| The rupture of blind fault earthquake are not transmitted to earth surface,which makes it difficult to determine the parameters of the seismogenic fault.The determination of the parameters of the seismogenic fault is the foundation of studying the rupture mode and focal mechanism of the earthquake and then investigating regional stress state and earthquake risk.Therefore,it is of great significance to study the problem of blind fault parameter determination.At 21:27 on January 19,2020 Beijing time(UTC+8),an MS6.4 earthquake occurred in Jiashi County,Kashgar,Xinjiang,China.The epicenter of this earthquake is located near the front fault of the Kalpintag thrust and nappe.It is another strong earthquake in this area after more than ten years.However,the earthquake rupture did not reach the surface,making it difficult to determine the fault parameters.At present,the results given by the existing studies are different,and the seismogenic fault of the earthquake is still inconclusive.This paper uses InSAR data to study the surface deformation characteristics,rupture characteristics and seismogenic mechanism of this earthquake event,and based on the optimal fault model,the regional Coulomb stress changes are studied.The research results have important reference significance for better understanding the Jiashi earthquake and assessing the regional earthquake risk.The results of this study are as follows:1.Using ESA Sentinel-1 satellite ascending and descending orbit SAR data to obtain the LOS coseismic deformation field of the Jiashi earthquake,and further solve the twodimensional deformation field.The characteristics of the deformation field reveal that the seismogenic fault is a north-dipping fault with an EW-trending trace,and the trace position is close to the southern margin of the InSAR coseismic deformation field.The surface deformation caused by this earthquake event is mainly distributed on the Kalpintag nappe and the Ozgertawu nappe.The maximum and minimal displacements along the line of sight(LOS)are 0.064m and 0.076m for the ascending interferogram and are 0.029m and 0.027m for decending inteferogram,respectively.The two-dimensional deformation results calculated by the joint ascending and descending data further confirm that the earthquake was a thrust event in front of the southern Tianshan Mountains.2.The geometric parameters and dynamic parameters of the Jiashi earthquake are inverted in two steps by Bayesian method.The results show that the earthquake was a thrust event with a small amount of strike-slip components.First,with the InSAR deformation data as the constraint,nonlinear inversion is performed to estimate the geometric parameters of the fault.Before the inversion,a reasonable search range is set according to prior information such as geological data.The posterior probability density of the fault parameters obtained in this paper has a narrow confidence.The results show that the strike,dip and depth of the fault bottom edge are predominantly distributed at 275.9～277.0°,9.1～11.4°,and 6.8～7.1km,respectively.Comparing and analyzing different results,it can be found that the fault geometric parameters constrained by InSAR data have better consistency than the results constrained by seismic waves,but for moment magnitudes,the results given by various seismic agencies are more consistent.Then,based on the estimation results of the fault parameters,a linear inversion is performed under the Bayesian framework to construct a slip distribution model.The results show that the earthquake rupture is distributed in a long and narrow area about 30 km along the strike and about 8 km along the dip.The sliding is mainly concentrated in the underground depth of 5.4～7.6km.Taking the maximum posterior probability solution as the optimal value,the maximum slip is 0.45m,which appears at 6.5km underground.Compared with the results of other methods,the slip distribution of the Jiashi earthquake obtained by the Bayesian method is more concentrated.The inversion result corresponds to a moment magnitude of 6.17,which is slightly larger than that of the USGS.In order to verify the effectiveness of the von Karman regularization method,the Laplacian regularization method is used for inversion and the results obtained by the two methods are compared and analyzed.The results obtained by the two methods have good agreement.3.Based on the determined optimal fault slip model,the coseismic Coulomb stress changes in the vicinity of the Jiashi earthquake and the triggering relationship of the main aftershocks are studied,and the stress adjustment of the adj acent Ozgertawu fault caused by the Jiashi earthquake is analyzed.The Jiashi earthquake did not fully rupture the locked faults in this area,and caused stress loading on the adjacent faults,so it is considered that the Keping nappe still has a high seismic risk.Combined with InSAR results,geological and geophysical data analysis,it is believed that the seismogenic fault of this Jiashi earthquake is the Keping fault. |
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