5:15 PM - 6:30 PM
[SVC28-P09] Estimating the underground pressure source of Miyakejima volcano by integrated processing of GNSS and leveling data
Keywords:Miyakejima, GNSS observation, leveling survey
Miyakejima is an active volcano located about 180 km south of Tokyo, and since the 20th century it erupted at intervals of about 20 years (1940, 1962, 1983, and 2000). Although there are continuous GNSS stations on Miyakejima, the number is limited and detailed crustal movements have not been obtained. Therefore, we conducted dense GNSS campaign observations six times from 2011 to 2019. Fukui et al. (2015) estimate the position and volume change of the pressure source on Miyakejima based on the observation results from 2011 to 2013, but consider only the data of the horizontal component of GNSS observation. This study accurately grasps the crustal movement of Miyakejima by enhancing GNSS observations and using leveling data during the latest 2013-2019 period, and we estimated in detail the location and temporal changes of the pressure source under Miyakejima volcano.
In September 2013, 2015, 2016 and 2019, we conducted GNSS campaign observations at benchmark points (up to 30 points) arranged so as to be distributed almost evenly over Miyakejima. In this study, 12 points of continuous data obtained from this GNSS campaign observation and 10 points of data during the same period of continuous observation points set up by the Geospatial Information Authority of Japan, Japan Meteorological Agency, and National Research Institute for Earth Science and Disaster Resilience used. We also used the data from the Miyakejima leveling survey conducted by the Tokyo Metropolitan Government almost every two years, and used the vertical fluctuations during the same period.
We used RTKLIB ver.2.4.2 (Takasu et al., 2007) to analyze the GNSS data, and we obtained the coordinate values of the GNSS stations. The horizontal displacement of GNSS from 2013 to 2019 showed radial displacement centered on the southwestern part of Miyakejima during all periods. On the other hand, the vertical displacement of leveling survey from 2014 to 2019 showed sedimentation on the northeastern side of Miyakejima with respect to the southwestern side during all periods.
The pressure source was estimated based on the GNSS horizontal displacement from 2013 to 2019 and the vertical displacement of leveling survey from 2014 to 2019. The optimum values of the position and volume change of the pressure source were obtained by using MaGCAP-V software (Meteorological Research Institute, 2008) for analyzing crustal activity for volcano. As a result, two pressure sources with different depths were estimated. One is a horizontal plate-shaped sill just below the Miyakejima crater and 0.3 km below sea level, and the other is a spherical pressure source located about 2.5 km southwest of the Miyakejima crater and 9.0 km below sea level. The volume change of each volume was -3.3 × 105 m3/yr for sill and +1.2 × 107 m3/yr for spherical pressure source. It is presumed that the sill in the shallow part contracts due to degassing from the crater, and the spherical pressure source in the deep part accumulates and expands due to the rise of magma from the deeper part.
In this study, the position of the pressure source in the island could be accurately determined by analyzing the fluctuation of the vertical components by leveling survey. The deep spherical pressure source was estimated at almost the same position as the result of Nishimura et al. (2002). In the addition, Nishimura et al. (2002) estimated that the volume accumulation rate of magma chamber deep underground during the last eruption rest period (1983~2000) was 10.2×106 m3/yr. On the other hand, the volume accumulation rate between 2000 and 2019 was estimated to be 12.6 × 106 m3 / yr from the Geospatial Information Authority of Japan data (2011), Fukui et al. (2015), and this study. Therefore, in the 2000 eruption, a caldera crater was formed, which is very different from previous eruptions, but since then, the deep underground magma chamber have been in the same position as in the 1983-2000 period, and have been increasing at about the same rate.
This work is partly supported by MEXT under its The Second Earthquake and Volcano Hazards Observation and Research Program, and also supported by Earthquake Research Institute, The University of Tokyo under JURP (2016-B-09). Continuous GNSS data was provided by GSI and JMA. Leveling survey data was provided by the Bureau of General Affairs of the Tokyo Metropolitan Government. Many member of the Japanese University Consortium for GPS Research (JUNCO) cooperated in the GNSS campaign observation. We would like to express our gratitude to all.
In September 2013, 2015, 2016 and 2019, we conducted GNSS campaign observations at benchmark points (up to 30 points) arranged so as to be distributed almost evenly over Miyakejima. In this study, 12 points of continuous data obtained from this GNSS campaign observation and 10 points of data during the same period of continuous observation points set up by the Geospatial Information Authority of Japan, Japan Meteorological Agency, and National Research Institute for Earth Science and Disaster Resilience used. We also used the data from the Miyakejima leveling survey conducted by the Tokyo Metropolitan Government almost every two years, and used the vertical fluctuations during the same period.
We used RTKLIB ver.2.4.2 (Takasu et al., 2007) to analyze the GNSS data, and we obtained the coordinate values of the GNSS stations. The horizontal displacement of GNSS from 2013 to 2019 showed radial displacement centered on the southwestern part of Miyakejima during all periods. On the other hand, the vertical displacement of leveling survey from 2014 to 2019 showed sedimentation on the northeastern side of Miyakejima with respect to the southwestern side during all periods.
The pressure source was estimated based on the GNSS horizontal displacement from 2013 to 2019 and the vertical displacement of leveling survey from 2014 to 2019. The optimum values of the position and volume change of the pressure source were obtained by using MaGCAP-V software (Meteorological Research Institute, 2008) for analyzing crustal activity for volcano. As a result, two pressure sources with different depths were estimated. One is a horizontal plate-shaped sill just below the Miyakejima crater and 0.3 km below sea level, and the other is a spherical pressure source located about 2.5 km southwest of the Miyakejima crater and 9.0 km below sea level. The volume change of each volume was -3.3 × 105 m3/yr for sill and +1.2 × 107 m3/yr for spherical pressure source. It is presumed that the sill in the shallow part contracts due to degassing from the crater, and the spherical pressure source in the deep part accumulates and expands due to the rise of magma from the deeper part.
In this study, the position of the pressure source in the island could be accurately determined by analyzing the fluctuation of the vertical components by leveling survey. The deep spherical pressure source was estimated at almost the same position as the result of Nishimura et al. (2002). In the addition, Nishimura et al. (2002) estimated that the volume accumulation rate of magma chamber deep underground during the last eruption rest period (1983~2000) was 10.2×106 m3/yr. On the other hand, the volume accumulation rate between 2000 and 2019 was estimated to be 12.6 × 106 m3 / yr from the Geospatial Information Authority of Japan data (2011), Fukui et al. (2015), and this study. Therefore, in the 2000 eruption, a caldera crater was formed, which is very different from previous eruptions, but since then, the deep underground magma chamber have been in the same position as in the 1983-2000 period, and have been increasing at about the same rate.
This work is partly supported by MEXT under its The Second Earthquake and Volcano Hazards Observation and Research Program, and also supported by Earthquake Research Institute, The University of Tokyo under JURP (2016-B-09). Continuous GNSS data was provided by GSI and JMA. Leveling survey data was provided by the Bureau of General Affairs of the Tokyo Metropolitan Government. Many member of the Japanese University Consortium for GPS Research (JUNCO) cooperated in the GNSS campaign observation. We would like to express our gratitude to all.