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Tomographic inversion of Pn travel times in western China

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Title: Tomographic inversion of Pn travel times in western China
Author(s): Tang, Zheng
Advisor(s): Song, Xiaodong
Department / Program: Geology
Discipline: Geology
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): western China Pn travel time tomography inversion crustal thickness Moho
Abstract: Western China, as a highly heterogeneous region in terms of its geology, has drawn much attention from geologists and geophysicists for many years. Pn tomography is a useful tool to explore the heterogeneity of the Earth's interior. In this study, we obtain a Pn velocity image and the crustal thickness for western China using a Pn tomographic inversion based on a large collection of Pn travel time data from various sources. Our tomography image reveals four significant features corresponding to the surface geology: (1) Four major basins bordering the Tibetan Plateau (TP) and/or Tien Shan (Tarim, Junggar, Qaidam, and Sichuan basin) display prominent high Pn velocities. These basins are tectonically stable with little deformation and lacking in seismic, thermal, and volcanic activity. (2) Several portions including western Tien Shan, Burma, and western Yunnan, show prominent low Pn velocities. An apparent feature is the bent low velocity belt (LVB), which extends from west to east beneath the northern TP. This passes through the Qiangtang block and the Songpan Ganzi fold belt (SGFB), then turns consistently with the SGFB along the eastern TP margin and continues further south to southwest along Yunnan and Burma. (3) In the Tibetan Plateau, low Pn velocities are found in the northern TP, while high Pn velocities are shown in the southern TP. The low Pn velocity in the north looks corresponds to Quaternary volcanism found in the region (Arnaud et al., 1992; Turner et al., 1993). A low velocity anomaly of north-south direction is also observed to cut through the high velocity southern plateau and seems to extend to the India plate. This feature is consistent with previous Pn studies of the Tibetan Plateau (Liang et al., 2004; Liang and Song, 2006). (4) Three important profiles of crustal thickness in Tibetan Plateau are obtained. They reveal significant features of the Moho and are consistent with previous studies (Kind et al., 2002; Liang and Song, 2006; Nabelek et al., 2009). Also, the shape of Moho is well correlated with the surface topography.
Issue Date: 2012-09-18
Rights Information: Copyright 2012 Zheng Tang
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08

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