An eikonal equation-based earthquake location method with joint inversion of the first P and sPg traveltimes

The first arrival times are widely used in earthquake location. However, the earthquake location methods using the first arrival times lack constraints on the focal depths due to the traveltimes of the first P-phase are less sensitive to focal depth. To improve the accuracy of focal depth, regional depth-phase methods have been proposed. The regional depth-phase methods greatly improve the precision of focal depth because the regional depth-phases are sensitive to the focal depth. Owing to the theoretical arrival time differences are calculated in one-dimensional layered models, the focal depths determined by the depth-phase location methods deviate from the real location when there exist large differences between the underground structures and the layered model. In order to improve the accuracy of focal depths and reduce the influence of model errors, we use the fast marching method to solve the eikonal equation and obtain the first P and sPg traveltimes in a heterogeneous model. Then, we conduct earthquake locations by joint inversion of the first P and sPg traveltimes. To validate the proposed method, we conduct synthetic and practical location studies of the 2022 Sichuan Luding M(s)6.8 earthquake. Results show that the proposed method can improve the accuracy of earthquake location.