Double-difference Earthquake Relocation And Tomography In The Chinese Capital Region

Earthquake location is a classic problem in seismology,and double-difference earthquake relocation is a very popular relocation method with high precision.Tomography is an imaging method used to invert the geophysical parameters of the earth.Wave-equation based travel time seismic tomography is a promising method to study the internal structure of the earth.The data of earthquake location is necessary for large-scale underground structure tomography using travel time data from seismic station.Whether the location of the earthquake is accurate enough seriously affects tomography results.In this paper,we use double-difference earthquake location method to relocate the earthquakes in the Chinese capital region.We use wave-equation based travel time seismic tomography to invert the underground earth structure and then compare the imaging results before and after earthquake relocation.After using double-difference relocation,the earthquake distribution in the depth slice becomes more random compared with the original earthquake location in the catalog data,which distributes in the stratified lines.It is found that the earthquake distribution is more concentrated in the section near the fault after relocation,which conforms to the geological knowledge about the location of the earthquake,that is,the earthquakes often occur in the area near the fault.The tomographic imaging was performed again using the data after double difference relocation.Wave-equation based travel time seismic tomography can simulate the seismic wave and extract the travel time residual,which can more effectively invert the fine structure under the earth than the traditional ray method.In this paper,the tomography result after earthquake relocation is compared with other tomography results.The tomography result after double difference earthquake relocation still has a strong transverse heterogeneity,and the velocity anomaly in the depth direction is more obvious.The six sections along the fault direction show the distribution of some large earthquakes with magnitude above 5.The results show that most of the earthquakes are distributed at the junction of low speed and high speed anomaly.After earthquake relocation,the deep structure is more clear.