2013年芦山MS7.0地震的震前及临震应变异常

距离芦山地震震中70 km的姑咱地震台YRY四分量钻孔应变仪2013年4月16—19日记录到8次幅度达到十倍固体潮幅的张性应变阶跃， 这在该仪器6年多运行期间尚属首次. 这些应变异常与芦山地震在时间、 空间上相关； 应变异常的主压应力方向与震前宝兴水压致裂地应力测量主压应力方向相近， 并与震前5个月中长达3个月的应变异常主压应力方向一致； 应变阶跃起始与远震震波同时到达. 综上认为， 4月16—19日的应变异常有可能是芦山地震发震断裂在破裂错动前地层蠕滑的反映. 

Borehole strain anomalies before the 20 April 2013 Lushan Ms7.0 earthquake

The YRY four-component borehole strainmeter of Guzan Station, 70 km away from the epicenter of Lushan earthquake, recorded eight tensile strain steps with the range of ten times of tidal amplitude on April 16—19, which has never happened over the past 6 years’observation. The strain anomalies are related to Lushan earthquake both in time and space. The principal stress direction deduced by the abnormal strain, similar to that of in-situ stress measurement by hydrofracturing at Baoxing before the earthquake, is in accordance with 3-months-records during the five months before the Lushan earthquake. Some of the strain steps occurred when teleseismic waves arrived. As mentioned above, we presume the strain anomalies of April 16—19 probably reflect the strata creeping before the rupturing of the Lushan earthquake generating fault.