Evaluating the Trench Parallel Flow Hypothesis with Numerical Models of Convection

EAR-0838026：用数值模式评估海沟平行流动假说斯科特·D·金当一些地震波(横波)穿过地球内部上方200公里的S时，它们可以分解成以不同速度传播的两个正交分量。这一信息可用于预测地幔这一部分的流动模式，是俯冲带附近地幔物质平行于俯冲大洋板块流动这一假说背后的关键观察结果。使用数值模型，我们将测试最近开发的实验室流体储罐实验，以模拟这种流动和来自地球的地震观测。我们的目标是确定在什么条件下在计算中观察到海沟平行流动，从而限制俯冲板块和地幔中的强度和化学变化。这一提议将检验这样一种假设，即在俯冲带，无论是俯冲板块上方还是下方，剪切波分裂观测都要求地幔流动的主要成分平行于海沟和板块的走向。首先，我们将演示我们可以用三维数值模型重现实验室的水槽实验。接下来，我们将通过解决以下问题来检验板块平行流假说：1)板块平行流是否依赖于海沟迁移速度(即板块是否回滚)？2)俯冲带附近的地幔流动模式在多大程度上取决于板块流变性？3)橄榄石到瓦德利石(410公里不连续)和环木岩到钙钛矿加钙钛矿(660公里不连续)的相变对于板块平行流是必要的吗？最后，4)下地幔粘度增加10-30倍对于能够产生板块平行流是必要的吗？我们将根据我们的数值结果计算有限应变，以便与地震观测结果进行比较。我们预计，较强的板块更有可能导致板块平行流动，因为较强的板块更能抵抗变形，因此地幔将被迫绕着板块流动，而较弱的板块更有可能响应地幔流动而变形，因此不需要绕着板块流动。我们还预计，环木岩向钙钛矿加铁方镁石的相变和下地幔顶部粘度的增加都会增加板条平行流的成分。

EAR-0838026: Evaluating the Trench Parallel Flow Hypothesis with Numerical Models of ConvectionScott D. KingWhen some seismic waves (shear waves) propagate through the upper 200 km of the Earth?s interior, they can be resolved into two orthogonal components that travel at different velocities. This information can be used to predict the pattern of flow in this part of the mantle and, is a key observation behind the hypothesis that mantle material flows parallel to the subducting oceanic plate in the vicinity of subduction zones. Using numerical models we will test recent laboratory fluid tank experiments developed to model this flow and the seismic observations from Earth. Our goal is to identify under what conditions trench parallel flow is observed in the calculations and thus place constraints on the strength and chemistry variations in the subducting slab and mantle. This proposal will test the hypothesis that shear wave splitting observations in subduction zones, both above and below the subducting slab, require that the dominant component of mantle flow that is parallel to the strike of the trench and slab. First we will demonstrate that we can reproduce laboratory tank experiments with a three dimensional numerical model. Next we will test the slab parallel flow hypothesis by addressing the following questions: 1) is slab parallel flow dependent on trench migration rate (i.e., whether or not slabs roll back)?; 2) to what extent does the pattern of mantle flow in the vicinity of a subduction zone depend on slab rheology?; 3) are the olivine to wadsleyite (410 km discontinuity) and the ringwoodite to perovskite plus ferropericlase (660 km discontinuity) phase transformations necessary for slab parallel flow?; and finally 4) is an increase in viscosity in the lower mantle by a factor of 10-30 essential to be able to generate slab parallel flow? We will calculate the finite strain from our numerical results to compare with the seismic observations. We anticipate that strong slabs are more likely to lead to slab parallel flow because strong slabs are more able to resist deforming and hence the mantle will be forced to flow around the slab while weaker slabs are more likely to deform in response to mantle flow and flow around a the slab will not be necessary. We also anticipate that the ringwoodite to perovskite plus ferropericlase phase transformation and an increase in viscosity at the top of the lower mantle will both increase the component of slab parallel flow.