Investigation of Lateral Variation in the Seismic Velocity Structure of theShallow Crust Beneath Eastern Massachusetts and Southern New Hampshire

摘要

This is one of five scientific reports describing specific research projectsconducted at Weston Observatory under Contract No. F19628-90-K-0035. The research conducted under this contract covers a range of topics related to seismology in general and to nuclear test monitoring in particular. This report describes a study in which group velocity dispersion was determined for short-period Rayleigh waves recorded from blasts detonated at the San-Vel quarry in Littleton, MA. Field data were recorded to complement network data in order to create a denser distribution of stations than was possible in past experiments. Group velocity dispersion was estimated for each path. The resulting dispersion curves were analyzed to investigate the relationship between group velocities and shallow crystal structure beneath eastern MA and southern NH. Our results suggest that the quarry lies in a 'trough' of low group velocities, where the group velocities systematically increase toward the E and W-NW directions. This creates a 'valley' of group velocities where the primary trend of the valley trough is N, and a secondary feature is a trough that trends in a NE direction. This NE trending feature is of particular interest because of a possible correlation with the trend of the Clinton-Newbury fault zone. Shallow crystal structure, Rg Wave dispersion, Quarry blasts, Chemical explosions.