Physics
Scientific paper
Nov 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986pepi...44..242t&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 44, Issue 3, p. 242-256.
Physics
Scientific paper
A method is presented to obtain travel times from estimates of tectonically regionalized P-wave tau functions and slowness-dependent source and receiver corrections (Tralli and Johnson). A quadratic programming algorithm interpolates the tau estimates constrained by the analytical properties of tau and the statistical uncertainties. The regionalized travel-time estimates are used to locate seismic sources in the epicentral distance range 15-95°. Since all the information on lateral velocity variations is contained in the tau functions, seismic sources in a laterally heterogeneous Earth are located without explicitly defining a laterally varying velocity model. The formulation is efficient in that the travel-time estimates and corrections are obtainable for any source and receiver pair on the globe and requires minimal computation time.
The P travel-time data are provided by the Bulletin of the ISC. Twenty-eight disclosed nuclear explosions at Nevada Test Site (NTS) allow estimation of a travel-time baseline bias. Azimuthal corrections for NTS events are also obtained. Nuclear explosions at NTS are then located, as are events in Eastern Kazakh and Novaya Zemlya in the Soviet Union, and in the Tuamotu Archipelago in French Polynesia. Three earthquakes along the San Andreas fault zone in west central California are also relocated for comparison with hypocentral parameters provided by local seismographic networks. All events are also located using the Jeffreys-Bullen P Tables and PREM (Dziewonski and Anderson) with a set of azimuthal station corrections (Dziewonski). A comparison of the reduction in sample variances of travel-time residuals provides a measure of the ability of tectonically regionalized tau functions to characterize lateral variations in mantle and crustal P velocities. Mean epicentral mislocations for NTS events are about 3 km whereas mislocations using J-B and PREM are about 7 km. For NTS and particularly Eastern Kazakh, the tau formulation yields consistently smaller sample variances, with a mean reduction of 30% compared to using J-B and 15% compared to using PREM.
Johnson Lane R.
Tralli David M.
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