Crustal isostasy model and strong earthquakes in the Tibetan Plateau and its surroundings
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摘要: 青藏高原作为中国大陆强震活动的主体区，不但构造变形历史复杂，而且高原内部与周边块体之间的重力异常差异也十分显著。本文基于EGM2008重力模型，计算得到了青藏高原及周边地区的区域布格重力异常和艾里均衡重力异常；并依据复合均衡模型原理，以Crust1.0地壳模型中莫霍面的深度为参考，反演得到了地壳剩余密度的分布，该结果适用于研究地壳横向密度的差异；最后，将反演结果与弹性板均衡理论模型反演得到的岩石层有效弹性厚度进行对比，结果表明，青藏高原与周边地块之间的地壳力学特性和平均密度存在显著差异，为强震孕育提供了动力学背景。以此为依据，可为潜在强震危险区位置的判断提供参考。Abstract: The majority of earthquakes in Chinese mainland focused on the Tibetan Plateau and its surroundings, where not only associated with the complex tectonic deformation history, but also have a significant gravity anomaly characteristic. In this paper, we employed the EGM2008 gravity model, and computed the regional Bouguer and Airy isostasy gravity anomaly in the Tibetan Plateau and its surroundings. On the theory of combined isostasy model, we refer to the Moho depth from the Crust1.0 model, and inverse the crustal residual density distribution, which can be used to study the lateral density difference. At last, we compared with the lithospheric effective elastic thickness derived from the elastic plate model. The results show that the mechanical property and average density have a significant difference between the crust blocks of the Tibetan Plateau and surroundings, which provided a geodynamic background for the great earthquake preparation. The results could also provide a reference for estimating potential earthquake hazard locations.
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Keywords:
- gravity inversion /
- gravity anomaly /
- earthquake /
- combined isostasy model /
- Tibe-tan Plateau
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图 1 青藏高原周缘地区主要构造和强震活动 （图中的构造参考Taylor，Yin，2009）
Figure 1. The tectonic background and seismicity in the Tibetan Plateau and its surrounding（The tectonics in this map is after Taylor，Yin，2009）
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图 2 研究区布格重力异常 （a） 和艾里均衡重力异常 （b）
Figure 2. The Bouguer （a） and isostatic （b） gravity anomaly in the studied area
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图 3 复合均衡 （a） 和弹性板均衡 （b） 模型示意图
ρc，ρm，Te分别为地壳密度，地幔密度和岩石圈有效弹性厚度（修改自Forsyth，1985）
Figure 3. The sketch map of the combined （a） and flexural isostatic （b） model
ρc，ρm，Te are the density of crust and mantle and the effective elastic thickness of lithosphere respectively （modified from Forsyth，1985）
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图 4 研究区弹性板厚度Te的特征分布 （引自Jordan，Watts，2005）
Figure 4. The elastic thickness Te map derived by the flexural isostatic model in the studied area （after Jordan，Watts，2005）
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图 5 地震活动 （a）、弹性板厚Te （b）和地壳厚度 （c） 直方图
Figure 5. Histograms of the seismicity （a），elastic thickness Te （b） and crustal thickness （c）
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图 6 基于Crust1.0模型计算得到的复合均衡密度异常分布
Figure 6. The density anomaly distribution derived from the combined isostatic model with Crust1.0 model
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图 7 青藏高原南北向地壳结构、有效弹性厚度Te与重力异常特征
Figure 7. The crustal structure，elastic thickness Te and gravity anomaly across the Tibetan Plateau along with south-north direction
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