Accurate evaluation of ocean tide loading effects for gravity in nearshore region: The FG5 measurements at Sakurajima Volcano in Kagoshima Bay, Japan

Abstract

We detected 5–10 microgal diurnal/semidiurnal gravity signals of ocean tide origin by the FG5 absolute gravimeter at two stations in Sakurajima volcano located 300 m and 2500 m away from the shore. We computed the gravity originating both from the global ocean tides and from the local ones in Kagoshima Bay, considering the fine‐scale sealand distribution around the stations. The observed FG5 records and the theoretical ocean tides agreed well with each other in both amplitude and phase, indicating that the oceanic loading effects can be predicted to an accuracy better than 2 microgal within several hundred meters of the shore in Sakurajima. The apparently puzzling errors that have so far arisen on nearshore LaCoste measurements were resolved by the correction of the effects.