Inversion of post-seismic GPS data for effective viscosity of Wenchuan region
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摘要: 利用2009—2011年汶川震区GPS水平速度场数据， 综合考虑汶川震后的余滑模型、 黏弹性松弛模型及用于描述地壳长期运动的弹性块体模型， 采用格网搜索法反演了汶川震区中下地壳的有效黏滞系数. 地壳介质黏滞系数不同是造成震后断层两侧地壳水平运动差异的主要因素. 研究发现， 龙门山断裂带两侧中下地壳介质的黏滞系数差别很大. 龙门山断裂以西川西块体中下地壳(16—40 km)的有效黏滞系数约为7×1019 Pa·s， 而龙门山断裂以西、 岷江断裂以东的岷江地块中下地壳(16—40 km)的有效黏滞系数约为1020 Pa·s， 比川西地块大. 龙门山断裂以东的四川盆地中下地壳(16—40 km)的有效黏滞系数约为7×1022 Pa·s， 比岷江地块和川西地块均大， 呈现极强的刚性运动特点. 此外， 由于同震破裂滑脱面的存在， 震中附近的余滑效应比较显著.Abstract: Combing with the after-slip model, the viscoelastic relaxation model and the elastic block model, this paper estimates the effective viscosity of middle to lower crust by fitting the observed GPS velocity in Wenchuan region in the period of 2009—2011. The results indicate that the effective viscosity of middle to lower crust in Wenchuan region varies largely for the two sides of Longmenshan fault zone, which impacts the kinematics’patterns of the crust in the study region. The effective viscosity of lower crust is about 7×1019 Pa·s to the western side of Longmenshan fault except the Minjiang block which contains a slightly stronger middle to lower crust; the effective viscosity is about 7×1022 Pa·s to the eastern side of Longmenshan fault, showing a strong rigid motion characteristics. In addition, the after-slip effect is notable because of the existing coseismic rupture surface.
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Keywords:
- effective viscosity /
- GPS /
- post-seismic deformation /
- Wenchuan earthquake
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图 1 观测的GPS水平形变场(黑色箭头)与模拟的GPS形变场(红色箭头)． 红色和黑色圆圈表示相应的误差椭圆
Figure 1. The measured (black arrows) and modeled (red arrows) GPS velocities where black and red circles denote corresponding errors
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图 2 残差加权平方和VTPV (Δ)与中下地壳黏滞系数η之间关系
Figure 2. Residuals VTPV (Δ) versus effective viscosity η of middle to lower crust
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图 3 龙门山断裂以东四川盆地残差加权平方和VTPV (ΔE)与中下地壳黏滞系数ηE之间关系
Figure 3. Residuals VTPV (ΔE) versus effective viscosity ηE for Sichuan basin
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图 4 门山断裂以西川西块体残差加权平方和VTPV (ΔW)与中下地壳黏滞系数ηW之间关系
Figure 4. Residuals VTPV (ΔW) versus effective viscosity ηW to the west of Longmenshan fault
表 1 汶川地震的地壳介质模型
Table 1 Parameters of crustal material model for Wenchuan earthquake
深度 /km vP /(km·s-1 ) vS /(km·s-1) ρ /(103 kg·m-3) η /(1019 Pa·s) 0—16 5.89 3.45 2.81 0 16—40 6.35 3.75 2.90 7 
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表 2 汶川地震震后龙门山断裂的余滑参数
Table 2 After-slip parameters of Longmenshan fault after Wenchuan earthquake
龙门山 断裂 α /° δ /° ΔVN /(mm·a-1) ΔVE /(mm·a-1) ΔVV /(mm·a-1) Us /(mm·a-1) Ud /(mm·a-1) Uo /(mm·a-1) 西南段 229 75 -4.72 13.51 105 7.10 102.80 36.34 东北段 229 65 -1.16 8.61 35 5.74 35.04 16.25
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表 3 龙门山断裂以东与观测GPS速度场最佳拟合结果
Table 3 The best-fitting-observed results of GPS velocity inversion in eastern side of Longmenshan fault
单位： mm·a-1 台站 VplaE VplaN VrelE VrelN VssE VssN VmodE VmodN VobsE rvelE VobsN rvelN H009 6.384 -1.968 0 0 -0.006 0.01 6.378 -1.958 3.03 -3.36 8.36 3.12 H011 6.373 -1.964 0 -0.001 0.002 0.006 6.375 -1.959 8.25 7.17 14.47 5.01 H012 6.363 -1.956 0 0 0.03 0.122 6.393 -1.834 11.38 -2.12 10.78 3.93 H043 6.351 -1.941 0 0 1.022 1.309 7.373 -0.632 7.1 -2.31 11.67 4.09 H048 6.344 -1.933 0 0 0.979 1.289 7.323 -0.644 6.74 1.6 8.41 3.15 H058 6.335 -1.925 0 0 4.417 5.929 10.752 4.004 3.51 -3.38 8.87 3.15 H060 6.328 -1.91 0 0 13.085 14.584 19.413 12.674 2.21 -4.2 14.85 4.92 H081 6.301 -1.907 0 0 0.628 0.655 6.929 -1.252 6.94 2.57 8.63 3.09 H072 6.314 -1.897 -0.001 0 3.839 3.924 10.152 2.027 5.49 -4.45 6.51 2.46 JB24 6.336 -1.968 0 0 0.091 0.164 6.427 -1.804 -0.86 -3.64 6.64 2.49 F375 6.355 -1.98 0 0 0.022 0.045 6.377 -1.935 -7.89 -2.52 6.19 2.39 F378 6.372 -1.988 0 0 0.006 0.006 6.378 -1.982 4.54 1.02 7.14 2.71 H009 6.384 -1.968 0 0 -0.006 0.01 6.378 -1.958 3.03 -3.36 8.36 3.12 注： rvelN和rvelE分别表示观测GPS速度北向和东向残差.
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表 4 龙门山断裂以西与观测GPS速度场最佳拟合结果
Table 4 The best-fitting observed results of GPS velocity inversion to the western side of Longmenshan fault
单位： mm·a-1 台站 VplaE VplaN VrelE VrelN VssE VssN VmodE VmodN VobsE rvelE VobsN rvelN H001 10.553 2.377 0.05 0.029 -0.007 0.008 10.595 2.413 5.65 1.8 6.8 2.65 H003 9.971 -0.45 0.146 0.37 -0.039 0.039 10.078 -0.04 5.88 -1.62 5.39 2.18 H005 11.185 0.23 0.193 0.28 -0.031 0.031 11.347 0.54 8.12 -4.44 5.36 2.16 H006 10.94 -0.5 0.202 0.45 -0.045 0.045 11.097 -0.003 9.18 2 5.86 2.34 H007 12.244 1.55 0.034 -0.02 -0.009 0.01 12.269 1.535 7.78 -2.02 5.75 2.26 H010 14.509 -0.637 -0.21 -0.31 -0.047 0.048 14.252 -0.9 16.83 7.81 13.66 4.65 H019 10.933 -2.575 0.02 0.82 -0.097 0.097 10.856 -1.657 8.18 -3.96 5.59 2.21 H021 12 -1.581 0.229 0.98 -0.094 0.094 12.134 -0.507 8.64 0.48 6.25 2.43 JB33 12.457 -3.777 -0.23 1.23 -0.188 0.195 12.039 -2.352 16.95 -6.61 6.89 2.72 H024 12.588 -2.986 -0.11 1.4 -0.182 0.185 12.296 -1.4 14.35 -4.87 7.5 2.97 H022 13.248 -2.0488 0.237 1.8 -0.184 0.184 13.301 -0.064 13.15 3.81 5.51 2.22 H025 13.494 -4.843 -0.35 1.26 -0.257 0.279 12.887 -3.304 15.82 -6.74 5.81 2.31 H031 13.974 -7.037 -0.29 0.58 -0.2 0.236 13.484 -6.221 15.11 -3.59 3.59 1.47 H030 14.489 -4.425 -0.248 2 -0.381 0.418 13.86 -2.007 14.5 -8.25 5.87 2.27 H034 15.162 -4.146 0.025 2.8 -0.519 0.575 14.668 -0.771 18.54 -1.69 5.29 2.1 H040 17.032 -9.115 0.14 0.07 -0.148 0.213 17.024 -8.832 14.3 -3.82 4.03 1.59 JB34 17.167 -7.492 0.18 0.34 -0.287 0.377 17.06 -6.775 19 -4.2 8.1 3.36 H045 17.779 -4.428 -1.6 1 -1.274 1.274 14.905 -2.154 33.18 -5.68 5.83 2.31 H046 16.72 -6.638 0 0.84 -0.385 0.482 16.335 -5.317 29.96 13.08 6.05 2.49 H047 17.888 -7.985 0.362 0.18 -0.246 0.336 18.003 -7.469 24.47 -4.19 6.53 2.67 H049 19 -4.24 -0.1 -4.5 4.075 4.841 22.968 -3.899 15.32 -4.02 9.8 3.66 H050 19.17 -5.524 0.8 -1.5 -0.948 0.954 19.023 -6.07 9.3 -9.66 7.96 3.03 H384 20.777 -6.157 -0.18 -0.34 0.346 1.295 20.942 -5.203 8.93 -9.41 17.04 5.76 注：rvelN和rvelE分别表示观测GPS速度与模拟GPS速度北向和东向残差．
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