基于声发射实验结果讨论大震前地震活动平静现象的机制

A DISCUSSION ON MECHANISM FOR SEISMIC QUIESCENCE BEFORE LARGE EARTHQUAKES BASED ON EXPERIMENTAL RESULTS OF ACOUSTIC EMISSION

基于岩石变形声发射实验结果讨论了大震前地震活动平静现象的机制。在双轴压缩、等位移速率加载条件下 ,挤压型雁列断层、含宏观凹凸体断层、Ⅲ型剪切断层等非连续断层在临近滑动失稳前 ,声发射活动均出现了明显的相对平静现象 ,表现为声发射事件的发生率和应变能释放水平显著降低。与此阶段相对应 ,断层带 (特别是非连续部位上新形成的一小段断层 )发生了蠕滑和匀阻化作用 ,并使得标本的差应力开始下降。根据实验结果提出 ,大地震前断层的“蠕滑 -匀阻化”

This paper discusses the mechanism for seismic quiescence before large earthquakes based on experimental results of acoustic emission during rock deformation. Under the condition of biaxial compression and constant loading point velocity, samples simulating discontinuous faults, including compressional en echelon faults, fault with macro asperity, and model Ⅲ shear fault, show relative quiescence of acoustic emission before slip instability, which is characterized by obvious decrease of occurrence rate and release of strain energy of acoustic emission events. The analysis indicates that the predominant deformation mode during this stage is creep sliding along fault zone, especially along the newborn fault segment in the discontinuous area, causing decrease of differential stress in the sample. The reason for occurrence of this stage is that a relatively uniform distribution of resistance along a fault zone is necessary for its slip instability, but uneven surface of newborn fault segment does not meet this condition, so the creep sliding is needed for resistance uniformization along the fault zone. Because there exist only very small asperities along the fault zone and the stress relaxation occurs in the whole sample during this stage, acoustic emission activity becomes weak. Based on the experimental results, it is suggested that the process of creep sliding and resistance uniformization along fault zone is one possible mechanism for seismic quiescence before large earthquake.