1993 Okushiri earthquake

Earthquake in Japan 1993 Okushiri earthquake 北海道南西沖地震.jpg Aerial view of tsunami damage on Okushiri Island. 1993-07-12 13:17:11 usp0005w12 219326 July 12, 1993 22:17 Japan 7.7 w y 1993 Okushiri earthquake shakemap.jpg 16.7 km on 42.851 139.197 inline,title Japan, Hokkaido 5M 7.7 – 107 km W of Iwanai, Japan https://earthquake.usgs.gov/earthquakes/eventpage/usp0005w12/executive United States Geological Survey VIII Yes 230 dead The 1993 southwest-off Hokkaido earthquake 北海道南西沖地震 Hokkaidō Nansei Oki Jishin or Okushiri earthquake occurred at 13:17:12 UTC on 12 July 1993 in the Sea of Japan near the island of Hokkaido.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 https://web.archive.org/web/20171029091019/http://www.jma.go.jp/jma/kishou/know/meimei/meimei2.html 2017-10-29 It had a magnitude of 7.7 on the moment magnitude scale and a maximum felt intensity of VIII (Severe) 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. Tectonic setting Eastern margin of the Sea of Japan The northwestern side of Honshu lies on the southeastern margin of the Sea of Japan, an area of oceanic crust created by back-arc spreading associated with the convergent boundary where the Pacific plate is subducted beneath the Okhotsk microplate. The spreading was active from the late Oligocene to the middle Miocene. The extensional tectonics associated with the spreading formed a series of N–S trending extensional faults and associated sedimentary basins. Currently the area is being deformed by contractional tectonics, causing inversion of these earlier basins, forming anticlinal structures.Sato H. Yoshida T. Takaya I. Sato T. Ikeda Y. Umino N. amp 2004 Late Cenozoic tectonic development of the back arc region of central northern Honshu, Japan, revealed by recent deep seismic profiling Journal of the Japanese Association for Petroleum Technology 69 2 145–154 0370-9868 10.3720/japt.69.145 free It has been suggested that the northwestern coast of Honshu represents an incipient subduction zone,Kanamori H. Astiz L. 1985 The 1983 Akita-Oki Earthquake (Mw=7.8) and its Implications for Systematics of Subduction Earthquakes Earthquake Prediction Research 3 305–317 http://www.gps.caltech.edu/uploads/File/People/kanamori/HKepr85.pdf 21 June 2012 dead https://web.archive.org/web/20131211212533/http://www.gps.caltech.edu/uploads/File/People/kanamori/HKepr85.pdf 11 December 2013 but there remain significant uncertainties about the existence of the Okhotsk Plate and the nature and precise location of its boundary in the Sea of Japan, if it does exist.Tetsuzo Seno Taro Sakurai Seth Stein 1996 Can the Okhotsk plate be discriminated from the North American plate? Journal of Geophysical Research 101 B5 11305–11315 10.1029/96JB00532 1996JGR...10111305S Apel E. V. Bürgmann R. Steblov G. Vasilenko N. King R. Prytkov A 2006 Independent active microplate tectonics of northeast Asia from GPS velocities and block modeling Geophysical Research Letters 33 L11303 L11303 10.1029/2006GL026077 2006GeoRL..3311303A free This region has been the location for several historical earthquakes, such as the 1964 Niigata and 1983 Sea of Japan earthquakes, with reverse fault mechanisms, on faults trending approximately north–south. Damage 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. The quake caused fires to start in the town of Okushiri, adding greatly to the total damage. Characteristics Earthquake The earthquake had two distinct shocks. The first lasted for 20 seconds, while the second lasted 35 seconds. 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.http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5357&t=101650&s=13&d=22,26,13,12&nd=display https://web.archive.org/web/20171012202441/http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5357&t=101650&s=13&d=22,26,13,12&nd=display dead 12 October 2017 Comments for the Significant Earthquake NGDC 6 November 2010 Tsunami The resulting tsunami inundated large parts of Okushiri, despite its tsunami defences. Okushiri had been struck by another tsunami 10 years 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.http://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5357&t=101650&s=18&d=99,91,95,93&nd=display https://web.archive.org/web/20171013013149/https://www.ngdc.noaa.gov/nndc/struts/results?eq_0=5357&t=101650&s=18&d=99,91,95,93&nd=display dead October 13, 2017 Comments for the Tsunami Event NGDC 6 November 2010 Landslide The Okushiri-port landslide involved a volume of 150,000 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.Yamagishi H. 2000 Recent Landslides in Western Hokkaido, Japan Pure and Applied Geophysics 157 6–8 1115–1134 10.1007/s000240050020 2000PApGe.157.1115Y 106398949 Aftermath 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.https://www.shippai.org/fkd/en/cfen/CA1000618.html Okushiri Tsunami Generated by southwest-off Hokkaido earthquake Nakao M. Failure Knowledge Database 23 December 2025 See also List of earthquakes in 1993 List of earthquakes in Japan 1993 Kushiro earthquake References External links 219326 Category:Earthquakes of the Heisei era Category:Tsunamis in Japan Category:Earthquakes in Hokkaido Hokkaido Okushiri Hokkaidō earthquake 1993 Category:1990s landslides Category:1993 natural disasters Category:July 1993 in Asia Category:Tsunamis in South Korea Category:July 1993 in Japan