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

点击翻译按钮获取中文摘要

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.