Presenter: Ching-Yu Cheng
Date: 2016/10/13
Abstract
Surface wave tomography based on dispersion or waveforms from earthquake data plays an important role in studies of the structure of the Earth’s crust and upper mantle on both regional and global scales. In the past decade, surface wave tomography based on ambient noise cross-correlations has greatly improved our understanding of regional crustal structures. These two articles used the same method of inversion and in Fang et al. [2015], the author presented all the methodology. Inverting surface wave dispersion data directly for 3-D variations of shear wavespeed, that is, without the intermediate step of phase or group velocity maps, using fast marching ray tracing and a wavelet-based sparsity-constrained tomographic inversion. The author successfully applied their algorithm to obtain the shallow crustal shear wavespeed structure in the Taipei basin. The results seem similar to that from two-step inversion, but computationally efficient compared to the latter. Chen et al. [2016] present the results of a joint Chinese and Taiwanese study to obtain a regional-scale, 3-D S-wave model that is derived from ambient seismic noise tomography with the aim of investigating the structure beneath the Taiwan Strait. The study find out a high velocity anomaly near the surface in the Penghu Archipelago that is underlain by a velocity decrease that likely indicates a thermal anomaly related to the still cooling magma reservoir and feeding system to the higher velocity volcanic edifice at the surface.
Reference
H. Fang, H. Yao, H. Zhang, Y. C. Huang and Robert D. van der Hilst (2015), Direct inversion of surface wave dispersion for three-dimensional shallow crustal structure based on ray tracing: methodology and application, Geophysical Journal International, 201, 1251–1263.
K. X. Chen, H. Kuo-Chen, D. Brown, Q. Li, Z. Ye, W. T. Liang, C. Y. Wang and H. Yao (2016), 3D ambient noise tomography across the Taiwan Strait: the structure of a magma-poor rifted margin, Tectonics, n/a-n/a, doi: 10.1002/2015TC004097.