Stress evolution before and after the 2008 Wenchuan, China earthquake

We examine the distribution of Coulomb stress before and following the M=7.9 Wenchuan earthquake and model the time dependent components of the stress field into the future. Our modelling shows that the combined (coseismic plus postseismic viscoelastic) stress change due to the preceding large events (M≥6.7) at the hypocentral area of the Wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95 yr depending on the rake of the rupture. On the other hand coseismic stress modelling of the Wenchuan earthquake shows strong interaction, particularly with the faults close to its SW and NE ends; such interactions have previously been shown to trigger further large earthquakes. In addition, redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the Xianshuihe, Kunlun and Tazang faults. Postseismic viscoelastic stress load on these distant faults over the next 22 yr since the earthquake could be up to 2.5 times larger than that of the coseismic stress increase alone. This would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes, resulting in clustering of large earthquakes in the region. This behaviour, however, strongly depends on the stage that these faults are in their seismic cycle which is not known currently. Given the high density of population in the area with several cities,Chengdu, Guangyuan and Hanzhong, of more than 1 million inhabitants, our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults.