The northern peripheral area of the Osaka basin is the most complicated in geological structure in the basin. It is featured by three geological structures; Arima-Takatsuki tectonic line sharply dividing the Hokusetsu mountains and the Osaka basin, the Senri hills located 2 or 3km south of the line, and the graben structure between them. To incorporate the subsurface structure in this area into a 3 dimensional model of the Osaka basin for the simulation of strong ground motions, we conducted a survey of the subsurface structure below this area using the reflection method and the microtremor array experiment. As a result, we revealed a shape of the basin-bedrock interface and S wave velocity structure in the sediments. Main results are summarized as follows. (1) Arima-Takatsuki tectonic line has a normal-fault component. (2) The depth of the graben structure is more than 1km. (3) The sediments of the Senri hills gradually increase their thickness toward the south. (4) The basement rock in the east of Butsunenjiyama fault raises up at least 0.5km relative to the basement rock in the other side.
