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逆冲断层产状对跨断层短水准影响
岳冲
中国地震局地质研究所 地震动力学国家重点实验室
摘要:
文章针对地震前跨断层水准不同的反应形式,构建垂直于龙门山地区含不同地壳分层、不同断层产状的二维有限元模型,通过接触分析及粘弹性有限元模拟,得到在相同约束条件下断层产状对地表跨断层短水准观测的影响,模拟结果显示:随断层水平投影距离的增加,断层面倾角固定(模型1)的模型,地表水准累积位移逐渐增大,但当水平投影距离大于20km后,断层倾角的减小对地表水准累积位移结果影响显著降低,地表水准累积位移维持在1.5m左右;而“铲式”断层的模型(模型2)在投影距离小于20km时,“铲式”断层构造阻碍了断层面的滑动,其水准变化速率仅为模型1的一半,跨断层水准测量对区域应力增强的反映能力进一步削弱,但当水平投影距离大于25km后,地表水准累积位移明显增加,最大水准位移达到1.75m;等效应力的结果显示“铲式”断层构造在水平投影距离为10km时引发等效应力陡增变化,且在10-20km投影距离之间积累更高等效应力值,进而在断层面底部和高低倾角转换区附近形成高应力与低应力差异区。
关键词:  跨断层短水准  有限元  铲式构造  等效应力
DOI:
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基金项目:中国地震台网中心青年科技基金(QNJJ201801);国家重点研发计划(2018YFC0807000)
The Influence of Thrust Fault Attitude on Cross-fault Short Level
yuechong
Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration
Abstract:
The paper aims for the different forms of cross-fault short level before earthquakes. 2D finite element models with different crustal stratification and fault attitude are built perpendicular to Longmen Shan Fault zone. By contact analysis and viscoelastic finite element method, the influence of fault attitude on cross-fault short level is obtained under the same constraint condition, the results show: with the increase of the horizontal projection distance of the fault, the cumulative displacements of surface level increase gradually in the models which have a fixed dip angle (model 1). But when the horizontal projection distance exceed 20 km, the influence of fault dip angle reduction on the cumulative displacements of surface level will be decreased significantly, and the cumulative displacements of surface level are maintained at about 1.5m. However, in the listric fault models (model 2), when the projection distance is less than 20km, the listric fault structure impedes the sliding of fault plane. The level change rate is only half of model 1, as a result, the ability to reflect the regional stress enhancement by cross-fault short level is further weakened. But when the horizontal projection distance exceeds 25 km, the cumulative displacements of surface level significantly increased, the maximum result reaches 1.75m. The results of equivalent stress show that the listric fault structure causes a sudden increase in equivalent stress when the horizontal projection distance is 10km, higher equivalent stress values are accumulated between 10-20km projection distance, and then high and low stress difference zones are formed at the bottom of the fault plane and near the conversion zone of low and high dip angles.
Key words:  cross-fault short-level  finite element  listric fault structure  equivalent stress