强震后地表变形的动力学机制研究——以1999年台湾集集地震为例
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摘要
强震后地表变形的动力学机制是地球动力学研究的重要方面,现在普遍认为震后变形主要由断层的震后余滑或由介质的黏弹性松弛所至.1999年台湾集集地震GPS观测系统记录到了空前的资料,为研究震后变形的动力学机制提供了难得的机会.本研究认为集集地震后地表变形由震后断层余滑、下地壳/上地幔的黏弹性松弛、震源区介质的破裂、孔隙弹性回跳、地下流体的运移、介质孔隙度及孔隙压的变化等多种因素共同影响决定.为抓住重点,研究中将介质的破裂、地下流体的运移和孔隙弹性回跳等因素等效为震源区介质的物性变化.文中运用黏弹性有限单元模型(麦克斯威尔体)、利用GPS观测的时间序列资料对震后余滑、地壳/地幔黏度以及等效的震源区介质物性变化进行了反演.反演模型给出了震后余滑的分布及变化特征,反演结果初步显示台湾地区的下地壳/上地幔的黏度分别为2.7×1018,4.2×1020Pa·s.此外,反演结果还给出每种影响因素对地表变形的贡献大小,在集集地震后的450d时间里,断层的震后余滑引起的地表变形占总变形的44.6%,下地壳/上地幔的黏性松弛占34.7%,等效的震源区介质的物性变化占20.7%.
引文
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14Marone C J,Scholz C H,Bilham R.On the mechanics of earthquake afterslip.J Geophys Res,1991,96:8441—8452
15Shen Z,Jackson D D,Feng Y,et al.Postseismic deformation following the Landers earthquake,California,28June1992.Bull Seismol Soc Am,1994,84(3):780—791
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17Ueda H,Ohtake M,Sato H.Afterslip on the plate interface following the1978Miyagi-Oki,Japan,earthquake,as revealed from geodetic measurement data.Tectonophysics,2001,338:45—57
18Hsu Y J,Bechor N,Segall P,et al.Rapid afterslip following the1999Chi-Chi,Taiwan Earthquake.Geophys Res Lett,2002,29(16),doi:10.1029/2002GL014967
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21Peltzer G,Rosen P,Rogez F.Poroelastic rebound along the Landers1992earthquake surface rupture.J Geophys Res,1998,103(B12):30131—30145
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23Jónsson S,Segall P,Pedersen R,et al.Post-earthquake ground movements correlated to pore-pressure transients.Nature,2003,424:179—183
24Perfettini 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,doi:10.1029/2003JB002488
25Savage J C.Postseismic relaxation associated with transient creep rheology.J Geophys Res,2007,112:B05412,doi:10.1029/2006JB004688
26王彦斌,王永,李建成,等.1999年台湾集集大震的地表断层破裂特征.地震地质,2000,22(2):97—103
27Shieh C F,Sheu S Y,Shih R C.Correlation between surface damage and the coseismic displacement and stress relaxation of the1999Chi-Chi earthquake.Geophys Res Lett,2001,28:3381―3384
28Chen K C,Huang B S,Wang J H,et al.Conjugate thrust faulting associated with the1999Chi-Chi,Taiwan,earthquake sequence.Geo-phys Res Lett,2002,29(8):1277,doi:10.1029/2001GL014250
29Wang C Y,Douglas S D,Wang C H,et al.Field relations among coseismic ground motion,water level change and liquefaction for the1999Chi-Chi(Mw=7.5)earthquake,Taiwan.Geophys Res Lett,2003,30(17),doi:10.1029/2003GL017601
30Wang J H.Energy release and heat generation during the1999Ms7.6Chi-Chi,Taiwan,earthquake.J Geophys Res,2006,111:B11312,doi:10.1029/2005JB004018
31Chen C H,Wang W H,Teng T L.3D velocity structure around the source area of the1999Chi-Chi,Taiwan,Earthquake:before and after the mainshock.Bull Seismol Soc Am,2001,91(5):1013—1027
32Savage J C.Equivalent strike-slip earthquake cycles in half-space and lithosphere-asthenosphere Earth models.J Geophys Res,1990,95:4873—4879
33Hearn E H,Burgmann R,Reilinger R E.Dynamics of Izmit earthquake postseismic deformation and loading of the Duzce earthquake hypocenter.Bull Seismol Soc Am,2002,92:172—193
34Yu S B,Kuo L C,Hsu Y J,et al.Preseismic deformation and coseismic displacements associated with the1999Chi-Chi,Taiwan,Earthquake.Bull Seismol Soc Am,2001,91(5):995—1012
35Johnson K M,Segall P.Imaging the ramp-décollement geometry of the Chelungpu fault using coseismic GPS displacements from the1999Chi-Chi,Taiwan earthquake.Tectonophysics,2004,378:123—139
36Yen H Y,Yeh Y H,Wu F T.Two-dimensional crustal structures of Taiwan from gravity data.Tectonics,1998,17(1):104—111
37Lin A T,Watts A B.Origin of the west Taiwan basin by orogenic loading and flexure of a rifted continental margin.J Geophys Res,2002,107(B9):2185,doi:10.1029/2001JB000669
38Dziewonski A M,Anderson D L.Preliminary reference Earth model.Phys Earth Planet Int,1981,25:297—356
39Lee J C,Chu H T,Angelier J,et al.Geometry and structure of northern surface ruptures of the1999Mw=7.6Chi-Chi Taiwan earth-quake:influence from inherited fold belt from inherited fold belt structures.J Struct Geol,2002,24:173—192
40郭振伏,武晓松,余陵,等.底排火箭复合增程弹助火箭推进剂结构完整性分析.弹道学报,2003,15(2):34—38
41周光泉,刘孝敏.粘弹性理论.合肥:中国科学技术大学出版社,1996
42Yu S B,Chen H Y,Kuo L C.Velocity field of GPS stations in the Taiwan area.Tectonophysics,1997,274:41—59
43Dondurur D,Sar C.A Fortran77computer code for damped least-squares inversion of Slingram electromagnetic anomalies over thin tabular conductors.Comp Geosci,2004,30:591—599
44Kao H,Chen W P.The Chi-Chi earthquake sequence:active,out-of-sequence thrust faulting in Taiwan.Science,2000,288:2346—2349
45Lin C H.Thermal modeling of continental subduction and exhumation constrained by heat flow and seismicity in Taiwan.Tectono-physics,2000,324:189—201
2Wahr J,Wyss M.Interpretation of postseismic deformation with a viscoelastic relaxation model.J Geophys Res,1980,85(B11):6471—6477
3Reilinger R.Evidence for postseismic viscoelastic relaxation following the1959M=7.5Hebgen Lake,Montana,earthquake.J Geophys Res,1986,91(B9):9488—9494
4Savage J C,Lisowski M,Svarc J L.Postseismic deformation following the1989(M=7.1)Loma Prieta,California,earthquake.J Geophys Res,1994,99(B7):13757—13765
5Bürgmann R,Segall P,Lisowski M,et al.Postseismic strain following the1989Loma Prieta earthquake from GPS and leveling meas-urements.J Geophys Res,1997,102(B3):4933—4955
6Kenner S J,Segall P.Postseismic deformation following the1906San Francisco earthquake.J Geophys Res,2000,105(B6):13195—13209
7Ueda H,Ohtake M,Sato H.Postseismic crustal deformation following the1993Hokkaido Nanseioki earthquake,northern Japan:evi-dence for a low-viscosity zone in the uppermost mantle.J Geophys Res,2003,108,doi:10.1029/2002JB002067
8Fialko Y.Evidence of fluid-filled upper crust from observations of postseismic deformation due to the1992Mw7.3Landers earthquake.J Geophys Res,2004,109:B08401,doi:10.1029/2004JB002985
9Zhu S B,Cai Y E.Inversion of viscous properties of crust and mantle from the GPS temporal series measurements.Chin J Geophys,2006,49(3):771—777
10Paul J,Lowry A R,Bilham R,et al.Postseismic deformation of the Andaman Islands following the26December,2004Great Sumatra—Andaman earthquake.Geophys Res Lett,2007,34:L19309,doi:10.1029/2007GL031024
11Miyazaki S,Larson K M.Coseismic and early postseismic slip for the2003Tokachi-oki earthquake sequence inferred from GPS data.Geophys Res Lett,2008,35:L04302,doi:10.1029/2007GL032309
12Deng J,Gurnis M,Kanamori H,et al.Viscoelastic flow in the lower crust after the1992Landers,California,earthquake.Science,1998,282:1689—1692
13Hu Y,Wang K,He J,et al.Three-dimensional viscoelastic finite element model for postseismic deformation of the great1960Chile earthquake.J Geophys Res,2004,109:B12403,doi:10.1029/2004JB003163
14Marone C J,Scholz C H,Bilham R.On the mechanics of earthquake afterslip.J Geophys Res,1991,96:8441—8452
15Shen Z,Jackson D D,Feng Y,et al.Postseismic deformation following the Landers earthquake,California,28June1992.Bull Seismol Soc Am,1994,84(3):780—791
16Savage J C,Svarc J L.Postseismic deformation associated with the1992Mw=7.3Landers earthquake,southern California.J Geophys Res,1997,102:7565—7577
17Ueda H,Ohtake M,Sato H.Afterslip on the plate interface following the1978Miyagi-Oki,Japan,earthquake,as revealed from geodetic measurement data.Tectonophysics,2001,338:45—57
18Hsu Y J,Bechor N,Segall P,et al.Rapid afterslip following the1999Chi-Chi,Taiwan Earthquake.Geophys Res Lett,2002,29(16),doi:10.1029/2002GL014967
19Yu S B,Hsu Y J,Kuo L C,et al.GPS measurement of postseismic deformation following the1999Chi-Chi,Taiwan,earthquake.J Geophys Res,2003,108,doi:10.1029/2003JB002396
20Peltzer G,Rosen P,Rogez F,et al.Postseismic rebound in fault step over caused by pore fluid flow.Science,1996,273:1202—1204
21Peltzer G,Rosen P,Rogez F.Poroelastic rebound along the Landers1992earthquake surface rupture.J Geophys Res,1998,103(B12):30131—30145
22Pollitz 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
23Jónsson S,Segall P,Pedersen R,et al.Post-earthquake ground movements correlated to pore-pressure transients.Nature,2003,424:179—183
24Perfettini 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,doi:10.1029/2003JB002488
25Savage J C.Postseismic relaxation associated with transient creep rheology.J Geophys Res,2007,112:B05412,doi:10.1029/2006JB004688
26王彦斌,王永,李建成,等.1999年台湾集集大震的地表断层破裂特征.地震地质,2000,22(2):97—103
27Shieh C F,Sheu S Y,Shih R C.Correlation between surface damage and the coseismic displacement and stress relaxation of the1999Chi-Chi earthquake.Geophys Res Lett,2001,28:3381―3384
28Chen K C,Huang B S,Wang J H,et al.Conjugate thrust faulting associated with the1999Chi-Chi,Taiwan,earthquake sequence.Geo-phys Res Lett,2002,29(8):1277,doi:10.1029/2001GL014250
29Wang C Y,Douglas S D,Wang C H,et al.Field relations among coseismic ground motion,water level change and liquefaction for the1999Chi-Chi(Mw=7.5)earthquake,Taiwan.Geophys Res Lett,2003,30(17),doi:10.1029/2003GL017601
30Wang J H.Energy release and heat generation during the1999Ms7.6Chi-Chi,Taiwan,earthquake.J Geophys Res,2006,111:B11312,doi:10.1029/2005JB004018
31Chen C H,Wang W H,Teng T L.3D velocity structure around the source area of the1999Chi-Chi,Taiwan,Earthquake:before and after the mainshock.Bull Seismol Soc Am,2001,91(5):1013—1027
32Savage J C.Equivalent strike-slip earthquake cycles in half-space and lithosphere-asthenosphere Earth models.J Geophys Res,1990,95:4873—4879
33Hearn E H,Burgmann R,Reilinger R E.Dynamics of Izmit earthquake postseismic deformation and loading of the Duzce earthquake hypocenter.Bull Seismol Soc Am,2002,92:172—193
34Yu S B,Kuo L C,Hsu Y J,et al.Preseismic deformation and coseismic displacements associated with the1999Chi-Chi,Taiwan,Earthquake.Bull Seismol Soc Am,2001,91(5):995—1012
35Johnson K M,Segall P.Imaging the ramp-décollement geometry of the Chelungpu fault using coseismic GPS displacements from the1999Chi-Chi,Taiwan earthquake.Tectonophysics,2004,378:123—139
36Yen H Y,Yeh Y H,Wu F T.Two-dimensional crustal structures of Taiwan from gravity data.Tectonics,1998,17(1):104—111
37Lin A T,Watts A B.Origin of the west Taiwan basin by orogenic loading and flexure of a rifted continental margin.J Geophys Res,2002,107(B9):2185,doi:10.1029/2001JB000669
38Dziewonski A M,Anderson D L.Preliminary reference Earth model.Phys Earth Planet Int,1981,25:297—356
39Lee J C,Chu H T,Angelier J,et al.Geometry and structure of northern surface ruptures of the1999Mw=7.6Chi-Chi Taiwan earth-quake:influence from inherited fold belt from inherited fold belt structures.J Struct Geol,2002,24:173—192
40郭振伏,武晓松,余陵,等.底排火箭复合增程弹助火箭推进剂结构完整性分析.弹道学报,2003,15(2):34—38
41周光泉,刘孝敏.粘弹性理论.合肥:中国科学技术大学出版社,1996
42Yu S B,Chen H Y,Kuo L C.Velocity field of GPS stations in the Taiwan area.Tectonophysics,1997,274:41—59
43Dondurur D,Sar C.A Fortran77computer code for damped least-squares inversion of Slingram electromagnetic anomalies over thin tabular conductors.Comp Geosci,2004,30:591—599
44Kao H,Chen W P.The Chi-Chi earthquake sequence:active,out-of-sequence thrust faulting in Taiwan.Science,2000,288:2346—2349
45Lin C H.Thermal modeling of continental subduction and exhumation constrained by heat flow and seismicity in Taiwan.Tectono-physics,2000,324:189—201
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