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四川宜宾地区S波分裂特征
吴朋1, 苏金蓉1, 黄春梅1, 黄东剑2, 段云歌1
1.四川省地震局, 成都市人民南路三段29号 610041;2.四川省宜宾市防震减灾局, 四川宜宾 644000
摘要:
本文采用纵横比与偏振分析相结合的方法测定了2013年4月25日~2015年12月31日四川宜宾地区10个台站S波分裂参数,即快波偏振方向和慢波延迟时间。结果表明,华蓥山断裂两侧台站呈现不同的快波偏振优势方向,断裂带以西的台站偏振优势方向为NW向,与区域应力场方向一致;位于断裂带以东的台站优势偏振方向为NE向,与断裂走向一致。在地震密集分布区域内的CNI台的优势偏振方向为NE向,与台站附近的断裂带走向基本一致。研究区域南段的3个台站(JLI、YAJ、XWE)优势偏振方向近NS向。各个台站平均慢波延迟时间在3.07~11.95ms/km范围内,慢波延迟时间最大的台站是CNI台,距离2013年4月25日06时10分ML5.2地震震中位置最近,这反映出震源区地震波各向异性程度较强。CNI台站的慢波延迟时间显示,在2015年2月7日ML 4.8地震前观测到慢波延迟时间有明显的上升趋势。
关键词:  S波分裂  快波偏振方向  慢波延迟时间  地震波各向异性
DOI:
分类号:P315
基金项目:地震科技星火计划项目(XH17029Y)和测震台网青年骨干培养专项(20160522)联合资助
Characteristic of shear-wave splitting in the Yibin area, Sichuan Province
Wu Peng1, Su Jinrong1, Huang Chunmei1, Huang Dongjian2, Duan Yunge1
1.Earthquake Administration of Sichuan Province, Chengdu 610041, China;2.Earthquake Administration of Yibin City, Yibin 644000, Sichuan, China
Abstract:
In this paper,the methods of aspect ratio and polarization analysis were used to determine the S-wave splitting parameters of 10 stations in Yibin,Sichuan from April 25,2013 to December 31,2015,i.e.,fast wave polarization direction and slow wave delay time. The results show the polarization directions of fast shear waves on both sides are different. In the west of Huaying Fault the dominant polarization directions of fast shear waves are NW in agreement with the directions of the regional principal compressive stress. In the east the dominant polarization directions of fast shear waves are NE,which is consistent with the strike of Huaying Fault. The dominant polarization directions of fast shear waves at the station CNI in the earthquake concentrated area are NE,which is almost consistent with the strike of faults near the stations. The dominant polarization directions of fast shear waves at the 3 stations(JLI,YAJ,and XWE)in the southern section of the study area are near NS. The average delay time of slow shear waves at each station is in the range of 3.31-11.95ms/km,the maximum delay time of slow shear wave is at the station CNI which is the nearest station from the epicenter of ML5.2 earthquake,reflecting the strong anisotropy in the source area. The delay times of slow shear waves at the station CNI are in disorder in the period after the two MS4.0 earthquakes. Characteristic increases of time-delays is observed before the ML4.8 earthquake on February 7,2015.
Key words:  Shear wave splitting  The polarization directions of fast shear waves  The delay time of slow shear wave  Anisotropy