1990年青海共和7.0级地震震后垂直形变研究
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摘要
根据1990年青海共和地震震后地表垂直形变,通过模型拟合得到了支配共和地区震后形变场时空演化的形变源及其力学机制.分析穿过断层的震前1期和震后6期水准数据,结果表明震后垂直形变具有以下特征:①震后震区上盘继续发生继承性的大幅度上升,其中震后头一年上升速率最大;②震后上升区范围显著,范围随时间变化不大,但较同震形变上升区范围增大;③震后相邻测站高差观测值的时间序列明显具有对数衰减特征或指数衰减特征,衰减特征时间分别为0.165年和1.344年.本文还发展了一个利用水准数据与连续介质位错模型研究震后形变机制的新方法.该方法用相邻水准点之间的原始高差观测值而非它们相对参照点的积分值来约束连续介质位错模型,可以有效减少误差累积带来的偏差并充分利用观测数据.利用这一方法的初步分析结果表明,断层震后滑移和介质黏弹性松弛共同导致了共和地震震后形变.前者表现为发生在断层面及其延伸部分的滑移,特别是位于主破裂上方沉积层内的滑移;后者则表现为下地壳与上地幔内的黏弹性松弛,黏滞系数为1020Pa.s量级.
We model leveling deformation data observed on the Earth's surface following the 1990 MS7.0 Gonghe earthquake,Qinghai province,to infer the postseismic deformation source and mechanism. By analyzing the leveling data observed one epoch before and six epochs after the quake across the coseismic fault,we find the following characteristics of the postseismic deformation:① the near field on the hanging-wall side of the coseismic rupture continued to uplift at large scale after the earthquake,with the highest rate measured in the first year; ② the scope of postseismic uplifting region was larger than that of coseismic uplifting,but did not change during the postseismic deformation period; ③ the time series of elevation change between two adjacent benchmarks can be modeled by a logarithmic relaxation function or an exponential relaxation function,and the relaxation time constants are 0.165 years and 1.344 years,respectively. In the paper we also introduce a new method using leveling data and dislocation model in continuum to investigate the source and mechanism of postseismic deformation. The new method utilizes the raw observations of elevation differences between two adjacent benchmarks,not their integrals with respect to a reference point,to constrain a dislocation model in a continuum,effectively reducing biases introduced from cumulative errors due to data integration and making full use of the leveling data. Our preliminary result suggests that two mechanisms operate simultaneously to produce the postseismic vertical deformation of the surface:(a) afterslip on the coseismic rupture fault plane of the main shock and its peripheral extensions,particularly upward to the sediment layer above the main rupture,and (b) viscoelastic relaxation of the lower crust and upper mantle,with a viscosity in the order of 1020 Pa·s.
We model leveling deformation data observed on the Earth's surface following the 1990 MS7.0 Gonghe earthquake,Qinghai province,to infer the postseismic deformation source and mechanism. By analyzing the leveling data observed one epoch before and six epochs after the quake across the coseismic fault,we find the following characteristics of the postseismic deformation:① the near field on the hanging-wall side of the coseismic rupture continued to uplift at large scale after the earthquake,with the highest rate measured in the first year; ② the scope of postseismic uplifting region was larger than that of coseismic uplifting,but did not change during the postseismic deformation period; ③ the time series of elevation change between two adjacent benchmarks can be modeled by a logarithmic relaxation function or an exponential relaxation function,and the relaxation time constants are 0.165 years and 1.344 years,respectively. In the paper we also introduce a new method using leveling data and dislocation model in continuum to investigate the source and mechanism of postseismic deformation. The new method utilizes the raw observations of elevation differences between two adjacent benchmarks,not their integrals with respect to a reference point,to constrain a dislocation model in a continuum,effectively reducing biases introduced from cumulative errors due to data integration and making full use of the leveling data. Our preliminary result suggests that two mechanisms operate simultaneously to produce the postseismic vertical deformation of the surface:(a) afterslip on the coseismic rupture fault plane of the main shock and its peripheral extensions,particularly upward to the sediment layer above the main rupture,and (b) viscoelastic relaxation of the lower crust and upper mantle,with a viscosity in the order of 1020 Pa·s.
引文
李旭,陈运泰.1996.用长周期地震体波波形资料反演1990年青海共和地震的震源过程[J].地震学报,18(3):279-286.
任金卫,王敏.2005.GPS观测的2001年昆仑山口西MS8.1级地震地壳变形[J].第四纪研究,25(1):34-44.
陶玮,沈正康,万永革,单新建,马超.2007.根据2001年MW7.8可可西里强震InSAR同震测量结果反演东昆仑断裂两侧地壳弹性介质差异[J].地球物理学报,50(3):744-751.
涂德龙.1990.1990年4月26日共和6.9级地震地质构造背景[J].高原地震,2(3):15-20.
王庆良,巩守文,张希,祝意青.1997.由1990年共和7.0级地震震后垂直形变求得的地球介质有效弛豫时间和黏滞系数[J].地震学报,19(5):480-486.
王庆良,王建华,朱桂枝,崔笃信,王文萍,陈忠实,宋兆山.2004.东昆仑山断裂带及昆仑山口西8.1级地震垂直形变研究[J].地震地质,26(2):273-280.
王文萍,王庆良.1999.利用遗传算法和最小二乘联合反演共和地震位错参数[J].地震学报,21(3):285-290.
Chen Y T,Xu L S,Li X,Zhao M.1996.Source process of the1990Gonghe,China,earthquake andtectonic stress fieldin the Northeastern Qinghai-Xizang(Tibetan)Plateau[J].Pure Appl Geophys,146(3/4):697-715.
Hideki U,Masakazu O,Haruo S.2003.Postseismic crustal deformation following the1993Hokkaido Nanseioki earth-quake,northern Japan:Evidence for a low-viscosity zone in the uppermost mantle[J].J Geophys Res,108(B3):2151.
Marone C,Scholz C H,Bilham R.1991.On the mechanics of earthquake afterslip[J].J Geophys Res,96(B5):8441-8452.
Nur A,Mavko G.1974.Postseismic viscoelastic rebound[J].Science,183(4212):204-206.
Okada Y.1985.Surface deformation due to shear and tensile faults in a half space[J].Bulle Seism Soc Amer,75(4):1135-1154.
Pollitz F F.1997.Gravitational viscoelastic postseismic relaxation on a layered spherical earth[J].J Geophys Res,102(B8):17921-17941.
Robert R.1986.Evidence for postseismic viscoelastic relaxation following the1959M=7.5Hebgen Lake MontanaEarthquake[J].J Geophys Res,91:9488-9494.
Shen Z K,Jackson D,Feng Y,Cline M,Ki m M,Feng P,Bock Y.1994.Postseismic deformationfollowingthe Landersearthquake,California,28June,1992[J].Bull Seism Soc Amer,84(3):780-791.
Shi XJ,Wen D,Bao X Y,Li C B,Huang Y.2006.Application of rock creep experi ment in calculating the viscoelasticparameters of earth medium[J].Science in China(Series D),49(5):492-498.
Ueda H,Ohtake M,Sato H.2001.Afterslip on the plate interface following the1978Miyagi-Oki,Japan,earthquake,as revealed fromgeodetic measurement data[J].Tectonophysics,338(1):45-57.
Wang R,Lorenzo-Martin F,Roth F.2006.PSGRN/PSCMP-a newcode for calculating co-and post-seismic deformation,geoid and gravity changes based on the viscoelastic-gravitational dislocation theory[J].Comput Geosci,32(4):527-541.
任金卫,王敏.2005.GPS观测的2001年昆仑山口西MS8.1级地震地壳变形[J].第四纪研究,25(1):34-44.
陶玮,沈正康,万永革,单新建,马超.2007.根据2001年MW7.8可可西里强震InSAR同震测量结果反演东昆仑断裂两侧地壳弹性介质差异[J].地球物理学报,50(3):744-751.
涂德龙.1990.1990年4月26日共和6.9级地震地质构造背景[J].高原地震,2(3):15-20.
王庆良,巩守文,张希,祝意青.1997.由1990年共和7.0级地震震后垂直形变求得的地球介质有效弛豫时间和黏滞系数[J].地震学报,19(5):480-486.
王庆良,王建华,朱桂枝,崔笃信,王文萍,陈忠实,宋兆山.2004.东昆仑山断裂带及昆仑山口西8.1级地震垂直形变研究[J].地震地质,26(2):273-280.
王文萍,王庆良.1999.利用遗传算法和最小二乘联合反演共和地震位错参数[J].地震学报,21(3):285-290.
Chen Y T,Xu L S,Li X,Zhao M.1996.Source process of the1990Gonghe,China,earthquake andtectonic stress fieldin the Northeastern Qinghai-Xizang(Tibetan)Plateau[J].Pure Appl Geophys,146(3/4):697-715.
Hideki U,Masakazu O,Haruo S.2003.Postseismic crustal deformation following the1993Hokkaido Nanseioki earth-quake,northern Japan:Evidence for a low-viscosity zone in the uppermost mantle[J].J Geophys Res,108(B3):2151.
Marone C,Scholz C H,Bilham R.1991.On the mechanics of earthquake afterslip[J].J Geophys Res,96(B5):8441-8452.
Nur A,Mavko G.1974.Postseismic viscoelastic rebound[J].Science,183(4212):204-206.
Okada Y.1985.Surface deformation due to shear and tensile faults in a half space[J].Bulle Seism Soc Amer,75(4):1135-1154.
Pollitz F F.1997.Gravitational viscoelastic postseismic relaxation on a layered spherical earth[J].J Geophys Res,102(B8):17921-17941.
Robert R.1986.Evidence for postseismic viscoelastic relaxation following the1959M=7.5Hebgen Lake MontanaEarthquake[J].J Geophys Res,91:9488-9494.
Shen Z K,Jackson D,Feng Y,Cline M,Ki m M,Feng P,Bock Y.1994.Postseismic deformationfollowingthe Landersearthquake,California,28June,1992[J].Bull Seism Soc Amer,84(3):780-791.
Shi XJ,Wen D,Bao X Y,Li C B,Huang Y.2006.Application of rock creep experi ment in calculating the viscoelasticparameters of earth medium[J].Science in China(Series D),49(5):492-498.
Ueda H,Ohtake M,Sato H.2001.Afterslip on the plate interface following the1978Miyagi-Oki,Japan,earthquake,as revealed fromgeodetic measurement data[J].Tectonophysics,338(1):45-57.
Wang R,Lorenzo-Martin F,Roth F.2006.PSGRN/PSCMP-a newcode for calculating co-and post-seismic deformation,geoid and gravity changes based on the viscoelastic-gravitational dislocation theory[J].Comput Geosci,32(4):527-541.
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