Validation of regional and teleseismic travel-time models by relocating
Ground-Truth events
Bulletin of the Seismological Society of America, 94 (3):
897--919 (Jun 1, 2004)DOI: 10.1785/0120030148
Abstract
Recently developed 3D global seismic velocity models have demonstrated
location improvements through independent regional and teleseismic
travel-time calibration. Concurrently, a large set of high-quality
ground-truth (GT) events with location accuracies 10 km or better
(GT0-GT10) has been collected for Europe, the Mediterranean, North
Africa, the Middle East, and western Eurasia. In this study we demonstrate
event location improvements using this new data set by applying the
regional and teleseismic model-based travel-time calibrations (independently
and jointly). Besides relocating events using all arrivals, a subset
of the GT events was also relocated using controlled station geometries
generated from a constrained boot-strapping technique. This approach
simulates sparse networks and reduces the effect of correlated errors
to ensure valid 90\\ error ellipse coverage statistics. With respect
to the GT events, we compared event relocations, with and without
travel-time calibrations, considering statistics of mislocation,
error ellipse area, 90\% coverage, origin time bias, origin time
errors, and misfit. Relocations of over 1200 GT events show that
Pn and/or P calibration reduced mislocation for 60\%-70\% of the
events. Joint regional Pn and teleseismic P travel-time calibration
provided the largest location improvements and achieved approximately
GT5 accuracy levels. Due to correlated errors, event locations using
large numbers of stations have deficient 90\% error ellipse coverage.
However, the coverages derived from the model errors are appropriate
for the simulated sparse regional and teleseismic networks. Our validation
effort demonstrates that the global model-based calibrations of Pn
and teleseismic P travel times reduce both location bias and uncertainty
over wide areas. 10.1785/0120030148