Abstract:

In order to study the effect of water load variation in the Three Gorge reservoir on the crustal deformation,we used the observation data of crustal deformation of tidal analysis and none-tidal analysis at Yichang seismic station from 2001 to 2014,and there was clear evidence that original parameters such as the minute value,the long trend, tide factor and phase lag showed anomaly during the process of the variation of water load in the Three Georges reservoir. Anomalies of the minute value and the long trend data were observed before the earthquake;moreover,4 hours before the earthquake (M_L4.6) in Quyuan town of Zigui county,the minute value of water tube tiltmeter declined significantly,and the amount of drop in north end and south end is up to 23×10^-3,10×10^-3 angular seconds,respectively;at the time of 3 months before the earthquake(M_S5.1) in Badong town,the EW component of hole strain gauge appeared to break the law of annual variation and changed from compression to tension;finally,tidal analysis results showed abnormal:the tidal factors of NS component of hole strain declined in phases from 2001 to 2014,and the change of synchronous anomalies of the tidal factors of NS and EW components took place in September,2009,in other words,data of NS component continued to fall and data of EW component rose slightly;adverse change of the tide phase lag of strain and tilt appeared in the period of water levels drop and before earthquakes(M_L≥4.0).

Key words: crustal deformation, Yichang seismic station, Three Gorges Reservoir, water load, anomaly before earthquake, tidal analysis