从波速比变化看汶川与芦山地震的孕震过程

为研究汶川和芦山地震的孕育过程，利用单台单震法，将地震丛发区内发生的地震粗略视为“广义重复地震”，系统分析龙门山断裂带及附近区域1990～2015年波速比时空变化过程。结果发现，波速比在汶川地震前降低，芦山地震后明显恢复。对于龙门山断裂带北段的地震丛发区，大部分台站波速比的同步时间变化过程可分为两个阶段：一是在汶川地震前，2000年～2008-05波速比出现异常降低-回返-发震过程，低值异常持续时间约8 a。汶川地震后，波速比快速回升。二是2010年开始再次显现波速比持续性稳定下降，在2013-04降至最低点，发生芦山地震，震后波速比再次快速回升到正常值。对于龙门山断裂带南段及附近的地震丛发区，大部分台站波速比的同步时间变化从2000年～2013-04波速比维持长时间的异常低值状态，低值持续时间约13 a，直至2013-04芦山地震后波速比快速回升。不论是龙门山南段还是北段，均可看到波速比基本一致的变化，2000～2013年的异常降低-恢复过程，显示了汶川8级地震与芦山7级地震的整体性和差异性，孕震过程长达14 a。由此可见，汶川地震和芦山地震很可能是同一动力学过程孕育的两次先后发生的强震。

Study of the Seismogenic Process from Wenchuan to the Lushan Earthquake Based on Wave Velocity Ratio Temporal Variation

Based on seismic phase date recorded by Sichuan digital seismic network, this study analyzes the spatial and temporal variations. In this study, we employ the idea of repeat earthquakes, select seismic active area as generalized repeat earthquakes, and analyze the velocity ratio of the cluster zone to different stations around. The results show that the velocity ratio obviously decreased before the Wenchuan earthquake and increased after the Lushan earthquake. These changes can be observed both north and south of Longmenshan fault. The temporal changes of velocity ratio from 2000 to 2013 show the integrity and difference between Wenchuan MS8.0 and Lushan MS7.0. It seems that it was the same dynamic process, the two large earthquakes occurred in this process.