Collaborative Research: A global examination of the subduction zone flow field from seismic anisotropy

合作研究：从地震各向异性对俯冲带流场进行全球检验

• 批准号: 0911151
• 负责人: Laurent Montesi
• 金额: $ 14.99万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911151&HistoricalAwards=false
• 关键词: Collaborative; Research; global; examination; subduction

What happens when a tectonic plate plunges back into the Earth?s interior at a subduction zone? Surprisingly, this simple question remains one of the fundamental unsolved problems in earth science. The flow pattern around the downgoing plate (often called the slab) is typically studied using seismic anisotropy, a property of the mantle that can be detected by recording seismic waves. In particular, measurements of shear wave splitting can be used to characterize seismic anisotropy in subduction zones. It is increasingly clear from such measurements that the simplest model of two-dimensional corner flow above the slab and entrained flow beneath the slab is likely incorrect. However, consensus on an alternative model has not been forthcoming. In this project, we will undertake a global survey of shear wave splitting observations with the goal of understanding what controls the mantle flow field in subduction zone regions. To do this, we will identify parameters that describe subduction zone dynamics that appear to exert a first-order control on shear wave splitting. Preliminary work has identified systematic variations in anisotropy both above and below the slab linked with the magnitude of trench migration velocity. This has led to the hypothesis that 3-D flow dominates beneath the slab and interacts with 2-D corner flow in the mantle wedge. In addition to a systematic evaluation of seismic anisotropy in subduction zones, we will construct laboratory and numerical models of mantle flow above and below the slab to identify diagnostic features of the flow field in shear wave splitting measurements and to explore the implications of our model for mantle dynamics. This project constitutes an interdisciplinary effort to understand and characterize the character of the mantle flow field that accompanies subduction using observations of seismic anisotropy and geodynamical modeling. With the increasing popularity of shear wave splitting as a tool for mapping mantle flow, a copious amount of data from subduction zones is now available. It is timely, therefore, to undertake a global survey of splitting observations with the goal of understanding which subduction parameters (such as convergence velocity, trench migration and curvature, age and spreading history of the downgoing plate, slab dip and morphology, seismicity, arc length, overriding plate thickness and stress, and volcanic production) appear to control the subduction zone flow field. From a preliminary survey, we hypothesize that 3-D flow dominates beneath the slab and that this flow field interacts with 2-D corner flow in the mantle wedge. We will complement our primary observational seismology goals with laboratory and numerical modeling studies. This forward modeling work will be used to validate the predictions of our working model, formulate alternative hypotheses, identify any second-order effects on the flow field, and explore the implications of our working model for larger-scale mantle dynamics. The availability of constraints on anisotropy from many regions around the globe and the combination of seismological observations and laboratory and numerical modeling suggest that a solution to the fundamental problem of interaction between downgoing slabs and the surrounding mantle is within reach.

当构造板坠入俯冲带的地球内部时，会发生什么？令人惊讶的是，这个简单的问题仍然是地球科学中基本的未解决问题之一。通常使用地震各向异性（通常称为地震的特性）来研究下板周围的流动模式（通常称为平板），可以通过记录地震波来检测。特别是，剪切波分裂的测量可用于表征俯冲带中的地震各向异性。从这样的测量值中越来越清楚地表明，在平板上方和平板下方的二维角流的最简单模型可能是不正确的。但是，尚未达成关于替代模型的共识。在这个项目中，我们将对剪切波分裂观测值进行全球调查，目的是了解俯冲带区域中地幔流场的原因。为此，我们将确定描述俯冲区动力学的参数，这些动力学似乎在剪切波分裂上施加一阶控制。初步工作已经确定了与沟槽迁移速度相关的平板上方和下方各向异性的系统变化。这导致了这样的假设：3-D流在平板下方占主导地位，并与地幔楔中的2-D角流相互作用。除了对俯冲带中的地震各向异性进行系统评估外，我们还将构建平板上方和下方地幔流的实验室和数值模型，以识别剪切波分裂测量中流场的诊断特征，并探索我们模型对地幔动力学的含义。该项目构成了跨学科的努力，以理解和表征使用地震各向异性和地球动力学建模的观测值伴随俯冲场的特征。随着剪切波拆分作为映射地幔流的工具的日益普及，现在可以使用大量数据。因此，及时进行全球对分裂观测的调查，以了解哪些俯冲参数（例如收敛速度，沟通式迁移和弯曲和弯曲，年龄以及下板的年龄和延伸历史，平板倾角和形态，Seisstorgy，Seisstrology，Seissicity，Seissicities，Seissicities，Seissicities，Seissicition，seasicition，arc长度长度，弧形长度，板块的厚度和压力，以及覆盖的范围，以及浮动的生产。从初步调查中，我们假设3-D流在平板下方占主导地位，并且该流场与地幔楔中的2-D角流相互作用。我们将通过实验室和数值建模研究来补充我们的主要观察性地震学目标。这项正向建模工作将用于验证我们的工作模型的预测，提出替代假设，确定对流场的任何二阶影响，并探讨我们工作模型对大型地幔动力学的含义。全球许多地区对各向异性的约束以及地震学观察和实验室和数值建模的结合的可用性表明，解决了下去板与周围地幔之间相互作用的基本问题的解决方案。