球体和黏弹性球体位错理论在尼泊尔M_S8.1地震中的应用与分析
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摘要
本文利用球体位错理论和黏弹性球体位错理论,基于USGS发布的尼泊尔地震断层滑动模型,分别计算该地震造成的同震水平和垂直位移场,两种位错理论计算结果高度吻合,且都与实测GPS同震位移在空间分布和量级上具有较好的一致性,表明了两种位错理论的可靠性和实用性.为了更好的比较和分析这两种位错模型,分别模拟尼泊尔地震同震水平和垂直位移场,两种位错模型模拟结果均验证了尼泊尔地震主要以逆冲滑动为主,该次地震造成的水平位移较大,地震造成的南北方向上的水平位移最突出,且集中在加德满都附近区域;但模拟结果也存在差异,在近场两组结果水平位移和垂直位移差异占同震信号的不足3%,在远场两组结果的水平位移差异占信号的5%～9%左右,而垂直位移差异占信号的比例普遍在10%以上,显示出地球的黏滞性对近场水平同震位移和垂直同震位移影响较小,对远场水平位移影响有限,但是对垂直位移影响较大,即表明在计算远场同震位移时应该考虑地球黏滞性的影响.
Based on spherical dislocation theory,visco-elastic spherical dislocation theory and USGS released the Nepal earthquake fault slip model to calculate surface horizontal and vertical co-seismic displacements caused by the Nepal earthquake, the results show that the calculation results of two kinds of dislocation theory coincide highly, which shows reliability and practicability of the two dislocations theory. Compared with the measured GPS data, it is found that the theoretical values of the two models have good consistency with the measured data in spatial distribution and magnitude. In order to compare and analyze the two models better, using the two kinds of dislocation model that simulate the co-seismic displacement caused by the Nepal earthquake respectively, two sets of simulation results confirm that the Nepal earthquake is mainly thrusting slide,the horizontal displacement caused by this earthquake is large, and the horizontal displacement in the north south direction caused by the earthquake is most prominent and concentrated in the vicinity of Kathmandu;but there are also differences in the simulation results, the difference of the co-seismic horizontal displacement and vertical displacement calculated by the two kinds of model accounts for less than 3% of the co-seismic signal in the near field and the difference of the co-seismic horizontal displacement of the two groups is about 5%～9% in the far field, while the difference of co-seismic vertical displacement calculated by the two models is more than 10% in the far field. It is found that the viscoelasticity of the earth has a smaller influence on the horizontal and vertical co-seismic displacement in the near field area, has a limited influence on the horizontal co-seismic displacement in the far field area, and has great influence on the vertical co-seismic displacement in the far field area.Therefore, the influence of the viscoelasticity of the earth should be considered in the calculation of the co-seismic displacement of the far field.
Based on spherical dislocation theory,visco-elastic spherical dislocation theory and USGS released the Nepal earthquake fault slip model to calculate surface horizontal and vertical co-seismic displacements caused by the Nepal earthquake, the results show that the calculation results of two kinds of dislocation theory coincide highly, which shows reliability and practicability of the two dislocations theory. Compared with the measured GPS data, it is found that the theoretical values of the two models have good consistency with the measured data in spatial distribution and magnitude. In order to compare and analyze the two models better, using the two kinds of dislocation model that simulate the co-seismic displacement caused by the Nepal earthquake respectively, two sets of simulation results confirm that the Nepal earthquake is mainly thrusting slide,the horizontal displacement caused by this earthquake is large, and the horizontal displacement in the north south direction caused by the earthquake is most prominent and concentrated in the vicinity of Kathmandu;but there are also differences in the simulation results, the difference of the co-seismic horizontal displacement and vertical displacement calculated by the two kinds of model accounts for less than 3% of the co-seismic signal in the near field and the difference of the co-seismic horizontal displacement of the two groups is about 5%～9% in the far field, while the difference of co-seismic vertical displacement calculated by the two models is more than 10% in the far field. It is found that the viscoelasticity of the earth has a smaller influence on the horizontal and vertical co-seismic displacement in the near field area, has a limited influence on the horizontal co-seismic displacement in the far field area, and has great influence on the vertical co-seismic displacement in the far field area.Therefore, the influence of the viscoelasticity of the earth should be considered in the calculation of the co-seismic displacement of the far field.
引文
Fu G Y,Gao S H,Zhang G Q,et al. 2015. Gravitational isostasy background and surface deformation response characteristics of the 2015 Nepal MS 8.1 earthquake [J]. Chinese Journal of Geophysics- Chinese Edition (in Chinese),58(6): 1900-1908,doi: 10.6038/cjg20150606.付广裕,高尚华,张国庆,等. 2015. 2015年尼泊尔MS 8.1地震的地壳重力均衡背景与地表形变响应特征[J]. 地球物理学报,58(6): 1900-1908,doi: 10.6038/cjg20150606.
Fu G Y,Sun W K. 2012. Effects of earth’s lateral heterogeneity on co-seismic gravity changes at deformed earth surface and space-fixed point [J]. Chinese J. Geophys. (in Chinese),55(8): 2728-2746,doi: 10.6038/j.issn. 0001-5733. 2012.08.025.付广裕,孙文科. 2012. 地球横向不均匀结构对地表以及空间固定点同震重力变化的影响[J]. 地球物理学报,55(8): 2728-2746,doi: 10.6038/j.issn. 0001-5733. 2012.08.025.
Fu G Y,Sun W K,Fukuda Y,et al. 2010. Coseismic displacements caused by point dislocations in a three-dimensional heterogeneous,spherical earth model [J]. Geophys J. Int.,183(2): 706-726.
Maruyama T. 1964. Statical Elastic Dislocations in an Infinite and Semi-Infinite Medium [J]. Bulletin of the Earthquake Research Institute,University of Tokyo,42: 289-368.
Okada Y. 1985. Surface deformation due to shear and tensile faults in a half-space [J]. Bulletin of the Seismological Society of America,75(4): 1135-1154.
Okubo S. 1991. Potential and gravity changes raised by point dislocations [J]. Geophys J. Int.,105(3): 573-586.
Steketee J A. 1958. On volterra’s dislocations in a semi-infinite elastic medium [J]. Canadian Journal of Physics,36(2): 192-205.
Su X N,Wang Z,Meng G J,et al. 2015. Pre-seismic strain accumulation and co-seismic deformation of 2015 Nepal MS 8.1 earthquake observed by GPS [J]. Chinese Science Bulletin (in Chinese),(22): 2115-2123.苏小宁,王振,孟国杰,等. 2015. GPS观测的2015年尼泊尔MS 8.1级地震震前应变积累及同震变形特征[J]. 科学通报,(22): 2115-2123.
Sun W K. 1992. Potential and Gravity Changes Caused by Dislocations in Spherically Symmetric Earth Models [J]. Bulletin of the Earthquake Research Institute,University of Tokyo,67(2): 89-238.
Sun W K,Okubo S. 1993. Surface potential and gravity changes due to internal dislocations in a spherical earth—I. Theory for a point dislocation [J]. Geophys J. Int.,114(3): 569-592.
Sun W K,Okubo S,Fu G Y. 2006. Green’s functions of coseismic strain changes and investigation of effects of Earth’s spherical curvature and radial heterogeneity [J]. Geophysical Journal International,167(3): 1273-1291.
Tanaka Y,Okuno J,Okubo S. 2006. A new method for the computation of global viscoelastic post-seismic deformation in a realistic earth model (I)-vertical displacement and gravity variation [J]. Geophys J. Int.,164(2): 273-289.
Tanaka Y,Okuno J,Okubo S. 2007. A new method for the computation of global viscoelastic post-seismic deformation in a realistic earth model (II)-Horizontal displacement [J]. Geophys J. Int.,170(3): 1031-1052.
Wang R J,Martin F L,Roth F. 2003. Computation of deformation induced by earthquakes in a multilayered elastic crust-FORTRAN programs EDGRN/EDCMP [J]. Computer & Geosciences,29(2) : 195-207.
Zhang B,Cheng H H,Shi Y L. 2015. Calculation of the co-seismic effect of ms8.1 earthquake,apirl 25,2015,nepal [J]. Chinese Journal of Geophysics (in Chinese),58(5): 1794-1803,doi: 10.6038/cjg20150529.张贝,程惠红,石耀霖. 2015. 2015年4月25日尼泊尔MS 8.1大地震的同震效应[J]. 地球物理学报,58(5): 1794-1803,doi: 10.6038/cjg20150529.
Fu G Y,Sun W K. 2012. Effects of earth’s lateral heterogeneity on co-seismic gravity changes at deformed earth surface and space-fixed point [J]. Chinese J. Geophys. (in Chinese),55(8): 2728-2746,doi: 10.6038/j.issn. 0001-5733. 2012.08.025.付广裕,孙文科. 2012. 地球横向不均匀结构对地表以及空间固定点同震重力变化的影响[J]. 地球物理学报,55(8): 2728-2746,doi: 10.6038/j.issn. 0001-5733. 2012.08.025.
Fu G Y,Sun W K,Fukuda Y,et al. 2010. Coseismic displacements caused by point dislocations in a three-dimensional heterogeneous,spherical earth model [J]. Geophys J. Int.,183(2): 706-726.
Maruyama T. 1964. Statical Elastic Dislocations in an Infinite and Semi-Infinite Medium [J]. Bulletin of the Earthquake Research Institute,University of Tokyo,42: 289-368.
Okada Y. 1985. Surface deformation due to shear and tensile faults in a half-space [J]. Bulletin of the Seismological Society of America,75(4): 1135-1154.
Okubo S. 1991. Potential and gravity changes raised by point dislocations [J]. Geophys J. Int.,105(3): 573-586.
Steketee J A. 1958. On volterra’s dislocations in a semi-infinite elastic medium [J]. Canadian Journal of Physics,36(2): 192-205.
Su X N,Wang Z,Meng G J,et al. 2015. Pre-seismic strain accumulation and co-seismic deformation of 2015 Nepal MS 8.1 earthquake observed by GPS [J]. Chinese Science Bulletin (in Chinese),(22): 2115-2123.苏小宁,王振,孟国杰,等. 2015. GPS观测的2015年尼泊尔MS 8.1级地震震前应变积累及同震变形特征[J]. 科学通报,(22): 2115-2123.
Sun W K. 1992. Potential and Gravity Changes Caused by Dislocations in Spherically Symmetric Earth Models [J]. Bulletin of the Earthquake Research Institute,University of Tokyo,67(2): 89-238.
Sun W K,Okubo S. 1993. Surface potential and gravity changes due to internal dislocations in a spherical earth—I. Theory for a point dislocation [J]. Geophys J. Int.,114(3): 569-592.
Sun W K,Okubo S,Fu G Y. 2006. Green’s functions of coseismic strain changes and investigation of effects of Earth’s spherical curvature and radial heterogeneity [J]. Geophysical Journal International,167(3): 1273-1291.
Tanaka Y,Okuno J,Okubo S. 2006. A new method for the computation of global viscoelastic post-seismic deformation in a realistic earth model (I)-vertical displacement and gravity variation [J]. Geophys J. Int.,164(2): 273-289.
Tanaka Y,Okuno J,Okubo S. 2007. A new method for the computation of global viscoelastic post-seismic deformation in a realistic earth model (II)-Horizontal displacement [J]. Geophys J. Int.,170(3): 1031-1052.
Wang R J,Martin F L,Roth F. 2003. Computation of deformation induced by earthquakes in a multilayered elastic crust-FORTRAN programs EDGRN/EDCMP [J]. Computer & Geosciences,29(2) : 195-207.
Zhang B,Cheng H H,Shi Y L. 2015. Calculation of the co-seismic effect of ms8.1 earthquake,apirl 25,2015,nepal [J]. Chinese Journal of Geophysics (in Chinese),58(5): 1794-1803,doi: 10.6038/cjg20150529.张贝,程惠红,石耀霖. 2015. 2015年4月25日尼泊尔MS 8.1大地震的同震效应[J]. 地球物理学报,58(5): 1794-1803,doi: 10.6038/cjg20150529.