Collaborative Research: Dynamics of Crust-Mantle Coupling through Combined Analysis and Modeling of EarthScope Seismic, Geodetic, and Geologic Data

这项合作研究工作正在整合来自EarthScope的地震学、大地测量学和地质学信息，以调查有关美国西部大盆地地区现今结构和演化的假设。地球范围计划和原型研究在该地区的初步发现导致了新的和可能相关的假说，这些假说呼应了大陆及其边缘观测和理论动力学中的突出研究主题：(1)地幔流场上俯冲板块的演化和控制，(2)下岩石圈对对流损失的稳定性，以及(3)岩石圈内亚水平脱钩层位的性质和程度。目前的主要动机是需要协调大盆地地区最近与这些主题直接相关的地球物理、大地测量和地质发现。在大盆地中心下方，地震成像揭示了活跃俯冲的胡安德富卡板块以东靠近美国西部最弱的方位各向异性区域的圆柱体质量，其波速高于平均波速，并伴随着快速极化方向的漩涡图案。当考虑到其他区域地球物理和地质模式时，可能解释这些观测结果的假设包括围绕岩石圈龙骨的地幔流动、由胡安德·富卡板块下沉驱动的环状流动、由岩石圈滴水驱动的地幔下流，以及许多其他可能性。大盆地最近的大地测量数据揭示了大地速度的瞬时变化，当与其他地方地质模式相结合时，这与存在活跃的脱钩层位的假设是一致的，可能位于莫霍面或大盆地下的其他深部脱钩带。此外，相对于与第四纪速率和变形方向相匹配的动态模型，从运动和连续GPS获得的时间平均应变速率解显示出与大地测量和地震异常相同的附近的收缩膨胀异常。如此广泛的地球物理、大地测量和地质异常在广泛延伸的大盆地之下的配置不太可能是巧合，但它们结合在一起，挑战了像大盆地这样的经典伸展构造体制的传统模型。通过一系列全面的假设检验来理解这些过程之间的关系，可以改变我们对岩石圈动力学的总体认识。该项目的重点是进行一套全面的新调查，以检验有关大盆地地区地幔流动、岩石圈脱钩和岩石圈失稳之间的联系的假设。这项工作利用了通过分析EarthScope UScope可移动阵列(TA)、EarthScope板块边界观测站(PBO)和EarthScope地质数据而开发的新结果。具体的数据集包括地震成像(层析成像、各向异性和接收器功能)、连续GPS、地震构造以及上地壳历史和晚第四纪地震应变释放的模式。这些分析的结果将为该项目开发的一系列新的3-D和4-D数值模型提供所需的数据。这项研究本身就是综合性的，因此是一个重要的机会，可以将地球范围计划的不同组成部分的结果结合起来，以适应历史上世界上最著名和最神秘的构造背景。从更广泛的影响角度来看，该项目代表着一项新的多学科努力，将四个独立的地球科学学科结合在一起，将最近由EarthScope支持的发现纳入大盆地演化的整体视角。为该项目收集和分析的数据将向科学界公开分发。该项目正在对几名年轻科学家进行多学科研究方面的培训。私营部门正在与地球范围国家办公室和IRIS协调，以几种形式提供该项目的发现和发现，包括IRIS活动地球模块，该模块深入盆地，范围从地表到上地幔，将作为大陆规模的构造力量如何塑造当今地表变形和更深层次动力学的例证。

This collaborative research effort is integrating seismological, geodetic, and geological information from EarthScope to investigate hypotheses regarding the present-day structure and evolution of the Great Basin region of the western United States. Initial discoveries enabled by the EarthScope program and prototype studies in this region have led to new and potentially related hypotheses that echo prominent research themes in observational and theoretical dynamics of the continents and their margins: (1) the evolution and control of subducting slabs on the mantle flow field, (2) the stability of the lower lithosphere against convective loss, and (3) the nature and extent of subhorizontal decoupling horizons within the lithosphere. The primary motivation for the current is the need to reconcile recent geophysical, geodetic, and geological findings in the Great Basin region directly related to these themes. Beneath the central Great Basin, seismic imaging reveals a cylindrical mass of higher than average wavespeeds east of the actively subducting Juan de Fuca plate near the zone of weakest azimuthal anisotropy in the western United States, along with a swirl-like pattern of fast polarization directions. When considered with other regional geophysical and geologic patterns, hypotheses that may explain these observations include mantle flow around a lithospheric keel, toroidal flow driven by the sinking of the Juan de Fuca slab, mantle downwelling driven by a lithospheric drip, and a number of other possibilities. Recent geodetic data for the Great Basin reveal transient changes in geodetic velocities, which when considered with other local geologic patterns, are consistent with the hypothesis that an active decoupling horizon exists, perhaps localized along the Moho or some other deep decoupling zone beneath the Great Basin. Further, relative to a dynamic model that matches Quaternary rates and orientations of deformation, a time-averaged strain rate solution obtained from campaign and continuous GPS shows a contractional dilatation anomaly in the same vicinity as the geodetic and seismic anomalies.The collocation of such a broad range of geophysical, geodetic, and geologic anomalies beneath the broadly extending Great Basin is unlikely to be coincidental, yet combined they defy conventional models of a classic extensional tectonic regime like the Great Basin. Understanding the relationship between these processes through a comprehensive series of hypothesis testing can transform our general insight of lithospheric dynamics. This project is focused on conducting a comprehensive suite of new investigations to test hypotheses focused on linkages between mantle flow, lithospheric decoupling, and lithospheric destabilization for the Great Basin region. This effort is utilizing new results developed through analyses of EarthScope USArray Transportable Array (TA), EarthScope Plate Boundary Observatory (PBO), and EarthScope Geology data. Specific datasets include seismic imaging (tomography, anisotropy, and receiver functions), continuous GPS, seismotectonics, and patterns of historic and late Quaternary seismic strain release in the upper crust. Results from these analyses will provide the required data for a series of new 3-D and 4-D numerical models developed within this project. This research is inherently integrative, and thus constitutes an important opportunity to combine results from different components of the EarthScope program for a tectonic setting that historically is among the best known and most enigmatic in the world. From a broader impacts perspective, this project represents a new multidisciplinary effort combining four separate Earth science disciplines to draw recent EarthScope-enabled discoveries into a holistic view of Great Basin evolution. Data collected and analyzed for this project will be distributed publicly to the scientific community. The project is enabling the training of several young scientists in multidisciplinary research. The PIs are coordinating with the EarthScope National Office and IRIS to provide findings and discoveries from this project in several forms, including an IRIS Active Earth module that looks into the Basin and Range from the surface through the upper mantle and will serve as an illustration of how continental-scale tectonic forces shape present-day surface deformation and deeper dynamics.