区域网GPS观测得到的汶川大地震前后的地壳垂直运动
|
摘要
中国地壳运动观测网络1 000个观测站的GPS非连续观测区域网分别在1999年、2001年、2004年、2007年和2009年作了5次观测。2008年5月12日汶川8.0级地震震中(31.0°N,103.4°E)恰好在区域网GPS观测站密集的地区。区域网长期、多期GPS观测可降低年周期变化影响,有利于获取此次地震前后的垂直位移趋势变化。简要讨论了GPS垂直位移观测的精度。分析了垂直位移观测的主要干扰——地面沉降,特别是华北地区因大量抽取地下水产生的严重地面沉降。为获取汶川地震前垂直运动信息,首先剔除因大量抽取地下水产生的大幅度沉降干扰结果,通过趋势面分析中国大陆垂直位移空间分布,显示了3个垂直位移沉降最显著区域。对比分析表明,临近汶川震区的沉降区,未见大量抽取地下水干扰影响。汶川地震前1999—2007年区域网GPS观测站得到的垂直位移表明,汶川地震紧临显著沉降区的西北侧,龙门山断层北段垂直运动闭锁。该沉降区与另两个沉降区的时空变化明显不同,也与区域网水平应变异常区的空间分布不同,但该沉降区与区域网水平应变异常区同时出现。大幅度同震垂直位移集中在龙门山断层北段震前垂直位移闭锁区。这些事实表明,汶川地震前GPS观测到的紧临震中的沉降区及垂直运动闭锁区与汶川地震的发生存在密切关系。
Five campaigns for non-continuous observations were carried out in the years of 1999,2001,2004,2007 and 2009 from the regional network of 1000 GPS stations of CMONOC(Crustal Movement Observation Network of China).The great Wenchuan M8.0 earthquake of May 12,2008 occurred in an area with dense GPS observation stations in the regional network.GPS observations in the regional network carried out in many campaigns for a long time can mitigate the effects of periodic annual changes of vertical displacements on long term trend and are favorable for detecting trend variations in vertical displacements.In this paper,the accuracy of vertical displacements obtained from GPS observations is briefly discussed.Ground subsidence,the major contamination in vertical displacements,particularly,large ground subsidence caused by ground water withdraw in large amount,is analyzed.In order to get vertical displacements before the Wenchuan earthquake,at first the results with large subsidence caused by ground water withdraw in large amount must be deleted.Spatial distributions on China mainland from trend surface mappings show 3 areas of significant ground subsidence.In the subsidence area close to the Wenchuan earthquake region there are dense GPS stations that are free from contaminations of ground water withdraw.The vertical displacements from 1999 to 2007 before the Wenchuan earthquake show significant subsidence in the area south east to the earthquake and the northern segment of the Longmenshan fault had been locked as shown in vertical displacements.This subsidence area showed different changes both in time and space from the changes of other 2 subsidence areas.This subsidence area and the area with anomalous strain accumulations appeared at the same time,but they were not overlapping.Large coseismic vertical displacements were located along the northern segment of the Longmenshan fault which was locked before the event.All these facts show that the subsidence area near the epicenter,detected by GPS observations before the earthquake,and the locked segment of the fault shown by vertical displacements were closely related with the occurrence of the Wenchuan earthquake.
Five campaigns for non-continuous observations were carried out in the years of 1999,2001,2004,2007 and 2009 from the regional network of 1000 GPS stations of CMONOC(Crustal Movement Observation Network of China).The great Wenchuan M8.0 earthquake of May 12,2008 occurred in an area with dense GPS observation stations in the regional network.GPS observations in the regional network carried out in many campaigns for a long time can mitigate the effects of periodic annual changes of vertical displacements on long term trend and are favorable for detecting trend variations in vertical displacements.In this paper,the accuracy of vertical displacements obtained from GPS observations is briefly discussed.Ground subsidence,the major contamination in vertical displacements,particularly,large ground subsidence caused by ground water withdraw in large amount,is analyzed.In order to get vertical displacements before the Wenchuan earthquake,at first the results with large subsidence caused by ground water withdraw in large amount must be deleted.Spatial distributions on China mainland from trend surface mappings show 3 areas of significant ground subsidence.In the subsidence area close to the Wenchuan earthquake region there are dense GPS stations that are free from contaminations of ground water withdraw.The vertical displacements from 1999 to 2007 before the Wenchuan earthquake show significant subsidence in the area south east to the earthquake and the northern segment of the Longmenshan fault had been locked as shown in vertical displacements.This subsidence area showed different changes both in time and space from the changes of other 2 subsidence areas.This subsidence area and the area with anomalous strain accumulations appeared at the same time,but they were not overlapping.Large coseismic vertical displacements were located along the northern segment of the Longmenshan fault which was locked before the event.All these facts show that the subsidence area near the epicenter,detected by GPS observations before the earthquake,and the locked segment of the fault shown by vertical displacements were closely related with the occurrence of the Wenchuan earthquake.
引文
[1]顾国华,王武星,徐岳仁,等.区域网GPS观测得到的汶川大地震前的地壳水平运动[J].地震学报,2009,31(6):597-605.
[2]顾国华,王武星,孟国杰,等.GPS测得的汶川大地震前后的地壳运动[J].武汉大学学报.信息科学版,2009,34(11):1 336-1 339.
[3]Dong D,Fang P,Bock Y,et al.Anatomy of apparent seasonal variations from GPS derived site po-sition time series[J].J G R,2002,107(B4):ETG9-1~ETG9-16.
[4]顾国华.基准站GPS连续观测得到的垂直位移时间序列[J].地震地质,2005,27(2):332-340.
[5]顾国华,申旭辉,王敏,等.中国大陆地壳水平运动基本特征[J].地震学报,2001,23(4):362-369.
[6]顾国华,符养,王武星.1999至2001年中国大陆现今地壳水平运动[J].地震学报,2004,26(增刊):58-63.
[7]顾国华.参考框架、坐标变换和地壳运动[J].测绘通报,2006,(8):24-28.
[8]顾国华.GNSS(GPS)观测研究地壳运动的新进展[J].国际地震动态,2007,(7):9-15.
[9]Geoffrey Blewitt,David Lavalle.Effect of annual signals on geodetic velocity[J].J G R,2002.107(B7):B000570.
[10]Geoff Blewitt.Overview of the SNARF Working Group,its activities,and accomplishments[M].2007.8th SNARF Workshop AGU Fall Meeting.San Francisco December 11.
[11]Williams,Simon D P,Bock Yehuda,et al.Error Analysis of Continuous GPS Position Time Series[J].J G R,2004,109(B3):B03412.
[12]顾国华,孟国杰,方颖.汶川大地震前后GPS观测的精密单历元解得到的震区地壳运动[J].地震学报,2011,即将发表.
[13]顾国华.GPS观测得到的中国大陆地壳垂直运动[J].地震,2005,25(2):1-9.
[2]顾国华,王武星,孟国杰,等.GPS测得的汶川大地震前后的地壳运动[J].武汉大学学报.信息科学版,2009,34(11):1 336-1 339.
[3]Dong D,Fang P,Bock Y,et al.Anatomy of apparent seasonal variations from GPS derived site po-sition time series[J].J G R,2002,107(B4):ETG9-1~ETG9-16.
[4]顾国华.基准站GPS连续观测得到的垂直位移时间序列[J].地震地质,2005,27(2):332-340.
[5]顾国华,申旭辉,王敏,等.中国大陆地壳水平运动基本特征[J].地震学报,2001,23(4):362-369.
[6]顾国华,符养,王武星.1999至2001年中国大陆现今地壳水平运动[J].地震学报,2004,26(增刊):58-63.
[7]顾国华.参考框架、坐标变换和地壳运动[J].测绘通报,2006,(8):24-28.
[8]顾国华.GNSS(GPS)观测研究地壳运动的新进展[J].国际地震动态,2007,(7):9-15.
[9]Geoffrey Blewitt,David Lavalle.Effect of annual signals on geodetic velocity[J].J G R,2002.107(B7):B000570.
[10]Geoff Blewitt.Overview of the SNARF Working Group,its activities,and accomplishments[M].2007.8th SNARF Workshop AGU Fall Meeting.San Francisco December 11.
[11]Williams,Simon D P,Bock Yehuda,et al.Error Analysis of Continuous GPS Position Time Series[J].J G R,2004,109(B3):B03412.
[12]顾国华,孟国杰,方颖.汶川大地震前后GPS观测的精密单历元解得到的震区地壳运动[J].地震学报,2011,即将发表.
[13]顾国华.GPS观测得到的中国大陆地壳垂直运动[J].地震,2005,25(2):1-9.
版权所有：© 2023 中国地质图书馆 中国地质调查局地学文献中心