Measuring and predicting sea floor pressure waves (Longuet-Higgins)

Ocean surface waves traveling in near-opposing directions with similar frequencies produce standing waves which create a second order pressure wave field that does not attenuate with depth (predicted by Longuet-Higgins in 1950). This second order pressure field oscillates at twice the frequency of the opposing waves and causes sea floor microseisms (~5-7um in height with frequencies 0.05 - 0.3 Hz) that can be detected at long distances. Our work aims to validate the presence of the second order pressure waves, predict where they regularly occur, and correlate their magnitude with environmental conditions. Here we present field measurements from sea floor pressure sensors deployed off Southern California and relate the results to surface wave buoys. We compare our field results to predicted areas of high microseism activity, estimated from coastal California wave buoy data.