多方法求解中小地震震源机制解的可靠性分析——以山西地震带3次中小地震为例

Reliability of Focal Mechanism Solutions for Small and Medium Earthquakes Based on Different Methods——Taking Three Events in Shanxi Seismic Belt as Examples

以近年来发生在山西地震带的3次代表性中小地震为例,基于P波初动、P波初动联合P/SV/SH振幅比、CAP波形反演与矩张量反演等多种方法,通过逐步增加参与计算的台站个数及选用不同的数据类型和数据量,全面展示了中小地震震源机制的求解过程与结果,并分析验证了不同数据类型、数据量及求解方法对中小地震震源机制解可靠性与稳定性的影响与约束。结果显示:1)基于P波初动获得稳定可靠的震源机制解至少需要8个以上初动清晰、对震中包裹性较好的P波初动数据;2)对于震级较小、台站记录不足的地震,增加振幅比可在一定程度上提高对结果的约束,但过多增加振幅比的同时,往往会显著增加矛盾比,而对结果的约束不明显;3)对于M;3.2这一级别的显著地震,CAP方法通常可以给出稳定且信度高的结果,但对于震级更大的中等地震,矩张量方法和CAP方法均可作为获得可靠震源机制解的理想选择。

Three representative small and medium earthquakes in Shanxi seismic belt in recent years were taken as examples.By using different methods,such as the first motion of P-wave,first motion of P-wave combining P/SV/SH amplitude ratio,CAP(Cut and Past),and moment tensor inversion,the reliability and stability of focal mechanism solutions of small and medium earthquakes were analyzed and verified by gradually increasing calculation stations and selecting different data types and data quantities.The results indicate that in practice,1)for a stable and reliable solution based on P-wave first motions,at least more than eight P-wave polarity data with clear initial motion and good inclusion in the earthquake are required;2)for small earthquakes with inadequate station records,increasing the amplitude ratio data improves constraints on the results to a certain extent,but increasing the amplitude ratio data often significantly increases the contradiction ratio,while the constraints on the results are not continuously improved;3)for M;≈3.2 earthquakes,the CAP method gives stable and reliable results,and for medium earthquakes with larger magnitude,moment tensor inversion method is also suggested to be an ideal choice to obtain reliable focal mechanism solutions.