Geochemical precursory characteristics of soil gas related to the 2019 Xiahe Ms5.7 earthquake across the northern margin of West Qinling fault zone,Central China

Abstract

Abstract The Xiahe Ms5.7 earthquake occurred on October 28, 2019, and was located within the national earthquake priority hazard zone designated as of 2019. We use the mobile observation data of soil gases Rn, Hg, H2, and CO2 from 2016 to 2019 of 11 profiles in the northern margin of the West Qinling fault zone, combining the sturdy body seismogenic model and numerical simulation results to investigate the spatial and temporal evolution characteristics of the cross-fault soil gas before the Xiahe Ms5.7 earthquake. This research showed that the seismic activity of the northern margin of the West Qinling fault zone varies significantly among the secondary fault zones, and the overall state is that the middle east section’s activity is weakened toward the west section, which has good coupling with the spatial distribution characteristics of the fault soil gas in this fault zone. The soil gas concentration intensity across the northern margin of the West Qinling fault zone showed a clear decreasing trend from HT1 to HT4 in the western section, which is the closest segment to the Xiahe Ms5.7 earthquake fault, and a turning up after a continuous decrease in Rn in HT1 and Hg and CO2 in HT2, and Rn, CO2, and Hg in HT4. The other measurement lines in the middle east section did not show similar precursor features. The decline characteristic of fault gas tectonic geochemistry is a good indicator of the interlocked section of fracture tectonic activity. The sturdy body seismogenic model can explain the relationship between the tectonic geochemical characteristics and the rupture locking, and it has theoretical support for determining the time, space, and intensity of seismogenesis. Strengthening the research on seismic models, obtaining a physical model that is “close to reality,” and generating a comprehensive and unified interpretation of the precursor field under the guidance of certain models is a practical approach for earthquake prediction and forecasting in the future. It is easy to make mistakes in terms of the location if we do not identify the mechanism. Thus, it is crucial to strengthen the flow monitoring and seismogenic model research of the deep fluids in the fracture zone.