The basic principle of the seismic reflection technique application is to measure the time taken for a seismic wave that travels from a source down into the ground where it is reflected back to the surface where it can be detected by a receiver geophone. This can be studied as long as you consider infinitely high frequencies infinitely narrow rays. Geometric seismology the speed of light 16 huygens principle 17 reflection and refraction 20 ray theory 23 fermats principle 24 fermats principle and reflection and refraction 28 diffraction 30 analogy 34 appendix a. Geol0029 seismology i ucl earth sciences ucl university. Seismology is a wide scope in geophysical science that seeks to analyze the nature of the subsurface. In april 2009 the hardback was reprinted as a paperback that corrected many typos. Basic principles of the seismic method in this chapter we introduce the basic notion of seismic waves.
For seismicexploration purposes, where measurements are taking place at the surface, the different arrivals of direct waves, reflected waves and refractedhead. Seismic waves are pulses of strain energy that propagate in solids and fluids. The material is based on several textbooks, monographs and journal articles. These algorithms have been implemented and used to estimate velocity distributions from both synthetic and field reflection seismograms. On land, vibration trucks can shake the ground very powerfully to produce sound waves. Seismic reflection methods applied to engineering, environmental. N in reflection seismology, between a seismic source and a r form of an increase of time with hyperbolic and it is the principal reflection or not. The general principles governing the reflection of light and sound are similar, for both normally travel in straight lines and both are wave phenomena.
How do we describe and input seismic sources superposition principle. Quantitative seismology, aki and richards, 2nd edition. Vibrators work on the principle of introducing a userspecified band of frequencies, known as the sweep, into the earth and then crosscorrelating that sweep function with the recorded data to define reflection events. Robinsonand deanclark 1252 the leading edge october 2006 figure 1. While the principles are not difficult to grasp, there are several pitfalls of shallow seismic reflection that should be presented. Reflectionrefraction seismology christian hubscher a and karsten gohlb ainstitute of geophysics, center for earth system research and sustainability, university of hamburg, hamburg, germany bdivision of geosciences, section of geophysics, alfred wegener institute, helmholtzcentre for polar and marine research, bremerhaven, germany synonyms controlledsource seismology. A primer computational seismology 1 what are the governing equations for elastic wave propagation. Seismic reflection method is the most commonly used geophysical technique which applies the principles of seismology for stratigraphic and structural mapping beneath the ground surface to depth of several hundred meters. Before we can do this we have to deal with some basic theory. Then, using equation compute the ptop reflection amplitudes as a function offset. The method requires a controlled seismic source of energy, such as dynamitetovex, a specialized air gun or a seismic vibrator, commonly known by the trademark name vibroseis. An introduction to seismology, earthquakes, and earth. Reflection seismology uses manmade sources to create sound waves.
Reflection amplitude variations with angle of incidence, and therefore with offset, can be modeled using the zoeppritz equations. The second edition of the akirichards textbook was published by university science books in august 2002 as a hardback. Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. The basic principle of all seismic methods is the controlled generation of elastic waves by a seismic source in order to obtain an image of the subsurface. Common examples include the reflection of light, sound, and water waves. Seismic reflection methods environmental geophysics us epa. These techniques provide detailed information about subsurface layering and rock geomechanical properties using seismic acoustical waves. The measured time is known as the two way time twt. Subsurface surveys extensive education and experience. This page was generated automatically upon download from the eth zurich. The reflection coefficient, r, shows that the quantity of the reflected energy. It appeared in one volume that was a substantial rewrite of the original twovolume first edition. An introduction to seismology, earthquakes, and earth structure seth stein department of geological sciences, northwestern university, evanston, illinois michael wysession department of earth and planetary sciences, washington university, st louis, missouri sub gsttingen 7 215 071 352 2002 b1602 blackwell publishing.
Ray tracing in practice nick rawlinson research school of earth sciences australian national university. Seismic refraction is a geophysical principle governed by snells law. An introduction to seismology, earthquakes, and earth structure. Seismic 2d reflection processing and interpretation of. Seismic rays are used instead of the wave front to describe the wave propagation. Reflection seismic 1 script research collection eth zurich. Basic principles of the seismic method tu delft opencourseware. The wave phenomena occurring at a boundary between two layers are discussed, such as snells law, re. Basic theory in reflection seismology, volume 1 1st edition. Angle of incidence angle of reflection contentsshow reflections reflections may occur in a number of wave and particle phenomena. Fermats principle consider the kinetic and potential energy along an arbitrary path between two points, a and b. Resolution is the ability to discern two closely spaced reflectors at depth. Sources in the water are typically airguns, large, metal canisters which fill up with compressed air that is suddenly released like the popping of a balloon. Velocity tends to increase with depth through earths crust and mantle, but drops sharply going from the mantle to the outer core.
Also, each student in the course is responsible for finding and presenting a seismic reflection study published in journals. We will discuss some classical concepts and also discuss some of the more current topics. While this physical consistency is the ultimate limiting factor in the utility of any inversion algorithm, our focus in this paper will be limited to the necessary. In principle, seismic data acquisition requires an energy source, a receiver, and a recording system. What are the most fundamental results in simple media. How the energy of an incident wave is proportioned i. In year 2001 olkiluoto was selected for the site of final disposal. In the earth, seismic waves can propagate as longitudinal p or as shear s waves. Results from reflection seismology, which was held june 2628, 1984 on the cornell university campus and which forms the basis for these two geodynamics series volumes. It was used in seismology for determining the mohorovicic discontinuity, and to discover the nuclei of earth. Pdf we prove that rays in linearly elastic anisotropic nonuniform media obey fermats principle of stationary traveltime. In figure 5,o is the angle of incidence by definition, the angle that the incident ray makes with the normal to the reflecting interface. Pdf fermats principle for seismic rays in elastic media. Refraction seismology refraction experiments are based on the times of arrival of the initial ground movement generated by a source recorded at a variety of distances.
The final project will be a 5page written paper on any topic of reflection seismology. Seismology science dealing with earthquakes seismic engineering the discipline the aim of which is to construct infrastructures and buildings resistant to earthquake and similar phenomena impacts and by this way to protect human lives and health and human property. The material in this volume provides the basic theory necessary to understand the principles behind imaging the subsurface of the earth using reflection and refraction seismology. If the wave reaches an interface, some of the energy will be transmitted, and some will be reflected. Note that the waves travels from medium 1 into medium 2. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Cerveny and hron 1980, cerveny 1985 chapter 8, and novotny 1999 chapter 6.
The corresponding angle of reflection is denoted 0. Reflection seismology is also used in shallow application for engineering, groundwater and environmental surveying. The method requires a controlled seismic source of energy, such as dynamite or tovex blast, a specialized air gun or a seismic vibrator, commonly known by the trademark name vibroseis. Reflection seismology wikipedia republished wiki 2. Seismic reflection is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the earths subsurface from reflected seismic waves. Fundamentals of petroleum geology pdf free download.
Ray tracing in practice introduction although 1d whole earth models are an acceptable. Huygens principle all points on a given wavefront are taken as point sources. If ac is set to the wavenumber along the propagation path of the incident wave, then ab is the horizontal wavenumber which is invariant as a result of reflection or refraction. Awesome book if you have tried the quantitative seismology of aki and richard and you had to study a set of different maths and physics books to deal with the presented complexity then now it s time to get a good rest and enjoy the integrity that has been brought to you by the principles of seismology by udias. The wave phenomena occurring at a boundary between two layers are discussed, such as snells. Principles of the seismology and seismic engineering.
The nyquist law determines the most elevated frequency in function of sampling rate. These studies are critiqued by the presenter and the group. The acoustic impedance is the product of the velocity and density. Now reflection seismology tries to get information from the reflected waves. For reflection seismology, the end product is a record section from a collection of wiggly traces that are recorded in the field from which information about the. This paper outlines the implementation details and enhancements of a previously described new concept in blind seismic deconvolution that is referred to as principle phase decomposition ppd. Reflection article about reflection by the free dictionary.
For modeling the reflection amplitudes, you need welllog curves for the pwave velocity, swave velocity, and density. High resolution seismic reflection practical basis wgeosoft. Thereby you would get a much smaller space in which waves would get back to the surface. Seismic energy sources, whether at the earths surface or in shallow boreholes, produce wave types known as. October 2017 learn how and when to remove this template message. The propagation velocity of seismic waves depends on density and elasticity of the medium as well as the type of wave. Physics and chemistry of the earths interior seismic reflection pdf.
Class exercises as well as exams involve interpretation of seismic reflection data. Reflection seismology or seismic reflection is a method of exploration geophysics that uses the principles of seismology to estimate the. Reflection seismology or seismic reflection is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the earths subsurface from reflected seismic waves. This law of reflection can be derived from fermats principle.
The method requires a controlled seismic source of energy, such as dynamite or tovex blast, a specialized air gun or a seismic vibrator, commonly known by. The aim of this lecture is to discuss the basic principles of reflection seismics. Currently construction of the underground research facility, onkalo, is going on at the olkiluoto site. What are consequences of the reciprocity principle. Marine seismology is simply seismology in which the observations are made at sea. This article may be confusing or unclear to readers.
Basic principles of reflection and refraction seismology. This article was most recently revised and updated by john p. Basic principles of the seismic method tu delft ocw. Reflection frequencies decrease with depth because of. Reflection seismology, analysis of vibrations caused by manmade explosions to determine earth structures, generally on a large scale. Seismic 2d reflection processing and interpretation of shallow refraction data abstract posiva oy takes care of the final disposal of spent nuclear fuel in finland. In principle, could be improved using aftershock calibration. Fermats principle states that the ray path taken is the one requiring the minimum amount of time. A method similar to reflection seismology which uses electromagnetic instead of elastic waves is known as groundpenetrating radar or gpr. The method requires a controlled seismic source of energy, such as dynamite or tovex blast, a. In seismology, we use ray tracing to study subsurface geology and.
An introduction to seismology, earthquakes, and earth structure seth stein department of geological sciences, northwestern university, evanston, illinois. It can be used to derive important details about the geometry of structures and their physical properties. After introduction of the history of seismology and instrument, the module will go through fundamental components of seismic wave theory, source theory and the use of seismic observations in constraining earths interior and earthquake source property. Reflection seismology is a type of geophysical imaging technique used to image the subsurface part of the earth and understand its geology. Basics seismic reflection events are caused by the impedance contrasts at layer interfaces. Principles of seismology agustin udias, agustin udias. Introduction basic concept fermats principle basic concept huygens principle basic concept snells law. Used in the fields of engineering geology, geotechnical engineering and exploration geophysics, seismic refraction traverses seismic lines are performed using a seismographs andor geophones, in an array and an energy source. Reflection seismology has a broad range of applications and is used primarily by the oil and gas industry to provide highresolution maps and build a coherent geological story from maps of processed seismic reflections. The principle of the bending method of ray tracing is to. In this technique, seismic acoustic echoes from explosive or vibratory, andor acoustic sources are.
Seismic studies to represent reliably the subsurface geology, require quality data, which depend on signaltonoise ratio and resolution, the latter being the ability to image thin geologic features separately. Both angles are typically measured with respect to the normal to the surface. This book describes basic seismology in the context of earthquakes and exploration seismology. Machine learning applications to geophysical data analysis. This module covers basic principle of modern seismology. Combined with seismic attribute analysis and other exploration geophysics tools, it aids geologists. Seismology is the study of earthquakes and associated phenomena, most notably the physical properties of the earths interior. Seismic techniques are commonly used to determine site geology, stratigraphy, and rock quality. In principle, what we need is a formulation of the seismic source, equations to describe elastic wave propagation once motion has. In reflection seismology we record seismic pulses that are reflected from boundaries which separate layers that have different acoustic impedances. N ow lets use huygens principle to derive the direction of a reflected ray that is not perpendicular to the reflecting surface. Seismic reflection events are caused by the impedance contrasts at layer interfaces having a minimum width fresnel zone. Normal moveout n in reflection seismology between a.
Digital imaging 39 reflection seismology 39digital processing. Seismic reflection is the most widely used geophysical technique. Earthquake location time reversal beamforming and array processing migration in reflection seismology adjoint methods. Major fields of application of seismic reflection include. The two most important seismic methods are reflection and. Later arriving complications in the recorded ground motion are discarded.
The term seismic interferometry refers to the principle of generating new seismic responses by crosscorrelating seismic observations at different receiver locations. Petroleum geology fundamentals of engineering geology. Greens function representations for seismic interferometry kees wapenaar. This website beta version contains information on geophysical methods, references to geophysical citations, and a glossary of geophysical terms related to environmental applications. Every point on the wave front is a source of a new wave that travels out of it in the form of spherical shells. Reflection seismology wikimili, the best wikipedia reader.
Raypaths are lines that show the direction that the seismic wave is propagating. You can investigate a hot new topic in data processing or analysis e. A clear indication of this trend are the results of the international symposium on deep structure of the continental crust. For free space, the onedimensional wave equation is derived. Thus, the data set derived from refraction experiments consists of a series of times versus distances. The first version of this principle was derived by claerbout 1968, who showed that the reflection. Reflection seismology sumeet trehan december, 20 submitted as coursework for ph240, stanford university, fall 20 introduction. Is the largest amplitude in the reflected or transmitted wave. The law of reflection and refraction can be derived by. Seismic resolution is controlled by the bandwidth of the signal, which is typically f30140 hz. Seismic refraction is a geophysical principle see refraction governed by snells law. Figure 4 is karchers 1921 migration diagram of the viola interface as given by an envelope of circular arcs. Basic principles of seismology university of alberta.
Seismic wave fields are recorded by a seismometer, hydrophone in water, or accelerometer. Seismology i wave propagation the propagation of light huygens principle before maxwells equations were developed huygens and fermat could describe the propagation of light using their empirically determined principles. An swave in rock approaching a boundary of a lake will have an swave reflection, a pwave reflection, and a likely pwave refraction into the lake water depending on the properties and incident angle. Each time a geophysicist does a prestack depth migration, he or she is using a method based upon the fundamental concept known as huygens principle which may be summarized as follows. The proof is based on a novel variational principle, from which numerical algorithms have been derived. After introduction of the history of seismology and instrument, the module will go through fundamental components of seismic wave theory, source theory and the use of seismic observations in constraining earths.
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