THE EFFECT OF DENSITY ON SEISMIC REFLECTIONS

Geophysics ◽  
1941 ◽  
Vol 6 (1) ◽  
pp. 45-51
Author(s):  
S. S. West
Keyword(s):  
Seismic Waves ◽  
Reflection Coefficients ◽  
Seismic Reflections ◽  
Existing Data

By means of existing data on the density of rocks, it is shown that reflection coefficients of seismic waves, calculated from velocities alone, often differ greatly from the actual values. Data on a large number of density discontinuities have been tabulated, and the true reflection coefficients calculated for six cases in which velocities are also known.

scholarly journals Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

2015 ◽  
Vol 9 (1) ◽  
pp. 367-384 ◽  
Author(s):  
A. Diez ◽  
O. Eisen
Keyword(s):  
Seismic Waves ◽  
Dynamic Behaviour ◽  
Ice Core ◽  
Ice Cores ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Reflection Coefficients ◽  
Seismic Velocities ◽  
Crystal Anisotropy ◽  
Elasticity Tensors

Abstract. A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice–bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

VELOCITY STRATIFICATION AS AN AID TO CORRELATION

Geophysics ◽  
1940 ◽  
Vol 5 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Roland F. Beers
Keyword(s):  
Experimental Data ◽  
Historical Development ◽  
Field Data ◽  
Reflection Coefficients ◽  
Stratigraphic Correlation ◽  
Seismic Reflections

This paper outlines the historical development of the concept “velocity stratification” from the field data of refraction and reflection seismographs. The concept is shown to form the basis of the phenomenon known as “seismic reflections.” Experimental data are interpreted to show approximately the magnitude of reflection coefficients. Employment of velocity stratification as a means of stratigraphic correlation is suggested. Means whereby data for these correlations may be collected are discussed. Finally the use of the method for attack on stratigraphic problems is outlined.

A model for transepithelial fluid transport

1978 ◽  
Vol 235 (6) ◽  
pp. F626-F637 ◽  
Author(s):  
E. H. Bresler
Keyword(s):  
Simple Model ◽  
Hydraulic Conductivity ◽  
Sodium Transport ◽  
Fluid Transport ◽  
Reflection Coefficients ◽  
Active Sodium ◽  
Active Sodium Transport ◽  
Existing Data ◽  
Lines Of Evidence

A number of experimental observations which are not easily, or at all, accommodated within the framework of the natriocentric theory for transepithelial fluid transport are discussed. These are shown to be not merely accommodated but actually predicted by a simple model for fluid transport in which the major osmotic force leading to fluid transport derives from solutes other than NaCl. The model is then analyzed for feasibility in light of existing data relating to reflection coefficients for NaCl and hydraulic conductivity. Certain lines of evidence for specific active sodium transport are critically reexamined.

scholarly journals Numerical modelling of wave processes in multilayered media with gas-containing layers: the comparison of 2D and 3D models

2019 ◽  
Vol 489 (4) ◽  
pp. 351-354
Author(s):  
P. V. Stognii ◽  
N. I. Khokhlov ◽  
I. B. Petrov
Keyword(s):  
Numerical Modelling ◽  
Seismic Waves ◽  
Oil And Gas ◽  
Arctic Region ◽  
3D Models ◽  
The Arctic ◽  
3 Dimensional ◽  
The North ◽  
Wave Patterns ◽  
Seismic Reflections

Today the Arctic region exploration is one of the most important courses for research in our country because large amounts of unexplored oil and gas deposits are located there. Large deposits of hydrocarbons are situated in water areas of the North seas. Gas explosions complicate the development of hydrocarbon deposits in these water areas. They occur as a result of an accidant opening and further spread of gas. It is impossible to carry out the frequent exploration of the area with gas layers, then the numerical modelling of the area with already detected gas deposits is conducted. In this work, we present the results of numerical modelling of seismic waves spread in multilayered geological models with gas-containing inclusions during the four-year period with the use of the grid-characteristic method. Then, the wave patterns of seismic reflections and seismograms for the described problem were obtained. We conducted the comparison of wave patterns and seismograms for the 2-dimensional and 3-dimensional cases. The results demonstrated a good coincidence.

scholarly journals Seismic wave propagation in anisotropic ice – Part 1: Elasticity tensor and derived quantities from ice-core properties

2014 ◽  
Vol 8 (4) ◽  
pp. 4349-4395 ◽  
Author(s):  
A. Diez ◽  
O. Eisen
Keyword(s):  
Seismic Waves ◽  
Ice Core ◽  
Ice Cores ◽  
Seismic Wave Propagation ◽  
Elasticity Tensor ◽  
Reflection Coefficients ◽  
Seismic Velocities ◽  
Ice Dynamics ◽  
Crystal Anisotropy ◽  
Elasticity Tensors

Abstract. A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy, to understand its contribution to ice dynamics, is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric does not only influence the flow behaviour of ice, but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, also recorded traveltimes. A framework is presented here to connect COF data with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics from ice-core data. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice-bed contact. Our work, therefore, provides a contribution to remotely determine the state of bulk ice anisotropy.

scholarly journals Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D″ layer

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Christopher Langrand ◽  
Denis Andrault ◽  
Stéphanie Durand ◽  
Zuzana Konôpková ◽  
Nadège Hilairet ◽  
...  
Keyword(s):  
Lower Mantle ◽  
Perovskite Structure ◽  
Reflection Coefficients ◽  
Transformation Kinetics ◽  
Grain Sizes ◽  
Order Of Magnitude ◽  
Two Phases ◽  
Seismic Reflections ◽  
Thick Layers ◽  
Lowermost Mantle

AbstractBridgmanite, the dominant mineral in the Earth’s lower mantle, crystallizes in the perovskite structure and transforms into post-perovskite at conditions relevant for the D$${}^{{\prime\prime} }$$″ layer. This transformation affects the dynamics of the Earth’s lowermost mantle and can explain a range of seismic observations. The thickness over which the two phases coexist, however, can extend over 100 km, casting doubt on the assignment of the observed seismic boundaries. Here, experiments show that the bridgmanite to post-perovskite transition in (Mg$${}_{0.86}$$0.86,Fe$${}_{0.14}$$0.14)SiO$${}_{3}$$3 is fast on geological timescales. The transformation kinetics, however, affects reflection coefficients of $$P$$P and $$S$$S waves by more than one order of magnitude. Thick layers of coexisting bridgmanite and post-perovskite can hence be detected using seismic reflections. Morever, the detection and wave period dependence of D$${}^{{\prime\prime} }$$″ reflections can be used to constrain significant features of the Earth’s lowermost mantle, such as the thickness of the coexistence layer, and obtain information on temperature and grain sizes.

Long-offset AVO inversion of PP reflections from plane interfaces using effective reflection coefficients

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. C65-C79 ◽  
Author(s):  
Lyubov Skopintseva ◽  
Milana Ayzenberg ◽  
Martin Landrø ◽  
Tatyana Nefedkina ◽  
Arkady M. Aizenberg
Keyword(s):  
Reflection Coefficient ◽  
Plane Wave ◽  
Seismic Waves ◽  
Wave Reflection ◽  
Point Sources ◽  
Model Parameters ◽  
Reflection Coefficients ◽  
Avo Inversion ◽  
Long Offset ◽  
Head Waves

A conventional amplitude variation with offset (AVO) inversion is based on geometrical seismics which exploit plane-wave reflection coefficients to describe the reflection phenomenon. Widely exploited linearizations of plane-wave coefficients are mostly valid at pre-critical offsets for media with almost flat and weak-contrast interfaces. Existing linearizations do not account for the seismic frequency range by ignoring the frequency content of the wavelet, which is a strong assumption. Plane-wave reflection coefficients do not fully describe the reflection of seismic waves at near-critical and post-critical offsets, because reflected seismic waves are typically generated by point sources. We propose an improved approach to AVO inversion, which is based on effective reflection coefficients (ERCs). ERCs generalize plane-wave coefficients for seismic waves generated by point sources and therefore more accurately describe near-critical and post-critical reflections where head waves are generated. Moreover, they are frequency-dependent and incorporate the local curvatures of the wavefront and the reflecting interface. In our study, we neglect the effect of interface curvature and demonstrate the advantages of our approach on synthetic data for a simple model with a plane interface separating two isotropic half-spaces. A comparison of the inversion results obtained with our approach and the results from an AVO inversion method based on the exact plane-wave reflection coefficient suggests that our method is superior, in particular for long-offset ranges which extend to and beyond the critical angle. We thus propose that long offsets can be successfully exploited in an AVO inversion under the correct assumption about the reflection coefficient. Such long-offset AVO inversion shows the potential of outperforming a conventional moderate-offset AVO inversion in the accuracy of estimated model parameters.

scholarly journals A Mathematical Model of Longitudinal Waves Incident at a Free Surface of a Pre-Stressed Dissipative Half-Space

Mathematics ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 2011
Author(s):  
Mahmoud M. Selim ◽  
Taher A. Nofal
Keyword(s):  
Free Surface ◽  
Reflection Coefficient ◽  
Longitudinal Wave ◽  
Initial Stress ◽  
Half Space ◽  
Seismic Waves ◽  
Initial Stresses ◽  
Reflection Coefficients ◽  
Longitudinal Waves ◽  
Stress Parameter

The aim of this work is to study the behavior of reflection of a longitudinal wave at a free surface of dissipative half-space under the effects of compressive initial stresses. When a longitudinal wave is incident on the free surface of an elastic dissipative half-space, two damped waves (Primarywaves and secondary waves are reflected. Among of these waves, P-waves are affected by compressional initial stresses. The governing equation and corresponding closed-form solutions are derived based on Biot’s incremental deformation theory. The equations of motion are solved analytically and the influence of initial stress parameter on the reflection coefficient of P-wave incidents at the free surface of dissipative half-space is studied in detail. Numerical computations are performed for actual Earth crust and the results analyzing the incident of longitudinal waves are discussed and presented graphically. The analytical solutions and numerical results reveal that the compressive initial stress parameter has notable effects on the reflection coefficient of longitudinal wave incidents on the free surface of dissipative medium. In addition, it has been observed that the presence of compressive initial stresses increases the phase velocity of the longitudinal waves. To the authors’ best knowledge, effects of compressive initial stresses on the reflection coefficients of the incident longitudinal wave on a free surface of dissipative half-space have not been studied before. Since the actual Earth is subject to initial stresses due to different resources, understanding the influences of compressive initial stresses on the reflection coefficient of a longitudinal wave helps seismologists and earthquake engineers to get accurate results of the reflection coefficients of seismic waves propagation in the Earth. Thus, the present study would be useful for seismology and earthquake engineering fields and further study about the nature of seismic waves.

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