abstract

Records of microseisms associated with norwesters have been analyzed, the records being taken with three electromagnetic seismographs. It has been observed that while no appreciable microseisms are recorded when the disturbance is very close to the observatory, prominent microseisms are recorded when the center of disturbance is over the Bay of Bengal and away from the coast. The records indicate that for the production of microseisms a layer of water about 1 km. thick under the center of disturbance is necessary, that the microseismic disturbance is transmitted through the ocean bottom, and that a beating of high waves on the steep coast is not necessary. A comparison of the recorded variation of the period and amplitude of the microseisms with the changes in position of the atmospheric disturbance, together with the theoretical results of studies on the propagation of Rayleigh waves, give a good estimate of the structure of the ocean bed as well as of the depth of the continental shelf.

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