(1) U S Geological Survey, DFC, Box 25046, Stop 967, Denver, CO 80225, USA; +1-303-273-8422; engdahl@gldfs.cr.usgs.gov
(2) MIT, Rm 54-514, Cambridge, MA 02139, USA; hilst@mit.eduposter/oral:
Routine global compilations of earthquake hypocenters and associated phase arrival times and residuals are often too inhomogeneous to be applied confidently to the construction of a reference Earth model. The main problems are phase mis-identification and mixed levels of hypocenter mislocations (especially in focal depth) introduced largely by errors in the 1-D Earth model used to locate the events and unaccounted for effects of lateral heterogeneity.
We relocate nearly 100,000 events that occurred during the period 1964-1995 which are well-constrained teleseismically by arrival times reported to the ISC and to the USGS/NEIC. Depth determination is significantly improved by using, in addition to regional and teleseismic P and S phases, the arrival times of PKiKP and PKPdf, and the teleseismic depth phases pP, pwP and sP in the relocation procedure. A global probability model developed for all later arriving phases is used to independently and objectively identify the depth phases. Resolution and other characteristics of the resulting data base, which is complete to about Mw 5.2, are examined by comparisons to global data bases that have been independently compiled. Differences are shown to largely result from an inappropriate reference model and/or the methods of data processing used. High-frequency phase travel times, which can be extracted from this higher-quality data base, have immediate application to the construction and/or testing of any new reference Earth model.