Microseism propagation between two sites on the deep seafloor

Pressure and electric field fluctuations detected at two sites separated by a distance of 32 km on the deep seafloor are found to be partially coherent at frequencies between 0.05 and 0.6 Hz. The phase relationships observed between the two sites suggest coherent wave trains from three source regions produce the observed coherence. Plausible estimates for the azimuths to the sources can be obtained if Rayleigh wave phase velocities are assumed. Each source region is associated with a different peak in the power spectra of the pressure and electric field fluctuations. One source region is along the California coastline where microseisms between 0.05 and 0.1 Hz are generated by the steepening and breaking of swell along that coast. The two other source regions are in deep water where microseisms are produced by nonlinear interaction of surface gravity waves. These microseisms have frequencies which are double the frequency of principal surface gravity wave components. A region to the southeast of the two sites is associated with microseisms near 0.16 Hz, and a region to the northwest is associated with microseisms near 0.25 Hz.