俯冲带深部应力场的二维弹性有限元数值模拟

基于一些简化的数值模型，根据弹性本构关系，用平面应变有限元方法计算了相变引起的体积变化、板块内部温度差、密度异常及边界力产生的应力场分布情况．数值模拟结果显示，热应力能够解释俯冲带深源地震的应力场方向特征，但解释不了深源地震的深度分布特征；有亚稳态橄榄石存在时密度异常所产生的应力场特征与地震观测结果所显示的应力场特征有所偏离；虽然橄榄石——尖晶石相变体积变化所产生的应力在橄榄石——尖晶石相变过渡区附近有最大值，其数值远远超过温度差和密度异常产生的应力场的最大剪应力数值，但在相变界面附近的区域，主压应力方向垂直于相变界面的方向，与地震观测结果所显示的主压应力的方向不一致．所以，不能用弹性模拟得出的俯冲带温度变化所产生的热应力、俯冲带密度变化所产生的应力、相变体积变化所产生的应力来对深源地震进行简单化的解释． 

2-D ELASTIC FEM SIMULATION ON STRESS STATE IN THE DEEP PART OF A SUBDUCTED SLAB

Based upon some simplified numerical models, we use a 2-D plane strain elastic FEM program to study the distributions of the stress fields produced by phase transformation from olivine to spinel, temperature variation, density difference and boundary action in a piece of subducted slab located in transition zone of the mantle. Thermal stress could explain the fault plane solutions of deep earthquakes, but not the distribution of deep earthquakes. When large extent metastable olivine is included, stress state caused by density differences contradicts with the results of fault plane solutions and with the distribution of deep seismicity. Although the stress produced by volume change of the phase transformation from olivine to spinel dominates the stress state, its main direction is different from the observed results. We conclude that elastic simulation could not explain characteristics of deep seismicity.