Structure of microseismic waves: estimation of direction of approach by comparison of vertical and horizontal components

Abstract

Analysis of microseisms recorded at Kew Observatory on 8 to 10 October 1951 affords further confirmation of the wave-interference theory of microseism generation, and allows those of 8 to 10 October to be attributed to a fast-moving depression between the Azores and Iceland. Although the bearing of the microseism-generating area changes by more than 90° during the period investigated, there is no appreciable difference in the ratio of the mean ampli­tudes of the north-south and east-west horizontal components as would be expected if the microseisms consisted entirely of Rayleigh waves. An investigation of the phase differences between the three components, using Lee’s method, suggests that the microseisms consist of Rayleigh and Love waves in comparable proportions. Making use of this assumption, the vertical component, which is not affected by the Love waves, is correlated with the two horizontal components with an electronic correlating device, and the bearing of the microseism area can be deduced from the correlation coefficients. The calculated bearings agree reasonably well with those obtained from the meteorological charts. The bearing of a storm on 12 to 15 November 1945, studied in a previous paper, was also calculated satisfactorily.