P-wave and S-wave tomography of the crust and uppermost mantle in China and surrounding areas

Abstract

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references.This thesis involves inverting the seismic structure of the crust and uppermost mantle in China from the P- and S-wave travel-time tomography. The main contributions of this research are: 1) introducing the adaptive moving window method to obtain 2338 1D P and S models in China; 2) introducing a tomographic method to perform the 3D body wave travel-time tomography with the Moho discontinuity included. Both horizontal and vertical resolutions are highly controlled and smooth transitions among adjacent locations are guaranteed in the final models. To achieve these objectives, the Monte-Carlo (random search) method and the Gauss-Newton method are applied iteratively to find the nonlinear least square solutions and to optimize the models in the crust and uppermost mantle. The models we obtained provide accurate travel-time calculation, ground-truth event relocation and seismogram fittings. These models can therefore be applied to reliable earthquake location. Geological, geodynamic, and volcanic implications of our models are discussed in this thesis. Our tomographic models provide new insights into the geological structure and tectonics of the region, such as lithological variations and large fault zones across the major geological terranes.(cont.) Compared with previous tomographic studies, we have used a larger, higher quality data set and applied an updated tomographic method to take into account the effects of the complex Moho geometry in this region. Our results cast a new light over the complex structure and seismotectonics of China and surrounding areas.by Youshun Sun.Ph.D