汶川地震前龙门山区域地壳密度动态变化分析
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摘要
利用龙门山区域重力网经平差处理和去基准点干扰、去高程变化影响的1997—2007年11期重复重力观测数据,借助密度的三维反演方法,分析研究了龙门山地区地壳各深度的介质密度的动态变化特征。结果显示:2008年汶川8.0级地震孕育发生过程中区域密度场的整体时空分布均表现出显著特征。从时间进程来看,震前10年的密度变化趋势呈现阶段性变化:密度变化平稳阶段—变化剧烈阶段(加速增加—缓慢减少)—变化缓慢减少阶段—密度变化缓慢增加阶段,密度变化程度由强到弱,表明大地震孕育达到了最后阶段;从空间分布来看,密度变化分布有分散—相对集中的趋势,震前地下密度场具有熵值减小的现象;密度变化剧烈的地方多发生在龙门山断裂带及其以西的川西高原上。此外,随深度的增加,密度变化趋势越来越明显。通过比较分析,在汶川地震前密度变化对重力的影响远远超过高程变化对重力的影响。
Based on repeated gravity observations data from 1996 to 2007of the Longmenshan gravity network,we first carried out adjustment processing,removing of benchmark interference and impact of elevation changes.Then by using 3-D inversion method to reflect underground density,we analyzed the characteristics of Longmenshan regional dynamic density in the depths of 25 km,20km and 15 km.The results show that in the Wenchuan earthquake inoculation process,regional density field showed obvious characteristics both in time and space distribution.From the point of time process,the density change trend ten years before the earthquake present periodic change:steady phase,dramatic stage,slowly reduce phase and slowly increase phase.The amount of density changes is from large to small,which shows that earthquake gestation has reached the final stage.From the point of space distribution,density change distribution has a tendency of"dispersion-relative concentration",which shows that before the earthquake underground density field exit entropy decreasing.In addition,the density dramatic change region tends to lie in Longmenshan fult zone and the western Sichuan plateau.Besides,with the increase of depth,the trend of density change is more and more obvious.Through comparative analysis,the influence of density change on gravity is far more than height change.
Based on repeated gravity observations data from 1996 to 2007of the Longmenshan gravity network,we first carried out adjustment processing,removing of benchmark interference and impact of elevation changes.Then by using 3-D inversion method to reflect underground density,we analyzed the characteristics of Longmenshan regional dynamic density in the depths of 25 km,20km and 15 km.The results show that in the Wenchuan earthquake inoculation process,regional density field showed obvious characteristics both in time and space distribution.From the point of time process,the density change trend ten years before the earthquake present periodic change:steady phase,dramatic stage,slowly reduce phase and slowly increase phase.The amount of density changes is from large to small,which shows that earthquake gestation has reached the final stage.From the point of space distribution,density change distribution has a tendency of"dispersion-relative concentration",which shows that before the earthquake underground density field exit entropy decreasing.In addition,the density dramatic change region tends to lie in Longmenshan fult zone and the western Sichuan plateau.Besides,with the increase of depth,the trend of density change is more and more obvious.Through comparative analysis,the influence of density change on gravity is far more than height change.
引文
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[6]柯小平,王勇,许厚泽.三维密度分布的遗传算法反演[J].大地测量与地球动力学,2009,29(1):41-45.
[7]玄松柏,申重阳,孙少安,等.地下密度变化三维反演的遗传算法研究[J].大地测量与地球动力学,2008,28(1):36-40.
[8]玄松柏,申重阳,李辉.丽江7.0地震前后地壳密度变化三维反演[J].大地测量与地球动力学,2010,30(1):14-20.
[9]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[J].科学通报,1997,42(18):1 919-1 930.
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[12]郑金涵,宋胜合,刘克人,等.利用重力资料反演京津唐张地区震质中[J].地震学报,2003,25(4):422-431.
[13]祝意清,梁伟锋,徐云马,等.汶川8.0级大震前后的重力场动态变化[J].地震学报,2010,32(6):633-640.
[14]孙少安,项爱民,周新.龙门山区域重力网起算基准的扰动分析[J].大地测量与地球动力学,2009,29(6):8-12.
[15]项爱民,孙少安,李辉.流动重力运行状态及质量评价[J].大地测量与地球动力学,2007,27(6):109-114.
[16]吴雪芳,田世华,吴国华.重力变化与地壳形变、地下水关系的研究[J].地震学报,1992,S1期:653-660.
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[19]何志堂,闫会杰,张训虎,等.降雨对大地原点重力影响的模拟计算[J].测绘技术装备,2009,11(4):9-12.
[20]高东东,吴勇,姜丽丽,等.德阳市城区地下水位动态特征及成因分析[M].四川地质学报,2012,32(1):74-79.
[21]王维佳.四川地区近60a大气可降水量分析[J].干旱气象,2009,27(4):346-349.
[22]张永堂,蒋国镭,王艳秋,等.地下水垂向入渗补给机理及补给量的研究[J].城市勘探,1996,3:12-15.
[23]王桂茹,尤春峰,张焕智.降雨渗入系数计算与分析[J].黑龙江水利科技,2002,2:24-26.
[24]何志堂,闫会杰,雷鹏,等.地下水变化对大地原点重力影响的估算[J].测绘标准化,2010,26(3):10-12.
[25]安玉林,陈玉东,黄金明.重磁勘探正反演方法理论研究的新进展[J].地学前缘,2003,10(1):141-149.
[26]曾华霖.重力场与重力勘探[M].北京:地质出版社,2005.
[27]桂林冶金地质学院.地球物理勘探译文集第1辑重磁方法[M].吉林:桂林冶金地质学院,1980.
[28]吴翼麟,牛安福,李爱萍.孕震区形变异常临近地震时的有序度研究[J].地壳形变与地震,1993,13(3):7-13.
1 http:∥baike.so.com/doc/5422145.html
[2]祝意青,徐云马,吕弋培,等.龙门山断裂带重力变化与汶MS8.0级地震关系研究[J].地球物理学报,2009,52(10):2 538-2 546.
[3]Boulanger,Chouteau M.Constraints in 3Dgravity inversion[J].Geophysics Prospecting,2001,49:265-280.
[4]Li Y,Oldenburg D W.3-D inversion of gravity data[J].Geophysics,1998,63:109-119.
[5]刘天佑.位场勘探数据处理新方法[J].北京:科学出版社,2007.
[6]柯小平,王勇,许厚泽.三维密度分布的遗传算法反演[J].大地测量与地球动力学,2009,29(1):41-45.
[7]玄松柏,申重阳,孙少安,等.地下密度变化三维反演的遗传算法研究[J].大地测量与地球动力学,2008,28(1):36-40.
[8]玄松柏,申重阳,李辉.丽江7.0地震前后地壳密度变化三维反演[J].大地测量与地球动力学,2010,30(1):14-20.
[9]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[J].科学通报,1997,42(18):1 919-1 930.
[10]Kuo J T,Zheng J H,Song S H.Determination of earthquake epicentroids by inversion of gravity variation data in the BTTZ region,China[J].Tectonophysics,1999,312(2):267-281.
[11]刘克人,刘瑞法,郑金涵,等.1991—1997年首都圈重力变化与地震预测[J].地震地磁观测与研究,1998,19(IA):100-106.
[12]郑金涵,宋胜合,刘克人,等.利用重力资料反演京津唐张地区震质中[J].地震学报,2003,25(4):422-431.
[13]祝意清,梁伟锋,徐云马,等.汶川8.0级大震前后的重力场动态变化[J].地震学报,2010,32(6):633-640.
[14]孙少安,项爱民,周新.龙门山区域重力网起算基准的扰动分析[J].大地测量与地球动力学,2009,29(6):8-12.
[15]项爱民,孙少安,李辉.流动重力运行状态及质量评价[J].大地测量与地球动力学,2007,27(6):109-114.
[16]吴雪芳,田世华,吴国华.重力变化与地壳形变、地下水关系的研究[J].地震学报,1992,S1期:653-660.
[17]Xie P,Arkin P A.Global precipitation:A 17-year monthly analysis based on gauge observations,satellite estimates,and numerical model outputs[J].Bull Amer Meteor Soc,1997,78:2 539-2 558.
[18]Kummerow C,Barnes W,Kozu T,el al.The Tropical Rainfall Measuring Mission(TRMM)sensor package[J].J Atmos Oceanic Teehnol,1998,15:808-816.
[19]何志堂,闫会杰,张训虎,等.降雨对大地原点重力影响的模拟计算[J].测绘技术装备,2009,11(4):9-12.
[20]高东东,吴勇,姜丽丽,等.德阳市城区地下水位动态特征及成因分析[M].四川地质学报,2012,32(1):74-79.
[21]王维佳.四川地区近60a大气可降水量分析[J].干旱气象,2009,27(4):346-349.
[22]张永堂,蒋国镭,王艳秋,等.地下水垂向入渗补给机理及补给量的研究[J].城市勘探,1996,3:12-15.
[23]王桂茹,尤春峰,张焕智.降雨渗入系数计算与分析[J].黑龙江水利科技,2002,2:24-26.
[24]何志堂,闫会杰,雷鹏,等.地下水变化对大地原点重力影响的估算[J].测绘标准化,2010,26(3):10-12.
[25]安玉林,陈玉东,黄金明.重磁勘探正反演方法理论研究的新进展[J].地学前缘,2003,10(1):141-149.
[26]曾华霖.重力场与重力勘探[M].北京:地质出版社,2005.
[27]桂林冶金地质学院.地球物理勘探译文集第1辑重磁方法[M].吉林:桂林冶金地质学院,1980.
[28]吴翼麟,牛安福,李爱萍.孕震区形变异常临近地震时的有序度研究[J].地壳形变与地震,1993,13(3):7-13.
1 http:∥baike.so.com/doc/5422145.html
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