Abstract
THE ground is never at rest, and a seismograph provided with an aperiodic pendulum and a large magnification will always record these ever-present movements. The types are often so complicated that it is not easy to distinguish those associated with definite weather disturbances. To obviate these difficulties, a Milne-Shaw seismograph was installed some four years ago in the underground constant temperature room of the Colaba Observatory, and its working condition was so arranged that it should just cease to record microseisms when the weather was undisturbed over the neighbouring seas, as in the months of January and February, when the wind velocity seldom exceeds 20 miles per hour over the sea areas. It was then noticed that microseisms made their appearance in the records whenever weather was disturbed over the Arabian Sea or the Bay of Bengal, so as to cause rough seas over a fairly wide area. In particular, three distinct types of microseisms were recognised, and these were associated with (1) the south-west monsoon, (2) the storms in the Arabian Sea and the Bay of Bengal, and (3) local disturbances, such as pronounced land and sea breezes. Those associated with the south-west monsoon are steady vibrations, having periods varying from 4 to 10 seconds, according to the strength of the air current over the sea.
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BANERJI, S. Microseisms Associated with Storms in the Indian Seas. Nature 123, 163 (1929). https://doi.org/10.1038/123163a0
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DOI: https://doi.org/10.1038/123163a0
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