August 14, 2012 – A Powerful 7.7 Magnitude Quake Struck Off the East Coast of the Kamchatka Peninsula, Russia – Seismotectonics of the Kuril-Kamchatka Arc: Note – This earthquake was just upgraded from 7.3 to 7.7 by the USGS.
About the Kuril-Kamchatka Arc: The arc extends about 2,100 kms (1,305 miles) from Hokkaido, Japan, along the Kuril Islands and the Pacific coast of the Kamchatka, Russia, peninsula to its intersection with the Aleutian arc near the Commander Islands, Russia. It marks the region where the Pacific plate subducts into the mantle beneath the Okhotsk micro plate, a part of the larger North America plate. This subduction is responsible for the generation of the Kuril Islands chain and the deep offshore Kuril-Kamchatka trench.
Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that decreases from 83 mm per year at the arc’s southern end to 75 mm per year near its northern edge.
Subduction zones such as the Kuril-Kamchatka arc are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the interface of the plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Kuril-Kamchatka arc earthquakes occur within the subducting Pacific plate and can reach depths of nearly 700 km. Since 1900, eight great earthquakes (M8.3 or larger) have occurred along the Kuril-Kamchatka arc. They are the M8.4 1923 Kamchatka earthquake, the M8.6 1933 Sanriku-oki, Japan earthquake, the M9.0 1952 Kuril Island earthquake, the M8.4 1958 Kuril Island earthquake, the M8.5 1963 Kuril Island earthquake, the M8.4 1994 Kuril Island earthquake, the M8.3 2003 Hokkiado, Japan earthquake, and the M8.3 2006 Kuril Island earthquake.
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