Source Parameters and Slip Distribution Inversion of 2013 Lushan Ms 7.0 Earthquake

On April 20th 2013, Ms 7.0 earthquake occurred on the southern section of the Longmen Shan fault, in Sichuan Province. In this research, the three-dimensional coseismic displacement field that GPS data from 33 continuous stations are used to invert for fault geometry parameters and the slip distribution. The MPSO (multiple peak particle swarm optimization) algorithm has been successfully applied to invert for the fault model parameters.Compared with the commonly used algorithm, such as genetic algorithm, simulated annealing and the overall minimum norm optimization algorithm, MPSO algorithm has the advantages of less control parameters, high global convergence efficiency, and is very suitable for nonlinear inversion of fault parameters. The result indicates that the seismogenic fault is a thrust with a strike of 206.47°, a dip of 44.11°, and length of 21.94 km. The minimum and maximum depth is 7.66 km and 17.84 km, respectively. The fracture surface was determined as listric surface by analysis. In order to obtain the detailed slip distribution, the listric surface model is set with the default dip angle varying from 50° on the top boundary of the surface to 21° on the bottom boundary. Our inversion result shows that the rupture surface has two slip peaks at different depths. The maximum slip is 0.68 m at the depth of 13 km. The inverted geodetic moment is 1.47×10¹⁹ N·m and the moment magnitude Mw is 6.74, which is consistent with the result of seismology.