Refraction of Microseisms

Abstract

IT is well established now that microseisms, the small tremors of varying intensity (in the range of 2–10 sec. period and of the order of a few microns in amplitude) recorded as more or less a permanent background by seismographs, are caused by sea waves associated with cyclonic depressions. The possibility of using these waves for location and tracking of storms has been investigated by many workers, and various techniques for estimating the direction of arrival have been put forward. But as the accuracy of estimation of direction of arrival is improved, corrections have to be applied to allow for the refraction of the waves due to variations in the velocity of propagation along the path from the generating area to the recording station. Microseisms are surface waves of the Rayleigh and Love type, and hence can be affected by variations in the geological structure of the Earth's crust and the changes in ocean depth along the path. While it is very difficult to estimate corrections for the geological configuration of the Earth's crust, the effect due to ocean depth can be calculated.