Where the Amur Plate is
The Amur Plate (also called the Amurian Plate) covers about 5.3 million square kilometers, or 1.04% of Earth’s surface. It holds almost all of the Korean Peninsula: 99.7% of South Korea and 90.9% of North Korea. It also carries 41.9% of Japan, mainly southwest Honshu, Shikoku and northern Kyushu, about a third of Mongolia, 16% of China in the northeast, and 10.5% of Russia in the Far East. The Sea of Japan lies on the plate as well.
Most of the plate is old continental crust. Its interior is quiet compared with its edges, and many textbook maps simply color it as part of Eurasia.
What happens at its edges
The longest boundary, 6,586 km, is with the Eurasian Plate. PB2002 classifies 4,019 km of it as continental rift and 1,927 km as continental transform, with a short collision segment. The relative speed is about 0.8-1.0 cm/yr. The best-known part is the Baikal Rift Zone in Siberia, where the crust is being pulled apart and Lake Baikal, the deepest lake on Earth, fills the rift valley.
To the east, the plate meets the Okhotsk Plate along 2,304 km of convergent boundary that runs through Sakhalin and along the eastern margin of the Sea of Japan into central Honshu. The two plates squeeze together at about 0.7-0.9 cm/yr. The fastest edge is in the southeast, where the Philippine Sea Plate subducts beneath southwest Japan at the Nankai Trough, 762 km long, at about 4.4-5.6 cm/yr.
Near Kyushu, a 383 km boundary with the Okinawa Plate is pulling apart at about 0.3-1.7 cm/yr as the Okinawa Trough opens. In eastern China, a 589 km transform boundary with the Yangtze Plate moves at only about 0.4 cm/yr.
Earthquakes
The dataset lists 77 earthquakes of magnitude 6.5 or larger on the plate since 1900, three of them magnitude 8 or more. All three struck near the Nankai Trough off southwest Japan: the 1946 Nankai earthquake (M8.3), the 1944 Tonankai earthquake (M8.1) and the 1941 Hyuganada earthquake (M8.0). These are megathrust events, where the overlying Amur Plate snaps back after being dragged down by the subducting Philippine Sea Plate.
Inland faults matter too. On New Year’s Day 2024, the Noto Peninsula earthquake (M7.5) struck on the Sea of Japan coast of central Honshu, near the zone where the Amur and Okhotsk plates converge. It raised parts of the coastline and generated a tsunami.
Volcanoes
The plate holds 23 volcanoes in the dataset. In Japan, subduction at the Nankai Trough feeds Mount Aso, Kuju and Unzen on Kyushu, where Unzen produced deadly pyroclastic flows in 1991. Ontake in central Honshu killed dozens of hikers in a sudden steam-driven eruption in 2014. Away from the trench, Paektu Mountain (Changbaishan) on the China and North Korea border produced one of the largest eruptions of the last 2,000 years around 946 CE. Halla on Jeju Island and the Wudalianchi volcanic field in northeast China are other examples.
Why geologists debate the Amur Plate
Geologists first separated the Amur Plate because the Baikal Rift showed that northeast Asia was pulling away from Siberia, which a single rigid Eurasian Plate cannot do. GPS measurements later showed that northeast Asia moves slightly differently from Europe and Siberia. The difference is small, about 1 cm/yr, and the northern boundary through Siberia and Mongolia is diffuse and poorly mapped. For these reasons some models treat Amur as a separate plate and others fold it into Eurasia.