Improving Seismic Event Location: An Alternative to Three-dimensional Structural Models

We devise and apply a method to account for the effect of the aspherical structure of the Earth in locating earthquakes. This technique relies upon the ability to detect the average structural signal present in the residuals between source and receiver and correct for this signal during location, using a phenomenological description that we call Empirical Heterogeneity Corrections (EHC). EHC are employed in the relocation of a large set of well-constrained teleseismic earthquakes selected among the events reported by the Bulletins of the International Seismological Centre 1964–1995. The rms length of EHC relocation vectors for these events is about 10ukm. The method is also tested against a selected set of ground-truth events, both earthquakes and explosions, whose locations are independently known by nonseismic means. The rms length of the mislocation vectors for the test events, compared to their original mislocation in the reference 1-D model SP6, is reduced in the EHC relocation by 17% for explosions and 12% for earthquakes. Our technique provides a successful alternative to the use of 3-D structural models, approximately reaching the same value of effectiveness in improving event location.