2006年文县5.0级地震的发震构造研究
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摘要
2006年6月21日文县5.0级地震发生在构造环境复杂的地区,该地区之前已有100多年没有发生过中强地震。该地震的发生说明该地区的地震活动开始增强。文县5.0级地震没有形成地表破裂带,给研究发震构造带来了一定的困难,通过1/20万地质图、遥感资料解译、震源机制反演以及地震序列精确定位的方法依然能够研究该地震的发震构造。为判定该地区未来的地震危险性,文中采用遥感资料解译、多种方法反演震源机制、双差法地震精定位的方法联合分析该地震的发震构造。1/20万地质图显示该区域存在多条断裂,遥感资料的解译结果表明石坊-临江断裂为较活动的断裂。2种方法所得震源机制结果表明该地震为左旋走滑兼有逆冲,主压应力方向为N60°E。双差法定位结果也支持该地震为走滑兼有逆冲,余震的分布与断裂的逆冲有关。结合多种结果联合分析认为该地震的发震构造为石坊-临江断裂,主压构造应力方向为N60°E。
No moderate and strong earthquake occurred for many years in Wenxian since the M 8.0 great earthquake occurring in 1879 A.D. The June 21,2006 Wenxian earthquake with M 5.0 occurred in an area where the tectonic setting is complex. Seismic activity level in Wenxian would enhance after the occurrence of this earthquake(M 5.0). Since the earthquake did not produce surface rupture zone,it is very difficulty to study the seismogenic fault. However,we can still study the seismogenic fault based on geological map(1∶200 000),remote sensing interpretation,inversion of focal mechanism and seismic sequence precise location method. In order to determine the future seismic risk of the region,the paper intends to analyze the earthquake causative structure by jointly using the remote sensing interpretation,various methods of inversion of focal mechanism,and double-difference earthquake location algorithm. The geological map(1:200 000)shows there are many faults in this area,and the interpretation of remote sensing reveals that only one fault named Shifang-Linjing Fault is active. Focal mechanisms derived from the two methods show that the earthquake is of left-lateral strike-slip and thrust,and the principal compressive stress is in the direction of N60°E. The results of double-difference earthquake locations also support this result. The distribution of aftershocks is related to the thrust faulting. Results of combined analyses show that the Shifang-Linjiang Fault is the seismogenic fault of this earthquake,and the direction of the principal compressive stress is N60°E.
No moderate and strong earthquake occurred for many years in Wenxian since the M 8.0 great earthquake occurring in 1879 A.D. The June 21,2006 Wenxian earthquake with M 5.0 occurred in an area where the tectonic setting is complex. Seismic activity level in Wenxian would enhance after the occurrence of this earthquake(M 5.0). Since the earthquake did not produce surface rupture zone,it is very difficulty to study the seismogenic fault. However,we can still study the seismogenic fault based on geological map(1∶200 000),remote sensing interpretation,inversion of focal mechanism and seismic sequence precise location method. In order to determine the future seismic risk of the region,the paper intends to analyze the earthquake causative structure by jointly using the remote sensing interpretation,various methods of inversion of focal mechanism,and double-difference earthquake location algorithm. The geological map(1:200 000)shows there are many faults in this area,and the interpretation of remote sensing reveals that only one fault named Shifang-Linjing Fault is active. Focal mechanisms derived from the two methods show that the earthquake is of left-lateral strike-slip and thrust,and the principal compressive stress is in the direction of N60°E. The results of double-difference earthquake locations also support this result. The distribution of aftershocks is related to the thrust faulting. Results of combined analyses show that the Shifang-Linjiang Fault is the seismogenic fault of this earthquake,and the direction of the principal compressive stress is N60°E.
引文
[1]中国地震局兰州地震研究所地震地质队,1975,文县地震地质工作小结。
[2]中国地震局兰州地震研究所地震地质队,1984,陕甘宁青大震调查。
[1]同424页[1]。
地质部陕西省地质局区域地质测量队.1967.1/20万地质图(碧口幅)[Z].北京:地质出版社.Geological Survey Team,Geological Bureau,Shanxi Province,Ministry of Geology.1967.1/200000Geological Map,Bikou Sheet[Z].Geological Publishing House,Beijing(in Chinese).
地质部陕西省地质局区域地质测量队.1970.1/20万地质图(文县幅)[Z].北京:地质出版社.Geological Survey Team,Geological Bureau,Shanxi Province,Ministry of Geology.1970.1/200000Geological Map,Wenxian Sheet[Z].Geological Publishing House,Beijing(in Chinese).
冯希杰,董星宏,刘春,等.2005.范家坝-临江断裂活动与1879年甘肃武都南8级地震的讨论[J].地震地质,27(1):155—163.FENG Xi-jie,DONG Xing-hong,LIUChun,et al.2005.Discussion on the activity of Fanjiaba-Linjiang Fault and theM8south Wudu,Gansu Province earthquake of1879[J].Seismology and Geology,27(1):155—163(in Chinese).
刘杰,郑斯华,康英,等.2004.利用P波和S波初动和振幅比计算中小地震的震源机制解[J].地震,24(1):19—26.LIUJie,ZHENG Si-hua,KANG Ying,et al.2004.The focal mechanism determinations of moderate and small earthquakes u-sing the first motion and amplitude ratio of P and S wave[J].Earthquake,24(1):19—26(in Chinese).
卢海峰,马保起,刘光勋.2006.甘肃文县北部NEE向断裂带新构造活动特征[J].地震研究,29(2):143—146.LU Hai-feng,MA Bao-qi,LIU Guang-xun.2006.Characteristics of the neotectonic movement of the NEE-striking faultbelt north of Wenxian county,Gansu[J].Journal of Seismological Research,29(2):143—146(in Chinese).
马占虎,周志宇,高晓明,等.2007.2006年甘肃文县5.0级地震灾害损失评估[J].西北地震学报,29(3):256—263.MA Zhan-hu,ZHOU Zhi-yu,GAO Xiao-ming,et al.2007.The earthquake disaster loss assessment for WenxianMS5.0earthquake on Jun.21,2006in Gansu Province[J].Northwestern Seismological Journal,29(3):256—263(inChinese).
王周元,范世宏,姬凤英,等.1984.甘肃地区地壳速度的非均匀分布[J].西北地震学报,18(2):18—25.WANG Zhou-yuan,FAN Shi-hong,JI Feng-ying,et al.1984.The inhomogeneity of crustal velocity in Gansu region[J].Northwestern Seismological Journal,18(2):18—25(in Chinese).
杨智娴,陈运泰,郑月军,等.2003.双差地震定位法在中国中西部地区地震精确定位中的应用[J].中国科学(D辑),33(增刊):129—134.YANG Zhi-xian,CHEN Yun-tai,ZHENG Yue-jun,et al.2003.Accurate relocation of earthquakes in central-westernChina using the double-difference earthquake location algorithm[J].Science in China(Ser D),33(Suppl):129—134(in Chinese).
曾秋生.1989.中国现今地壳应力状态[J].地质力学学报,12:197—207.ZENG Qiu-sheng.1989.Present state of stress of the crust in China[J].Bulletin of the Geomechanics,12:197—207(in Chinese).
Snoke J A,Munsey J W,Teague A G,et al.1984.A program for focal mechanism determination by combined use ofpolarity and SV-P amplitude ratio data[J].Earthquake Notes,55(3):15.
Snoke J A.1989.Earthquake mechanism[A].In:James D E(ed).Encyclopedia of Geophysics.Van Nostrand Rein-bold Company,New York.239—245.
Waldhauser F,Ellsworth W L.2000.A double difference earthquake location algorithm:Method and application to theNorthern Hayward Fault,California[J].Bull Seism Soc Amer,90(6):1353—1368.
[2]中国地震局兰州地震研究所地震地质队,1984,陕甘宁青大震调查。
[1]同424页[1]。
地质部陕西省地质局区域地质测量队.1967.1/20万地质图(碧口幅)[Z].北京:地质出版社.Geological Survey Team,Geological Bureau,Shanxi Province,Ministry of Geology.1967.1/200000Geological Map,Bikou Sheet[Z].Geological Publishing House,Beijing(in Chinese).
地质部陕西省地质局区域地质测量队.1970.1/20万地质图(文县幅)[Z].北京:地质出版社.Geological Survey Team,Geological Bureau,Shanxi Province,Ministry of Geology.1970.1/200000Geological Map,Wenxian Sheet[Z].Geological Publishing House,Beijing(in Chinese).
冯希杰,董星宏,刘春,等.2005.范家坝-临江断裂活动与1879年甘肃武都南8级地震的讨论[J].地震地质,27(1):155—163.FENG Xi-jie,DONG Xing-hong,LIUChun,et al.2005.Discussion on the activity of Fanjiaba-Linjiang Fault and theM8south Wudu,Gansu Province earthquake of1879[J].Seismology and Geology,27(1):155—163(in Chinese).
刘杰,郑斯华,康英,等.2004.利用P波和S波初动和振幅比计算中小地震的震源机制解[J].地震,24(1):19—26.LIUJie,ZHENG Si-hua,KANG Ying,et al.2004.The focal mechanism determinations of moderate and small earthquakes u-sing the first motion and amplitude ratio of P and S wave[J].Earthquake,24(1):19—26(in Chinese).
卢海峰,马保起,刘光勋.2006.甘肃文县北部NEE向断裂带新构造活动特征[J].地震研究,29(2):143—146.LU Hai-feng,MA Bao-qi,LIU Guang-xun.2006.Characteristics of the neotectonic movement of the NEE-striking faultbelt north of Wenxian county,Gansu[J].Journal of Seismological Research,29(2):143—146(in Chinese).
马占虎,周志宇,高晓明,等.2007.2006年甘肃文县5.0级地震灾害损失评估[J].西北地震学报,29(3):256—263.MA Zhan-hu,ZHOU Zhi-yu,GAO Xiao-ming,et al.2007.The earthquake disaster loss assessment for WenxianMS5.0earthquake on Jun.21,2006in Gansu Province[J].Northwestern Seismological Journal,29(3):256—263(inChinese).
王周元,范世宏,姬凤英,等.1984.甘肃地区地壳速度的非均匀分布[J].西北地震学报,18(2):18—25.WANG Zhou-yuan,FAN Shi-hong,JI Feng-ying,et al.1984.The inhomogeneity of crustal velocity in Gansu region[J].Northwestern Seismological Journal,18(2):18—25(in Chinese).
杨智娴,陈运泰,郑月军,等.2003.双差地震定位法在中国中西部地区地震精确定位中的应用[J].中国科学(D辑),33(增刊):129—134.YANG Zhi-xian,CHEN Yun-tai,ZHENG Yue-jun,et al.2003.Accurate relocation of earthquakes in central-westernChina using the double-difference earthquake location algorithm[J].Science in China(Ser D),33(Suppl):129—134(in Chinese).
曾秋生.1989.中国现今地壳应力状态[J].地质力学学报,12:197—207.ZENG Qiu-sheng.1989.Present state of stress of the crust in China[J].Bulletin of the Geomechanics,12:197—207(in Chinese).
Snoke J A,Munsey J W,Teague A G,et al.1984.A program for focal mechanism determination by combined use ofpolarity and SV-P amplitude ratio data[J].Earthquake Notes,55(3):15.
Snoke J A.1989.Earthquake mechanism[A].In:James D E(ed).Encyclopedia of Geophysics.Van Nostrand Rein-bold Company,New York.239—245.
Waldhauser F,Ellsworth W L.2000.A double difference earthquake location algorithm:Method and application to theNorthern Hayward Fault,California[J].Bull Seism Soc Amer,90(6):1353—1368.
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