The 1973 Nemuro earthquake, also known as the Nemuro-Oki (Nemuro Peninsula Offshore) earthquake (Japanese: 根室半島沖地震, Hepburn: Nemurohantō oki jishin) 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 7.8 on the moment magnitude scale (Mw ), 8.1 on the tsunami magnitude scale (Mt ) and 7.4 on the Japan Meteorological Agency magnitude scale (MJMA ).[2]
   Kushiro Tokyo | |
| UTC time | 1973-06-17 03:55:02 |
|---|---|
| USGS-ANSS | ComCat |
| Local date | 17 June 1973 |
| Local time | 11:55 JST |
| Magnitude | 7.8 Mw 7.4 MJMA 8.1 Mt |
| Depth | 48 km |
| Epicenter | 43°13′59″N 145°47′06″E / 43.233°N 145.785°E |
| Type | Thrust |
| Areas affected | Japan |
| Max. intensity | MMI VIII (Severe) JMA 5−–JMA 5+ |
| Tsunami | Yes |
| Aftershocks | 7.1 Ms [1] |
| Casualties | 27 injured |
The earthquake had a maximum Mercalli intensity of VIII (Severe) and measured level 5 on the 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 at US$5 million.[3]
Historical seismicity
The name Nemuro-Oki earthquake itself refers to several large historical earthquakes that have struck near the Nemuro Peninsula. Earthquakes here are of the megathrust type that occurr along subduction zones when the Pacific Plate dives beneath the 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.[4] An average recurrence interval of 72.2 years span between each large earthquake along this section of the subduction zone.[5]
In 1894, another subduction megathrust earthquake with an estimated magnitude of 8.3 Mw ruptured a 200 km section of the subduction zone.[6] 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.[7] At least one person was killed and some residents were injured.[8]
Earthquake
The 1973 magnitude 7.8 earthquake stuck at a depth of 48 km beneath the Nemuro Peninsula.[9] A rectangular rupture patch is located between that of the 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 thought to be a repeat of the 1894 earthquake, but was later discovered that the 1973 quake had only rupture the eastern half.[10] 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.[11]
Focal mechanism analysis revealed that this earthquake was the result of thrust faulting along the subduction plate boundary. Waveform inversion on teleseismic seismographs show that the earthquake ruptured up, towards the trench, or in a south–southeast direction. Maximum slip along the fault is estimated at 2.7 meters.[4]
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 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.[12]
Due to the advanced tsunami warning systems in place and frequent tsunami and earthquake drills in the region, impact from the tsunami was minimal.
See also
References
- ^ "M 7.1 - Kuril Islands". earthquake.usgs.gov. USGS. Retrieved 16 April 2021.
- ^ Kenji Satake (2015). "Geological and historical evidence of irregular recurrent earthquakes in Japan". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 373. The Royal Society. doi:10.1098/rsta.2014.0375. Retrieved 16 April 2021.
- ^ "Significant Earthquake Information JAPAN: HOKKAIDO ISLAND". ngdc.noaa.gov. NCEI. Retrieved 16 April 2021.
- ^ a b Nishimura, T. (2009). "Slip distribution of the 1973 Nemuro-oki earthquake estimated from the re-examined geodetic data" (PDF). Earth Planets Space. 61: 1203–1214. doi:10.1186/BF03352973. Retrieved 16 April 2021.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ "Other Trench-type Earthquakes (Headquarters for Earthquake Research Promotion)". Seismological Investigation and Research Promotion Headquarters (in Japanese). 2009. Retrieved 16 April 2021.
- ^ Satake, K., Nanayama, F., Yamaki, S. (2008). "Fault models of unusual tsunami in the 17th century along the Kuril trench" (PDF). Earth Planets Space. 60: 925–935. doi:10.1186/BF03352848. Retrieved 16 April 2021.
{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link) - ^ "Tsunami Event Information SE. HOKKAIDO ISLAND". ngdc.noaa.gov. NCEI. Retrieved 16 April 2021.
- ^ "Significant Earthquake Information JAPAN: OFF COAST OF HONSHU". ngdc.noaa.gov. NCEI. Retrieved 16 April 2021.
- ^ "M 7.7 - Hokkaido, Japan region". earthquake.usgs.gov. USGS. Retrieved 16 April 2021.
- ^ "History of Hokkaido Tsunami". Tsunami Digital Library. Retrieved 16 April 2021.
- ^ Tokutaro Hatori (23 October 1975). "1973年 根 室半 島沖津波 とそ の後の津 波活動" [Tsunami Activity in Eastern Hokkaido after the Off Nemuro Peninsula Earthquake in 1973]. Earthquake 2nd. 28 (4). Earthquake Research Institute, University of Tokyo: J-Stage. doi:10.4294/zisin1948.28.4_461. Retrieved 16 April 2021.
- ^ "On the Earthquake off Nemuro Peninsula, June 17, 1973" (PDF). Japan Meteorological Agency. Retrieved 16 April 2021.
External links
- The International Seismological Centre has a bibliography and/or authoritative data for this event.