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

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区域的应力和流变学的量化。我们通过对岩石圈/地幔对流系统进行全面的全球处理来解决这个问题。我们首先求解岩石圈的深度积分 3-D 力平衡方程（使用薄片近似），其中有效体积力输入为：（1）深度积分垂直应力的水平变化（重力势能差 - GPE）和（2）施加到岩石圈底部的水平和径向牵引力，与大规模地幔环流相关。 GPE 估计依赖于准确的（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。板块运动是自发的，而不是强加的。对流模型具有径向和横向粘度变化，并且由层析成像和俯冲历史推断出的更深密度浮力驱动。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，而观测约束模型对岩石圈底部存在的牵引力的大小和分布施加了限制。因此，岩石圈系统的这种建模在约束对流模型中也发挥着重要作用。我们还计算岩石圈的正向动态模型，预测完整的水平速度梯度张量场（可以与 GPS 测量进行比较）以及偏应力场。正演模型结合了转换断层带内的各向异性处理，使我们能够改进对板块和板块边界区域内深度积分有效粘度的估计，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与完整 3-D 对流模型耦合的完整 3-D 岩石圈模型。我们将建设全球基础设施，纳入 3-D 俯冲、3-D 大陆造山运动、各向异性带（例如走滑断层）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完整的 3-D 弯曲。为了在理解岩石圈与地幔循环相互作用的问题上取得进一步进展，对岩石圈进行全球尺度的 3D 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。 由于这项工作对偏应力的绝对大小和岩石圈强度的横向变化施加了限制，因此它对于理解断层力学，甚至地震破裂能量收支和地震周期具有重要意义。 3-D 球形处理非常精确，并且正在向研究人员提供代码和方法。

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.