Versíon en Español
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
Shake map showing intensity of the first quake. Star marks the epicenter.
According to the United States Geological Survey (USGS), at least two strong earthquakes with a magnitude of 6.7 and 6.8 rocked the west coast of Honshu, Japan killing 8 people and injuring hundreds. 

A two hour fire was reported at the Kashiwazaki Nuclear Power Plant number 6 reactor transformer, which is the biggest nuclear power facility in the world, causing radioactive water to leak into the sea. Officials at the plant state that the water will cause no damage to the surrounding environment.

The epicenter of the first quake was located 65 km (40 miles) southwest of Niigata city, a major city on the west coast of Honshu, of 55.4 km (34.4 miles). The second quake, a 6.8, was recorded almost 12 hours later approximately 140 km (90 miles) northwest of Fukui Island, Honshu, Japan and had a depth of 350.7 km (217.9 miles).

"Many people told me they want to return to their normal lives as quickly as possible. The government will make every effort to help with recovery," said Japanese Prime Minister, Shinzo Abe.

The National Oceanic and Atmospheric Administration (NOAA) Pacific Tsunami Warning Center says that no major tsunamis are expected, but small waves could impact areas locally close to the epicenter.Small, 50 centimeter tsunamis "were reported on coastal areas close to epicenter," said a statement on the USGS website which also added that in Kashiwazaki, "buildings collapsed, roads and bridges were damaged." The USGS says that damage is "moderate to heavy."

"A strong earthquake has occurred, but a tsunami is not expected along the California, Oregon, Washington, British Columbia, or Alaska coast. No tsunami warning or watch is in effect for these areas," added the NOAA statement.