THE SHEAR-WAVE SPLITTING OF GAIZHOU EARTHQUAKE SWARM IN LIAONING

doi:10.3969/j.issn.0253-4967.2016.04.020

Abstract

Abstract:

An M_L4.7 earthquake occurred on February 2,2012 in Liaoning Gaizhou (40.56°N,122.36°E),since then,small earthquakes are frequent in this area,and until now the seismic activity does not stop,several earthquakes with magnitude larger than 4.0 have occurred.As of October 30,2014,1223 earthquakes have happened in the Gaizhou area,including 934 earthquakes with the magnitude M_L1.0~1.9,247 with the magnitude M_L2.0~2.9 and 45 with the magnitude M_L3.0~3.9.Meanwhile,earthquakes are continuously active in Haicheng area where the M_S7.3 earthquake happened in 1975,and there are over 1100 earthquakes (M_L ≥ 1.0) having occurred since the Gaizhou earthquake swarm activity.Because the polarization direction of the fast shear wave is very sensitive to the variation of the principal stress environment,the shear wave splitting parameter can reflect the regional stress state and the local structural features,especially effective for the analysis of small-scale stress environment characteristics.So based on the seismic activities of the two earthquake clusters,this study analyzes the characteristics of shear-wave splitting in Gaizhou-Haicheng area.Preliminary results show that predominant polarization direction of fast shear-waves in the old earthquake region of Haicheng is stable,consistent with the direction of regional stress field.Due to presence of active fault below the Gaixian station (GAX),the predominant polarization direction of fast shear-waves is more complicated.There are two predominant polarizations,consistent respectively with Jinzhou Fault strike which is below the station and the maximum principal stress direction in this area.In addition,Gaizhou earthquake swarm activity increased after December 22,2013,and after the time node,the predominant polarization direction of fast shear-waves in Gaixian station is SEE,which is close to the predominant polarization direction of fast shear-waves in Yingkou station,at the same time consistent with the maximum principal stress direction of this region.Thus it can be inferred,the enhanced activity of Gaizhou earthquake swarm since December 22,2014 may be related to local enhancement of regional stress.In addition,the average time-delays of slow waves in station YKO and GAX show that there are no obvious changes before and after the time point of December 22,2013,which is different greatly with the previous related researches on the variation of slow wave time-delays,and there is no possibility that the Gaizhou earthquake swarm evolved into foreshock sequences from current preliminary results.We should do more work to study the details of the time delay variation of shear wave splitting parameter.

Key words: shear-wave splitting, Gaizhou earthquake swarm, polarization of fast shear-waves

摘要：

2012年2月2日，在辽宁盖州（40.56°N，122.36°E）发生M_L4.7地震，此后该地区小震不断，地震活动持续至今仍未停止，发生多次4级以上地震。与此同时，海城地震老震区小震持续活动，自盖州震群活动以来，亦发生1 100多次M_L≥1.0地震。基于这2丛地震活动，研究了盖州-海城地区的剪切波分裂特征。初步研究结果表明，海城老震区快剪切波优势偏振方向较为稳定，与该地区区域应力场方向基本一致。由于盖县台下方存在活动断裂，其快剪切波的优势偏振方向较为复杂，存在2个优势偏振方向，分别与台站下方的金州断裂走向和该区最大主应力方向一致。此外，2013年12月22日之后，盖州震群活动突然增强，与此同时，自该时间之后，盖县台（GAX）所反映出的快剪切波优势偏振方向为SEE向，与营口台（YKO）的快剪切波优势方向基本接近，同时与该区最大主应力方位较为一致。由此可以推断，盖州震群自2013年12月22日的这组增强活动或与区域应力的局部增强有关。但这2个震群的慢波时间延迟变化相对较小，与以往相关研究中强震前慢波时间延迟的变化差异较大。

关键词: 盖州震群, 剪切波分裂, 快波偏振方向

CLC Number:

P315.6

LI Jin, GAO Yuan, ZHANG Bo, WANG Liang, GAO Rong. THE SHEAR-WAVE SPLITTING OF GAIZHOU EARTHQUAKE SWARM IN LIAONING[J]. SEISMOLOGY AND GEOLOGY, 2016, 38(4): 1058-1069.

李金, 高原, 张博, 王亮, 高荣. 辽宁盖州海城地区地壳剪切波分裂特征[J]. 地震地质, 2016, 38(4): 1058-1069.

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