Seismic Source Mechanism Automatic Waveform Inversion For Moderate To Strong Earthquakes In The Chuan-Dian Area Based On 3D Velocity Model With Surface Topography

Seismic source mechanism inversion is a fundamental task in seismological research.Over the past few decades,researchers have developed and automated a variety of seismic source mechanism inversion algorithms,however,related work in China is still at the experimental stage,with only preliminary implementation of an automated seismic event information dissemination system.Reliable automated seismic source mechanism inversion algorithms are a significant enhancement to the seismic event processing process.In this paper,we design and implement a waveform-matching-based automated seismic source mechanism inversion algorithm to address this problem.In the inversion process,we consider the effect of waveform pre-processing methods and take measures to control the data quality during the inversion process.Finally,we use an efficient search algorithm to improve the efficiency of the source mechanism inversion.The method is tested on synthetic data and shown to be robust to noise and velocity perturbations.Having improved the efficiency of the source mechanism inversion,we also wish to improve the waveform matching effect of the full waveform source mechanism inversion.Compared to the Green’s function calculated from a 1D layered velocity model,the Green’s function calculated using a 3D velocity model with topography can improve the waveform matching and hence the inversion of the source mechanism.We use the spectral element method(SEM)to implement wavefield modelling using a 3D velocity model with topography,and the reciprocity theorem to calculate the Green’s functions database within a specified area around the station.We validate the results of the Green’s function calculation by comparing this method with other methods under different velocity models to demonstrate the correctness of this method,and then we show the effect of horizontal velocity structure and topography on the Green’s function waveform compared to the 1D velocity model,respectively.We have combined these two efforts to develop a practical application for the inversion of the source mechanism of moderate to strong earthquakes in the Chuan-Dian area.First,we computed the 3D Green’s functions database for 109 permanent stations within 200 km of the Chuan-Dian area based on the high precision 3D velocity model SWChina-CVM2.0,and then we used the developed source mechanism inversion method to invert for the focal mechanism and moment tensor of 229 ML≥4.0 events in the Chuan-Dian area.The inversion results show consistency with the local fault structure and are also in good agreement with the results of manually processed source mechanism solution catalogues published by others.