THE INTERPRETATION OF ELECTROMAGNETIC REFLECTION DATA IN GEOPHYSICAL EXPLORATION PART II.—METALLIC MODEL EXPERIMENTS

Geophysics ◽  
1952 ◽  
Vol 17 (4) ◽  
pp. 806-826 ◽  
Author(s):  
W. Jacque Yost ◽  
R. L. Caldwell ◽  
C. I. Beard ◽  
C. D. McClure ◽  
E. N. Skomal
Keyword(s):  
Electrical Conductivity ◽  
Pulse Shape ◽  
Salt Dome ◽  
Geophysical Data ◽  
Experimental Check ◽  
Virtual Image ◽  
Electromagnetic Pulses ◽  
Model Experiments ◽  
Reflection Data ◽  
The Earth

A metallic model of a horizontally stratified section of the earth’s crust has been constructed to provide information of considerable value in the interpretation of geophysical data. Modeling considerations and experimental arrangements are discussed in detail for a system employing loops of wire as transmitter and receiver for the study of propagation of electromagnetic energy in and on a semi‐infinite conductor. An experimental check of the theory given in Part I (Yost, 1952) has been made for the case of a semi‐infinite conducting medium underlying a semi‐infinite insulator. Discontinuities in electrical conductivity within such a medium have been shown to reflect electromagnetic pulses back to the surface. A detailed study of the shape of these pulses from single reflectors has been made showing that certain characteristics of the pulse shape can be correlated with the depth and nature of the reflecting horizon. The reflected signals can be approximately described by considering the discontinuities as reflectors which, in turn, can be replaced by virtual “image” oscillators in a homogeneous structure. The extent to which this approximation holds is discussed in the light of experiments with the model. An example is given of the use of a non‐concentric loop arrangement for geophysical profiling of a limited reflector, such as a salt dome. Finally, data are given to show the agreement between model signals and field results obtained from a known resistivity contrast in the earth.

ELECTRIC EARTH TRANSIENTS IN GEOPHYSICAL PROSPECTING

Geophysics ◽  
1936 ◽  
Vol 1 (2) ◽  
pp. 271-277 ◽  
Author(s):  
Louis Statham
Keyword(s):  
Electric Current ◽  
Salt Dome ◽  
Geophysical Prospecting ◽  
The Earth ◽  
Electrical Methods ◽  
The Times

A suddenly applied electric current is passed through the earth by means of spaced electrodes. The form of the potential transient as it appears outside the current electrodes is studied. The potential transient is extremely rapid and refined methods of recording are necessary. Means for measuring the relative times of the transient potentials received from different points are discussed. A survey taken over a known deep salt dome is shown; anomalous times of the transients are found to exist over the dome. No correlation is seen between the times of the transients and the resistivity as found by ordinary electrical methods.

Electrical conductivity anomalies in the earth

1978 ◽  
Vol 3 (3) ◽  
pp. 225-253 ◽  
Author(s):  
Yoshimori Honkura
Keyword(s):  
Electrical Conductivity ◽  
The Earth ◽  
Conductivity Anomalies

Diffraction of elastic waves by the core of the Earth

1961 ◽  
Vol 51 (1) ◽  
pp. 35-49
Author(s):  
Leon Knopoff ◽  
Freeman Gilbert
Keyword(s):  
Half Plane ◽  
Elastic Waves ◽  
Amplitude Distribution ◽  
Laboratory Model ◽  
Shadow Zone ◽  
Adequate Explanation ◽  
Model Experiments ◽  
The Core ◽  
The Earth ◽  
Diffraction Of Elastic Waves

Abstract The problem of the diffraction of a seismic pulse by the core of the Earth is investigated theoretically. The result is compared to that of diffraction by a half-plane. The differences are striking. Laboratory model experiments have been performed to verify the theoretical approximations in their regions of validity, and to complement the theory elsewhere. The curves, thus obtained, of the theoretical amplitude distribution in the shadow of the Earth's core agree very well with the observations of Gutenberg. It is therefore concluded that diffraction is a completely adequate explanation for the amplitude distribution in the shadow zone.

Tectonic Microphonics

2021 ◽  
Vol 45 (1) ◽  
pp. 65-78
Author(s):  
Kirsten Paige
Keyword(s):  
National Security ◽  
Geophysical Data ◽  
Scientific Development ◽  
Global Networks ◽  
The Earth ◽  
Important Index ◽  
Nation States ◽  
Human Labor ◽  
The Status

“Tectonic Microphonics” explores the politics of seismologists’ use of the microphone to listen to the deep, elusive sounds of the Earth in the years around 1900. It argues that seismological representatives of three emerging nation-states and empires—Italy, Japan, and Britain—used the microphone to lay claim to elusive geophysical data, encrypted in fleeting, earthly sounds. It suggests that seismologists’ enhanced knowledge of the subterranean movements of the Earth, a purported consequence of their microphonic aurality, represented a form of geopolitical currency. Such powers of prediction were viewed as an important index of national security and scientific development: the microphone thus represented an opportunity for occupants of seismic geographies (like Italy and Japan) to overcome what Deborah Coen has referred to as the “deterministic geography of security and risk” that, for some geologists, reduced them to the status of “barbarians.” At the same time, this article demonstrates that valorizing the civilizing consequences of this form of technologically mediated aurality relied upon extractive ecologies of capitalism and exploitative human labor that were often obscured by scientific users and their global networks of collaborators and enablers. As the article's concluding section shows, these activities came on the heels of the birth of one of the earliest ideas of the Anthropocene, circulated in the writings of an Italian geologist as a term for the agency of white, European, “steam-powered” men (a circumscribed Anthropos) over the Earth, its fossil resources, and its less-than-human laborers. This article concludes by arguing that the microphone established a standard of anthropogenic aurality fit for the birth of the age of the Anthropocene.

A "SELF-CONSISTENT SOLUTION" METHOD FOR DETERMINING THE ELECTRICAL CONDUCTIVITY IN THE SUBSURFACE REGIONS OF THE EARTH

1964 ◽  
Vol 1 (3) ◽  
pp. 206-210
Author(s):  
Tomiya Watanabe
Keyword(s):  
Electrical Conductivity ◽  
Boundary Conditions ◽  
Solution Method ◽  
Magnetic Method ◽  
Entire Surface ◽  
Conductivity Distribution ◽  
The Earth ◽  
Self Consistent ◽  
Consistent Solution ◽  
The Magnetic Field

The assumptions on which the so-called magneto-telluric method to determine the subsurface conductivity of the earth is based are examined and it is shown how the method can be revised to get rid of those assumptions which are not necessarily legitimate. The principle of this revised or generalized magneto-telluric method is that the magnetic and telluric field components which observation can provide over the entire surface of the earth are more than sufficient viewed as boundary conditions to determine the electromagnetic field inside the earth with a prescribed conductivity distribution and, therefore, the extra boundary conditions can be consistent with each other only by the correctly prescribed (or chosen) distribution of electrical conductivity. The purely magnetic method to determine the conductivity, which relies on the assumption that the magnetic field in space above the surface of the earth, is a potential field, is also revised to free it of the assumption which, does not hold true unconditionally.

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