Temporal variation characteristics of shear-wave splitting for the Rushan earthquake swarm of Shandong Province
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摘要: 2013年10月1日山东乳山发生ML3.8地震后， 该地区的地震活动呈现出小震群特征， 且持续至今， 其中2014—2015年先后发生了4次ML4.1—5.0显著性地震， 造成了较大的社会影响． 本文利用山东数字地震台网中乳山台记录的地震波形资料， 测定了来自乳山震群中224次小地震的剪切波分裂参数． 研究结果表明： 快剪切波的偏振优势方向与山东半岛地区的主压应力方向基本一致； 剪切波分裂时间延迟在这4次显著性地震发生前后均产生明显的变化， 分裂时间延迟平均在震前1个月左右开始出现升高异常， 在震前约12天出现下降异常变化． 这些特征均可作为利用应力进行地震预测的前兆指标．Abstract: The seismicity in Rushan region of Shandong Province is characterized by small swarms after the ML3.8 Rushan earthquake on October 1, 2013, and this situation continues up to now. Four earthquakes with ML4.7, ML4.5, ML4.1 and ML5.0 occurred from January of 2014 to May of 2015 cause great social effects. Based on the seismic records from the Rushan station, this paper calculated the shear-wave splitting parameters of 224 small earthquakes of Rushan earthquake swarm. The result shows that the polarization direction of the fast shear-wave is consistent with the principal compressive stress direction of the Shandong peninsula; on the other hand, the time delay has obvious change before and after the four earthquakes, that is, it raised about one month and declined about twelve days before earthquake. All the characteristics can be taken as the precursor indicator for earthquake prediction based on stress.
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Keywords:
- Rushan earthquake swarm /
- stress accumulation /
- shear-wave splitting /
- time delay
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图 2 本文所选用的乳山地震事件P波与S波到时差ΔtS-P分布直方图
Figure 2. Histogram of the difference ΔtS-P between the arrival times of the P and S waves for the Rushan earthquakes used in this paper
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图 3 台站及乳山震群分布
Figure 3. Distribution of Rushan earthquake swarm and stations Triangles denote the stations，and dots denote Rushan earthquake swarm
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图 4 乳山台(RSH)记录的2014年1月30日ML-0.8地震波形(ΔtS-P=1.6 s)
Figure 4. Seismic waveform of an earthquake with ML-0.8 on January 30，2014 with ΔtS-P of 1.6 s recorded by the station RSH
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图 5 乳山台(RSH)记录的2014年1月29日ML0.0地震波形(ΔtS-P=1.5 s)
Figure 5. Seismic waveform of an earthquake with ML0.0 on January 29，2014 with ΔtS-P of 1.5 s recorded by the station RSH
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图 6 乳山台(RSH)记录的2013年12月3日ML1.0地震波形(ΔtS-P=1.5 s)
Figure 6. Seismic waveform of an earthquake with ML1.0 on December 3，2013 with ΔtS-P of 1.5 s recorded by the station RSH
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图 7 3个地震事件的水平分量剪切波偏振图
左图为剪切波质点运动轨迹图，S1和S2分别表示快、 慢剪切波的振动起始位置； 右图为 NS和EW分量的剪切波波形，两条短竖线标明了偏振图中所显示的剪切波波形范围(a)2014年1月30日ML-0.8地震，波形见图 4;(b)2014年1月29日ML0.0地震，波形见图 5;(c)2013年12月3日ML1.0地震，波形见图 6
Figure 7. Horizontal shear-wave polarization of three earthquakes
Left panels show the trails of shear-wave particle motion，where S1 and S2 indicate the start position of fast and slow shear-waves，respectively; right panels show the waveforms of NS and EW component of shear-waves，where the short bars mark the scope of shear-wave waveforms shown in the left panels (a)ML-0.8 earthquake on January 30，2014 with waveform shown in Fig. 4;(b)ML0.0 earthquake on January 29，2014 with waveform shown in Fig. 5;(c)ML1.0 earthquake on December 3，2013 with waveform shown in Fig. 6
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图 8 3个地震事件偏振分析检验
左图为经过时间延迟校正后的剪切波偏振图； 右图为时间延迟校正后的快、 慢剪切波波形，短竖线所指同图 7.(a)2014年1月30日ML-0.8地震，波形见图 4;(b)2014年1月29日ML0.0地震，波形见图 5;(c)2013年12月3日ML1.0地震，波形见图 6
Figure 8. Check of polarization analysis of three earthquakes
Left panels show the shear-wave polarization with time delay effect being eliminated，and right panels show the waveforms of fast and slow shear-waves，where the meaning of short bars see Fig. 7(a)ML-0.8 earthquake on January 30，2014 with waveforms shown in Fig. 4；(b)ML0.0 earthquake on January 29，2014 with waveforms shown in Fig. 5;(c)ML1.0 earthquake on December 3，2013 with waveforms shown in Fig. 6
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图 9 乳山(RSH)台记录到的224次地震的慢剪切波时间延迟变化
(a)时间延迟原始数据变化;(b)对原始数据进行线性5点平滑处理后的时间延迟变化，实线为均值，虚线为标准差
Figure 9. Time delay variation of slow shear-wave for the 224 events recorded by the RSH station
(a)Original time delay;(b)The result of five-point fitting，where the horizontal solid line represents the mean，the dashed lines are the standard deviation
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图 10 乳山台(RSH)快剪切波偏振方向等面积投影玫瑰图
Figure 10. Equal-area project rose diagram of fast shear-wave polarization for the RSH station
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期刊类型引用(3)
1. 郑毅权，雷军. 腾冲地区中小震群横波分裂到时差变化研究. 北京大学学报(自然科学版). 2023(03): 375-387 . 
百度学术
2. 王鹏，郑建常. 山东乳山震群遗漏地震检测及震源区活动特征分析. 中国地震. 2021(02): 400-414 . 百度学术
3. 苗庆杰，高原，刘希强，曲均浩，郑建常. 基于地壳介质各向异性分析乳山地震近场区构造应力特征. 大地测量与地球动力学. 2017(03): 234-239 . 百度学术
其他类型引用(1)
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