汶川地震破裂近场震后变形观测及其意义
摘要
汶川地震破裂带上的近场震后变形,是一种震后的蠕滑行为,而且大部分表现为与同震滑移的方向相反.地震断层的活动通常划分成震前、同震、震后和震间4个阶段,反映了一次地震从孕育、发生到结束的整个演化过程,而不同活动阶段的变形特征反映出不同的应力状态和力学性质.汶川地震沿龙门山断裂带形成了两条长分别为250和72km的地表破裂带.为了了解汶川地震地表破裂带的震后变形特征,对中央主破裂带上人为破坏较轻的断层崖或断层挠曲崖进行反复测量,结果显示在19个观测点中,13个观测点(68%)的断层崖或断层挠曲崖的高度(垂直同震位移)震后降低回落,平均降低了9.7%;5个观测点(26%)没有发生变化;1个观测点(6%)的在震后继续抬升,抬升了12.8%,而且该观测点位于中央主破裂带的南西端部.尽管这种变化中存在着上冲断层盘虚假抬升后压实回落的影响,但主要是沿汶川地震破裂带发生的震后滑移造成的,而且大部分震后滑移(68%)与同震滑移的方向相反.除破裂端部存在同震位移亏损,弹性能释放不完全外,其他部位同震位移要么与震间累积达到平衡,要么过冲产生能量亏损,揭示了汶川地震的能量可能基本释放完全,发生7级以上强余震的可能性不大.此外,这种震后变形特征还告诉我们,在进行活动断层构造地貌研究时,特别是通过断层崖高度(或其他水平位错量)判断断层运动速率和估计古地震事件大小时,除侵蚀作用产生的误差外,还需要考虑10%左右来自震后滑移的系统误差.
引文
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8Kreemer C,Blewitt G,Maerten F.Co-and postseismic deformation of the28March2005Nias Mw8.7earthquake from continuous GPS data.Geophys Res Lett,2006,33:L07307
9Savage J C,Svarc J L.Postseismic relaxation following the1992M7.3Landers and1999M7.1Hector Mine earthquakes,southern Cali-fornia.J Geophys Res,2009,114:B01401
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13Pollitz F F.Transient rheology of the uppermost mantle beneath the Mojave Desert,California.Earth Planet Sci Lett,2003,215:89—104
14Owen S,Anderson G,Agnew D C,et al.Early postseismic deformation from the16October1999M w7.1Hector Mine,California,earth-quake as measured by survey-mode GPS.Bull Seismol Soc Am,2002,92:1423—1432
15Jacobs A,Sandwell D,Fialko Y,et al.The1999(M w7.1)Hector Mine,California,earthquake:Near-field postseismic deformation from ERS interferometry.Bull Seismol Soc Am,2002,92:1433—1442
16Freed A M,Bürgmann R,Herring T.Far-reaching transient motions after Mojave earthquakes require broad mantle flow beneath a strong crust.Geophys Res Lett,2007,34:L19302
17USGS Earthquake Center.http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2008ryan.php,2008
18陈运泰.汶川特大地震的震级和断层长度.科技导报,2008,26:26—27
19徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造.地震地质,2008,30:597—629
20李传友,魏占玉.汶川Ms8.0地震地表破裂带北端位置的修订.地震地质,2009,31:1—8
21冉勇康,史翔,王虎,等.汶川M8地震最大地表同震垂直位移量及其地表变形样式.科学通报,2010,55:154—162
22邓起东,冉勇康,杨晓平,等.中国活动构造图(1:400万).北京:地震出版社,2007
23冉勇康,陈立春,陈桂华,等.汶川Ms8.0地震发震断裂大地震原地重复现象初探.地震地质,2008,30:630—643
24Reid H F.The mechanism of earthquake.In:The California Earthquake of April18,1906,Report of the State Earthquake Investigation Commis-sion.Vol.2,Washington DC:Carnegie Institute,1910.1—192
25Thatcher W.The earthquake deformation cycle,recurrence,and the time-predictable model.J Geophys Res,1984,89:5674—5680
26何昌荣.断层上的地震成核过程与前兆模拟研究.中国地震,2000,16:1—13
27Dieterich J H.Modelling of rock friction:1.Experimental results and constitutive equations.J Geophys Res,1979,84:2161—2168
28Dieterich J H,Kilgore B.Direct observation of frictional contacts:New insights for state-dependent properties.Pure Appl Geophys,1994,143:283—302
29He C,Wong T F,Beeler N M.Scaling of stress drop with recurrence interval and loading velocity for laboratory-derived fault strength re-lations.J Geophys Res,2003,108:2037
30Rice J R.Heating and weakening of faults during earthquake slip.J Geophys Res,2006,111:B05311
31何宏林,孙昭民,魏占玉,等.汶川Ms8.0地震地表破裂带白沙河段破裂及其位移特征.地震地质,2008,30:658—672
32王萍,付碧宏,张斌,等.汶川8.0级地震地表破裂带与岩性关系.地球物理学报,2009,52:131—139
2Scholz C H.The Mechanics of Earthquake and Faulting.2nd ed.Cambridge:Cambridge University Press,2002
3Shen Z K,Jackson D D,Feng Y,et al.Postseismic deformation following the Landers earthquake,California,28June1992.Bull Seismol Soc Am,1994,84:780—791
4Perfettini H,Avouac J P.Postseismic relaxation driven by brittle creep:A possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks,application to the Chi-Chi earthquake,Taiwan.J Geophys Res,2004,109:B02304
5Barbot S,Hamiel Y,Fialko Y.Space geodetic investigation of the coseismic and postseismic deformation due to the2003Mw7.2Altai earthquake:Implications for the local lithospheric rheology.J Geophys Res,2008,113:B03403
6Gahalaut V K,Jade S,Catherine J K,et al.GPS measurements of postseismic deformation in the Andaman-Nicobar region following the giant2004Sumatra-Andaman earthquake.J Geophys Res,2008,113:B08401
7Kayanne H,Ikeda Y,Echigo T,et al.Coseismic and postseismic creep in the Andaman Islands associated with the2004Suma-tra-Andaman earthquake.Geophys Res Lett,2007,34:L01310
8Kreemer C,Blewitt G,Maerten F.Co-and postseismic deformation of the28March2005Nias Mw8.7earthquake from continuous GPS data.Geophys Res Lett,2006,33:L07307
9Savage J C,Svarc J L.Postseismic relaxation following the1992M7.3Landers and1999M7.1Hector Mine earthquakes,southern Cali-fornia.J Geophys Res,2009,114:B01401
10Perfettini H,Avouac J P.Modeling afterslip and aftershocks following the1992Landers earthquake.J Geophys Res,2007,112:B07409
11Peltzer G,Rosen P,Rogez F,et al.Poroelastic rebound along the Landers1992earthquake surface rupture.J Geophys Res,1998,103:30131—30145
12Pollitz F F,Wicks C,Thatcher W.Mantle flow beneath a continental strike-slip fault:Postseismic deformation after the1999Hector Mine earthquake.Science,2001,293:1814—1818
13Pollitz F F.Transient rheology of the uppermost mantle beneath the Mojave Desert,California.Earth Planet Sci Lett,2003,215:89—104
14Owen S,Anderson G,Agnew D C,et al.Early postseismic deformation from the16October1999M w7.1Hector Mine,California,earth-quake as measured by survey-mode GPS.Bull Seismol Soc Am,2002,92:1423—1432
15Jacobs A,Sandwell D,Fialko Y,et al.The1999(M w7.1)Hector Mine,California,earthquake:Near-field postseismic deformation from ERS interferometry.Bull Seismol Soc Am,2002,92:1433—1442
16Freed A M,Bürgmann R,Herring T.Far-reaching transient motions after Mojave earthquakes require broad mantle flow beneath a strong crust.Geophys Res Lett,2007,34:L19302
17USGS Earthquake Center.http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2008ryan.php,2008
18陈运泰.汶川特大地震的震级和断层长度.科技导报,2008,26:26—27
19徐锡伟,闻学泽,叶建青,等.汶川Ms8.0地震地表破裂带及其发震构造.地震地质,2008,30:597—629
20李传友,魏占玉.汶川Ms8.0地震地表破裂带北端位置的修订.地震地质,2009,31:1—8
21冉勇康,史翔,王虎,等.汶川M8地震最大地表同震垂直位移量及其地表变形样式.科学通报,2010,55:154—162
22邓起东,冉勇康,杨晓平,等.中国活动构造图(1:400万).北京:地震出版社,2007
23冉勇康,陈立春,陈桂华,等.汶川Ms8.0地震发震断裂大地震原地重复现象初探.地震地质,2008,30:630—643
24Reid H F.The mechanism of earthquake.In:The California Earthquake of April18,1906,Report of the State Earthquake Investigation Commis-sion.Vol.2,Washington DC:Carnegie Institute,1910.1—192
25Thatcher W.The earthquake deformation cycle,recurrence,and the time-predictable model.J Geophys Res,1984,89:5674—5680
26何昌荣.断层上的地震成核过程与前兆模拟研究.中国地震,2000,16:1—13
27Dieterich J H.Modelling of rock friction:1.Experimental results and constitutive equations.J Geophys Res,1979,84:2161—2168
28Dieterich J H,Kilgore B.Direct observation of frictional contacts:New insights for state-dependent properties.Pure Appl Geophys,1994,143:283—302
29He C,Wong T F,Beeler N M.Scaling of stress drop with recurrence interval and loading velocity for laboratory-derived fault strength re-lations.J Geophys Res,2003,108:2037
30Rice J R.Heating and weakening of faults during earthquake slip.J Geophys Res,2006,111:B05311
31何宏林,孙昭民,魏占玉,等.汶川Ms8.0地震地表破裂带白沙河段破裂及其位移特征.地震地质,2008,30:658—672
32王萍,付碧宏,张斌,等.汶川8.0级地震地表破裂带与岩性关系.地球物理学报,2009,52:131—139
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