地震波から推定した日光白根火山群の深部構造

概要

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Deep structure of Nikko-Shirane volcano has been revealed through seismic studies using data collected by the 1993 Joint Seismic Observation and other temporary observations in the Nikko-Ashio area, located at the southernmost part of the northeastern Japan arc. Seismic tomography studies clearly show the existence of a P-wave low-velocity, low-Q body with a diameter of about 10 km beneath Nikko-Shirane and Nantai volcanoes, which inclines toward the northwest in the crust and reaches the uppermost mantle. This low-velocity, low-Q body is considered to reflect a main pathway of magma supply to Nikko-Shirane volcano and to Nantai volcano. Mid-crustal S-wave reflector bodies with thicknesses of about 100 m or so have been detected extensively around Nikko-Shirane volcano; some are away from the low-velocity. low-Q body, suggesting the existence of another pathway of magma supply.
1997-04-25