2013年四川芦山Ms7.0地震前的重力变化
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摘要
利用川西地区2010—2012年期间的流动重力观测资料,系统分析了区域重力场变化及其与2013年4月20日四川芦山7.0级地震发生的关系.结果主要表明:①区域重力场异常变化与北东向龙门山断裂带南段和北北西向马尔康断裂带在空间上关系密切,反映沿该两断裂带(段)在2010—2012年期间发生了引起地表重力变化效应的构造活动或变形.②芦山7.0级地震前,测区内出现了较大空间范围的区域性重力异常,而震源区附近产生了局部重力异常,沿龙门山断裂带南段形成了重力变化高梯度带,其中,宝兴、天全、康定、泸定、石棉一带重力差异变化达100×10-8 m.s-2以上;这些可能反映芦山地震前,区域及震源区附近均产生与该地震孕育、发生有关的构造运动或应力增强作用.③重力场差分动态演化图像和重力场累积变化动态图像均反映芦山7.0级地震孕育过程的最后2～3年出现较显著的流动重力异常变化,可视为该地震的中期前兆信息;本文第一作者等也曾基于该流动重力异常变化在芦山7.0级地震前做过一定程度的中期预测,尤其是地点预测.本文的例子再次证明流动重力观测能较好地捕捉到强震孕育发生过程中,特别是该过程最后阶段的重力异常变化信息.因此,区域流动重力场观测对未来强震的中-长期预测,尤其是在发震地点的判定上具有优势.
Using the observation data of relative gravity measurements in western Sichuan region from 2010 to 2012, we have systematically analyzed the spatial-temporal variation of the regional gravity field and their relation to the occurrence of the Ms=7.0 Lushan earthquake on April 20, 2013. Our research mainly shows that: (1) Spatially the anomaly change of the regional gravity field is closely related to both the southern segment of the NE-trending Longmenshan fault zone and the NNW-trending Markang fault, suggesting that the active tectonic action or deformation happened along the two fault zones (or segments) during 2010 to 2012, which would have induced the variation in the ground gravity observation. (2) Before the Ms=7.0 Lushan earthquake, regional gravity anomaly appeared in the whole study region and local gravity anomalies at and near the potential source area. Among the region and the areas with gravity anomalies, the anomaly variations near Baoxing, Tianquan, Kangding, Luding and Shimian were up to and over 100×10-8m·s-2 , apparently reflecting an enhancement of tectonic or stress′s action in the study region and at and near the potential source area, that could be related to the preparation and occurrence of the earthquake. (3) The dynamic evolution patterns of the regional gravity changes and those patterns of cumulated gravity variations suggest that significant anomalies of gravity variations in the relative gravity measurements appeared indeed in the last 2 to 3 years in the preparation of the Ms=7.0 Lushan earthquake, and such anomalies can be regarded as one of the medium-term precursory of the earthquake. In a certain degree, the first author of this paper and others once made a medium-term forecast before the Lushan earthquake, especially made a forecast for the locality of the earthquake based on the anomaly gravity variations. The case studied in this article demonstrates again that through relative gravity survey people can catch anomalous gravity variation that would be related to the process of earthquake preparation, especially to those anomaly variations appearing in the last stage of the process. Therefore, relative gravity survey has unique advantages in the medium- to long-term earthquake forecast, especially for forecasting localities of potential earthquakes.
Using the observation data of relative gravity measurements in western Sichuan region from 2010 to 2012, we have systematically analyzed the spatial-temporal variation of the regional gravity field and their relation to the occurrence of the Ms=7.0 Lushan earthquake on April 20, 2013. Our research mainly shows that: (1) Spatially the anomaly change of the regional gravity field is closely related to both the southern segment of the NE-trending Longmenshan fault zone and the NNW-trending Markang fault, suggesting that the active tectonic action or deformation happened along the two fault zones (or segments) during 2010 to 2012, which would have induced the variation in the ground gravity observation. (2) Before the Ms=7.0 Lushan earthquake, regional gravity anomaly appeared in the whole study region and local gravity anomalies at and near the potential source area. Among the region and the areas with gravity anomalies, the anomaly variations near Baoxing, Tianquan, Kangding, Luding and Shimian were up to and over 100×10-8m·s-2 , apparently reflecting an enhancement of tectonic or stress′s action in the study region and at and near the potential source area, that could be related to the preparation and occurrence of the earthquake. (3) The dynamic evolution patterns of the regional gravity changes and those patterns of cumulated gravity variations suggest that significant anomalies of gravity variations in the relative gravity measurements appeared indeed in the last 2 to 3 years in the preparation of the Ms=7.0 Lushan earthquake, and such anomalies can be regarded as one of the medium-term precursory of the earthquake. In a certain degree, the first author of this paper and others once made a medium-term forecast before the Lushan earthquake, especially made a forecast for the locality of the earthquake based on the anomaly gravity variations. The case studied in this article demonstrates again that through relative gravity survey people can catch anomalous gravity variation that would be related to the process of earthquake preparation, especially to those anomaly variations appearing in the last stage of the process. Therefore, relative gravity survey has unique advantages in the medium- to long-term earthquake forecast, especially for forecasting localities of potential earthquakes.
引文
[1]Zhu Y Q,Zhan F B,Zhou J,et al.Gravity measurementsand their variations before the 2008 Wenchuan Earthquake.Bulletin of the Seismological Society of America,2010,100(5B):2815-2824.
[2]祝意青,梁伟锋,徐云马等.汶川MS8.0地震前后的重力场动态变化.地震学报,2010,32(6):633-640.Zhu Y Q,Liang W F,Xu Y M,et al.Dynamic variation ofgravity field before and after Wenchuan MS8.0earthquake.Acta Seismologica Sinica(in Chinese),2010,32(6):633-640.
[3]祝意青,梁伟锋,徐云马.重力资料对2008年汶川MS8.0地震的中期预测.国际地震动态,2008,(7):36-39.Zhu Y Q,Liang W F,Xu Y M.Medium-term prediction ofMS8.0earthquake in Wenchuan,Sichuan by mobile gravity.Recent Developments in World Seismology(in Chinese),2008,(7):36-39.
[4]祝意青,苏琴,梁伟锋等.川西地区重力变化与汶川地震.大地测量与地球动力学,2010,30(2):1-5.Zhu Y Q,Su Q,Liang W F,et al.Gravity variation ofwestern Sichuan area and Wenchuan earthquake.Journal ofGeodesy and Geodynamics(in Chinese),2010,30(2):1-5.
[5]贾民育,詹洁辉.中国地震重力监测体系的结构与能力.地震学报,2000,22(4):360-367.Jia M Y,Zhan J H.The structure and ability of the Chinaseismological gravity monitoring system.Acta SeismologicaSinica(in Chinese),2000,22(4):360-367.
[6]祝意青,王庆良,徐云马.我国流动重力监测预报发展的思考.国际地震动态,2008,(9):19-25.Zhu Y Q,Wang Q L,Xu Y M.Thoughts on thedevelopment of Earthquake Monitoring and Prediction inmobile gravity.Recent Developments in World Seismology(in Chinese),2008,(9):19-25.
[7]李辉,徐如刚,申重阳等.大华北地震动态重力监测网分形特征研究.大地测量与地球动力学,2010,30(5):15-18.Li H,Xu R G,Shen C Y,et al.Fractal characteristics ofseismological dynamic gravity network in northern China.Journal of Geodesy and Geodynamics(in Chinese),2010,30(5):15-18.
[8]祝意青,闻学泽,张晶等.华北中部重力场的动态变化及其强震危险含义.地球物理学报,2013,56(2):531-541.Zhu Y Q,Wen X Z,Zhang J,et al.Dynamic variation ofgravity field in middle North China and its implication forseismic potential.Chinese J.Geophys.(in Chinese),2013,56(2):531-541.
[9]祝意青,李辉,朱桂芝等.青藏块体东北缘重力场演化与地震活动.地震学报,2004,26(增):71-78.Zhu Y Q,Li H,Zhu G Z,et al.Gravity evolution andearthquake activities of the Northeastern edge of Qinghai-Tibet block.Acta Seismologica Sinica(in Chinese),2004,17(Suppl.):71-78.
[10]祝意青,徐云马,吕弋培等.龙门山断裂带重力变化与汶川8.0级地震关系研究.地球物理学报,2009,52(10):2538-2546.Zhu Y Q,Xu Y M,LüG P,et al.Relations between gravityvariation of Longmenshan fault zone and Wenchuan MS8.0earthquake.Chinese J.Geophys.(in Chinese),2009,52(10):2538-2546.
[11]祝意青,胡斌,朱桂芝等.民乐6.1、岷县5.2级地震前区域重力场变化研究.大地测量与地球动力学,2005,25(1):24-29.Zhu Y Q,Hu B,Zhu G Z,et al.Research on the variation ofgravity field before Minle MS6.1and Minxian MS5.2earthquakes.Journal of Geodesy and Geodynamics(in Chinese),2005,25(1):24-29.
[12]祝意青,梁伟锋,陈石等.青藏高原东北缘重力变化机理研究.大地测量与地球动力学,2012,32(3):1-6.Zhu Y Q,Liang W F,Chen S,et al.Study on mechanism ofgravity field change in northeastern margin of Qinghai-TibetPlateau.Journal of Geodesy and Geodynamics(in Chinese),2012,32(3):1-6.
[13]楼海,王椿镛,吕智勇等.2008年汶川MS8.0级地震的深部构造环境.中国科学D辑(地球科学),2008,38(10):1207-1220.Lu H,Wang C Y,LüZ Y,et al.Deep tectonic condition ofthe MS8.0Wenchuan earthquake of Sichuan,China.Sciencein China(Series D)(in Chinese),2008,38(10):1207-1220.
[14]张季生,高锐,曾令森等.龙门山及邻区重、磁异常特征及与地震关系的研究.地球物理学报,2009,52(2):572-578.Zhang J S,Gao R,Zeng L S,et al.Relationship betweencharacteristics of gravity and magnetic anomalies and theearthquake in Longmenshan range and adjacent areas.ChineseJ.Geophys.(in Chinese),2009,52(2):572-578.
[15]顾功叙,Kuo J T,刘克人等.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.科学通报,1997,42(18):1919-1930.Gu G X,Kuo J T,Liu K R,et al.Seismogenesis andoccurrence of earthquakes as observed by temporallycontinuous gravity variations in China.Chinese ScienceBulletin(in Chinese),1997,42(18):1919-1930.
[16]Chen Y T,Gu H D,Lu Z X.Variations of gravity before andafter the Haicheng earthquake,1975,and the Tangshanearthquake,1976.Physics of the Earth and PlanetaryInteriors,1979,18(4):330-338.
[17]M7专项工作组.中国大陆大地震中—长期危险性研究.北京:地震出版社,2012.Working Group of M7.Study on the Mid-Long-TermPotential of Large Earthquakes on the Chinese Continent(inChinese).Beijing:Seismological Press,2012.
[2]祝意青,梁伟锋,徐云马等.汶川MS8.0地震前后的重力场动态变化.地震学报,2010,32(6):633-640.Zhu Y Q,Liang W F,Xu Y M,et al.Dynamic variation ofgravity field before and after Wenchuan MS8.0earthquake.Acta Seismologica Sinica(in Chinese),2010,32(6):633-640.
[3]祝意青,梁伟锋,徐云马.重力资料对2008年汶川MS8.0地震的中期预测.国际地震动态,2008,(7):36-39.Zhu Y Q,Liang W F,Xu Y M.Medium-term prediction ofMS8.0earthquake in Wenchuan,Sichuan by mobile gravity.Recent Developments in World Seismology(in Chinese),2008,(7):36-39.
[4]祝意青,苏琴,梁伟锋等.川西地区重力变化与汶川地震.大地测量与地球动力学,2010,30(2):1-5.Zhu Y Q,Su Q,Liang W F,et al.Gravity variation ofwestern Sichuan area and Wenchuan earthquake.Journal ofGeodesy and Geodynamics(in Chinese),2010,30(2):1-5.
[5]贾民育,詹洁辉.中国地震重力监测体系的结构与能力.地震学报,2000,22(4):360-367.Jia M Y,Zhan J H.The structure and ability of the Chinaseismological gravity monitoring system.Acta SeismologicaSinica(in Chinese),2000,22(4):360-367.
[6]祝意青,王庆良,徐云马.我国流动重力监测预报发展的思考.国际地震动态,2008,(9):19-25.Zhu Y Q,Wang Q L,Xu Y M.Thoughts on thedevelopment of Earthquake Monitoring and Prediction inmobile gravity.Recent Developments in World Seismology(in Chinese),2008,(9):19-25.
[7]李辉,徐如刚,申重阳等.大华北地震动态重力监测网分形特征研究.大地测量与地球动力学,2010,30(5):15-18.Li H,Xu R G,Shen C Y,et al.Fractal characteristics ofseismological dynamic gravity network in northern China.Journal of Geodesy and Geodynamics(in Chinese),2010,30(5):15-18.
[8]祝意青,闻学泽,张晶等.华北中部重力场的动态变化及其强震危险含义.地球物理学报,2013,56(2):531-541.Zhu Y Q,Wen X Z,Zhang J,et al.Dynamic variation ofgravity field in middle North China and its implication forseismic potential.Chinese J.Geophys.(in Chinese),2013,56(2):531-541.
[9]祝意青,李辉,朱桂芝等.青藏块体东北缘重力场演化与地震活动.地震学报,2004,26(增):71-78.Zhu Y Q,Li H,Zhu G Z,et al.Gravity evolution andearthquake activities of the Northeastern edge of Qinghai-Tibet block.Acta Seismologica Sinica(in Chinese),2004,17(Suppl.):71-78.
[10]祝意青,徐云马,吕弋培等.龙门山断裂带重力变化与汶川8.0级地震关系研究.地球物理学报,2009,52(10):2538-2546.Zhu Y Q,Xu Y M,LüG P,et al.Relations between gravityvariation of Longmenshan fault zone and Wenchuan MS8.0earthquake.Chinese J.Geophys.(in Chinese),2009,52(10):2538-2546.
[11]祝意青,胡斌,朱桂芝等.民乐6.1、岷县5.2级地震前区域重力场变化研究.大地测量与地球动力学,2005,25(1):24-29.Zhu Y Q,Hu B,Zhu G Z,et al.Research on the variation ofgravity field before Minle MS6.1and Minxian MS5.2earthquakes.Journal of Geodesy and Geodynamics(in Chinese),2005,25(1):24-29.
[12]祝意青,梁伟锋,陈石等.青藏高原东北缘重力变化机理研究.大地测量与地球动力学,2012,32(3):1-6.Zhu Y Q,Liang W F,Chen S,et al.Study on mechanism ofgravity field change in northeastern margin of Qinghai-TibetPlateau.Journal of Geodesy and Geodynamics(in Chinese),2012,32(3):1-6.
[13]楼海,王椿镛,吕智勇等.2008年汶川MS8.0级地震的深部构造环境.中国科学D辑(地球科学),2008,38(10):1207-1220.Lu H,Wang C Y,LüZ Y,et al.Deep tectonic condition ofthe MS8.0Wenchuan earthquake of Sichuan,China.Sciencein China(Series D)(in Chinese),2008,38(10):1207-1220.
[14]张季生,高锐,曾令森等.龙门山及邻区重、磁异常特征及与地震关系的研究.地球物理学报,2009,52(2):572-578.Zhang J S,Gao R,Zeng L S,et al.Relationship betweencharacteristics of gravity and magnetic anomalies and theearthquake in Longmenshan range and adjacent areas.ChineseJ.Geophys.(in Chinese),2009,52(2):572-578.
[15]顾功叙,Kuo J T,刘克人等.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.科学通报,1997,42(18):1919-1930.Gu G X,Kuo J T,Liu K R,et al.Seismogenesis andoccurrence of earthquakes as observed by temporallycontinuous gravity variations in China.Chinese ScienceBulletin(in Chinese),1997,42(18):1919-1930.
[16]Chen Y T,Gu H D,Lu Z X.Variations of gravity before andafter the Haicheng earthquake,1975,and the Tangshanearthquake,1976.Physics of the Earth and PlanetaryInteriors,1979,18(4):330-338.
[17]M7专项工作组.中国大陆大地震中—长期危险性研究.北京:地震出版社,2012.Working Group of M7.Study on the Mid-Long-TermPotential of Large Earthquakes on the Chinese Continent(inChinese).Beijing:Seismological Press,2012.
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