Structure and Deformation of the Crust and Upper Mantle Beneath SE Tibet

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。我们研究的主要目的是提高我们对地球结构和变形的理解。利用新的地震资料和方法研究了西藏东南部的地壳和岩石圈地幔。从地质角度看，四川盆地与喜马拉雅东结带之间的区域具有重要意义，原因有二。首先，作为横贯中国地震带的南端，它是东南亚大陆地震最活跃的地区之一。2008年5月12日发生在四川西部的毁灭性地震，造成了巨大的人员伤亡和财产和自然破坏，是对这一事实的残酷提醒。其次，这是了解青藏高原碰撞后演化和东扩的关键区域。根据过期的大陆动力拨款，我们在西藏东南部部署了25个宽带地震仪（2003年8月至2004年9月）。该阵列数据的地壳结构层析反演揭示了广泛的低速（可能是机械弱）带。这些带可能控制着该地区的变形和地震活动，但它们的性质、三维结构和相互联系以及对活动断层的地震作用的重要性尚不清楚。2006年，中国地震局在同一地区安装了300个宽带（gralp）传感器阵列，这些数据为我们的项目提供了数据。中国地震局的数据分析将在地质研究所（中国地震局，北京）进行。这项中美合作将涉及麻省理工学院的一名研究生和博士后，以及CEA的学生和研究人员。为研究岩石圈的非均质性和各向异性提供了前所未有的机会，并提高了我们对最近遭受破坏性地震袭击的人口稠密地区的地震构造和危险性的理解。建立浅层和深层结构之间的联系以及区域过程与局部地震活动之间的关系需要对非均质各向异性岩石圈进行多尺度地震成像。我们可以通过建立在数据分析（环境噪声干涉测量），方法（Eikonal和有限频率断层扫描）以及壮观阵列数据（CEA）的可用性方面的最新进展来应对这一挑战。作为合乎逻辑的第一步，我们将添加（短周期）来自（密集间隔的）CEA阵列的数据，以解决（浅）地壳非均质性和（方位）各向异性（包括瑞利波和洛夫波）。这将为地壳结构与地震活动性的关系提供许多新的见解。为了进一步提高分辨率，我们将干涉测量与全波反演相结合。我们采用分层方法。我们首先考虑一种渐近方法（Eikonal层析成像），为随后的全波（伴随）层析成像（具有三维有限频率核）创建一个三维起始模型。SEM合成将用于定量模型评估和验证。提出的噪声干涉测量和有限频率断层扫描的组合也可以应用于来自USArray的数据，例如。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The main objective of our research is to improve our understanding of the structure and deformation of Earth?s crust and lithospheric mantle beneath SE Tibet using new seismic data and methods. From a geological perspective, the region between Sichuan basin and the eastern Himalaya Syntaxis is important for two reasons. First, as the southern end of the trans-China seismic belt it is among the most seismically active regions of continental SE Asia. The devastating 12 May 2008 earthquake in western Sichuan province, which caused massive loss of human life and damage to property and nature, is a grim reminder of this fact. Second, this is a critical region for understanding the post-collision evolution and eastward expansion of the Tibetan plateau. Under an expired Continental Dynamics grant we deployed 25 broadband seismometers in SE Tibet (08/2003-09/2004). Tomographic inversion for crustal structure of the data from this array has revealed widespread low velocity (and presumably mechanically weak) zones. These zones may control deformation and seismicity in the region, but their nature, 3-D structure and interconnectivity, and importance for seismogenesis on active faults are not yet well known. In 2006 the China Earthquake Administration installed in the same region an array of 300 broadband (Güralp) sensors, and this data is available to us for the purpose of our project. The analysis of CEA data will be conducted at the Institute of Geology (CEA, Beijing). This Sino-US collaboration, which will involve a graduate student and post-doc at MIT as well as students and research staff at CEA, gives an unprecedented opportunity to study the heterogeneity and anisotropy of the lithosphere and improve our understanding of the seismo-tectonics and hazard of a densely populated region that was recently hit by a devastating earthquakeEstablishing the connection between shallow and deep structures and the relationship between regional processes and localized seismicity requires multi-scale seismic imaging of heterogeneous, anisotropic lithosphere. We can meet this challenge by building on recent advances in data analysis (ambient noise interferometry), methodology (Eikonal and finite-frequency tomography), and the availability of spectacular array data (CEA). As a logical first step we will add (short period) data from the (densely spaced) CEA array to resolve (shallow) crustal heterogeneity and (azimuthal) anisotropy (both for Rayleigh and Love waves). This will give much new insight into crust structure in relation to seismicity. To improve resolution further we will combine interferometry with full wave inversion. We take a hierarchical approach. We first consider an asymptotic method (Eikonal tomography) to create a 3D starting model for subsequent full-wave (adjoint) tomography (with 3D finite frequency kernels). SEM synthetics will be used for quantitative model evaluation and validation. The proposed combination of noise interferometry and finite frequency tomography can also be applied to data from, for instance, USArray.