March 11, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

The 2011 off the Pacific Coast of Tohoku Earthquake

* On March 11 at 14:46 (JST), there was a M8.8 (preliminary) earthquake at a depth of approximately 25km, off-shore of Sanriku. This event had a maximum seismic intensity 7 observed in Miyagi prefecture. This earthquake caused large tsunamis on the Pacific coast from the Hokkaido, Tohoku and Kanto regions, with tsunami heights over 7.3m in Soma, of 4.2m in Oarai, and over 4.1m in Kamaishi.

* The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.

* The maximum aftershock was a M7.5 (preliminary) one that occurred at 15:08 on March 11, as of 18:00 on March 11. There were three earthquakes of M7.0 or over, off-shore of the Pacific coast from Iwate through Ibaraki prefectures.

* According to the GPS data, crustal movements associated with this event were observed and there were movements of approximately 4m toward the east-southeast at the Kahoku observation point (Miyagi prefecture).

* The magnitude of the main shock, M8.8, is the largest in Japan. There is fear that large aftershocks will hereafter occur.

* It is thought that the hypocenter area extends widely from the region off-shore of Iwate to Ibaraki prefectures. The Earthquake Research Committee evaluated earthquake motion and tsunami for the individual region off-shore of Miyagi prefecture, to the east off-shore south of Sanriku along the trench, and to the south off-shore of Ibaraki prefecture, but occurrence of the earthquake that is linked to all of these regions is out of hypothesis.