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National Information Service for Earthquake Engineering
University of California, Berkeley |
Three-Dimensional Variations in Vp/Vs in the Vicinity of the Loma Prieta Earthquake.
Shashank R. Atre & Clifford H. Thurber, University of Wisconsin-Madison, Madison, Wisconsin.
An inversion of S minus P seismic wave arrival time data primarily from the PASSCAL array deployed in the aftershock zone of the 1989 Loma Prieta, California, earthquake has yielded a three-dimensional mode for Vp/Vs variations along the Loma Prieta rupture zone. The inversion methode uses three-dimensional ray tracing in an existing laterally\ heterogeneous P-wave velocity model to determine the initial paths for S waves, assuming a constant Vp/Vs. The model represents spatial variations on a three-dimensional grid with node spacings of 3 to 15 km. The reduction in data variance, computed exactly by applying the Vp/Vs perturbations to the S velocity structure, exceeds 60% for the single-step inversion.
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