Magma prospecting in Usu volcano, Hokkaido, Japan, using magnetotelluric soundings

Matsushima, Nobuo; Oshima, Hiromitsu; Ogawa, Yasuo; Takakura, Shinichi; Satoh, Hideyuki; Utsugi, Mitsuru; Nishida, Yasunori

doi:10.1016/s0377-0273(00)00320-6

Cited by 52 publications

(28 citation statements)

References 10 publications

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“…The resistivity structure described in the preceding paragraph is typical for an active volcano (e.g., Usu volcano (Ogawa et al, 1998;Matsushima et al, 2001); Galunggung Volcano (Wannamaker et al, 2004); Kusatsu-shirane volcano (Nurhasan et al, 2006); Asama volcano (Aizawa et al, 2008); Aso volcano ; Rotokawa geothermal field (Heise et al, 2008)). In general, such an extremely low resistivity is interpreted as low permeability clay due to hydrothermal alteration (e.g., Ogawa et al, 1998;Revil et al, 2002); it is believed that low permeability clay behaves as a sealing zone, and that high temperature fluids are maintained and circulate within the relatively high resistivity region (e.g., Björnsson et al, 1986;Ussher et al, 2000).…”

Section: Resistivity Of the Deeper Aquifermentioning

confidence: 97%

Two-dimensional resistivity structure of Unzen Volcano revealed by AMT and MT surveys

et al. 2013

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AMT and MT surveys were conducted to investigate at high resolution the spatial resistivity structure of Unzen volcano, with consideration given to understanding its regional dimensionality. Our phase tensor analysis supports the conclusion that the resistivity structure is two-dimensional, with the strike in the E-W direction. Two-dimensional inversions suggest that Unzen volcano is likely to comprise 4 layers: a high resistivity surface (greater than 1000 m), an intermediate second layer (20 to several hundreds of m), a low resistivity third layer (less than 20 m), and a relatively high resistivity basement. We assume the upper-most high resistivity layer consists of undersaturated lava and pyroclastic flow deposits. The second and third layers are likely to be water-saturated and form an aquifer that seems to correlate well with the emergence of groundwater discharge at the surface. In deeper areas beneath the summit, a region with a resistivity of 20-80 m is surrounded by areas of extremely low resistivity (less than 3 m); this structural features in Unzen volcano was first identified in this study, but is typical of the resistivity structure observed in active volcanoes. Interpreting the results of well logs and geodetic studies of Unzen volcano in light of the findings of the present study and the resistivity structure of other active volcanoes, we suggest that Unzen volcano possesses a hydrothermal system of high-temperature fluids beneath its edifice; this hydrothermal system may play a non-negligible role in controlling heat and mass transfer in the magmatic system of Unzen volcano.

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Section: Resistivity Of the Deeper Aquifermentioning

confidence: 97%

Two-dimensional resistivity structure of Unzen Volcano revealed by AMT and MT surveys

et al. 2013

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“…MT soundings have been successfully used at many volcanic and geothermal areas to reveal hydrothermal convection systems and magma reservoirs (e.g., Matsushima et al, 2001;Aizawa et al, 2008;Kanda et al, 2008). MT soundings have also been used to locate volcanic fluid paths (e.g., Nurhasan et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal system beneath the crater of Tarumai volcano, Japan: 3-D resistivity structure revealed using audio-magnetotellurics and induction vector

Yamaya

Mogi

Hashimoto

et al. 2009

Journal of Volcanology and Geothermal Research

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Audio-magnetotelluric (AMT) measurements were recorded in the crater area of Tarumai volcano, northeastern Japan. This survey brought the specific structures beneath the lava dome of Tarumai volcano, enabling us to interpret the relationship between the subsurface structure and fumarolic activity in the vicinity of a lava dome. Three-dimensional resistivity modeling was performed to achieve this purpose. The measured induction vectors pointed toward the center of the dome, implying the topographic effect. However, estimation of the topographic effect showed that the measured vector was not explained only by this effect. This suggested that the distribution of induction vectors still held information of the subsurface structure and could be helpful in determining the geometry of 3-D bodies. The 3-D modeling was based on a quasi-one-dimensional layered structure that included topography. The final model revealed that the andesitic lava dome is characterized by comparatively low resistivity (50 Ωm), and that two conductive bodies (50 and 1-5 Ωm) are present beneath the lava dome. The shallower of these conductors is interpreted as an aquifer, such as a buried crater lake. The deeper, extremely conductive body corresponded to a convecting zone containing rising hydrothermal fluid. The shallower aquifer critically controls the temperature and chemical components of the fumarolic gasses. High-temperature gas supplied from deeper part that encounters the shallow aquifer loses its water-soluble components and heat, resulting in weak and low-temperature fumaroles. In contrast, most of the gas, which ascends outside the area of the shallower aquifer, is released as high-temperature fumaroles. This study provides an insight that the shallow aquifer in the crater area plays a significant role in the property of fumaroles at the volcanic surface.

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“…Katsui et al (1985) performed a topographic survey around the summit area to estimate the location of the magma that swelled Usu-Shinzan and discussed the magma intrusion process beneath Usu-Shinzan. Later, the magma body was clearly imaged at a depth of around sea level by magnetotelluric surveys (Matsushima et al, 2001, Ogawa et al, 1998. While a shallow part of the volcano to depths of 2-4 km is a conspicuous conductor (1-500 ・・m), a resistive block of 500-1000 m is situated beneath Usu-Shinzan at depths of 300-500 m below sea level (Matsushima et al, 2001).…”

Section: Recent Eruptions Of Usu Volcanomentioning

confidence: 99%

“…Later, the magma body was clearly imaged at a depth of around sea level by magnetotelluric surveys (Matsushima et al, 2001, Ogawa et al, 1998. While a shallow part of the volcano to depths of 2-4 km is a conspicuous conductor (1-500 ・・m), a resistive block of 500-1000 m is situated beneath Usu-Shinzan at depths of 300-500 m below sea level (Matsushima et al, 2001). The estimated extent of the intrusion is 600 m high and 300 m wide, which becomes 1.8 × 10 8 m 3 assuming that the intrusion is a 1000-m-long slab.…”

Section: Recent Eruptions Of Usu Volcanomentioning

confidence: 99%

“…The hypocenters of the precursory earthquakes of the 2000 eruption were mainly located at depths of 2-3.5 km below sea level (Onizawa et al, 2007). The shallow intrusion of magma during the 1977-1982 eruption was estimated under Usu-Shinzan by magnetotelluric surveys (Ogawa et al, 1998, Matsushima et al, 2001.…”

Section: -2 Interpretation Of the Crustal Activity Under The Summitmentioning

confidence: 99%

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Inter-eruptive volcanism at Usu volcano: Micro-earthquakes and dome subsidence

Aoyama

Onizawa

Kobayashi

et al. 2009

Journal of Volcanology and Geothermal Research

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Magma prospecting in Usu volcano, Hokkaido, Japan, using magnetotelluric soundings

Cited by 52 publications

References 10 publications

Two-dimensional resistivity structure of Unzen Volcano revealed by AMT and MT surveys

Two-dimensional resistivity structure of Unzen Volcano revealed by AMT and MT surveys

Hydrothermal system beneath the crater of Tarumai volcano, Japan: 3-D resistivity structure revealed using audio-magnetotellurics and induction vector

Inter-eruptive volcanism at Usu volcano: Micro-earthquakes and dome subsidence

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