孕震过程中波速比及S波分裂时空变化的数值模拟  

NUMERICAL SIMULATION OF SPATIAL AND TEMPORAL VARIATION OF V_P/V_S AND SHEAR WAVE SPLITTING IN EARTHQUAKE PREPARATION

作　　者：张永仙[1] 张国民[1] 石耀霖[2] 

机构地区：[1]国家地震局分析预报中心,中国北京100036 [2]中国科学院中国科技大学研究生院,中国北京100039

出　　处：《地震》1994年第6期26-33,共8页Earthquake

基　　金：地震联合基金会资助项目

摘　　要：本文利用有限元方法模拟计算了强震发生前孕震区的波速比及S波分裂的时空变化,结果表明,孕震过程中,随着应力的局部集中,岩体发生扩容,引起裂隙的增生及定向排列,从而使孕震区产生各向异性,引起波速比的变化及S波分裂现象。在不同阶段,穿过同一路径的地震射线其波速比和S波分裂特征不同;在同一时刻,沿不同路径传播的地震射线其波速比及S波分裂也不同。总体看来,平行于孕震断层传播的地震波速比变化比垂直于孕震断层传播的地震波速比变化大;靠近断层的射线及穿过断层端部附近的射线及其波速比变化更明显一些。而S波时间延迟则表现为:孕震过程初期,穿过震源区的射线其S波延迟大于周围射线S波延迟,而孕震过程后期,穿过震源区的射线其S波延迟小于周围射线的S波延迟。计算结果还表明,S波延迟在震前有增大的趋势。In this paper, spatial and temporal variations of VP/ Vs and shear wave splitting in seismogenic zone before strong earthquake occurrence were simulated by using finite element method. The results show that stress concentration in earthquake preparation leads to rock dilatancy and development of oriented cracks. Therefore, the seismogenic zone turns to be anisotropic and causes changes of P/ Vs and shear wave splitting. In different time stages, characteristics of VP / Vs and shear wave splitting are different for the same ray path; while in the same time, characteristics of VP/ Vs and shear wave splitting are different along different paths. Generally, variation of VP/ Vs is bigger when the wave propagates parallel to the strike of the fault, and that is smaller when the wave propagates perpendicular to the fault strike; the change of VP / Vs is more obvious when the wave propagates near the fault or through the ends of the fault. For time delay of shear wave splitting, it is bigger when the wave goes through the source area while it is smaller when the wave goes through the periphery area in early stage of earthquake preparation. In later stage of earthquake preparation, time delay of shear wave splitting is smaller when the wave goes through the source area while it is bigger when the wave goes through the periphery area. The result also show that time delay of shear wave splitting tends to grow up before earthquake occurrence.

关 键 词：孕震过程 波速比 S波分裂 时空变化 数值模拟 

分 类 号：P315.1[天文地球—地震学]