Locking Status and Earthquake Potential Hazard along the Middle-South Xianshuihe Fault

Rumeng Guo,Wen Tian,Wenting Zhang,Jianqiao Xu,Yong Zheng

doi:10.3390/rs10122048

Abstract

By combining the seismogenic environment, seismic recurrence periods of strong historical earthquakes, precise locations of small–moderate earthquakes, and Coulomb stress changes of moderate–strong earthquakes, we analyze the potential locking status of a seismically quiet segment of Xianshuihe fault between Daofu County and Kangding City (SDK). The interseismic surface velocities between 1999 and 2017 are obtained from updated global positioning system (GPS) observations in this region. After removing the post-seismic relaxation effect caused by the 2008 Mw 7.9 Wenchuan earthquake that occurred around the fault segment, the observed velocities reveal a pronounced symmetric slip pattern along the SDK trace. The far field slip rate is 7.8 ± 0.4 mm/a, and the fault SDK is confirmed to be in an interseismic silent phase. The optimal locking depth is estimated at 7 km, which is perfectly distributed on the upper edge of the relocated hypocenters. A moment deficit analysis shows cumulative seismic moment between 1955 and 2018, corresponding to an Mw 6.6 event. Finally, based on a viscoelastic deformation model, we find that moderate–strong earthquakes in the surrounding area increase the Coulomb stress level by up to 2 bars on the SDK, significantly enhancing the future seismic potential.

Highlights

Located at the junction of the Songpan–Ganzi fold, Sichuan Basin, and Sichuan–Yunnan terrane, the Xianshuihe–Xiaojiang fault system is a mature continental transform fault system that transmits convergent deformation between the Indian and Eurasian plates [1]
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The 2D screw dislocation method assumes that the fault is locked from the surface to depth D, but that it slips by a constant amount below that depth; in reality, the locking scale varies in different areas, so that the real locking depth could be even deeper, and the locking scale should be smaller than 100%, so that there are some small earthquakes occurring in the locking areas

Summary

Introduction

Located at the junction of the Songpan–Ganzi fold, Sichuan Basin, and Sichuan–Yunnan terrane, the Xianshuihe–Xiaojiang fault system (hereafter abbreviated as XXFS) is a mature continental transform fault system that transmits convergent deformation between the Indian and Eurasian plates [1]. Zhao et al [4] imaged the spatial variation in the locking status of the fault system before and after the 2008 Mw 7.9 Wenchuan earthquake, by ignoring post-seismic viscoelastic relaxation All of these studies provide important insights to the seismogenic background and seismic hazard of the region. We build a viscoelastic model to quantify the relaxation effect of past earthquakes during the studied period, and correct the observed GPS deformation by removing the post-seismic effect. Through these steps, a relatively pure deformation field that caused by the status of fault SDK is built to study the fault-locking status. We combine the CFS changes that are triggered by surrounding moderate–strong earthquakes, and cumulative seismic moment to analyze future seismic hazards on the SDK

Data Collection

Signal Decomposition

Limitations

Conclusions