Contribution of horizontal seismic oscillations of underwater slopes in the variation of bottom pressure

The relationship between the variations of bottom pressure and the components of acceleration of bottom movements was investigated making use of signals registered by deepwater observatories DONET during the Tohoku earthquake occurred on 11.03.2011. Cross-spectral analysis confirmed the existence of a frequency range of "forced oscillations", in which the pressure variations are proportional to the vertical component of the ocean bottom acceleration. A theoretical analysis of the problem of forced oscillations of a water layer of constant and variable depth is performed. A formula is obtained that relates the variations of the ocean bottom pressure with the components of the acceleration of the bottom movement and the components of the ocean depth gradient. It is shown that horizontal movements of steep underwater slopes are able to make a significant contribution to the variation of ocean bottom pressure directly above the slope and at a distance from the slope no more than 1-2 ocean depths.