Results from Prior NSF Support − Part 1 Title: Collaborative Research: Complex Upper Mantle Structure Beneath Northeastern US Investigated Through Shear Wave Tomography (collaborative project between LDEO and Yale University) Period 08/15/97−07/31/99 William Menke (LDEO), Award Number: EAR−9706195, Amount: $63993.00

The purpose of this research was to test the proposition that the mantle beneath New York and Southern New England is divided into several "anisotropic domains" that are the seismic expression of the plate tectonic process of "terrain accretion". Were such the case, we would expect different directions of the shear wave fast direction and different mean shear wave velocities in each of the several terranes (whose existence has been established geologically). Thus we assembled shear wave traveltime and splitting databases for all the broadband seismic stations that were operated − even only temporarily − in northeastern North America for a 5−year period. We analyzed the splitting data by comparing it to synthetic measurements drawn from synthetic seismograms computed for anisotropic models. We tomographically inverted the traveltime data. Much of the data analysis and modeling code was custom−written (by us) for this project.