JOINT INVERSION OF THE RUPTURE PROCESS OF 2018 ML5.7 XINGWEN EARTHQUAKE BASED ON SEISMIC AND INSAR OBSERVATIONS
The ML5.7 Xingwen earthquake on December 16,2018 is very likely induced by shale gas hydraulic fracturing,which caused not only massive landslides and rock collapse,but also some casualties in the surrounding area,with the direct economic loss of about 50 million CNY.It is of great significance to determine the source rupturing process of such an induced earthquake with large magnitude.Finite fault inversion is one of the commonly adopted methods to determine coseismic slip displacement distribution.For finite fault inversion,various data have different sensitivities to various aspects of the rupture process.The seismic data can provide the historical information about the earthquake rupture process because it contains the Doppler effect of the space-time rupture behavior on the fault.In comparison,the near-field geodetic data(such as InSAR and GPS)can constrain the fault parameters and the static slip distribution well because they contain the surface motion information.Therefore,the reliability of the inversion for the complex seismic rupture process can greatly be improved by combined use of seismicdata and InSAR data.In this study,strong-motion seismic data recorded at 8 near-field stations are chosen and filtered by a band-pass of 0.15-0.60Hz.The same InSAR data used in Wang et al.(2022)is adopted in this joint study.For inversion,a sufficiently large potential fault plane of 15km long and 10km wide is chosen and divided into 15x10 subfaults.Finally,the rupture process is obtained by joint inversion of strong-motion seismic data and InSAR data.The results show that the earthquake is characterzied by a typical unilateral rupture with the rupturing direction nearly towards the north.The duration of the rupture process was 6s,and the energy release was mainly concentrated in the first 5s.The rupture process is segmented and can be divided into two stages.The first stage is distributed from 1-3s and is located in the range of 0～5km from the source;and the 2nd stage is distributed from 3-5s and is located between 6 and 8km from the source.The coseismic slip is mainly concentrated in areas shallower than 5km,with a peak slip of approximately 0.27m.This can be used to explain why the Xingwen earthquake with a magnitude of ML 5.7 caused relatively serious damages.Combined with the distribution of foreshocks and aftershocks,it can be seen that the foreshocks were mainly concentrated to the eastern edge of the major coseismicslip zone,which are close to some hydraulic fracturing wells.This suggests that these foreshocks occuring at the edge of the main rupture zone has a certain correlation with fluids,and the presence of fluids further leads to the fault weakening of the mainshock due to the increase of pore pressure and the decrease of effective compressive stress,which plays a triggering role in the occurrence of the Xingwen earthquake.The aftershocks are mainly distributed around the main slip zone,which are caused by after slips after the mainshock.The results from seismic inversion,InSAR inversion and joint inversion of the two data types reveal that the Xingwen earthquake is a northward unilateral rupture.The rupture propagation direction and coseismic slip distribution may be related to the physical property changes along the fault plane.Compared with the two single inversion results,the joint inversion overcomes the influence of uneven distribution of seismic stations,improves the resolution of slip distribution,and produces results that are more consistent with the real physical process.The slip model obtained by joint inversion in this study can be helpful for further understanding the mechanisms of induced earthquake,the correlation between induced earthquake and geological structure,earthquake disaster assessment and post-earthquake disaster prevention and hazard mitigation.
Xingwen earthquakeearthquake rupture processinduced earthquakefinite fault inversionjoint inversion of seismic and InSAR data
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