Dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution: A case study of the 2017 Mw 6.5 Jiuzhaigou earthquake

Abstract

Heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes. We propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 Mw 6.5 Jiuzhaigou earthquake, which occurred in the intersection area of the Minjiang, Tazang and Huya faults, in Sichuan Province, China, with the slip distributed on two distinct left-lateral strike-slip faults as shown in previous geodetic and seismic joint inversion. We use the seismic efficiency empirical relation to infer the average stress, and the average stress drop is estimated using the static stress drop. With the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks, different principal stresses are calculated with different combinations of average stress and average stress drop. The initial normal and residual stresses can be determined using the projection of the principal stresses. The initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop, which is generated by a set of Gaussian random numbers with a given mean and the variance, and mapped one-by-one with the given slip on the fault so that the area with a large slip has a large stress drop. By comparing the slip from dynamic rupture simulations and the input joint inversion result, we show that the case with a 36 MPa average stress and 2.1 MPa average stress drop provides the best-fitting slip snapshots. The dynamic Coulomb stress change shows that the 2017 Mw 6.5 Jiuzhaigou earthquake could bring the southeast of the Tazang fault and the middle of the Minjiang fault closer to failure. This work provides a new insight to understand the initial stresses of nature earthquakes.