July 24, 2008
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On July 24, at 00:26 (JST) there was a M6.8 (provisional) earthquake at a depth of approximately 110km under central Iwate prefecture [under the northern coastal region in Iwate prefecture]. This event had a maximum seismic intensity 6 Upper in Hirono-cho, Iwate prefecture, and maximum seismic intensity 6 Lower in Aomori and Iwate prefectures, and caused some damage.
* The focal mechanism had a tension axis in the direction of the subducting Pacific plate. This event occurred at a rather deep location within the Pacific plate (in the lower surface of the double seismic zone). In the past, there was a similar earthquake (M6.4) in the lower surface of the double seismic zone in 2001.
* Seismic activity was a main shock-aftershock sequence. As is often the case with deep earthquakes, the aftershock activity has been at a low level. The largest aftershock until 17:00 on July 24 was a M5.0 (preliminary) event that occurred at 11:28 on July 24, which had a maximum seismic intensity 3.
* Accelerations of 593gal on the vertical component and 1,019gal on the horizontal component were recorded at the Tamayama station in Iwate prefecture (in Morioka city). However, since the short period component was prominent, damage to buildings was thought not to have been very large for the amplitudes of the acceleration. In addition, it is thought that this earthquake had large motions transmitted to relatively far distances because the waves traveled within the Pacific plate in which there is low attenuation.
* There have been no remarkable crustal movements seen on the GPS data.
[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.