Active seismotectonics of the East Anatolian Fault

SUMMARY The East Anatolian Fault (EAF) is a 700-km-long left-lateral transform fault located between the Anatolian and Arabian plates. The proximity of the Euler Pole to the Arabia–Anatolia Plate boundary leads to rapid changes in plate velocity along the boundary, which is manifested by the decreasing slip rates from east (10 mm yr–1) to west (∼1–4 mm yr–1). The EAF displays heterogeneous seismicity patterns with seismic gaps, localized clusters and broad diffuse zones. In this study, in order to understand the origin of these complexities and quantify the seismic hazard along the EAF, we present an improved seismicity catalogue with more than 26 000 earthquakes and 160 focal mechanisms from regional moment tensor inversion between 2007 and 2020. The focal mechanisms and seismicity show that the EAF dips towards north and forms a well-defined plate boundary in the east between Palu and Çelikhan with almost pure left-lateral motion. Further west, the boundary becomes broader with activity along subparallel faults. Focal mechanisms show heterogeneous stress orientations in consistence with geodetically determined strain rate field. The stress orientations show a transition from strike-slip to extension towards the west of Çelikhan. Amongst all segments of EAF, the Pütürge segment, which holds the near-repeating earthquakes in the vicinity of the nucleation of the 2020 Mw 6.8 earthquake, is distinguished with its steady and high rate of seismicity. Further east, the neighbouring Palu segment is characterized by several distinct moderate earthquakes. We do not observe any change in the seismicity rate on these segments of the EAF following large earthquakes. In order to quantify the seismic hazard along the EAF, we calculate the recurrence time and maximum magnitude for each segment by using an extended seismicity catalogue of 150 yr including the large historical earthquakes and the geodetic strain rate. The results show ∼150 yr recurrence time with Mmax∼6.7–7.0 along the seismically active Palu and Pütürge segments on the east, while relatively silent western segments yield longer recurrence times; 237–772 for Pazarcık and 414–917 for Amanos segments with slightly larger magnitudes (Mmax ∼7–7.4). We infer that the seismicity patterns and strain-rate field along the EAF are shaped by several factors such as strong geometrical irregularities, heterogeneous coupling and complex plate motion leading to rapid change of fault slip rate.