A 3D CRUSTAL VELOCITY MODEL OF THE LONGMEN SHAN FAULT ZONE IN SICHUAN, CHINA

On May 12, 2008, the M7.9 Wenchuan earthquake ruptured the ground surface along a nearly 300-km-long segment of the Longmen Shan fault zone (LSFZ) in Sichuan, China. The event claimed the lives of an estimated 87,000 people and left millions more injured or homeless. The large magnitude of the earthquake has been attributed to slip (~3 to 6 m) along multiple fault surfaces in the LSFZ, mainly the Beichuan and Pengguan Faults. In order to thoroughly investigate the structural mechanisms and lithological characteristics that facilitated the devastating event, wave propagation and ground motion simulations require a good crustal velocity model. Here we present a new 3D crustal velocity model of the Beichuan and Pengguan Faults based on a compilation of previously published seismic refraction, seismic reflection, earthquake tomography, and gravity studies. Point data (x, y, z) were extracted from these sources based upon a six-layered crustal structure, and then interpolated to create the surfaces that define the boundaries of the velocity layers of our model. We used an open-source spatial database manager to compile the velocity surfaces along with fault geometries and regional topography, and to assign values of compressional and shear-wave velocity and density to the volumes of the model. The result is a continuous block model of crustal velocities that can be refined and customized by scientists to calculate wave propagation simulations. The approach can be quickly and easily duplicated in any region of the world for which an adequate amount of seismic velocity data is available.