Relationship between the reservoir storage and crustal QS dynamic variation in Zipingpu reservoir area

Using a two-dimensional seismic attenuation tomography technique, the crustal QS dynamic variation in Zipingpu reservoir area, Sichuan province, was obtained by inverting S-wave data from relocated earthquakes from 16 Aug. 2004 to 11 May 2008 with the double-difference algorithm. Monthly moving average QS value in different-sized regions and earthquake frequency for different magnitude range were compared with the water level of the Zipingpu reservoir, respectively (the window length is 1 year and the step length is 1 month). The result shows that low-QS region expanded and QS value dropped significantly around the reservoir area during the first fast water-loading period. In particular, QS value varied remarkably in the southwestern, northeastern andmiddle part of the reservoir area. Monthly moving average QS values for different-sized regions in the Zipingpu reservoir area decrease with elapsed impoundment time and increased water level, and the QS value in the middle reservoir area dropped sharply. Furthermore, the impoundment enhanced seismic activity in the reservoir area, and mainly increased activity of small earthquakes of ML0.0mdash;2.0.