Source Specific Station Corrections (SSSCS) for International Monitoring System (IMS) Seismic Stations in North Africa, Middle East and Western Asia

摘要

To date, IDC regional travel time corrections have been successfully implemented for Fennoscandia and North America. Corrections and associated modeling errors to Pn, Pg, Sn, and Lg IASPEI91 travel time tables are specified on 1 by 1 degree latitude and longitude 'source specific' grids within 20 degrees of each International Monitoring System (IMS) station. International Data Center (IDC) location software is configured to read and apply these grids when locating events in the Reviewed Event Bulletin (REB). In order to develop regional travel time corrections for IMS stations in North Africa, Middle East, and Western Asia, a consortium was formed of experts in IDC software integration/testing/validation, regional/global body/surface-wave tomography, tectonic regionalization, 3D ray-tracing, and ground truth (GT) data collection with the goal to improve location accuracy and precision while maintaining honest 90% coverage ellipses. The three-year R&D program will provide Source Specific Station Corrections (SSSCs) for all IMS primary and auxiliary seismic stations in the region. Corrections will be developed, tested, and validated in two phases. A preliminary set of SSSCs will be delivered and tested by late 2001. A refined set of SSSCs will be delivered and tested by early 2003. The preliminary set will develop corrections for surface sources only based on an initial preliminary regionalization and set of crustal and upper mantle models. The 3D model will be based on a hierarchy of global 3D models, regional models, and tectonic regionalization. Travel times will be computed by 3D ray tracing from each station to a grid of source locations. Modeling errors for the initial correction set may be conservatively large. Meanwhile, a concerted effort has begun to gather ground truth (GT) location data in the region for validation. All GT origins, GT arrivals, velocity models, regionalizations, SSSCs, and metadata will be delivered for testing and validation.