Offshore observations make it possible to detect tsunamis in advance prior to their arrivals at the shoreline. For this purpose, ocean bottom pressure gauges are widely used. However, in near- and intermediate fields, ocean bottom pressure records usually exhibit a complicated interference of signals related not only to gravitational wave (i.e., tsunami), but also to hydroacoustic and seismic waves.Network of offshore observatories recently deployed in Japan is capable of providing high sampling rate of records of ocean bottom pressure and seismic (acceleration and velocity) signals.
In the present study, by taking advantage of simultaneous measurements of pressure and seismic signals that were recorded during the recent tsunamigenic earthquakes, i.e., the 2011 Tohoku earthquake and the related 2013 October earthquake, we reveal particular features of these signals. The bottom pressure follows the bottom acceleration in the inter-mediate frequency band.