5:15 PM - 6:30 PM
[SVC28-P22] Development of volcano deformation calculation system using boundary element method (2)
Keywords:volcano deformation, BEM
Volcanic deformation data observed by tilt meter and/or GNSS stations were useful for monitoring and evaluating the volcanic activities. The Japan Meteorological Agency (JMA) has been constructing such observation stations around volcanoes, and these observed data were used for monitoring operation of volcanic activities. Because these observation stations around volcanoes were located on the steep topography of the volcano, the observed data were affected by the topography. It was important to consider the effect of the topography in the analysis of the observation data. To investigate the influence of topography on the analysis results of volcanic deformation data, we have developed a program for calculating volcanic deformation which considering the effect of topography by using the boundary element method (BEM). As a result, when the depth of the deformation source was about the same as the elevation of the observation station, the analysis result assuming an elastic half space was overestimated or underestimated the depth and the magnitude of the deformation source (Kawaguchi, 2020, JpGU). To utilize the developed program for the volcano monitoring operation by the JMA, we have developed functions for creating the mesh model of volcanic topography and converting the calculation results for data at observation station. In this study, we introduce the developing system and report the examples of its application.
The volcano deformation calculation system was consisted by the functions of creating a mesh model of the topography of volcano, calculating the volcanic deformation using the BEM, and converting of the calculation results into observational data. The mesh model of the topography of volcano and pressure sources was made by setting some parameters such as the name of the volcano and the location of the pressure source. The topography of the volcano was created using a 10-meter mesh digital elevation model (DEM) of the Geospatial Information Authority of Japan. A spherical or ellipsoidal pressure source can be set as the deformation source. The calculated results were output as displacement for each coordinate of the mesh model. These results were converted into the tilt change and displacement of each observation station for analysis. The converted tilt changes and displacements were output in the format of input files of MaGCAP-V developed by the Meteorological Research Institute, JMA. We have developed the program that can be applied to 20 volcanoes.
As an example of application of this system, we created the topographic model of Izu-Oshima volcano and calculate the volcanic deformation. Assuming a dike penetration, we set a pressure source below the summit area. The tilt changes and displacements at the observation stations at Izu-Oshima volcano were numerically calculated. As a result, when the depth of the pressure source was 1,000 m below sea level, the difference in calculated tilt changes and displacements were small compared to the those obtained by assuming the elastic half space. When the elevation of the pressure source was set to 0 m above sea level, the calculated tilt changes and displacements were more than twice as large as those obtained by assuming the elastic half space at some stations.
The volcano deformation calculation system was consisted by the functions of creating a mesh model of the topography of volcano, calculating the volcanic deformation using the BEM, and converting of the calculation results into observational data. The mesh model of the topography of volcano and pressure sources was made by setting some parameters such as the name of the volcano and the location of the pressure source. The topography of the volcano was created using a 10-meter mesh digital elevation model (DEM) of the Geospatial Information Authority of Japan. A spherical or ellipsoidal pressure source can be set as the deformation source. The calculated results were output as displacement for each coordinate of the mesh model. These results were converted into the tilt change and displacement of each observation station for analysis. The converted tilt changes and displacements were output in the format of input files of MaGCAP-V developed by the Meteorological Research Institute, JMA. We have developed the program that can be applied to 20 volcanoes.
As an example of application of this system, we created the topographic model of Izu-Oshima volcano and calculate the volcanic deformation. Assuming a dike penetration, we set a pressure source below the summit area. The tilt changes and displacements at the observation stations at Izu-Oshima volcano were numerically calculated. As a result, when the depth of the pressure source was 1,000 m below sea level, the difference in calculated tilt changes and displacements were small compared to the those obtained by assuming the elastic half space. When the elevation of the pressure source was set to 0 m above sea level, the calculated tilt changes and displacements were more than twice as large as those obtained by assuming the elastic half space at some stations.