5:15 PM - 6:45 PM
[SVC26-P18] Estimation of Shallow Pressure Sources at Sakurajima Volcano Using Crustal Deformation Data
Keywords:Sakurajima volcano, Precise levelling survey, Ground deformation, Finite sphere model
Pressure source analysis based on various deformation observations has been conducted at Sakurajima, an extremely active volcano, and it has been suggested that multiple pressure sources exist in the underground. In this study, a pressure source estimation for shallow pressure sources beneath Sakurajima was conducted by applying a finite-size cavity model (McTigue, 1987) to data obtained by precise leveling observations.
Pressure sources in the shallow subsurface have a large influence on crustal deformation depending on their size. When analyzing shallow pressure sources using the point pressure source model (Mogi, 1958), this effect is not included in the calculations, which may lead to errors in the pressure source estimation results. Therefore, in this study, using two pressure source models applied to crustal deformation data from repeated first-order level survey observations from 2016 to 2022, we estimated the location, depth, radius, and volume change of pressure sources by performing a least-squares parameter analysis using a finite sphere model. The same estimations were also performed for the case with three pressure source models, to compare the results of the two models. Next, the crustal movement solutions of the finite sphere model and the Mogi model were calculated for each crustal movement caused by pressure changes in the three pressure sources. The difference in crustal vertical motion, was then calculated and compared between the results of the present analysis and those obtained when the Mogi model was used in the analysis.
The results of the pressure source calculations indicate that the two pressure source models estimate an expansion source with a radius of 130 m at a depth of 9 m below the Aira caldera and a contraction source with a radius of 120 m at a depth of 4.2 km below the Minamidake of Sakurajima.(Fig.1(a))The volume change of pressure sources over 6 years was estimated to be 12 milion (m3) and -4.9 milion (m3), respectively. The three pressure source models estimated an expansion source with a radius of 130 m and 60 m at a depth of 9 m below the Aira caldera and 3.0 km in the northern part of Sakurajima, respectively, and a contraction source with a radius of 100 m at a depth of 2.6 km below the Minamidake of Sakurajima .(Fig.1(b))The pressure source volume change over 6 years was 7.6 milion (m3) and 0.9 milion (m3), -2.9 milion (m3), respectively. The residuals between the computed ground motions and the actual observed values were smaller when the three pressure source models were applied, and the level survey data were well explained. The AIC value was 3200 when the analysis was performed applying the two pressure source model and 2540 for the three pressure source model. In the future, we will perform pressure source analysis taking into account horizontal variations obtained from GNSS observations.
Pressure sources in the shallow subsurface have a large influence on crustal deformation depending on their size. When analyzing shallow pressure sources using the point pressure source model (Mogi, 1958), this effect is not included in the calculations, which may lead to errors in the pressure source estimation results. Therefore, in this study, using two pressure source models applied to crustal deformation data from repeated first-order level survey observations from 2016 to 2022, we estimated the location, depth, radius, and volume change of pressure sources by performing a least-squares parameter analysis using a finite sphere model. The same estimations were also performed for the case with three pressure source models, to compare the results of the two models. Next, the crustal movement solutions of the finite sphere model and the Mogi model were calculated for each crustal movement caused by pressure changes in the three pressure sources. The difference in crustal vertical motion, was then calculated and compared between the results of the present analysis and those obtained when the Mogi model was used in the analysis.
The results of the pressure source calculations indicate that the two pressure source models estimate an expansion source with a radius of 130 m at a depth of 9 m below the Aira caldera and a contraction source with a radius of 120 m at a depth of 4.2 km below the Minamidake of Sakurajima.(Fig.1(a))The volume change of pressure sources over 6 years was estimated to be 12 milion (m3) and -4.9 milion (m3), respectively. The three pressure source models estimated an expansion source with a radius of 130 m and 60 m at a depth of 9 m below the Aira caldera and 3.0 km in the northern part of Sakurajima, respectively, and a contraction source with a radius of 100 m at a depth of 2.6 km below the Minamidake of Sakurajima .(Fig.1(b))The pressure source volume change over 6 years was 7.6 milion (m3) and 0.9 milion (m3), -2.9 milion (m3), respectively. The residuals between the computed ground motions and the actual observed values were smaller when the three pressure source models were applied, and the level survey data were well explained. The AIC value was 3200 when the analysis was performed applying the two pressure source model and 2540 for the three pressure source model. In the future, we will perform pressure source analysis taking into account horizontal variations obtained from GNSS observations.