A comparison of free oscillations of oceanic and continental earth models

1967 ◽  
Vol 57 (5) ◽  
pp. 1047-1061
Author(s):  
John S. Derr
Keyword(s):  
Group Velocity ◽  
Upper Mantle ◽  
Crust And Upper Mantle ◽  
Torsional Oscillations ◽  
The Earth ◽  
Earth Models ◽  
Rayleigh And Love Waves ◽  
The Difference ◽  
Spheroidal Oscillations ◽  
Oceanic Model

Abstract It is well-known that Rayleigh and Love waves over continental and oceanic structures have different periods (T) for a given order (n). In the present study, this difference is explored over the spectrum for periods greater than 30 sec, and particularly the graver fundamental spheroidal and torsional oscillations. The oceanic model is the same as the continental model below 400 km depth, is adjusted between 400 km and 10 km to preserve the Earth's overall mass and moment of inertia, and has 5 km of crust and 5 km of ocean. For torsional oscillations, the difference in period for a given n is about 3 sec throughout the range of 2 ≦ n ≦ 120, or 0.15 per cent to 3.3 per cent. However, the two curves for the group velocity are not parallel in this range: continental group velocity increases monotonically with T, while oceanic group velocity has a broad minimum for 160 < T < 200 sec. For spheroidal oscillations, the difference in period for a given n is about 2 sec for 2 ≦ n ≦ 120, or 0.1 per cent to 2 per cent. For n = 0, the difference is only 0.1 sec or 0.008 per cent. The two group velocity curves are almost parallel with minima in the same range, 205 to 210 sec. Comparison with the precision of available measurements of the free periods shows that the presence of an oceanic crust and upper mantle is important for fitting models of the earth to any set of free oscillation observations.

Reflections from discontinuities beneath antarctica

1971 ◽  
Vol 61 (5) ◽  
pp. 1441-1451
Author(s):  
R. D. Adams
Keyword(s):  
North American ◽  
Upper Mantle ◽  
Deep Structure ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Nuclear Explosions ◽  
Novaya Zemlya ◽  
The Earth ◽  
Velocity Channel ◽  
Upper Boundary

abstract Early reflections of the phase P′P′ recorded at North American seismograph stations from nuclear explosions in Novaya Zemlya are used to examine the crust and upper mantle beneath a region of eastern Antarctica. Many reflections are observed from depths less than 120 km, indicating considerable inhomogeneity at these depths in the Earth. No regular horizons were found throughout the area, but some correlation was observed among reflections at closely-spaced stations, and, at many stations, reflections were observed from depths of between 60 and 80 km, corresponding to a likely upper boundary of the low-velocity channel. Deeper reflections were found at depths of near 420 and 650 km. The latter boundary was particularly well-observed and appears to be sharply defined at a depth that is constant to within a few kilometers. The boundary at 420 km is not so well defined by reflections of P′P′, but reflects well longer-period PP waves, arriving at wider angles of incidence. This boundary appears to be at least as pronounced, but not so sharp as that near 650 km. The deep structure beneath Antarctica presents no obvious difference from that beneath other continental areas.

scholarly journals Earth as a Gravitational-Wave Interferometr

2019 ◽  
Vol 224 ◽  
pp. 03012
Author(s):  
Vadim Il’chenko
Keyword(s):  
Gravitational Wave ◽  
Upper Mantle ◽  
Oscillatory System ◽  
Average Depth ◽  
Lunar Tide ◽  
Crust And Upper Mantle ◽  
The Earth ◽  
Order Of Magnitude ◽  
Gravitational Wave Interferometer ◽  
Gravitational Influence

Based on the principle of Equivalence of Gravitating Masses (EGM) and tectonostratigraphic model of the Earth outer shell structure (the Earth crust and upper mantle), the average depth of the lunar mass gravitational influence on the Earth was calculated as ~1600 km. The developed model is based on the mechanism of rocks tectonic layering of the Earth crust-mantle shell as an oscillatory system with dynamic conditions of a standing wave, regularly excited by the lunar tide and immediately passing into the damping mode. After comparing the average depth of solid lunar tide impact of ~1600 km with the height of the solid lunar tide “hump” on the Earth surface of 0.5 m, a “tensile strain” was calculated with an amplitude only one order of magnitude larger than the amplitude of the gravitational wave recorded by the Advanced LIGO interferometer: A≈10-18 m (the merger result of a black holes pair ca 1.3 Ga ago). The results of the present study suggest that the crust-mantle shell of the Earth may be used as a gravitational-wave interferometer.

scholarly journals Symposium on the Crust and Upper Mantle of the Earth

1964 ◽  
Vol 73 (3) ◽  
pp. 137-138
Author(s):  
Hisashi KUNO ◽  
Hitoshi TAKEUCHI ◽  
Seiya UEDA
Keyword(s):  
Upper Mantle ◽  
Crust And Upper Mantle ◽  
The Earth

Electrical properties of the lithosphere in the western desert, Egypt, using magnetotelluric sounding

2021 ◽  
Author(s):  
Hossam Marzouk ◽  
Tarek Arafa-Hamed ◽  
Michael Becken ◽  
Mohamed Abdel Zaher ◽  
Matthew Comeau
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Western Desert ◽  
Velocity Data ◽  
Profile Data ◽  
Crust And Upper Mantle ◽  
Near Surface ◽  
The Earth ◽  
Nubian Aquifer ◽  
Dakhla Oasis

<p>We present electrical resistivity models of the crust and upper mantle estimated from 2D inversions of broadband magnetotellurics (MT) data acquired from two profiles in the western desert of Egypt, which can contribute to the understanding of the structural setup of this region. The first profile data are collected from 14 stations along a 250 km profile, in EW direction profile runs along latitude ~25.5°N from Kharga oasis to Dakhla oasis. The second profile comprises 19 stations measured along a 130 km profile in NS direction centered at longitude 28°E and crossing the Farafra. The acquisition for both profiles continued for 1 to 3 days at each station, which allowed for the calculation of impedances for periods from 0.01 sec up to  4096 sec at some sites. The wide frequency band corresponds to a maximal skin depths of up to 150 km that can provide penetration to the top of the asthenosphere. The inversion models display high-conductivity sediments cover at the near surface (<1-2 km), which can be associated with the Nubian aquifer. Along the EW-profile from Kaharge to Dhakla, the crustal basement is overly highly resistive and homogeneous und underlain by a more conductive lithospheric mantle below depths of 30-40 km. Along the N-S profile across Farafra, only the southern portion exhibits a highly resistive crust, whereas beneath Farafra northwards, moderate crustal conductivities are encountered. A comparison has been made between the resultant resistivity models with the 1° tessellated updated crust and lithospheric model of the Earth (LITHO1.0) which was developed by <em>Pasyanos, 2014</em> on the basis of seismic velocity data. The obtained results show a remarkable consistency between the resistivity models and the calculated crustal boundaries. Especially at the Kharga-Dakhla profile a clear matching can be noticed at the upper and lower boundaries of a characteristic anomaly with the Moho and LAB boundaries respectively.</p>

1. The mineral world

2014 ◽  
Author(s):  
David Vaughan
Keyword(s):  
Crystal Structure ◽  
Chemical Composition ◽  
Upper Mantle ◽  
Earth’S Crust ◽  
Crust And Upper Mantle ◽  
Big Ten ◽  
The Earth ◽  
Earth's Crust

Minerals are the fundamental components of the Earth. ‘The mineral world’ describes the fields of mineralogy and crystallography that study them. There are approximately 4,400 known minerals, but the ‘big ten’ minerals that are most abundant in the rocks of the Earth’s crust and Upper Mantle are calcite, quartz, olivines, pyroxenes, amphiboles, muscovite, biotite, orthoclase, albite, and anorthite. The two essential characteristics of any mineral are its chemical composition and its crystal structure. Minerals can be assigned to one of seven crystal classes depending on their elements of symmetry. There is further subdivision into 32 crystal classes. Minerals are classified by chemical composition into mineral groups such as silicates, and carbonates.

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