冰川均衡调整对东亚重力和海平面变化的影响
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摘要
新的全球冰川均衡调整(GIA)模型RF3L20(β=0.4)+ICE-4G考虑了地幔黏滞度沿横向的变化,其黏滞度参数得到大地测量、历史相对海平面变化观测和地震剪切波层析模型的较好约束.本文利用该模型预测了东亚现今重力变化和海平面变化,根据当前末次冰川时空变化和黏滞度参考模型中下地幔下部黏滞度认识的差异,评估了预测的不确定性.结果表明,GIA对东亚地区重力场和海平面长期变化有显著的影响:例如,在哈尔滨、长春、泰安、蓟县、郑州、武汉等测站,GIA重力影响达几十纳伽,可用超导重力仪和未来原子重力仪观测出来;在东亚大陆GIA对GRACE监测的等效水柱长期变化的影响为3%～10%,其中青藏高原西部、华北和三峡地区的影响较大.在东海—太平洋区,GIA的相对影响高达20%～40%;GIA使东亚海域绝对海平面以0.27～0.37mm/a的速率在长期下降,在黄海、东海卫星测高监测的绝对海平面长期变化中,GIA的相对影响分别达6.9%和7.5%;在58个验潮站,平均相对海平面长期上升速率为2.22mm/a,GIA影响为—0.17mm/a,其中14个测站GIA的影响达—0.3～—0.4mm/a.本文GIA预测的结果,对在东亚地区发现弱的地球动力学过程信号、监测水质量长期变化、监测海平面长期变化和分析其机制,提供精密的改正模型.
We have developed a new glacial isostatic adjustment (GIA) model, RF3L20(β=0. 4) +ICE-4G, which is well constrained by geodetic measurements, relative sea levels and shear-wave seismic tomographic data. Based on this model we will show how GIA affects the secular rate of change of gravity and sea level in East Asia. An advantage of this model is that the viscosities in the mantle are allowed to vary both in the radial and lateral directions. The laterally homogeneous reference viscosities are given by model RF3 (modified from Peltier' s VM2). Lateral viscosity perturbations are converted from seismic tomographic data using the well-known scaling relationship multiplied by the factor β. The latter is used to quantify the contribution of thermal effect to lateral variation in shear wave velocity, and is chosen to be 0. 4 by fitting the GIA data. In addition, the deglacial phase of the ice loads is given by the ICE-4G model. We assess the uncertainties of the GIA predictions by considering the differences between two reference viscosity models and two ice models. The GIA predictions are computed using the coupled-Laplace Finite-Element Method. The results show that GIA has obvious effects on the secular rate of change of gravity and sea level in East Asia. For example, the GIA effect on gravity can be several tens of nGals per year which can be detected by superconducting gravimeter and future atomic gravimeters at the geodetic stations Harbin, Changchun, Taian, Jixian, Zhengzhou and Wuhan. Also GIA is estimated to contribute 3 %～10 % on the secular trends of equivalent water heights on land in East Asia. The larger GIA effect appears in the west Tibetan Plateau, North China and Three Gorges Area. From East China Sea to the Pacific Ocean, the relative effects of GIA can be 20%～40%. GIA has caused a long-term depression of the absolute sea level in the ocean area by 0. 27～0. 37 mm/a. For the secular change in absolute sea level measured by satellite altimetry, the GIA effects can be 6. 9% and 7. 5% in Yellow Sea and East China Sea respectively. For the 58 tide gauges, the average value of the observed long term RSL rate is 2. 22 mm/a while the GIA effect is -0. 17 mm/a and the relative effect is 8. 3%. For the 14 gauges, the GIA effects are -0. 3～-0. 4 mm/a. Therefore the results of this paper provide useful GIA corrections, so that the weak signals from geodynamic processes in the East Asia can be revealed.
We have developed a new glacial isostatic adjustment (GIA) model, RF3L20(β=0. 4) +ICE-4G, which is well constrained by geodetic measurements, relative sea levels and shear-wave seismic tomographic data. Based on this model we will show how GIA affects the secular rate of change of gravity and sea level in East Asia. An advantage of this model is that the viscosities in the mantle are allowed to vary both in the radial and lateral directions. The laterally homogeneous reference viscosities are given by model RF3 (modified from Peltier' s VM2). Lateral viscosity perturbations are converted from seismic tomographic data using the well-known scaling relationship multiplied by the factor β. The latter is used to quantify the contribution of thermal effect to lateral variation in shear wave velocity, and is chosen to be 0. 4 by fitting the GIA data. In addition, the deglacial phase of the ice loads is given by the ICE-4G model. We assess the uncertainties of the GIA predictions by considering the differences between two reference viscosity models and two ice models. The GIA predictions are computed using the coupled-Laplace Finite-Element Method. The results show that GIA has obvious effects on the secular rate of change of gravity and sea level in East Asia. For example, the GIA effect on gravity can be several tens of nGals per year which can be detected by superconducting gravimeter and future atomic gravimeters at the geodetic stations Harbin, Changchun, Taian, Jixian, Zhengzhou and Wuhan. Also GIA is estimated to contribute 3 %～10 % on the secular trends of equivalent water heights on land in East Asia. The larger GIA effect appears in the west Tibetan Plateau, North China and Three Gorges Area. From East China Sea to the Pacific Ocean, the relative effects of GIA can be 20%～40%. GIA has caused a long-term depression of the absolute sea level in the ocean area by 0. 27～0. 37 mm/a. For the secular change in absolute sea level measured by satellite altimetry, the GIA effects can be 6. 9% and 7. 5% in Yellow Sea and East China Sea respectively. For the 58 tide gauges, the average value of the observed long term RSL rate is 2. 22 mm/a while the GIA effect is -0. 17 mm/a and the relative effect is 8. 3%. For the 14 gauges, the GIA effects are -0. 3～-0. 4 mm/a. Therefore the results of this paper provide useful GIA corrections, so that the weak signals from geodynamic processes in the East Asia can be revealed.
引文
[1] 汪汉胜,Wu Patrick,许厚泽.冰川均衡调整(GIA)的研究.地球物理进展,2009,24(6) :1958～1967 Wang H S,Wu P,Xu H Z.A review of research in glacial isostatic adjustment.Progress in Geophysics(in Chinese),2009,24(6) :1958～1967
[2] Haskell N A.The motion of a fluid under a surface load,1． Physics,1935,6:265～269
[3] Niskanen E.On the upheaval of Land in Fennoscandia.Ann.Acad.Sci.Fennicae A,1939,53:1～30
[4] Peltier W R.The impulse response of a Maxwell Earth.Rev.Geophys.Space Phys.,1974,17:649～669
[5] Peltier W R,Andrews J T.Glacial isostatic adjustment Ⅰ:The forward problem.Geophys.J.R.astr.Soc.,1976,46:605～646
[6] Wu P,Peltier W R.Viscous gravitational relaxation.Geophys.J.R.astr.Soc.,1982,70:435～485
[7] Peltier W R.New constraints on transient lower mantle rheology and internal mantle buoyancy from glacial rebound data.Nature,1985,318(6047) :614～617
[8] 汪汉胜,许厚泽,李国营.SNREI弹性地球模型表面负荷勒夫数数值计算的新进展.地球物理学报,1996,39(增刊):182～189 Wang H S,Xu H Z,Li G Y.Improvement of computations of load Love numbers of SNREI earth model.Chinese J.Geophys.(in Chinese),1996,39(Suppl.):182～189
[9] 汪汉胜,李国营,许厚泽.SNRVE黏弹性地球模型连续分布的简正模及其意义.地球物理学报,1997,40(1) :78～84 Wang H S,Li G Y,Xu H Z.Continuously distributed normal modes of the SNRVE earth model and their effects.Chinese J.Geophys.(in Chinese),1997,40(1) :78～84
[10] Zhong S,Paulson A,Wahr J.Three-dimensional finiteelement modelling of Earth's viscoelastic deformation:effects of lateral variations in lithospheric thickness.Geophys.J. Int.,2003,155(2) :679～695
[11] Wu P,Van der Wal W.Postglacial sea-levels on a spherical self gravitating viscoelastic earth:effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle.Earth Planet.Sci.Lett.,2003,211:57～68
[12] Latychev K,Mitrovica J X,Tromp J,et al.Glacial isostatic adjustment on 3-D earth models:a finite-volume formulation.Geophys.J.Int.,2005,161:421～444
[13] Paulson A,Zhong S,Wahr J.Modelling post-glacial rebound with lateral viscosity variations.Geoptys.J.Int.,2005,163(1) :357～371
[14] Spada G,Antonioli A,Cianetti S,Giunchi C.Glacial isostatic adjustment and relative sea-level changes:the role of lithospheric and upper mantle heterogeneities in a 3-D spherical Earth.Geophys.J.Int.,2006,165:692～702
[15] Wu P.Using commercial finite element packages for the study of Earth deformations,sea levels and the state of stress.Geophys.J.Int.,2004,158:401～408
[16] Wu P,Wang H,Schotman H.Postglacial induced surface motions,sea-levels and geoid rates on a spherical,selfgravitating laterally heterogeneous earth.Journal of Geodynamics,2005,39:127～142
[17] Wang H,Wu P.Effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced relative sea levels and long wavelength gravity field in a spherical,selfgravitating Maxwell Earth.Earth Planet.Sci.Lett.,2006,249:368～383
[18] Wang H,Wu P.Effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced surface motion on a spherical,self-gravitating Maxwell Earth.Earth Planet.Sci.Lett.,2006,244:576～589
[19] Sella G F,Stein S,Dixon T H,et al.Observation of glacial isostatic adjustment in“stable”North America with GPS.Geophys.Res.Lett.,2007,34:L02306
[20] Kuo C Y,Shum C K,Braun A,et al.Vertical motion determined using satellite altimetry and tide gauges.Terr.Atmos.Ocean.Sci.,2008,19(1-2) :21～35
[21] Tushingham A M,Peltier W R.Ice-3G.a new global model of late Pleistocene deglaciation based upon geophysical predictions of post-glacial relative sea level change.J.Geophys.Res.,1991,96:4497～4523
[22] Wang H,Wu P,van der Wal W.Using postglacial sea level,crustal velocities and gravity-rate of-change to constrain the influence of thermal effects on mantle lateral heterogeneities.Journal of Geodynamics,2008,46(3-5) :104～117
[23] 汪汉胜,Wu Patrick,van der Wal Wouter等.大地测量观测和相对海平面联合约束的冰川均衡调整模型.地球物理学报,2009,52(10) :2450～2460 Wang H S,Wu P,van der Wal W,et al.Glacial isostatic adjustment model constrained by geodetic measurements and relative sea level.Chinese J.Geophys.(in Chinese),2009, 52(10) :2450～2460
[24] Peltier W R.Postglacial variations in the level of the sea:implications for climate dynamics and solid-earth geophysics.Reviews of Geophysics,1998,36:603～689
[25] Wang H,Wu P,Wang Z.An approach for spherical harmoric analysis of non-smooth data.Computers & Geosciences,2006,32:1654～1668
[26] Wahr J,Molenaar M,Bryan F.Time-variability of the Earth's gravity field:hydrological and oceanic effects and their possible detection using GRACE.J.Geophys.Res.,1998,103:30205
[27] 汪汉胜,王志勇,袁旭东等.基于GRAcE时变重力场的三峡水库补给水系水储量变化.地球物理学报,2007,50(3) :76～82 Wang H S,Wang Z Y,Yuan X D,et al.Water storage changes in Three Gorges water systems area inferred from GRACE time-variable gravity data.Chinese J.Geophys.(in Chinese),2007,50(3) :76～82
[28] Swenson S,Wahr J.Post-processing removal of correlated errors in GRACE data.Geophys.Res.Lett.,2006,33,L08402
[29] Mitrovica J X,Forte A M.Radial profile of mantle viscosity:results from a joint inversion of convection and post-glacial rebound observables.J.Geophys.Res.,1997,102(B2) :2751～2769
[30] Peltier W R.Global glacial isostasy and the surface of the ice age earth:the ICE-SG(VM2) Model and GRACE.Annual Review of Earth and Planetary Science,2004,32:111～149
[31] Center for Space Research,The University of Texas at Austin.GRACE L-2 products-version UTCSR RL-04． ftp://podaac.jpl.nasa.gov/pub/grace/data/L2/csr/,2010
[32] Center for Space Research,The University of Texas at Austin.Release notes for GRACE L-2 products-version UTCSR RL-04． ftp://podaac.jpl.nasa.gov/pub/grace/doc/ReleaseNotes_csr_RL04． txt,2010
[33] Bettadpur S.GRACE level-2 gravity field product user handbook.ftp://podaac.jpl.nasa.gov/pub/grace/doc/L2UserHandbook_v2． 3． pdf,2007
[34] Chambers D P.Evaluation of new GRACE time variable gravity data over the ocean.Geophys.Res.Lett.,2006,33:L17603
[35] 詹金刚,王勇,程永寿.中国近海海平面变化特征分析.地球物理学报,2009,52(7) :1725～1733 Zhan J G,Wang Y,Cheng Y S.The analysis of China sea level change.Chinese J.Geophys.(in Chinese),2009,52(7) :1725～1733
[36] Yan M,Zuo J C,Du L,et al.Sea level variation/change and steric contribution in the East China Sea.Proceedings of the seventeenth International Offshore and Polar Engineering Conference,Lisbon Portugal,2007． 1～4:2377～2382
[37] 丁允辉.海平面变化对中国海工程水位推算的影响[硕士论文].青岛:中国海洋大学研究生院,2005 Ding Y H.The effect of sea level variation on the calculation of engineering water level[Master's thesis](in Chinese).Qingdao:Graduate School of Ocean University of China,2005
[2] Haskell N A.The motion of a fluid under a surface load,1． Physics,1935,6:265～269
[3] Niskanen E.On the upheaval of Land in Fennoscandia.Ann.Acad.Sci.Fennicae A,1939,53:1～30
[4] Peltier W R.The impulse response of a Maxwell Earth.Rev.Geophys.Space Phys.,1974,17:649～669
[5] Peltier W R,Andrews J T.Glacial isostatic adjustment Ⅰ:The forward problem.Geophys.J.R.astr.Soc.,1976,46:605～646
[6] Wu P,Peltier W R.Viscous gravitational relaxation.Geophys.J.R.astr.Soc.,1982,70:435～485
[7] Peltier W R.New constraints on transient lower mantle rheology and internal mantle buoyancy from glacial rebound data.Nature,1985,318(6047) :614～617
[8] 汪汉胜,许厚泽,李国营.SNREI弹性地球模型表面负荷勒夫数数值计算的新进展.地球物理学报,1996,39(增刊):182～189 Wang H S,Xu H Z,Li G Y.Improvement of computations of load Love numbers of SNREI earth model.Chinese J.Geophys.(in Chinese),1996,39(Suppl.):182～189
[9] 汪汉胜,李国营,许厚泽.SNRVE黏弹性地球模型连续分布的简正模及其意义.地球物理学报,1997,40(1) :78～84 Wang H S,Li G Y,Xu H Z.Continuously distributed normal modes of the SNRVE earth model and their effects.Chinese J.Geophys.(in Chinese),1997,40(1) :78～84
[10] Zhong S,Paulson A,Wahr J.Three-dimensional finiteelement modelling of Earth's viscoelastic deformation:effects of lateral variations in lithospheric thickness.Geophys.J. Int.,2003,155(2) :679～695
[11] Wu P,Van der Wal W.Postglacial sea-levels on a spherical self gravitating viscoelastic earth:effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle.Earth Planet.Sci.Lett.,2003,211:57～68
[12] Latychev K,Mitrovica J X,Tromp J,et al.Glacial isostatic adjustment on 3-D earth models:a finite-volume formulation.Geophys.J.Int.,2005,161:421～444
[13] Paulson A,Zhong S,Wahr J.Modelling post-glacial rebound with lateral viscosity variations.Geoptys.J.Int.,2005,163(1) :357～371
[14] Spada G,Antonioli A,Cianetti S,Giunchi C.Glacial isostatic adjustment and relative sea-level changes:the role of lithospheric and upper mantle heterogeneities in a 3-D spherical Earth.Geophys.J.Int.,2006,165:692～702
[15] Wu P.Using commercial finite element packages for the study of Earth deformations,sea levels and the state of stress.Geophys.J.Int.,2004,158:401～408
[16] Wu P,Wang H,Schotman H.Postglacial induced surface motions,sea-levels and geoid rates on a spherical,selfgravitating laterally heterogeneous earth.Journal of Geodynamics,2005,39:127～142
[17] Wang H,Wu P.Effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced relative sea levels and long wavelength gravity field in a spherical,selfgravitating Maxwell Earth.Earth Planet.Sci.Lett.,2006,249:368～383
[18] Wang H,Wu P.Effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced surface motion on a spherical,self-gravitating Maxwell Earth.Earth Planet.Sci.Lett.,2006,244:576～589
[19] Sella G F,Stein S,Dixon T H,et al.Observation of glacial isostatic adjustment in“stable”North America with GPS.Geophys.Res.Lett.,2007,34:L02306
[20] Kuo C Y,Shum C K,Braun A,et al.Vertical motion determined using satellite altimetry and tide gauges.Terr.Atmos.Ocean.Sci.,2008,19(1-2) :21～35
[21] Tushingham A M,Peltier W R.Ice-3G.a new global model of late Pleistocene deglaciation based upon geophysical predictions of post-glacial relative sea level change.J.Geophys.Res.,1991,96:4497～4523
[22] Wang H,Wu P,van der Wal W.Using postglacial sea level,crustal velocities and gravity-rate of-change to constrain the influence of thermal effects on mantle lateral heterogeneities.Journal of Geodynamics,2008,46(3-5) :104～117
[23] 汪汉胜,Wu Patrick,van der Wal Wouter等.大地测量观测和相对海平面联合约束的冰川均衡调整模型.地球物理学报,2009,52(10) :2450～2460 Wang H S,Wu P,van der Wal W,et al.Glacial isostatic adjustment model constrained by geodetic measurements and relative sea level.Chinese J.Geophys.(in Chinese),2009, 52(10) :2450～2460
[24] Peltier W R.Postglacial variations in the level of the sea:implications for climate dynamics and solid-earth geophysics.Reviews of Geophysics,1998,36:603～689
[25] Wang H,Wu P,Wang Z.An approach for spherical harmoric analysis of non-smooth data.Computers & Geosciences,2006,32:1654～1668
[26] Wahr J,Molenaar M,Bryan F.Time-variability of the Earth's gravity field:hydrological and oceanic effects and their possible detection using GRACE.J.Geophys.Res.,1998,103:30205
[27] 汪汉胜,王志勇,袁旭东等.基于GRAcE时变重力场的三峡水库补给水系水储量变化.地球物理学报,2007,50(3) :76～82 Wang H S,Wang Z Y,Yuan X D,et al.Water storage changes in Three Gorges water systems area inferred from GRACE time-variable gravity data.Chinese J.Geophys.(in Chinese),2007,50(3) :76～82
[28] Swenson S,Wahr J.Post-processing removal of correlated errors in GRACE data.Geophys.Res.Lett.,2006,33,L08402
[29] Mitrovica J X,Forte A M.Radial profile of mantle viscosity:results from a joint inversion of convection and post-glacial rebound observables.J.Geophys.Res.,1997,102(B2) :2751～2769
[30] Peltier W R.Global glacial isostasy and the surface of the ice age earth:the ICE-SG(VM2) Model and GRACE.Annual Review of Earth and Planetary Science,2004,32:111～149
[31] Center for Space Research,The University of Texas at Austin.GRACE L-2 products-version UTCSR RL-04． ftp://podaac.jpl.nasa.gov/pub/grace/data/L2/csr/,2010
[32] Center for Space Research,The University of Texas at Austin.Release notes for GRACE L-2 products-version UTCSR RL-04． ftp://podaac.jpl.nasa.gov/pub/grace/doc/ReleaseNotes_csr_RL04． txt,2010
[33] Bettadpur S.GRACE level-2 gravity field product user handbook.ftp://podaac.jpl.nasa.gov/pub/grace/doc/L2UserHandbook_v2． 3． pdf,2007
[34] Chambers D P.Evaluation of new GRACE time variable gravity data over the ocean.Geophys.Res.Lett.,2006,33:L17603
[35] 詹金刚,王勇,程永寿.中国近海海平面变化特征分析.地球物理学报,2009,52(7) :1725～1733 Zhan J G,Wang Y,Cheng Y S.The analysis of China sea level change.Chinese J.Geophys.(in Chinese),2009,52(7) :1725～1733
[36] Yan M,Zuo J C,Du L,et al.Sea level variation/change and steric contribution in the East China Sea.Proceedings of the seventeenth International Offshore and Polar Engineering Conference,Lisbon Portugal,2007． 1～4:2377～2382
[37] 丁允辉.海平面变化对中国海工程水位推算的影响[硕士论文].青岛:中国海洋大学研究生院,2005 Ding Y H.The effect of sea level variation on the calculation of engineering water level[Master's thesis](in Chinese).Qingdao:Graduate School of Ocean University of China,2005
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