[S-VC32] Active Volcanism

[SVC32-P24] Estimation of crustal deformation of Miyakejima volcano and its pressure sources by using GNSS data

*Rin Matsubara¹, Takeshi Matsushima¹, Ayuka Joudoi¹, Atsushi Watanabe², Jun Oikawa², Yosuke Aoki², Yusaku Ohta³ (1.Kyushu University, 2.Tokyo University, 3.Tohoku University)

Keywords:Miyakejima volcano, fiite-sphere model, sill

Miyakejima has repeatedly erupted about every 20 years. More than 24 years have passed since the last eruption in 2000, and the next eruption is feared. Watanabe, et al(2021 JpGU SVC28-P09) estimated a spherical expansion pressure source at a depth of 9.0 km, about 2.5 km southwest of the Miyakejima crater, and a contraction of a horizontal plate sill at a depth of 0.3 km below sea level, just below the Miyakejima crater, from the results of six tight GNSS campaign observations conducted from 2011 to 2019 and from level surveys within Miyakejima Island. In this study, we estimate the amount of recent crustal deformation on Miyakejima based on the coordinates of continuous GNSS stations and GNSS campaign stations on Miyakejima, and also estimate the source of subsurface pressure. Currently, continuous GNSS observations are conducted on Miyakejima by GSI (4 stations), JMA (5 stations), National Research Institute for Earth Science and Disaster Prevention (4 stations), etc. In this study, we use these continuous GNSS data. In addition, while GNSS campaign observations have been conducted on Miyakejima in 2011, 2013, 2015, 2016, and 2019, campaign observations were conducted in September 2024 for the first time in about five years, mainly by Kyushu University, and the obtained data were used for the analysis. The period of data use is the same as that of the previous study (Watanabe, et al. 2021), and the data obtained from the campaign observations during 2013 - 2024 were used for the analysis. The obtained data were subjected to baseline analysis using the GNSS real-time post-processing baseline analysis software RTKLIBver. 2.4.3 (Takasu, 2013) based on the GSI's GEONET Miyake 4 (960600), and the coordinates were obtained every 30 seconds, and then averaged to obtain the coordinates of each point. The coordinates of each point were obtained by averaging them. The GEONET Miyake 4 baseline coordinates were obtained by averaging the GSI's daily coordinates (F5 solution) for the months of August and September, including the campaign observation period. Subsequently, the amount of crustal deformation during each period was obtained by creating a displacement vector map from the difference of the coordinate values. Finally, we estimated the pressure sources beneath Miyakejima Island that can sufficiently explain the observed displacements. For pressure source estimation in this study, we used pydeform (Munekane et al.,2016), a crustal source estimation software that can relatively accurately estimate changes in pressure sources with finite magnitude in shallow areas.

The analysis showed that the baseline length has been elongated at all stations over the past 11 years, and that the entire Miyakejima Island has been radially displaced from the center of the island. Based on these crustal deformation data, we estimated a spherical pressure source and a horizontal plate sill. This model is consistent with a previous study (Watanabe, et al. 2021 JpGU SVC28-P09). Regarding the volume change, expansion was observed in the spherical pressure source. This indicates that magma has been continuously supplied to the Miyakejima basement since the last eruption in 2000.

We plan to use level survey data to obtain more detailed crustal deformation data and to estimate a more accurate model of the subsurface pressure source.

Acknowledgments: In this study, JVDN provided us with the coordinate values of GNSS point data observed by GSI, JMA, and NIED, which were analyzed by NIED. In addition, more than 50 researchers from all over Japan cooperated in the Miyakejima GNSS campaign observation in September 2024 to set up the observation points.
We used pydeform developed by Munekane, et al. (2016) for crustal source analysis.We thank them for their cooperation.