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对2013年芦山Ms7.0级地震序列的横波分裂的时空变化现象进行了研究.通过在横波窗内S波质点运动图的分析,从位于龙门山断裂带南段芦山地震震源区地震台站的记录中提取了S波分裂的快波偏振方向和慢波的到时延迟.在研究区,观测到各台站的快波偏振优势方向从南向北有分区特征,慢波到时延迟的随时间有趋势性变化.空间上,快波偏振优势方向在南部为北东向,与龙门山断裂走向一致,而北部为北西向,与区域主压应力方向一致,位于断裂带上的台站TQU和BAX表现出特殊性,可能受到龙门山断裂带的直接影响,体现了断裂带上的应力场方向变化的特殊性.时间上,慢波到时延迟在主震后迅速增大,持续一段时间后又减小;横波分裂现象主要由台站下方岩层中随应力分布排列的微裂隙控制,本文结果揭示了主震和余震过程中区域应力场的变化,芦山地震震源区的地壳应力在主震后得到了增强,随着余震活动导致的应力释放,后期应力减小.
The temporal and spatial variations of shear wave splitting in the Lushan Ms7.0 earthquake sequence in 2013 were studied.According to the analysis of S-wave particle motions in the transverse wave window, from the seismic stations located at the Lushan earthquake focal zone in the southern segment of the Longmenshan fault zone The arrival time of the fast wave polarization direction and the slow wave of the S-wave splitting are extracted from the records.In the study area, the dominant polarization direction of fast wave at each station is observed to be zonal characteristic from south to north, In the space, the predominant polarization direction of fast wave is north-easterly in the south, consistent with the Longmenshan fault, and northward is northwestward, which is consistent with the principal compressive stress in the region. The stations TQU And BAX are special and may be directly affected by the Longmenshan fault zone, which reflects the particularity of the direction of stress field changes in the fault zone. In time, the slow wave arrival time delay increases rapidly after the main shock and continues for a period of time And then decrease. The shear-wave splitting phenomenon is mainly controlled by the micro-fractures arranged along the stress distribution in the rock below the station. The results of this paper reveal the changes of regional stress field during the main shock and aftershock. The crustal stress in the focal region of Lushan earthquake is After the earthquake has been enhanced with the aftershock activity leads to stress relief, post-stress decreases.