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

合作研究：通过 EarthScope 地震、大地测量和地质数据的组合分析和建模研究壳幔耦合动力学

• 批准号: 1053317
• 负责人: Matthew Fouch
• 金额: $ 23.15万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-15 至 2012-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1053317&HistoricalAwards=false
• 关键词: Collaborative; Research; Dynamics; Crust; Mantle

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.

这项合作研究工作整合了来自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。EarthScope项目的初步发现和该地区的原型研究已经产生了新的和潜在相关的假设，这些假设呼应了大陆及其边缘观测和理论动力学的突出研究主题：(1)地幔流场上俯冲板块的演化和控制，(2)下层岩石圈对对流损失的稳定性，以及(3)岩石圈内亚水平解耦层的性质和范围。当前的主要动机是需要调和最近在大盆地地区与这些主题直接相关的地球物理、大地测量和地质发现。在大盆地中央下方，地震成像显示，在美国西部方位角各向异性最弱带附近，活跃俯冲的胡安·德·富卡板块以东有一个高于平均波速的圆柱形体，同时还有一个快速极化方向的旋涡状模式。当考虑到其他区域地球物理和地质模式时，可以解释这些观测结果的假设包括岩石圈龙骨周围的地幔流动，胡安德富卡板块下沉驱动的环形流，岩石圈滴流驱动的地幔下行，以及许多其他可能性。最近大盆地的大地测量数据揭示了大地测量速度的瞬态变化，当考虑到其他局部地质模式时，这与存在活跃解耦层的假设一致，可能沿莫霍或大盆地下方的其他深层解耦带定位。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，在与大地测量和地震异常相同的附近，存在收缩扩张异常。如此广泛的地球物理、大地测量和地质异常在大盆地下的组合不太可能是巧合，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系的传统模型。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一般认识。该项目的重点是开展一套全面的新调查，以测试大盆地地区地幔流动、岩石圈解耦和岩石圈不稳定之间联系的假设。这项工作利用了通过分析EarthScope USArray可移动阵列（TA）、EarthScope板块边界观测站（PBO）和EarthScope地质数据得出的新结果。具体数据集包括地震成像（层析成像、各向异性和接收函数）、连续GPS、地震构造以及历史和晚第四纪上地壳地震应变释放模式。这些分析的结果将为该项目开发的一系列新的三维和四维数值模型提供所需的数据。这项研究本质上是综合的，因此构成了一个重要的机会，可以将地球范围项目不同组成部分的结果结合起来，研究一个历史上最著名、最神秘的构造环境。从更广泛的影响角度来看，该项目代表了一项新的多学科努力，结合了四个独立的地球科学学科，将最近的地球观测发现纳入大盆地演化的整体观点。为该项目收集和分析的数据将公开分发给科学界。该项目正在培训几名从事多学科研究的青年科学家。pi正在与EarthScope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，该模块从地表到上地幔观察盆地和范围，并将作为大陆尺度构造力如何塑造当今地表变形和更深动力学的说明。