In relative measurement of crustal stress, in ordel to calculate stress value from and strain value observed in a borehole it is necessary to find out the elastic constant of the rock formation where a strainmeter sensor is situated (including the coupling medium).In this paper horizontal stress caused by tidal deformation will be calculated from tidal generation force potential of the sun and the moon acting on the earth by use of Love Numbers. The stress will be regarded as the known stress in calibration of the same place, the coupling coefficients of area strain and differential strain will be calculated through harmonic analysis of observational data of strain tides. The equivalent elastic constant of the surrounding rock will be calculated by use of these coefficients and the elastic constant of the steel shell of the strainmeter sensor.At last the practical formulas for calculating equivalent elastic constant of surrounding rock have been reduced, The equivalent elastic constants of surrounding rock of the boreholes in two stations where two types of strainmeters have been installed have been calculated. The calculated result basically tallies with the actual condition.
Crustal Deformation and Earthquake