March 13, 2014 Earthquake: Southwestern, Japan

Felt (V) at Fuchu and Iwakuni; (IV) at Okayama and Otake; (III) at Osaka, Honshu. Also felt (IV) at Bungotakada and Fukuoka, Kyushu. Felt throughout southern Japan from Kyoto, Honshu to Kagoshima, Kyushu. Also felt at Daegu, South Korea. Recorded (5U JMA) in Ehime. Yawatahama, Ehime, Japan - CDI: 7; Matsuyama, Ehime, Japan - CDI: 6; Mihara, Hiroshima, Japan - CDI: 6; Oita, Oita, Japan - CDI: 6; Ozu, Ehime, Japan - CDI: 5; Kure, Hiroshima, Japan - CDI: 5

Tectonic Summary

Seismotectonics of Japan and Vicinity

Japan and the surrounding islands straddle four major tectonic plates: Pacific plate; North America plate; Eurasia plate; and Philippine Sea plate. The Pacific plate is subducted into the mantle, beneath Hokkaido and northern Honshu, along the eastern margin of the Okhotsk microplate, a proposed subdivision of the North America plate. Farther south, the Pacific plate is subducted beneath volcanic islands along the eastern margin of the Philippine Sea plate. This 2,200 km-long zone of subduction of the Pacific plate is responsible for the creation of the deep offshore Ogasawara and Japan trenches as well as parallel chains of islands and volcanoes, typical of Circumpacific island arcs. Similarly, the Philippine Sea plate is itself subducting under the Eurasia plate along a zone, extending from Taiwan to southern Honshu that comprises the Ryukyu Islands and the Nansei-Shoto trench.

Subduction zones at the Japanese island arcs are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding plates 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, Japanese arc earthquakes occur within the subducting Pacific and Philippine Sea plates and can reach depths of nearly 700 km. Since 1900, three great earthquakes occurred off Japan and three north of Hokkaido. They are the M8.4 1933 Sanriku-oki earthquake, the M8.3 2003 Tokachi-oki earthquake, the M9.0 2011 Tohoku earthquake, the M8.4 1958 Etorofu earthquake, the M8.5 1963 Kuril earthquake, and the M8.3 1994 Shikotan earthquake.

(above from reference #1053)

An overnight earthquake has caused minor injuries and scattered damage in southwestern Japan and delayed trains Friday morning. The 2:06 a.m. quake had a magnitude of 6.3 according to the U.S. Geological Survey. It struck offshore in the Inland Sea between three of Japan's four main islands and nearest to the northern coast of the island of Kyushu. It was also felt on nearby parts of Honshu and Shikoku islands. Japanese media tallied at least 18 injuries, including people who were knocked out of their beds. The quake burst some water pipes, but didn't appear to cause any significant damage. Japanese television showed roped-off debris that had fallen from the facade of one building. (reference #10902)