2005 Fukuoka Earthquake - M5.8 Aftershock On April 20

M5.8 Aftershock On April 20

A new after-quake hit at 6:11 a.m. April 20 on Japan's southern main island of Kyūshū, the Central Meteorological Agency reported. Although considerable time had passed since the first quake, the aftershock was not unexpected. The quake, which swayed buildings and shattered some outer walls, was measured to have magnitude of 5.8. 2 and 56 people were severely and slightly injured and treated at a hospital in Fukuoka due to the quake and there were temporary closures of major highways, railway services and Fukuoka's airport. Following reports that the city has only prepared for earthquakes up to a magnitude of 6.5, the aftershock renewed fears that the quakes might cause the Kego faultline to become active again beneath Fukuoka, leading to an earthquake as big as, or bigger than, the March 20 quake.

In order to more accurately estimate the risk of ongoing or increased seismic activity, teams from Tokyo University, Kōchi University, Hiroshima University and Ōita University surveyed Hakata Bay to determine how far the Kego fault extends. Preliminary results, announced May 1, 2005 indicated that the fault extends nearly as far as Nokonoshima, 2.5 km out in to the bay, though no sign of recent activity along the fault was uncovered. The teams also discovered a new fault in the Higashi-ku portion of Hakata Bay. Later findings indicated that the faultline responsible for both the March 20 and April 20 quakes was likely an extension of the Kego fault, making its total length approximately 40 km.