Deep Low‐Frequency Earthquakes Beneath the Hakone Volcano, Central Japan, and their Relation to Volcanic Activity

Yukutake, Yohei; Abe, Yuki; Doke, Ryosuke

doi:10.1029/2019gl084357

Cited by 32 publications

(38 citation statements)

References 26 publications

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“…Our GNSS analysis detected the inflation of a deep spherical source in late March 2015, well before the onset of the seismic swarm activity in late April. It is interesting to note that a deep low-frequency event (DLF) began at approximately the same time as the inflation (Yukutake and Abe 2018;Mannen et al 2018). However, the DLF occurred at 15-30 km depth, much deeper than the deep spherical source at 5-6 km depth (see Fig.…”

Section: Discussionmentioning

confidence: 99%

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Temporal changes in inflation sources during the 2015 unrest and eruption of Hakone volcano, Japan

Harada

Doke

Mannen

et al. 2018

Earth Planets Space

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Global navigation satellite system data from Hakone volcano, central Japan, together with GEONET data from the Geospatial Information Authority of Japan, were used to investigate the processes associated with the volcanic activity in 2015, which culminated in a small phreatic eruption in late June 2015. Three deep and shallow sources, namely spherical, open crack, and sill, were employed to elucidate the volcanic processes using the observed GNSS displacements, and the MaGCAP-V software was used to estimate the volumetric changes of these sources. Our detailed analysis shows that a deep inflation source at 6.5 km below sea level started to inflate in late March 2015 at a rate of ~ 9.3 × 10 4 m 3 /day until mid-June. The inflation rate then slowed to ~ 2.1 × 10 4 m 3 /day and ceased at the end of August 2015. A shallow open crack at 0.8 km above sea level started to inflate in May 2015 at a rate of 1.7 × 10 3 m 3 / day. There was no significant volumetric change in the shallow sill source during the volcanic unrest, which is evident from interferometric synthetic aperture radar analysis. The inflation of the deep source continued even after the eruption without a significant slowdown in inflation rate. The inflation stopped in August 2015, approximately 1 month after the eruption ceased. This observation implies that the transportation of magmatic fluid to a deep inflation source (6.5 km) triggered the 2015 unrest. The magmatic fluid may have then migrated from the deep source to the shallow open crack. The phreatic eruption was then caused by the formation of a crack that extended to the surface. However, steam emissions from the vent area during and after the eruption were apparently insufficient to mitigate the internal pressure of the shallow open crack. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Discussionmentioning

confidence: 99%

“…3). Yukutake and Abe (2018) hypothesized that the DLF event may be due to an increase in magmatic fluid pressure. This suggests that such fluid may have migrated to shallower depths, potentially generating inflation of the deep spherical source discussed here.…”

Section: Discussionmentioning

confidence: 99%

Temporal changes in inflation sources during the 2015 unrest and eruption of Hakone volcano, Japan

Harada

Doke

Mannen

et al. 2018

Earth Planets Space

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“…Journal of Geophysical Research: Solid Earth with the supply of magmatic fluids from deep zone (Yukutake et al, 2019), occur in this moderate-attenuation area (Figures 9f and 10b).…”

Section: 1029/2020jb020341mentioning

confidence: 95%

Seismic Constraint on the Fluid‐Bearing Systems Feeding Hakone Volcano, Central Japan

et al. 2020

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Investigating heterogeneous structures beneath active volcanoes is important for better understanding of volcanic activity and improved mitigation of volcanic risk. In central Japan, Hakone volcano has recently shown shallow earthquake swarms and deep low-frequency earthquakes (DLFEs), which are probably related to geothermal or deep magmatic activity. In order to image the feeding system beneath this volcano, we estimate 3-D P wave attenuation structure using waveform data recorded at permanent and densely distributed temporary seismograph stations. We first determine corner frequencies of the earthquakes and then perform a joint inversion to obtain attenuation terms (t*) and site responses. Values of t* are finally inverted to estimate the attenuation structure to a depth of 50 km. High-attenuation zones at depths ≤5 km suggest that fracture zones are permeated with hydrothermal fluids. A high-strain rate zone revealed by geodetic observations is spatially correlated with a high-attenuation volume at depths of 5-10 km, suggesting that the anelastic deformation is dominant in the high-attenuation zones. A subvertical volume of moderate attenuation that is imaged at depths of 10-20 km beneath Hakone volcano is connected to the top of a zone of partial melting beneath Mt. Fuji at depths ≥30 km through a subhorizontal channel at a depth of~25 km. DLFEs in the lower crust and fluid-related activity such as earthquake swarms in the upper crust occur in this volume. The zone is thus interpreted as a fluid-bearing pathway, which allows the rise of magmatic fluids to Hakone volcano.

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“…At approximately 20 km beneath the northern caldera rim of the volcano, DLFs occur sporadically. Since many of the DLF swarm events were followed by in ation of the edi ce and shallow volcano-tectonic earthquake swarms, DLFs are interpreted as a signal indicating migration of magmatic uid (Yukutake et al 2015(Yukutake et al , 2019. A seismic tomography study revealed velocity structure beneath Hakone volcano and showed that the volcano has an active magma-hydrothermal system (Yukutake et al 2015).…”

Section: Subsurface Structure Of Hakone Volcanomentioning

confidence: 99%

“…The 2001 unrest accompanied an earthquake swarm, and deep and shallow in ation as observed by Global Navigation Satellite System (GNSS) and a tiltmeter network, and culminated with a blowout of a steam production well (SPW) in Owakudani (500 m deep). Since the 2001 unrest, major volcanic unrest episodes comprising earthquake swarms, deep in ation detected by a GNSS network, and deep low frequency events (DLF) were observed in 2006, 2008-2009and 2013(Harada et al 2018Yukutake et al 2019). In terms of seismicity, these events can be intensive as historical unrest episodes before 1960.…”

Section: Introductionmentioning

confidence: 99%

Volcanic Unrest at Hakone Volcano after the 2015 phreatic eruption — Reactivation of a Ruptured Hydrothermal System?

Mannen

Abe

Daita

et al. 2020

Preprint

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Since the beginning of the 21st century, volcanic unrest has occurred every 2–5 years at Hakone volcano. After the 2015 eruption, unrest activity changed significantly in terms of seismicity and geochemistry. In this paper, characteristics of the post-eruptive volcanic unrest that occurred in 2017 and 2019 are described, and changes in the hydrothermal system of the volcano caused by the eruption are discussed. Like the pre- and co-eruptive unrest, each post-eruptive unrest episode was detected by deep inflation below the volcano (~ 10 km) and deep low frequency events, which can be interpreted as reflecting supply of magma or magmatic fluid from depth. The seismic activity during the post-eruptive unrest episodes also increased; however, seismic activity beneath the eruption center during the unrest episodes was significantly lower, especially in the shallow region (~2 km), while sporadic seismic swarms were observed beneath the caldera rim, ~3 km away from the center. The 2015 eruption established routes for steam from the hydrothermal system (≥ 150 m deep) to the surface through the cap-rock, allowing emission of super-heated steam (~ 160 ºC), which was absent before the eruption. This steam showed an increase in magmatic/hydrothermal gas ratios (SO2/H2S and HCl/H2S) in the 2019 unrest, which may be interpreted as magmatic intrusion at shallow depth; however, no indicative seismic and geodetic signals were observed. Net SO2 emission during the post-eruptive unrest episodes, which remained within the usual range of the post-eruptive period, is also inconsistent with shallow intrusion. We consider that the post-eruptive unrest episodes were also triggered by newly derived magma or magmatic fluid from depth; however, the breached cap-rock was unable to allow subsequent pressurization of the hydrothermal system beneath the volcano center and suppressed seismic activity significantly. The heat released from the newly derived magma or fluid dried the vapor-dominated portion of the hydrothermal system and inhibited scrubbing of SO2 and HCl to allow a higher magmatic/hydrothermal gas ratio. The 2015 eruption could have also breached the sealing zone near the brittle–plastic transition and the subsequent self-sealing process seems not to have completed based on the observations during the post-eruptive unrest episodes.

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Deep Low‐Frequency Earthquakes Beneath the Hakone Volcano, Central Japan, and their Relation to Volcanic Activity

Cited by 32 publications

References 26 publications

Temporal changes in inflation sources during the 2015 unrest and eruption of Hakone volcano, Japan

Temporal changes in inflation sources during the 2015 unrest and eruption of Hakone volcano, Japan

Seismic Constraint on the Fluid‐Bearing Systems Feeding Hakone Volcano, Central Japan

Volcanic Unrest at Hakone Volcano after the 2015 phreatic eruption — Reactivation of a Ruptured Hydrothermal System?

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