Microgravity Changes and Ground Deformation at Rabaul Caldera, 1973–1985

Abstract

A progressive gravity decrease of more than 410 µgal took place at Rabaul Caldera, Papua New Guinea, between August 1973 and July 1985. The gravity change correlates with ground deformation at the caldera, particularly with uplift of more than 1.8 m. The patterns of gravity, elevation, horizontal distance and tilt changes indicate a principal source of inflationary deformation beneath the east-central part of the caldera. These phenomena, together with increases in seismicity, are expressions of a new phase of caldera unrest which commenced in 1971 and intensified markedly during late 1983 and 1984.