Evaluation of Location Accuracy Using Pn and Pg Arrivals

摘要

Seismic event locations obtained by using P sub g and P sub n arrivals may cause severe errors because the Earth's crust is laterally heterogeneous. Location errors are attributed to the fact that crustal velocities and thicknesses for each source-to-station path are different from those of the standard crustal model used in the location program. To overcome this difficulty, we have installed a number of crustal models in a location program and made it possible for each station to be assigned an appropriate model. Travel times for each phase are computed by using the selected earth model and the specified phase. The merit of this method is evaluated by relocating 12 explosions in the western United States. When each station model was chosen individually from a number of regional models, location errors were slightly larger than errors using only one (regional) model for all stations. However, errors were reduced when each station was assigned its own model for a set of finely localized crustal models. Errors were also reduced when the local crustal model appropriate to the source region was used for all stations. This suggests that a crustal model for the source and a separate model for each station would result in even better locations. The addition of P sub g arrivals to the set of P sub n arrival reduced location error by about 30%. However, the difference is not great enough for this small sample but we can be sure that it is significantly different from zero.