Micro-tsunami detected by cabled ocean-bottom tsunami meters off Sanriku

On 31 May, 1998, a moderate-to-strong earthquake (Mw6.1) occurred off Sanriku, Japan. Conventional or traditional tide gauges nearby did not observe any tsunami signal. Two tsunami meters (TMs) deployed on the deep ocean-bottom off Sanriku, however, could observe a long-period (similar toseveral minutes) hydro-pressure change following the event. We carry out 3-D numerical computation based on hydrodynamic equations to ascertain the origin of the hydro-pressure change observed by the TMs. We assume a rectangular fault model, with a constant rupture velocity, deduced from the aftershock distribution previously determined. The boundary condition of the 3-D numerical computation is the dynamic motion of ocean-bottom due to the given fault rupture. As a result, we verify that the long-period hydro-pressure change is associated with "micro-tsunami" with amplitudes of only 10 nun in sea surface level.