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- Volume 5, Issue 3, 1957
Geophysical Prospecting - Volume 5, Issue 3, 1957
Volume 5, Issue 3, 1957
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THE USE OF NEAR SURFACE TEMPERATURE MEASUREMENTS FOR DISCOVERING ANOMALIES DUE TO CAUSES AT DEPTHS*
More LessAbstractIn this paper an attempt has been made to evaluate the possibilities of determining subsurface features from temperature measurements made at shallow depths. The temperatures at the observation depth used are subject to seasonable variations. The amount of this variation differs, and these differences have been attributed to structural features. Local differences in temperature are also caused by surface factors such as the thermal conductivity of the soil, the vegetation and the micro‐climate. The differences in temperature due to surface factors are so great that the variation in heat flow caused by differing thermal conductivities of the rocks at depth cannot be detected at the surface. It is not possible therefore to use this method to determine the position of subsurface structures such as domes, anticlines or horsts.
It is also shown that concentrations of radioactive elements in the rocks do not provide any measurable heating.
The method has been successfully applied to the problem of finding fissures, cracks and similar features provided that convective heat transport from depth to the surface has taken place along these features. In order to compute the area through which a given amount of water at a given depth must pass to give a specific temperature increase a model has been considered. From the shape of the temperature anomaly above a fissure carrying such heated water, the places at which the rising water enters the groundwater stream can be seen immediately. It is possible to estimate the amount of rising water by computing the amount of heat energy transferred to the surface.
The method is particularly suitable for determining the position of steam deposits in regions of recent vulcanicity. In such a region a location, hitherto unknown, was found where steam rising from depth condenses beneath the surface.
The area and form of the anomaly indicate the extent in depth of this steam bearing zone. By means of observations made at the individual points, it was also possible to compute approximately the energy being released at the surface. This value can give an indication of the extent to which the steam deposits regenerate themselves.
Finally it has been shown that percolating canal water can be detected thermally near the canal banks. Such anomalies are dependent on the season.
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TECHNIQUE NOUVELLE DE MODÈLES RÉDUITS POUR LA PROSPECTION ÉLECTRIQUE
Authors L. CAGNIARD and R. N. NEALEAbstractThe use of small scale models in the interpretation of results of electric prospecting involves two majors difficulties: (1) the dimensions of the models and of the tanks in which the experiment is performed must be of unwieldy large sizes if one wants to be quite free from side effects; (2) the precise geometrical relation, in respect to the model, of the successive points where the interesting data are measured, requires an intricate installation, and is costly in both time and money.
The technique which is described in this paper eliminates these difficulties as well as some others. The surface of the ground is represented by the lower face of a thick horizontal plate of plexiglas which is laid at the surface of the liquid filling the tank. This plate is pierced by a great number of small holes whose coordinates have been measured initially with the necessary precision. The electrodes are then introduced into these holes without creating any perturbation in the distribution of the lines of current flow. A solution of copper sulphate is used as the liquid in conjunction with copper electrodes. In this way, a D.C. excitation is possible, combining precision with convenience.
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ON THE EFFECT OF THE TANK WALL MATERIAL IN GEOELECTRICAL MODEL EXPERIMENTS
More LessAbstractThe effect of the composition of the tank walls on apparent resistivity determinations made in model experiments has been investigated for the two extreme cases of an insulating and a perfectly conducting tank wall: The resulting errors have been determined both by calculation and by experiment.
Experiments are described which demonstrate that the magnitude of the effect can be considerably reduced by specially constructed tank walls.
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SUPERMULTIPLICATION DES CHARGES ET DES SISMOGRAPHES AU SAHARA (ZONE NORD)*
Authors GILBERT POMMIER and HENRI RICHARDABSTRACTIn desert countries, reflection seismic prospecting is often very difficult due to bad surface conditions, which adversely affect the quality of the reflections. From the beginning the Northern Sahara proved to be particularly unfavourable. In 1954 a series of systematic tests led to a shooting method which gave satisfactory results. This method used a high multiplicity of the shotholes (up to 100 per shotpoint) combined with a high multiplicity of geophones (up to, and sometimes more than 100 per trace). The method has proved effective and relatively economical to run since 1954. The evident conclusion is, that, under special conditions, high multiplicity may be very helpful in the future.
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THE VARIATION WITH DISTANCE OF THE AMPLITUDE OF CRITICALLY REFRACTED WAVES *)
More LessAbstractAmplitude measurements have been made of the height of the first peak of an arrival refracted from a shallow refractor. If the amplitude is assumed to decay as the inverse mth power of the distance, the least squares value for m is found to be 2.16 ± .04. Because of this value and because of the character of the recorded event it is concluded that the arrival is a simple critical refraction. After applying the theoretical ‘spread’ factor for critical refraction there remains a residual attenuation of 1.96 ± 0.28 decibels per 1000 feet. The predominant frequency in the pulse is about 20 c.p.s. and this attenuation agrees with the losses found for such a frequency by extrapolation of the published results of other workers. Although no evidence could be seen on the records for a change of pulse frequency with distance, the quoted result would be consistent with a dependence of residual attenuation on the first power of the frequency, and would be inconsistent with a dependence on the second power of the frequency.
It is concluded that studies of the amplitudes of refracted events will give useful estimates of the attenuation factors of rocks.
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SEISMIC MODEL EXPERIMENT ON THIN LAYERS*
Authors E. CARABELLI and R. FOLICALDISummarySeismic two‐dimensional model experiments have been made at the Laboratory of Fondazione Lerici in the Polytechnic School of Milan.
For this purpose the Laboratory has developed and constructed a complete equipment including pulse generators, piezoelectric transducers and amplifiers for detecting the waves propagation through the models.
We record here experiments concerning reflections from horizontal layers thin in relation to the wave lengths propagated through the media.
Layers, with a thickness from a 50th of the total wave length to several wave lengths were used. These strata consist of materials sometimes with lower and sometimes with higher velocities than the homogeneous surrounding medium.
The object of this investigation was to clarify the effects of the very thin reflecting layers, individually and in combination, on the reflected arrivals and to determine the influence of the layers upon the reflected energy in comparison with their thickness.
We are also studying at what minimum distance, as a fraction of the wave length, the reflection of a horizon appears on the seismogram in an independent event.
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THEORETISGHE UNTERSUCHUNGEN ÜBER DEN EINFLUSS DER VERWITTERUNGSSCHICHT AUF DAS SPEKTRUM ELASTISCHER WELLEN IN DER REFLEXIONSSEISMIK
Authors HEINZ MENZEL and OTTO ROSENBACHAbstractThe following assumptions are made in the mathematical treatment of the problem. Below a plane earth's surface there is a three‐layered elastic medium the interfaces of which are parallel to the earth's surface. The uppermost layer represents the weathered layer in which the velocity of propagation of seismic waves increases linearly with depth. The two lower layers, the so‐called intermediate layer and the substratum each have a constant velocity. The surface of the earth is acted on simultaneously by a normal pressure N in the form of a Heaviside pulse. The seismic wave thus generated is propagated through the elastic media.
The aim of the investigation is to study the shape of the wave
1) in the intermediate layer, after the wave has entered it the first time
2) at the earth's surface, after the wave has been reflected once at the interface between the intermediate layer and the substratum.
The mathematical solutions can in both cases be expressed as series of Bessel functions. Some numerical examples illustrate the quasi‐periodic nature of the solutions. The pseudo‐frequency is determined by the gradient of velocity in the uppermost layer; it assumes a value of approximately 50 c.p.s. for a gradient of appr.
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Volumes & issues
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Volume 72 (2023 - 2024)
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Volume 71 (2022 - 2023)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 68 (2020)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 58 (2010)
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Volume 57 (2009)
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Volume 56 (2008)
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Volume 55 (2007)
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Volume 54 (2006)
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Volume 18 (1970 - 2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 51 (2003)
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Volume 50 (2002)
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Volume 49 (2001)
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Volume 48 (2000)
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Volume 47 (1999)
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Volume 46 (1998)
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Volume 45 (1997)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1994)
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Volume 41 (1993)
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Volume 40 (1992)
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Volume 39 (1991)
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Volume 38 (1990)
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Volume 37 (1989)
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Volume 36 (1988)
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Volume 35 (1987)
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Volume 34 (1986)
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Volume 33 (1985)
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Volume 32 (1984)
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Volume 31 (1983)
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Volume 30 (1982)
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Volume 29 (1981)
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Volume 28 (1980)
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Volume 27 (1979)
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Volume 26 (1978)
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Volume 25 (1977)
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Volume 24 (1976)
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Volume 23 (1975)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1972)
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Volume 19 (1971)
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Volume 17 (1969)
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Volume 16 (1968)
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Volume 15 (1967)
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Volume 14 (1966)
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Volume 13 (1965)
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Volume 12 (1964)
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Volume 11 (1963)
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Volume 10 (1962)
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Volume 9 (1961)
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Volume 8 (1960)
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Volume 7 (1959)
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Volume 6 (1958)
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Volume 5 (1957)
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Volume 4 (1956)
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Volume 3 (1955)
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Volume 2 (1954)
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Volume 1 (1953)