THE EARTH SURFACE DEFORMATIONS CAUSED BY AIR PRESSURE VARIATIONS

Abstract

The relationship between the tilts and strains of rocks and air pressure variations is investigated using deformation measurements from the Protvino observatory. Deformations due to air pressure are large in the observation area. The deformation response to the observed air pressure variations is compared with calculated values. In addition, the effective elasticity of the rock is determined from measured deformations in the underground galleries of the observatory after creating a load on the Earth surface. The observed tilts are considerably larger than the calculated values, for local as well as atmospheric loading, and the rock shear modulus determined from the tilt data is anomalously small compared to the mean shear modulus value for the crust. The observed horizontal strain data indicate no anomaly in the rock shear modulus value. The cavity effects at the observatory cannot explain this phenomenon. It may be caused by the rocks high fracturing. It is supposed, that the influence of cracks on the rock horizontal deformations is small if the cracks are closed and have the vertical direction. In case of large wavelength the large tilts correspond to the great displacements. These displacements may worsen the accuracy of geodetic measurements, especially when measuring vertical crustal movements.