Structure of the Tibetan Crust and Upper Mantle and Its Geodynamic Implications

本研究将研究西藏地壳和上地幔的大尺度结构，并探讨其地球动力学意义。一个初步的三维地震模型的两个特点激发了这项工作，并确定了主要的问题，这项工作提出解决。首先，在地幔的高，低速异常的一致的三维模式下的青藏高原。什么样的地球动力学过程可以解释这种模式？其次，强烈的中地壳径向各向异性的特点，西藏地壳，初步分析表明，相干，周期依赖的方位各向异性。西藏地壳有限应变发展的哪些模型与这些观测结果是一致的？这项工作将改进目前的地震模型，并研究其地球动力学含义。将通过增加更多的面波频散测量和在反演中引入新的测量方法来改进模型，例如，地壳和地幔泛音测量和接收器功能。反演生成可接受模型的集合，而不是单个最佳拟合模型，从而产生测试假设所需的有意义的不确定性信息。几个地球动力学的方案，可能会解释在上地幔的速度异常的模式方面，在西藏之下将进行调查，包括：印度岩石圈的俯冲、亚洲岩石圈的西南逆冲和西藏岩石圈的拆离或对流搬运，本文将研究推断的地壳各向异性与西藏地壳有限应变发展的三种模型之间的关系。学生将接受地震层析成像和地球动力学之间接口的培训。地震模型将以课堂上有用的形式放置。这项工作的合作者包括地球系统教育数字图书馆（DLESE，www.dlese.org）和联合国志愿人员组织的研究人员，他们也是GEON大规模信息技术研究项目（www.geongrid.org）的一部分。

This research will study the large-scale structure of the crust and upper mantle beneath Tibet andinvestigate its geodynamic implications. Two features of a preliminary 3-D seismic model motivate this work and define the primary questions that the work proposes to address.First, a coherent 3-D pattern of high and low speed anomalies in the mantle underlies the Tibetan plateau. What geodynamic processes can account for this pattern? Second, strong mid-crustal radial anisotropy characterizes the Tibetan crust, and preliminary analysis implies coherent, period-dependent azimuthal anisotropy. Which models of the development of finite strain in the Tibetan crust are consistent with these observations?The work will improve the current seismic model and investigate its geodynamical implications.The model will be improved by adding more surface wave dispersion measurements and by introducing new kinds of measurements into the inversion; e.g., crustal and mantle overtone measurements and receiverfunctions. The inversion generates an ensemble of acceptable models, rather than a single best-fitting model, thereby producing meaningful uncertainty information needed to test hypotheses. Several geodynamic scenarios that may explain aspects of the pattern of velocity anomalies in the upper mantlebeneath Tibet will be investigated, including; the underthrusting of Indian lithosphere, southwestwardthrusting of Asian lithosphere, and the detachment or convective removal of Tibetan lithosphere.In addition, the relation between inferred crustal anisotropy and three models of the development of finitestrain in the Tibetan crust will be investigated.A graduate student will receive training at the interface between seismic tomography andgeodynamics. The seismic models will be placed in a form that is useful in the classroom. Collaborators in this effort include researchers at the Digital Library for Earth Systems Education (DLESE, www.dlese.org) and UNAVCO, who are also part of the GEON large scale information technology research project (www.geongrid.org).