紫坪铺库区小震产生的库仑应力变化及其与汶川地震的关系

Coulomb stress changes induced by small earthquakes in the Zipingpu reservoir area and its significance to the Wenchuan earthquake

本文选取自2004年8月至2008年5月12日汶川地震发生前,紫坪铺库区发生的2.1<M_(L)<4.0的65次小震,分别计算了历次地震在汶川地震震源处产生的应力扰动量,随后根据不同机构给出的汶川地震震源机制解求取震源区的静态库仑应力改变量,讨论了紫坪铺库区小震与汶川地震的关系.在不同计算参数下,小震震群在汶川震源处产生的静态库仑应力扰动量之和为6±3 Pa,尽管分析认为小震群可能在汶川震源处产生较大的动态应力扰动,约为百帕量级,但均远未达到触发阈值,认为小震群并未直接对汶川地震有触发作用.推测小震群之间相互作用产生连续振动改变了周边区域介质的渗透率及强度,进而可能与汶川地震的发生具有间接关系.

We chose 65 small earthquakes with M_(L) greater than 2.1 and less than 4.0 occurred in the Zipingpu reservoir area from August 2004 to May 12,2008 before the Wenchuan earthquake,then respectively calculated their static stress changes at the source of the Wenchuan earthquake.According to different focal mechanism solutions of the Wenchuan earthquake,we figured up the Coulomb stress change,and discussed the relationship between these small earthquakes and the Wenchuan earthquake.Under different calculation parameters,the sum of the static Coulomb stress disturbances generated by the small earthquakes at the Wenchuan earthquake source is 6±3 Pa,although small earthquake may have a large dynamic stress disturbance at the Wenchuan earthquake source,about the order of hectopascals,they are far from reaching the trigger threshold.Therefore it is believed that small earthquakes did not directly trigger the Wenchuan earthquake.It is speculated that the interaction between small earthquakes caused continuous vibration,and changed the permeability and strength of the surrounding medium,which may indirectly affected the occurrence of the Wenchuan earthquake.