JMA is reporting that very strong earthquake M 7.1 struck off the east coast of Honshu at 17:10 UTC today. They measured depth at 10 km. Both USGS and EMSC are reporting major M 7.1 at depth of 10 and 7.3 km, respectively. JMA initially recorded M 6.8 but was changed also to M 7.1.
USGS shake intensity map (Credit: USGS)
EMSC shake map (Credit: EMSC)
Tsunami warnings were in effect for east coast of Honshu.
|Tsunami Forecast Region||Category of Tsunami Warning/Advisory|
|IWATE PREF.||TSUNAMI ADVISORY|
|MIYAGI PREF.||TSUNAMI ADVISORY|
|FUKUSHIMA PREF.||TSUNAMI ADVISORY|
|IBARAKI PREF.||TSUNAMI ADVISORY|
|KUJUKURI AND SOTOBO AREA, CHIBA PREF.||TSUNAMI ADVISORY|
According to JMA, all tsunami advisories are now canceled (19:05 UTC). Though there may be slight sea-level change in coastal regions, no tsunami damage is expected. They advised to pay attention when fishing, swimming or engaging in other activities, as there may still be slight sea-level changes for the time being. No Major Tsunami Warnings, Tsunami Warnings and Advisories are currently in effect.
Epicenter was located 325 km (202 miles) ESE of Ishinomaki and 475 km (295 miles) ENE of Tokyo, Japan.
This is 320 km east of Fukushima NPP. The operator of Japan's wrecked Fukushima nuclear plant said there was no damage or spike in radiation levels at the station after the quake. All workers was precautionary evacuated to higher ground. Tohoku Electric Power Company officials said they measured a 55-centimeter tsunami at a port at Miyagi Prefecture's Onagawa nuclear plant.
Distance of today's earthquake from Fukushima Daiichi NPP - 320 km. image credit: Google Earth
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.
Featured image: USGS