A Study of Microseisms in South Africa

Summary Microseisms have been recorded at Hermanus near Cape Town since 1961 October, using an N. I. O. two-component horizontal seismograph. Wave records have also been taken by means of a shipborne wave recorder aboard R. S. Africana II. The spectra of waves and microseisms due to a storm in 1962 April are compared and there is a two to one frequency relationship as would be expected from the wave interference theory of microseism generation. Estimates were made of the direction of approach of the microseisms, assuming various models and allowing for the effect of refraction. The evidence on the whole suggests that the microseisms consist of a mixture of Rayleigh and Love waves coming from the same range of directions.