Research On Inversion Of Coseismic Slip Distribution And Stress Triggering Of Earthquakes

Coseismic slip is helpful to describe the geometry,strength,and friction characteristics of active faults and to calculate the stress in the area around the seismogenic fault,which can be used to evaluate the risk of the surrounding fault.Geodetic data are widely used in inversion of coseismic slip distribution because of their high observation accuracy and wide coverage.The inversion of unstable slip distribution is sometimes resolved by Tikhonov regularization technique thanks to the ill-posed constant matrix.The determination of regularization parameters is that the key of inversion.In addition,geophysics information totally categories have different characteristics and different blessings in inversion,thus it's of nice significance to form full use of the benefits of multi-source information to confirm the responsibility of inversion results and improve the accuracy of inversion.Secondly,the occurrence of large earthquakes may be accompanied by large aftershocks or foreshocks,and the study of the triggering relationship between serial earthquakes can better understand the source rupture process of earthquakes.In this paper,the regularization parameters,the determination of relative weight ratio in joint inversion and the triggering relationship between serial earthquakes are studied.This article main research content and the work is as follows:1.The method of determining the regularization parameters in the inversion of the coseismic slip distribution is studied.To address the problems of the L-curve method,which is the most commonly used method for regularization parameter determination,such as the parameters are mostly artificially selected and depend on the data fit,this paper introduces the A-optimal design method to the field of coseismic slip distribution inversion,and designs a simulation experiment to verify the effectiveness and superiority of the A-optimal design method.The results show that the A-optimal design method has the advantages of accurate localization and high inversion accuracy compared with the classical method,and the A-optimal design method can read the regularization parameters directly without relying on the data fit.2.The determination method of relative weight ratio in multi-source data joint inversion is studied.In the joint inversion,when the variance component estimation method is used to determine the relative weight ratio,it does not take into account the morbid nature of geodetic inversion.The regularization solution is used to replace the least squares solution,so as to introduce bias,resulting in inaccurate variance component estimation.In this paper,bias correction variance component estimation method is used to eliminate the influence of bias introduced by regularization solution.Simulation experiments show that the variance component estimation method after bias correction can better reflect the slip distribution.In this paper,the deviation introduced by the initial value of iteration is considered in the variance component estimation of bias correction for parameters,and the theory is more rigorous.The results of Visso earthquake and Norcia earthquake show that the deviation correction is reasonable and advantageous.3.The triggering relationship between sequential earthquakes is studied.In the inversion of slip distribution of seismic sequences,the time span of In SAR data is large,which contains the deformation caused by multiple earthquakes.It is difficult to use In SAR data to invert the slip distribution of single earthquake.In this paper,the cooperative inversion method is used to invert the slip distribution of single earthquake in seismic sequences.At the same time,the joint inversion method and the proposed method are used for simulation experiments.The experimental results show that the proposed method is effective.The slip distribution of M_w6.4 foreshock and M_w7.1 main shock of Ridgecrest earthquake is inverted by this method.The results show that the M_w7.1 main shock is a northwest right-lateral strike-slip fault,and the M_w6.4 foreshock includes northwest right-lateral strike-slip fault and northeast left-lateral strike-slip fault.The maximum slips generated by the two earthquakes are 4.45 m and 1.0 m,respectively.The cumulative released seismic moments are 4.49×10¹⁹N·m and 5.31×10¹⁸ N·m,and the corresponding moment magnitudes are M_w7.07 and M_w6.45.The calculation results of static coulomb stress show that the main shock of M_w7.1 is triggered by the foreshock of M_w6.4.