[U-13] February 2023 Earthquake Sequence of the East Anatolian fault zone in Turkey

[U13-07] Cascading ruptures due to dynamic and static stress transfer associated with the 2023 Kahramanmaraş, Turkey, earthquake

*Shinji Toda¹ (1.International Research Institute of Disaster Science, Tohoku University)

Keywords:Turkiye earthquake, East Anatolian fault, Coulomb stress change

The 2023 Kahramanmaras, Turkey earthquake of Mw 7.8 that brought unparallel damage to the areas due to its widespread strong ground motion. The earthquake was caused by dynamic rupture of ~300 km in total involving three fault segments of the East Anatolian Fault (EAF). About nine hours after the mainshock, another Mw 7.5 earthquake ruptured ~160-km-long Surgu-Cardak fault that is a branch of the EAF. The epicenter of the M7.8 event locates ~20 km south of the center of the EAF rupture zone, which is indeed southern edge of the previously mapped small branch fault named Narli fault. The AFAD hypocenter catalog also demonstrates the seismicity rate near the epicenter has significantly risen since mid 2022 like a long-lasting seismic swarm, which enables us to consider active nucleation process to trigger the Narli fault rupture. This 20-km-long Narli fault rupture consequently led to a bilateral ~300-km-long faulting along the EAF (e.g., Melgar et al., 2023). The M7.8 rupture zone is composed of three distinctive segments, Amanos, Pazarcik, and Erkenek (Duman and Emre, 2013). Cumulative strain on the Pazarcik segment in particular was estimated to have been high due to the long-elapsed time since the last historical event of possibly 1513 A.D. Secular and transferred stress on the Pazarcik segment since 1822 modelled by Nalbant et al. (2002) also reached ~15 bar and regarded as the most hazardous fault segment along the EAF. To retrospectively evaluate whether the M7.8 mainoshock triggered the subsequent M7.5 earthquake, we calculated static Coulomb stress change on the Surgu-Cardak fault imparted by the M7.8 rupture using the USGS finite fault model. We found up to 3 bars of Coulomb stress were imparted to the central portion of the fault, which is roughly 10% of a typical stress drop in an earthquake, and sufficient to trigger an earthquake if the fault was already close to failure.