2004 Chūetsu earthquake

The Chūetsu earthquakes (中越地震, Chūetsu jishin) occurred in Niigata Prefecture, Japan, at 17:56 local time (08:56 UTC) on Saturday, October 23, 2004. The Japan Meteorological Agency (JMA) named it the "Heisei 16 Niigata Prefecture Chuetsu Earthquake" (平成16年新潟県中越地震, Heisei ju-roku-nen Niigata-ken Chuetsu Jishin). Niigata Prefecture is located in the Hokuriku region of Honshu, the largest island of Japan. The initial earthquake had a magnitude of 6.6 and caused noticeable shaking across almost half of Honshu, including parts of the Tōhoku, Hokuriku, Chūbu, and Kantō regions.

The first quake struck the Chuetsu area of Niigata Prefecture, Japan on the Muikamachi Fault zone, with a reading of 7 on the Japanese shindo intensity scale at Kawaguchi, Niigata. The moment magnitude of the earthquake is estimated at 6.6. For comparison, the Great Hanshin earthquake, which devastated much of Kobe, measured 7 on the shindo scale, with a magnitude of 7.3. The earthquake occurred at a depth of 15.8 km. The JMA gave the coordinates of the earthquake as 37°18′N 138°48′E / 37.3°N 138.8°E / 37.3; 138.8.

A second earthquake occurred at 18:11, 16 minutes after the first. This one, at a much shallower depth, had a shindo intensity of 6+ and a magnitude of 5.9. A third, at 18:34, had a shindo intensity of 6−. At 19:45, another intensity 6− earthquake occurred. Intervening and subsequent earthquakes of lesser intensity also shook the region. During the first 116 hours, 15 earthquakes with intensities of shindo 5− or higher rocked the Chuetsu region.

In a press release, the Geographical Survey Institute (GSI) of the Government of Japan published preliminary estimates that a fault having a length of 22 km and a width of 17 km moved approximately 1.4 m.

This was the deadliest earthquake to strike Japan since the January 1995 Great Hanshin earthquake, until the 2011 Tōhoku earthquake.

This was also the first time a snake robot was used at a natural disaster site. A Souryu serpentine robot was used in a house in Nagaoka City that was damaged during this earthquake.

The following is a list of major earthquakes that have occurred in Niigata Prefecture since October 23, 2004:

As late as November 3, the 39th fatality attributable to the earthquakes occurred as perceptible aftershocks continued. 68 dead and 4,795 injuries were reported in Niigata Prefecture. Over one hundred thousand people fled their homes. The earthquakes caused houses to collapse in Ojiya and damaged thousands in the area.