抄録
Spatial distribution of b value in the frequency-magnitude relation is investigated for upper plane events of the double-planed deep seismic zone beneath the northeastern Japan arc, Locally high b value areas are detected at three locations west of the volcanic front. Inclined low S-wave velocity zone in the mantle wedge has extremely low values at locations just above these three high b value areas in the subducted Pacific slab. The close spatial relation between S-wave velocity distribution and earthquake size distribution suggests along-arc variation of magma source within the slab beneath this volcanic arc.
