Japan Geoscience Union Meeting 2023

Presentation information

[J] Online Poster

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC30] Hydrothermal systems of volcanoes

Tue. May 23, 2023 9:00 AM - 10:30 AM Online Poster Zoom Room (5) (Online Poster)

convener:Yasuhiro Fujimitsu(Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University), Wataru Kanda(Multidisciplinary Resilience Research Center, Institute of Innovative Research, Tokyo Institute of Technology), Takeshi Ohba(Department of chemistry, School of Science, Tokia University)

On-site poster schedule(2023/5/21 17:15-18:45)

9:00 AM - 10:30 AM

[SVC30-P01] The 2022 seismic unrest of Ontake Volcano using Matched Filter

*Yoshiko Yamanaka1, Yuta Maeda1, Shinichiro Horikawa1, Toshiko Terakawa1 (1.Graduate School of Encironmental Studies, University of NAGOYA)

Keywords:Mt. Ontake, Matched Filter, seismicity

Seismic activity at Mt. Ontake has gradually decreased since the 2014 eruption. From late February to early March 2022, seismic activity increased and the eruption alert level raised from 1 to 2 by the Japan Meteorological Agency. The largest earthquake (M1.2 according to the epicenter determination by Nagoya University) accompanied by the very long period events and tilt change occurred around 14:20 on February 23. In early March, tremors with a duration of about 1 minute accompanied by very long period events occurred frequently.
Since October 2017, Nagoya University has installed 10 seismic stations on the summit of Mt. Ontake as a test operation of a compact, low-power-consumption seismic telemetry system (Horikawa et al., 2017 VSJ). Using these data, it is now possible to determine the epicenter of earthquakes just below the summit with relatively high accuracy. These data were used to determine the hypocenters. We found that the seismic activity just below the summit began on February 23 and occurred within a cluster near sea level, which is the deepest group of seismic activity since 2014. (Maeda et al., 2022 VSJ)
In order to investigate the relationship between the volcanic activity of Ontake volcano and the seismic activity in and around the summit area, Yamanaka (2021 SSJ) has analyzed seismic activity since 2006 using the Matched Filter. Previous analyses have shown that volcanic activities at Mt. Ontake were often accompanied by seismic activities at depths of around 30 km or 10 km at the southern foot of Mt. Ontake, and that these activities move toward the summit of Mt. Ontake.
Therefore, we used the Matched Filter to analyze this activity. The results indicate that the seismic activity started around February 18 at 5 km below sea level at the southern foot of Mt. Ontake. On the 22nd, seismic activity became more active near the sea level just below the summit, and continued until around March 10. The pattern of seismic activity before and after the eruptions in 2007 and 2014 was similar to this activity, but the seismic activities associated with past two eruptions were much more active and lasted longer than this one.
Another noteworthy point of the recent activity is the increase in seismic activity at a depth of about 30 km in the vicinity of Lake Matsubara. This is a location where deep low frequency earthquakes occur. Kurihara & Obara (2021) pointed out that deep low frequency earthquakes are related to volcanic activities. The present analysis is based on high-frequency waveforms, so it is necessary to analyze low-frequency waves in the future.