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.

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.