| The piezoelectric and seismo-electrokinetic phenomena are manifested by electrical and
electromagnetic processes that occur in rocks under the influence of elastic oscillations
triggered by shots or mechanical impacts (hits) (e.g., Neishtadt and Osipov, 1958; Neishtadt,
1961; Parkhomenko, 1971; Neishtadt et al., 1986; Maxwell et al., 1992; Butler et al., 1994;
Kepic et al., 1995; Neishtadt et al., 1996; Mikhalov et al., 1997; Boulytchov, 2000; Dupuis et
al., 2009; Schakel et al., 2011; Neishtadt and Eppelbaum, 2012; Jouniaux and Zyserman,
2016).
The developed classification divides the above phenomena into the following types: (1)
the seismo-electrokinetic (electrokinetic) phenomenon E, which occurs in polyphase media
due to the mutual displacement of the solid and liquid phases; (2) the piezoelectric
phenomenon, which occurs in rocks that contain piezoactive minerals; (3) the shot-triggered
phenomenon, which is observed in rocks in the vicinity of a shot or hit point; (4)
the seismoelectric phenomenon I, manifested by the change of the electric current
passing through rocks, and (5) high-frequency impulse electromagnetic radiation,
which is generated by massive base-metal bodies. This paper describes the above
phenomena in detail, describing their nature, manifestation patterns, and registration
techniques. Because the manifestation patterns of the above phenomena are different in
different rocks, these phenomena can be used as a basis for geophysical exploration
techniques. The piezoelectric method is an example of a successful application of
piezoelectric and seismo-electrokinetic phenomena in exploration geophysics. It has been
successfully applied in mineral exploration and environmental features research in
Russia, USA, Canada, Australia, Belorussia, Azerbaijan, Georgia, Israel and other
countries.
This method uses comparatively new geophysical parameter – piezoelectric activity of
rocks, ores, and minerals. It enables direct exploration for pegmatite, apatite-nepheline,
essentially sphalerite, and ore-quartz deposits of gold, tin, tungsten, molybdenum,
zinc, crystal, and other raw materials. This method also enables differentiation of
rocks such as bauxites, kimberlites, etc., from the host rocks, by their electrokinetic
properties.
Classification of some rocks, ores, and minerals by their piezoactivity is given in Table 1.
These objects (targets) transform wave elastic oscillations into electromagnetic ones. It
should be taken into account that anomalous bodies may be detected not only by positive, but
also by negative anomalies, if low-piezoactive body occurs in the higher piezoactive
medium.
The piezoelectric method is an example of successful application of piezoelectric and
seismo-electrokinetic phenomena in exploration and environmental geophysics and designed
for delineation of targets differing from the host media by piezoelectric properties (Neishtadt
et al., 2006, Neishtadt and Eppelbaum, 2012). This method is employed in surface, downhole,
and underground modes.
Recent testing of piezeoelectric effects of archaeological samples composed from fired
clay have shown values of 2.0 − 3.0 ⋅ 10−14 C/N.
However, absence of reliable procedures for solving the direct and inverse problems of
piezoelectric anomalies (PEA), drastically hampers further progression of the method.
Therefore, it was suggested to adapt the tomography procedure, widely used in the seismic
prospecting, to the PEA modeling. Diffraction of seismic waves has been computed
for models of circular cylinder, thin inclined bed and thick bed (Alperovich et al.,
1997). As a result, spatial-time distribution of the electromagnetic field caused by the
seismic wave has been found. The computations have shown that effectiveness and
reliability of PEA analysis may be critically enhanced by considering total electro- and
magnetograms as differentiated from the conventional approaches. Distribution of the
electromagnetic field obtained by solving the direct problem was the basis for an
inverse problem, i.e. revealing depth of a body occurrence, its location in a space as
well as determining physical properties. At the same time, this method has not
received a wide practical application taking into account complexity of real geological
media. Careful analysis piezo- and seismoelectric anomalies shows the possibility
of application of quantitative analysis of these effects advanced methodologies
developed in magnetic prospecting for complex physical-geological conditions
(Eppelbaum et al., 2000, 2001, 2010; Eppelbaum, 2010; 2011, 2015). Employment of
these methodologies (improved modifications of tangents, characteristic points areal
methods) for obtaining quantitative characteristics of ore bodies, environmental
features and archaeological targets (models of horizontal circular cylinder, sphere,
thin bed, thick bed and thin horizontal plate were utilized) have demonstrated their
effectiveness.
Case study at the archaeological site Tel Kara Hadid
Field piezoelectric observations were conducted at the ancient archaeological site Tel Kara
Hadid with gold-quartz mineralization in southern Israel within the Precambrian terrain
at the northern extension of the Arabian-Nubian Shield (Neishtadt et al., 2006).
The area of the archaeological site is located eight kilometers north of the town of
Eilat, in an area of strong industrial noise. Ancient river alluvial terraces (extremely
heterogeneous at a local scale, varying from boulders to silt) cover the quartz veins and
complicate their identification. Piezoelectric measurements conducted over a quartz vein
covered by surface sediments (approximately of 0.4 m thickness) produced a sharp
(500 μV ) piezoelectric anomaly. Values recorded over the host rocks (clays and
shales of basic composition) were close to zero. The observed piezoelectric anomaly
was successfully interpreted by the use of methodologies developed in magnetic
prospecting.
For effective integration of piezo- and seismoelectric interpretation results with other
geophysical methods, some schemes developed in theory of information (Eppelbaum, 2014)
and wavelet theory (Eppelbaum et al., 2011) can be effectively applied.
Table 1. Classification of some rocks, ores, and minerals by their piezoactivity d (10−14
Coulomb/Newton) (after Neishdadt et al., 2006 and Neishtadt and Eppelbaum, 2012, with
modifications)
Piezoactivity groupRock, Ore, Mineral dmin − dmaxdaver
Quartz-tourmaline-cassiterite ore 0.8-28 15.7
Antimonite-quartz ore 0.2-1.35 0.6
I Apatite-nepheline ore 0-5 0.9
Galenite-sphalerite ore 0.2-7.7 3.3
Ijolite 0.1-8 1.2
Melteigite 0.2-5 1.6
Pegmatite 0.1-4.8 1.3
Skarn with galenite-sphalerite mineralization0.1-3 0.6
II Sphalerite-galenite ore 0.3-7.7 3.8
Turjaite 0.9-4.8 2.2
Urtite 0.1-32.5 3.4
Juvite 0.2-5.4 1.8
Aleurolite silicificated 0-0.5 0.2
Aplite 0-1.7 0.6
Breccia aleurolite-quartz 0.1-0.4 0.2
Gneiss 0-1.4 0.2
Granite 0-1.6 0.4
Granodiorite 0-0.2 0.1
Quartzite 0-3.3 0.6
III Pegmatite ceramic 0-1 0.15
Sandstone silicificated and tourmalinised 0.1-1.4 0.5
Feldspars 0-0.4 0.15
Porphyrite 0-0.3 0.1
Ristschorrite 0.3-0.9 0.5
Schist argillaceous 0-0.6 0.2
Hornfels 0-0.4 0.2
Skarn sphaleritic-garnet 0-1 0.3
Skarn pyroxene-garnet 0-0.2 0.1
Aleurolite, amphibolites, andesite, gabbro, 0-0.1 0.05
IV greisens, diabase, sandstone
Argillite, beresite, dacite, diorite-porphyrite, 0 0
felsite-liparite, limestone, tuff, fenite
I – highly active — piezo-activity of samples is greater than 5.0 ⋅ 10−14 C/N
II – moderately active — piezo-activity of samples is (0.5 − 5.0) ⋅ 10−14 C/N
III – weakly active — piezo-activity of samples is lower than 0.5 ⋅ 10−14 C/N
IV – non-active — piezo-activity of samples are near zero.
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