27 May 2003
Headquarters for Earthquake Research Promotion
Earthquake Research Committee

Seismic Activity off-shore of Miyagi prefecture on May 26, 2003

*On May 26, at 18:24 (JST) there was a M7.0 (preliminary magnitude) earthquake at a depth of approximately 70km off-shore of Miyagi prefecture. This event had a maximum seismic intensity 6 Lower in Iwate and Miyagi prefectures, and caused some damage. The focal mechanism had a compression axis in the direction of the subducting Pacific plate. It is thought that this event occurred within the Pacific plate. The activity had a main shock - aftershock sequence. At 0:44 (JST) on May 27, there was a M4.9 (preliminary magnitude) aftershock with a maximum seismic intensity 4, which was the largest aftershock, as of 12:00 (JST) on May 27.

*According to the GPS data, horizontal crustal movements associated with the main shock, were observed in the area west of the epicenter, with the largest displacement of 1.5 cm, which is consistent with the focal mechanism.

*The Earthquake Research Committee has expected the repeat of the 1978 Off-shore Miyagi prefecture earthquake to occur in the near future, however, the recent earthquake is not thought to be this earthquake. The recent event occurred 80 km to the NNW from the epicenter of the 1978 Off-shore Miyagi prefecture earthquake. The depth and the focal mechanism of recent event were different from those of the 1978 event.

*4 months before the 1978 Off-shore Miyagi prefecture earthquake, there was a M6.7 earthquake in the vicinity of the current event. It is thought that that event also occurred within the plate.

*It is estimated that there is a 60 percent chance of occurrence of M5.0 or greater aftershocks within the 24 hours from 13:00 on May 27. If a magnitude of about 5.0 aftershock occurs, there will presumably be shaking with largest maximum seismic intensity 4.