Stressing Rates and Seismicity on the Major Faults in Eastern Tibetan Plateau

Abstract

Intensive studies following the 2008 Wenchuan and 2013 Lushan earthquakes have shown that these two events have changed stresses on major faults in eastern Tibetan Plateau. However, these stress changes are small perturbations to total stresses on these faults. To evaluate full stress evolution on faults and the associated earthquake hazard, we need to consider the effects of all regional large earthquakes and tectonic stressing on faults. Here we use a three-dimensional viscoelastoplastic finite element model to investigate stress evolution and long-term temporal patterns of seismicity on major faults in eastern Tibet. We first simulate stress changes due to coseismic slips and postseismic viscoelastic stress relaxation by regional 28 big earthquakes since 1327 and find that nine events, including the Wenchuan earthquake, occurred where Coulomb stress was decreased by the preceding events. We then evaluate interseismic stressing rates using the geodynamic model and GPS data and find the highest rate on Xianshuihe fault (~1,000–4,950 Pa/yr) and the lowest rate on Longmenshan fault (~150–1,133 Pa/yr). Including interseismic stressing in stress evolution shows that the Wenchuan earthquake ruptured where Coulomb stress had increased since 1327 and stresses on southern Xianshuihe and central Anninghe faults would have reached prerupture stress levels of their preceding ruptures. Finally, we analyze synthetic seismicity on faults and find that earthquakes on each fault tend to occur in clusters, separated by quiescent periods whose lengths are inversely related with fault slip rates. The time spans of earthquake clusters are affected by fault slip rates, fault configuration, and rheology.