噴火活動に伴う桜島火山および姶良カルデラ周辺の地盤変動

Abstract

Vertical and the horizontal deformations of the ground have occurred at Sakurajima andaround Aira Caldera, associated with the eruptive activity of Sakurajima Volcano. Thesecular variation of these ground deformations since 1891 have been examined by the data ofgeodetic surveys repeated.The fundamental relations between ground deformations and volcanic activities atSakurajima are concluded as follows, (1) In flank eruption: Flank eruption with lava flows causes remarkable deflation of theground around Aira Caldera immediately after the eruption. However, inflation of theground begins anew within a few years and that inflation continues till the next eruption.There are local ground deformations which exceed the elastic limits of the earth's crust nearthe fissure line in Sakurajima.(2) In summit eruption: Aira Caldera indicates gradual inflation of the ground in thecalm stage of summit eruptions, and reverses to a slow deflation when the eruptive activityreaches its peak.The deflation of the ground occures around the caldera in proportion to the amount ofmagma which is extruded to the ground surface as lava flows, tephra and so on. The inflationof the ground will be continued untill the future eruption, while magma is supplied and storedagain in the magma reservoir beneath the center of Aira Caldera. Such a history of theground deformations associated with the volcanic activity repeats itself at Sakurajima andaround Aira Caldera.