June 12, 2006 Japan Earthquake

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Posting Date: June 13, 2006, 9:30:00 AM

A strong earthquake struck Japan’s southern island of Kyushu on Monday, June 12, 2006, at 5:01 a.m. local time, 8:01 p.m. UTC. The USGS has estimated the earthquake’s magnitude at 6.3. The epicenter was located about 90 km east southeast of Fukuoka, and about 825 km west southwest of Tokyo at an estimated depth of 155 km. A mild aftershock measuring 4.8 followed shortly after the mainshock. At least eight people were injured in the quake, though no major damage was reported. Some rail lines in Kyushu and Shikoku were temporarily suspended or running at reduced speeds as a precautionary measure. No tsunami warnings were issued for the earthquake. This earthquake occurred along the Philippine Sea/Eurasia subduction zone at the Nankai trough. The Philippine Sea plate subducts under the Kyushu and Shikoku islands in southwestern Japan at a rate of 4-5 cm/yr. The Nankai trough subduction zone is a relatively young system compared to the subduction zone at the Japan trench in central and northern Japan. However, a series of large earthquakes of magnitude greater than 8.0, including the recent 1946 Nankado and 1944 Tonankai great earthquakes, have occurred along this subduction zone. Within the crust of the overriding plate is the largest active crustal fault in the Japanese islands—the median Tectonic Line—that runs across the Shikoku and Kyushu islands. Therefore seismic hazard threats in this area come from both large subduction zone earthquakes and crustal events, such as the 1995 Kobe earthquake, that occurred along one of the active fault branches within the Median Tectonic Line. Based on the source parameters of this event, it occurred at a deep part of the subduction zone and is therefore an intra-slab earthquake. It is one of the largest recorded deep events in the vicinity. The epicentral area is also very volcanically active. In March 2005, a shallower magnitude 6.6 earthquake struck about 40 km northwest of Fukuoka, killing one and injuring about 400. The largest historical event in the area was a magnitude 7.0 earthquake that occurred in 1700 A.D., about 40 km to the northwest. Because of both the depth of this earthquake and the fact that it occurred in a sparsely populated region, the AIR earthquake team does not expect any significant losses.

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Posting Date: June 13, 2006, 9:30:00 AM