Analysis of the recent regional stress field of Erzincan Basin (Türkiye) and its surroundings using small to moderate earthquakes

Abstract

The Erzincan Basin is one of the most actively deforming geologic features in Eastern Anatolia owing to the high seismic activity taking place in the surrounding area. In the last century, the 1939 Mw = 7.9 and the 1992 Mw = 6.8 earthquakes are the two largest events that devastated the city of Erzincan caused the loss of more than 33,000 and 600 lives, respectively. This study analyzes the seismicity in the vicinity of the Basin. The main trace of the North Anatolian Fault Zone (NAFZ) crossing the Erzincan Basin reveals relatively lower seismicity pattern in terms of small earthquakes. On the contrary, remarkable off-fault seismic activity occurs along the secondary segments. The segments located to the south of NAFZ are striking at high angles to the main trace. The potential of the secondary faults to generate Mw = 6.0 earthquakes was revealed by the 2003 Pülümür earthquakes, pointing out their significant contribution in shaping the Erzincan Basin. The fault segment ruptured by the Pülümür event is located to the east of the subparallel Ovacık fault showing left-lateral strike-slip sense of motion. Similar seismic lineaments exist to the west of the Ovacık fault. All these secondary segments are laying to the south of the NAFZ main trace. In this study, the stress tensor analysis of the Erzincan Basin was conducted using the azimuths and plunges of the P- and T-axes obtained from the focal mechanism solutions of the earthquakes that occurred in the region. The focal mechanisms of the events around those segments have P- and T-axes oriented close to N–S and E–W, respectively. On the contrary, to the north of NAFZ prominent seismic activity takes place only along a segment striking almost E–W accommodating events mostly showing right-lateral strike-slip faulting. These facts indicate a complex stress field acting around the Erzincan Basin.