測定された地殻応力変化と観測された地殻ひずみ変化の比較

Abstract

The observation of crustal strain has been carried out at Ikuno Geophysical ObservationStation using 4 components of extensometers since 1977. The observed results at Ikunomake it clear that changes of maximum tilt direction and principal strain axis have occurredsystematically. These phenomena suggest time changes of stress field in the northwesternpart of Kinki District.To confirm these stress changes, in Jan. 1988, measurement of three-dimensional absolutecrustal stress was made using hydro-fracturing methods in three boreholes near the observa-tion station. In Aug. 1988, using the same boreholes, the measurements of absolute stresswere again made repeatedly. Then, stress changes were estimated and further, strainchanges were calculated through the stress-strain relation in the two-dimensional modeling.The obtained data were finally comparative-studied with those data obtained by the exten-someters.Because of the fact that absolute stress values themselves are low, measurements werenot very accurate. On the other hand, the amounts of observed strain changes, due to cavityeffect and inhomogeneity of rock in the observational tunnel, lead to noticeable errors ofanalysis. As a whole, the observed strain changes agree well in characteristics with calcu-lated strain changes from the results of stress measurements within the observational error.But Young's modulus must be taken 200 Gpa, several times of elastic constant (E=26 Gpa)by the uniaxial compression test of in situ rock.Object of this paper, however, is not to show coincidence of both the measured values.The real purpose is to indicate a future prospect which enables Earthquake Prediction Studyto elevate from conventional "qualitative" discussion to "quantitative" one by this compara-tive observation of stress and strain.