Modeling the Spatiotemporal Seismicity Patterns of the Longmen Shan Fault Zone Based on the Coulomb Rate and State Model

In the past two decades, three major earthquakes have occurred near the Longmen Shan fault zone, Sichuan, China (the 2008 Mw 7.9 Wenchuan, 2013 Mw 6.6 Lushan, and 2017 Mw 6.5 Jiuzhaigou earthquakes), in response to the continuous collision of the Indian and Eurasian plates, and have produced numerous aftershocks. Recent studies have demonstrated that physics-based aftershock forecasting holds the potential capability to meet the demands of earthquake forecasting. I have successfully modeled the spatiotemporal seismicity of the Longmen Shan fault zone by applying the coulomb rate and state model by including high-quality data products (e.g., source models and receive faults) and optimized rate-and-state parameters in the calculation. I also investigate the roles of secondary triggering of aftershocks and the friction coefficient in seismicity modeling. The findings suggest that the friction coefficient plays an important role in modeling the observed seismicity, and that the secondary triggering of aftershocks in the Longmen Shan fault zone moderately affects the predicted seismicity.

Shallow Structure of the Longmen Shan Fault Zone from a High-Density, Short-Period Seismic Array

ABSTRACT The Longmen Shan fault zone that was shocked by the 12 May 2008 M 8.0 Wenchuan earthquake acts as the boundary between the western edge of the Sichuan basin and the steep eastern margin of the Songpan-Ganze block. In this study, continuous seismic data recorded by 176 temporary short-period seismic stations between 22 October and 20 November 2017 are used to study the shallow crustal structure of the Longmen Shan fault zone by applying ambient-noise tomography and horizontal-to-vertical spectral ratio (HVSR) analysis. From ambient-noise analysis, fundamental-mode Rayleigh-wave dispersion curves between 0.25 and 1 Hz are extracted. Then, the direct surface-wave tomographic method is used to invert surface-wave dispersion data for the 3D shallow shear-wave velocity structure. Our results show that low shear-wave velocities are mainly distributed around the surface rupture trace of the Wenchuan earthquake at least down to 2 km. From the HVSR method, the sites are sorted into two types according to the pattern of HVSR curves with single peak or double peak. By converting frequency to depth, the results show that the sediments are thicker near the surface rupture. The low-velocity zone based on ambient-noise tomography agrees well with the distribution of sedimentary cover estimated from HVSR, which are generally consistent with geological information. Our results provide high-resolution shallow crustal velocity structure for future detailed studies of the Longmen Shan fault.