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Nobi (Mino-Owari), 1891

At 6:38 a.m. on October 28, the Neodani Fault in northern Gifu Prefecture ruptured. The force generated by the strike-slip earthquake pushed one edge of the fault approximately six meters upward, and the fault scarp remains visible at Midori, in Motosu City, Gifu Prefecture (fig. 1).

Seismic waves extended outward from the Neodani Valley, causing extensive destruction and loss of life in Gifu and Aichi prefectures and the cities of Gifu and Nagoya. The M8.0 earthquake killed 7,273, injured 17,175, destroyed approximately 140,000 structures, and damaged another 80,000. The Nōbi earthquake was felt from Sendai in the north to Kagoshima in the south. Areas of most severe ground motion reached seven on the Japanese seismic intensity scale, the maximum value.[1]

Meiji Sanriku, 1896

The Tōhoku region is subject to shaking from fault ruptures in four types of locations: (1) ocean trench earthquakes off the Sanriku or Fukushima

Figure 1 The Neodani fault scarp in 2011.

The 1891 Nobi earthquake raised the landmass to the right of the fault approximately six meters. Photo by Gregory Smits. coast; (2) intraplate earthquakes originating under northern Honshu or the Pacific; (3) shallow-focus inland earthquakes; and (4) intraplate earthquakes originating under the Sea of Japan. Three of these four types of earthquakes often generate tsunamis.[2] The Meiji Sanriku earthquake was an example of the first type.[3]

Along the Sanriku coast, the geographical interface between human settlements and the sea has often amplified the destructive power of tsunami waves. The coastline is deeply indented, and many of its bays and inlets are shaped roughly like a bugle, the bell end of which opens to the ocean. Fishing villages have been located at the narrow interiors of these bays at the precise point where tsunami wave height would be highest when a fixed quantity of water is forced into an increasingly narrow, shallow area.[4] The maximum wave height at Ryōri Village was 38.2 meters. This situation is one reason that the tsunami from the Meiji Sanriku earthquake killed twenty-two thousand when it struck on the evening of June 15. It was the deadliest tsunami in Japan's history, and it is likely to remain so even after the March 11, 2011, disaster in the same area.[5]

One important phenomenon that occurs in perhaps 10 percent of seismic events in the Tōhoku region is that an earthquake causing only mild ground motion produces a large, destructive tsunami. These dangerous events are known as “tsunami earthquakes,” a term coined in 1972 by Hiroo Kanamori of the California Institute of Technology. The Meiji Sanriku earthquake and tsunami of 1896 is the most recent example of the earth shaking so mildly that people did not expect the massive tsunami wave trains that followed. Two causal factors responsible for making Meiji Sanriku into a tsunami earthquake were the fault rupturing slowly and the rupture breaking and displacing accumulated sediments at the plate boundary.[6] The best estimate for the Meiji Sanriku earthquake is that a portion of the fault about 250 kilometers long ruptured over the course of about one hundred seconds. The resulting seismic land waves would have had such a long period that people would barely have felt them. The relatively slow fault rupture pushed unconsolidated sediments upward to produce a massive tsunami.[7]

Great Kanto, 1923

At two minutes before noon, while many cooking fires were burning on a windy day, a M7.9 earthquake shook Tokyo, its suburbs, and nearby areas of Kanagawa Prefecture. The Great Kantō Earthquake of September 1, 1923, remains the deadliest seismic event in Japan's recorded history, killing over
105,000. The epicenter was located in the northwest part of Sagami Bay. Although many people died as a direct result of the shaking, more deadly were the firestorms that swept through this densely populated urban area. The earthquake also generated tsunami waves, with maximum heights ranging from six to twelve meters throughout the area. Uplift in the region was common, reaching a maximum of about two meters.[8]

Showa Sanriku (Sanriku), 1933

At 2:31 in the morning of March 2, 1933, the M8.1 Shōwa Sanriku earthquake shook residents awake. Originating near the location of the 1896 Meiji Sanriku earthquake, the 1933 earthquake was the result of the rupture of an intraplate fault. Although geologically different from its 1896 predecessor, the 1933 earthquake was functionally similar in that it threw off large tsunami waves. The maximum wave height at Ryōri was 28.7 meters. The Shōwa Sanriku earthquake and tsunami resulted in slightly more than three thousand deaths and over one thousand injuries. The relatively low death toll compared with 1896 was in part the result of severe ground motion from the earthquake and social memory of the 1896 tsunami prompting people to flee to high ground. The shaking, waves, and fire combined destroyed over six thousand houses, and local residents endured seventy-seven aftershocks of M6 or higher for six months following the main shock.[9]

  • [1] Okada, Jishin chizu, 121–122; Usami, Higai jishin, 207–211; and Chūō bōsai kaigi, 1891 Nōbi jishin hōkokusho, Nihon shisutemu kaihatsu kenkyūsho, 2008, esp. 209.
  • [2] Okada Jishin chizu (Tōkyō shoseki, 2006), 52.
  • [3] For an account of modern Tōhoku tsunamigenic earthquakes, see Gregory Smits, “Danger in the Lowground: Historical Context for the March 11, 2011 Tōhoku Earthquake and Tsunami,” in Asia-Pacific Journal 9, issue 20, no. 4 (May 16, 2011).
  • [4] Itō Kazuaki, Jishin to funka no Nihonshi (Iwanami shoten, 2002), 106–107.
  • [5] For a comprehensive survey of the geology and damage from this earthquake, see Usami, Higai jishin, 219–230.
  • [6] Koshimura Shun’ichi and Shutō Nobuo, “Meiji Sanriku jishin tsunami,” in Chūō bōsai kaigi, 1896 Meiji Sanriku jishin tsunami hōkokusho, 2005, 15–17.
  • [7] Koshimura and Shutō, “Meiji Sanriku jishin tsunami,” 15, 17–20.
  • [8] Okada, Jishin chizu, 88–91; Usami, Higai jishin, 272–278; and Chūō bōsai kaigi, 1923 Kantō daishinsai hōkokusho, dai ippen (Nihon shisutemu kaihatsu kenkyūsho, 2006), esp. 238.
  • [9] Okada, Jishin chizu, p. 59; Itō, Jishin to funka no Nihonshi, 117; and Usami, Higai jishin, 302–306. For photos of Ryōri Bay before and after the 1933 tsunami, see http://protea.dbms.cs.gunma-u.ac.jp/TSUNAMI/tsunami_data/ IwateShowaShinsai_kawamoto/image/IwateShowaShinsai_00024.jpg.
 
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