Detailed plate boundary structure off northeast Japan coast

In 1997, a seismic experiment using an airgun array and ocean bottom seismo graphs (OBSs) was performed in the forearc region of the northeast Japan (N ET) are. The objectives of this experiment were to clarify whole of the vel ocity structure around the forearc region of NET are including a detailed p late boundary structure and the heterogeneous structure. In this paper, we estimated the heterogeneous velocity structure around the forearc region of northeast Japan by applying 2-D ray tracing and travel time inversion to t he airgun-OBS data. The depth where the island are Moho comes into contact with the subducting oceanic crust is about 20 km. We suggest the existence of an oceanic layer1 overlying the oceanic crust subducting down to at leas t near 18 km by comparing observed waveforms with these calculated using th e reflectivity method.