Mapping the crustal strucutre under active volcanoes in central Tohoku, Japan using P and PmP data

We present high-resolution tomographic images of the crust under the active arc volcanoes in the central part of Northeast Japan (Tohoku) determined by using arrival times of first P waves and post-critically reflected waves from the Moho discontinuity (PmP). Results of detailed resolution analyses show that the addition of PmP data can improve significantly the resolution of the lower crustal structure. After the PmP data are included in the tomographic inversion, the low-velocity (low-V) anomalies in the lower crust under the active volcanoes can be better imaged. The low-V zones are clearly visible in the entire crust beneath the volcanoes extending from the surface down to the Moho discontinuity. Arc-magma related, deep, low-frequency microearthquakes are located around the low-V zones in the lower crust under the volcanoes, which occurrence is probably associated with the movement of fluid magma under the volcanoes.