Refraction of Microseisms approaching Cochin

Abstract

FOR the proper interpretation of microseisms at a particular station it is essential to know the variation in velocity of seismic waves as they approach the station. This variation in velocity or the refraction of seismic waves has a considerable effect on the amplitude and direction of the microseisms recorded at a station and depends on the geology of the ocean bottom and bathymetric structure of the ocean between the source and the recording station. As it is extremely difficult to allow for the geology of the medium because of the scarcity of information about it, the effect due to the bathymetry of the ocean can be determined and refraction diagrams constructed if microseisms can be assumed to be Rayleigh waves propagated in a model consisting of a homogeneous compressible fluid medium over a uniform elastic medium. The propagation of Rayleigh waves in a layered medium was first described by Stoneley¹ and the velocities of such waves called Stoneley waves were computed later by several authors^2–4. The ocean can be considered as approximating such a model and the consequent variation Of Rayleigh wave velocity with ocean depth can be determined.