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[SVC31-P08] Intermittent Inflation on Azuma Volcano (Japan) Detected by PALSAR-2 and Sentinel-1 Data
Keywords:Satellite SAR, Azuma volcano, Ground deformation, Hydrothermal system
Monitoring ground deformations at active volcanoes can yield an understanding of the shallow hydrothermal systems and mechanisms of phreatic eruptions. InSAR data are helpful to detect ground deformation appearing on a local extent associated with pressure changes of a shallow hydrothermal system on active volcanoes.
Azuma volcano is one of the active volcanoes locating on the prefecture border of Fukushima and Yamagata Prefecture. Since 2014, intermittent seismic activity and emission of volcanic gas/steam over the geothermal area have been reported on Azuma volcano. Here, we investigate the spatiotemporal variation of the ground deformation using satellite SAR data and the pressure condition of the shallow hydrothermal system on Azuma volcano.
PALSAR-2 and Sentinel-1 data acquired in 2014-2020 were applied to multi-temporal InSAR analysis for extracting spatiotemporal variations in the deformations at Azuma volcano. Azuma volcano is covered by dense vegetation except for a region of the geothermal area, called the Oana crater, in summer and by heavy snow in winter. These usually caused decorrelation problems. Therefore, Sentinel-1 data are expected to detect deformation signals from late spring to early autumn each year at the Oana crater.
Time-series of PALSAR-2 line-of-sight (LOS) showed a wide range of deformations elongated in the east-west direction in 2015 and local deformations at the Oana crater with peaks in 2015 and 2019. The most part of deformation appeared at the Oana crater in 2015 returned into zero over approximately 2 years, while a deformation at another geothermal area about 500 m northwestward from the Oana crater maintained 2-3 cm of LOS change during the same time. Sentinel-1 LOS changes revealed detailed temporal variations of the deformations during non-snow coverage periods in each year, and complemented the temporal characteristics of the deformations at the Oana crater detected by PALSAR-2 data.
We inferred the geometry of pressure source for explaining the observation data using an analytical solution of surface deformations associated with volume change of a sphere and a prolong ellipsoid, and a sill opening. The model parameters were optimized by Markov Chain Monte Carlo algorithm. The observed local deformations at the Oana crater in 2015 and 2019 were reproduced by a prolonged ellipsoid or a flat source (sill) tilting toward the southeast with ~300 m below the surface. For the far-field deformation in 2015, an opening of a flat source (sill) locating at about 1.5 km below the surface (at the sea level) is an optimal geometry rather than a volume change of a sphere and a prolonged ellipsoid, although the model parameter for the far-field deformation in 2015 are optimized by using the LOS change acquired from one direction. The timing of the deformation is strongly consistent with a period of intense seismic activity at a shallower depth at Azuma volcano. Considering the deformation associated with the 2011 Tohoku-oki earthquake, our observation data and modeling result reveal geometries of two shallower pressure sources beneath Azuma volcano.
Azuma volcano is one of the active volcanoes locating on the prefecture border of Fukushima and Yamagata Prefecture. Since 2014, intermittent seismic activity and emission of volcanic gas/steam over the geothermal area have been reported on Azuma volcano. Here, we investigate the spatiotemporal variation of the ground deformation using satellite SAR data and the pressure condition of the shallow hydrothermal system on Azuma volcano.
PALSAR-2 and Sentinel-1 data acquired in 2014-2020 were applied to multi-temporal InSAR analysis for extracting spatiotemporal variations in the deformations at Azuma volcano. Azuma volcano is covered by dense vegetation except for a region of the geothermal area, called the Oana crater, in summer and by heavy snow in winter. These usually caused decorrelation problems. Therefore, Sentinel-1 data are expected to detect deformation signals from late spring to early autumn each year at the Oana crater.
Time-series of PALSAR-2 line-of-sight (LOS) showed a wide range of deformations elongated in the east-west direction in 2015 and local deformations at the Oana crater with peaks in 2015 and 2019. The most part of deformation appeared at the Oana crater in 2015 returned into zero over approximately 2 years, while a deformation at another geothermal area about 500 m northwestward from the Oana crater maintained 2-3 cm of LOS change during the same time. Sentinel-1 LOS changes revealed detailed temporal variations of the deformations during non-snow coverage periods in each year, and complemented the temporal characteristics of the deformations at the Oana crater detected by PALSAR-2 data.
We inferred the geometry of pressure source for explaining the observation data using an analytical solution of surface deformations associated with volume change of a sphere and a prolong ellipsoid, and a sill opening. The model parameters were optimized by Markov Chain Monte Carlo algorithm. The observed local deformations at the Oana crater in 2015 and 2019 were reproduced by a prolonged ellipsoid or a flat source (sill) tilting toward the southeast with ~300 m below the surface. For the far-field deformation in 2015, an opening of a flat source (sill) locating at about 1.5 km below the surface (at the sea level) is an optimal geometry rather than a volume change of a sphere and a prolonged ellipsoid, although the model parameter for the far-field deformation in 2015 are optimized by using the LOS change acquired from one direction. The timing of the deformation is strongly consistent with a period of intense seismic activity at a shallower depth at Azuma volcano. Considering the deformation associated with the 2011 Tohoku-oki earthquake, our observation data and modeling result reveal geometries of two shallower pressure sources beneath Azuma volcano.