Reflection seismology

Seismic reflection data

Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a seismic vibrator, commonly known by the trademark name Vibroseis. Reflection seismology is similar to sonar and echolocation. This article is about surface seismic surveys, for vertical seismic profiles, see VSP.

Outline of the method

Seismic waves are mechanical perturbations that travel in the Earth at a speed governed by the acoustic impedance of the medium in which they are travelling. The acoustic (or seismic) impedance, Z, is defined by the equation:

$Z=V\rho \$,

where V is the seismic wave velocity and ρ (Greek rho) is the density of the rock.

When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring the time taken for the waves to travel from the source, reflect off an interface and be detected by an array of receivers (or geophones) at the surface. Knowing the travel times from the source to various receivers, and the velocity of the seismic waves, a geophysicist then attempts to reconstruct the pathways of the waves in order to build up an image of the subsurface.

In common with other geophysical methods, reflection seismology may be seen as a type of inverse problem. That is, given a set of data collected by experimentation and the physical laws that apply to the experiment, the experimenter wishes to develop an abstract model of the physical system being studied. In the case of reflection seismology, the experimental data are recorded seismograms, and the desired result is a model of the structure and physical properties of the Earth's crust. In common with other types of inverse problems, the results obtained from reflection seismology are usually not unique (more than one model adequately fits the data) and may be sensitive to relatively small errors in data collection, processing, or analysis. For these reasons, great care must be taken when interpreting the results of a reflection seismic survey.

The reflection experiment

The general principle of seismic reflection is to send elastic waves (using an energy source such as dynamite explosion or Vibroseis) into the Earth, where each layer within the Earth reflects a portion of the wave’s energy back and allows the rest to refract through. These reflected energy waves are recorded over a predetermined time period (called the record length) by receivers that detect the motion of the ground in which they are placed. On land, the typical receiver used is a small, portable instrument known as a geophone, which converts ground motion into an analogue electrical signal. In water, hydrophones are used, which convert pressure changes into electrical signals. Each receiver’s response to a single shot is known as a “trace” and is recorded onto a magnetic tape, then the shot location is moved along and the process is repeated. Typically, the recorded signals are subjected to significant amounts of signal processing before they are ready to be interpreted and this is an area of significant active research within industry and academia. In general, the more complex the geology of the area under study, the more sophisticated are the techniques required to remove noise and increase resolution. Modern seismic reflection surveys contain large amount of data and so require large amounts of computer processing, often performed on supercomputers or computer clusters.

Reflection and transmission at normal incidence

P-wave reflects off an interface at normal incidence

When a seismic wave encounters a boundary between two materials with different acoustic impedances, some of the energy in the wave will be reflected at the boundary, while some of the energy will be transmitted through the boundary. The amplitude of the reflected wave is predicted by multiplying the amplitude of the incident wave by the seismic reflection coefficient $R$, determined by the impedance contrast between the two materials.

For a wave that hits a boundary at normal incidence (head-on), the expression for the reflection coefficient is simply

$R=\frac{Z_1 - Z_0}{Z_1 + Z_0}$,

where $Z_0$ and $Z_1$ are the impedance of the first and second medium, respectively.

Similarly, the amplitude of the incident wave is multiplied by the transmission coefficient to predict the amplitude of the wave transmitted through the boundary. The formula for the normal-incidence transmission coefficient (the ratio of transmitted to incident pressure amplitudes) is

$T=\frac{2 Z_0}{Z_1 + Z_0}$.

As the sum of the amplitudes of the reflected and transmitted wave has to be equal to the amplitude of the incident wave, it is easy to show that

$1-R=\frac{Z_1 + Z_0- Z_1+ Z_0}{Z_1 + Z_0}=\frac{Z_0 + Z_0}{Z_1 + Z_0} = T$.

By observing changes in the strength of reflectors, seismologists can infer changes in the seismic impedances. In turn, they use this information to infer changes in the properties of the rocks at the interface, such as density and elastic modulus.

Reflection and transmission at non-normal incidence

Diagram showing the mode conversions that occur when a P-wave reflects off an interface at non-normal incidence

The situation becomes much more complicated in the case of non-normal incidence, due to mode conversion between P-waves and S-waves, and is described by the Zoeppritz equations. In 1919, Karl Zoeppritz derived 4 equations that determine the amplitudes of reflected and refracted waves at a planar interface for an incident P-wave as a function of the angle of incidence and six independent elastic parameters. These equations have 4 unknowns and can be solved but they do not give an intuitive understanding for how the reflection amplitudes vary with the rock properties involved.

The reflection and transmission coefficients, which govern the amplitude of each reflection, vary with angle of incidence and can be used to obtain information about (among many other things) the fluid content of the rock. Practical use of non-normal incidence phenomena, known as AVO (see amplitude versus offset) has been facilitated by theoretical work to derive workable approximations to the Zoeppritz equations and by advances in computer processing capacity. AVO studies attempt with some success to predict the fluid content (oil, gas, or water) of potential reservoirs, to lower the risk of drilling unproductive wells and to identify new petroleum reservoirs. The 3-term simplification of the Zoeppritz equations that is most commonly used was developed in 1985 and is known as the "Shuey equation". A further 2-term simplification is known as the "Shuey approximation", is valid for angles of incidence less than 30 degrees (usually the case in seismic surveys) and is given below:

$R(\theta ) = R(0) + G \sin^2 \theta$

where $R(\theta)$ = reflection coefficient at zero-offset (normal incidence); $G$ = AVO gradient, describing reflection behaviour at intermediate offsets and $(\theta)$ = angle of incidence. This equation reduces to that of normal incidence at $(\theta)$=0.

Interpretation of reflections

The time it takes for a reflection from a particular boundary to arrive at the geophone is called the travel time. If the seismic wave velocity in the rock is known, then the travel time may be used to estimate the depth to the reflector. For a simple vertically traveling wave, the travel time $t$ from the surface to the reflector and back is called the Two-Way Time (TWT) and is given by the formula

$t = 2\frac{d}{V}$,

where $d$ is the depth of the reflector and $V$ is the wave velocity in the rock.

A series of apparently related reflections on several seismograms is often referred to as a reflection event. By correlating reflection events, a seismologist can create an estimated cross-section of the geologic structure that generated the reflections. Interpretation of large surveys is usually performed with programs using high-end three dimensional computer graphics.

Sources of noise

Sources of noise on a seismic record. Top-left: air wave; top-right: head wave; bottom-left: surface wave; bottom-right: multiple.

In addition to reflections off interfaces within the subsuface, there are a number of other seismic responses detected by receivers and are either unwanted or unneeded:

Air wave

The airwave travels directly from the source to the receiver and is an example of coherent noise. It is easily recognisable because it travels at a speed of 330 m/s, the speed of sound in air.

Ground Roll / Rayleigh wave / Surface wave

A Rayleigh wave typically propagates along a free surface of a solid, but the elastic constants and density of air are very low compared to those of rocks so the surface of the Earth is approximately a free surface. Low velocity, low frequency and high amplitude Rayleigh waves are frequently present on a seismic record and can obscure signal, degrading overall data quality. They are known within the industry as ‘Ground Roll’ and are an example of coherent noise that can be attenuated with a carefully designed seismic survey. The velocity of these waves varies with wavelength, so they are said to be dispersive and the shape of the wavetrain varies with distance.

Refraction / Head wave / Conical wave

A head wave refracts at an interface, travelling along it, within the lower medium and produces oscillatory motion parallel to the interface. This motion causes a disturbance in the upper medium that is detected on the surface. The same phenomenon is utilised in seismic refraction.

Multiple reflection

An event on the seismic record that has incurred more than one reflection is called a “multiple”. Multiples can be either short-path of long-path depending upon whether they interfere with primary reflections or not. .

Cultural noise

Cultural noise includes noise from planes, helicopters and electrical pylons and all of these can be detected by the receivers.

Applications

Reflection seismology is used extensively in a number of fields and its applications can be categorised into three groups, each defined by their depth of investigation:

• Near-surface applications – an application that aims to understand geology at depths of up to approximately 1km, typically used for engineering and environmental surveys, as well as coal and mineral exploration. A more recently developed application for seismic reflection is for geothermal energy surveys, although the depth of investigation can be up to 2km deep in this case.

• Hydrocarbon exploration - used by the hydrocarbon industry to provide a high resolution map of acoustic impedance contrasts at depths of up to 10km within the subsurface. This can be combined with seismic attribute analysis and other exploration geophysics tools and used to help geologists build a geological model of the area of interest.

• Crustal studies – investigation into the structure and origin of the Earth's crust, through to the Moho discontinuity and beyond, at depths of up to 100km.

A method similar to reflection seismology which uses electromagnetic instead of elastic waves, and has a smaller depth of penetration, is known as Ground-penetrating radar or GPR.

Hydrocarbon exploration

Reflection seismology, more commonly referred to as “seismic reflection” or abbreviated to “seismic” within the hydrocarbon industry, is used by petroleum geologists and geophysicists to map and interpret potential petroleum reservoirs. The size and scale of seismic surveys has increased alongside the significant concurrent increases in computer power during the last 25 years. This has led the seismic industry from laboriously – and therefore rarely – acquiring small 3D surveys in the 1980s to now routinely acquiring large-scale high resolution 3D surveys. The goals and basic principles have remained the same, but the methods have slightly changed over the years.

The primary environments for seismic exploration are land, the transition zone and marine:

Land - The land environment covers almost every type of terrain that exists on Earth, each bringing its own logistical problems. Examples of this environment are jungle, desert, arctic tundra, forest, urban settings, mountain regions and savannah.

Transition Zone (TZ) - The transition zone is considered to be the area where the land meets the sea, presenting unique challenges because the water is too shallow for large seismic vessels but too deep for the use of traditional methods of acquisition on land. Examples of this environment are river deltas, swamps and marshes, coral reefs, beach tidal areas and the surf zone. Transition zone seismic crews will often work on land, in the transition zone and in the shallow water marine environment on a single project in order to obtain a complete map of the subsurface.

Marine - The marine zone is either in shallow water areas (water depths of less than 30 to 40 metres would normally be considered shallow water areas for 3D marine seismic operations) or in the deep water areas normally associated with the seas and oceans (such as the Gulf of Mexico).

Seismic surveys are typically designed by National oil companies and International oil companies who hire service companies such as CGGVeritas, Petroleum Geo-Services and WesternGeco to acquire them. Another company is then hired to process the data, although this can often be the same company that acquired the survey. Finally the finished seismic volume is delivered the the oil company so that it can be geologically interpreted.

Land survey acquisition

Desert land seismic camp

Land crews tend to be quite large entities, employing anywhere from a few hundred to a few thousand people. They normally require substantial logistical support to cover not only the seismic operation itself, but also to support the main camp (for catering, waste management and disposal, camp accommodations, washing facilities, water supply, laundry etc.), fly camps (temporary camps set up away from the main camp on large land seismic operations, for example where the distance is too far to drive back to the main camp with vibrator trucks), all of the crew's vehicles (maintenance, fuel, spares etc.), security, possible helicopter operations, restocking of the explosive magazine, medical support and many other logistical and support functions.

Outside of the camp personnel, the basic components of a seismic land crew are the surveyors, layout and loading crew, shooters and recorders and the pick up crew. The general principle is for the surveyors to survey in shot and receiver points on source and receiver lines (the latitude and longitude coordinates of which are pre-determined by the client / contractor) using mobile GPS stations. When a shot or receiver point is reached, this position will be staked out or marked with the shot or receiver station number and line number.

Once sufficient lines of shot and receiver points have been surveyed in and shot holes have been drilled to the appropriate depth, loaders put explosive charges into the shot holes on the source lines (according to the project specification) and the receiver stations will be laid out with geophone spreads on the receiver lines. When corresponding shot and receiver lines are ready, the shooters prepare a single shot hole ready for firing, whilst the recording shack will be hooked up to the geophone spread laid on the corresponding receiver line to record the reflected data. Once a charge is ready to be shot, the recording shack initiates the shot hole firing sequence via a radio link and records the seismic data from the whole geophone spread onto magnetic medium. Once a shot is completed, the shooters move to the next shot hole and the shoot / record sequence begins again.

Receiver line on a desert land crew with recorder truck

Once lines have been shot, loaders continue to load shot holes on new source lines and the pick up crews pick up and relay geophone spreads onto new receiver lines as required in the acquisition plan. For vibrator crews, aka "Vibroseis" (vibrations are created by the computer-coordinated vibration of hydraulically controlled plates on vibrator trucks), the vibrator trucks move from shot hole to shot hole on the designated source line instead of the loaders and shooters.

Land surveys require crews to deploy the hundreds or thousands of geophones necessary to record the data. Most surveys today are conducted by laying out a two-dimensional array of geophones together with a two-dimensional pattern of source points. This allows the interpreter to create a three-dimensional image of the geology beneath the array, so these are called 3D surveys. Less expensive survey methods use one-dimensional lines of geophones that only allowed the interpreter to make two-dimensional cross-sections.

Marine survey acquisition (streamer)

Marine seismic survey using a towed streamer

Seismic data collected by the USGS in the Gulf of Mexico

Deep water marine seismic surveys are conducted using purpose built vessels capable of towing one or more seismic cables or "streamers" (see figure) just below the sea surface, along with an energy source towed just below the surface and between the stern of the vessel and the head of the streamers. Modern 3D surveys use multiple streamers deployed in parallel and often multiple energy sources (commonly two), to record data suitable for the three-dimensional interpretation of the structures beneath the sea bed. A single vessel may tow anything up to 10+ streamers, each 6 km+ in length, spaced 50–150 m apart. Hydrophones are built into the streamers at regular intervals; these record and digitize the energy waves which are reflected back from sub-sea structures. To accurately calculate where subsurface features are located, navigators compute the position of both the energy source and each hydrophone group which records the signal. The positioning accuracy required is achieved using a combination of acoustic networks, compasses and GPS receivers (often used with a radio correction applied call a differential GPS or DGPS).

A modification on this basic technique can also be used to record sub surface data directly underneath offshore structures, predominantly exploration and production platforms and other permanent offshore structures such as FPSO's (floating production, storage and offloading unit) which cannot be moved to facilitate a survey vessel; this technique is known as undershooting. This requires a separate source vessel and a streamer vessel to pass either side of the obstruction, firing the energy source on the source vessel and recording the reflected data on the towed streamers on the streamer vessel. Both vessels are linked by a data telemetry system to co-ordinate and synchronise the firing and recording operations. By varying the distance from the source and streamer vessel to the obstruction (changing the offset), a wide swathe of data can be collected from underneath the obstruction without any disturbance to the permanent offshore operation.

Marine survey acquisition (OBC)

Marine surveys can also be conducted using sensors attached to an Ocean Bottom Cable (OBC) laid out on the ocean bottom rather than in towed streamers. Due to operational limitations, most of these types of surveys are conducted in water depths less than 70 meters, however OBC crews in recent years have acquired 3D surveys in depths up to 2000 meters. One operational advantage is that obstacles (such as platforms) do not limit the acquisition as much as they do for streamer surveys. Most of the OBC surveys use dual component receivers, combining a pressure sensor (hydrophone) and a vertical particle velocity sensor (vertical geophone). OBC surveys can also use four component, i.e. a hydrophone components plus the three orthogonal velocity sensors. Four component OBC surveys have the advantage of being able to also record shear waves, which do not travel through water. Multiple component OBC surveys hence can lead to improved subsurface imaging. Ocean Bottom Cable surveys can also cost significantly more than conventional streamer surveys over the same area. This additional cost is usually only justified when the improved imaging is required for accurate reservoir delineation, or when surface obstacles prevent a conventional streamer survey from being acquired in the area.

Seismic data processing

See also: Deconvolution and Seismic migration

There are three main processes in seismic data processing: deconvolution, common-midpoint (CMP) stacking and migration.

Deconvolution is a process that tries to extract the reflectivity series of the Earth, under the assumption that a seismic trace is just the reflectivity series of the Earth convolved with distorting filters. This process improves temporal resolution by collapsing the seismic wavelet, but it is nonunique unless further information is available such as well logs, or further assumptions are made. Deconvolution operations can be cascaded, with each individual deconvolution designed to remove a particular type of distortion.

CMP stacking is a robust process that uses the fact that a particular location in the subsurface will have been sampled numerous times and at different offsets. This allows a geophysicist to construct a group of traces with a range of offsets that all sample the same subsurface location, known as a Common Midpoint Gather. The average amplitude is then calculated along a time sample, resulting in significantly lowering the random noise but also losing all valuable information about the relationship between seismic amplitude and offset. Less significant processes that are applied shortly before the CMP stack are NMO correction and statics correction. Unlike marine seismic data, land seismic data has to be corrected for the elevation differences between the shot and receiver locations. This correction is in the form of a vertical time shift to a flat datum and is known as a statics correction, but will need further correcting later in the processing sequence because the velocity of the near-surface is not accurately known. This further correction is known as a residual statics correction.

Seismic migration is the process by which seismic events are geometrically re-located in either space or time to the location the event occurred in the subsurface rather than the location that it was recorded at the surface, thereby creating a more accurate image of the subsurface.

Seismic attribute analysis

See also: Seismic attribute

Seismic attribute analysis involves extracting or deriving a quantity from seismic data that can be analysed in order to enhance information that might be more subtle in a traditional seismic image, leading to a better geological or geophysical interpretation of the data. Examples of attributes that can be analysed include mean amplitude, which can lead to the delineation of bright spots and dim spots, coherency and amplitude versus offset. Attributes that can show the presence of hydrocarbons are called direct hydrocarbon indicators.

Crustal studies

The use of reflection seismology in studies of tectonics and the Earth's crust was pioneered by groups such as the Consortium for Continental Reflection Profiling (COCORP) [2],[3].

Environmental impact

As with all human activities, reflection seismic experiments may impact the Earth's natural environment. On land, conducting a seismic survey may require the building of roads in order to transport equipment and personnel. Even if roads are not required, vegetation may need to be cleared for the deployment of geophones. If the survey is in a relatively undeveloped area, significant habitat disturbance may result. Many land crews now use helicopters instead of land vehicles in remote areas. Most countries require that seismic surveys are conducted according to environmental standards established by government regulation. Higher environmental standards have encouraged the development of lower impact seismic vehicles and acquisition methodologies. Similarly modern seismic processing techniques allow seismic lines to deviate around natural obstacles, or use pre-existing non-straight tracks and trails with less loss of data quality than would once have been the case. The more recent use of inertial navigation instruments for land survey instead of theodolites decreased the impact of seismic by allowing the winding of survey lines between trees.

The main environmental concern for marine surveys is the potential of seismic sources to disturb animal life, especially cetaceans such as whales, porpoises, and dolphins. Surveys involves towing an array of 15-45 pneumatic air guns below the ocean surface behind the survey vessel and emit sound pulses of a “predominantly low frequency (10–300 Hz), high intensity (215-250 dB). These animals have sensitive hearing, and some scientists believe the underwater sound waves created by air guns might disturb the animals or even damage their ears. Seismic surveying can damage the reproductive processes, auditory functions and other damaging effects to highly lucrative marine species (lobster, crab) and it poses potentially fatal effects to marine mammals.^{[citation needed]} Seismic testing is not fully responsible for whales running ashore or becoming stranded, but there is evidence that it plays a major role.^{[citation needed]} Studies of seismic effects on several whale species such as Gray, Bowhead, Blue, Humpback and Sperm whales indicated substantial effects in behavior, breathing, feeding and diving patterns.^{[citation needed]} Dr. Bernd Würsig, a professor for marine biology at Texas A&M University in Galveston, Texas states that the Gray whale will avoid its regular migratory and feeding grounds by >30 km in areas of seismic testing. Similarly the breathing of gray whales was shown to be more rapid, indicating discomfort and panic in the whale. It is circumstantial evidence such as this that has led researchers to believe that avoidance and panic might be responsible for increased whale beachings although research is ongoing into these questions.

However, the research carried out by both the E&P (exploration and production) sector and by environmental groups needs to be considered carefully in terms of impartiality as both may reference research or publish data that only promotes their own aims and goals. For example, the following quote comes from a position paper published by an E&P representative group which would appear to contradict the conclusions stated above. The quote from the executive summary states that:

"The sound produced during seismic surveys is comparable in magnitude to many naturally occurring and other man-made sound sources. Furthermore, the specific characteristics of seismic sounds and the operational procedures employed during seismic surveys are such that the resulting risks to marine mammals are expected to be exceptionally low. In fact, three decades of world-wide seismic surveying activity and a variety of research projects have shown no evidence which would suggest that sound from E&P seismic activities has resulted in any physical or auditory injury to any marine mammal species."

History

Reflections and refractions of seismic waves at geologic interfaces within the Earth were first observed on recordings of earthquake-generated seismic waves. The basic model of the Earth's deep interior is based on observations of earthquake-generated seismic waves transmitted through the Earth’s interior (e.g., Mohorovičić, 1910). The use of human-generated seismic waves to map in detail the geology of the upper few kilometers of the Earth's crust followed shortly thereafter and has developed mainly due to commercial enterprise, particularly the petroleum industry.

The Canadian inventor Reginald Fessenden was the first to conceive of using reflected seismic waves to infer geology. His work was initially on the propagation of acoustic waves in water, motivated by the sinking of the Titanic by an iceberg in 1912. He also worked on methods of detecting submarines during World War I. He applied for the first patent on a seismic exploration method in 1914, which was issued in 1917. Due to the war, he was unable to follow up on the idea. Meanwhile, Ludger Mintrop, a German mine surveyor, devised a mechanical seismograph in 1914 that he successfully used to detect salt domes in Germany. He applied for a German patent in 1919 that was issued in 1926. In 1921 he founded the company Seismos, which was hired to conduct seismic exploration in Texas and Mexico, resulting in the discovery of the first commercial discovery of oil using the seismic method in 1924. John Clarence Karcher discovered seismic reflections independently while working for the United States Bureau of Standards (now the National Institute of Standards and Technology) on methods of sound ranging to detect artillery. In discussion with colleagues, the idea developed that these reflections could aid in exploration for petroleum. With several others, many affiliated with the University of Oklahoma, Karcher helped to form the Geological Engineering Company, incorporated in Oklahoma in April, 1920. The first field tests were conducted near Oklahoma City, Oklahoma in 1921.

The company soon folded due to a drop in the price of oil. In 1925, oil prices had rebounded, and Karcher helped to form Geophysical Research Corporation (GRC) as part of the oil company Amerada. In 1930, Karcher left GRC and helped to found Geophysical Service Incorporated (GSI). GSI was one of the most successful seismic contracting companies for over 50 years and was the parent of an even more successful company, Texas Instruments. Early GSI employee Henry Salvatori left that company in 1933 to found another major seismic contractor, Western Geophysical. As of 2005, after several mergers and acquisitions, the heritages of GSI and Western Geophysical still exist, along with several pioneering European companies such as GECO, Seismos, and Prakla, as part of the seismic contracting company WesternGeco. Many other companies using reflection seismology in hydrocarbon exploration, hydrology, engineering studies, and other applications have been formed since the method was first invented. Major service companies today include CGGVeritas, ION Geophysical, Petroleum Geo-Services and Fugro. Most major oil companies also have actively conducted research into seismic methods as well as collected and processed seismic data using their own personnel and technology. Reflection seismology has also found applications in non-commercial research by academic and government scientists around the world.

See also

• Deconvolution
• SEG Y, a popular file format for seismic reflection data
• Depth conversion, the conversion of acoustic waves two-way travel time to actual depth
• Seismic waves
• Seismic refraction
• Swell filter
• Passive seismic
• Seismic migration
• Synthetic seismogram
• Seismic Unix, open source software for processing of seismic reflection data
• Exploration geophysics

Further reading

The following books cover important topics in reflection seismology. Most require some knowledge of mathematics, geology, and/or physics at the university level or above.

• Brown, Alistair R. (2004). Interpretation of three-dimensional seismic data (sixth ed. ed.). Society of Exploration Geophysicists and American Association of Petroleum Geologists. ISBN 0891813640. 
• Biondi, B. (2006). 3d Seismic Imaging: Three Dimensional Seismic Imaging. Society of Exploration Geophysicists. ISBN 0-07-011117-0. http://sepwww.stanford.edu/data/media/public/sep//biondo/3DSI_frame.html. 
• Claerbout, Jon F. (1976). Fundamentals of geophysical data processing. McGraw-Hill. ISBN 1560801379. http://sepwww.stanford.edu/data/media/public/sep//prof/fgdp/toc_html/. 
• Ikelle, Luc T. and Lasse Amundsen (2005). Introduction to Petroleum Seismology. Society of Exploration Geophysicists. ISBN 1-56080-129-8. 
• Scales, John (1997). Theory of seismic imaging. Golden, Colorado: Samizdat Press. http://samizdat.mines.edu/imaging/. 
• Yilmaz, Öz (2001). Seismic data analysis. Society of Exploration Geophysicists. ISBN 1-56080-094-1. 
• Chapman, C. H. (2004), Fundamentals of Seismic Wave Propagation (Cambridge University Press, Cambridge).

Further research in reflection seismology may be found particularly in books and journals of the Society of Exploration Geophysicists, the American Geophysical Union, and the European Association of Geoscientists and Engineers.

References

• Biography of Henry Salvatori
• History of reflection seismology in Oklahoma
• Milson, J., 2005, Field Geophysics, University College of London, Wiley Publications

External links

• Reflection Seismology Literature at Seismic Laboratory for Imaging and Modeling
• Reflection Seismology Literature at Stanford Exploration Project
• Website of the International Association of Geophysical Contractors
• IAGC/OGP position paper on seismic surveys and marine mammals (PDF)
• Tutorial on seismic reflection data processing
• A guide to marine High-Resolution Seismic / Sub-Bottom Profiler acquisition and processing and image galleries
• Overview of IAGC Marine Geophysical Operations Educational CD - 1 http://www.youtube.com/watch?v=2XlI6rp5F48