HR: 0830h
AN: S21D-0332    [PDF]
TI: Relative Constraints on Correction Surfaces for More Effective use of Low-Order Ground Truth
AU: * Rowe, C A
EM: char@lanl.gov
AF: Los Alamos National Laboratory, EES-11, M.S. D-408, Los Alamos, NM 87545 United States
AU: Phillips, W S
EM: wsp@lanl.gov
AF: Los Alamos National Laboratory, EES-11, M.S. D-408, Los Alamos, NM 87545 United States
AU: Steck, L K
EM: lsteck@lanl.gov
AF: Los Alamos National Laboratory, EES-11, M.S. D-408, Los Alamos, NM 87545 United States
AB: We are developing a technique for applying relative constraints among travel time correction surfaces for stations within a network, whose goal is to improve the usefulness of lower order ground truth events within a catalog. Using the NCEDC catalog to develop and test our method, we demonstrate that for well-picked events the traveltime residual differences for events colinear with a given station pair vary slowly with little scatter for source-receiver separations involving local Pg phases. For the NCEDC catalog we observe that the consistency of residual relationships is good for events whose alignment with a station pair is neither parallel, nor in close proximity, to a major fault. Such fault-parallel station and event geometries lead to nodal arrivals and large pick and/or traveltime inconsistencies, which are manifested as large fluctuations in the residual differentials. Mislocation of earthquakes results in a geometrically-dependent uncertainty in the residual diffentials. As a first step we have modeled relative traveltime perturbations in a three-dimensional extension of the USGS 1-D Coast Range crustal model. For events placed in a dense grid within the model, we build a spatially-varying function of uncertainty in traveltime differentials caused by perturbations of each source within a 3-D Gaussian distribution about its "true" location. The resulting pattern of uncertainties suggests that the colinear residual relationships may be expanded to cover a significant azimuth range, allowing us to constrain correction surfaces over broad regions despite minor mislocatoins in the hypocenters upon which they are based. This in turn can improve locations for low-order ground truth events by suplying station correction constraints where they were previously unavailable or poorly defined. By including GT0 events in the procedure, we hope to establish absolute constraints on these surfaces.
DE: 7215 Earthquake parameters
DE: 7294 Instruments and techniques
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting