层状介质中断层位错引起的重力异常及其数值模拟

NUMERICAL SIMULATION OF GRAVITY ANOMALY CAUSED BY FAULT DISLOCATION IN LAYERED MEDIA

摘要:

修正了文献[1]给出的两个公式和计算机程序中的个别错误,并根据文献[1]利用层状介质中的位错理论及其与相应重力变化的关系^[2,5],通过数值模拟方法研究了矩形位错面在不同尺度、倾向、埋深和位错的情况下有不同取向、量值的重力异常变化。此外,还对唐山地震、共和地震的重力资料作了几个测点的计算以探索地震物理前兆场空间和强度分布的复杂性。结果表明,断层错动引起的重力变化在空间、强度上的分布是十分复杂的。它是位错地表形变和地下层界面形变效应共同作用的产物,既可以是正异常,也可以是负异常。位错源的几何条件、埋深条件、位错方向和量值等对重力的空间、强度分布和范围有较强的影响。这就说明对于地震与重力异常的关系不能一概而论,要考虑一次地震特定条件的影响。本研究也为我们理解其它地震前兆物理场的复杂性提供了有益的启示。

Abstract:

Based on reference[1] and the dislocation theory and corresponding gravity change in the layered media offered by previous papers, authors modified two equations presented by reference[1] and studied the relation between dislocating gravity variations and the rectangular planes with different sizes, buried depths, dislocating directions and dislocating magnitudes by numerical simulating method. The dislocating conditions and gravitational anomaly of the Tangshan (M 7.8) and Gonghe (M 7.0) earthquakes were also simulated for several points in this paper to probe the complexity of the space and intensity distributions of the earthquake precursor field. The results show that the gravity change caused by dislocating is very complicated in space and intensity distributions, which is the combined result of deformation and stress variation due to dislocating effect, both negative and positive gravity variations can appear in earthquake effect area. The dislocating plane conditions above mentioned have strong influence on gravitational space and intensity distributions.The simulating results suggest that if one wants to analyze the gravity anomaly caused by an earthquake, one should consider the concrete mechanism of the event. An enlightenment for understanding the complexity of other geophysical precursors of earthquakes is provided in this paper.