9600304 Earle This award supports a 12 month Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowship for Dr. Paul Earle at the Earthquake Research Institute, University of Tokyo, Tokyo, Japan. Dr. Earle will work with Dr. Yoshio Fukao, director of the Earthquake Research Institute, on a research project entitled, "The Teleseismic Survey of the Upper-Mantle Reflectivity Structure Beneath the Mid-Atlantic Region." The proposed research will determine the sharpness (depth extent) and topography (depth variations) of seismic discontinuities occurring at average depths of 410- and 660- km. At present, seismic stations located in Japan form part of a unique geometry for studying the discontinuity structure below the Mid-Atlantic Ridge. Energy originating from earth-quakes in the Tonga and New Hebridies trenches reflects from discontinuities beneath the Mid-Atlantic Ridge before arriving in Japan. This energy is recorded on two Japanese seismic arrays: the J-array (over 300 short-period seismometers blanketing Japan) and POSEIDON (a network of more than 30 modern broadband seismometers located in and surrounding the Japanese islands). The research will use seismograms from earthquakes of magnitude > 5.6 occurring after April 1991 (birth of the J-array) to examine seismic wave arrivals which have interacted with seismic discontinuities. Drs. Fukao and Earle will develop automated methods to analyze over 70,000 seismograms contained in this data base. Array processing techniques will aid in the positive identification of these small amplitude reflections and will be used to place constraints on the Earth's chemical composition, temperature variations, and the nature of material flow within it. ***
