Abnormal Phenomena of Volume Strain before Large Earthquakes

摘要

This paper studies the imminent anomalies observed by the Sacks volume strainmeter in Erzhangying station and Tiantanghe station before 80 earthquakes with M S≥7. 0 which took place from January 2011 to April 2014 all over the world. Then,preconditions for anomaly identification are put forward for complex earthquake cases. Statistical results show that volume strain observation has a better earthquake reflecting ability for earthquakes with magnitudes larger than 7. 0 and epicentral distance within 8000 km. In addition,these results also reflect that the volume strain observation can better reflect precursory anomalies of such earthquakes. Based on categorization and description of those anomalies,we divide the anomalies into three types,that is,earth tide distortion type,abrupt change type and slow earthquake type. Furthermore,the paper makes a statistical analysis of these types and preliminarily discusses their mechanical properties as well. According to research,volume strain anomaly has an indicative significance to future strong earthquakes in the world.