Saturday, January 13, 2007 at 04:23:20 UTC
(Friday, January 12, 2007 at 08:23:20 PM, Pacific Standard Time)
Epicenter: Latitude 46.272°N, Longitude 154.455°E
Depth: approximately 10 kilometers.
A great* earthquake occurred Friday evening Portland time between Japan and the Kamchatka Peninsula and was well recorded on school seismographs across the US (see Corvallis, OR, seismogram below). The epicenter is indicated by the pink star on Map A and is located just east of the Kuril Trench where the Pacific Plate subducts beneath the Eurasian Plate. This earthquake occurred WITHIN the upper part of the Pacific Plate, not on the boundary between the Pacific and Eurasian plates. The mechanism of the earthquake indicates that the earthquake was produced by “extensional forces” that occur in the upper parts of oceanic plates as they are bent downwards when they approach a subduction zone. This earthquake of January 13, 2007 has an epicenter that is 95 kilometers southeast from the epicenter of a great earthquake (M8.3) that occurred November 15, 2006 (indicated by yellow star on Map B). That earthquake was a “classic subduction zone earthquake” created by sudden slip on the boundary between the Pacific and Eurasian plates. Map C shows the rate and direction of motion of the Pacific Plate with respect to the Eurasian Plate. The rate of convergence at this subduction zone plate boundary is quite high at about 8 cm/year.
The earthquake that occurred last Friday generated a small tsunami. The height of the tsunami that arrived at Hanasaki, Japan (Hokkaido) about 1 hour 40 minutes after the earthquake was only 10 centimeters. The largest tsunami height (that we know of) was 32 centimeters recorded at Shemya, Alaska (western Aleutian Islands) about 2 hours and 50 minutes after the earthquake. Unlike the tsunami generated by the earthquake of November 15, 2006, that produced waves approaching 2 meters in height at Crescent City, California, the tsunami from this latest Kuril Islands earthquake did not produce significant waves along the Pacific Northwest coast.
*The USGS has eight earthquake classifications ranging from “micro” to “great.” See: http://earthquake.usgs.gov/eqcenter/recenteqsww/glossary.php
Map A Earthquake of Jan 13, 2007 Map B Earthquake of Nov 15, 2006
Map C Pacific and Eurasian plates of northwest Pacific Ocean
Arrows indicate motion of the Pacific Plate toward the northeastern part of the Eurasian Plate. The rate of convergence at this plate boundary is about 8 cm/year. At the Kuril Trench (dark purple-blue indicating deep ocean trench), the Pacific Plate subducts beneath the Eurasian Plate.