Near-surface and topographic distortions in electromagnetic induction

Jiracek, George R.

doi:10.1007/bf01901659

Cited by 206 publications

(117 citation statements)

References 59 publications

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“…In fact, UZ402 and UZ403 are located at the by precipitous cliffs. We attribute these shifts to the location of the transects near precipitous cliffs, as it is known that steep topographical changes can influence MT observations (e.g., Wannamaker et al, 1986;Jiracek, 1990).…”

Section: Dimensionality and Strike Estimationmentioning

confidence: 99%

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: Dimensionality and Strike Estimationmentioning

confidence: 99%

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

et al. 2013

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“…As noted in the review by Jiracek (1990), any resistivity contrast due to small-scale heterogeneities in the vicinity of the electric field measurement can give rise to a particular class of perturbation referred to as galvanic distortion or static shift. Such effects are observed irrespective of electrode type (e.g.…”

Section: A Synthetic Examplementioning

confidence: 99%

Quantitative 2D VLF data interpretation

Beamish

2000

Journal of Applied Geophysics

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The ability of the VLF-R (Resistivity) method to provide quantitative subsurface resistivity information is examined. The frequencies used in conventional VLF (15 to 30 kHz) provide the deepest penetrations of the multi-frequency, extended method of RadioMT. Both methods are considered. VLF data, being effectively single frequency, are insufficient to resolve 1D (vertical) structure in any detail. At the site investigation scale, however, it is the departures from the background (vertically uniform) structure that are of interest. Improved methodologies for the quantitative assessment of VLF data derive from advances in regularised inversion techniques. Hydrogeological and waste-site examples of VLF-R survey data, aided by wide-band (VLF/RadioMT) synthetic modelling and inversion studies, are used to illustrate their shallow (0 to 20 m) resolution capabilities in conductive environments.

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“…Static distortion effects (e.g. Jiracek 1990) provide parallel offsets in the apparent resistivity data (the amplitude information) but leave the phase data (containing the time terms) undistorted. Such effects are pervasive throughout the Clevelandia survey data.…”

Section: The Mt Datamentioning

confidence: 99%