EFFECT OF A FLUID CORE ON PROPAGATION OF AN SH‐TORQUE PULSE FROM A POINT‐SOURCE IN A SPHERE

Geophysics ◽  
1966 ◽  
Vol 31 (4) ◽  
pp. 741-763 ◽  
Author(s):  
Z. Alterman ◽  
P. Kornfeld
Keyword(s):  
Exact Solution ◽  
Point Source ◽  
Arrival Time ◽  
Elastic Solid ◽  
Steepest Descent ◽  
Surface Source ◽  
Homogeneous Sphere ◽  
The Core ◽  
Fluid Core ◽  
Deep Source

An exact solution is obtained for the displacement of the surface of a sphere consisting of a fluid core and an elastic solid mantle, due to an impulsive SH‐torque source. Theoretical seismograms are computed for several distances from a surface source and from a deep source, and are compared with results for a homogeneous sphere. The seismograms show reflected pulses of H‐type and of Lg‐type, and pulses after diffraction at the core and at the surface. In agreement with observation and as expected by steepest‐descent analysis, it is found that the Lg‐type pulses start before the ray arrival time. Traveltime and amplitude curves for reflected and diffracted pulses are given.

scholarly journals The Excess Secular Change in the Obliquity of the Ecliptic and Its Relation to the Internal Motion of the Earth

1972 ◽  
Vol 48 ◽  
pp. 192-195 ◽  
Author(s):  
Chuichi Kakuta ◽  
Shinko Aoki
Keyword(s):  
Time Variation ◽  
Rotational Speed ◽  
Internal Motion ◽  
Secular Change ◽  
Electrically Conducting ◽  
The Core ◽  
The Earth ◽  
Fluid Core ◽  
Electrical Conductivities ◽  
Long Time

The previous result (Aoki, 1969) on the explanation of the excess secular change in the obliquity of the ecliptic frictional couplings in the rigid constituents, the mantle and the core, is extended by using a model of an elastic and electrically conducting mantle and a hydromagnetic core. The secular change of the obliquity of the ecliptic referred to the mantle is found to be 1/3.2 times of the observed value, if the electrical conductivities of the fluid core and the mantle are assumed to be 3·10−6 emu and 3·10−9 emu respectively. A large secular deceleration of the Earth's rotational speed obtained in the previous result is proved to be strongly reduced because of weak excitation of the perturbing potential for a long time variation.

scholarly journals Pressure torque of torsional Alfvén modes acting on an ellipsoidal mantle

2020 ◽  
Vol 222 (1) ◽  
pp. 338-351 ◽  
Author(s):  
F Gerick ◽  
D Jault ◽  
J Noir ◽  
J Vidal
Keyword(s):  
Fluid Dynamics ◽  
Rotation Axis ◽  
Fluid Velocity ◽  
Rotation Frequency ◽  
Length Of Day ◽  
Core Mantle Boundary ◽  
The Core ◽  
Fluid Core ◽  
Spherical Core ◽  
Net Pressure

SUMMARY We investigate the pressure torque between the fluid core and the solid mantle arising from magnetohydrodynamic modes in a rapidly rotating planetary core. A 2-D reduced model of the core fluid dynamics is developed to account for the non-spherical core–mantle boundary. The simplification of such a quasi-geostrophic model rests on the assumption of invariance of the equatorial components of the fluid velocity along the rotation axis. We use this model to investigate and quantify the axial torques of linear modes, focusing on the torsional Alfvén modes (TM) in an ellipsoid. We verify that the periods of these modes do not depend on the rotation frequency. Furthermore, they possess angular momentum resulting in a net pressure torque acting on the mantle. This torque scales linearly with the equatorial ellipticity. We estimate that for the TM calculated here topographic coupling to the mantle is too weak to account for the variations in the Earth’s length-of-day.

GEOCHEMICAL INTERPRETATION OF SOME OILS AND CONDENSATES FROM THE DAMPIER SUB- BASIN OF WESTERN AUSTRALIA

1982 ◽  
Vol 22 (1) ◽  
pp. 179 ◽  
Author(s):  
I. Brikké
Keyword(s):  
Chemical Composition ◽  
Western Australia ◽  
Land Plant ◽  
Early Triassic ◽  
Normal Alkane ◽  
Geological Interpretation ◽  
The Core ◽  
Strong Affinity ◽  
Strong Emphasis ◽  
Deep Source

Twenty oils and condensates from the Dampier Sub-basin have been analysed for their gross composition and normal alkane distribution.The chemical composition (GLC traces) enables two groups to be distinguished:Oils and condensates low in C22 + n-alkanes. These are essentially found in the Rankin Platform. In this group, the sample from Eaglehawk 1 shows characteristics of a bacterially-altered product.Oils richer in C22 + n-alkanes. These are found in the Lewis Trough, but also in the Rankin Platform/Kendrew Terrace where subtle differences may suggest different origins.The geological interpretation puts strong emphasis on time of trapping. The oils and condensates of the first group (except at Angel) are trapped at the contact with the 'Main Unconformity'. Oils formed earlier than the Neocomian have been destroyed, altered (Eaglehawk 1) or trapped in deeper reservoirs, so that only mature to very mature hydrocarbons (low in C22 + n-alkanes) were available for trapping after sealing by Neocomian shales. Maturity considerations indicate that a deep source within the core of the Rankin Platform unit (Middle/Early Triassic Locker Shale and/or older) is the most likely generator of these hydrocarbons.The oils of the second group, on maturity grounds and to some extent on type correlation, may originate from Jurassic sources in the Lewis Trough. Some oils attributable to the second group are present on the Rankin Platform and/or Kendrew Terrace trapped by intraformational/fault seals and having the full composition of crudes; however, lower land-plant contribution inferred from the n-alkanes, suggests a 'Locker Shale' origin.The source of the Angel hydrocarbons is more enigmatic, but their strong affinity with the hydrocarbons from the Rankin Platform points to a similarity of origin.

A simple exact solution for a point source above a reacting surface

1991 ◽  
Vol 89 (4B) ◽  
pp. 1991-1991
Author(s):  
Xiao Di ◽  
Kenneth E. Gilbert
Keyword(s):  
Exact Solution ◽  
Point Source

AN AUTOMATED MULTI-OBJECTIVE INVIGILATOR-EXAM ASSIGNMENT SYSTEM

2010 ◽  
Vol 09 (02) ◽  
pp. 223-238 ◽  
Author(s):  
ZEHRA KAMISLI OZTURK ◽  
GURKAN OZTURK ◽  
MUJGAN SAGIR
Keyword(s):  
Mathematical Model ◽  
Exact Solution ◽  
User Interfaces ◽  
Assignment Problem ◽  
Real Life ◽  
Web Based ◽  
Multi Objective ◽  
The Core ◽  
Real Life Problem ◽  
The Mathematical Model

This paper is concerned with the invigilator-exam assignment problem. A web-based Automated Invigilator Assignment System (AIAS), consists of a mathematical model; a database storing the information and web-based user interfaces is constructed to solve the problem by providing an environment for a practical usage. The core of the system is the mathematical model developed for obtaining the exact solution. We conclude the paper by presenting a real-life problem solved by the proposed approach.

p-Δ curves for a point source lying on a boundary

1977 ◽  
Vol 67 (6) ◽  
pp. 1521-1527
Author(s):  
George A. McMechan
Keyword(s):  
Point Source ◽  
Ocean Surface ◽  
Ocean Bottom ◽  
Surface Source

abstract A point source located at a boundary is an approximation to the physical configuration of an earthquake or an explosion at the ocean bottom. The p-Δ curves that correspond to arrivals from such a source, as observed at the ocean surface and at the ocean bottom, can be constructed by geometrical manipulations of the surface source to surface receiver p-Δ curve. p-Δ curves for multiply reflected arrivals can also be similarly constructed.

Motion of a rigid disc in an elastic solid

1971 ◽  
Vol 61 (6) ◽  
pp. 1717-1729
Author(s):  
A. K. Mal
Keyword(s):  
Exact Solution ◽  
Elastic Solid ◽  
Approximate Solutions ◽  
Compressional Wave ◽  
Fredholm Integral Equations ◽  
High Frequencies ◽  
Incident Plane ◽  
Smooth Contact ◽  
Rigid Disc ◽  
Quantities Of Interest

abstract A rigid circular disc embedded in an infinite, isotropic elastic solid is assumed to be excited by a normally-incident plane, harmonic compressional wave. The disc is assumed to be either in perfectly welded or perfectly smooth contact with the surrounding solid. In each case, the problem is reduced to the solution of Fredholm integral equations of the second kind. For the case of the welded contact, exact numeral solutions valid at any given frequency are given. Approximate solutions valid at low and high frequencies are obtained for both cases and are compared with the exact solution. The displacement and compliance of the disc as well as other quantities of interest are presented graphically as functions of frequency.

Point source of light in the center of a homogeneous sphere and in an infinite medium

Astrophysics ◽  
2012 ◽  
Vol 55 (2) ◽  
pp. 275-291 ◽  
Author(s):  
A. G. Barseghyan ◽  
V. V. Ter-Avetisyan
Keyword(s):  
Point Source ◽  
Infinite Medium ◽  
Homogeneous Sphere
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