DIRECTION STUDIES USING MICROSEISM GROUND-PARTICLE MOTION
LAMONT GEOLOGICAL OBSERVATORY PALISADES NY
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Ground-particle trajectories were constructed for Palisades microseisms originating in storms with various positions and azimuths with respect to the continental margin. Good directional correlations were obtained between microseism approach directions as determined from ground-particle motions, and source directions for sources either on the continental shelf or on an azimuth normal to the continental margin. No correlation was determined between particle motion and source direction for deep-water sources or sources on an azimuth oblique to the coast. This lack of correlation is attributed either to simple refraction at the continental edge or to a combination of refraction and interference between waves having multiple refraction paths. It was considered significant that microseisms propagate across more than 5000 km of continent with little attenuation and that good directional correlation exists between ground-particle motion and cyclone direction after long continental propagation. A relationship between these microseisms and short- period surface waves Rayleigh waves is suggested because the latter have propagation characteristics of refraction and continental preference similar to those of microseisms. The study indicated that tripartite procedures can be successful only under certain conditions and could not be generally applicable even if all defects in the procedure were eliminated.