汶川—映秀M_S8.0地震的介质破裂与深部物质运移的动力机制

The Dynamical Mechanism for Medium Rapture and Motion of Deep Matler on Wenchuan-Yingxiu M_S8.0 Earthquarce,2008

2008年5月22日14时28分在龙门山造山带发生了震惊世界的汶川—映秀MS8.0大地震。这次大地震形成了迄今为止在三维空间分布最为复杂、在水平方向(NE)延伸最长的逆冲型破裂带。笔者分析和讨论了大地震发生后在地表引发的破裂现象和震源深处与其周边地域介质在受力作用下的破裂与'破裂链'的逐步形成和辐射效应。基于该大地震'孕育'、发生和发展的深部介质和构造环境与深层动力过程的研究提出:汶川—映秀8.0级地震的发震断层是龙门山断裂系地表以不同角度西倾的3条断裂带向深部汇聚,青藏高原东北缘松潘—甘孜地域下地壳与上地幔盖层物质向东南减薄,在受到四川盆地'刚性'壳、幔介质阻隔下而沿龙门山断裂系抬升,二者在震源深处,即(15±5)km处强烈碰撞而形成的一条NE向的深部汇聚断裂带。汇聚断裂带即为MS8.0地震和一系列余震的发震断裂带,而不是简单地、形式地将地表的某一条或某两条断裂带视为发震断裂带,因为震源是一个体积。大地震发生后的地表破裂、次生灾害等,即浅层过程的调查和分析对恢复生产、重建家园有着重要意义。显然,在地表和深井中若能长期进行破裂效应的观测,以捕捉地震强烈活动地区震源深处介质与结构发生的初始微破裂和其形成'破裂链'的深层动力过程,这对短临地震预测很可能是一个十分重要的途径。这里必须指出:强烈地震'孕育'、发生和发展的深部介质和环境与其深层动力过程乃是厘定强烈地震成因的关键所在。

At 14.28 on May 12, 2008, the Ms8.0 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 Ms8.0 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） kin. This fault belt is the origin causing the Wenchuan 8.0 earthquake and all its aftershoeks. 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.