1993 Hokkaidō earthquake

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1993 Southwest-off Hokkaido Earthquake
1993 Hokkaidō earthquake is located in Japan
1993 Hokkaidō earthquake
Date July 12, 1993 (1993-07-12)
Magnitude 7.7 Mw
Depth 17 km
Epicenter 42°51′04″N 139°11′49″E / 42.851°N 139.197°E / 42.851; 139.197Coordinates: 42°51′04″N 139°11′49″E / 42.851°N 139.197°E / 42.851; 139.197
Areas affected Japan, Hokkaido
Tsunami yes
Casualties 230

The 1993 southwest-off Hokkaido earthquake (北海道南西沖地震 Hokkaidō Nansei Oki Jishin?) occurred at 13:17:12 UTC on 12 July 1993 in the Sea of Japan near the island of Hokkaido.[1] It had a magnitude of 7.7 on the moment magnitude scale and a maximum felt intensity of VIII (Destructive) on the Mercalli intensity scale. It triggered a major tsunami that caused deaths on Hokkaidō and in southeastern Russia, with a total of 230 fatalities recorded. The island of Okushiri was hardest hit, with 165 casualties from the earthquake, the tsunami and a large landslide.[2]

Tectonic setting[edit]

The earthquake occurred in the backarc region of the convergent boundary where the Pacific Plate subducts beneath the Eurasian Plate.

Damage[edit]

The earthquake shaking caused moderately severe damage, VIII on the Mercalli scale. The tsunami reached Okushiri between 2 and 7 minutes after the earthquake. A tsunami warning was given 5 minutes after the earthquake by the JMA. However, this was too late for the inhabitants of Okushiri.[2] The quake caused fires to start in the town of Okushiri, adding greatly to the total damage.

Characteristics[edit]

Earthquake[edit]

The earthquake had two distinct shocks. The first lasted for 20 seconds, while the second lasted 35 seconds.[3]

The rupture occurred on a fault that dipped at 24 degrees to the east. It had an estimated length of 150 km with a displacement of 2.5 m. The island of Okushiri subsided by 5–80 cm.[2]

Tsunami[edit]

The tsunami inundated large parts of Okushiri, despite its tsunami defenses. Okushiri had been struck by another tsunami 10 year earlier. A maximum run-up of 32 m was recorded on the western part of the island near Monai. A tsunami was widely observed in the Sea of Japan with a run-up of 3.5 m at Akita in northern Honshu, up to 4.0 m in southeastern Russia and up to 2.6 m on the coast of South Korea.[4]

Landslide[edit]

The Okushiri-port landslide involved a volume of 1.5 x 105 m³ of rock. The slide failure occurred at the base of a volcanic breccia bed. The slide occurred in two phases that may match the two separate shocks recorded for the earthquake.[3]

Aftermath[edit]

The destructive power of this tsunami led to an overhaul of the sea defences on Okushiri involving the construction of tsunami sluices on a river and strengthened embankments. New escape routes were also provided and help was given for households to purchase emergency broadcast receivers.[5]

References[edit]

  1. ^ Japan Meteorological Agency officially named this earthquake 平成5年(1993年)北海道南西沖地震 (Heisei 5 nen (1993 nen) Hokkaidō nansei-oki jishin, literally the 1993 Southwest-off Hokkaido Earthquake). 気象庁が命名した気象及び地震火山現象
  2. ^ a b c NGDC. "Comments for the Significant Earthquake". Retrieved 6 November 2010. 
  3. ^ a b Yamagishi, H. (2000). "Recent Landslides in Western Hokkaido, Japan". Pure and Applied Geophysics 157 (6-8): 1115–1134. Bibcode:2000PApGe.157.1115Y. doi:10.1007/s000240050020. Retrieved 6 November 2010. 
  4. ^ NGDC. "Comments for the Tsunami Event". Retrieved 6 November 2010. 
  5. ^ Nakao, M. "Okushiri Tsunami Generated by southwest-off Hokkaido earthquake". Failure Knowledge Database. Retrieved 6 November 2010.