Abstract:

At 14:28 on May 12, 2008, the M_s8.0 Wenchuan-Yingxiu great earthquake in Longmenshan orogenic zone shocked the worldwide. An overthrust rupture zone has formed which is hitherto the most complicated in 3D spatial distributions and the longest in horizontal extension(NE). The authors analyse and discuss the ruptures induced on the ground and in the depth near source media area under the stresses. The formation of this “rupture chain” and radiation effects are also emphasized. The viewpoint about this earthquake mechanism is put forward based on studies about deep medium and structure environment and dynamical process of the earthquake preparation, generation and development. The earthquake generating faults of the M_s8.0 Wenchuan-Yingxiu earthquake are 3 west-dipped ground faults within Longmenshan fault system which extended together in depth with different angles. The substance from lower crust and upper mantle cover in Songpan-Ganzi area of northeast Tibetan Plateau reduced its thickness to the southeast and rose along Longmenshan fault system under the barrier effect of rigid crust and mantle of Sichuan basin. The 3 faults and the substances then collided strongly and formed a deep converage fault zone in NE direction at the depth of (15±5) km. This fault belt is the origin causing the Wenchuan 8.0 earthquake and all its  aftershocks. Hence, one or more faults on the ground should not be simply considered as earthquake generating fault, because earthquake source is of volume behavior. The survey and analysis about shallow process such as ground rupture and secondary disaster of the earthquake are very important for recovery production and reconstruct rehabilitate ones homeland. The long-term observation about rupture effects on the ground or in deep well can capture initial micro-rupture and deep dynamical process of formation of rupture chain at the depth of source in strong active areas of earthquake. It will be an important way for imminent earthquake prediction. It must be pointed out that, the environment of deep medium and structure environment and processes of brewing and generation of strong earthquakes are very important for the seismogenesis.

Key words: Wenchuan earthquake, surface ruptures, rupture chains, earthquake source mechanism, earthquake generating fault zone, deep medium and structural environment, imminent earthquake prediction