-velocity anomalies are charted. Also, small b-values (<1.0) are estimated in the region encompassing the KMES, especially at upper crustal depths. The KMES source zone is characterized by low b-value, low to average Vp, low Vs, and average/high Vp/Vs ratios. Hit count rates and the resolution test show that the mapped velocity anomalies are robust down to a depth of 45 km. Therefore, the moderate/high Vp/Vs and small b-values at the upper and middle crustal depths along the EAFZ may give constraints on the next earthquake hazards of the study region. The present findings provide deeper insight into the physical properties and the seismogenic potential of the crustal zones in proximity to the active fault segments of the Anatolian Plateau and the northwestern part of Arabia.

Büyüksaraç, Aydin; Senkaya, Mustafa; Alkan, Hamdi; Bektas, Ozcan; Öztürk, Serkan; Pirti, Atinc; Yücel, Mehmet Ali

The Simav Fault Zone (SFZ) in Western Anatolia remains one of the most active tectonic regions in Turkey, and the 2025 S & imath;nd & imath;rg & imath; earthquake swarm has renewed concern regarding evolving seismic hazard. This study analyzes the swarm on the S & imath;nd & imath;rg & imath; Segment using Coulomb stress modelling, spatial distributions of b- and p-value, gravity and magnetic anomalies, geothermal data, and GNSS observations. Coulomb stress calculations show that the M-W = 6.1 and M-W = 6.0 mainshocks produced stress increases of similar to 0.1 bar that effectively loaded adjacent segments of the SFZ, D & uuml;vertepe Fault Zone (DFZ), and Gelenbe Fault Zone (GFZ), guiding the east-southeast and northward migration of aftershocks. Spatial statistics indicate a b-value ranging from 0.6 to 1.3 and a p-value between 0.3 and 1.0. The lower b-values (< 1.0) and p-values (< 0.5) mark high-stress regions near the mainshock, and higher values characterize more stable zones. Gravity anomalies delineate a dense volcanic-ophiolitic body in the southwest and a caldera-like depression south of the SFZ, while magnetic anomalies highlight the structural continuation and interaction of the SFZ with the GFZ. GNSS stations recorded centimetre-to millimetre-scale motions: BAL1 moved similar to 1.34 cm horizontally with minor uplift, DEI1 experienced similar to 1.12 cm displacement with small vertical fluctuations, and KIKA shifted similar to 0.85 cm southwestward with largely stable elevation. Together, these results show that the 2025 swarm was controlled by stress transfer within a mechanically heterogeneous tectonomagmatic system. The identified stress-enhanced corridors along the SFZ and DFZ may act as future nucleation zones, emphasizing the need for sustained monitoring of this evolving fault network.

Öztürk, Serkan; Alkan, Hamdi

The current and future earthquake hazard in and around Bitlis were tired to reveal by utilizing the September 25, 2024, Yumrukaya-Tatvan earthquake (Mw=4.5) and its aftershocks, b-value and Z-value distributions, occurrence probabilities and recurrence periods of earthquakes and variations in Coulomb stress within the scope of this study. Also, it was tried to determine which fault systems in the study area is related to the Yumrukaya-Tatvan mainshock, characterized by strike-slip faulting. b-value in G-R relation was computed as 0.84∓0.06 and small b-values (<1.0) were imaged in the north-northwest-southeast directions throughout the South East Anatolian Thrust Zone and Muş Fault Zone, and west of Lake Van. At the beginning of 2025, significant seismic quiescence was observed near the Muş Fault Zone and the south and southeast of the South East Anatolian Thrust Zone. Recurrence periods for the events with the magnitudes of Mw=5.0, 5.5 and 6.2 were computed as ~10, ~26 and ~100 years, respectively. Additionally, occurrence probabilities of earthquakes with these magnitudes in the intermediate-term (~10 years) were calculated as ~64%, ~32% and ~10%, respectively. Positive Coulomb stress changes carry out a movement from the Kavakbaşı Fault zone in the west and the Beğendik segment in the east toward the South East Anatolian Thrust Zone in the east-southeast. In this region, there is no active fault/fault system according to the General Directorate of Mineral Research and Exploration. Thus, these findings are significant clues showing that multiple parameter seismo-tectonic analyses are important in determining the earthquake hazard for the September 25, 2024 earthquake, and that regions with small b-values and seismic quiescence and regions with positive Coulomb stress changes may indicate current hazard and possible earthquake zones in the future.

Alkan, Hamdi; Öztürk, Serkan; Bektaş, Özcan; Büyüksaraç, Aydın

The Marmara Region is an active tectonic region in northwestern Türkiye, which comprises some important strike-slip active fault mechanisms and important tectonic units, located near the western part of the North Anatolian Fault Zone. In the historical and instrumental period, the Marmara Region experienced large/devastating earthquakes. Considering this continuous activity, in this study, we investigate the tectonic structure and performed future seismic hazard estimation of the region based on some seismotectonic parameters. For this evaluation, we plot the Coulomb stress change maps of 1912 Mürefte-Şarköy, 1953 Yenice-Gönen and 1999 İzmit mainshocks with the earthquakes (MW ≥ 4.5) that occurred in the study region after 2003. For the estimation of b-value, occurrence probabilities and return periods of earthquakes, we used a homogenous local seismicity catalogue consisting of 119.029 events for the period between 1912 and 2023. In the findings of this study, the lower b-values and increasing Coulomb stress changes which are trigger stress failure compatible are observed in the west and northwest of the Marmara Sea. In contrast, the higher/moderate b-values and decreasing Coulomb stress values are observed in the east and southeast of the Marmara Sea. The results of probability assessments show that an earthquake with Mw = 6.5 may occur with a probability of 98% in the west of the Marmara Sea after 2025. As a remarkable fact, a comprehensive assessment of these types of variables will supply important findings for earthquake hazard and potential in the study region.

Senkaya, Mustafa; Alkan, Hamdi; Öztürk, Serkan; Büyüksaraç, Aydın

The 6 February 2023 Mw 7.7–7.6 Kahramanmaraş earthquake sequence has significantly impacted the East Anatolian Fault zone, including the city of Malatya and its immediate surroundings. In addition to the aftershocks of February 2023, the Mw 5.9 Kale earthquake that occurred on October 16, 2024, further underscores the ongoing seismic activity in the region. This study analyzes the distribution of b-values derived from a comprehensive dataset comprising 14,549 earthquakes and the Coulomb stress variations associated with the aftershocks of the February 2023 sequence and the Kale earthquake. The primary objective of this analysis is to enhance the understanding of the tectonic setting that contributed to the occurrence of the Kale earthquake. The findings indicate that the low b-values and stress transfer through the Pütürge segment toward the unnamed fault near Kale are significant contributing factors to the occurrence of the Kale earthquake. Additionally, positive stress variations from Doğanşehir to Malatya’s city center suggest a potential fault oriented toward the city center that may increase the current earthquake hazard. Furthermore, the distribution of seismic events around Malatya suggests a possible barrier supported by previous magnetic data analysis between Malatya and Kale. Lastly, the observed stress variations for the Kale earthquake indicate the likelihood of upcoming seismic events in both the northeast and southwest directions of the Kale.

Öztürk, Serkan; Alkan, Hamdi

Hakkari (Türkiye), depremsellik ve tektonizma olarak Güneydoğu Anadolu Bölgesinin en aktif illerinden bir tanesidir. Aletsel ve tarihsel dönemde, Hakkari ili ve civarında bulunan bu fay ve fay zonları birçok yıkıcı/hasar verici deprem üretmiştir. Son yıllarda Aralık 2023 (Mw=4.7) ve Şubat 2024’de (Mw=4.3) meydana gelen depremler, bu bölgedeki güncel depremselliğin önemli göstergelerindendir. Analizlerden elde edilen bulgulara göre, bölgede ortalama b-değeri 0.880.09 olup en düşük b-değerleri Yüksekova-Şemdinli Fay Zonu civarında gözlenmiştir. Buna ek olarak, pozitif Coulomb gerilme değişimleri Hakkari ili ve civarında KB-GD ve KD-GB yönlü olarak ortaya çıkmıştır. Diğer taraftan, seçilen bölge için Mw=5.0 büyüklüğündeki bir depremin tekrarlama zamanı ~16 yıldır. Ayrıca, Mw=5.0 büyüklüğündeki bir depremin 10, 16 ve 20 yılda oluşma olasılıkları ise sırasıyla ~%45, ~%62 ve ~%69 olarak hesaplanmıştır. Sonuç olarak, bu çalışmada hesaplanan sismotektonik parametrelerin birlikte değerlendirilmesi ile Hakkari ili ve civarının güncel sismik tehlike potansiyeli ortaya çıkarılmıştır.

Öztürk, Serkan; Alkan, Hamdi

In the present study, an evaluation of the region-time-magnitude behaviours of the earthquake occurrences in the West Anatolian Region (WAR), Türkiye, is carried out using the statistical and seis-motectonic parameters such as the b-value of Gutenberg-Richter relation, occurrence probabilities, and return periods of earthquakes. We also have mapped the Coulomb stress changes to observe the current and future earthquake hazard. In recent years, several large earthquakes such as the 1919 Soma (Mw = 6.7) and the 2022 and 2024 Aegean Sea (Mw = 5.3 and Mw = 5.1) revealed earthquake potential in the WAR. Coulomb stress analyses of 41 local events with mostly normal fault mechanisms have shown that posi-tive lobes (> 0.0 in bars) are mainly confined in the crust and uppermost mantle depths around Samos, Kos, and south of Lesvos. The smaller b-values (< 1.0) are observed in the same regions. On the contrary, we have observed a higher b-value from the offshore to onshore, south to north-trending direction, and negative scattered stress lobes (< 0.0 in bars) in slightly NW–SE oriented. The relationship between an increased b-value and negative stress change may indicate a similar seismicity for the region. In addition, we have analyzed the occurrence probabilities and return periods of the earthquakes, which showed us that Mw = 6.0 may occur at 75% in the intermediate term with an estimation of ~7 years. Our results reflect that these types of multiple-parameter assessments are important to define regional seismicity, seismic, tectonic, and statistical behaviours. Consequently, the areas with reductions in b-values and increments in stress imply the possible seismic hazard in the intermediate/long term.

Öztürk, Serkan; Akkaya, İsmail; Alkan, Hamdi

Çaldıran fault zone (CFZ) are significant seismically active zone that generated many destructive earthquakes. In this fault system, the last of these major earthquakes occurred on 1976 (Ms = 7.3). Therefore, based on the seismotectonic b-value, earthquake probability, recurrence times and Coulomb stress changes, we investigate the future earthquake potential and positive/negative stress changes in this fault zone. The events with a magnitude greater than 3.6 are used to investigate stress transfer direction regarding the seismotectonic parameters. The results indicate that the regions having smaller b-values are obtained along with the SE of CFZ, whilst higher b-values are calculated around the east of Lake Van. On the other hand, the northeast of CFZ represents current stress accumulation. Similarly, the Coulomb stress variations of 1976 earthquake show that stress accumulated at different depths in the northwest of this fault system. In addition, considering the long-term slip rates and horizontal offset in previous studies, the recurrence time of earthquakes has approximately 302 years for a magnitude greater than 6.0. Finally, these comprehensive analyses explain the implications of seismic hazard evaluation and forecasting of possible next earthquake occurrences in this region.

Öztürk, Serkan; Alkan, Hamdi

A detailed spatial-temporal analysis of the seismic activity in and around the Lake Van region was performed using several seismotectonic parameters such as b-value, Z-value, relative intensity (RI), pattern informatics (PI), and Coulomb stress changes. Correlations between these parameters were analyzed to esti-mate and forecast potential seismic hazards in the Lake Van region. Particular attention was paid to the parts of the study region that exhibited smaller b-values, higher Z-values, and high-stress changes at the beginning of 2022 and to the locations of earthquake hotspots determined from the composite earthquake forecast map for 2022–2032, i.e., Muradiye, Çaldıran, Özalp, Erçek, Van city center and Gevaş covering the faults of Çaldıran, Yeniköşk, Erciş, Malazgirt and the fault zones of Saray and Van. To provide more accurate interpretations regarding potential earthquake occurrences in the near future, the seismotectonic parameters analyzed in the scope of this study were compared with the corresponding seismological, geological, geodetical, and geochemical variables reported in the literature. This comparison showed that, firstly, our results are consistent with those reported in previous studies, and, secondly, all these variables should be interpreted in combination to correctly assess strong earthquake hazards. Furthermore, this type of multiple-parameter analysis may be important for the description of seismic, tectonic, and structural characteristics of the nature of the crust. Our findings show that almost all seismotectonic parameters indicative of anomaly regions, i.e., lower b-values, higher Z-values, high-stress distribution, and hotspots, were recorded in the same parts of the study region. Thus, the anomaly regions detected at the beginning of 2019 and between 2022 and 2032 may be considered to be potential zones of future great earthquakes. To summarize, the correlations among these variables may provide accurate information for assessing and forecasting earthquake hazards in this region.

Alkan, Hamdi; Öztürk, Serkan; Akkaya, İsmail

The Yedisu Seismic Gap is one of the most important seismic gaps throughout the North Anatolian Fault Zone since it has not produced destructive earthquakes for a long time. To analyze the characteristics of future seismic hazards, the interrelationships between seismotectonic b-values, Coulomb stress changes, and S-wave velocity models of crust are presented in and around the Yedisu Seismic Gap located northwest of the Karlıova Triple Junction. For this purpose, the most up-to-date earthquake catalog and the focal mechanism solutions of recent earthquakes are used to image the different depth intervals. Results show that the relatively positive stresses are accumulating along the Varto Fault Zone and Kargapazarı and Yedisu Segments between 5 and 15 km depth intervals. At the same time, the lower b-values between 0.6 and 1.0 are found in the same segments. However, in the volcanic regions around the Karlıova Triple Junction, the low S-wave velocity zones may be related to high b-values, negative stress changes, and volcanic structures. The region between the Turnadağ volcano and the Varto caldera shows scattered stress and b-value changes in the upper crust. Moreover, the probability of earthquakes for Mw = 6.0, 7.0, and 7.7 in the intermediate term (10 years) is estimated as ~ 65%, ~ 17%, and ~ 5%, respectively. Recurrence of earthquakes with Mw = 6.0, 7.0, and 7.7 are calculated as ~ 10, ~ 55, and ~ 187 years, respectively. Consequently, the regions characterized by low strong b-values and positive stress loading reveal high earthquake hazard potential on the whole in the next decade.

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.