鲜水河断裂带地区重力场动态变化及其与5级以上地震的关系
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摘要
文中系统整理并计算了1988年以来鲜水河断裂带地区流动重力复测资料,参照以往震例研究总结提出的重力场变化异常指标,分析了区域重力场时-空动态变化及其与测区内发生5级以上地震的关系,进一步研究了区域重力场变化的时-空分布特征及其机理,讨论了近期区域重力场动态变化的强震危险含义。结果表明:1)流动重力测量具备了检测地壳运动与5级以上地震事件的能力; 2) 1988年以来测区发生的13次5级以上地震中的8个地震与年际重力场变化有较为确定的对应关系,可依据年际重力场变化确定前兆异常,其中3个6级以上地震在异常图像发展3～4a后发生,4个发生在无资料区的地震事件不能确定前兆异常; 3)测区重力场的1个明显特征是2004年以前区域重力场时空动态变化图像呈整体的南北贯通,且年度间为正、负值交替变化,其间所发生的5级以上地震不沿鲜水河断裂带分布。重力场变化值反映2004年以前存在2个相似的地壳物质移动波,对应了研究区地震时空分布由强到弱的过程。2010年以后的图像变化为年度内的局部正、负值区域同时存在,无年度间的正负交替变化现象,其间5级以上地震基本发生在断裂带上。1988年以来测区重力场动态变化与地震分布符合印度板块NE向运动强、弱分期的动力学模式,可据此优化重力异常指标。根据文中的分析总结和近期重力场变化趋势,提出磨西断裂北段区域具有中-长期强震危险性的初步结论。
Xianshuihe Fault,a main strong earthquake activity belt in southwest China,begins from Ganzi in the northwest,passes through Luhuo,Daofu,and Kangding,and then extents along the Dadu River valley. The fault is divided into two parts at Shimian,one part turns to south and converses to Anninghe Fault extending further to south,the other part,continuing to extend to southeast,cutting through Xiaoxiangling and then changing to Daliangshan Faults in the north of the Yuexi Basin,has the length of about 400 km. Since 1700 AD, there have happened 22 earthquakes larger than magnitude 6. 0 and 8 earthquakes larger than magnitude 7. 0. In this paper,we systematically collated and computed the gravity repetition measurement data along the Xianshuihe fault zone since 1988,and by referring to the anomaly index of gravity field of the predecessor achievements,analyzed the spatial-temporal variation of the regional gravity field and the relation to the occurrence of ≥M_S5. 0 earthquakes. The mechanism of the regional gravity changes is further studied, and also the implication of strong earthquake risk because of the dynamic variation of gravity field in the near future is discussed.The results show that: 1) The mobile gravity observation has the ability to detect crustal activity and M_S≥5. 0 earthquake events. 2) There is definite correspondence between interannual gravitational field change and the 8 earthquakes among the 13 M_S≥5. 0 earthquakes occurring in the surveying area since 1988,which can be determined according to the change of interannual gravitational field. Three M≥6. 0 earthquakes occurred 3 ～ 4 years after the abnormal image was developed,4 earthquakes that occurred in the region of no data available were not determined. 3) A significant feature of the spatial-temporal variation of the regional gravity is a northsouth run-through image before 2004,and characterized by the alternatively positive or negative variation in different year,the earthquakes of M_S≥5. 0 occurring in this period were not distributed along the fault. Gravity variation magnitude indicates that there were two similar crustal material movement waves before 2004,corresponding to the course of earthquake space-time distribution from strong to weak in the study area. After 2010,the variation image shows that the local positive and negative zones are concurrent within a year,different from the image before 2004,and earthquakes of M_S≥5. 0 basically occurred on the fault. It is believed that the variation of gravity field since 1988 and the seismic distribution fit with the geodynamic mode of strong and weak stages of the northeast motion of Indian plate. According to the conclusion we can try to optimize gravity anomaly index. After the Kangding earthquake in 2014,the north segment of Moxi Fault was still subject to negative high value changes till 2017 and then the gravity variation was further developed to a four quadrant distribution image. Based on the analysis of this paper and the previous variation trend of gravity field,we believe that the north segment of Moxi Fault has the background of medium-long term,strong or large earthquake risk.
Xianshuihe Fault,a main strong earthquake activity belt in southwest China,begins from Ganzi in the northwest,passes through Luhuo,Daofu,and Kangding,and then extents along the Dadu River valley. The fault is divided into two parts at Shimian,one part turns to south and converses to Anninghe Fault extending further to south,the other part,continuing to extend to southeast,cutting through Xiaoxiangling and then changing to Daliangshan Faults in the north of the Yuexi Basin,has the length of about 400 km. Since 1700 AD, there have happened 22 earthquakes larger than magnitude 6. 0 and 8 earthquakes larger than magnitude 7. 0. In this paper,we systematically collated and computed the gravity repetition measurement data along the Xianshuihe fault zone since 1988,and by referring to the anomaly index of gravity field of the predecessor achievements,analyzed the spatial-temporal variation of the regional gravity field and the relation to the occurrence of ≥M_S5. 0 earthquakes. The mechanism of the regional gravity changes is further studied, and also the implication of strong earthquake risk because of the dynamic variation of gravity field in the near future is discussed.The results show that: 1) The mobile gravity observation has the ability to detect crustal activity and M_S≥5. 0 earthquake events. 2) There is definite correspondence between interannual gravitational field change and the 8 earthquakes among the 13 M_S≥5. 0 earthquakes occurring in the surveying area since 1988,which can be determined according to the change of interannual gravitational field. Three M≥6. 0 earthquakes occurred 3 ～ 4 years after the abnormal image was developed,4 earthquakes that occurred in the region of no data available were not determined. 3) A significant feature of the spatial-temporal variation of the regional gravity is a northsouth run-through image before 2004,and characterized by the alternatively positive or negative variation in different year,the earthquakes of M_S≥5. 0 occurring in this period were not distributed along the fault. Gravity variation magnitude indicates that there were two similar crustal material movement waves before 2004,corresponding to the course of earthquake space-time distribution from strong to weak in the study area. After 2010,the variation image shows that the local positive and negative zones are concurrent within a year,different from the image before 2004,and earthquakes of M_S≥5. 0 basically occurred on the fault. It is believed that the variation of gravity field since 1988 and the seismic distribution fit with the geodynamic mode of strong and weak stages of the northeast motion of Indian plate. According to the conclusion we can try to optimize gravity anomaly index. After the Kangding earthquake in 2014,the north segment of Moxi Fault was still subject to negative high value changes till 2017 and then the gravity variation was further developed to a four quadrant distribution image. Based on the analysis of this paper and the previous variation trend of gravity field,we believe that the north segment of Moxi Fault has the background of medium-long term,strong or large earthquake risk.
引文
陈运泰,顾浩鼎,卢造勋.1980.1975年海城地震与1976年唐山地震前后重力变化[J].地震学报,2(1):21-30.CHEN Yun-tai,GU Hao-ding,LU Zao-xun.1980.Variations of gravity before the Haicheng earthquake,1975 and the Tangshan earthquake,1976[J].Acta Seismologica Sinica,2(1):21-30(in Chinese).
顾功叙,Kuo J T,刘克人,等.1997.中国京津唐张地区时间上连续的重力变化与地震的孕育和发生[J].科学通报,42(18):1919-1930.GU Gong-xu,Kuo J T,LIU Ke-ren,et al.1997.Seismogenesis and occurrence of earthquakes as observed by temporally continuous gravity variations in China[J].Chinese Science Bulletin,42(18):1919-1930(in Chinese).
李辉,申重阳,孙少安,等.2009.中国大陆近期重力场动态变化图像[J].大地测量与地球动力学,29(3):1-10.LI Hui,SHEN Chong-yang,SUN Shao-an,et al.2009.Dynamic gravity change in recent years in China continent[J].Journal of Geodesy and Geodynamics,29(3):1-10(in Chinese).
马瑾,刘力强,刘培洵,等.2007.断层失稳错动热场前兆模式:雁列断层的实验研究[J].地球物理学报,50(4):1141-1149.MA Jin,LIU Li-qiang,LIU Pei-xun,et al.2007.Thermal precursory pattern of fault unstable slip:An experimental study of en echelon fault[J].Chinese Journal of Geophysics,50(4):1141-1149(in Chinese).
申重阳,李辉,付广裕.2003.丽江7.0级地震重力前兆模式研究[J].地震学报,25(2):163-171.SHEN Chong-yang,LI Hui,FU Guang-yu.2003.Study on a gravity precursor mode of Lijiang earthquake with MS=7.0[J].Acta Seismologica Sinica,25(2):163-171(in Chinese).
申重阳,李辉,孙少安,等.2009.重力场动态变化与汶川MS8.0地震孕育过程[J].地球物理学报,52(10):2547-2557.SHEN Chong-yang,LI Hui,SU Shao-an,et al.2009.Dynamic variations of gravity and the preparation process of the Wenchuan MS8.0 earthquake[J].Chinese Journal of Geophysics,52(10):2547-2557(in Chinese).
孙少安,项爱民.1999.区域重力场相对基准的建立[J].地壳形变与地震,19(1):78-81.SUN Shao-an,XIANG Ai-min.1999.Establishment of relative datum for regional gravitational field[J].Crustal Deformation and Earthquake,19(1):78-81(in Chinese).
许厚泽.2003.重力观测在中国地壳运动观测网络中的作用[J].大地测量与地球动力学,23(3):1-3.XU Hou-ze.2003.Function of gravimetry in CMONOC[J].Journal of Geodesy and Geodynamics,23(3):1-3(in Chinese).
祝意青,李铁明,郝明,等.2016.2016年青海门源MS6.4地震前重力变化[J].地球物理学报,59(10):3744-3752.ZHU Yi-qing,LI Tie-ming,HAO Ming,et al.2016.Gravity changes before the Menyuan,Qinghai MS6.4 earthquake of 2016[J].Chinese Journal of Geophysics,59(10):3744-3752(in Chinese).
祝意青,梁伟锋,赵云峰,等.2017.2017年四川九寨沟MS7.0地震前区域重力场变化[J].地球物理学报,60(10):4124-4131.ZHU Yi-qing,LIANG Wei-feng,ZHAO Yun-feng,et al.2017.Gravity changes before the Jiuzhaigou,Sichuan,MS7.0 earthquake of 2017[J].Chinese Journal of Geophysics,60(10):4124-4131(in Chinese).
祝意青,刘芳,李铁明,等.2015.川滇地区重力场动态变化及其强震危险含义[J].地球物理学报,58(11):4187-4196.ZHU Yi-qing,LIU Fang,LI Tie-ming,et al.2015.Dynamic variation of the gravity field in the Sichuan-Yunnan region and its implication for seismic risk[J].Chinese Journal of Geophysics,58(11):4187-4196(in Chinese).
祝意青,闻学泽,孙和平,等.2013.2013年四川芦山MS7.0地震前的重力变化[J].地球物理学报,56(6):1887-1894.ZHU Yi-qing,WEN Xue-ze,SUN He-ping,et al.2013.Gravity changes before the Lushan,Sichuan,MS=7.0earthquake of 2013[J].Chinese Journal of Geophysics,56(6):1887-1894(in Chinese).
祝意青,赵云峰,李铁明,等.2014.2013年甘肃岷县漳县6.6级地震前后重力场动态变化[J].地震地质,36(3):667-676.doi:10.3969/j.issn.0253-4967.2014.03.010.ZHU Yi-qing,ZHAO Yun-feng,LI Tie-ming,et al.2014.Dynamic variation of gravity field before and after the Minxian-Zhangxian MS6.6 earthquake on July 22,2013,Gansu,China[J].Seismology and Geology,36(3):667-676(in Chinese).
Barnes D F.1966.Gravity changes during the Alaska earthquake[J].Journal of Geophysical Research,71(2):451-456.
Chen Y T,Gu H D,Lu Z X.1979.Variations of gravity before and after the Haicheng earthquake,1975 and the Tangshan earthquake,1976[J].Physics of the Earth and Planetary Interiors,18(4):330-338.
Fujii Y.1966.Gravity changes in the shock area of the Niigata earthquake,16 June 1964[J].Zisin,19(3):200-216.
Hunt T M.1979.Gravity changes associated with the 1968 Inangahua earthquake[J].New Zealand Journal of Geology and Geophysics,13(4):1050-1051.
Imanishi Y T,Sato T,Higashi T,et al.2004.A network of superconducting gravimeters detects submicrogal coseismic gravity changes[J].Science,306(5695):476-478.
Kissinger C.1975.Process during the Matsushiro,Japan earthquake swarm as revealed by leveling,gravity and spring flow observations[J].Geology,3(2):57-62.
Kuo J T,Zheng J H,Song S H,et al.1999.Determination of earthquake epicentroids by inversion of gravity variation data in the BTTZ region,China[J].Tectonophysics,312(2):267-281.
Okubo S.1992.Potential and gravity changes due to shear and tensile faults in a half-space[J].Geophysical Journal International,97(B5):7137-7144.
Oliver H W,Robbins S I,Grannell R B,et al.1975.Surface and subsurface movements determined by remeasuring gravity[M]//Oakeshott G B,et al.(Eds).San Fernando California Earthquake of 9 February 1971.Saoramento,Calif,16:l95-211.
Zhu Y Q,Zhan F B,Zhou J,et al.2010.Gravity measurements and their variations before the 2008 Wenchuan Earthquake[J].Bulletin of the Seismological Society of America,100(5B):2815-2824.
顾功叙,Kuo J T,刘克人,等.1997.中国京津唐张地区时间上连续的重力变化与地震的孕育和发生[J].科学通报,42(18):1919-1930.GU Gong-xu,Kuo J T,LIU Ke-ren,et al.1997.Seismogenesis and occurrence of earthquakes as observed by temporally continuous gravity variations in China[J].Chinese Science Bulletin,42(18):1919-1930(in Chinese).
李辉,申重阳,孙少安,等.2009.中国大陆近期重力场动态变化图像[J].大地测量与地球动力学,29(3):1-10.LI Hui,SHEN Chong-yang,SUN Shao-an,et al.2009.Dynamic gravity change in recent years in China continent[J].Journal of Geodesy and Geodynamics,29(3):1-10(in Chinese).
马瑾,刘力强,刘培洵,等.2007.断层失稳错动热场前兆模式:雁列断层的实验研究[J].地球物理学报,50(4):1141-1149.MA Jin,LIU Li-qiang,LIU Pei-xun,et al.2007.Thermal precursory pattern of fault unstable slip:An experimental study of en echelon fault[J].Chinese Journal of Geophysics,50(4):1141-1149(in Chinese).
申重阳,李辉,付广裕.2003.丽江7.0级地震重力前兆模式研究[J].地震学报,25(2):163-171.SHEN Chong-yang,LI Hui,FU Guang-yu.2003.Study on a gravity precursor mode of Lijiang earthquake with MS=7.0[J].Acta Seismologica Sinica,25(2):163-171(in Chinese).
申重阳,李辉,孙少安,等.2009.重力场动态变化与汶川MS8.0地震孕育过程[J].地球物理学报,52(10):2547-2557.SHEN Chong-yang,LI Hui,SU Shao-an,et al.2009.Dynamic variations of gravity and the preparation process of the Wenchuan MS8.0 earthquake[J].Chinese Journal of Geophysics,52(10):2547-2557(in Chinese).
孙少安,项爱民.1999.区域重力场相对基准的建立[J].地壳形变与地震,19(1):78-81.SUN Shao-an,XIANG Ai-min.1999.Establishment of relative datum for regional gravitational field[J].Crustal Deformation and Earthquake,19(1):78-81(in Chinese).
许厚泽.2003.重力观测在中国地壳运动观测网络中的作用[J].大地测量与地球动力学,23(3):1-3.XU Hou-ze.2003.Function of gravimetry in CMONOC[J].Journal of Geodesy and Geodynamics,23(3):1-3(in Chinese).
祝意青,李铁明,郝明,等.2016.2016年青海门源MS6.4地震前重力变化[J].地球物理学报,59(10):3744-3752.ZHU Yi-qing,LI Tie-ming,HAO Ming,et al.2016.Gravity changes before the Menyuan,Qinghai MS6.4 earthquake of 2016[J].Chinese Journal of Geophysics,59(10):3744-3752(in Chinese).
祝意青,梁伟锋,赵云峰,等.2017.2017年四川九寨沟MS7.0地震前区域重力场变化[J].地球物理学报,60(10):4124-4131.ZHU Yi-qing,LIANG Wei-feng,ZHAO Yun-feng,et al.2017.Gravity changes before the Jiuzhaigou,Sichuan,MS7.0 earthquake of 2017[J].Chinese Journal of Geophysics,60(10):4124-4131(in Chinese).
祝意青,刘芳,李铁明,等.2015.川滇地区重力场动态变化及其强震危险含义[J].地球物理学报,58(11):4187-4196.ZHU Yi-qing,LIU Fang,LI Tie-ming,et al.2015.Dynamic variation of the gravity field in the Sichuan-Yunnan region and its implication for seismic risk[J].Chinese Journal of Geophysics,58(11):4187-4196(in Chinese).
祝意青,闻学泽,孙和平,等.2013.2013年四川芦山MS7.0地震前的重力变化[J].地球物理学报,56(6):1887-1894.ZHU Yi-qing,WEN Xue-ze,SUN He-ping,et al.2013.Gravity changes before the Lushan,Sichuan,MS=7.0earthquake of 2013[J].Chinese Journal of Geophysics,56(6):1887-1894(in Chinese).
祝意青,赵云峰,李铁明,等.2014.2013年甘肃岷县漳县6.6级地震前后重力场动态变化[J].地震地质,36(3):667-676.doi:10.3969/j.issn.0253-4967.2014.03.010.ZHU Yi-qing,ZHAO Yun-feng,LI Tie-ming,et al.2014.Dynamic variation of gravity field before and after the Minxian-Zhangxian MS6.6 earthquake on July 22,2013,Gansu,China[J].Seismology and Geology,36(3):667-676(in Chinese).
Barnes D F.1966.Gravity changes during the Alaska earthquake[J].Journal of Geophysical Research,71(2):451-456.
Chen Y T,Gu H D,Lu Z X.1979.Variations of gravity before and after the Haicheng earthquake,1975 and the Tangshan earthquake,1976[J].Physics of the Earth and Planetary Interiors,18(4):330-338.
Fujii Y.1966.Gravity changes in the shock area of the Niigata earthquake,16 June 1964[J].Zisin,19(3):200-216.
Hunt T M.1979.Gravity changes associated with the 1968 Inangahua earthquake[J].New Zealand Journal of Geology and Geophysics,13(4):1050-1051.
Imanishi Y T,Sato T,Higashi T,et al.2004.A network of superconducting gravimeters detects submicrogal coseismic gravity changes[J].Science,306(5695):476-478.
Kissinger C.1975.Process during the Matsushiro,Japan earthquake swarm as revealed by leveling,gravity and spring flow observations[J].Geology,3(2):57-62.
Kuo J T,Zheng J H,Song S H,et al.1999.Determination of earthquake epicentroids by inversion of gravity variation data in the BTTZ region,China[J].Tectonophysics,312(2):267-281.
Okubo S.1992.Potential and gravity changes due to shear and tensile faults in a half-space[J].Geophysical Journal International,97(B5):7137-7144.
Oliver H W,Robbins S I,Grannell R B,et al.1975.Surface and subsurface movements determined by remeasuring gravity[M]//Oakeshott G B,et al.(Eds).San Fernando California Earthquake of 9 February 1971.Saoramento,Calif,16:l95-211.
Zhu Y Q,Zhan F B,Zhou J,et al.2010.Gravity measurements and their variations before the 2008 Wenchuan Earthquake[J].Bulletin of the Seismological Society of America,100(5B):2815-2824.