郯庐断裂带安徽段中小地震震源机制及现代应力场特征
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摘要
应用垂直向P波和SV波振幅比和联合利用P波、SV波和SH波的初动和振幅比两种计算震源机制解的方法,得到郯庐断裂带安徽段及邻近地区1970年以来239次中小地震的震源机制解;基于震源机制解,根据力轴张量计算法反演得到郯庐断裂带安徽段及其两个分段的平均构造应力场,与震源机制参数统计结果一致,表现为近EW向的水平挤压和近NS向的水平拉张作用;分析最大主压应力轴σ1的方位角随时间变化特征,结果表明郯庐断裂带安徽段两个分段的σ1的方位角总体变化趋势一致,均呈现出1998年前后由顺时针偏转转折至逆时针偏转。
The focal mechanisms of 239moderate and small earthquakes since 1970 in the Anhui sector of Tanlu fault zone were calculated with two methods:using the amplitude ratios of vertical P and SV waves in combination with the first motion of P,SV,and SH waves,and with 93focal mechanisms in the northern sub-sector and 146focal mechanisms in the southern sub-sector.Based on these abundant focal mechanisms,we have discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Anhui sector of Tanlu fault zone.The statistical analysis of the parameters of focal mechanism solutions shows that most moderate and small earthquakes occurring in the Anhui sector of Tanlu fault zone are of the strike-slip type,amounting to 54%of the total.Reverse faulting and normal faulting earthquakes occur less frequently,representing about 26% and 20% of the total,respectively.Azimuth and obliquity distribution of the P axis and the T axis are of obvious advantages,showing that the tectonic stress field in the Anhui sector of Tanlu fault zone and its sub-sectors is horizontally compressed in approximately the EW direction and horizontally dilated in approximately the NS direction.We further inverted the mean tectonic stress field in the Anhui sector of Tanlu fault zone and its subsectors with the force axis tensor computing method,and the results are as follows:in the Anhui sector of Tanlu fault zone,for the azimuth of maximum principal(compressive)stress axis(compression axis),σ1is 265°and its plunge is 6°;for the azimuth of the minimum principal(extensional)stress axis(tension axis),σ3is 356°and its plunge is 9°;in the northern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 260°and its plunge is 4°;for the azimuth of the minimum principal stress axis,σ3is 350°and its plunge is 2°;in the southern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 269°and its plunge is 8°;for the azimuth of the minimum principal stress axis,σ3is 1°and its plunge is 11°.These results indicate that the Anhui sector of Tanlu fault zone and its sub-sectors are horizontally compressed approximately in the EW direction and horizontally dilated approximately in the NS direction,which is in accord with statistical results of focal mechanism parameters.We analyzed the variation curve of the azimuth of maximum principal stress axis(σ1)versus time,which shows that the total variation trend of theσ1azimuth versus time is consistent between two sub-sectors of the Anhui sector of Tanlu fault zone,meaning both show the transition from clockwise deflection to counter-clockwise deflection in about 1998.Theσ1azimuth of the northern sub-sector experienced continued clockwise deflection from 1988to 1993,with deflected amplitude amounts to 23°,then the transition showed in 1994;a MS5.2earthquake in Cangshan,Shandong in 1995occurred after the transitions recovered,which is in accord with the variation of the trend of the P axis azimuth obtained by Zhou Cuiying([Year]),who used the method of composite focal mechanism solutions of moderate and small earthquakes.
The focal mechanisms of 239moderate and small earthquakes since 1970 in the Anhui sector of Tanlu fault zone were calculated with two methods:using the amplitude ratios of vertical P and SV waves in combination with the first motion of P,SV,and SH waves,and with 93focal mechanisms in the northern sub-sector and 146focal mechanisms in the southern sub-sector.Based on these abundant focal mechanisms,we have discussed in detail the earthquake fault types and the characteristics of the modern tectonic stress field in the Anhui sector of Tanlu fault zone.The statistical analysis of the parameters of focal mechanism solutions shows that most moderate and small earthquakes occurring in the Anhui sector of Tanlu fault zone are of the strike-slip type,amounting to 54%of the total.Reverse faulting and normal faulting earthquakes occur less frequently,representing about 26% and 20% of the total,respectively.Azimuth and obliquity distribution of the P axis and the T axis are of obvious advantages,showing that the tectonic stress field in the Anhui sector of Tanlu fault zone and its sub-sectors is horizontally compressed in approximately the EW direction and horizontally dilated in approximately the NS direction.We further inverted the mean tectonic stress field in the Anhui sector of Tanlu fault zone and its subsectors with the force axis tensor computing method,and the results are as follows:in the Anhui sector of Tanlu fault zone,for the azimuth of maximum principal(compressive)stress axis(compression axis),σ1is 265°and its plunge is 6°;for the azimuth of the minimum principal(extensional)stress axis(tension axis),σ3is 356°and its plunge is 9°;in the northern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 260°and its plunge is 4°;for the azimuth of the minimum principal stress axis,σ3is 350°and its plunge is 2°;in the southern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 269°and its plunge is 8°;for the azimuth of the minimum principal stress axis,σ3is 1°and its plunge is 11°.These results indicate that the Anhui sector of Tanlu fault zone and its sub-sectors are horizontally compressed approximately in the EW direction and horizontally dilated approximately in the NS direction,which is in accord with statistical results of focal mechanism parameters.We analyzed the variation curve of the azimuth of maximum principal stress axis(σ1)versus time,which shows that the total variation trend of theσ1azimuth versus time is consistent between two sub-sectors of the Anhui sector of Tanlu fault zone,meaning both show the transition from clockwise deflection to counter-clockwise deflection in about 1998.Theσ1azimuth of the northern sub-sector experienced continued clockwise deflection from 1988to 1993,with deflected amplitude amounts to 23°,then the transition showed in 1994;a MS5.2earthquake in Cangshan,Shandong in 1995occurred after the transitions recovered,which is in accord with the variation of the trend of the P axis azimuth obtained by Zhou Cuiying([Year]),who used the method of composite focal mechanism solutions of moderate and small earthquakes.
引文
[1]Xu J W,Zhu G,Tong W X,et al.Formation and Evolution of the Tancheng-Lujiang Wrench FauIt System:A Major Shear System to the Northern of the Pacific Ocean[J].Tectonophysics,1987,134(4):273-3l0.
[2]姚大全,刘加灿,翟洪涛,等.地震韵律研究方法初探——以郯庐断裂带龙泉山西麓剖面研究为例[J].地震研究,2005,28(1):49-52.YAO Da-quan,LIU Jia-can,ZHAI Hong-tao,et al.Preliminary Research Method of Seismic Rhythms——Taking the Research on the Longquanshan West-foot Profile in the Tancheng-Lujiang Fault Zone as An Example[J].Journal of Seismological Research,2005,28(1):49-52.(in Chinese)
[3]魏光兴,刁守中,周翠英.郯庐带地震活动性研究[M].北京:地震出版社,1993:110-166.Wei G X,Diao S Z,Zhou C Y.Research on Seismic Activity of Tanlu Fault Zone[M].Beijing:Seismological Press,1993:110-166.(in Chinese)
[4]夏瑞良,刘东旺.郯庐断裂带南段的地震活动及应力场特征[J].福建地震,1995,11(4):13-19.XIA Rui-liang,LIU Dong-wang.The Characteristics of the Earthquake Activity and Stress Field in South Tanlu Faults[J].Fujian Earthquake,1995,11(4):13-19.(in Chinese).
[5]刘东旺,夏瑞良,刘泽民,等.郯庐断裂带安徽段现代地震活动及应力场特征[J].地质科学,2006,41(2):278-290.LIU Dong-wang,XIA Rui-liang,LIU Ze-min,et al.Characteristics of Recent Seismic and Stress Field in Anhui sector of the Tanlu Fault Zone[J].Chinese Jour.Geol.,2006,41(2):278-290.(in Chinese)
[6]钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.ZHONG Jimao,CHENG Wan-zheng.Determination of Directions of the Mean Stress Field in Sichuan-Yunnan Region from A Number of Focal Mechanism Solutions[J].Acta Seismologica Sinica,2006,28(4):337-346.(in Chinese)
[7]高国英,聂晓红,龙海英.近期新疆震源机制解与地震活动特征研究[J].西北地震学报,2012,34(1):57-63.GAO Guo-ying,NIE Xiao-hong,LONG Hai-ying.Research on the Characteristics of Recent Focal Mechanism Solution and Seismic Activity in Xinjiang Area[J].Northwestern Seismological Jouranl,2012,34(1):57-63.(in Chinese)
[8]梁尚鸿,李幼铭,束沛镒,等.利用区域地震台网P、珔S振幅比资料测定小震震源参数[J].地球物理学报,1984,27(3):249-256.LIANG Shang-hong,LI You-ming,SHU Pei-yi,et al.Determined the Focal Mechanism Solution of Micro Earthquakes from Amplitude Ratio ofP andS Recorded by Area Seismological Network[J].Chinese Jour.Geophys.,1984,27(3):249-256.(in Chinese)
[9]Snoke J A,Munsey J W,Teague A G,et al.A Program for Focal Mechanism Determination by Combined Use of Polarity and SV-P Amplitude Ratio Data[J].Earthquake Notes,1984,55(3):15-20.
[10]Snoke J A.Earthquake Mechanism[G]∥James D E.Encyclopedia of Geophysics.New York:Van Nostrand Reinhold Company,1989:239-245.
[11]http://www.iris.edu/software/downloads/processing/.
[12]胡新亮,刁桂苓,马瑾,等.利用数字地震记录的P,珔S振幅比资料测定小震震源机制解的可靠性分析[J].地震地质,2004,26(2):347-354.HU Xin-liang,DIAO Gui-ling,MA Jin,et al.Reliability Analysis of Focal Mechanism Solutions of Micro Earthquakes Determined from Amplitude Ratio ofP andS Recorded by Digital Seismograph[J].Seismology and Geology,2004,26(2):347-354.(in Chinese)
[13]倪红玉,刘泽民,沈小七,等.利用FOCMEC方法计算震源机制解的影响因素分析[J].华北地震科学,2011,29(3):1-7.NI Hong-yu,LIU Ze-min,SHEN Xiao-qi,et al.Analysis on the Factors of Determining the Focal Mechanism Using FOCMEC Method[J].North China Earthquake Seiences,2011,29(3):1-7.(in Chinese)
[14]刘杰,郑斯华,康英,等.利用P波和S波的初动和振幅比计算中小地震的震源机制解[J].地震,2004,24(1):19-26.LIU Jie,ZHENG Si-hua,KANG Ying,et al.The FocalMechanism Determinations of Moderate-small Earthquakes Using the First Motion and Amplitude Ratio ofP andS Wave[J].Earthquake,2004,24(1):19-26.(in Chinese)
[15]阚荣举,张四昌,晏凤桐,等.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,1977,20(2):96-107.KAN Rong-ju,ZHANG Si-chang,YAN Feng-tong,et al.Study on the Current Tectonics Stress Field and the Characteristics of Current Tectonic Activity in the Southwest China[J].Chinese Journal of Geophysics,1977,20(2):96-107.(in Chinese)
[16]阮祥,程万正,乔惠珍,等.安宁河-则木河地震带震源参数及应力状态的研究[J].西北地震学报,2011,33(1):46-50.RUAN Xiang,CHENG Wan-zheng,QIAO Hui-zhen,et al.Research on Source Parameters and Stress State in Anninghe-Zemuhe Earthquake Belt[J].Northwestern seismological Jouranl,2011,33(1):46-50.(in Chinese)
[17]林向东,徐平,武敏捷,等.小江断裂中段及邻区构造应力场分布特征[J].中国地震,2010,26(2):192-200.LIN Xiang-dong,XU Ping,WU Min-jie,et al.Inversion of Stress Field in Middle Section of the Xiaojiang Fault and Its Adjacent Area[J].Earthquake research in China,2010,26(2):192-200.(in Chinese)
[18]陈连旺,杨树新,谢富仁.华北块体现今构造应力场及其年变化特征[G]∥中国大陆地壳应力环境研究.北京:地质出版社,2003:105-117.CHEN Lian-wan,YANG Shu-xin,XIE Fu-ren.Annual Changes of Tectonic Stress Field In North China Block[G]∥The Research on Crustal Stress Environment in China.Beijing:Geological Publishing House,2003:105-117.(in Chinese)
[19]刘泽民,刘东旺,李玲利,等.利用多个震源机制解求东大别地区平均应力场[J].地震学报,2011,33(5):605-613.LIU Ze-min,LIU Dong-wang,LI Ling-li,et al.Determination of Mean Stress Field in Eastern Dabie Region from Focal Mechanism Solution Analysis[J].Acta Seismologica sinica,2011,33(5):605-613.(in Chinese)
[20]周翠英,华爱军,王梅,等.1995年苍山5.2级地震前应力场的动态变化[J].地震地质,1997,19(2):135-140.ZHOU Cuiying,HUA Aijun,WANG Mei,et al.Dynamic Changes of Stress Field before the Cangshan M5.2Earthquake in 1995[J].Seismology and Geology,1997,19(2):135-140.(in Chinese)
[2]姚大全,刘加灿,翟洪涛,等.地震韵律研究方法初探——以郯庐断裂带龙泉山西麓剖面研究为例[J].地震研究,2005,28(1):49-52.YAO Da-quan,LIU Jia-can,ZHAI Hong-tao,et al.Preliminary Research Method of Seismic Rhythms——Taking the Research on the Longquanshan West-foot Profile in the Tancheng-Lujiang Fault Zone as An Example[J].Journal of Seismological Research,2005,28(1):49-52.(in Chinese)
[3]魏光兴,刁守中,周翠英.郯庐带地震活动性研究[M].北京:地震出版社,1993:110-166.Wei G X,Diao S Z,Zhou C Y.Research on Seismic Activity of Tanlu Fault Zone[M].Beijing:Seismological Press,1993:110-166.(in Chinese)
[4]夏瑞良,刘东旺.郯庐断裂带南段的地震活动及应力场特征[J].福建地震,1995,11(4):13-19.XIA Rui-liang,LIU Dong-wang.The Characteristics of the Earthquake Activity and Stress Field in South Tanlu Faults[J].Fujian Earthquake,1995,11(4):13-19.(in Chinese).
[5]刘东旺,夏瑞良,刘泽民,等.郯庐断裂带安徽段现代地震活动及应力场特征[J].地质科学,2006,41(2):278-290.LIU Dong-wang,XIA Rui-liang,LIU Ze-min,et al.Characteristics of Recent Seismic and Stress Field in Anhui sector of the Tanlu Fault Zone[J].Chinese Jour.Geol.,2006,41(2):278-290.(in Chinese)
[6]钟继茂,程万正.由多个地震震源机制解求川滇地区平均应力场方向[J].地震学报,2006,28(4):337-346.ZHONG Jimao,CHENG Wan-zheng.Determination of Directions of the Mean Stress Field in Sichuan-Yunnan Region from A Number of Focal Mechanism Solutions[J].Acta Seismologica Sinica,2006,28(4):337-346.(in Chinese)
[7]高国英,聂晓红,龙海英.近期新疆震源机制解与地震活动特征研究[J].西北地震学报,2012,34(1):57-63.GAO Guo-ying,NIE Xiao-hong,LONG Hai-ying.Research on the Characteristics of Recent Focal Mechanism Solution and Seismic Activity in Xinjiang Area[J].Northwestern Seismological Jouranl,2012,34(1):57-63.(in Chinese)
[8]梁尚鸿,李幼铭,束沛镒,等.利用区域地震台网P、珔S振幅比资料测定小震震源参数[J].地球物理学报,1984,27(3):249-256.LIANG Shang-hong,LI You-ming,SHU Pei-yi,et al.Determined the Focal Mechanism Solution of Micro Earthquakes from Amplitude Ratio ofP andS Recorded by Area Seismological Network[J].Chinese Jour.Geophys.,1984,27(3):249-256.(in Chinese)
[9]Snoke J A,Munsey J W,Teague A G,et al.A Program for Focal Mechanism Determination by Combined Use of Polarity and SV-P Amplitude Ratio Data[J].Earthquake Notes,1984,55(3):15-20.
[10]Snoke J A.Earthquake Mechanism[G]∥James D E.Encyclopedia of Geophysics.New York:Van Nostrand Reinhold Company,1989:239-245.
[11]http://www.iris.edu/software/downloads/processing/.
[12]胡新亮,刁桂苓,马瑾,等.利用数字地震记录的P,珔S振幅比资料测定小震震源机制解的可靠性分析[J].地震地质,2004,26(2):347-354.HU Xin-liang,DIAO Gui-ling,MA Jin,et al.Reliability Analysis of Focal Mechanism Solutions of Micro Earthquakes Determined from Amplitude Ratio ofP andS Recorded by Digital Seismograph[J].Seismology and Geology,2004,26(2):347-354.(in Chinese)
[13]倪红玉,刘泽民,沈小七,等.利用FOCMEC方法计算震源机制解的影响因素分析[J].华北地震科学,2011,29(3):1-7.NI Hong-yu,LIU Ze-min,SHEN Xiao-qi,et al.Analysis on the Factors of Determining the Focal Mechanism Using FOCMEC Method[J].North China Earthquake Seiences,2011,29(3):1-7.(in Chinese)
[14]刘杰,郑斯华,康英,等.利用P波和S波的初动和振幅比计算中小地震的震源机制解[J].地震,2004,24(1):19-26.LIU Jie,ZHENG Si-hua,KANG Ying,et al.The FocalMechanism Determinations of Moderate-small Earthquakes Using the First Motion and Amplitude Ratio ofP andS Wave[J].Earthquake,2004,24(1):19-26.(in Chinese)
[15]阚荣举,张四昌,晏凤桐,等.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,1977,20(2):96-107.KAN Rong-ju,ZHANG Si-chang,YAN Feng-tong,et al.Study on the Current Tectonics Stress Field and the Characteristics of Current Tectonic Activity in the Southwest China[J].Chinese Journal of Geophysics,1977,20(2):96-107.(in Chinese)
[16]阮祥,程万正,乔惠珍,等.安宁河-则木河地震带震源参数及应力状态的研究[J].西北地震学报,2011,33(1):46-50.RUAN Xiang,CHENG Wan-zheng,QIAO Hui-zhen,et al.Research on Source Parameters and Stress State in Anninghe-Zemuhe Earthquake Belt[J].Northwestern seismological Jouranl,2011,33(1):46-50.(in Chinese)
[17]林向东,徐平,武敏捷,等.小江断裂中段及邻区构造应力场分布特征[J].中国地震,2010,26(2):192-200.LIN Xiang-dong,XU Ping,WU Min-jie,et al.Inversion of Stress Field in Middle Section of the Xiaojiang Fault and Its Adjacent Area[J].Earthquake research in China,2010,26(2):192-200.(in Chinese)
[18]陈连旺,杨树新,谢富仁.华北块体现今构造应力场及其年变化特征[G]∥中国大陆地壳应力环境研究.北京:地质出版社,2003:105-117.CHEN Lian-wan,YANG Shu-xin,XIE Fu-ren.Annual Changes of Tectonic Stress Field In North China Block[G]∥The Research on Crustal Stress Environment in China.Beijing:Geological Publishing House,2003:105-117.(in Chinese)
[19]刘泽民,刘东旺,李玲利,等.利用多个震源机制解求东大别地区平均应力场[J].地震学报,2011,33(5):605-613.LIU Ze-min,LIU Dong-wang,LI Ling-li,et al.Determination of Mean Stress Field in Eastern Dabie Region from Focal Mechanism Solution Analysis[J].Acta Seismologica sinica,2011,33(5):605-613.(in Chinese)
[20]周翠英,华爱军,王梅,等.1995年苍山5.2级地震前应力场的动态变化[J].地震地质,1997,19(2):135-140.ZHOU Cuiying,HUA Aijun,WANG Mei,et al.Dynamic Changes of Stress Field before the Cangshan M5.2Earthquake in 1995[J].Seismology and Geology,1997,19(2):135-140.(in Chinese)
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