耿达短水准观测资料在汶川M_S8.0地震前后异常的辨别
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摘要
耿达短水准AB测线观测资料2006—2007年出现了累计4.59mm的张性变化,但同时段该场地A点附近进行建筑施工,这引起了该变化是否属于汶川地震前兆异常的争论.通过对耿达短水准场地现场地质和观测环境考察,在综合分析观测资料和场地内建筑施工有关信息的基础上,使用岩土力学分析程序计算施工对A点点位的影响的数值解.结果显示,建筑施工导致了约3.6mm的竖向沉降,这与同时段短水准观测的A点点位的变化幅度相似,发展趋势一致.认为耿达短水准AB测线测值从2006—2007年出现的变化是由于A点附近建筑施工影响所致.本文还对耿达短水准观测的2008年5月12日汶川MS8.0地震同震变化进行了分析,认为A点位于很厚的洪积扇上,当汶川地震发生时,在强烈地震动的作用下,洪积层内部空隙结构产生崩溃性破坏,从而形成地表的下沉,其沉降幅度与类似烈度条件下黄土场地的沉降幅度相当.
A total of 4.59 mm tensional change appeared in Gengda site fault-cross short-line leveling route AB observational data from 2006 to 2007,but a construction project surrounding leveling point A was carried out in the same period. This led an argument on whether the change is a precursory anomaly,or not,of the May 12,2008 Wenchuan MS8.0 earthquake. This paper introduced the field geological and environmental investigations at Gengda leveling site,and then,by using a rock and soil mechanics computation program and analyzing comprehensive observation data and construction information,we numerically calculated point A’s vertical displacement possibly induced by the construction. The calculated result shows that a subsidence of about 3.6 mm is caused by the construction progress,and its variation is similar to the leveling data change in range and trend. Therefore,we draw the conclusion that the change of Gengda leveling route AB observational data from 2006 to 2007 is caused by the construction works near point A. We also analyzed the coseismic change of Wenchuan earthquake observed by Gengda leveling. Because point A is located on a very thick proluvial fan,and when the Wenchuan earthquake occurred,the internal gap structure of torrential deposit damaged by strong ground motion,as a result,the ground surface subsided,and its subsidence range is similar to the loess field under the same seismic intensity condition.
A total of 4.59 mm tensional change appeared in Gengda site fault-cross short-line leveling route AB observational data from 2006 to 2007,but a construction project surrounding leveling point A was carried out in the same period. This led an argument on whether the change is a precursory anomaly,or not,of the May 12,2008 Wenchuan MS8.0 earthquake. This paper introduced the field geological and environmental investigations at Gengda leveling site,and then,by using a rock and soil mechanics computation program and analyzing comprehensive observation data and construction information,we numerically calculated point A’s vertical displacement possibly induced by the construction. The calculated result shows that a subsidence of about 3.6 mm is caused by the construction progress,and its variation is similar to the leveling data change in range and trend. Therefore,we draw the conclusion that the change of Gengda leveling route AB observational data from 2006 to 2007 is caused by the construction works near point A. We also analyzed the coseismic change of Wenchuan earthquake observed by Gengda leveling. Because point A is located on a very thick proluvial fan,and when the Wenchuan earthquake occurred,the internal gap structure of torrential deposit damaged by strong ground motion,as a result,the ground surface subsided,and its subsidence range is similar to the loess field under the same seismic intensity condition.
引文
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杨涛,周德培,周应华.2004.用FLAC3D分析高边坡的开挖病害[C]∥第八次全国岩石力学与工程学术大会论文集.北京:科学出版社:723-726.
杨涛,周德培,苏金蓉.2006.大变形有限元法分析边坡稳定性[J].山地学报,24(1):101-104.
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周硕愚,吴云,施顺英,陈志遥.2009.汶川8.0级地震前断层形变异常及与其它大震的比较[J].地震学报,31(2):140-151.
Itasca Consulting Group,Inc.2002.FLAC3D,Fast Lagrangian Analysis of Continua in3Di mension,Version2.1,User’s Manual[M].USA:Itasca Consulting Group,Inc.
薄万举,杨国华,张风霜.2009.汶川MS8.0地震孕震机理的形变证据与模型推演[J].地震,29(1):85-91.
黄润秋,许强.1995.显式拉格朗日差分分析在岩石边坡工程中的应用[J].岩石力学与工程学报,14(4):346-354.
焦青,杨选辉,许丽卿,王博.2008.汶川8.0级地震前后龙门山断裂活动特征浅析[J].大地测量与地球动力学,28(4):7-11.
寇晓东,周维垣,杨若琼.2001.FLAC3D进行三峡船闸高边坡稳定分析[J].岩石力学与工程学报,20(1):6-10.
牛安福,张凌空,闫伟,贾晓东,李晓帆.2009.汶川地震前南北地震带中北段地形变变化特征的研究[J].地震,29(1):100-107.
王峻,王兰民,李兰.1997.黄土场地震陷量的试验预测[J].西北地震学报,19(2):62-66.
王峻,王兰民,李兰.2005.永登5.8级地震中黄土震陷灾害的探讨[J].地震研究,28(4):393-397.
王兰民,孙军杰,徐舜华,秋仁东,何丽君,胡明清,吴志坚.2008.爆破模拟地震动条件下黄土场地震陷研究[J].岩石力学与工程学报,27(5):913-921.
谢和平,周宏伟,王金安,李隆忠,Kwasniewski M A.1999.FLAC3D在煤矿开采沉陷预测中的应用及对比分析[J].岩石力学与工程学报,18(4):397-401.
徐强,严明,黄润秋.2002.某水电站左岸深裂缝对工程荷下边坡稳定性影响的FLAC3D分析[J].地质灾害与环境保护,13(1):81-84.
徐锡伟,闻学泽,叶建青,马保起,陈杰,周荣军,何宏林,田勤俭,何玉林,王志才,孙昭民,冯希杰,于贵华,陈立春,陈桂华,于慎鄂,冉勇康,李细光,李陈侠,安艳芬.2008.汶川MS8.0地震地表破裂带及其发震构造[J].地震地质,30(3):597-629.
杨涛,周德培,周应华.2004.用FLAC3D分析高边坡的开挖病害[C]∥第八次全国岩石力学与工程学术大会论文集.北京:科学出版社:723-726.
杨涛,周德培,苏金蓉.2006.大变形有限元法分析边坡稳定性[J].山地学报,24(1):101-104.
张冬丽,王兰民,王玉华.2002.有限元分析方法在黄土地基震陷预测中的应用[J].西北地震学报,24(3):208-214.
周硕愚,吴云,施顺英,陈志遥.2009.汶川8.0级地震前断层形变异常及与其它大震的比较[J].地震学报,31(2):140-151.
Itasca Consulting Group,Inc.2002.FLAC3D,Fast Lagrangian Analysis of Continua in3Di mension,Version2.1,User’s Manual[M].USA:Itasca Consulting Group,Inc.
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