2013年芦山M_S7.0地震前后姑咱台四分量钻孔应变时频特征分析

Time-frequency characteristics of four-component borehole strain at Guzan station before and after 2013 Lushan M_S7.0 earthquake

2013年4月20日芦山MS7.0地震前,四川省姑咱台四分量钻孔应变仪再度记录到类似于2008年汶川MS8.0地震前的高频应变畸变信号.为了对该畸变信号各频率成分的时频演化特征进行细致分析,讨论应变异常的可信度及其与芦山地震的相关性,本文利用S变换方法对应变数据进行了处理.结果表明,研究时段内时频域中共出现两簇高能量异常,一簇开始于2012年10月并持续了约4个月,另一簇则开始于芦山MS7.0地震前数天.同时段远震的影响及施工干扰并不能构成该异常的主体,因此该异常可信度较高.异常中包含了周期由数分钟至数小时的信号成分,其中较短周期的信号成分震前出现较晚,震后衰减较快.震后异常信号的整体能量开始逐步衰减,异常信号成分减少,至2013年8月末应变观测记录已基本恢复至正常状态,整个应变异常显示的时频演化过程与芦山MS7.0地震具有较高相关性.

The four-component borehole strainmeter at Guzan station in Sichuan Province recorded abnormal strain signals with high frequency before the 20 April 2013 Lushan MS7.0 earthquake,which were similar to the signals before the Wenchuan MS8.0 earthquake.The strain data were processed in the way of S transform in order to analyze the evolutionary process of each component of abnormal signals in time-frequency domain,and study the validity of the anoma-lies and its relation with Lushan earthquake.The result shows that two clusters of anomalies with high energy appeared during the research period,one in Octo-ber of 2012 lasting for four months,and the other several days before the earth-quake.The validity of the anomalies is high,considering that the disturbance of teleseismograms and engineering construction during this period are not the main cause for the anomalies.The anomalies are composed of all kinds of sig-nals with various periods from several minutes to hours,of which the short-period signals appeared later and decayed sooner.The whole energy of the anomalies after the earthquake began to decay gradually,and the signal compo-nents began to reduce,too.The strain observation had returned to normal by the end of August 2013.The whole evolutionary process of strain anomalies in time-frequency domain has very close relations to the Lushan MS 7 .0 earthquake.