Precise Observation of Earth Tides by Employing Superconducting Gravity Meters, Laser Extensometers and Laser Tiltmeters

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1. Precise observation of earth tides by employing superconducting gravity me aser extensometers were carried out. Earth tides were analyzed by applying the Bayesian Tidal Analysis Program 'BAYtAP-G' to both gravity and strain data. Results obtained are as follows ;(1)Comparison of two superconducting gravity meters installed on the same base in an observation room at Kyoto University indicated that tidal signals were in excellent agreement in both amplitudes and in phases, but their long-term drifts were inconsistent with each other. This may be mainly due to instrumental noises.(2)A search of tidal strain data from laser extensometers at the Amagase Crustal Movement Observatory, Kyoto, during the period of 32 months revealed no evidence of anomalous changes related to the occurrence of earthquakes.(3)Tidal strains observed with laser extensometers at three observatories(Amagase, Kishu and Rokko-Takao)in Kinki district were compared with theoretically expected ones in which the ocean tidal loading effects calculated for four Earth's models(1066A, G-B, oceanic mantle and shielded mantle models)were included. At the present stage, however, differences between observed and expected tidal strains are too large to be used in discussion to determine what model is suitable for Kinki district.2. A water-tube ti-Itmeter using a laser interferometric device was developed and installed at the Kamigamo Geophysical Observatory, Kyoto. Precise measurement of ground-tilt using this instrument have been carried out since March, 1992.