Sendai, Japan Earthquake

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Posting Date: July 25, 2003, 1:00:00 PM

A moderate earthquake struck northern Japan early Saturday, July 26, 2003, at 12:13 a.m. local time (15:13 UTC). The U. S. Geological Survey (USGS) placed the earthquake epicenter in the Miyagi prefecture, about 10 miles (20 km) north northeast of the northern city of Sendai and 55 miles (85 km) north northeast of Fukushima. The USGS has estimated the moment magnitude at 5.3. The Japanese Meteorological Agency has issued a preliminary estimate of 5.5. Focal depth is estimated at about 9 miles (14 km). There were reports of aftershocks, including one magnitude 3.4 within 30 minutes of the original tremor. The earthquake was a shallow crustal event that occurred along one of the thrust faults on the east coast of central Honshu, near Sendai. The subduction of the Pacific plate under the Eurasian plate along the Japan trench generates high compressional stress in Honshu. Although most of the large earthquakes in this area have been associated with subduction zones along the trench, tectonic stress has generated a series of thrust faults in the overriding plate trending north to northeast. The fault that runs past the city of Sendai has been fairly active in the past. Four events of magnitude 6.0 to 6.9 have been associated with this fault since the 1600s. The latest of these earthquakes is the 1956 M6.0, which occurred about 40 km southwest of the current event. In today's earthquake, the initial violent tremor lasted about a minute in the towns of Yamotocho and Narusecho, about 360 km (190 miles) northeast of Tokyo. There were scattered reports of damage to rock walls and water pipes, but no major structural damage. Some roads were closed and trains lines temporarily halted for safety checks. Power outages were reported in towns nearest to the epicenter. About 11 people are reported to have been injured. The AIR earthquake team has run this event through the AIR Japan earthquake model. Results indicate that insured losses will not be significant.

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Posting Date: July 25, 2003, 1:00:00 PM