One year observation of crustal strains using a portable laser extensometer system was carried out at Kishu in Kui Peninsula, Southwestern Japan, during 19871988. The system comprising a frequency-stabilized laser source and two Michelson-type inter-ferometers was designed to detect two-axial horizontal linear strains simultaneously. The laser beam emitted from the laser source was divided into two beams for con-structing a set of orthogonal interferometers (L-1: N80°E and L-2: N10°W). The L-1 component was kept in an air-tight stainless steel pipe having an effective length of 15.42 m. On the other hand, the L-2 component 2.82 m in length was not sealed by an air-tight pipe but opened in the air. Resolving powers of these extensometers were 1.03×10-9 and 5.62×10-9, respectively. With regard to the L-2 component, the relation between the apparent strain (s) and the change of atmospheric pressure (P) was determined as follows, ε(×10-6)=2.13×P(mb). (1)After eliminating the effect of atmospheric pressure by applying (1) to the data of L-2, strain changes of the order of 10-8 could be detected. The L-1 component enabled strain changes of the order of 10-9 to be investigated. Strain accumulations obtained from L-1 and L-2 were 1.4×108/day and 6.5×10-8/day, respectively. Tidal strains were analyzed by applying the program 'BAYTAP-G' to the 152 days records of L-1 and L-2. Amplitudes and phase lags of 12 major constituents were determined.
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