美国南加州地区1981—2011年MW≥6.0地震前发震应力场与构造应力场趋于一致现象研究

定义了“P轴分布集中度”， 用以研究中强地震前中小地震震源机制变化． 利用美国南加州地区1981—2011年地震的震源机制解资料, 分析了该地区8次M_W≥6.0地震前由小震震源机制求得的发震应力场P轴的集中情况． 结果表明， 其中7次地震前均观察到了“P轴分布集中度”值具有极小值， 即小震发震应力场P轴向区域构造应力场主压应力的集中现象， 为中强震预测提供了一种方法． 

Consistency of seismogenic stress field of preshocks to the tectonic stress field before eight earthquakes (MW≥6.0) in southern California of United States from 1981 to 2011

This paper defines an index called “concentration ratio of P axis distribution” used for analyzing the variation of focal mechanisms of small earthquakes before moderate-strong earthquakes. And then based on the focal mechanism solutions of earthquakes in southern California in the period of 1981—2011, this paper investigates the seismogenic stress field of small events concentrating on the local tectonic stress field before eight main shocks (M_W≥6.0) in the southern California. The results show a phenomenon that the “concentration ratio of P axis distribution” has a minimum was observed before seven earthquakes, that is, the seismogenic stress field of small events concentrates on the local tectonic stress field. It provides a method for the risk prediction of moderate-strong earthquakes.