强余震的空间分布特征及其理论解释

本文是《强余震的时间分布特征及其理论解释》(地球物理学报,1979年1期)的继续。文中分析了我国11个强震的余震序列,结果表明,强余震的空间分布有以下特点: 1.强余震的平面分布。强余震主要分布在断层的两端附近及主震震中附近。 2.强余震的空间迁移具有以下特征: (1)强余震的迁移范围与主震破裂长度相当,且随着时间的推移,迁移的范围越来越大;(2)其总的迁移范围及迁移方向与主震破裂方式有关。对单侧破裂的较大主震,强余震相对其震中呈单侧迁移;对双侧破裂的主震,其强余震相对其主震震中会呈现松弛振荡式迁移;对于双震型地震,强余震往往对第一个主震表现为单侧迁移,对于第二个主震表现为两头跳现象。 3.强余震的垂向分布:位于主破裂的断层面内,且在其前缘上。 本文从断裂力学和流变学角度,对上述观测事实进行了初步理论解释。 

ON SPATIAL DISTRIBUTION OF LARGE AFTERSHOCKS OF THE SEQUENCE OF A MAJOR EARTHQUAKE AND PRELIMINARY THEORETICAL EXPLANATION

Sequences of 11 major earthquakes occurred in the continental area of China have been analysed for the characteristics of their spatial distribution of large aftershocks. It is found that:1. The large aftershocks are located in three areas: in the vicinities of the ends of the earthquake fault and the epicenter of the main shock.2. The characteristics of spatial migration of the large aftershocks are as follows: (1) The migration distance of the large aftershocks corresponds to the rupture length of the main shock, and increases with time; (2) The distance and direction of migration are related to the rupture pattern. For stronger main shocks with unilateral rupture, the migration of large aftershocks relative to the epicenter of the main shock will be unilateral; for an earthquake with bilateral rupture, the migration of the large aftershocks will be some what similar to relaxation oscillation from one end of the earthquake fault to the other relative to the epicenter of the main shock. For a twin earthquake (two main shocks), the large aftershocks migrate usually in a unilateral manner relative to the first main shock while in a bilateral manner relative to the second main shock.3. The vertical distribution of the large aftershocks in a section is within the fault plane and mostly are located on the front of the fault.A preliminary theoretical explanation for the above observational results has been attempted based upon the principles of rheology and fracture mechanics.