3:30 PM - 5:00 PM
[SVC35-P04] Subtheme B4 : Development of Techniques for Revealing Internal Structure and Conditions
Keywords:Mobile observations, Electromagnetic exploration, Phreatomagmatic eruption fields
"Theme B: Development of advanced volcano observation techniques" (Theme B), which is a part of the " Integrated Program for Next Generation Volcano Research and Human Resource Development" (Volcano-PJ), consists of four subthemes and aims to respond to requests for the evaluation of the imminence of volcanic eruptions. Among these four subthemes, Subtheme B4 is mainly concerned with the development of data acquisition and data analysis tools that contribute to the assessment of the imminence of volcanic eruptions by making full use of geophysical methods.
Subtheme B4 aims to conduct mobile multi-parameter observations and electromagnetic explorations at volcanoes that are likely to erupt in the near future or that are likely to cause major disasters in its eruption, and to clarify the level of volcanic activity at the time of observations and the structure immediately below the volcano through analysis of the acquired data. Specifically, about 10 volcanoes are targeted for observation, including Kirishima, Hakone, Kuttara, Miyakejima, Kusatsu-Shirane, Zao, Usu, IzuOshima, Mt Fuji and Niigata-Yakeyama, with mobile observations or electromagnetic explorations being conducted on two volcanoes every year for about two years, taking into account the characteristics of each volcano. So far, observations have been carried out on eight of the ten volcanoes mentioned above, and information on the state of the volcano interior has been obtained. The results of these observations provide the basis for assessing the imminence of future changes in volcanic activity.
Structural exploration has been carried out on several volcanoes and the comparison of the results has revealed some commonalities as eruption-generating areas. For example, a sequence of zones of low-frequency earthquakes suggesting fluid movement, zones suggesting partial melting of rock or the presence of magma, and zones suggesting hydrothermal reservoir, from deeper to shallower zones. The upper end of the hydrothermal reservoir appears to be a brittle-ductile boundary, and minerals such as silica are thought to form a sealing-zone, sealing the upper part of the hydrothermal reservoir. Shallower than the sealing-zone, the VT seismicity is active as it enters the brittle zone. Furthermore, near the surface in the shallower zone, low resistivity layers are distributed suggesting an existence of caprock that is rich in the clay mineral smectite. Deformation sources of expansion are often observed just below the sealing zone and caprock, suggesting that fluids rising from depth are prevented from ascending further and accumulate at these depths. Eruptions that occur under such structures are thought to be caused by the pressure rise due to fluid accumulation that destroys the caprock.
As tools for immediate analysis of data obtained from such observations, a seismic array data analysis system, a subsurface resistivity and hydrothermal flow analysis system, a comprehensive analysis system for volcanic seismic activity, a remote thermal information analysis system and a continuous seismic wavefield analysis system are being developed. Since these tools cannot be made practical with uniform specifications that ignore the characteristics and environment of individual volcanoes, the aim is to make them more widely available by using them to analyze data of mobile observations conducted under various conditions (e.g. station placement, station density, topography).
The data and analysis results obtained in Subtheme B4 are provided to the database currently being created under Volcano PJ's Theme A. When carrying out field observations, we collaborate with the Consortium for Volcano Research and Human Resource Development to accept young researchers and graduate students, providing on-the-job training opportunities.
Subtheme B4 aims to conduct mobile multi-parameter observations and electromagnetic explorations at volcanoes that are likely to erupt in the near future or that are likely to cause major disasters in its eruption, and to clarify the level of volcanic activity at the time of observations and the structure immediately below the volcano through analysis of the acquired data. Specifically, about 10 volcanoes are targeted for observation, including Kirishima, Hakone, Kuttara, Miyakejima, Kusatsu-Shirane, Zao, Usu, IzuOshima, Mt Fuji and Niigata-Yakeyama, with mobile observations or electromagnetic explorations being conducted on two volcanoes every year for about two years, taking into account the characteristics of each volcano. So far, observations have been carried out on eight of the ten volcanoes mentioned above, and information on the state of the volcano interior has been obtained. The results of these observations provide the basis for assessing the imminence of future changes in volcanic activity.
Structural exploration has been carried out on several volcanoes and the comparison of the results has revealed some commonalities as eruption-generating areas. For example, a sequence of zones of low-frequency earthquakes suggesting fluid movement, zones suggesting partial melting of rock or the presence of magma, and zones suggesting hydrothermal reservoir, from deeper to shallower zones. The upper end of the hydrothermal reservoir appears to be a brittle-ductile boundary, and minerals such as silica are thought to form a sealing-zone, sealing the upper part of the hydrothermal reservoir. Shallower than the sealing-zone, the VT seismicity is active as it enters the brittle zone. Furthermore, near the surface in the shallower zone, low resistivity layers are distributed suggesting an existence of caprock that is rich in the clay mineral smectite. Deformation sources of expansion are often observed just below the sealing zone and caprock, suggesting that fluids rising from depth are prevented from ascending further and accumulate at these depths. Eruptions that occur under such structures are thought to be caused by the pressure rise due to fluid accumulation that destroys the caprock.
As tools for immediate analysis of data obtained from such observations, a seismic array data analysis system, a subsurface resistivity and hydrothermal flow analysis system, a comprehensive analysis system for volcanic seismic activity, a remote thermal information analysis system and a continuous seismic wavefield analysis system are being developed. Since these tools cannot be made practical with uniform specifications that ignore the characteristics and environment of individual volcanoes, the aim is to make them more widely available by using them to analyze data of mobile observations conducted under various conditions (e.g. station placement, station density, topography).
The data and analysis results obtained in Subtheme B4 are provided to the database currently being created under Volcano PJ's Theme A. When carrying out field observations, we collaborate with the Consortium for Volcano Research and Human Resource Development to accept young researchers and graduate students, providing on-the-job training opportunities.