Numeric Modeling of the Strain Accumulation and Release of the 2008 Wenchuan, Sichuan, China, Earthquake

Abstract

Abstract As one of the most devastating earthquakes, the 2008 Wenchuan earthquake occurred on imbricate, high-angle listric-reverse faults. The faults dip ∼70 ° above 15 km depth, become 30° to 40° below ∼15 km depth, and presumably root into a subhorizontal brittle-ductile transition zone below about 22±2 km depth. In this paper we use the viscoelastic finite-element method to simulate coseismic deformation and stress change, and recurrence of major earthquakes associated with the high-angle listric-reverse fault. Our modeling shows that changes of coseismic equivalent stress mainly occur in the vicinity of the seismogenic fault, especially the hanging wall of the fault in the depth range above 12 km. Modeled coseismic slip distribution and modeled average recurrent interval corroborate with geological, geodetic, and seismological observations. We modeled 250,000 yr slip history of the fault slip. The result shows that minor slips, which obey slip-predictable model, take place on 30°–40° dipping fault plane at depth below 15 km. When the isotropic stress accumulation on the gentle fault reaches the critical level, the entire gently dipping fault ruptures to form a large slip. The large slips on the gently dipping fault comply with a time-predictable model of recurrences. These larger slips on the gently dipping fault occur simultaneously with slips on the steeply dipping fault and might have triggered slips on the steeply dipping fault to form great events such as the 2008 Wenchuan earthquake.