PROPAGATION OF ELASTIC WAVES IN THE EARTH

Geophysics ◽  
1940 ◽  
Vol 5 (1) ◽  
pp. 1-14 ◽  
Author(s):  
L. G. Howell ◽  
C. H. Kean ◽  
R. R. Thompson

An investigation of elastic‐wave propagation in near‐surface materials using single‐frequency continuous waves and pulses, over a range of 20 to 1400 cycles, is described. While only touching upon the diverse problems involved in a study of this kind the results indicate a complexity requiring considerable research if a proper understanding, commensurate with the importance of the problem, is to be attained.

Geophysics ◽  
1972 ◽  
Vol 37 (3) ◽  
pp. 445-455 ◽  
Author(s):  
C. N. G. Dampney ◽  
B. B. Mohanty ◽  
G. F. West

Simple electronic circuitry and axially polarized ceramic transducers are employed to generate and detect elastic waves in a two‐dimensional analog model. The absence of reverberation and the basic simplicity. of construction underlie the advantages of this system. If the form of the fundamental wavelet in the model itself, as modified by the linear filtering effects of the remainder of the system, can be found, then calibration is achieved. This permits direct comparison of theoretical and experimental seismograms for a given model if its impulse response is known. A technique is developed for calibration and verified by comparing Lamb’s theoretical and experimental seismograms for elastic wave propagation over the edge of a half plate. This comparison also allows a critical examination of the basic assumptions inherent in a model seismic system.


Author(s):  
И.Б. Петров

Существует значительное количество прикладных задач, для решения которых применяется математическое моделирование динамических процессов в деформируемых средах. К таким задачам относят моделирование распространения упругих волн в геологических средах, в том числе с учетом ледовых образований, их рассеяния на зонах трещиноватости. Актуальность этих постановок обусловлена важностью решения обратных задач сейсмической разведки, обработки данных сейсмической разведки с целью уточнения запасов углеводородов и определения расположения углеводородов и других полезных ископаемых. Поэтому приобретает важность разработка высокоточных численных методов, позволяющих моделировать упругие волны в деформируемых средах. Одним из этих методов является сеточно-характеристический численный метод, примененный в данной работе. Этот численный метод применяется для решения прямых задач, то есть для расчета распространения упругих волн при известных параметрах рассматриваемой среды. А для решения обратной задачи по восстановлению параметров геологической среды по данным сейсмической разведки можно применять нейронные сети, для обучения которых можно использовать многократное решение прямых задач сеточно-характеристическим методом. В данной работе приведены примеры решения разнообразных прямых задач по распространению упругих волн в неоднородных геологических средах, в том числе в зоне Арктики, а также представлена постановка задачи по обучению нейронных сетей и графики, показывающие эффективность их обучения с использованием двух различных подходов. Many problems can be solved with the simulation of dynamic processes in deformable media. They are the simulation of elastic wave propagation in rocks including ice formations, and wave scattering on rock-fracture zones. Such studies are important for solving inverse problems of seismic exploration and seismic data processing to get a better estimation of hydrocarbon reserves, locate hydrocarbons and other minerals. Therefore, it is necessary to develop high-precision numerical methods used to simulate elastic waves in deformable media. One of such methods is the grid-characteristic approach used in this work. It is suitable for solving direct problems, i.e., to analyze the propagation of elastic waves in a medium with known properties. Neural networks can be applied to solve the inverse problem: reconstructing the geology from seismic survey data. Multiple solving of direct problems by the gridcharacteristic approach is used for network training. This paper contains some examples of solving a range of direct problems on the elastic wave propagation in heterogeneous rocks, also in the Arctic zone, and the problem statement for training neural networks and graphs is proposed to demonstrate the efficiency of training with two approaches.


Author(s):  
Bernhard R. Tittmann

Elastic wave propagation in porous media will be introduced by a discussion of scattering to show the use of broad frequency band pulses in relating the attenuation, velocity and backscattering to information on porosity. Examples will be given for microporosity in castings and powder metal components. This will be followed by a discussion of the influence of volatiles within the pores on the absorption of elastic waves in porous ceramics and rocks. Implications of these findings will be given for ultrasonic device applications and for the interpretation of the lunar seismic experiments carried out as part of the Apollo missions to the moon.


2019 ◽  
Vol 127 ◽  
pp. 02013 ◽  
Author(s):  
Vladimir Korochentsev ◽  
Jingwei Yin ◽  
Anastasiya Viland ◽  
Tatyana Lobova ◽  
Natalia Soshina

A theoretical model for the propagation of elastic waves of arbitrary wave sizes from 0.5 to 20 units in an ice layer has been developed. The calculation was based on Green’s function theory for Helmholtz equation. Special “directed” Green’s functions were introduced. They make it possible to anayze wave fields in closes volumes limited by different-angle impedances. The developed calculation algorithms allow one to anayze fields on medium-powered computers for 15 minutes. The suggested methods are capable of estimating elastic wave interactions with different impedances in bays, lakes and other volumes with limited wave sizes.


1960 ◽  
Vol S7-II (6) ◽  
pp. 801-820
Author(s):  
G. D. Afanasev

Abstract The results of recent studies of elastic wave propagation within the earth are reviewed and different interpretations of the earth's interior which have been proposed, particularly in recent American works, are outlined. The results of these studies and of oceanographic work are incompatible with certain classic theories. The main facts are the differences between the continental and oceanic crust and the relatively recent (Tertiary and Quaternary) age of the great zones of continental subsidence, where a transformation from a continental to an oceanic-type crust is implied. The concept of permanent ocean basins is rejected. Differences between the continental and oceanic crust are considered essentially a function of physical state rather than petrographic composition. Continental zones that have subsided are characterized by greater seismic velocities because of the extra pressure to which they have been subjected in the course of the ages.


2015 ◽  
Vol 20 (1) ◽  
pp. 159-170 ◽  
Author(s):  
M. Rucka ◽  
B. Zima

Abstract This study deals with experimental and numerical investigations of elastic wave propagation in steel bars partially embedded in mortar. The bars with different bonding lengths were tested. Two types of damage were considered: damage of the steel bar and damage of the mortar. Longitudinal waves were excited by a piezoelectric actuator and a vibrometer was used to non-contact measurements of velocity signals. Numerical calculations were performed using the finite elements method. As a result, this paper discusses the possibility of condition assessment in bars embedded in mortar by means of elastic waves.


2018 ◽  
Vol 8 (11) ◽  
pp. 2105 ◽  
Author(s):  
Yimin Wei ◽  
Xuan Shi ◽  
Qi Liu ◽  
Wenhua Chen

The transverse crack in a non-uniform shaft possesses different crack modes, and it can affect the propagation characteristics of the elastic waves in the shaft. The influence of the crack mode as well as the location and the depth of the crack and the rotating speed to the propagation characteristics is investigated in this paper. Firstly, the transfer matrix for the elastic wave in a non-uniform shaft is obtained by deducing the local flexibility coefficients of the three typical crack modes, in which the transverse crack is modeled as a local spring. After that, the influence of the crack mode to the propagation characteristics is studied both in a numerical and an experimental way. Finally, the influence of the location and the depth of the transverse crack as well as the rotating speed of the shaft is studied too. It is found that Mode III is the most suitable mode in this paper, the location of the crack will make the stopbands fluctuating, the depth mainly affects the bandwidth of the stopbands, and the increase of the rotating speed will shift up the stopbands without changing the bandwidths. The results can help to detect and locate a transverse crack.


2014 ◽  
Vol 553 ◽  
pp. 705-710 ◽  
Author(s):  
Tian Wei Wang ◽  
Chun Hui Yang

In this study, to accurately identify the functions of piezoelectric actuators and sensors for the generation and collection of elastic waves in typical engineering structures, several effective models of surface-bounded flat PZT disks are further developed and validated for numerical modelling of elastic wave propagations. Based on these models, a series of finite element models of elastic waves in plates are devised using both implicit and explicit dynamics analysis techniques and those numerical simulations are conducted and verified one another. The results flowed from the present research is being used to study the elastic wave propagation in pipes and develop an online structural health monitoring (SHM) system with an integrated piezoelectric actuator-sensor network.


Author(s):  
Agnès Maurel ◽  
Fernando Lund ◽  
Maurine Montagnat

The propagation of elastic waves in polycrystals is revisited, with an emphasis on configurations relevant to the study of ice. Randomly oriented hexagonal single crystals are considered with specific, non-uniform, probability distributions for their major axis. Three typical textures or fabrics (i.e. preferred grain orientations) are studied in detail: one cluster fabric and two girdle fabrics, as found in ice recovered from deep ice cores. After computing the averaged elasticity tensor for the considered textures, wave propagation is studied using a wave equation with elastic constants c =〈 c 〉+ δc that are equal to an average plus deviations, presumed small, from that average. This allows for the use of the Voigt average in the wave equation, and velocities are obtained solving the appropriate Christoffel equation. The velocity for vertical propagation, as appropriate to interpret sonic logging measurements, is analysed in more details. Our formulae are shown to be accurate at the 0.5% level and they provide a rationale for previous empirical fits to wave propagation velocities with a quantitative agreement at the 0.07–0.7% level. We conclude that, within the formalism presented here, it is appropriate to use, with confidence, velocity measurements to characterize ice fabrics.


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