Modeling On Physical Processes Of Earthquakes

The genesis and occurrence of earthquakes and their subsequent impacts are complex physical processes. Studies of these processes help understand the mechanics of earthquakes and the future physical state of the Earth. The physical processes of earthquakes are studied in the following aspects in this paper:1. Study on seismic stress triggeringFault interaction and earthquake occurrence have attracted much attention in seismological community during recent years. Many studies showed that rupture of one fault could encourage or discourage earthquake nucleation on a neighboring fault, depending on the relative geometry of the two faults and the earthquake rupture mechanisms.Firstly we study stress transfer and triggering of large earthquakes along the East Kunlun fault system, northern Tibetan Plateau. Five M >7 earthquakes occurred along the fault zone during the past 70 years are considered: the 1937 M7.5 Huashi Canyon, the 1963 MS 7.1 Dulan, the 1973 MS 7.3 Manyi, the 1997 MS7.5 Manyi, and the 2001 MW 7.8 Kokoxili earthquakes. We simulate stress evolution process produced by seismic dislocation in layered viscoelastic media, and calculate Coulomb failure stress change on the fault plane of each subsequent earthquake. The result shows that the Coulomb failure stress on the fault plane of the Kokoxili earthquake was increased by the previous 4 earthquakes, and viscoelastic relaxation gradually enhanced the Coulomb failure stress field as time elapsed. By evaluating Coulomb failure stress change produced by coseismic rupture and viscoelastic relaxation of the 4 preceding large earthquakes, we find that Coulomb failure stress change produced by viscoelastic relaxation is much more significant than that produced by coseismic deformation in 3 of the 4 earthquakes. The stress field simulation indicates that after the Kokoxili earthquake Coulomb failure stress in the Xidatan-Dongdatan segment (between the Kokoxili and Dulan segments) of the East Kunlun fault is increased as much as 0.05～0.10MPa, implying significantly increased earthquake potential in this region.Secondly we simulate the evolution process of cumulative Coulomb failure stress change ( ) in Northeast Tibetan Palteau since 1920 and North China since 1303, manifested by secular tectonic stress loading and occurrence of large earthquakes. Secular tectonic stress loading is averaged from crustal strain rates derived from GPS. Assuming a layered visco-elastic medium, we calculate stress evolution resulted from secular tectonic loading and coseismic and postseismic deformation. At the eve of each large earthquake the accumulated stress field is project to the fault surface of that earthquake and the is evaluated to assess the triggering effect of . Our results show that in northeast Tibet Planetau, 17 out of 20 earthquakes occurred in the regions with positive , yielding a triggering rate of 81.3%. In North China, statistics shows that 39 out of the 48 subsequent events were triggered by positive , yielding a triggering rate of 81.3%. Our study shows very high correlation between positive and earthquake occurrences. Relatively high in North China at present time is concentrated around the Bohai Sea, the west segment of the Northern Qinling fault, western end of the Zhangjiakou-Bohai seismic zone, and the Taiyuan basin, Shanxi graben, suggesting relatively higher earthquake potential in these areas.