High Sensitivity Tripartite Observation of Matswshiro Earthquakes. : Part 1.

The high sensitivity tripartite observation was commenced at Hoshina (36° 35'N, 138° 16'E), Nagano Prefecture, about 7 kilometers northeast of the town of Matsushiro on October 31, 1965, with a view to investigate the activities of micro and ultra-micro earthquakes in the area of Matsushiro Earthquakes. The observation was done as one of the programs projected by the Earthquake Research Institute, University of Tokyo, concerned with Matsushiro Earthquakes. This paper is the first report of the result of the tripartite observation carried out on the period from October 31 to December 18, 1965, the second observation by the same method was started after ieterruption of sixty days on February 20, 1966. However, the result of the observation in the second period including an overall analysis of the whole period in comparison with the observational result of other kinds carried out by other members concerning Matsushiro Earthquakes will be reported as the second report.松代地震地域における微小及び極微小地震の活動を調べる目的で,高感度3点方式による観測が1965年10月31日から行われた.観測点の位置は松代町の北東約7kmにある保科(36°35'N, 138°16'E)である.この観測は松代地震に関連して東京大学地震研究所が計画した各分野にわたるプログラムの一部として行われたものである