Slip rate and high-resolution seismic structures along the creeping section of the Haiyuan Fault, NE Tibet

Abstract:

The Haiyuan fault is a major left-lateral strike-slip fault along the northeastern boundary of the Tibetan Plateau. The 1920 Haiyuan and 1927 Gulang earthquakes occurred along and round this fault system, but the section between the both ruptures, 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 Tianzhu seismic gap. However, the driving mechanism, fine structure of the creep section and its relationship with earthquakes are not clear.

We conducted a systematic search for repeating earthquakes along Haiyuan fault based on seismic data recorded by permanent stations in 10 years (2009-2018). Based on waveform cross-correlations, we found several repeating clusters at Laohushan section. These repeaters occurred to the west of the peak creep observed from InSAR observation. The inferred slip rate based on the repeating earthquakes is around 2 mm/yr, consistent with numbers from geodetic observations. In addition, we observed repeating earthquakes in the aftershock zone of the 1927 Gulang earthquake. We infer that these repeating events are likely driven by long-term postseismic relaxation processes associated with both historic earthquakes. In order to better image the fine-scale seismic structure along the creeping section, we deployed 60 dense nodal stations across and along the Laohushan section with station spacing ranging from 10 to 50 m. The deployment duration is between 2020/07/01 to 2020/08/01. We plan to use the collected seismic data to image the width and depth extent of the damage zone, and the velocity contrast across the fault interface. Updated results will be present at the meeting.