Microseisms associated with cyclones over north-east Australian waters

An examination has been made of microseisms at Brisbane in relation to four major cyclones during 1955, 1956 and 1957 supplemented by data from Townsville in 1957. Theory demands that amplitude should vary with the inverse square root of the distance. From the data considered this requirement is not confirmed but it is likely that the apparent failure may be due to the uncertainty of actual pressure intensity and precise location of the cyclones. A fair relation is obtained between amplitude of microseisms (A), distance (D) and central pressure (P) of the cyclone in the form: Log ADn=C - KP where n, C and K are constants. It is shown that amplitudes may be affected by the depth of the ocean over which the cyclone is moving. Limited data were available for comparing the ratios of amplitudes from the two stations Townsville and Brisbane especially as development in intensity of the February 1957 cyclone occurred during the period when it was over shallow water. As a criterion of shallow and deep water the 1,000 fathom depth contour was used. There is also a suggestion that the Townsville amplitudes are relatively high. The four cyclones did not give sufficient data to separate the conditions of cyclone development from progress of the mature storm.