Microseisms at Berkeley and Surf on near-by coasts*

Abstract

Summary and Conclusions The amplitudes of microseisms recorded at Berkeley correlate over six-months and yearly periods with surf strength on near-by beaches quite as well as the observations of surf strength at adjacent stations correlate with each other, all the correlation ratios being between 0.53 and 0.58. During a winter month the correlation between microseisms and surf rose to 0.81. A consideration of energies leads to the conclusion that the energy of average large microseisms at Berkeley can be explained as due to surf on near-by beaches if about 10−7 of the potential energy of probable-sized deep-water waves is eventually transformed into elastic Rayleigh waves at the near-by beaches. Not all microseisms at Berkeley are caused by near-by surf, but many may very well be. It is possible to pick periods when one is large and the other is not, and vice versa. It is also possible to find times when very heavy seas and very large microseisms begin together in a most conspicuous fashion.