Significant tsunami observed at ocean-bottom pressure gauges during the 2011 off the Pacific coast of Tohoku Earthquake

Abstract

The 2011 Tohoku Earthquake caused a devastating tsunami along the shoreline from the Tohoku to Kanto districts. Although many of the tide gauge stations along the Tohoku coast were saturated or damaged due to the tsunami, two cabled ocean-bottom tsunami sensors installed off Kamaishi successfully recorded the tsunami waveform just above the source rupture area. The records indicated a characteristic two-stage tsunami development sequence: a smoothly increasing tsunami amplitude from 0 to 2 m during the first 800 s from the earthquake origin time, and a short-period impulsive tsunami with a peak of more than 5 m in the following 200 s. Such observations strongly suggest the lack of any sea floor upheaval at the stations during the earthquake, and the occurrence of an extremely large slip in the shallow portion of the subducting Pacific Plate near the trench axis. The source model derived from the offshore tsunami records indicates that a very large slip of 57 m occurred off Miyagi near the trench axis, south of the rupture area of the 1896 Meiji Sanriku tsunami earthquake, and was the major source of the highly destructive tsunami that subsequently developed.

Experiments on generation of surface waves by an underwater moving bottom

“…6 The insets of figure 5 depict the bottom and the free-surface elevations at r = 0, ζ 0 (t) and η 0 (t), as a function of time. We observe in all cases that the free surface and the bottom are synchronized at the beginning of the motion.…”

Field measurements and numerical modeling for the run-up heights and inundation distances of the 2011 Tohoku-oki tsunami at Sendai Plain, Japan

“…Soon thereafter, a large tsunami (designated hereinafter as the 2011 Tohoku-oki tsunami) struck the Pacific coast of eastern Japan (e.g. Fujii et al, 2011;Hayashi et al, 2011;Maeda et al, 2011;Mori et al, 2011). After late March, the joint survey group conducted many field surveys to measure the run-up height, flow depth (= inundation depth), and inundation area of the tsunami along the Pacific coast of eastern Japan.…”

Dispersion and nonlinear effects in the 2011 Tohoku‐Oki earthquake tsunami

“…The ocean-bottom pressure gauges deployed in the focal area recorded the huge tsunami [Saito et al, 2011] produced by the seafloor rise of $ 5 m . The oncoming huge tsunami was recorded from offshore to onshore along the Sanriku coast Maeda et al, 2011]. The inundation heights and area were investigated widely along the Pacific coast of northeastern Honshu, Japan, by the 2011 Tohoku Earthquake Tsunami Joint Survey Group [e.g., Mori et al, 2011] and also by aerial photographs [Nakajima and Koarai, 2011].…”