Fault structures of the Haichenghe fault zone in Liaoning, China from high-precision location based on dense array observation

Abstract

The Haichenghe strike-slip blind fault, which experienced the M 7.3 Haicheng earthquake in 1975, is one of the most active seismic zones in eastern China. To better understand the fault structures, we deployed a dense array of 23 broadband seismic stations in the area in 2022, with an average distance interval of ~ 6 km. Combining the automatic workflow LOC-FLOW with manual review, we detect 1339 events with a completeness of magnitude ~ ML -0.1 using data recorded at the dense array and the Liaoning regional Seismic Network from Oct. 1 to Oct. 31 in 2022. Of these, we relocated 877 earthquakes using Hypoinverse and HypoDD. The relocations finely delineate the NWW-striking Haichenghe fault, including the NW and SE segments, and its NE-trending conjugate fault. They also clearly feature two seismic gaps, one corresponding to the fragmentation zone generated by the M 7.3 Haicheng earthquake and the other being consistent with the low-velocity zone between NW and SE segments. Based on relocations, we further identify 10 clusters of recurrent events with a median magnitude of ML 0.8. We observed a phenomenon that several clusters are occurred right after the ML 3.7 event, the largest event during the observation. We suggest that, as a larger-magnitude earthquake, the ML 3.7 event resulted in the stress change along the fault plane and triggered the small-magnitude repeaters. Our results indicate that dense array observation in the study area could provide an abundant seismological basis for studying the Haichenghe blind fault.