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基于2000年7月—2009年6月龙门山及其邻区的震源机制解资料,采用Gephart&Forsyth方法,反演得到了汶川地震前后该地区构造应力主方向的空间分布.结果显示:沿鲜水河断裂带及其北部地区,构造应力场变化显著,区域构造应力的最大主应力方位由NNW变为NW,断层错动类型由正断型兼走滑型变为走滑型;沿龙门山断裂带的构造应力最大主应力方向仍然为近EW和NE向,但其EW向范围在向NE方向扩张,其南部汶川地震震中附近异常带范围在收缩.另一方面,对上述时间段龙门山及其邻区不同时段构造应力场的反演结果表明,其构造应力场的特征参数(包括R值、应力洛德参数μ以及3个主应力的方位角和仰角等)均从第13时窗开始出现显著变化,这表明第13时窗(2006年12月—2007年1月)是一个构造应力显著变化的特征窗口.在该时窗内,地震能量积累达到一个临界状态,是汶川MS8.0地震发生的时间节点.
Based on the focal mechanism solution data of Longmenshan and its adjacent areas from July 2000 to June 2009, Gephart & Forsyth method was used to obtain the spatial distribution of the main tectonic stress in the area before and after the Wenchuan earthquake. The results show that along the Xianshui River In the fault zone and its northern region, the tectonic stress field changes significantly. The maximum principal stress of regional tectonic stress changes from NNW to NW, and the fault type of fault changes from normal faulting and strike-slip to strike-slip type. Along the Longmenshan fault zone The maximum principal stress direction of tectonic stress is still near EW and NE, but its EW direction expands in the direction of NE, and the anomalous zone shrinks near the epicenter of the southern Wenchuan earthquake.On the other hand, The inversion results of tectonic stress field at different periods show that the characteristic parameters of tectonic stress field (including R value, stress Lode parameters μ and azimuth and elevation angles of three principal stresses) begin to appear from the 13th time window Which indicates that the 13th time window (December 2006-January 2007) is a characteristic window of tectonic stress change, in which time the seismic energy accumulation reaches a critical state, which is the result of Wenchuan MS8.0 earthquake When it happened Node.