11:45 AM - 12:00 PM
[STT35-05] Spatio-temporal Variations in the 2014 Post-Eruptive Deflation Process of Mt. Ontake using InSAR analysis
Keywords:InSAR, ALOS-2, Mt. Ontake, Deflation of the mountain, GBIS
The phreatic eruption in 2014 at Mt. Ontake resulted in the deflation of the mountain. (1) After the eruption, the GNSS baseline length (OchiaiKaratani-Tanohara baseline) owned by JMA had been shortening at 7.5 mm/year, but after 2020, it decreased to 2.5 mm/year. The reason of this decrease has not been explained yet. (2) Narita and Murakami (2018) found local subsidence around the vents using InSAR data from 2014 to 2017 and estimated a nearly spherical pressure source reflecting a hydrothermal reservoir at 500 m depth. However, this modeling was based on the short-term data during the 10 months after the eruption, and surface deformation after 2020 has not been studied yet. (3) Narita et al. (2019) also considered the mass balance between the volume of plumes and the deflation volume of the spherical pressure source using plume images from 2014 to 2017. They estimated that 70 % of the plumes were supplied by a deeper pressure source. However, its details have not been clarified yet. Therefore, in order to solve three problems mentioned above, this study aims to analyze the spatio-temporal variations of the deflation of the mountain since the 2014 eruption based on the long-term data, and to estimate the pressure state within the mountain in order to clarify the overall picture of the deflation.
This study performed InSAR analysis using SAR images (Path 19, 20, 121, and 126) of ALOS-2 for the period of 2014 through 2023 to obtain time-series data of surface deformation in the LOS direction. In addition, 2.5-D analysis (Fujiwara et al., 2000) was performed using descending (19, 20) and ascending (126) data to obtain time-series data of surface deformation in the quasi-east-west and quasi-up-down directions. RINC (Ozawa et al., 2016) and rinc_gui (Okuyama, 2018) were used for the analysis, and the F5 solution of GEONET Takane (950281) was set as the reference of the deformation. Finally, we used GBIS (Bagrardi and Hooper, 2018) to estimate the model parameters of the pressure sources from the time-series data of surface deformation.
As a result, the surface deformation time-series for all LOS directions were almost consistent, and localized subsidence was detected in the southwest part of the summit. Although the cumulative displacement of InSAR time-series was an order of magnitude greater than that of the JMA's GNSS baseline length mentioned above, the deformation pattern was fairly consistent. The quasi-east-west and quasi-up-down time-series were also compared with those of the campaign GNSS observation data (from 2016 to 2022) owned by Nagoya University, and they were almost consistent. Finally, the source model parameter estimation resulted in the existence of an elongated rugby-ball shaped ellipsoidal pressure source (Yang et al., 1988). Followed by this estimated result, we interpreted that this ellipsoid reflects the path of hydrothermal fluid and it was partially broken due to the 2014 eruption connecting to the spherical pressure source estimated by Narita and Murakami (2018). In conclusion, we considered that the process of mountain body contraction after the 2014 eruption is the deflation of the spherical pressure source during the active volcanism after the eruption and the deflation of the ellipsoid pressure source during the period of quiescence after the eruption.
I would like to extend my sincerest gratitude to PIXEL for sharing the PALSAR-2 SLC data, and to JAXA for providing these data under a cooperative research contract. I acknowledge JAXA's ownership of the PALSAR-2 data. This study was supported by the ERI JURP 2021-B-03 grant in Earthquake Research Institute at the University of Tokyo. I am also grateful to GSI for Ellipsoidal height data generated from their 10m-mesh digital elevation model, and to the developers of the EGM96 geoid model (Lemoine et al. 1997), which were instrumental in processing of the interferograms for this study. I am fully grateful to academic and technical staffs from Earthquake and Volcano Research Center Graduate School of Environmental Studies, Nagoya University for providing GNSS data in Mt. Ontake.
This study performed InSAR analysis using SAR images (Path 19, 20, 121, and 126) of ALOS-2 for the period of 2014 through 2023 to obtain time-series data of surface deformation in the LOS direction. In addition, 2.5-D analysis (Fujiwara et al., 2000) was performed using descending (19, 20) and ascending (126) data to obtain time-series data of surface deformation in the quasi-east-west and quasi-up-down directions. RINC (Ozawa et al., 2016) and rinc_gui (Okuyama, 2018) were used for the analysis, and the F5 solution of GEONET Takane (950281) was set as the reference of the deformation. Finally, we used GBIS (Bagrardi and Hooper, 2018) to estimate the model parameters of the pressure sources from the time-series data of surface deformation.
As a result, the surface deformation time-series for all LOS directions were almost consistent, and localized subsidence was detected in the southwest part of the summit. Although the cumulative displacement of InSAR time-series was an order of magnitude greater than that of the JMA's GNSS baseline length mentioned above, the deformation pattern was fairly consistent. The quasi-east-west and quasi-up-down time-series were also compared with those of the campaign GNSS observation data (from 2016 to 2022) owned by Nagoya University, and they were almost consistent. Finally, the source model parameter estimation resulted in the existence of an elongated rugby-ball shaped ellipsoidal pressure source (Yang et al., 1988). Followed by this estimated result, we interpreted that this ellipsoid reflects the path of hydrothermal fluid and it was partially broken due to the 2014 eruption connecting to the spherical pressure source estimated by Narita and Murakami (2018). In conclusion, we considered that the process of mountain body contraction after the 2014 eruption is the deflation of the spherical pressure source during the active volcanism after the eruption and the deflation of the ellipsoid pressure source during the period of quiescence after the eruption.
I would like to extend my sincerest gratitude to PIXEL for sharing the PALSAR-2 SLC data, and to JAXA for providing these data under a cooperative research contract. I acknowledge JAXA's ownership of the PALSAR-2 data. This study was supported by the ERI JURP 2021-B-03 grant in Earthquake Research Institute at the University of Tokyo. I am also grateful to GSI for Ellipsoidal height data generated from their 10m-mesh digital elevation model, and to the developers of the EGM96 geoid model (Lemoine et al. 1997), which were instrumental in processing of the interferograms for this study. I am fully grateful to academic and technical staffs from Earthquake and Volcano Research Center Graduate School of Environmental Studies, Nagoya University for providing GNSS data in Mt. Ontake.