CAP方法反演2014年山东乳山M4.2、M4.0地震震源机制解
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摘要
选用山东数字地震台网波形资料,利用CAP方法反演乳山2014年1月7日M4.2及4月4日M4.0地震震源机制解。反演结果显示,两次地震均在矩心深度为6km处获得最佳震源机制解,其节面参数基本一致,属于近走滑型地震。震中附近流动台站的震源距计算表明地震序列震源深度应略小于7km,与CAP方法反演结果具有一致性,表明地震的主体破裂发生在上地壳。
There have been many intensive small earthquakes since the M3.8earthquake occurred in Rushan,Shandong on October 1,2013.Two earthquakes(M4.2and M4.0)occurred separately on January 7and April 4,2014.There have never been so many earthquakes in Rushan.A focal mechanism describes the nature and source rupture process and is an important foundation to understand the stress state of the source region,earthquake faults,and for analyzing the causes of a seismic event.Therefore,seismic interpretation and post-earthquake seismogenic stress distribution mechanisms play very important roles in determining earthquake focal mechanisms.In this study,using waveforms from the Shandong Seismological Network and comparing the synthetic and the observed seismograms,the focal mechanism of the Rushan M4.2and M4.0earthquakes in 2014 are inverted using the CAP(Cut and paste)method.The results show that the two earthquakes get their best focal mechanism at 6km depth,and that the parameters of the nodal planes are similar,belonging to the strike-slip type.At a depth of 6km,the correlation coefficients of 40 phases of the M4.2earthquake greater than 0.7that were recorded by eight stations are 37,which accounts for 93%.The correlation coefficients greater than 0.9are 28,accounting for about 70%.Similarly,at a depth of 6km,the correlation coefficients of 40 phases of the M4.0earthquake that were recorded by the eight stations are all greater than 0.7and the correlation coefficients greater than 0.9are 31,accounting for about 78%.Therefore,the synthetic seismograms of the two earthquakes fit the observed seismograms well demonstrating that the inversion results are credible.The focal mechanism shows that the moment magnitude of the M4.2earthquake was MW =4.3;one nodal plane has a strike of 290°,rake of 84°,and dip of 22°and the other nodal plane has a strike of 189°,rake of 68°,and dip of 174°.The moment magnitude of the M4.0earthquake is MW =4.2,one nodal plane has a strike of 289°,rake of 90°,and dip of 27°and the other nodal plane has a strike of 199°,rake of 63°,and a dip of 180°,The hypocentral distance was calculated by the mobile seismic station near the epicenter.The results show that the focal depth is slightly less than 7km,which is consistent with the inversion results of the CAP method,and therefore,the main rupture of the earthquake was in the upper crust.The parameters of the Rushan fault nearest to the epicenter(strike of 10°normal fault)are not consistent with the focal mechanisms of the two earthquakes,which show that the Rushan fault is not the seismic fault and that the seismic faults may be concealed faults.
There have been many intensive small earthquakes since the M3.8earthquake occurred in Rushan,Shandong on October 1,2013.Two earthquakes(M4.2and M4.0)occurred separately on January 7and April 4,2014.There have never been so many earthquakes in Rushan.A focal mechanism describes the nature and source rupture process and is an important foundation to understand the stress state of the source region,earthquake faults,and for analyzing the causes of a seismic event.Therefore,seismic interpretation and post-earthquake seismogenic stress distribution mechanisms play very important roles in determining earthquake focal mechanisms.In this study,using waveforms from the Shandong Seismological Network and comparing the synthetic and the observed seismograms,the focal mechanism of the Rushan M4.2and M4.0earthquakes in 2014 are inverted using the CAP(Cut and paste)method.The results show that the two earthquakes get their best focal mechanism at 6km depth,and that the parameters of the nodal planes are similar,belonging to the strike-slip type.At a depth of 6km,the correlation coefficients of 40 phases of the M4.2earthquake greater than 0.7that were recorded by eight stations are 37,which accounts for 93%.The correlation coefficients greater than 0.9are 28,accounting for about 70%.Similarly,at a depth of 6km,the correlation coefficients of 40 phases of the M4.0earthquake that were recorded by the eight stations are all greater than 0.7and the correlation coefficients greater than 0.9are 31,accounting for about 78%.Therefore,the synthetic seismograms of the two earthquakes fit the observed seismograms well demonstrating that the inversion results are credible.The focal mechanism shows that the moment magnitude of the M4.2earthquake was MW =4.3;one nodal plane has a strike of 290°,rake of 84°,and dip of 22°and the other nodal plane has a strike of 189°,rake of 68°,and dip of 174°.The moment magnitude of the M4.0earthquake is MW =4.2,one nodal plane has a strike of 289°,rake of 90°,and dip of 27°and the other nodal plane has a strike of 199°,rake of 63°,and a dip of 180°,The hypocentral distance was calculated by the mobile seismic station near the epicenter.The results show that the focal depth is slightly less than 7km,which is consistent with the inversion results of the CAP method,and therefore,the main rupture of the earthquake was in the upper crust.The parameters of the Rushan fault nearest to the epicenter(strike of 10°normal fault)are not consistent with the focal mechanisms of the two earthquakes,which show that the Rushan fault is not the seismic fault and that the seismic faults may be concealed faults.
引文
[1]Zhao L S,Helmberger D V.Source Estimation from Broadband Regional Seismograms[J].Bull Seis Soc Amer,1994,84(1):91-104.
[2]Zhu L P,Helmberger D V.Advancement in Source Estimation Techniques Using Broadband Regional Seismograms[J].Bull Seism Soc Amer,1996,86(5):1634-1641.
[3]郑勇,马宏生,吕坚,等.汶川地震强余震(MS5.6)的震源机制解及其与发震构造的关系[J].中国科学:D辑(地球科学),2009,39(4):413-426.Zheng Y,Ma H S,LüJ,et al.Source Mechanism of Strong Aftershock of(MS≧5.6)of Wenchuan Earthquake and the Implication for Seismotectonic[J].Sci China:Ser D,2009,39(4):413-426.(in Chinese)
[4]韦生吉,倪四道,崇加军,等.2003年8月16日赤峰地震:一个可能发生在下地壳的地震?[J].地球物理学报,2009,52(1):111-119.Wei S J,Ni S D,Chong J J,et al.The 16August 2003Chifeng Earthquake:Is it a Lower Crust Earthquake?[J].Chinese J Geophys,2009,52(1):111-119.(in Chinese)
[5]韩立波,蒋长胜,包丰.2010年河南太康MS4.6地震序列震源参数的精确定位[J].地球物理学报,2012,55(9):2973-2981.HAN Li-bo,JIANG Chang-sheng,Bao Feng.Source Parameter Determination of 2010Taikang MS4.6Earthquake Sequences[J].Chinese J Geophys,2012,55(9):2973-2981.(in Chinese)
[6]洪德全,王行舟,倪红玉,等.多种方法研究2012年7月20日江苏高邮MS4.9地震震源机制解深度[J].地球物理学进展,2013,28(4):1757-1765.Hong D Q,Wang X Z,Ni H Y,et al.Focal Mechanism and Focal Depth of July 20,2012Jiangsu Gaoyou MS4.9Earthquake[J].Progress in Geophys,2013,28(4):1757-1765.(in Chinese)
[7]宋美琴,李华玥,韩立波,等.用CAP方法反演2010年6月5日山西阳曲MS4.6地震震源机制解[J].地震工程学报,2013,35(3):692-697.Song M Q,Li H Y,Han L B,et al.Focal Mechanism of the MS4.6 Yangqu Earthquake of June 5[J].China Earthquake Engineering Journal,2013,35(3):692-697.(in Chinese)
[8]李晓峰,裴惠娟,徐辉,等.2013年7月22日岷县漳县6.6级地震震源机制解[J].地震工程学报,2013,35(3):459-462.Li X F,Pei H J,Xu H,et al.Focal Mechanism of the MinxianZhangxian MS6.6Earthquake[J].China Earthquake Engineering Journal,2013,35(3):459-462.(in Chinese)
[9]Zhu L P,Rivera L A.A Note on the Dynamic and Static Displacements from a Point Source in Multilayered Media[J].Geophys J In,2002,148:619-627.
[10]张岭,刘劲松,郑天珧,等.利用Ground-Truth资料和Messy GA方法反演渤海湾盆地及其邻区地壳P波速度模型[J].地球物理学进展,2005,20(1):186-197.Zhang L,Liu J S,Zheng T Y,et al.Inverse Crustal P-wave Velocity Model of Bohai Bay Basin and its Adjacent Area by Using Messy GA with Ground-truth Data[J].Progress in Geophys,2005,20(1):186-97.(in Chinese)
[11]李霞,刘希强,李亚军,等.山东及邻区地震的重新定位及其与活动构造的关系[J].中国地震,2012,28(4);381-392.Li X,Liu X Q,Li Y J,et al.Relocation of Earthquake in Shandong and its Neighboring Areas in China and Relationship Between Their Tectonics[J].Earthquake Research in China,2012,28(4):381-392.(in Chinese)
[12]顾瑾萍,郑建常,张永仙.华北三维虚波速度地震异常分析[J].地震,2005,25(4):58-64.Gu J P,Zheng J C,Zhang Y X.Three Dimension Velocity Imaging of Seismic Pseudo Wave in North China with Seismic Anomaly[J].Earthquake,2005,25(4):58-64.(in Chinese)
[13]刘洪瑞,肖凤莲.泰安地区近震波速及地壳厚度的测定[J].地震地磁观测与研究,1992,13(4):25-29.Liu H R,Xiao F L.Survey of Near Earthquake Wave Velocity and Thickness of the Earth’s Crust Around Tai’an Area[J].Seismological and Geomagnetic Observation and Research,1992,13(4):25-29.(in Chinese)
[14]魏光兴,季同仁,杨家岭.渤海地区地震基本参数的校订[J].地震研究,1983,6(2):179-188.Wei G X,Ji T R,Yang J L.A Revision of Basal Parameters for Earthquakes in the Bohai Sea Area[J].Journal of Seismolgical Research,1992,13(4):25-29.(in Chinese)
[15]宋明春,王来明.对胶南造山带基础地质问题的新认识[J].中国区域地质,2000,19(1):1-6.Song M C,Wang L M.The Latest Understandings of Fundamental Geology of Jiaonan Orogenic Belt[J].Regional Geology of China,2000,19(1):1-6.(in Chinese)
[16]孔庆友,邹国强.山东省矿产资源储量报告编制指南[M].济南:山东省地图出版社,2010,274-280.Kong Q Y,Zou G Q.Preparation Guidelines of Shandong Province Mineral Resources Reserves Report[M].Jinan:Map Publishing House of Shandong Province,2010:274-280.(in Chinese)
[2]Zhu L P,Helmberger D V.Advancement in Source Estimation Techniques Using Broadband Regional Seismograms[J].Bull Seism Soc Amer,1996,86(5):1634-1641.
[3]郑勇,马宏生,吕坚,等.汶川地震强余震(MS5.6)的震源机制解及其与发震构造的关系[J].中国科学:D辑(地球科学),2009,39(4):413-426.Zheng Y,Ma H S,LüJ,et al.Source Mechanism of Strong Aftershock of(MS≧5.6)of Wenchuan Earthquake and the Implication for Seismotectonic[J].Sci China:Ser D,2009,39(4):413-426.(in Chinese)
[4]韦生吉,倪四道,崇加军,等.2003年8月16日赤峰地震:一个可能发生在下地壳的地震?[J].地球物理学报,2009,52(1):111-119.Wei S J,Ni S D,Chong J J,et al.The 16August 2003Chifeng Earthquake:Is it a Lower Crust Earthquake?[J].Chinese J Geophys,2009,52(1):111-119.(in Chinese)
[5]韩立波,蒋长胜,包丰.2010年河南太康MS4.6地震序列震源参数的精确定位[J].地球物理学报,2012,55(9):2973-2981.HAN Li-bo,JIANG Chang-sheng,Bao Feng.Source Parameter Determination of 2010Taikang MS4.6Earthquake Sequences[J].Chinese J Geophys,2012,55(9):2973-2981.(in Chinese)
[6]洪德全,王行舟,倪红玉,等.多种方法研究2012年7月20日江苏高邮MS4.9地震震源机制解深度[J].地球物理学进展,2013,28(4):1757-1765.Hong D Q,Wang X Z,Ni H Y,et al.Focal Mechanism and Focal Depth of July 20,2012Jiangsu Gaoyou MS4.9Earthquake[J].Progress in Geophys,2013,28(4):1757-1765.(in Chinese)
[7]宋美琴,李华玥,韩立波,等.用CAP方法反演2010年6月5日山西阳曲MS4.6地震震源机制解[J].地震工程学报,2013,35(3):692-697.Song M Q,Li H Y,Han L B,et al.Focal Mechanism of the MS4.6 Yangqu Earthquake of June 5[J].China Earthquake Engineering Journal,2013,35(3):692-697.(in Chinese)
[8]李晓峰,裴惠娟,徐辉,等.2013年7月22日岷县漳县6.6级地震震源机制解[J].地震工程学报,2013,35(3):459-462.Li X F,Pei H J,Xu H,et al.Focal Mechanism of the MinxianZhangxian MS6.6Earthquake[J].China Earthquake Engineering Journal,2013,35(3):459-462.(in Chinese)
[9]Zhu L P,Rivera L A.A Note on the Dynamic and Static Displacements from a Point Source in Multilayered Media[J].Geophys J In,2002,148:619-627.
[10]张岭,刘劲松,郑天珧,等.利用Ground-Truth资料和Messy GA方法反演渤海湾盆地及其邻区地壳P波速度模型[J].地球物理学进展,2005,20(1):186-197.Zhang L,Liu J S,Zheng T Y,et al.Inverse Crustal P-wave Velocity Model of Bohai Bay Basin and its Adjacent Area by Using Messy GA with Ground-truth Data[J].Progress in Geophys,2005,20(1):186-97.(in Chinese)
[11]李霞,刘希强,李亚军,等.山东及邻区地震的重新定位及其与活动构造的关系[J].中国地震,2012,28(4);381-392.Li X,Liu X Q,Li Y J,et al.Relocation of Earthquake in Shandong and its Neighboring Areas in China and Relationship Between Their Tectonics[J].Earthquake Research in China,2012,28(4):381-392.(in Chinese)
[12]顾瑾萍,郑建常,张永仙.华北三维虚波速度地震异常分析[J].地震,2005,25(4):58-64.Gu J P,Zheng J C,Zhang Y X.Three Dimension Velocity Imaging of Seismic Pseudo Wave in North China with Seismic Anomaly[J].Earthquake,2005,25(4):58-64.(in Chinese)
[13]刘洪瑞,肖凤莲.泰安地区近震波速及地壳厚度的测定[J].地震地磁观测与研究,1992,13(4):25-29.Liu H R,Xiao F L.Survey of Near Earthquake Wave Velocity and Thickness of the Earth’s Crust Around Tai’an Area[J].Seismological and Geomagnetic Observation and Research,1992,13(4):25-29.(in Chinese)
[14]魏光兴,季同仁,杨家岭.渤海地区地震基本参数的校订[J].地震研究,1983,6(2):179-188.Wei G X,Ji T R,Yang J L.A Revision of Basal Parameters for Earthquakes in the Bohai Sea Area[J].Journal of Seismolgical Research,1992,13(4):25-29.(in Chinese)
[15]宋明春,王来明.对胶南造山带基础地质问题的新认识[J].中国区域地质,2000,19(1):1-6.Song M C,Wang L M.The Latest Understandings of Fundamental Geology of Jiaonan Orogenic Belt[J].Regional Geology of China,2000,19(1):1-6.(in Chinese)
[16]孔庆友,邹国强.山东省矿产资源储量报告编制指南[M].济南:山东省地图出版社,2010,274-280.Kong Q Y,Zou G Q.Preparation Guidelines of Shandong Province Mineral Resources Reserves Report[M].Jinan:Map Publishing House of Shandong Province,2010:274-280.(in Chinese)
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