Coseismic change and precipitation effect in temporal gravity variation at Inuyama, Japan: A case of the 2004 off the Kii peninsula earthquakes observed with a superconducting gravimeter

Coseismic gravity change, correlated with the 2004 off the Kii peninsula earthquakes (∼M7), was detected with a superconducting gravimeter installed at the Inuyama station of Nagoya University, central Japan, where distances from epicenters were ∼250 km. The influence of precipitation in the vicinity of the site just before the earthquakes was included in the observed temporal gravity variation. Therefore the precipitation effect was removed using a simple tank model with the Radar-AMeDAS precipitation data. As a result, the magnitude of the coseismic gravity decrease was ∼10 nm s−2 (1 μGal). The gravity changes were calculated using a dislocation model with two fault models those defined by GPS estimates. These theoretical values corresponded to the observed value in the order of 1 μGal.