Permalink : http://hdl.handle.net/2115/21509

JaLCDOI : 10.14943/gbhu.69.191

Series of Mogi's single source model display characteristic family curves on the logarithmic graph of vertical displacement versus horizontal distance. The family curves on log-log plots are simply characterized by the flat part at short distances and constant decay at farther distances. The specific corner distances, which are defined by the bending corner of the curves, are mainly controlled by the source depth. The edifice scale deformation associated with the 2000 eruption of Mt. Usu is far from that predicted by Mogi's single source. The vertical displacement shows much more sharp decay with distance around 5-6 Km and uplift-to-subsidence reversal at much farther distances on the logarithmic graph. This steep decay and a farther reversal can be well explained by a simplified twin spherical source model, with shallow inflation and deep deflation. It provides better fitness to the data, when the deflation volume at 10 Km is assumed to be nearly equivalent to the inflation volume at 2 Km. Similar result is also evident for the horizontal model. The combined twin source model of shallow inflation and deep deflationi is also applied to the available leveling data for the histolical 3 eruptions of Mt. Usu in 1910, 1943-45 and 1977-82. Edifice-scale deformations accompanied by 4 dome-building eruptions in 20th century can be also well explained by shallow inflation and deep deflation source. Strong similarity between the 2000 and the 1910 eruptions is especially interesting considering the smilarity of mutual surface eruptives activities and crypto-dome formations.