On the Effect of Atmospheric Pressure upon Ground Tilt

Abstract

The Fourier transforms of the tiltmetric and barometric records at the Oura and Akibasan stations in Wakayama City have been obtained and compared to investigate the effect of atmospheric pressure on the ground tilt observed by tiltmeters of the horizontal pendulum type. The result shows that the amplitude ratio of ground tilt to pressure increases as the frequency increases and that the phase difference between them also varies slightly with the frequency. This suggests that pressure influence on the tiltmetric record consists of two parts. One is a local term which is proportional to the change of pressure and possibly related to purely local influence including instrumental disturbance. The other is proportional to the time derivative which may also be either related to the purely local effect of the pressure or related to ground deformation due to the extensive loading effect of the pressure. The same treatment has been carried out as to the tiltmetric and barometric data observed at the Amagase Observatory in Kyoto, the result of which shows that there is no contradiction of the above inference for the interpretation of the atmospheric disturbance at Amagase.