Very strong and shallow M6.8 earthquake hit Honshu, Japan

Very strong and shallow M6.8 earthquake hit Honshu, Japan

Extremely dangerous earthquake measuring M6.8 (JMA) on the Richter scale hit Honshu, Japan on November 22, 2014 at 13:08 UTC (22:08 local time). USGS is reporting M6.2 at depth of 10 km (6.2 miles). JMA is also reporting depth of 10 km.

Epicenter was located 16 km (10 miles) NNE of Omachi, 24 km (15 miles) W of Nagano-shi, 33 km (21 miles) N of Hotaka, 36 km (22 miles) W of Suzaka, 191 km (119 miles) NW of Tokyo, Japan.

There are 4 119 469 people within 100 km. By latest reports 20 were injured.

USGS issued green alert level for shaking-related fatalities. Yellow alert was issued for economic losses. Some damage is possible and the impact should be relatively localized. Estimated economic losses are less than 1% of GDP of Japan. Past events with this alert level have required a local or regional level response

Overall, the population in this region resides in structures that are resistant to earthquake shaking, though some vulnerable structures exist. 

Recent earthquakes in this area have caused secondary hazards such as landslides, fires, and liquefaction that might have contributed to losses.

The Nagano prefecture authority has reported that the Kashiwazaki-Kariwa nuclear power plant sustained NO damage but has been shut down as a precautionary measure.

Important ER update at 14:27 UTC: Several buildings collapsed and people possibly buried in Nagano Prefecture. (Source NHK Japan).

Multiple landslides have been notices. One of these landslides is blocking the Shirasawa tunnel who links Nagano with Hakuba

16:12 UTC: As we are after midnight in Japan, rescue operations take more time. In some parts of the epicenter area the power is down. There are also reports of broken water pipes, a ruptured fuel tank leaking 1000 liter of oil. Collapsed walls etc. It will take at least 5 to 6 hours (early morning) before we will get a good picture of the damage.

16:23 UTC: The damage looks rather limited if we take the strong Magnitude into consideration. One of the main reasons is the earthquake type. Based on the USGS beach-ball below we are looking at a thrust focal mechanism (2 plates pushing towards each other. The resulting movements are far less dangerous than transform earthquakes (the type which hit China today). An additional reason to have weaken the shaking is the location it occurred, the rocky Japanese Alps. This kind of underground does not transmit the earthquake waves like it would be the case in for example a sediment valley.

Population exposure

Population per ˜1 sq. km. from LandScan

Selected cities exposed

from GeoNames Database of Cities with 1 000 or more residents

MMI  City Population  
VII Omachi 31k
VI Nagano-shi 360k
V Suzaka 54k
V Itoigawa 31k
V Suwa 55k
V Iiyama 25k
III Tokyo 8,337k
III Nagoya-shi 2,191k
III Yokohama-shi  3,574k
III Osaka-shi 2,592k
III Kobe-shi 1,528k

(k = x1,000)

 

Update - November 24, 17:17 UTC:

ER reports the final numbers: 37 injured people (32 slight and 5 serious), 47 collapsed residential houses, 94 seriously damaged residential houses and 282 slightly damaged residential houses. 38 damaged public buildings and/or infrastructure.

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. (USGS) More information on regional seismicity and tectonics

Featured image: USGS

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