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{{short description|Earthquake off the Hokkaido coast in Japan}}
{{Infobox earthquake
|title = 1973 Nemuro Peninsula offshore earthquake<br /><small>根室半島沖地震 (''Nemurohantō oki jishin'')</small>
|timestamp = 1973-06-17 03:55:02
|anss-url = usp0000270
|isc-event = 759446
|isc-event-B = 759790
|local-date = 17 June 1973
|local-time = 1112:55 [[Japan Standard Time|JST]]
|map =
|map2 = {{Location map+|Japan|relief=1|width=250|float=none|border=none|caption=|places=
{{Location map~|Japan|lat=43.233|long=145.785|mark=Bullseye1.png|marksize=40|position=top}}
{{Location map~|Japan|lat=42.983|long=144.383|label=Kushiro|position=left|mark=Green pog.svg}}
{{Location map~|Japan|lat=35.7|long=139.715|label=Tokyo|position=left|mark=Green pog.svg}}}}
|magnitude = 7.8–7.9 {{M|w|link=y}}<br>7.4 {{M|j|link=yes}}<br>8.1 {{M|t|link=yes}}
|depth = {{convert|48 |km|sp=us|abbr=on}}
|location = {{coord|43.233|N|145.785|E|type:event_scale:50000000|display=inline,title}}
|type = [[Thrust fault|Thrust]]
|countries affected = [[Japan]]
|intensity = {{MMI|8}}<br><br>{{JMA|5-}} – {{JMA|5+}}
|damage =
|tsunami = 5.98 meters<ref name="NCEI" Yes/>
|landslide =
|aftershocks = 7.1 {{M|s}} (June 1973)<ref name="M 7.1">{{cite web |title=M 7.1 -– Kuril Islands |url=https://earthquake.usgs.gov/earthquakes/eventpage/usp00002bv/executive#executive |website=earthquake.usgs.gov |publisher=USGSUnited States Geological Survey |access-date=16 April 2021}}</ref> and 7.05–7.6 {{M|sw}} (June 1975)<ref name="Ioki" />
|casualties = 27 injured
}}
 
The '''1973 Nemuro earthquake''', also known as the {{nihongo|'''Nemuro-Oki (Nemuro Peninsula Offshore) earthquake'''|根室半島沖地震|Nemurohantō oki jishin|lead=yes}} in scientific literature, occurred on June 17 at 1112:55 local time. It stuckstruck with an epicenter just off the [[Nemuro Peninsula]] in northern [[Hokkaidō]], and[[Japan]]. It measured 7.7 to 78–7.9 on the moment magnitude scale ({{M|w}}),<ref name="M 7.7 usgs" /> 8.1 on the tsunami magnitude scale ({{M|t}}) and 7.4 on the [[Japan Meteorological Agency]] magnitude scale ({{M|j}}).<ref>{{cite journal |author1=Kenji Satake |title=Geological and historical evidence of irregular recurrent earthquakes in Japan |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |date=2015 |volume=373 |issue=2053 |doi=10.1098/rsta.2014.0375 |urlpublisher=https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2014.0375The Royal Society|access-datepmid=16 April 202126392616 |publisherbibcode=The2015RSPTA.37340375S Royal Society|doi-access=free }}</ref>
 
The earthquake had a maximum [[Mercalli intensity]] of VIII (''Severe'') and measured level 5 on the [[Japan Meteorological Agency seismic intensity scale|JMA intensity scale]]. It also triggered a [[tsunami]] with observed heights of nearly 3 meters hitting the coastal regions of Hokkaidō and, causing damage. No deaths were recorded but twenty-seven individuals suffered injuries, mostly due to falling objects. TotalThe total damage from thisthe earthquake is estimated to beat US$5 million.<ref>{{cite web |title=Significant Earthquake Information JAPAN: HOKKAIDO ISLAND |url=https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/4638 |website=ngdc.noaa.gov |publisher=NCEI |access-date=16 April 2021}}</ref>
 
==Historical seismicity==
The term '''Nemuro-Oki earthquake''' itself refers to large historical earthquakes that have struck near the Nemuro Peninsula on the island of Hokkaidō in Japan. Earthquakes here are of the [[megathrust]] type that occurroccur along [[subduction zones]] when the [[Pacific Plateplate]] dives beneath the [[Okhotsk Platemicroplate|Okhotsk Sea Plateplate]] along the [[Kuril Trench]], located off the east coast of Hokkaidō and [[Kuril Islands]]. Subduction rate along the trench is estimated at 8 &nbsp;cm/yr.<ref name="Slip distribution">{{cite journal |last1=Nishimura, T. |title=Slip distribution of the 1973 Nemuro-oki earthquake estimated from the re-examined geodetic data |journal=Earth Planets Space |date=2009 |volume=61 |issue=11 |pages=1203–1214 |doi=10.1186/BF03352973 |bibcode=2009EP&S...61.1203N |url=https://link.springer.com/content/pdf/10.1186/BF03352973.pdf |access-date=16 April 2021|doi-access=free }}</ref> An average recurrence interval of 72.2 years spanspans between each large earthquake along this section of the subduction zone.<ref>{{cite web |title=Other Trench-type Earthquakes (Headquarters for Earthquake Research Promotion) |url=http://www5d.biglobe.ne.jp/~kabataf/hyouka_chisima_trench.htm |website=Seismological Investigation and Research Promotion Headquarters |access-date=16 April 2021 |language=Japanese |date=2009}}</ref>
 
In 1894, a large subduction megathrust earthquake with an estimated magnitude of 8.3 {{M|w}} ruptured a 200 &nbsp;km section of the subduction zone.<ref name="Tsunami">{{cite journal |last1=Satake, K., Nanayama, F., Yamaki, S. |title=Fault models of unusual tsunami in the 17th century along the Kuril trench |journal=Earth Planets Space |date=2008 |volume=60 |issue=9 |pages=925–935 |doi=10.1186/BF03352848 |bibcode=2008EP&S...60..925S |url=https://core.ac.uk/download/pdf/205064828.pdf |access-date=16 April 2021|doi-access=free }}</ref> It generated a tsunami with wave heights of up to 4 meters slamming into the coast between 20 minutes to one hour after the earthquake. Both the earthquake and tsunami damaged many homes and caused ground fissures. The waves washed away many homes, a few vessels and bridges.<ref>{{cite web |title=Tsunami Event Information SE. HOKKAIDO ISLAND |url=https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/event-more-info/1208 |website=ngdc.noaa.gov |publisher=NCEI |access-date=16 April 2021}}</ref> At least one person was killed and some residents were injured.<ref>{{cite web |title=Significant Earthquake Information JAPAN: OFF COAST OF HONSHU |url=https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/2443 |website=ngdc.noaa.gov |publisher=NCEI |access-date=16 April 2021}}</ref>
 
==Earthquake==
[[File:M 7.7 - Hokkaido, Japan region - Shakemap.jpg|260px|thumb|USGS ShakeMap of the 1973 Nemuro Peninsula earthquake.]]
The 1973 magnitude 7.9 earthquake stuckstruck at a depth of 48 &nbsp;km beneath the Nemuro Peninsula.<ref name="M 7.7 usgs">{{cite web |title=M 7.7 -– Hokkaido, Japan region |url=https://earthquake.usgs.gov/earthquakes/eventpage/usp0000270/executive |websitepublisher=earthquake.usgs.govUnited |publisher=USGSStates Geological Survey |access-date=16 April 2021}}</ref> A rectangular rupture patch is located between that of the [[1952 Hokkaido earthquake|1952 Tokachi]] and 1969 Kuril Islands earthquakes waswere the source area of the 1973 event. This section of the subduction zone was previously designated a [[seismic gap]] due to the lack of seismic activity throughout the last 80 years, and itis thought to be capable of a magnitude 8.0 quake. Because of its location, this event was believed to be a repeat of the 1894 earthquake, but was later discovered that the 1973 quake had only ruptureruptured the eastern half.<ref name="History of Hokkaido Tsunami">{{cite web |title=History of Hokkaido Tsunami |url=http://tsunami-dl.jp/document/150 |website=Tsunami Digital Library |access-date=16 April 2021}}</ref> Therefore, the 1973 event was a much smaller event than in 1894. An 80 &nbsp;km-long section in the subduction zone between the 1973 and 1952 rupture zones still exist, with the possibility of generating a large earthquake.<ref name="October 1975">{{cite journal |author1=Tokutaro Hatori |title=Tsunami Activity in Eastern Hokkaido after the off Nemuro Peninsula Earthquake in 1973 |journal=EarthquakeZisin (Journal of the Seismological Society of Japan) |series=2nd series |date=23 October 1975 |volume=28 |issue=4 |pages=461–471 |doi=10.4294/zisin1948.28.4_461 |url=https://www.jstage.jst.go.jp/article/zisin1948/28/4/28_4_461/_pdf/-char/ja |access-date=16 April 2021 |trans-title=Tsunami Activity in Eastern Hokkaido after the Off Nemuro Peninsula Earthquake in 1973 |publisher=J-Stage |location=Earthquake Research Institute, University of Tokyo|doi-access=free }}</ref>
 
[[Focal mechanism]] analysis revealed that this earthquake was the result of thrust faulting along the subduction plate boundary. Waveform inversion on teleseismic [[seismographs]] showshowed that the earthquake ruptured upupwards, towardsto the trench, or in a south–southeast direction. MaximumThe maximum slip along the fault is estimated at 2.7 meters.<ref name="Slip distribution" />
 
==Tsunami==
Immediately after the earthquake, at 13:06 local time, the Sapporo District Meteorological Observatory broadcast a tsunami warning to residents along the Pacific coast of Hokkaidō. Residents of the Tōhoku region would receive a tsunami warning at 13:13. The tsunami with aheights maximumranging height offrom 2.81 to 5.98 meters struck the coast a few hours later at 15:20,<ref name="NCEI">{{cite web |title=Tsunami Event Information |url=https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/event-more-info/2060 |website=earthquake.usgs.gov |publisher=NCEI |access-date=29 June 2021}}</ref> causing damage to about 300 buildings. No deaths were reported from the tsunami.<ref>{{cite web |title=On the Earthquake off Nemuro Peninsula, June 17, 1973 |url=https://cais.gsi.go.jp/YOCHIREN/report/kaihou10/01_01.pdf |websitepublisher=Japan Meteorological Agency |access-date=16 April 2021}}</ref>
 
Due to the advanced [[tsunami warning systems]] in place and frequent tsunami and earthquake drills in the region, impact from the tsunami was minimal.
 
==Aftershocks==
Seven days after the mainshock, a magnitude ({{M|s}}) 7.1 earthquake struck west of the Nemuro Peninsula at a depth of 50 &nbsp;km.<ref name="M 7.1" /> It had a maximum Mercalli intensity of VIII or a JMA intensity of 5, lasting for less than a minute. In the community of Goryachiy Plyazh and Golovnino on Kunashir Island, it was felt stronger than the mainshock. Some frightened residents jumped from the windows of their homes. One person was injured and some minor damage was reported in Kushiro, Hokkaidō.<ref>{{cite web|title=Significant Earthquake: RUSSIA: KURIL ISLANDS| url=https://www.ngdc.noaa.gov/hazel/view/hazards/earthquake/event-more-info/4639|publisher=[[National Geophysical Data Center]]| accessdate=May 9, 2021 |date=June 24, 1973}}</ref>
 
===1975 Kuril Islands earthquake===
The '''1975 Kuril Islands earthquake''' which struck on June 10, nearly two years after the 1973 event1975, was also considered an aftershock.<ref name="Yoshio">{{cite journal |last1=Yoshio |first1=Fukao |title=Tsunami earthquakes and subduction processes near deep-sea trenches |journal=JOURNALJournal OFof GEOPHYSICALGeophysical RESEARCHResearch |date=10 May 1979 |volume=84 |issue=B5 |pages=2303-23142303–2314 |doi=10.1029/JB084iB05p02303 |bibcode=1979JGR....84.2303F |url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JB084iB05p02303 |access-date=11 June 2021}}</ref> It ruptured the shallow interface of the Kuril SunductionSubduction Zone with a focal depth of 15 &nbsp;km, between the rupture zones of the 1973 and [[1969 Kuril Islands earthquake|1969 earthquakes]]. Although it had a smaller surface wave magnitude and JMA magnitude of 7.1,<ref name="Sapporo">{{cite journal |title=北海道東部沖地震のお知らせ |journal=Sapporo District Meteorological Observatory |date=1976 |trans-title=Report on the Earthquake Off E coast of Hokkaido |language=Japaneseja}}</ref><ref name="M 7.0">{{cite web |title=M 7.0 -– Kuril Islands |url=https://earthquake.usgs.gov/earthquakes/eventpage/usp0000bdp/executive |websitepublisher=earthquake.usgs.govUnited |publisher=USGSStates Geological Survey |access-date=11 June 2021}}</ref> it generated tsunami run-ups higher than the mainshock, at 5.5 meters.<ref name="Bryant">{{cite book |last1=Bryant |first1=Edward |title=Tsunami: The Underrated Hazard |date=2008 |publisher=Springer-Verlag Berlin Heidelberg |isbn=978-3-642-09361-6 |edition=2 |url=https://www.springer.com/gp/book/9783642093616|pages=129-138129–138|chapter=5. Earthquake-generated tsunami|chapter-url=https://books.google.com/books?id=6lvl6i7r2CcC&pg=PA131}}</ref> Further analysis of event data has enabled the calculationrecalculation forof the moment magnitude and tsunami magnitude of the earthquake. Two studies in 1978 and 1977 calculated the magnitude atto be {{M|w}} 7.5–7.6 and 7.7, respectively.<ref name="Ioki">{{cite journal |last1=Ioki, K., Tanioka, Y. |title=Rupture Process of the 1969 and 1975 Kurile Earthquakes Estimated from Tsunami Waveform Analyses |journal=Pure and Applied Geophysics |date=2016 |volume=173 |issue=12 |pages=4179–4187 |doi=10.1007/s00024-016-1402-0 |urlbibcode=https://link2016PApGe.springer173.com/article/10.1007/s00024-016-1402-04179I |access-date=11 June 2021|doi-access=free }}</ref> Estimating the tsunami magnitude of the event using tsunami data placesassigned this event atan {{M|t}} of 7.9. The 1975 aftershock is considered a [[tsunami earthquake]] due to the disproportionately large tsunami that it generated.<ref name="Ioki" />▼
 
▲The '''1975 Kuril Islands earthquake''' which struck on June 10, nearly two years after the 1973 event was also considered an aftershock.<ref name="Yoshio">{{cite journal |last1=Yoshio |first1=Fukao |title=Tsunami earthquakes and subduction processes near deep-sea trenches |journal=JOURNAL OF GEOPHYSICAL RESEARCH |date=10 May 1979 |volume=84 |issue=B5 |pages=2303-2314 |doi=10.1029/JB084iB05p02303 |url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JB084iB05p02303 |access-date=11 June 2021}}</ref> It ruptured the shallow interface of the Kuril Sunduction Zone with a focal depth of 15 km, between the rupture zones of the 1973 and 1969 earthquakes. Although it had a smaller surface wave magnitude and JMA magnitude of 7.1,<ref name="Sapporo">{{cite journal |title=北海道東部沖地震のお知らせ |journal=Sapporo District Meteorological Observatory |date=1976 |trans-title=Report on the Earthquake Off E coast of Hokkaido |language=Japanese}}</ref><ref name="M 7.0">{{cite web |title=M 7.0 - Kuril Islands |url=https://earthquake.usgs.gov/earthquakes/eventpage/usp0000bdp/executive |website=earthquake.usgs.gov |publisher=USGS |access-date=11 June 2021}}</ref> it generated tsunami run-ups higher than the mainshock, at 5.5 meters.<ref name="Bryant">{{cite book |last1=Bryant |first1=Edward |title=Tsunami: The Underrated Hazard |date=2008 |publisher=Springer-Verlag Berlin Heidelberg |isbn=978-3-642-09361-6 |edition=2 |url=https://www.springer.com/gp/book/9783642093616|pages=129-138|chapter=5. Earthquake-generated tsunami|chapter-url=https://books.google.com/books?id=6lvl6i7r2CcC&pg=PA131}}</ref> Further analysis of event data has enabled the calculation for the moment magnitude and tsunami magnitude of the earthquake. Two studies in 1978 and 1977 calculated the magnitude at {{M|w}} 7.5–7.6 and 7.7 respectively.<ref name="Ioki">{{cite journal |last1=Ioki, K., Tanioka, Y. |title=Rupture Process of the 1969 and 1975 Kurile Earthquakes Estimated from Tsunami Waveform Analyses |journal=Pure and Applied Geophysics |date=2016 |volume=173 |pages=4179–4187 |doi=10.1007/s00024-016-1402-0 |url=https://link.springer.com/article/10.1007/s00024-016-1402-0 |access-date=11 June 2021|doi-access=free }}</ref> Estimating the tsunami magnitude of the event using tsunami data places this event at {{M|t}} 7.9. The 1975 aftershock is considered a [[tsunami earthquake]] due to the disproportionately large tsunami that it generated.<ref name="Ioki" />
 
==See also==
Line 67 ⟶ 66:
 
[[Category:1973 earthquakes]]
[[Category:197320th-century floods in Asia]]
[[Category:19731970s in Japanfloods]]
[[Category:June 1973 events in Asia]]
[[Category:Tsunamis in Japan]]
[[Category:Earthquakes of the Showa period]]
[[Category:Earthquakes in Hokkaido]]
[[Category:1973 disasters in Japan]]
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