断层转动引起的空间重力变化特征

Study on spatial gravity variation caused by fault rotation

以向错理论为基础,利用经典点源位错理论的解析式,推导得出了断层三维滑动和转动引起的空间重力变化.计算并分析了简单断层三维转动引起的空间重力变化特征,并基于子断层叠加法,采用数值方法模拟计算了智利大震同震断层转动引起的空间重力变化,将计算结果与断层滑动模拟的结果进行了对比.结果表明:断层单分量转动ω_1产生的空间重力变化分布区域具有明显的不对称性,单分量转动ω_2、ω_3时均呈现沿断层倾向方向为轴的对称分布特征;当断层同时以ω_1ω_2转动时,ω_1的转动效应将打破整个重力变化分布区域的的空间对称性.当断层同时以ω_2ω_3转动时,ω_2的转动效应对转动结果起主导作用;断层转动和断层滑动在计算大震同震引起的空间重力变化时,计算结果具有相同的量级.相较于断层滑动,断层转动引起的重力变化在空间上呈显著的不均匀分布,重力变化分布区域相对更大.

Based on the theory of disclination model, the formula to express relationship between spatial gravity change and fault three- dimensional slide and rotation is derived by using the formula of point source dislocation theory. In order to verify the validity of this method, the spatial gravity variation caused by the three- dimensional rotation of simple fault is simulated and analyzed. Based on the sub fault superposition method, a numerical method is used to simulate the seismic spatial gravity changes caused by rotation of the faults during 2010 Chile Mw 8.8 earthquake. The simulation results are compared with those simulated by slide model which has same fault parameters as rotation model except slide components and rotations in, the same region. The results show that：When the fault rotates with a single component ω1 , the spatial gravity distribution region has obvious asymmetry. However, the gravity variation shows the symmetrical distribution characteristic of the axial direction along the fault dip direction, when a single fault occurs with a single component ω2 or ω3 ; Another simulation proves that the rotation effect of the ω1 will break the spatial symmetry of the distribution of the whole gravity change results when a single fault rotates in two ways with ω1 and ω2 at the same time. In addition, when the fanlt rotation occurs with ω2 and ω3 at the same time, the rotation effect of the ω2 will play a leading role in the spatial gravity variation results; According to the numerical simulation of Chile earthquake, the spatial gravity variation induced by fault rotation is as same order as that induced by fault slide in magnitude. Compared to the fault slide, the gravity change caused by fault rotation is uneven distributed in space, and the distribution area is relatively larger.