Observationally Constrained High Resolution Dynamics of the Present-Day Lithosphere-Mantle System

当今岩石圈-地幔系统的观测约束高分辨率动力学

• 批准号: 0911300
• 负责人: William Holt
• 金额: $ 23.3万
• 依托单位: SUNY at Stony Brook
• 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 2012-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911300&HistoricalAwards=false
• 关键词: Observationally; Constrained; Resolution; Dynamics; Present

One of the most challenging problems in geophysics is the quantification of stresses and rheology of the Earth's plates and plate boundary zones. We address this problem through a comprehensive global treatment of the lithosphere/mantle convection system. We first solve the depth-integrated 3-D force-balance equations (using thin sheet approximation) for the lithosphere, where the effective body force inputs are: (1) the horizontal variations in depth integrated vertical stress (gravity potential energy differences - GPE) and (2) the horizontal and radial tractions applied to the base of the lithosphere, associated with large-scale mantle circulation. GPE estimates rely on accurate (seismically-defined) crustal and upper mantle structure. Mantle circulation models satisfy plate motions, geoid, and dynamic topography. Plate motions are self-generated, and not imposed. Convection models have both radial and lateral viscosity variations, and are driven by deeper density buoyancies, inferred from tomography and history of subduction. Modeling performed to date has provided an unprecedented quality of fit between model deviatoric stress fields and stress indicators; the GPE differences calibrate the magnitudes of deviatoric stress, and the observationally - constrained modeling has placed limits on the magnitude and distribution of tractions that exist at the base of the lithosphere. This modeling of the lithosphere system, therefore, plays an important role in constraining convection models as well. We are also calculating forward dynamic models of the lithosphere that predict the full horizontal velocity gradient tensor field (which can be compared with GPS measurements), along with the deviatoric stress field. The forward modeling, which incorporates anisotropic treatment within transform fault zones, enables us to refine our estimates of depth integrated effective viscosity within the plates and plate boundary zones and further refine coupling models. A final and important part of this project is to investigate full 3-D lithosphere models that are coupled to full 3-D convection models. We will build the global infrastructure, incorporating subduction in 3-D, continental orogeny in 3-D, the role of anisotropic zones (e.g., strike-slip faults), layered elastic and viscous systems, viscoelastic and power law mantle rheology, and full 3-D flexure. This global-scale 3-D treatment of the lithosphere is necessary in order to make further progress on the problem of understanding lithosphere interaction with mantle circulation. This observationally-based treatment will have a significant impact on the understanding of the lithosphere/convection system. Because this work places constraints on the absolute magnitudes of deviatoric stress and the lateral variations in strength of the lithosphere, it has implications for understanding fault mechanics, and even the earthquake rupture energy budget and earthquake cycle. The 3-D spherical treatment is precise and the codes and method are being made available to researchers.

地球物理学中最具挑战性的问题之一是地球板块和板块边界带的应力和流变的量化。我们通过对岩石圈/地幔对流系统的综合全球处理来解决这个问题。我们首先求解了岩石圈的深度积分三维力平衡方程（使用薄片近似），其中有效的体力输入为：(1)深度积分垂直应力的水平变化（重力位能差- GPE）和(2)施加于岩石圈底部的水平和径向牵引力，与大尺度地幔环流相关。GPE估计依赖于精确的（地震定义的）地壳和上地幔结构。地幔环流模型满足板块运动、大地水准面和动态地形。板块运动是自行产生的，而不是强加的。对流模式具有径向和横向的粘度变化，并由层析成像和俯冲历史推断出的更深的密度浮力驱动。迄今为止进行的建模在模型偏应力场和应力指标之间提供了前所未有的拟合质量；GPE差异校准了偏应力的大小，而观测受限的模拟对存在于岩石圈底部的牵引力的大小和分布施加了限制。因此，岩石圈系统的这种模拟在约束对流模式方面也起着重要的作用。我们还计算了岩石圈的正演动态模型，该模型可以预测整个水平速度梯度张量场（可以与GPS测量结果进行比较）以及偏应力场。正演模拟结合了变换断裂带内的各向异性处理，使我们能够改进板块和板块边界带内深度综合有效粘度的估计，并进一步改进耦合模型。该项目的最后一个重要部分是研究耦合到全三维对流模型的全三维岩石圈模型。我们将建立全球基础设施，包括三维俯冲，三维大陆造山运动，各向异性带（如走滑断层）的作用，层状弹性和粘性系统，粘弹性和幂律地幔流变学，以及全三维挠曲。为了进一步了解岩石圈与地幔环流的相互作用问题，这种全球尺度的岩石圈三维处理是必要的。这种基于观测的处理将对岩石圈/对流系统的理解产生重大影响。由于这项工作限制了偏应力的绝对大小和岩石圈强度的横向变化，它对理解断层力学，甚至地震破裂能量收支和地震周期都有意义。三维球面处理是精确的，代码和方法正在提供给研究人员。