Systematic Search for Repeating Earthquakes Along the Haiyuan Fault System in Northeastern Tibet

Abstract

AbstractRepeating earthquakes have been found at many faults around the world. The Haiyuan fault is a major left‐lateral strike‐slip fault along the northeastern boundary of the Tibetan Plateau. Two great earthquakes (1920 Haiyuan and 1927 Gulang) have occurred on and round this fault system, but the section between the ruptures of the two earthquakes, also known as the Tianzhu seismic gap, remains unbroken. Shallow creep has been observed from geodetic data at the Laohushan section of the Haiyuan fault near the eastern end of the seismic gap. However, the driving mechanism and depth extent of shallow creep are not clear. Here we conduct a systematic search for repeating earthquakes in northeastern Tibet based on seismic data recorded by permanent stations in 10 years (2009–2018). Based on waveform cross‐correlations, we find several repeating earthquake clusters at the Laohushan section. This is consistent with the shallow creep inferred from the geodetic data, indicating repeating earthquakes can be driven by nearby aseismic slip. Approximately 300 repeaters were found within clusters of intense seismicity near the rupture zones of the 1927 M8.0 Gulang and 2016 M6.4 Menyuan earthquakes. Relocation of events in the cluster near the Gulang earthquake delineates two possible unmapped faults orthogonal to the Haiyuan fault. In addition, we also identify several repeating earthquakes generated by mining activities with different waveforms and occurrence patterns. Our study suggests that repeating earthquakes around the Haiyuan fault are likely driven by long‐term postseismic relaxation process associated with the 1920 Haiyuan and 1927 Gulang earthquakes.