Abstract
Continuous observation of crustal deformation in Tohoku University was begun in the late 1960's. At present, more than 20 observation stations are operated. At older stations extensometers and watertube tiltmeters were installed in a tunnel. At newly established stations, borehole strainmeter (volumetric strainmeter or 3-component strainmeter)and borehole tiltmeters were installed at a depth of from 100 to 500m. Many researches based on the continuous observation were performed up to 2000. Development of instruments and investigation on strain migration were performed in the 1970's. In the 1980's and the 1990's strain changes related to big earthquake (e. g. 1983 Nihonkai-Chubu Earthquake, 1994 Sanriku Haruka Oki Earthquake, etc.) were analyzed, and pre-seismic and post-seismic slip of earthquakes were detected on the strain records. Although experimental method to correct annual change and short term noise caused by precipitation are not yet developed well, we can recognize the accordance of change in strain trend with seismicity off Sanriku area. Characteristics of secular change, annual change and short term noise are not understood well for borehole sites.
