09:45 〜 10:00
[SVC30-04] The gravity signature of the magmatic systems beneath the Izu-Bonin-Mariana submarine volcanoes
★Invited Papers
キーワード：Volcanism, Gravity, Altimetry, Caldera
The Izu-Bonin-Mariana (IBM) island arc hosts one of the highest concentrations of submarine volcanoes, that pose significant local and global hazards (e.g., landslides, ash plumes, pumice rafts, tsunamis). The magmatic systems under most submarine volcanoes are poorly known, and most of them have not been imaged by geophysical techniques, due to their inaccessibility and the cost of conducting research cruises. Improving our understanding of magmatic storage will help assess hazards and risks, ultimately contributing to the mitigation of the eruption and tsunami risk in the Pacific.
In this study, we investigate the magmatic systems underlying the volcanoes of the IBM arc using gravity data derived from satellite altimetry. We have identified 60 volcanoes in the IBM arc for which the bathymetry is known from direct measurements (e.g., singlebeam, multibeam, seismic, sounding), ensuring that we do not use satellite-derived bathymetry and maintain the independence of the two datasets. The main objective is to create an arc-wide inventory of magma storage (volume, depth) and provide models of the magmatic systems under the 60 volcanoes. In contrast to traditional nadir altimetry used up to now, the Surface Water and Ocean Topography (SWOT) mission launched in December 2022 uses radar interferometry to measure Sea Surface Height (SSH) across two 50 km-wide swaths with a 21-day repeat orbit. The analysis of one year of SWOT data shows a dramatic increase in the accuracy and resolution of the SWOT gravity field, already exceeding that of current gravity models (based on 30 years of nadir altimetry). We use the deflection of the vertical eastern and northern components from SWOT data to calculate the first vertical derivative of the vertical component of gravity (i.e., the Vertical Gravity Gradient or VGG). We then calculate and remove the gravity effect of the bathymetry using Parker’s expansion, estimate and remove the regional gravity field, and obtain the residual VGG Bouguer anomaly for each volcano. We classify the Bouguer gravity anomalies based on the commonly observed patterns, their characteristics wavelength, maximum amplitude, and polarity, and analyze the trends observed along the arc. Finally, we calculate a suite of forward models to calculate the gravity effect expected for a caldera infill, hydrothermal system, and magmatic system, using rectangular prisms with a constant gravity contrast with the oceanic crust. Varying the geometry, depth, and density contrast within expected ranges for a given volcano, we obtain a graph of all possible parameter combinations to explain the measured anomaly and constrain its source.
The next step in the project involves inverting the gravity anomalies to obtain 3D density models, which will then be integrated with dynamic earthquake and tsunami models to better constrain the sources of tsunamigenic earthquakes at active caldera systems. The newly generated database of previously unknown magmatic system characteristics will be used to address key questions critical to the understanding of subduction zones and their associated volcanic hazards. This arc-scale survey will also highlight priority areas for future targeted, multidisciplinary studies and research cruises in the IBM arc.
In this study, we investigate the magmatic systems underlying the volcanoes of the IBM arc using gravity data derived from satellite altimetry. We have identified 60 volcanoes in the IBM arc for which the bathymetry is known from direct measurements (e.g., singlebeam, multibeam, seismic, sounding), ensuring that we do not use satellite-derived bathymetry and maintain the independence of the two datasets. The main objective is to create an arc-wide inventory of magma storage (volume, depth) and provide models of the magmatic systems under the 60 volcanoes. In contrast to traditional nadir altimetry used up to now, the Surface Water and Ocean Topography (SWOT) mission launched in December 2022 uses radar interferometry to measure Sea Surface Height (SSH) across two 50 km-wide swaths with a 21-day repeat orbit. The analysis of one year of SWOT data shows a dramatic increase in the accuracy and resolution of the SWOT gravity field, already exceeding that of current gravity models (based on 30 years of nadir altimetry). We use the deflection of the vertical eastern and northern components from SWOT data to calculate the first vertical derivative of the vertical component of gravity (i.e., the Vertical Gravity Gradient or VGG). We then calculate and remove the gravity effect of the bathymetry using Parker’s expansion, estimate and remove the regional gravity field, and obtain the residual VGG Bouguer anomaly for each volcano. We classify the Bouguer gravity anomalies based on the commonly observed patterns, their characteristics wavelength, maximum amplitude, and polarity, and analyze the trends observed along the arc. Finally, we calculate a suite of forward models to calculate the gravity effect expected for a caldera infill, hydrothermal system, and magmatic system, using rectangular prisms with a constant gravity contrast with the oceanic crust. Varying the geometry, depth, and density contrast within expected ranges for a given volcano, we obtain a graph of all possible parameter combinations to explain the measured anomaly and constrain its source.
The next step in the project involves inverting the gravity anomalies to obtain 3D density models, which will then be integrated with dynamic earthquake and tsunami models to better constrain the sources of tsunamigenic earthquakes at active caldera systems. The newly generated database of previously unknown magmatic system characteristics will be used to address key questions critical to the understanding of subduction zones and their associated volcanic hazards. This arc-scale survey will also highlight priority areas for future targeted, multidisciplinary studies and research cruises in the IBM arc.