2017~2018年山东长岛震群双差波速比特征分析

Analysis on Features of 2017-2018 Changdao Earthquake Swarms Based on the Wave Velocity Ratio Using a Double-Difference Method

通过限定震群集中区范围,剔除同一台站记录的震中位置相近且具有相同路径的地震波,使用双差波速比两次差分的方法,对2017~2018年长岛地区发生的2个震群的波速比值开展特征分析。通过对震相数据敏感性分析得出,双差波速比方法对Pg波到时较为敏感,资料处理时需要将Pg、Sg波震相误差分别控制在0.02 s和0.20 s以内。最终分析结果显示,长岛震群波速比值在1.69~1.78范围内波动,波速比变化与震群活动过程密切相关;震群几次较大余震发生前,波速比呈现低值状态;主震和余震的波速比变化存在差异,可能反映二者发震机理有所不同。

By limiting the diameter of the earthquake swarm concentration area,and deducing the same ray path of two earthquakes at similar distances recorded by a single seismic station,using the method of double difference wave velocity ratio,we carry out characteristic analysis of the wave velocity ratio of the two earthquake swarms in Changdao area from 2017 to 2018.Through the sensitivity analysis of seismic phase data,we conclude that the method of double-difference wave velocity ratio is comparatively sensitive to the noise in arrival time,especially for Pg-wave.The phase errors of Pg-wave and Sg-wave should be controlled within 0.02 to 0.20 s.The final analysis results show that the wave velocity ratio of Changdao earthquake swarm fluctuates in the range of 1.69-1.78,and the change of wave velocity ratio is closely related to the activity process of earthquake swarm.Before the occurrence of several large aftershocks,the wave velocity ratio showed a low state.The wave velocity ratio between main shock and aftershock varies,which may reflect differing seismogenic mechanisms.