Very strong and shallow M6.9 earthquake hit near the east coast of Honshu, Japan


A very strong and shallow M6.9 (JMA) earthquake was registered near the east coast of Honshu, Japan at 23:06 UTC on February 16, 2015. JMA is reporting depth of 10 km (6.2 miles). USGS is reporting M6.8 at a depth of 23 km (14.2 miles). 

JMA is describing this quake as an aftershock of the M9.0 which hit Japan on March 11, 2011 and caused the meltdown of three reactors at the Fukushima Daiichi Nuclear Power Plant.

Epicenter was located 83 km (52 miles) ENE of Miyako, 90 km (56 miles) ENE of Yamada, 99 km (62 miles) ENE of Otsuchi, 106 km (66 miles) NE of Kamaishi and 538 km (334 miles) NNE of capital Tokyo.

There are 120 213 people living within 100 km radius. 

JMA issued Tsunami advisory for the coastal area of the Iwate prefecture with expected waves ranging from 0.2 to 1 meter maximum.

The quake was followed by a series of aftershocks, the largest of which was M5.7 (50 km deep/JMA) that hit at 04:46 UTC on February 17.

Local authorities in Iwate issued evacuation advisories to more than 19 000 people.

Tohoku Electric Power Co, which operates the Onagawa and Higashidori nuclear plants in nearby Miyagi and Aomori prefectures, told NHK it found no irregularities at the facilities after the quake.

A 20 cm (8 inches) tsunami wave was recorded off the city of Kuji at 00:07 UTC. Waves of up to 10 centimeters were recorded along other parts of the coastline of Iwate prefecture.

"So far we have seen a minor tsunami but we continue to warn our citizens not to approach the coast as second and third waves could be higher," said Masayuki Yamazaki, an official in the anti-disaster office in Miyako.

USGS issued green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

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 and fires that might have contributed to losses.

Image credit: USGS

  1. 5.848km SE of Hachinohe, Japan2015-02-17 04:46:38 UTC40.4 km
  2. 4.3193km E of Miyako, Japan2015-02-17 02:45:12 UTC10.0 km
  3. 4.996km E of Miyako, Japan2015-02-17 02:29:51 UTC20.3 km
  4. 4.685km E of Miyako, Japan2015-02-17 01:15:02 UTC10.0 km
  5. 4.7108km ENE of Miyako, Japan2015-02-17 00:50:02 UTC8.9 km
  6. 6.783km ENE of Miyako, Japan2015-02-16 23:06:27 UTC23.0 km
Data sorce: USGS (Updated at 08:12 UTC on February 17, 2015)

Tectonic summary

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)

Featured image: USGS

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