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Subduction zone Calibration and teleseismic relocation of thrust zone events in the central Aleutian Islands

KAZUYA FUJITA^*, E. R. ENGDAHL and NORMAN H. SLEEP

DEPARTMENT OF GEOLOGICAL SCIENCES NORTHWESTERN UNIVERSITY, EVANSTON, ILLINOIS 60201
COOPERATIVE INSTITUTE FOR RESEARCH IN ENVIRONMENTAL SCIENCES UNIVERSITY OF COLORADO/NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, BOULDER, COLORADO 80309

Abstract

Teleseismically determined epicenters for thrust zone earthquakes in the central Aleutian Islands are systematically mislocated by about 40 km to the north relative to local network solutions. We attribute the mislocation to travel-time anomalies produced by the higher P-wave velocity in the subducting slab. These travel-time anomalies can be estimated by seismic ray tracing through a thermally modeled velocity structure for the slab. Observed teleseismic station residuals and slab travel-time anomalies computed from local network hypocenters, plotted as a function of event distance to the center of curvature of the island arc, show good agreement. This distance versus residual relationship can be used to validate the local network hypocenters and to constrain the length of subducting lithosphere. Computed slab source corrections, when incorporated in a standard location program, reduce teleseismic mislocations to 20 km; the addition of empirical station corrections reduces the mislocation to about 10 to 15 km. Depth and origin time estimates can be further improved through use of better station corrections, a local station within 2°, and depth phases.

Footnotes

^* Present address: Department of Geology, Michigan State University, East Lansing, Michigan 48824.

Present address: U.S. Geological Survey, MS 967, Box 25046, Denver Federal Center, Denver, Colorado 80225.

Present address: Department of Geophysics, Stanford University, Stanford, California 94305.

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