芦山M7.0地震前姑咱台钻孔应变观测异常

Abnormal Strain Changes Prior to the M7.0 Lushan Earthquake Observed by a Borehole Strainmeter at Guzan

芦山M7.0地震前数天,姑咱台YRY-4型钻孔应变仪记录到显著的异常变化。对照异常变化的形态特征,可以首先排除建设楼房、修整操场和开凿隧道等影响。最可能的干扰剩下两个:台站观测院门前的道路施工和水库蓄、放水导致大渡河水位变化。结合实地调查,对比应变和测震观测的相关性、应变和大渡河流量变化的相关性,以及对观测应变变化特征的分析,姑咱台的观测异常不是这两种干扰因素的影响,应该与芦山地震有成因联系。

For several days just before the M7.0Lushan earthquake,the YRY-4four-gauge borehole strainmeter at Guzan,Sichuan,recorded prominent abnormal changes.The strain anomalies are striking on the smooth background of several years recording after Wenchuan earthquake.However,as the small town of Guzan is in rapid development presently,constructions of various kinds significantly affect the observation.Whether or not the observed anomalies before the Lushan earthquake were caused by any of the constructions is a question that must be answered.Among all the interferences,apartment building,sports ground reconstruction and tunnel cutting can be first excluded by an analysis of the typical figure of the anomalies.Two other possible interferences are：the road construction in front of the station,and the flow variation of the nearby Daduhe river due to the building of an upstream reservoir.Local investigation,comparison of strain and seismographic recordings,comparison of strain and Daduhe river flow recordings,and analysis of the sense of the strain anomalies have been carried out.It is concluded that the abnormal variations cannot be attributed to any interferences,but should be related to Lushan earthquake.