Dipole‐dipole Deep Geoelectric Soundings Over Geological Structures*

Alfano, L.

doi:10.1111/j.1365-2478.1980.tb01226.x

Cited by 13 publications

(6 citation statements)

References 2 publications

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“…The improvement in ®eld technology and data processing has led to the successful use of the DC dipole±dipole method in structural studies of the earth's crust. Continuous polar dipole±dipole spreads (Alfano 1980) were used for resistivity imaging of geothermal ®elds (Risk, Caldwell and Bibby 1995;Monteiro, Andrade and Mendes 1997;Pe Ârez and Go Âmez 1997), volcanic areas (Giudici and Alfano 1997;Friedel et al 1998) and other geological structures at depths of some kilometres. Giudici and Alfano (1998) investigated vertical fault zones using magnetotelluric and DC electrical soundings.…”

Section: Introductionmentioning

confidence: 99%

Electrical resistivity tomography to investigate geological structures of the earth's upper crust

Storz¹,

Jacobs²

2000

Geophysical Prospecting

166

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It is important to have detailed knowledge of the electrical properties of the earth's crust in order to recognize geological structures and to understand tectonic processes. In the area surrounding the German Continental Deep Drilling Project (KTB), we have used DC dipole–dipole soundings to investigate the electrical conductivity distribution down to a depth of several kilometres. We have adapted the electrical resistivity tomography (ERT) technique, a well‐established near‐surface method, to large‐scale experiments. Independent transmitting and receiving units were used to realize the concept of simultaneous multichannel registration of the scalar electrical potential at 44 dipoles. The measured data yielded apparent resistivities which were inverted to a 2D resistivity model ranging from the surface down to a depth of 4 km. Two highly conductive structures with steep inclination were detected. They are expected to be major fault zones embedded in a metamorphic body. The rather low resistivity (ρ < 10 Ωm) can be explained by the existence of graphitic minerals and/or electrolytic fluids.

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Section: Introductionmentioning

confidence: 99%

Electrical resistivity tomography to investigate geological structures of the earth's upper crust

Storz¹,

Jacobs²

2000

Geophysical Prospecting

166

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“…To this purpose, we resorted to the transformation principle of axial dipole curves into equivalent half-Schlumberger' s ( M N fixed, A mobile). This test appears fully realizable because of the concurrence of the following circumstances : 1. the paper by Vedrintsev (1966) already quoted reports explicit formulas for the Schlumberger array; 2. when the sounding is parallel to the strike direction, no matter whether the array is in the internal or external regions, Schlumberger and half-Schlumberger soundings produce the same apparent resistivity curves; 3. the same occurs when the sounding is perpendicular to the strike with M N fixed in the midst of the internal region, and the two external regions have identical resistivities ( p i = p 3 ) ; 4. the transformation of axial dipole sounding curves into equivalent half-Schlumberger curves ( M N fixed, A mobile) is always possible for whatever underground structure (Alfano 1980, Patella 1981; 5. a very simple algorithm is available to transform numerically axial curves into half-Schlumberger curves (Patella 1974(Patella , 1981.…”

Section: Comparison W I T H Alpin's Resultsmentioning

confidence: 99%

“…Recent investigations have demonstrated that the adoption of the axial dipole configuration permits transformation into equivalent half-Schlumberger curves ( M N fixed and A mobile) even in the case of arbitrary underground structures (Alfano 1980, Patella 1981. Moreover, it has been proved that the transformation is an intrinsic smoothing, or low-pass filtering process, if applied to field dipole curves affected by " high-frequency " noise (Patella 1984).…”

Section: Introductionmentioning

confidence: 99%

Geoelectric Axial Dipole Sounding Curves for a Class of Two‐dimensional Earth Structures*

Patella

Tramacere

1986

Geophysical Prospecting

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PATELLA, D. and TRAMACERE, A. 1986 Geoelectric Axial Dipole Sounding Curves For a Class of Geophysical Prospecting 34, With the aim of studying the behaviour of geoelectric axial dipole vertical soundings over complex geology, a systematic theoretical approach is presented for a class of earth structures characterized by horizontal and vertical parallel boundary planes. The twodimensional cylindrical bodies of infinite length and rectangular cross-section are constrained to have resistivities satisfying Alfano's condition at every intersection line of the graticule, in order to adopt the image-point theory. A detailed analysis is performed for models with any number of horizontal boundaries and two vertical discontinuities. The apparent resistivity formulas are obtained and selected apparent resistivity curves are drawn for different parameter combinations and various directions of the sounding expansion axis. The class under consideration contains as a particular case the HVC model elaborated in Alpin's monograph, where only a small collection of master curves is available for the axial array. The reconstruction of those curves by the present formulation shows the existence of large discrepancies. A test based on the transformation to equivalent half-Schlumberger sounding curves supports the conclusion that an unidentified error must exist in some part of the theoretical approach of the Russian researchers. Finally, some field sounding curves based on geothermal and volcanological surveys are presented and interpreted by complete curve matching, essentially to show the applicability of the theoretical solutions.

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“…Usually, square-wave signals are injected, because the signal can easily be recognized. Alfano (1980) imaged geological structures in dipole-dipole experiments. The longest measured profiles measure up to 22 km length: Storz et al (2000) imaged fault zones at the German continental deep-drilling site KTB (Kontinentale Tiefbohrung) and Schütze and Flechsig (2002) conducted such a profile across the flanks of the long valley caldera by using a large-scale dipole-dipole experiment to image fluid flow (Pribnow et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Response on comments from Anonymous Referee #1

Oppermann¹

2017

Preprint

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We present a new versatile datalogger that can be used for a wide range of possible applications in geosciences. It is adjustable in signal strength and sampling frequency, battery saving and can remotely be controlled over a Global System for Mobile Communication (GSM) connection so that it saves running costs, particularly in monitoring experiments. The internet connection allows for checking functionality, controlling schedules and optimizing pre-amplification. We mainly use it for large-scale electrical resistivity tomography (ERT), where it independently registers voltage time series on three channels, while a square-wave current is injected. For the analysis of this time series we present a new approach that is based on the lock-in (LI) method, mainly known from electronic circuits. The method searches the working point (phase) using three different functions based on a mask signal, and determines the amplitude using a direct current (DC) correlation function. We use synthetic data with different types of noise to compare the new method with existing approaches, i.e. selective stacking and a modified fast Fourier transformation (FFT)-based approach that assumes a 1/f noise characteristics. All methods give comparable results, but the LI is better than the well-established stacking method. The FFT approach can be even better but only if the noise strictly follows the assumed characteristics. If overshoots are present in the data, which is typical in the field, FFT performs worse even with good data, which is why we conclude that the new LI approach is the most robust solution. This is also proved by a field data set from a long 2-D ERT profile.

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Dipole‐dipole Deep Geoelectric Soundings Over Geological Structures*

Cited by 13 publications

References 2 publications

Electrical resistivity tomography to investigate geological structures of the earth's upper crust

Electrical resistivity tomography to investigate geological structures of the earth's upper crust

Geoelectric Axial Dipole Sounding Curves for a Class of Two‐dimensional Earth Structures*

Response on comments from Anonymous Referee #1

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