Fixed-Point GPS Observation of Crustal Movement Associated with the 1989 Seismic Swarm and Submarine Volcanic Activities off Ito, Central Japan.

Abstract

Continuous geodetic baseline measurements using the fixed-point GPS baseline determination network have been undertaken in the Kanto-Tokai district, central Japan. A crustal deformation which was associated with the 1989 seismic swarm and which preceded a volcanic eruption east of the Izu Peninsula was observed. We observed time variations of a 10km length baseline vector between Hatsushima (HTS) and Ito (ITO) across the swarm area, as well as those of a 40km length baseline vector between HTS and Shimoda (SMD). It was found that the position of ITO, south of the activity region, moved 8.2cm southward, 2.5cm eastward and 8.7cm upward, and the position of HTS, north of the region, moved 8.6cm eastward, 5.5cm northward and 3.3cm upward, resulting in the baseline extension of 14.5cm during the period of the active swarm prior to the submarine volcanic eruption. The detected crustal movements were found to be consistent with a proposed fault model.