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Earthquake Summary
Earthquake Summary Poster
The following is a release by the United States Geological Survey, National Earthquake Information Center: An earthquake occurred about 145 km (90 miles) west-northwest of Fukui or 460 km (285 miles) west-northwest of Tokyo at 8:17 AM MDT, Jul 16, 2007 (11:17 PM local time in Japan). The magnitude and location may be revised when additional data and further analysis results are available. There have been no reports of damage.
Tectonic Summary
The recent magnitude 6.8 earthquake occurred 140 km off the west coast of Honshu, Japan at a depth of 350 km below the Sea of Japan. This oblique thrust event was likely caused by the release of stress built by the internal deformation of the Pacific plate as it subducts beneath the Okhotsk plate. The Okhotsk plate is a thin plate that lies between the Pacific Ocean and the Eurasian landmass. The north-south trending Japan Trench lies 700 km to the east of this earthquake, and is the surface expression of the boundary between the plates.
This deep-focus earthquake was preceded 13 hours earlier by a shallow crustal magnitude 6.6 quake roughly 330 km to the east. The two earthquakes were generated by different mechanisms. The shallow-focus earthquake was caused by deformation within the crust of the Okhotsk plate and the deep-focus quake was likely caused by the internal deformation of the Pacific plate. Given their different mechanisms and physical separation of at about 10 rupture lengths, the deep-focus earthquake is not considered an aftershock of the first.
Intermediate- and deep-focus earthquakes generally cause less damage than shallow-focus earthquakes since the energy generated by the deep events is released further from the surface and therefore produces less shaking than by quakes that are closer to the surface.
Deadly earthquakes have occurred in this region: In 2004, a magnitude 6.6 earthquake occurred in the Niigata Prefecture, 360 km to the northeast of the recent quake, killing 40 people and injuring about 3,000. In June, 1964, a M7.5 earthquake occurred about 425 km to the northeast of the recent quake killing 37 people; and in April, 1995 a M5.4 earthquake 380 km to the northeast, injured at least 39 people.
During the 20th century Japan has suffered nine devastating earthquakes that killed more that 1000 people each. Among these are the 1923 M7.9 earthquake that triggered the great Tokyo fire that killed 143,000 people and the more recent 1995 M6.9 Kobe earthquake that killed about 5,500 people.
Tsunami Information
Carte des intensités du premier tremblement de terre. L'étoile indique l'épicentre.

Selon l'United States Geological Survey (USGS), deux importants séismes atteignant au moins 6,7 et 6,8 degrés sur l'échelle de Richter ont secoué la côte est de Honshu (Japon), tuant 8 personnes et en blessant plusieurs centaines.
Un incendie de deux heures s'est produit dans le transformateur du réacteur n°6 de la centrale nucléaire de Kashiwazaki-Kariwa, qui est la plus grande centrale nucléaire du monde, produisant une fuite d'eau radioactive dans la mer. La direction de la centrale prévoit que cette eau pourrait causer des dégâts dans l'environnement immédiat de la centrale.
L'épicentre du premier séisme a été localisé à 65 km au sud ouest de la ville de Niigata, une grande ville de la côte ouest de Honshu, à une profondeur de 55,4 km. Le second a été enregistré 12 heures plus tard environ, à 140 km au nord-ouest de l'île de Fukui, à une profondeur de 350,7 km.
, a indiqué le Premier ministre japonais, Shinzo Abe.
Le centre de prévention des tsunamis du Pacifique du National Oceanic and Atmospheric Administration (NOAA)  a indiqué qu'aucun raz-de-marée majeur n'est attendu, mais que de petites vagues pourraient frapper localement des zones proches de l'épicentre. Des petits (50 cm) tsunamis , a indiqué un comuniqué de l'USGS sur son site internet, qui ajoute aussi qu'à Kashiwazaki, . L'USGS a indiqué que les dégâts étaient de .