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Magnitude 8.3 - HOKKAIDO, JAPAN REGION

2003 September 25 19:50:06 UTC

Preliminary Earthquake Report

Largest Earthquake in 2003

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Magnitude 8.3
Date-Time Thursday, September 25, 2003 at 19:50:06 (UTC)
= Coordinated Universal Time
Friday, September 26, 2003 at 4:50:06 AM
= local time at epicenter
Time of Earthquake in other Time Zones
Location 41.775°N, 143.904°E
Depth 27 km (17 miles) set by location program
Region HOKKAIDO, JAPAN REGION
Distances 139 km (86 miles) SSW (197°) from Kushiro, Hokkaido, Japan
443 km (275 miles) SSE (156°) from Wakkanai, Hokkaido, Japan
Location Uncertainty horizontal +/- 3.9 km (2.4 miles); depth fixed by location program
Parameters Nst=325, Nph=325, Dmin=582.6 km, Rmss=0.85 sec, Gp= 36°,
M-type=teleseismic moment magnitude (Mw), Version=U
Source USGS NEIC (WDCS-D)
Event ID uszdap

Tectonic Summary
The preliminary location and focal-mechanism of this earthquake imply that it occurred as the result of thrust-faulting on the plate interface between the overriding North American plate (which extends into the northeast corner of the Eurasian landmass) and the subducting Pacific plate. The Pacific plate is moving west-northwest at a rate of about 8.2 cm per year relative to the North American plate. In addition to experiencing great thrust earthquakes that originate on the interface between the plates, eastern Hokkaido experiences great earthquakes that originate from the interior of subducted Pacific plate. The earthquakes of March 4, 1952, and May 16, 1968 (cited below) were interface-thrust earthquakes, whereas the earthquake of January 15, 1993 (cited below) occurred within the interior of the subducted Pacific plate. The recent earthquake appears to have involved rupture of the same section of the plate interface that ruptured in 1952.

Magnitude 8 and greater earthquakes are capable of devastating large areas. The shallow September 25 Hokkaido earthquake occurred about 60 km offshore. If the earthquake had occurred directly beneath a populated region, damage would have been more severe.

Previous Deadly Earthquakes in this Region

Date UTC Magnitude Fatalities Damage
1952 March 4 8.1 31 31 killed, 72 injured; 713 houses destroyed, 5,980 damaged. 28 killed and warehouses destroyed at Kushiro. 3 killed and 309 houses destroyed at Kiratapu. 1,000 houses destroyed or damaged at Shiranuka and 400 schools collapsed at Sapporo. 10-foot tsunami.
1968 May 16 7.9 48 Damage estimate at 25 million USD.
1993 January 15 7.6 2 614 injured and substantial damage (VI JMA) at Kushiro, Hokkaido and Hachinohe, Honshu. Felt (V JMA) at Hiroo, Nemuro, Obihiro, Otaru and Urakawa; (IV JMA) at Hakodate and Tomakomai; (III JMA) at Sapporo, Hokkaido. Felt (IV JMA) at Aomori and Morioka; (III JMA) at Akita, Fukushima, Sendai, Tokyo and Yokohama, Honshu. Also felt (VII) on Shikotan and (VI) at Kurilsk, Kuril Islands. Landslides and subsidence occurred in the epicentral area.

The last great earthquake (magnitude 8 or greater) in the world was a magnitude 8.4 that occurred on June 23, 2001, near the coast of Peru. This earthquake killed at least 75, including 26 killed by the associated tsunami.

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