Abstract
A function of global monitoring of nuclear explosions is the development of Earth models for predicting seismic travel times for more accurate calculation of event locations. Most monitoring agencies rely on fast, distance-dependent one-dimensional (1D) Earth models to calculate seismic event locations quickly and in near real-time. RSTT (Regional Seismic Travel Time) is a seismic velocity model and computer software package that captures the major effects of three-dimensional crust and upper mantle structure on regional seismic travel times, while still allowing for fast prediction speed (milliseconds). We describe updates to the RSTT model using a refined data set of regional phases (i.e., Pn, Pg, Sn, Lg) using the Bayesloc relative relocation algorithm. The tomographic inversion shown here acts to refine the previous RSTT public model (rstt201404um) and displays significant features related to areas of global tectonic complexity as well as further reduction in arrival residual values. Validation of the updated RSTT model demonstrates significant reduction in median epicenter mislocation (15.3 km) using all regional phases compared to the iasp91 1D model (22.1 km) as well as to the current station correction approach used at the Comprehensive Nuclear-Test-Ban Treaty Organization International Data Centre (18.9 km).
Highlights
One of the main functions involved with global monitoring of nuclear explosions is the development of Earth models for predicting seismic travel times
The Regional Seismic Travel Time (RSTT) model and software are developed by the three United States National Nuclear Security Administration (NNSA) National Laboratories (Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Sandia National Laboratories) in order to more accurately predict travel times from regional seismic phases ([ 15–18°) that typically cause degradation in event location accuracy when combined with teleseismic phases (Z20°)
The calculated turning-point depth follows from the assumption of a starting upper mantle velocity and constant gradient, with any ray being rejected showing a significant deviation from this assumption
Summary
HIPP, DOUG DODGE, and Abstract—A function of global monitoring of nuclear explosions is the development of Earth models for predicting seismic travel times for more accurate calculation of event locations. Most monitoring agencies rely on fast, distance-dependent one-dimensional (1D) Earth models to calculate seismic event locations quickly and in near real-time. We describe updates to the RSTT model using a refined data set of regional phases (i.e., Pn, Pg, Sn, Lg) using the Bayesloc relative relocation algorithm. Validation of the updated RSTT model demonstrates significant reduction in median epicenter mislocation (15.3 km) using all regional phases compared to the iasp91 1D model (22.1 km) as well as to the current station correction approach used at the Comprehensive NuclearTest-Ban Treaty Organization International Data Centre (18.9 km)
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