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Magnitude 6.5 - NEAR THE WEST COAST OF HONSHU, JAPAN
2004 October 23 08:56:01 UTC

Preliminary Earthquake Report
U.S. Geological Survey, National Earthquake Information Center
World Data Center for Seismology, Denver

A strong earthquake occurred at 08:56:01 (UTC) on Saturday, October 23, 2004. The magnitude 6.5 event has been located in NEAR THE WEST COAST OF HONSHU, JAPAN. (This event has been reviewed by a seismologist.)
Small globe showing earthquake

Small map showing earthquake

Magnitude 6.5
Date-Time Saturday, October 23, 2004 at 08:56:01 (UTC)
= Coordinated Universal Time
Saturday, October 23, 2004 at 5:56:01 PM
= local time at epicenter

Time of Earthquake in other Time Zones
Location 37.199°N, 138.812°E
Depth 15.8 km (9.8 miles) set by location program
Region NEAR THE WEST COAST OF HONSHU, JAPAN
Distances
80 km (50 miles) SSW of Niigata, Honshu, Japan
85 km (50 miles) NE of Nagano, Honshu, Japan
90 km (55 miles) NNW of Maebashi, Honshu, Japan
190 km (120 miles) NNW of TOKYO, Japan
Location Uncertainty horizontal +/- 6.7 km (4.2 miles); depth fixed by location program
Parameters Nst=232, Nph=232, Dmin=91 km, Rmss=1.02 sec, Gp= 65°,
M-type=moment magnitude (Mw), Version=9
Source USGS NEIC (WDCS-D)
Event ID uspyal

The Islands of Japan lie on a ring of seismically active plate boundaries that surround the Pacific Ocean known as the Ring of Fire. Earthquakes throughout Japan are caused by the relative motion of several major and minor tectonic plates including the Pacific plate, the Philippine Sea plate, the Okhotsk plate, and the Amur plate. Earthquakes result from slippage on the interface between the plates and on faults some distance from the plates boundaries. This thrust earthquake, of October 23rd 2004, occurred within the Okhotsk plate about 350 km east of the Japan Trench where the Pacific plate subducts beneath the overriding Okhotsk plate. Within the last 30 years, there have been several significant earthquakes in region nearby this earthquake. These include a June, 1964 magnitude 7.4 quake that occurred 125 km to the north and killed 36 people and an April, 1995 magnitude 5.4 quake that occurred 90 km to the north and injured at least 39 people. This century, the country of Japan has suffered nine devastating earthquakes that have killed more than 1000 people. These include the 1923 magnitude 7.9 earthquake that triggered the great Tokyo fire and killed 143,000 people and the more recent 1995 6.9 Kobe earthquake that killed 5,500 people.

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The official magnitude for this earthquake is indicated at the top of this page. This was the best available estimate of the earthquake's size, at the time that this page was created. Other magnitudes associated with web pages linked from here are those determined at various times following the earthquake with different types of seismic data. Although, given the data used, they are legitimate estimates of magnitude, they are not considered the official magnitude.


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