Effects of fault geometry and pore fluid on the dynamic rupture process of the 2008 Mw 7.9 Wenchuan earthquake, China, on a multi-fault system

Wenqiang Zhang, & Yajing Liu

Published September 8, 2024, SCEC Contribution #13939, 2024 SCEC Annual Meeting Poster #146

The 2008 Wenchuan Mw7.9 earthquake, China, occurred in the Longmenshan thrust belt on the eastern margin of the Tibetan Plateau. Coseismic surface rupture extended ~ 240 km along the Beichuan-Yingxiu fault (BYF) and ~ 70 km along the Pengguan fault (PGF), two major faults that are sub-parallel on the surface and intersect at depth forming an imbricate structure. Recently, a high-resolution three-dimensional (3D) Wenchuan earthquake rupture zone fault geometry model was constructed based on the results of surface rupture field surveys, aftershock locations, focal mechanisms, and seismic reflection profiles. The 3D fault geometry shows that the Wenchuan mainshock caused rupture on several secondary geometric structures, including the ~20-km-long Yingxiu fault nearly parallel to the BYF near the southwest end and the 6-8 km Xiaoyudong tear fault nearly perpendicular to the BYF. Although the ~50-km-long Miyaluo fault did not rupture during the mainshock, it experienced significant aftershocks. Due to limitations in numerical implementation, previous modeling studies of the Wenchuan dynamic rupture had to adopt a simplified fault geometry or neglect secondary geometric structures such as branch/intersecting faults to ensure numerical stability. In this work, we use our recently developed discontinuous Galerkin finite element method (Zhang et al., 2023) to simulate the Wenchuan earthquake rupture process along the Longmenshan multi-fault system, constrained by observations such as the surface ruptures, GPS coseismic displacements, and ground motions. Our preliminary results show that fault geometry controls the first-order characteristics of coseismic slip distribution and the rupture-jump process of the BYF and PGF imbricate faults. In addition, based on the post-Wenchuan fault zone permeability measurement (Chen et al., 2011, 2013), we will discuss the competing effects of thermal pressurization and dilatancy on the rupture process, especially on the rupture propagation speed.

Key Words
Wenchuan earthquake, dynamic rupture, multi-faults, pore fluid

Citation
Zhang, W., & Liu, Y. (2024, 09). Effects of fault geometry and pore fluid on the dynamic rupture process of the 2008 Mw 7.9 Wenchuan earthquake, China, on a multi-fault system. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)