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.

scholarly journals Attenuation of seismic waves in the earth's mantle

1958 ◽  
Vol 48 (3) ◽  
pp. 269-282 ◽  
Author(s):  
B. Gutenberg
Keyword(s):  
Absorption Coefficient ◽  
Elastic Waves ◽  
Laboratory Experiments ◽  
Seismic Waves ◽  
Body Waves ◽  
The Core ◽  
Earth’S Mantle ◽  
The Earth ◽  
Theoretical Considerations

Abstract Contrasting with conclusions from laboratory experiments that the absorption coefficient k for amplitudes of elastic waves is proportional to 1/T, or, from theoretical considerations, that it should be proportional to 1/T or to 1/T2, observations of body waves through the mantle of the earth show little if any decrease in absorption with increasing period T. In teleseismic records S rarely shows periods of less than 4 seconds, while in P periods of 1 second are observed to the greatest distances. The value k = 0.06 per 1,000 km., found previously for P, P′P′ and P′P′P′ through the mantle and the core, is confirmed for P and PP and is found also for S in the mantle.

Ups and Downs

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Mantle Convection ◽  
Laboratory Experiments ◽  
Inner Core ◽  
Computer Modelling ◽  
Great Depth ◽  
New Horizons ◽  
The Core ◽  
The Earth ◽  
The World ◽  
The 1960S

Despite the dumbing-down of education in recent years, it would be unusual to find a ten-year-old who could not name the major continents on a map of the world. Yet how many adults have the faintest idea of the structures that exist within the Earth? Understandably, knowledge is limited by the fact that the Earth’s interior is less accessible than the surface of Pluto, mapped in 2016 by the NASA New Horizons spacecraft. Indeed, Pluto, 7.5 billion kilometres from Earth, was discovered six years earlier than the similar-sized inner core of our planet. Fortunately, modern seismic techniques enable us to image the mantle right down to the core, while laboratory experiments simulating the pressures and temperatures at great depth, combined with computer modelling of mantle convection, help identify its mineral and chemical composition. The results are providing the most rapid advances in our understanding of how this planet works since the great revolution of the 1960s.

Dead-Ends and New Directions

2021 ◽  
Vol 15 (4) ◽  
pp. 327-347
Author(s):  
Jean Francesco A.L. Gomes
Keyword(s):  
Natural History ◽  
Scientific Theory ◽  
Good Science ◽  
Orthodox Christian ◽  
The Core ◽  
The Earth ◽  
New Directions ◽  
History Of ◽  
Evolutionary Science ◽  
Doctrine Of Creation

Abstract The aim of this article is to investigate how Abraham Kuyper and some late neo-Calvinists have addressed the doctrine of creation in light of the challenges posed by evolutionary scientific theory. I argue that most neo-Calvinists today, particularly scholars from the Vrije Universiteit Amsterdam (VU), continue Kuyper’s legacy by holding the core principles of a creationist worldview. Yet, they have taken a new direction by explaining the natural history of the earth in evolutionary terms. In my analysis, Kuyper’s heirs at the VU today offer judicious parameters to guide Christians in conversation with evolutionary science, precisely because of their high appreciation of good science and awareness of the nonnegotiable elements that make up the orthodox Christian narrative.

The density variation of the earth's central core*

1942 ◽  
Vol 32 (1) ◽  
pp. 19-29
Author(s):  
K. E. Bullen
Keyword(s):  
Pure Iron ◽  
Outer Boundary ◽  
Density Variation ◽  
Central Core ◽  
Good Precision ◽  
Wide Margin ◽  
The Core ◽  
The Earth ◽  
The Mean ◽  
Published Paper

ABSTRACT A detailed analysis of the problem of the earth's density variation has been extended to the earth's central core. It is shown that in the region between the outer boundary of the core and a distance of about 1400 km. from the earth's center the density ranges from 9.4 gm/cm.3 to 11.5 gm/cm.3 within an uncertainty which, if certain general assumptions are true, does not exceed 3 per cent. The density and pressure figures are, moreover, compatible with the existence of fairly pure iron in this part of the earth. The result for the earth's outer mantle as given in a previously published paper, together with those in the present paper, are found to give with good precision the density distribution in a region occupying 99 per cent of the earth's volume. Values of the density within 1400 km. of the earth's center are subject, however, to a wide margin of uncertainty, and there appears to be no means of resolving this uncertainty for the present. The most that can be said is that the mean density in the latter region is greater than 12.3 gm/cm.3 and may quite possibly be several gm/cm.3 in excess of this figure. In the present paper figures are also included for the variation of gravity and the distribution of pressure within the central core. The gravity results are shown to be subject to an appreciable uncertainty except within about 1000 km. of the outer boundary of the core, but the pressure results are expected to be closely accurate at all depths.

Free spheroidal vibrations of the earth at very long periods, Part I— Calculation of periods for several earth models

1963 ◽  
Vol 53 (3) ◽  
pp. 483-501 ◽  
Author(s):  
Leonard E. Alsop
Keyword(s):  
Inner Core ◽  
Computer Programs ◽  
Free Vibrations ◽  
Stoneley Waves ◽  
The Core ◽  
The Earth ◽  
Earth Models ◽  
Shear Modes ◽  
Phase And Group Velocities ◽  
Group Velocities

Abstract Periods of free vibrations of the spheroidal type have been calculated numerically on an IBM 7090 for the fundamental and first two shear modes for periods greater than about two hundred seconds. Calculations were made for four different earth models. Phase and group velocities were also computed and are tabulated herein for the first two shear modes. The behavior of particle motions for different modes is discussed. In particular, particle motions for the two shear modes indicate that they behave in some period ranges like Stoneley waves tied to the core-mantle interface. Calculations have been made also for a model which presumes a solid inner core and will be discussed in Part II. The two computer programs which were made for these calculations are described briefly.

Development of Web-based Technology for Environmental Engineering Education System

2020 ◽  
Vol 50 (4) ◽  
pp. 04-05
Author(s):  
Procopio Cocci
Keyword(s):  
Engineering Education ◽  
Education System ◽  
Environmental Engineering ◽  
Web Based ◽  
The Core ◽  
The Earth ◽  
Training Mode ◽  
Natural Information ◽  
Good For ◽  
Ecological Building

The objective of the ecological building instruction ought not just train understudies' natural information, the more significant thing is that it prepares understudies' natural ethics and structures the conduct which is good for the earth, and these must be shaped by training, in actuality. In the customary showing model of training, one instructor can just guide one practice simultaneously. With the improvement of organization innovation, instructor can control the distinctive practice exercises firing up in various areas or in various occasions by network. In light of the incorporation of viable need and intuitive qualities of condition instruction, the creator set forward an online domain training mode named "practice-intelligent partake in". The Core of this mode is to prepare understudies' natural ethics by training and to understand educators' guidance through organization.

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