1973 Nemuro earthquake: Difference between revisions

|isc-event = 759446

|magnitude = 7.88–7.9 {{M|w|link=y}}<br>7.4 {{M|j|link=yes}}<br>8.1 {{M|t|link=yes}}

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 11:55 local time. It stuck with an epicenter just off the [[Nemuro Peninsula]] in northern [[Hokkaidō]] and measured 7.87 to 7.9 on the moment magnitude scale ({{M|w}}), 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 |url=https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2014.0375 |access-date=16 April 2021 |publisher=The 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. Total damage from this earthquake is estimated atto be 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>

The name '''Nemuro-Oki earthquake''' itself refers to several 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 occurr along [[subduction zones]] when the [[Pacific Plate]] dives beneath the [[Okhotsk Plate|Okhotsk Sea Plate]] along the [[Kuril Trench]], located off the east coast of Hokkaidō and [[Kuril Islands]]. Subduction rate along the trench is estimated at 8 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 |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 span 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, anothera large subduction megathrust earthquake with an estimated magnitude of 8.3 {{M|w}} ruptured a 200 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 |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>

The 1973 magnitude 7.89 earthquake stuck at a depth of 48 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 |website=earthquake.usgs.gov |publisher=USGS |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 was 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 it thought to be capable of a magnitude 8.0 quake. Because of its location, this event was thoughtbelieved to be a repeat of the 1894 earthquake, but was later discovered that the 1973 quake had only rupture 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 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=Earthquake 2nd |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>

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 a maximum height of 2.81 meters struck the coast a few hours later at 15:20 , 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 |website=Japan Meteorological Agency |access-date=16 April 2021}}</ref>