Distribution of melt beneath Mount St Helens and Mount Adams inferred from magnetotelluric data

Hill, G. J.; Caldwell, T. G.; Heise, Wiebke; Chertkoff, D. G.; Bibby, H. M.; Burgess, M. K.; Cull, J. P.; Fernand, Raymond Alexander

doi:10.1038/ngeo661

Cited by 167 publications

(158 citation statements)

References 30 publications

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“…The origin of these electric conductors has early been attributed to graphite (Frost et al 1989;Jödicke 1992). More recently, links to aqueous fluids and secondary minerals in fault zones (Korja et al 2008;Brasse et al 2009;Weckmann et al 2012), to partial melt (Unsworth et al 2005;Hill et al 2009), and to metamorphic processes (Wannamaker et al 2014;Zhang et al 2015) have been discussed. Worldwide, it is observed that these conductors have an upper depth limit near the brittle-ductile transition (Jones 1992;Jiracek 1995).…”

Section: Introductionmentioning

confidence: 99%

“…Kohl & Rybach 1996), the dynamics of electric resistivity, covering several orders of magnitudes compared to typical crustal rock, characterize mid-crustal conductors (e.g. Unsworth et al 2004;Hill et al 2009;Wannamaker et al 2014). The origin of these electric conductors has early been attributed to graphite (Frost et al 1989;Jödicke 1992).…”

Section: Introductionmentioning

confidence: 99%

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Resistivity distribution from mid-crustal conductor to near-surface across the 1200 km long Liquiñe-Ofqui Fault System, southern Chile

Schill

Pavez

Díaz

et al. 2016

Geophysical Journal International

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Resistivity distribution from mid-crustal conductor to near-surface across the 1200 km long Liquiñe-Ofqui Fault System, southern Chile

Schill

Pavez

Díaz

et al. 2016

Geophysical Journal International

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“…The magnetotelluric (MT) method involves the measurement of time-varying natural electromagnetic fields for the remote detection of small volumes of fluid or melt in the crust and upper mantle (e.g., Hill et al 2009;Wannamaker et al 2009;Ingham et al 2009;Aizawa et al 2014). The bulk resistivity of the fluid-or meltbearing rock is not controlled by the resistivity of the host rock, which is normally as resistive as 10 6 Ωm, but by the interconnectivity of the conductive fluid or melt in pore spaces or along grain boundaries, which can reduce the host resistivity to below 1 Ωm.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional magnetotelluric imaging of crustal fluids and seismicity around Naruko volcano, NE Japan

et al. 2014

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We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the aim of imaging 3-D distribution of fluids in the crust for its volcanic and seismogenic implications. The data were recorded at 77 sites in total: 30 sites are new and are arranged in an approximately 5 × 5 km grid whereas the remaining older sites constitute two separate east-west profiles. We ran a 3-D inversion using full components of impedance tensors in the period range between 0.13 and 400 s. The resulting model showed that a sub-vertical conductor exists a few kilometers below Naruko volcano. The conductor extends from the surface of the volcano and dips towards the south, away from the volcano towards the backbone range. High levels of seismicity are observed in the upper crust above and around the conductors. We suggest that the seismicity is fluid driven and that a fluid trap is created by the precipitation of quartz owing to a reduction in solubility at shallow depth. The Quaternary volcanic front is characterized by a sharp resistivity contrast and a high-resistivity zone and extends 10 to 15 km towards the east. A fore-arc conductor was observed at mid-crustal levels even farther towards the east. The sub-vertical conductors along the arc and the fore-arc conductor have resistivities of 1 to 10 Ωm. Assuming a Hashin-Shtrikman model with saline fluids of 0.1-Ωm resistivity, a porosity of 1.5% to 15% is required to explain the observed conductive anomalies.

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“…High-density accumulates, which may have a magmatic origin, are also observed and are thought to play an important role in the transport of such fluids within the crust. The low-velocity vertical anomaly gently dips towards SE; a low-scattering, high-intrinsic scattering anomaly retrieved at~10 km depth by scattering tomography [12]; an high-conductivity anomaly retrieved by means of magnetotelluric tomography and interpreted as an extended crustal magma sill [21]; and a deep low-velocity anomaly, obtained using full-waveform tomography and interpreted as the shallowest extension of a mantle wedge [22].…”

Section: Mount St Helens Volcano Usa: Geological and Seismic Structurementioning

confidence: 99%

Investigating the Apparent Seismic Diffusivity of Near-Receiver Geology at Mount St. Helens Volcano, USA

et al. 2017

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Abstract:We present an expanded approach of the diffusive approximation to map strongly scattering geological structures in volcanic environments using seismic coda intensities and a diffusive approximation. Seismic data from a remarkably consistent hydrothermal source of Long-Period (LP) earthquakes, that was active during the late 2004 portion of the 2004-2008 dome building eruption of Mount St. Helens Volcano, are used to obtain coefficient values for diffusion and attenuation, and describe the rate at which seismic energy radiates into the surrounding medium. The results are then spatially plotted as a function of near-receiver geology to generate maps of near-surface geological and geophysical features. They indicate that the diffusion coefficient is a marker of the near-receiver geology, while the attenuation coefficients are sensitive to deeper volcanic structures. As previously observed by other studies, two main scattering regimes affect the coda envelopes: a diffusive, multiple-scattering regime close to the volcanic edifice and a much weaker, single-to-multiple scattering regime at higher source-receiver offsets. Within the diffusive, multiple-scattering regime, the spatial variations of the diffusion coefficient are sufficiently robust to show the features of laterally-extended, coherent, shallow geological structures.

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Distribution of melt beneath Mount St Helens and Mount Adams inferred from magnetotelluric data

Cited by 167 publications

References 30 publications

Resistivity distribution from mid-crustal conductor to near-surface across the 1200 km long Liquiñe-Ofqui Fault System, southern Chile

Resistivity distribution from mid-crustal conductor to near-surface across the 1200 km long Liquiñe-Ofqui Fault System, southern Chile

Three-dimensional magnetotelluric imaging of crustal fluids and seismicity around Naruko volcano, NE Japan

Investigating the Apparent Seismic Diffusivity of Near-Receiver Geology at Mount St. Helens Volcano, USA

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