Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan

Terakawa, Toshiko; Yamanaka, Yasuhiro; Nakamichi, Haruhisa; Watanabe, Toshiki; Yamazaki, Fumihito; Horikawa, Shinichiro; Okuda, Takashi

doi:10.1016/j.tecto.2013.10.005

Cited by 15 publications

(26 citation statements)

References 30 publications

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“…Fluid pressures within the faults/cracks further increased, resulting in a reduction of the effective normal stress on faults/cracks (e.g., Hubbert and Rubey 1959;Terakawa et al 2013;Terakawa 2014). This reduction in fault strength facilitated the growth of small faults/cracks into larger ones, producing highermagnitude earthquakes (Fig.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

confidence: 99%

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

et al. 2015

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“…The seismic-aseismic boundary of larger earthquakes (M > 6) is found at distances of about 10 km from the center of the volcano, suggesting the presence of higher heat flux and thinned seismogenic crustal layer near the volcano (Ito, 1993). Over-pressurized fluid reservoirs have also been identified at depths between 5 and 12 km below the southeast and east flanks of Mount Ontake (Terakawa et al, 2013). Finally, 3 He/ 4 He ratios of natural spring water at the most proximal site (Nigorigo) to the central cone of Ontake volcano were (Fig.…”

Section: Source Of Heat and Magmatic Gas In The 2014 Eruptionmentioning

confidence: 92%

“…The estimated source depth of Gl and Xtn (2-4 km) is comparable with the depth of the hot pressurized fluid (magma) injected during the 2007 event. As such, we consider the over-pressurized fluid reservoir detected by Terakawa et al (2013) to be a magma reservoir, rather than steam. Magma injection occurred during the 2007 event, but there was little or no inflation before the 2014 eruption .…”

Section: Source Of Heat and Magmatic Gas In The 2014 Eruptionmentioning

confidence: 99%

Heat source of the 2014 phreatic eruption of Mount Ontake, Japan

et al. 2020

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We present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of Mount Ontake, Japan, on 27 September 2014, which resulted in 63 fatalities. Ash from the eruption comprises primarily hydrothermally altered, white-toned rock fragments. However, the ash contains trace amounts (< 0.7 wt%) of vitreous lessaltered particles (LAPs), which are only altered on their surfaces, suggesting rapid ascent through the hydrothermal system. The LAPs are classified into two categories: "glassy" and "crystalline." Glassy LAPs comprise high-silica rhyolitic glass (74-83 wt% SiO 2 ) with rounded quartz, chalcedony-free vesicles, and reversely zoned plagioclase (cores = 47 mol% An; rims = 70 mol% An), indicating magma re-heating. Crystalline LAPs have a groundmass-like texture that suggests eutectic crystallization at shallow depths. Thermodynamic calculations indicate that the pre-eruptive temperatures of the glassy and crystalline LAPs were 700-1300°C and~700°C, respectively, and that the storage depth was < 4 km (pressure < 100 MPa). The observed petrological features suggest that the LAPs were sourced from a magma recently intruded at shallow depths. Although crustal deformation (i.e., the volume change associated with magmatic intrusion) was insignificant prior to the 2014 eruption, a clear signature of crustal deformation was observed in 2007, the source of which was located 3 km below the summit. We suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption.

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“…They discussed effects of mantle-derived gases to explain the crustal deformations. Terakawa et al (2013) and Terakawa (2017) determined earthquake focal mechanisms and inferred an over-pressured fluid reservoir located beside and northeast of the aftershock area of the 2017 Southern Nagano prefecture earthquake.…”

Section: Introductionmentioning

confidence: 99%

A 3D electrical resistivity model around the focal zone of the 2017 southern Nagano Prefecture earthquake (MJMA 5.6): implications for relationship between seismicity and crustal heterogeneity

Ichihara

Kanehiro

Mogi

et al. 2018

Earth Planets Space

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Effects of pore fluid pressure and tectonic stress on diverse seismic activities around the Mt. Ontake volcano, central Japan

Cited by 15 publications

References 30 publications

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

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

Heat source of the 2014 phreatic eruption of Mount Ontake, Japan

A 3D electrical resistivity model around the focal zone of the 2017 southern Nagano Prefecture earthquake (MJMA 5.6): implications for relationship between seismicity and crustal heterogeneity

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