The horizontal deformations of the earth’s crust at two volcanic areas in Kyusyu, Japan have been observed with repeated measurements of the base-line lengths by means of a Geodimeter AGA Model 6 since 1968 and their results for the last three years are reported. In the Sakura-jima area, the network consisted of five base-lines was constructed on the western flank of the volcano Sakura-jima. Each base-line changes its length monotonously for the last three years and principal strain are deduced to be 4∿5×10
-6/year (NNE-SSW) and 0~-1×10
-6/year (ESE-WNW). This results are similar to the manner of horizontal deformations of the earth's crust in the vicinity of Sakura-jima at the great Sakura-jima eruption in 1914 which was found by the triangulations after the eruption (F. Omori, 1920). On the other hand, just after the 1968 Ebino-Yoshimatsu earthquake swarm, a base-line network was established at Yoshimatsu area, western part of Kakuto caldera, where a part of epicentral region is involved. Each base-line changes its length irregularly for the last three years. Taking errors into consideration, we cannot drew any definite conclusions at present for the horizontal deformations in this area, but it seems that there is some correspondence between direction of axes of principal strains and the distributions of initial motion of P wave of Ebino-Yoshimatsu earthquakes (pull~contraction : push~extension).
抄録全体を表示