A further explore the source features of the 2016 Mw 5.9 Menyuan earthquake by empirical Green's functions and dynamic simulations

Abstract

A quantitative understanding of the factors that control earthquake rupture propagation is critical because it is helpful to estimate the eventual magnitude of an earthquake, which has significant implications for seismic hazard assessment. Previous studies suggest that the complex fault geometry and the heterogeneous material properties of the fault zone can slow and/or stop the rupture propagation. The 2016 Mw 5.9 Menyuan earthquake occurred near the Haiyuan fault system on the northeastern Tibetan plateau. Although some of the kinematic rupture properties of this earthquake have been known, the rupture process and some in-depth source properties remain to be understood. In this study, we first use the empirical Green's functions approach to reveal that the apparent source time functions (ASTFs) of this event display an approximately equal bell shape and have a total duration of about 3 s, which suggests that the rupture process of this earthquake is simple and exhibits no rupture directivity. Moreover, the spectra of ASTFs are very smooth and have no spectral holes. Then, we conduct two end-member spontaneous rupture models, namely the runaway rupture and the self-arresting rupture, to further explain the observed features of the ASTFs. We use the curved grid finite difference method (CG-FDM) to simulate the spontaneous rupture process with a linear slip-weakening friction law. Our results show that the synthetic data from the dynamic source fits well with the InSAR observations and strong ground motions, which indicates that the dynamic source captures the main features of this event. Significantly, the observed smooth spectra of ASTFs can be well explained by the self-arresting rupture process, which implies that this earthquake might be a self-arresting event. In other words, this earthquake may spontaneously stop before reaching the barriers. This finding suggests that some earthquake rupture processes may be deterministic by the initial stress state in which they nucleated. This work increases our understanding of what controls earthquake rupture propagation.