Abstract
The 2011 Tohoku earthquake generated a huge, destructive tsunami with coastal heights of up to 40 m recorded along northern Honshu. The Sanriku coast experienced similar tsunamis and damage from the 1896 and 1933 Sanriku earthquakes, whereas the only damaging tsunamis on both the Ibaraki and Chiba coasts in the previous century were from the 1960 and 2010 Chile earthquakes. We summarized 12 field surveys in which the height of the 2011 tsunami was recorded at 296 points, along with descriptions of the survey method, reliability, and accuracy. We then compared them with the above-mentioned tsunamis at locations for which specific measurements were given in previous reports. On the Sanriku coast, the 2011 tsunami heights are positively correlated with the previous Sanriku tsunamis, indicating that local variations resulting from the irregular coastline were more dominant factors than the earthquake location, type, or magnitude for near-field tsunamis. The correlations with the Chilean tsunami heights are less significant due to the differences between the local and trans-Pacific tsunamis. On the Ibaraki and Chiba coasts, the 2011 Tohoku and the two Chilean tsunami heights are positively correlated, showing the general decrease toward the south with small local variations such as large heights near peninsulas.
Highlights
IntroductionOn March 11, 2011, a giant earthquake, officially named the ‘‘2011 off the Pacific coast of Tohoku earthquake’’ by the Japan Meteorological Agency
On March 11, 2011, a giant earthquake, officially named the ‘‘2011 off the Pacific coast of Tohoku earthquake’’ by the Japan Meteorological Agency (JMA), occurred along the Japan Trench where the Pacific plate subducts beneath the Okhotsk plate (Fig. 1)
R runup height; I inundation height; P tsunami height in ports a 2011 heights above sea level at time of maximum tsunami b Rel.: reliability, A: most reliable based on clear physical evidence or eyewitness account; B: mostly based on natural traces; C: least reliable based on equivocal evidence c Acc.: accuracy, a: measurement error \0.2 m; b 0.2 B error B 0.5 m; c error [0.5 m d Iki: runup heights taken from IKI (1897). 1 foot = 0.305 m
Summary
On March 11, 2011, a giant earthquake, officially named the ‘‘2011 off the Pacific coast of Tohoku earthquake’’ by the Japan Meteorological Agency. (JMA), occurred along the Japan Trench where the Pacific plate subducts beneath the Okhotsk plate (Fig. 1) This earthquake, which we refer to as the 2011 Tohoku earthquake in this paper, was the largest earthquake in Japan since the beginning of modern instrumental observations. For the Pacific coasts of Ibaraki and Chiba prefectures, we compare the 2011 tsunami heights with the 1960 and 2010 Chilean tsunami heights because no damaging tsunamis were recorded from near-field earthquakes in the last century. On the other areas of the Sanriku coast, and the Ibaraki and Chiba coasts, local variations are smaller and the general pattern of tsunami heights reflects the location, slip distribution, and magnitude of the parent earthquake. For the Sanriku coast, we compare the 2011 tsunami heights and inundation areas with two local tsunamis (i.e., the 1896 and 1933 Sanriku tsunamis) and two trans-Pacific tsunamis (i.e., 1960 and 2010 Chilean tsunamis) at selected
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