Detection of a crack-like conduit beneath the active crater
at Aso volcano, Japan
Mare Yamamoto, Hitoshi Kawakatsu, Satoshi Kaneshima,
Takehiko Mori, Tomoki Tsutsui, Yasuaki Sudo, Yuichi Morita
Geophys. Res. Lett., 26 3677-3680, 1999
Abstract
To constrain the source of long period tremors (LPTs),
we deployed a very dense broadband seismic network consisting of
totally twenty-four stations around the active crater
of Aso volcano in Kyushu, Japan.
The observed spatial variation of the signal amplitudes reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation)
of an inclined tensile crack with a strike almost parallel to the chain of craters.
The detected crack has a dimension of 1\,km and its center is located a few
hundred meters southwest of the active fumarole, at a depth of about 1.8\,km.
The extension of the crack plane meets the
crater chain including the active fumarole at the surface,
suggesting that the crack has played an important role in transporting
steam (gasses) and/or lava to the craters from below.
This work also demonstrates a powerful usage of broadband seismometers
as geodetic instruments to constrain subsurface structures at active volcanoes.