中上地壳应变分配模型及其地震学研究意义

Strain partitioning model in the middle-upper crust and its application to seismic research

应变分配 (Strain Partitioning)作为一种基本应变形式 ,即下地壳和岩石圈地幔内的斜向应变在中上地壳内解藕为相互独立的一个正应变分量和一个剪应变分量的现象。在平面上表现为平行排列、同时活动的走滑断裂系统和相应的正应变构造型式。应变分配是一种极为普遍的构造现象。应变分配的发生主要受主断面倾角、与主应力轴交角、区域应力场状态以及构造带结构和物质组成的影响。作为断层相互作用的一种主要模型 ,应变分配模型的最直接证据来源于地震学方面 ,包括震源机制、震源深度及其分区特征等的研究结果。反过来 ,应变分配模型的建立 ,将在确定震源体的独立性、判断震源发震能力、判断地震序列特征、确定地震发展趋势方面为地震科学研究尤其是地震中长期危险性预测研究提供进一步的理论依据。

Strain partitioning is the phenomenon that the oblique strain in the lower crust and lithospheric mantle is partitioned into near pure tangential and normal strain in the middle upper crust, strain partitioning is expressed as an active thrust parallel strike slip faulting. There′re 4 or 5 parameters influencing strain partitioning: dip of faults, convergence obliquity, coupling condition or stress field, strength of overriding block etc. Being a main model on fault interaction, strain partitioning model is directly supported by seismic data, such as focal mechanism, focal depth and their zonation. On the other hand, a reasonable strain partitioning model will be helpful to evaluate the independence and potentiality of earthquake source, to determine seismic sequence and seismic tendency.