坂田式三成分ひずみ計の基礎

抄録

The Sakata-type three-component strainmeter, invented and developed by the author, is expected to serve as a long-period strain seismograph as well as a research tool for short-term earthquake prediction, since detection of co-seismic strain steps has confirmed a quantitative reliability of the instrument as a three-component borehole strainmeter. The strainmeter measures the change in area of three separate chambers composing the underground sensing part. Three components of strain, two principal strains and their azimuth, are derived from the observed three values. Since this method of strain measurement is new and different from the conventional one based on the changes in three separate distances, it is important to make the principle of operation well understood to avoid confusion. In this report the basic equations, presented separately in several papers by the author, are gathered and arranged in a uniform manner. A major portion of this is concerned with the case where chamber partitions are assumed to be free from any resistive forces. Although this case is fictional the results will help us to understand the actual case where partitions have finite rigidity, and an approximate method of solution is presented. The basic theory of the three-component strainmeter based on the method of measuring three diameter changes is also given in the appendix for comparison.