Source mechanism of a very-long-period event at Mt Ontake, central Japan: Response of a hydrothermal system to magma intrusion beneath the summit

Nakamichi, Haruhisa; Kumagai, Hiroyuki; Nakano, Masataka; Okubo, Makoto; Kimata, Fumiaki; Ito, Yoshihiro; Obara, Kazushige

doi:10.1016/j.jvolgeores.2009.09.006

Cited by 59 publications

(70 citation statements)

References 29 publications

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“…However, the magnitude of the response in the medium, long, and dike stacked data was much smaller in the 2014 activity than in the 2007 activity; these results indicate that the amount of inflation of the deep source was smaller in 2014 than in 2007. Nakamichi et al (2009) To summarize, we were able to detect slight changes prior to the eruption in 2014 in the short stacked data by a quasi-real-time analysis using IGS ultra-rapid ephemeris data. Therefore, the stacking method effectively enhanced our ability to detect volcanic activity in GNSS monitoring data.…”

Section: Resultsmentioning

confidence: 70%

Detection of crustal deformation prior to the 2014 Mt. Ontake eruption by the stacking method

Miyaoka

Takagi²

2016

Earth Planet Sp

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The phreatic eruption of Mt. Ontake in central Japan occurred in September 27, 2014. No obvious crustal deformation was observed prior to the eruption, and the magnitudes of other precursor phenomena were very small. In this study, we used the stacking method to detect crustal deformation prior to the eruption. The stacking method is a technique to improve the signal-to-noise ratio by stacking multiple records of crustal deformation. We succeeded in detecting a slight crustal deformation caused by a volume change in the shallow region beneath the volcano's summit from 1 month prior to the eruption. We also detected a slight crustal deformation that may have been caused by a volume increase in the deep region from one and a half months before the eruption. The magnitude of the volume change in the shallow region did not differ significantly in the 2014 eruption compared to the volume change during the small Mt. Ontake eruption in 2007, and the volume change in the deep region was rather smaller in 2014 than in 2007.

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Section: Resultsmentioning

confidence: 70%

Detection of crustal deformation prior to the 2014 Mt. Ontake eruption by the stacking method

Miyaoka

Takagi²

2016

Earth Planet Sp

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“…In 1979, Mount Ontake produced its first phreatic eruption in recorded history, ejecting ash, gas, and debris into the sky (volcanic explosivity index (VEI) = 2, Smithsonian 2015). The 1979 eruption was followed by minor phreatic explosions in 1991 and 2007 (e.g., Nakamichi et al 2009;Japan Meteorological 2014). On 27 September 2014, at 11:52 a.m. JST (UTC + 9), Mount Ontake produced another phreatic (steam type) eruption, spraying volcanic ash, gas, and debris on surrounding areas.…”

Section: Introductionmentioning

confidence: 99%

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

et al. 2015

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We analyzed seismicity linked to the 2014 phreatic eruption of Mount Ontake, Japan, on 27 September 2014. We first relocated shallow volcano tectonic (VT) earthquakes and long-period (LP) events from August to September 2014. By applying a matched-filter technique to continuous waveforms using these relocated earthquakes, we detected numerous additional micro-earthquakes beneath the craters. The relocated VT earthquakes aligned on a near-vertical plane oriented NNW-SSE, suggesting they occurred around a conduit related to the intrusion of magmatic-hydrothermal fluids into the craters. The frequency of VT earthquakes gradually increased from 6 September 2014 and reached a peak on 11 September 2014. After the peak, seismicity levels remained elevated until the eruption. b-values gradually increased from 1.2 to 1.7 from 11 to 16 September 2014 then declined gradually and dropped to 0.8 just before the eruption. During the 10-min period immediately preceding the phreatic eruption, VT earthquakes migrated in the up-dip direction as well as laterally along the NNW-SSE feature. The migrating seismicity coincided with an accelerated increase of pre-eruptive tremor amplitude and with an anomalous tiltmeter signal that indicated summit upheaval. Therefore, the migrating seismicity suggests that the vertical conduit was filled with pressurized fluids, which rapidly propagated to the surface during the final 10 min before the eruption.

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“…Murase et al (2016) also suggested the tensile crack model from precise leveling measurements. At the same time, the shallow source was located at the hypocenter of the very long-period seismic event associated with the 2007 eruption (Nakamichi et al 2009). …”

Section: Discussionmentioning

confidence: 97%

Shallow pressure sources associated with the 2007 and 2014 phreatic eruptions of Mt. Ontake, Japan

Takagi

Onizawa

2016

Earth Planet Sp

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Source mechanism of a very-long-period event at Mt Ontake, central Japan: Response of a hydrothermal system to magma intrusion beneath the summit

Cited by 59 publications

References 29 publications

Detection of crustal deformation prior to the 2014 Mt. Ontake eruption by the stacking method

Detection of crustal deformation prior to the 2014 Mt. Ontake eruption by the stacking method

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan

Shallow pressure sources associated with the 2007 and 2014 phreatic eruptions of Mt. Ontake, Japan

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