Gravity changes associated with seismic activities

Abstract

Repeated gravity surveys have been carried out in several places for the purpose of detecting small changes in gravity accompanied with seismic land-deformations and faulting motions. Statistically significant gravity changes were found during the 1964 Niigata earthquake and the 1963-67 volcanic activities in Oshima Island. On the basis of the gravity-elevation relation, many authors estimated crustal density change induced by the Matsushiro earthquake swarm. A recent highlight in gravimetric work is a gravity decrease with a free-air rate over the earthquake swarm area in the eastern part of Izu Peninsula. The rounded dome-like gravity-decreasing area has been gradually extended in a N-S direction. Another topic is a tidal gravity change recorded by an Askania gravimeter in the epicentral area during the 1974 Izu Hanto-oki earthquake. The post-seismic change in daily-mean tidal factor, ranging from 1.1 to 1,6, was correlated with daily maximum amplitude of volcanic tremor observed beside the crater of Oshima Island, 40 km distant from the tidal station. © 1977, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.