We process the JAMSTEC ocean-bottom pressure gauges and ocean-bottom seismometers datasets obtained during the 2003 Tokachi-oki tsunamigenic earthquake-the first records which have ever been obtained in a large tsunami source. On these records, we discover the unique phenomenon in tsunami source-hydroacoustic resonance, i.e. manifestation of long-lasting elastic oscillations of water column at the minimal normal frequency (≈ 0.14 Hz). The concept of a weakly coupled system is applied in 3D numerical simulation of the Tokachi-oki event. First, we simulate earthquake ground motion due to seismic fault rupturing. Then, compressible water column disturbance resulting from the dynamic seismic ground motion is simulated using the velocity of bottom deformation as an input to the water column. Comparison between JAMSTEC in-situ measurements and synthetic signals is carried out.

Water pressure changes have been recorded during the 2011 Tohoku earthquake (Mw9.0) by two oceanbottom pressure gauges of the JAMSTEC cabled observatory located approximately 400 km north of the tsunami source. In the present study, observed water pressure fluctuations have been interpreted by timefrequency processing analysis, followed by a comparison with those fluctuations of ocean-bottomseismometers. Acoustic resonance has been involved due to seismic waves even in the intermediate-field. The present study suggests that water pressure fluctuations during the 2011 Tohoku earthquake are dominated by oceanbottom acceleration and velocity for the intermediate frequency range and the high-frequency range, respectively, and its threshold roughly coincides with the fundamental acoustic resonant frequency. Water pressure amplitude is independent, in contrast, on bottom oscillations in the low-frequency range, for which the threshold is related to intermediate waves rather than shallow water waves.

The December 26, 2004 Sumatra-Andaman earthquake that registered a moment magnitude (M w ) of 9.1 was one of the largest earthquakes in the world since 1900. The devastating tsunami that resulted from this earthquake caused more casualties than any previously reported tsunami. The number of fatalities and missing persons in the most seriously affected countries were 736,322,212. This paper describes two field visits to assess tsunami effects in Sri Lanka by a combined team of Japanese and Sri Lankan researchers. The first field visit from December 30, 2004 -January 04, 2005 covered the western and southern coasts of Sri Lanka including the cities of Moratuwa, Beruwala, Bentota, Pereliya, Hikkaduwa, Galle, Talpe, Matara, Tangalla and Hambantota. The objectives of the first field visit were to investigate the damage caused by the tsunami and to obtain eyewitness information about wave arrival times. The second field visit from March 10-18, 2005 covered the eastern and southern coasts of Sri Lanka and included Trincomalee, Batticaloa, Arugam Bay, Yala National Park and Kirinda. The objectives of the second visit were mainly to obtain eyewitness information about wave arrival times and inundation data, and to take relevant measurements using GPS instruments.

A simulation of the tsunami run-up during the 2011 Great Tohoku Earthquake was performed to investigate the mechanisms and differences in overturning failures of buildings in Onagawa, based on a two-dimensional (2-D) shallow water equation with video evidence recorded in the town as reference. The time histories of inundation depth and flow velocity predicted by the analysis enable one to develop a simplified method to estimate the hydrodynamic and buoyant forces acting on a building, as well as its factors of safety against sliding, uplift, and overturning in the time domain. This method was applied to five well-documented cases of buildings that did or did not overturn during the tsunami. Results showed that the proposed method is capable of predicting the differences in building performance qualitatively, including the likelihood, time, and direction of toppling. The results also suggested that the seaward overturning of one building is likely due to its specific topographical location with a hill closely behind that makes the tsunami load significantly less during run-up than during backwash.

The translational accelerations recorded by strong-motion seismometers are often contaminated by baseline offsets that prevent recovering the ground displacements by double integration. Detailed analysis of the K-NET95 strong-motion seismometer, and the improvement of the visual display of the recorded accelerations' Fourier transform by addition of long zero pads to the acceleration records, made it possible to distinguish the origins of the long-period noise that contaminate the translational accelerations recorded in the near field of two studied earthquakes, the 2004 Niigata-ken Chuetsu earthquake and the 2007 Niigata-ken Chuetsu-Oki earthquake, Japan. They are the residual rotation of the instrument (residual tilt) or the 1=f digital semiconductor noise. The quantification of these two terms allows us to discuss the low-frequency content of the records and to describe when it is possible to obtain realistic displacement time histories. It happens when the residual tilt is removed in the time-domain or when the 1=f semiconductor noise overshadows the translational acceleration records up to sufficiently small frequencies. As a check of the method, displacement time histories obtained from acceleration records are compared with nearby 1-Hz GPS data. Good similitudes are obtained in the near field for collocated instruments.