Mapping variability in the thermo-mechanical structure of the North American Plate and upper mantle

地球望远镜提供了一种前所未有的地球视角，使有关地球内部物理的新解释和问题得以出现。除了地球结构、动力学和演化等纯粹的基础研究问题外，了解热结构和机械结构对于理解与社会有关的问题至关重要，如地球对冰盖融化和海平面上升的反应、黄石公园下的火山潜力以及高温地热能生产的地热梯度的区域起源。北美中部和东部的构造板块或岩石圈在构造上是稳定的，但北美西部有复杂的近期岩浆活动和变形历史(6000万年)，以及相应的薄而多样的岩石圈结构。PIS正在开发基于美国阵列的地震数据来解释上地幔的热机械结构(温度和强度)的计算方法。该方法的核心是系统地计算从地震波传播(秒)到地幔对流(数百万年)以及介于两者之间的广泛时间范围内的力学特性。这些性质取决于温度、应力和其他热力学“状态”变量。当我们确定在一个时间尺度上与观测值一致的模型时，这些模型在其他时间尺度上约束物理属性。这个特别的项目关注的是来自地幔的热量如何从板块底部侵蚀构造板块，从而影响火山和地震发生在离地表更近的地方。该项目的广泛影响分为三类：(1)开发独特、非常灵活和综合的社区代码及其被地震界采用的好处；(2)三名早期职业科学家的进步；以及(3)为海登天文馆、学校课程和普通公众的“地震穹顶”计划开发的地球范围数据可视化产品的新开发。该项目的目的是推进地震测量的定量解释，以限制北美浅层上地幔的热机械结构。特别是，PIs正在探索通过熔体渗透到板材中而发生热化学腐蚀的可能性。超宽带流变学(VBR)计算器是该项目的核心，其计算方法旨在在岩石学、地震学、矿物/岩石物理学和地球动力学之间建立实用和透明的桥梁。该项目扩展了VBR计算器，用于计算从地震波传播到冰川均衡调整到构造板块运动等地球物理感兴趣的广泛时间范围内的随频率变化的力学性质。通过在美国大陆的多个地点使用单一方法，我们能够直接比较分析从地震波场得出的地区平均测量值的一维模型，重点是速度、衰减和接收器函数。初步结果表明，有单一的正演模式能较好地拟合北美稳定岩石圈和软流圈的平均值。然而，“北美构造”(TNA)速度剖面不能用单一的、简单的稳态热剖面来拟合，这表明还没有达到稳定状态的更复杂的热历史。在拟议的研究中，新的具有熔体迁移热平流的一维开放系统两相流模型正在开发中，并被添加到VBR库中。这些模型进一步刻画了这种不平衡的特征，产生了岩石圈腐蚀率，虽然降低了，但物理上是真实的。开放系统模型的结果被用于预测接收器功能的幅度和宽度，使地震测量能够在每种设置中提供关于热机械结构的更详细的约束。

EarthScope provides an unprecedented view into the Earth, enabling the emergence of new interpretations and questions concerning the physics of the Earth's interior. In addition to the purely basic research questions of earth structure, dynamics and evolution, understanding the thermal and mechanical structure is central to understanding societally relevant problems such as the Earth's response to melting ice sheets and rising sea levels, the volcanic potential beneath Yellowstone, and the regional origin of the geothermal gradient for high temperature geothermal energy production. The tectonic plate, or lithosphere, beneath Central and Eastern North America is tectonically stable, but Western North America has a complex recent history (60 million years) of magmatism and deformation, and a correspondingly thin and varied lithosphere structure. The PIs are developing computational methods for interpreting the thermo-mechanical structure (the temperature and the strength) of the upper mantle based on seismic data from the USArray. The core of the method is the systematic calculation of mechanical properties across a vast range of time scale, from seismic wave propagation (seconds) to mantle convection (millions of years) and everything in between. These properties depend on temperature, stress and other thermodynamic "state" variables. When we identify models that are consistent with observations at one time scale, those models constrain physical properties at other time scales. This particular project focuses on how heat from the mantle can corrode the tectonic plates from their underside, influencing where volcanoes and earthquakes occur closer to the surface. The broader impacts of this project fall into three categories: (1) the benefits of development of a unique, very flexible and integrative community code and its uptake by the seismology community; (2) advancement of three early career scientists; and (3) new development of visualization of EarthScope data products for the "SeismoDome" program in the Hayden Planetarium, school curricula and the general public. The aim of this project is to advance the quantitative interpretation of seismic measurements to constrain the thermo-mechanical structure of the shallow upper mantle beneath North America. In particular, the PIs are exploring the possibility that thermal-chemical corrosion occurs by melt infiltration into the plate. Central to this project, the Very Broadband Rheology (VBR) Calculator comprises computational methods intended to form practical and transparent bridges between petrology, seismology, mineral/rock physics and geodynamics. This project expands upon the VBR Calculator for calculation of frequency dependent mechanical properties across the broad range of time scales of geophysical interest, from seismic wave propagation to glacial isostatic adjustment to tectonic plate motions. By using a single approach at multiple locations around the continental US, we enable a direct comparative analysis of 1-D models of regional averages of measurements derived from the seismic wave field, with an emphasis on velocity, attenuation, and receiver functions. Initial results show that there are single forward models that can fit the average Vs "Stable North American" (SNA) lithosphere and asthenosphere. However, the "Tectonic North America" (TNA) velocity profile cannot be fit by a single, simple, steady-state thermal profile, indicating a more complex thermal history that has not reached a steady state. In the proposed research, new 1D open-system two phase flow models with heat advection by melt migration are being developed and added to the VBR library. These models characterize this kind of disequilibrium much further, producing lithospheric corrosion rates with reduced but realistic physics. The open system model results is being used to predict receiver function amplitude and width, enabling the seismic measurements to provide more detailed constraints on the thermal-mechanical structure in each setting.