Abstract：For several days just before the M7.0 Lushan earthquake, the YRY-4 four-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.
QIU Zehua,YANG Guang,TANG Lei et al. Abnormal Strain Changes Prior to the M7.0 Lushan Earthquake Observed
by a Borehole Strainmeter at Guzan[J]. jgg, 2015, 35(1): 158-161.
