Effect of lateral topographic density variations on subsurface structure estimation by gravity
inversion – a case study in Aso Caldera, Japan
Koji Matsuo, Geospatial Information Authority of Japan, Ibaraki, Japan, Tomokazu Kobayashi,
GSI of Japan, Tsukuba, Japan, Ryosuke Ando, University of Tokyo, Department of Earth and
Planetary Science, Bunkyo-ku, Japan and Takayuki Nakano, Geospatial Information
Authority of Japan, Geography and Crustal Dynamic Research Center, Tsukuba, Japan
Gravity data observed on the topographic surface is strongly influenced by the gravitational
attraction of topography. Therefore, the appropriate correction of the gravitational attraction
of topography to gravity data is a key to subsurface structure estimation of the ground by
gravity inversion. The gravitational attraction of topography, or topographic gravity effect, is
commonly computed from a topographic elevation model under an assumption of a constant
density (2,670 kg/m3). This assumption is inappropriate in volcanic regions with variable
geological structures. In this study, we compute the topographic gravity effect considering a
laterally varying topographic density, and investigate this effect on the subsurface structure
estimation by gravity inversion. The study area is the Aso Caldera of Japan where the various
geophysical and geologic data are available.