区域网GPS观测得到的2008年汶川M_S8.0地震前的地壳水平运动
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摘要
2008年5月12日汶川(31.0°N,103.4°E)MS8.0大地震发生在中国地壳运动观测网络区域网GPS观测站相当密集的地区.1000个站的GPS非连续观测区域网分别在1999,2001,2004年和2007年作了4次观测.震前区域网GPS观测站得到的水平位移表明,汶川大地震主要力源是印度板块向北对中国大陆的挤压,但同时也受到东部与南部板块的挤压.与其它地区相比,震前震中附近水平位移最显著的特点是,汶川地震发生在南北地震带上位移分叉部位,即震中北部明显向东北位移,震中南部明显向东南位移,而震中附近的水平位移则明显小于其北面和南面的水平位移.简要讨论了应变计算结果的精度.为获取地震前的异常信息,分别采用趋势曲面拟合和统计方法研究了汶川地震前(1999—2007年)区域网的应变积累,寻找震中的大致区域.除了2001年昆仑山口西大地震震中及其周围地区外,1999—2007年震前区域网的应变积累的趋势曲面拟合表明,汶川地震发生在中国大陆第一剪应变积累大、范围最广的区域的东侧,且在此区域内积累较大的面压缩区的东北边缘.应变分量的统计分析表明,震前其分布在此区域及其附近同样有明显的异常,剪应变和面膨胀积累均增强.
The Wenchuan MS8.0 earthquake on May 12,2008,occurred in an area with dense GPS observation stations in the regional network of CMONOC (the Crustal Movement Observation Network of China).The regional network with 1000 GPS stations for non-continuous observations carried observations in 1999,2001,2004 and 2007. Horizontal displacements at GPS stations in the regional network before the Wenchuan earthquake show that the main driving tectonic force of the earthquake was the northward pushing of the Indian plate,with additional pushing of plates on the eastern and southern side.In comparison with the displacements in other regions,a most striking feature of the horizontal displacements near and around the earthquake area is the eastward diverging motion,that is,the stations north of the epicenter moved in the ENE direction while those south of epicenter moved in ESE direction,with small displacements at stations near the epicenter.The accuracy of estimated strains is briefly discussed.In order to obtain the anomalous information before the earthquake,both methods of trend surface fit and statistics have been used in the study with the aim of looking for potential epicentral area from the strain accumulation in the regional network observed from 1999 to 2007 before the Wenchuan earthquake.Besides the epicentral area of the 2001 Kunlun Mountain earthquake of MS8.1 in 2001,the best fit result of a trend surface of strain accumulation from 1999 to 2007 in the regional network before the earthquake show that the Wenchuan earthquake occurred at the eastern fringe of a large region with remarkable accumulation of the first shear strain,and also at the northeastern fringe of a smaller region with significant areal compression accumulation.Statistics of the accumulation of strain components show that there were also anomalous strain distribution patterns in this region and its neighborhood with increasing accumulation of both shear strain and areal compression.
The Wenchuan MS8.0 earthquake on May 12,2008,occurred in an area with dense GPS observation stations in the regional network of CMONOC (the Crustal Movement Observation Network of China).The regional network with 1000 GPS stations for non-continuous observations carried observations in 1999,2001,2004 and 2007. Horizontal displacements at GPS stations in the regional network before the Wenchuan earthquake show that the main driving tectonic force of the earthquake was the northward pushing of the Indian plate,with additional pushing of plates on the eastern and southern side.In comparison with the displacements in other regions,a most striking feature of the horizontal displacements near and around the earthquake area is the eastward diverging motion,that is,the stations north of the epicenter moved in the ENE direction while those south of epicenter moved in ESE direction,with small displacements at stations near the epicenter.The accuracy of estimated strains is briefly discussed.In order to obtain the anomalous information before the earthquake,both methods of trend surface fit and statistics have been used in the study with the aim of looking for potential epicentral area from the strain accumulation in the regional network observed from 1999 to 2007 before the Wenchuan earthquake.Besides the epicentral area of the 2001 Kunlun Mountain earthquake of MS8.1 in 2001,the best fit result of a trend surface of strain accumulation from 1999 to 2007 in the regional network before the earthquake show that the Wenchuan earthquake occurred at the eastern fringe of a large region with remarkable accumulation of the first shear strain,and also at the northeastern fringe of a smaller region with significant areal compression accumulation.Statistics of the accumulation of strain components show that there were also anomalous strain distribution patterns in this region and its neighborhood with increasing accumulation of both shear strain and areal compression.
引文
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顾国华,符养,王武星.2004.1999—2001年中国大陆现今地壳水平运动[J].地震学报,26(增刊):58--63.
顾国华.2006.参考框架、坐标变换和地壳运动[J].测绘通报,(8):24--28.
顾国华,王丽凤.2006.GPS观测得到的1998至2000年中国大陆地壳应变[J].地震,26(3):1--8.
顾国华.2007.GNSS(GPS)观测研究地壳运动的新进展[J].国际地震动态,(7):9--15.
顾国华,王武星.2009.GPS测得的汶川大地震同震位移[J].地震,29(1):92--99.
Dong D P,Fang Y,Bock Y,Cheng MK,Miyasaki S.2002.Anatomy of apparent seasonal variations from GPS derivedsite position ti me series[J].J Geophys Res,107(B4):2075.
Blewitt G.2007.Overviewof the SNARF Working Group,its activities,and accomplishments[C]∥20078th SNARFWorkshop AGU Fall Meeting.San Francisco December11.
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