5:15 PM - 6:45 PM
[SVC26-P06] Gravity Anomaly Analysis at Kusatsu-Shirane Volcano
Keywords:gravity anomaly, density structure, Kusatsu-Shirane Volcano, resistivity structure
Kusatsu-Shirane Volcano is a stratovolcano located near the border between Gunma and Nagano prefectures. Due to repeated phreatic eruptions in recent years, many geophysical studies have been conducted. It was pointed out that a resistivity structure model inferred from magnetotelluric (MT) data obtained around the volcano indicated a good correlation between the Bouguer gravity anomaly and the resistivity distribution at a relatively shallow depth. However, no comparison was made with the density structure that causes gravity anomaly, and only a qualitative interpretation was made. Therefore, the objective of this study was to estimate the subsurface density structure using gravity anomaly data from a wide area around Kusatsu-Shirane Volcano and to compare it with the resistivity structure model of the previous study. As a result of the analysis, it was found that the normally used assumed density of subsurface rocks did not sufficiently remove the influence of topography. Therefore, we first searched the optimal assumed density of the Bouguer anomaly for estimating the density structure using the gravity data from 1590 points around Kusatsu-Shirane Volcano. The residual gravity anomaly was obtained by applying an upward continuation to the Bouguer anomaly based on the newly estimated assumed density to extract the long wavelength components and eliminate it as a broad trend surface. The obtained residual gravity anomaly was used for inversion to estimate the 3-D density structure. The estimated density structure model was compared with the resistivity structure model, and a relationship was found between them in relatively shallow structures, supporting the interpretation from the previous study.