HR: 17:00h
AN: S22F-05    [PDF]
TI: Location of Earthquakes in Three-dimensional Media Using Repeated, Multiple-Event Locations Over Spatial Grids of Control Points
AU: * Pavlis, G L
EM: pavlis@indiana.edu
AF: Indiana University, Department of Geological Sciences 1001 East 10th Street, Bloomington, IN 47405
AU: Vernon, F L
EM: vernon@epicenter.ucsd.edu
AF: University of California, San Diego, Scripps Institute of Oceanography 9500 Gilman Drive, LaJolla, CA 92093-0225
AB: We describe a new approach to the large-scale relocation of seismic catalogs based on a variation of conventional multiple event location methods. We associate every event in a catalog with one or more points in a 3D grid of control points. Events associated with each point are located together with an implementation of the Progressive Multiple Event Location (PMEL) algorithm. PMEL estimates a set of path corrections from a given control point to each seismic station along with a set of revised locations. In the estimation we use a set of matrix projectors that allow the unresolvable (absolute) location bias to be extracted from a 3D reference model and project only components of information the available data constrain. This allows us to construct empirically derived travel time correction fields in 3D that are highly data adaptive; the density of control points can be very high where seismicity is intense and low where earthquakes are rare. The 3D model is used only to fill in gaps between control points and correct smoothly varying, bias problems. The algorithm is highly parallel and we found major improvements in performance were possible on massively parallel computers. We applied this approach to data from the Anza network and the Tien Shan (Ghengis) experiment catalog. With the Anza data we achieved remarkable improvements in data fit with most relocation residuals smMaller than 0.02 s which is approximately 1/10 of the catalog residuals. In contrast the variance reduction in the Tien Shan data was much smaller (50%) with 1 s scale residuals common. This difference is attributed to measurement precision. The Anza catalog is dominated by impulse, local P and S phases while the Tien Shan catalog is dominated by emergent, regional phases.
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting