AN ESTIMATION OF SITE AMPLIFICATION BY IRREGULAR SUBSURFACE STRUCTURE NEAR KEGO FAULT FROM AFTERSHOCK RECORDS OF THE 2005 WEST OFF FUKUOKA PREFECTURE EARTHQUAKE

Abstract

We conducted aftershock observations in Chuo Ward, Fukuoka city to make clear reasons why building damage had been concentrated near Kego Fault during the 2005 West off Fukuoka Prefecture earthquake. We found significantly large site amplification in the area limited within a distance of about 200 meters from Kego Fault to the northeast direction. Amplification factors in this area are evaluated to be about 3 times in PGA and PGV, and it corresponds to the increment of about 1 in seismic intensity. It can be interpreted that the amplification is affected by irregular shallow subsurface structure like basin edge effect.