Measurement of Earth Tidal Strain in Amagase Observatory

Abstract

In Amagase Observatory, the continuous observations of ground strain have been carried out since 1967 with roller type super-invar-bar extensometers. In 1995, we replaced the detectors of roller type magnifier with those of differential transformer and roller bar supporting system with stainless wires, because ground strains may be diminished by frictional forces between the super-invar-bar and supporting roller or roller type magnifier device in the tidal strain amplitude ranges. We analyzed earth tidal strains using new type extensometers. As a result, we can discuss tidal factors more precisely than those obtained by previous type extensometers.