Extending Regional Seismic Travel Time (RSTT) Tomography to New Regions
LAWRENCE LIVERMORE NATIONAL LAB CA
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Lowering the global seismic detection threshold can be accomplished by introducing data recorded at regional distances 2000 km from the event into global monitoring systems. Unfortunately, introduction of regional data degrades average epicenter accuracy compared to locations constrained solely by data recorded at greater distances. Location accuracy degrades because regional seismic travel time RSTT prediction error is generally greater than prediction error for waves that travel to greater distances. In previous work we developed a computationally efficient method to capture the first-order effects of three-dimensional 3-D crust and upper mantle structure on RSTTs. Previous results demonstrate that RSTT prediction accuracy is greatly improved by seismic tomography, in which model velocities are adjusted so that predicted travel times are in agreement with travel times that are based on a dataset of accurate event locations and arrival-time measurements. We have conducted RSTT tomography for the regional phases Pn, Pg, Sn, and Lg across Eurasia and for the Pn phase across North America. After tomography across Eurasia and North America, rigorous tests find that the standard deviation of Pn travel time residuals is reduced from approximately 1.75 seconds ak135 model to approximately 1.25 seconds. Further, the median location error is reduced from approximately 15 km to 9 km for network configurations that effectively average out measurement error. Reduction of epicenter error, millisecond travel time computation, and the flexibility to compute travel times between arbitrary points onin the globe all make the RSTT method ideal for routine location work and for use in seismic monitoring systems.
- Geology, Geochemistry and Mineralogy