Abstract

Rayleigh waves recorded on the three components of the Harvard station are used to determine the direction of approach of microseisms. In Case History I, it was observed that microseisms did not radiate exclusively from the center of a well-developed low-pressure storm area and that they remained strong and continued for many hours after the storm center moved inland over Nova Scotia, northeast of the Harvard station, coming at that time from east, southeast, and south. In Case History II, a short but distinct microseismic storm ran its course as a cold front advanced to the coast and out over the ocean, but there was no atmospheric storm system within the region covered by the U. S. Weather Map.

It is proposed that microseisms are generated when a pressure gradient of magnitude as yet undefined moves over the crust and, in effect, kneads the surface layer in such a way as to set up vibrations.

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