不同应力状态和摩擦系数对综合P波辐射花样影响的模拟研究

摘要

为研究不同应力状态(包括主应力相对大小)和摩擦系数对大量地震P波初动辐射花样(综合P波辐射花样)的影响,首先给出了不同应力状态下的剪应力、摩擦应力和库仑破裂应力在断层面法向上的三维分布.表明即使在不考虑摩擦的情况下,剪应力在不同取向断层面上的分布也有很大差别,摩擦应力也在不同取向断层面上造成一定影响.其次,根据库仑破裂应力与单个地震产生的P波辐射花样大小成比例的原则,假定地震断层面均匀取样整个方向空间,将各种取向断层面产生的P波辐射花样叠加,给出了不同应力状态和摩擦系数情况下产生的大量地震综合P波辐射花样的空间分布.发现主应力的相对大小和摩擦系数同时影响综合P波辐射花样的空间形态,在一定程度上,辐射花样从一种形态改变为另一种形态可通过改变任一参数进行,表明同时反演此两种参数是困难的.但通过其他手段确定摩擦系数后,可以采用P波初动信息得到较为合理的应力相对大小.该研究为考虑摩擦系数、采用大量P波初动资料精确确定应力场提供了新的思路.%In order to study the impact of stress ratio and friction coefficient on P-wave radiation patterns from a large number of earthquakes, we present how the shear stress, friction stress and Coulomb failure stress of the fault varies as a function of its orientation with respect to different stress ratios. The results show that the shear stress on the fault plane with various orientations indicates larger differences comparing to friction stress variations for different fault orientations.Assuming the spatial distribution of Coulomb failure stress is relevant to the P wave radiation pattern, and fault plane orientations are randomly distributed over the whole space, we superpose P wave radiation patterns from all fault orientations, and illustrate the characteristics of composite P wave radiation pattern in terms of different stress ratio and friction coefficient. We find that the stress ratio and friction coefficient both affect the composite P wave radiation pattern. To some extent, the shape of the composite P wave radiation can be changed by varying any of the two parameters, indicating the difficult to solve both of the parameters indepdently.However, if the friction coefficient can be determined by other methods, we can obtain a reasonable stress ratio by using P wave first motions. This work provides new idea to accurately determine stress field considering friction coefficient by large number of P first motion polarity data.