2001 Volume 52 Issue 4-5 Pages 207-214
Usu Volcano at the southwestern part of Hokkaido, Japan, started phreatomagmatic and phreatic eruptions at the northwestern and western flanks of the volcano from March 31, 2000. Significant crustal deformations with intensive earthquake swarms were observed from two days before the first eruption. Deformation rates were dramatically decreased after the first eruption. The continuous EDM measurements were started from April 12 to monitor the crustal deformations at the volcano. Two EDM instruments were installed at 3.4 km SSW and 3.3 km W from uplifting center. Nine mirror targets were installed along the western foot of the volcano. Measured data until the end of September are given in this report. All measured distances were shortened about 6 cm/day in maximum in the middle of April. The shorting rates were exponentially decreased before the movements were almost stopped until the end of July. Although, moving vectors of some mirror targets near the uplifting center were changed to opposite directions from the end of July.
