Development and Applications of Double-difference Seismic Tomography |
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| Authors: | Haijiang Zhang Clifford Thurber |
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| Institution: | (1) Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706, USA |
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| Abstract: | Double-difference (DD) tomography is a generalization of DD location; it simultaneously solves for the three-dimensional velocity
structure and seismic event locations. DD tomography uses a combination of absolute and more accurate differential arrival
times and hierarchically determines the velocity structure from larger scale to smaller scale. This method is able to produce
more accurate event locations and velocity structure near the source region than standard tomography, which uses only absolute
arrival times. We conduct a stability and uncertainty analysis of DD tomography based on a synthetic data set. Currently three
versions of the DD tomography algorithms exist: tomoDD, tomoFDD and tomoADD. TomoDD assumes a flat earth model and uses a pseudo-bending ray-tracing algorithm to find rays between events and stations while
tomoFDD uses a finite-difference travel-time algorithm and the curvature of the Earth is considered. Both codes are based on a regularly
distributed inversion grid, with the former for a local scale and the latter for a regional scale. In contrast, tomoADD adapts the inversion mesh to match with the data distribution based on tetrahedral and Voronoi diagrams. We discuss examples
of applying DD tomography to characterize fault zone structure, image high-resolution structure of subduction zones, and determine
the velocity structure of volcanoes. |
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| Keywords: | Double-difference tomography fault zone subduction zone volcano |
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