利用区域和水库地震台网记录的数字地震波资料,研究了汶川8.0级地震前的2000年1月1日~2008年5月11日紫坪铺水库区的地震活动及震源参数。结果表明:汶川8.0级地震前该区域小震活动持续,地震活动水平为ML2~3,自2005年9月紫坪铺水库蓄水以来,特别是2008年2月地震活动明显增加,但从长期的序列来看,地震活动频次和强度仍在区域地震活动的正常起伏范围。汶川8.0级地震发生前近3个月内,中小地震的视应力差值Δσapp普遍大于0,计算得到的视应力总大于其拟合值。汶川8.0级地震震中位于低应力区,而相对较高的视应力差值分布在震中以东地区,局部出现视应力增加的现象。

Based on the digital seismic waveform data observed from regional and reservoir seismic networks, the seismicity and source parameters of Zipingpu Dam from January 1, 2000 to May 11, 2008 before the Wenchuan MS810 earthquake is studied. The analysis results show a continuous activity of small earthquakes before Wenchuan MS810 earthquake, and the level of seismic activity was from ML210 to ML 310 in recent years. The impoundment of Zipingpu Dam started in September 2005, the obvious increment of seismic activities occurred on February 20081 But according to the analysis results of a more long time series, the frequency and intensity of seismic activities still do not exceed its range, which still belongs to a fluctuation of regional seismic activities or tectonic activity. At the same t ime, we also research the spatio-temporal distribution and change of apparent stress difference in source region before great earthquake, and the result shows that the apparent stress values of small earthquakes are generally higher than fitted values of apparent stress in reservoir area during near three months before the Wenchuan MS810 earthquake.It can be seen from spatial distribut ion of apparent stress difference, the epicenter ofWenchuan MS810 earthquake located at low stress distribution area, and the relatively high apparent stress difference is in the east area of epicenter. Local area presents the phenomenon of apparent stress increment.