| Okhotsk plate | |
|---|---|
 | |
| Type | Minor |
| Movement1 | South-west |
| Speed1 | 13–14 mm/year |
| Features | Hokkaido,Kamchatka Peninsula,Kantō,Kuril Islands,Magadan Oblast,Sakhalin Island,Sea of Okhotsk,Tōhoku |
| 1Relative to theAfrican plate | |
TheOkhotsk plate[1] is aminor tectonic plate covering theKamchatka Peninsula,Magadan Oblast, andSakhalin Island of Russia;Hokkaido,Kantō andTōhoku regions of Japan; theSea of Okhotsk, as well as the disputedKuril Islands.
Japan's principal fault system is the zone where theAmur plate, the Eastern edge of the Eurasian plate, meets the Okhotsk plate, sometimes considered the Western edge of theNorth American plate.[2]
It is controversial whether the northern Honshu, Okhotsk and North American plate constitute separate blocks or plates. "A slightly better fit to data is obtained" when the proposed blocks, Honshu and Okhotsk, are independent of North America, so some studies make this an assumption of their analysis.[3]
The boundary is aleft-lateral movingtransform fault, theUlakhan Fault originating from atriple junction in theChersky Range.
During the 1970s Japan was thought to be located on the Eurasian plate at a quadruple junction with the North American plate, the Pacific plate and the Philippines Plate. At that time the western boundary of the North American plate was drawn through southernHokkaido. In the 1980s, the boundary of the North American plate was extended to theJapan Sea and theItoigawa-Shizuoka Tectonic Line (I-STL) due to earthquakes occurring at the eastern edge of the Japan Sea. 1990s research supported a proposal of an Okhotsk microplate independent from the North American plate.[4][3]
The southern boundary through I-STL was proposed by Peter Bird in 2003 and places Japan on the Okhotsk Plate.[5] Other researchers have proposed a plate boundary that passed throughHokkaido during theNeogene. Under their proposal, northeastern Japan and western Hokkaido would have been part of theEurasian plate in the Neogene.[4]
Theboundary between Okhotsk microplate and Amurian microplate might be responsible for many strong earthquakes that occurred in theSea of Japan as well as inSakhalin Island, such as theMW7.1 (MS7.5 according to other sources)earthquake of May 27, 1995 in northern Sakhalin.[6][7][8] The earthquake devastated the town ofNeftegorsk, which was not rebuilt afterwards. Other notableintraplate earthquakes such as the1983 Sea of Japan earthquake,1993 Hokkaidō earthquake and the2024 Noto earthquake have triggered tsunamis in the Sea of Japan.
The boundary between Okhotsk microplate and Pacific plate is asubduction zone, where the Pacific plate subducts beneath the Okhotsk Plate. Many giantmegathrust earthquakes have occurred here, some of them among the largest ever recorded, including theKamchatka earthquakes of1737 (Mw 9.0-9.3),1952 (Mw 9.0) and2025 (Mw 8.8). Such strong megathrust earthquakes can also occur near theKuril Islands, as the Mw 8.3 earthquake of November 15, 2006,[9][10]Hokkaido, as the Mw 8.3 earthquake of September 26, 2003[11][12] andHonshu, as the Mw 9.0 earthquake of March 11, 2011.[13]
GPS measurements and other studies show that the Okhotsk microplate is slowly rotating in a clockwise direction. Models indicate that it rotates 0.2 deg/Myr about a pole located north ofSakhalin.[14]
In 2011 aMw 9.0–9.1underseamegathrust earthquake caused by thesubduction of the Pacific plate below the Okhotsk microplate. The worst effected areas inTohoku, Japan experiencedaround six minutes of shaking. The main slip occurred at the "North America or Okhotsk plate".[15]
