A New Regional 3-D Velocity Model of the India-Pakistan Region
Abstract
We have developed a 3-D velocity model for the crust and upper mantle in the India-Pakistan region (WINPAK3D) to improve regional event location. Results of extensive testing demonstrate that the 3-D model improves location accuracy for this region, specifically for the case of small, regionally recorded events, for which teleseismic data may not be available. The initial model for the region was developed by integrating the results of more than sixty previous studies related to crustal and upper mantle velocity structure. During the final year of this effort, we have developed a 3-D joint velocity tomography/event relocation to improve this preliminary velocity model. The algorithm applies an iterative, conjugate gradients technique to minimize the misfit between calculated and observed travel times from multiple stations and events, subject to smoothness and geologic constraints. Events are relocated using the grid search location method of Rodi and Toksoz (2000) after each update of the 3-D velocity model. Travel times and their sensitivities to the velocity structure are computed with an extension of the 3-D Podvin- Lecomte (1991) method. We are applying our tomography algorithm to a suite of 580 events containing over 7,800 arrivals from the Engdahl et al. (1998) database. A critical aspect of model development is validation, which we have addressed in three ways: (1) cross validation analysis for a variety of events, (2) comparison of model-determined hypocenters with known event location, and (3) comparison of model-derived and empirically derived source-specific station corrections (SSSC's) generated for the International Monitoring System (IMS) auxiliary seismic station located at Nilore, Pakistan. The 3-D model provides improvement in regional location compared to a global 1-D model.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2001
- Accession Number
- ADA515135
Entities
People
- Anca Rosca
- Carolynn Vincent
- Delaine Reiter
- Michelle Johnson
- William Rodi