Theoretical Simulation of Co-Seismic and Post-Seismic Deformations and Gravity Changes of Lushan Earthquake
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摘要: 为了研究芦山地震的孕震过程和震源区的长期构造过程以及解释实测的震后形变和重力资料, 采用分层介质模型, 利用数值模拟的方法, 考虑区域流变系数, 计算了地震引起的地表同震、震后的形变和重力变化以及区域内部分GPS与重力连续观测台站的震后形变和重力变化的时间序列.结果表明: 芦山地震的地表同震形变显示出发震断层明显的逆冲特性; 粘弹性松弛效应引起的震后地表形变和重力变化比同震形变和重力变化的范围明显扩大, 但随着粘滞系数的增加, 变化量明显减小; 观测台站的震后变化时变曲线显示震后形变和重力变化在震后50 a间变化显著, 100 a后基本平缓, 趋于稳定; 模拟计算的GPS台站中除了MEIG台和MYAN台以外, 其余台站的震后观测必须考虑粘弹性松弛的影响.Abstract: This paper aims at studying the seismogenic process and long-term tectonic process of the source area and explain the post-seismic deformation and gravity data in Lushan earthquake. Based on the layered half-space model, we calculate the co- and post-seismic surface deformations and gravity changes and their time series gained by the GPS and gravity stations, considering regional rheological coefficients, and using the numerical simulation method. It is found that the surface co-seismic deformation shows seismogenic fault is of obvious thrusting characteristics The range of influence of viscoelastic relaxation is significantly enlarged than that of the co-seismic, but changes gradually reduce with the increase of viscousity coefficients. The time-variable curves of the stations show that post-seismic deformation and gravity changes are significant in 50 years after the earthquake, become gentle after 100 years and tend to be stable. The post-seismic observations of the GPS stations are convinced to consider the effect of viscoelastic relaxation except for the MEIG and the MYAN.
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Key words:
- Lushan earthquake /
- ground deformation /
- gravity change /
- viscoelastic relaxation /
- geophysics
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图 1 芦山地震滑动模型
模型1为刘成利等(2013)给出的模型；模型2为王卫民等(2013)给出的模型
Fig. 1. The slip distribution models of Lushan earthquake
图 2 地表同震形变和重力变化
上图为模型1模拟的结果，下图为模型2模拟的结果；紫色和棕色矩形分别为模型1和模型2断层面在地表的投影.a.地表同震水平形变；b.地表垂直形变；c.同震重力变化
Fig. 2. Surface coseismic deformation and gravity changes
图 3 不同粘滞系数模型引起的10 a后地表水平形变
图a, b, c, d分别对应模型A, 模型B, 模型C, 模型D模拟的结果
Fig. 3. Surface horizontal deformation caused by the models with different viscosity coefficients 10 years after the earthquake
图 4 不同粘滞系数模型引起的10 a后地表垂直形变
图a, b, c, d分别对应模型A、模型B、模型C、模型D模拟的结果
Fig. 4. Surface vertical deformation caused by the models with different viscosity coefficients 10 years after the earthquake
图 5 粘弹性松弛效应引起的震后200 a形变和重力变化
a.总的水平形变；b.总的垂直形变；c.总的重力变化
Fig. 5. The surface deformation and gravity change caused by viscoelastic relaxation 200 years after the earthquake
图 6 10个GPS和6个重力连续观测台站的震后形变和重力变化时间序列
Fig. 6. Time series of the post-seismic deformation and gravity changes of 10 GPS and 6 gravity continuous observation stations
表 1 芦山地震区域分层介质模型参数
Table 1. Parameters of the layered earth model of Lushan earthquake
层位 深度(km) Vp(km/s) Vs(km/s) 密度(kg/m3) 平均泊松比 软沉积层 1 2.5 1.2 2 100 硬沉积层 1 4.0 2.1 2 400 上地壳 20 6.1 3.5 2 750 0.26 中地壳 20 6.3 3.6 2 800 下地壳 4 7.2 4.0 3 100 地壳以下 ∞ 8.0 4.6 3 350 0.25 
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表 2 GPS连续观测台站同震形变模拟结果与实测结果的比较
Table 2. Comparison of the simulated coseismic deformation with the measured results at GPS stations
GPS台站 经向形变(mm) 纬向形变(mm) 垂向形变(mm) 观测结果 模拟结果 观测结果 模拟结果 观测结果 模拟结果 LESH -2.7(±1.2) -2.064 0 0.8(±1.0) 1.842 00 0.3(±4.9) 0.028 96 LUZH -0.5(±0.6) -0.299 4 -0.7(±0.5) 0.183 50 3.9(±2.7) 0.055 11 MEIG -1.4(±1.2) -0.118 2 -0.3(±1.1) 0.195 30 -0.4(±5.4) -0.056 94 MYAN -0.5(±1.1) -0.124 8 0.1(±1.0) 0.010 71 -1.4(±4.7) -0.091 12 QLAI -11.6(±1.0) -3.941 0 0.8(±0.9) 2.540 00 -4.9(±4.1) -0.790 10 ROXI -0.1(±1.2) -0.985 9 -0.5(±1.1) 0.607 50 -4.3(±5.8) 0.101 90 YAAN -7.0(±1.1) -3.283 0 6.4(±1.0) 0.873 30 -3.5(±4.5) -1.207 00 注: 括号中数字表示观测误差；模拟结果均为采用模型1计算得到.
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表 3 成都台和姑咱台同震重力变化模拟结果与实测结果的比较
Table 3. Comparison of the simulated coseismic gravity changes with the measured results at Chengdu station and Guza station
重力台站 模拟的同震重力变化(10-8 m·s-2) 实测同震重力变化(10-8 m·s-2) 成都台 0.10(±15) 0 姑咱台 0.03(±15) -10 注: 括号中数字表示观测误差；模拟结果均为采用模型1计算得到.
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