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Topic: Seismic reflection

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	Reflection seismology - Wikipedia, the free encyclopedia
		Reflection seismology is a branch of seismology that uses reflected seismic waves to produce images of the Earth's subsurface.
		The amplitude of the reflected wave is predicted by multiplying the amplitude of the incoming wave by the seismic reflection coefficient R, determined by the impedance contrast between the two materials.
		In this case, the expressions for the reflection and transmission coefficients are found by applying appropriate boundary conditions to the wave equation, a topic beyond the scope of this article.
	en.wikipedia.org /wiki/Reflection_seismology (2117 words)

	About the seismic reflection profiling technique
		The process that moves the reflections in their correct spatial position is referred to as migration, and the resulting seismic section is referred to as a migrated section.
		Seismic reflection profiling is the principal method by which the petroleum industry explores for hydrocarbon-trapping structures in sedimentary basins.
		The source moves along the seismic line and generates seismic waves at regular intervals such that points in the subsurface, such as point P in Figure 1, are sampled more than once by rays impinging on that point at different angles.
	www.litho.ucalgary.ca /atlas/seismic.html (693 words)

	Utah BLM Stone Cabin 3D Seismic Survey (Site not responding. Last check: 2007-10-24)
		Seismic exploration is the use of seismic energy to probe beneath the surface of the earth, usually as an aid in searching for economic deposits of oil, gas or minerals, but also for engineering, archeological and scientific studies.
		When seismic waves generated by dynamite or vibroseis reach a bedding plane separating rocks of different acoustic density, then a portion of the waves reflects back to the surface, causing the ground surface to rise or fall depending on whether the expansion or compression phase of the wave is being recorded.
		Most onshore seismic data is acquired using vibroseis, where the energy source is a giant vibrator truck in which a pad in the middle of the truck rests directly on the ground to raise the truck so that the pad supports the full weight of the vehicle.
	www.ut.blm.gov /stonecabin/seismicscience.htm (1847 words)

	NJDEP - New Jersey Geological Survey - Seismic Methods
		Seismic refraction surveys are commonly used to determine the thickness of unconsolidated materials overlying bedrock (overburden thickness) and depth to the water table.
		The seismic reflection method records acoutic waves at the surface that are reflected off of subsurface stratigrphic interfaces where changes in the material density and conductive velocity of the acoustic waves are significant.
		Seismic reflection surveys are used for determining the thickness and structure of subsurface geology and are commonly applied in hydrocarbon and mineral exploration, earthquake and tectonic studies, and in the marine enviromant for resolving stratigraphic details (for example, the location and thickness of beach-sand deposits).
	www.state.nj.us /dep/njgs/geophys/seis.htm (315 words)

	Oilfield Glossary: Term 'reflection' (Site not responding. Last check: 2007-10-24)
		There are two laws of reflection, which state (1) that incident rays, reflected rays and the normal to the reflecting interface at the point of incidence are coplanar, and (2) that the angle of incidence is equal to the angle of reflection.
		Reflection seismic surveys are useful for mapping geologic structures in the subsurface, interpreting sedimentary environments and evaluating hydrocarbon accumulations that might occur as amplitude anomalies.
		Reflection surveys are complicated by the variation of velocity as well as the various types of wave energy that are propagated within the Earth.
	www.glossary.oilfield.slb.com /Display.cfm?Term=reflection (154 words)

	Seismic Techniques (Site not responding. Last check: 2007-10-24)
		Due to the dependence of seismic velocity on the elasticity and density of the material through which the energy is passing, seismic refraction surveys provide a measure of material strengths and can consequently be used as an aid in assessing rippability and rock quality.
		Seismic reflection profiling involves the measurement of the two-way travel time of seismic waves transmitted from surface and reflected back to the surface at the interfaces between contrasting geological layers.
		In most reflection surveys shots are deployed at a number of different positions in relation to the geophone array in order to obtain reflections from the same point on the interface at different geophones in the array.
	www.geophysics.co.uk /mets3.html (3087 words)

	KGS--Shallow Seismic
		Seismic Reflection is commonly used to provide images of the subsurface, particularly in oil and gas exploration.
		Seismic reflection technology has been applied to characterizing the shallow geology at locations that are environmentally contaminated; in detecting shallow subsurface voids that might be related to sinkholes, tunnels, or construction; in mapping faults or bedrock surfaces; and in other situations.
		More recently, near Ellsworth, KS seismic reflection was used to examine the cause of a large sinkhole that threatened to damage a nearby highway.
	www.kgs.ku.edu /Geophysics/shalseis.html (501 words)

	Seismic Refraction / Reflection
		Seismic surveys are also a cost-effective way to extend information derived from borehole logs over a much larger area, minimizing the need for costly multiple borings.
		Crosshole seismic surveys are used to determine geotechnical properties of rock and soil.
		Seismic surveys measure the time it takes for reflected/refracted energy waves travelling through the earth to return to the surface.
	www.hager-richter.com /seismic.htm (499 words)

	Reflection Seismic Profiling of the Wabash Valley Fault System in the Illinois Basin
		A strong reflection seismic event is interpreted as the response to a low-velocity layer of approximately 200-m thickness within the Upper Cambrian Eau Claire Formation.
		Seismicity in the area may be related to zones of crustal weakness associated with these structures.
		Seismic lines 1–3 were acquired by students under our direction as part of a field course in seismic exploration at the University of Southern Indiana during the summers of 1988-90.
	igs.indiana.edu /geology/structure/seismicProfiling/index.cfm (1252 words)

	SOFIA - OFR 02-325 - Methods - Lake Belt Study Area: High-Resolution Seismic Reflection Survey, Miami-Dade County ...
		Seismic reflection data is used to image and map sedimentary and structural features of the seafloor and subsurface.
		Seismic reflection profiles are acquired by means of an acoustic source (usually generated electronically) and a hydrophone or hydrophone array.
		Colors highlight high-amplitude reflections that may indicate horizons or surfaces that are acoustically different from the surrounding rock material and are not intended to be consistent in all figures, except for the top green highlighted reflection as the first contact of canal bottom bedrock.
	sflwww.er.usgs.gov /publications/ofr/02-325/methods.html (1794 words)

	Seismic Reflection Methods
		The unique advantage of seismic reflection data is that it permits mapping of many horizon or layers with each shot..
		A variant of seismic reflection used at the surface of water bodies is subbottom profiling or imaging.
		Some of this energy transmitted by the source is reflected from the sediments at the water bottom, and the reflections are recorded by the receiver and stored digitally.
	www.freewebtown.com /geophysics2/seis2.html (2920 words)

	Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in ... (Site not responding. Last check: 2007-10-24)
		Seismic reflection and refraction data acquired in Canada Basin, Northwind Ridge and Northwind Basin, Arctic Ocean in 1988, 1992 and 1993.
		Seismic reflection and refraction data were collected in generally ice-covered waters of the Canada Basin and the eastern part of the Chukchi Continental Borderland of the Amerasia Basin, Arctic Ocean, during the late summers of 1988, 1992, and 1993.
		In 1992 and 1993, 500 and 1,900 km, respectively, of seismic reflection profile data were acquired with an improved six air gun, 674 to 1303 cubic inch tuned seismic source array and the same two-channel streamer.
	pubs.usgs.gov /of/2004/1243 (372 words)

	Sea-Floor Mapping Technology -- Data Acquisition (Site not responding. Last check: 2007-10-24)
		Seismic profiles are analogous to two-dimensional geologic cross-sections, however the vertical scale is in units of time, not distance.
		Seismic reflection profiling is accomplished by towing a sound source that emits acoustic energy in timed intervals behind a research vessel.
		The reflected acoustic signal is received by a ship-towed hydrophone (or array of hydrophones), which converts the reflected signal to a bipolar analog signal.
	woodshole.er.usgs.gov /operations/sfmapping/dataacq.htm (432 words)

	The Seismic Reflection Method - Frontier Geosciences Inc
		The goal of a high resolution seismic survey is to provide an image of the subsurface that is as detailed as possible, within the limits imposed by the nature of acoustic wave propagation in the earth.
		The 2D seismic method entails propagation of the acoustic waves through the earth from a surface pattern of source and receiver points.
		A number of seismic events are present in each seismogram in addition to the reflections of interest.
	www.frontiergeo.com /seis_reflect.html (477 words)

	High-resolution multichannel seismic-reflection data acquired in the northern Gulf of Mexico, 1998-99
		Marine seismic reflection data are used to image and map sedimentary and structural features of the seafloor and subsurface.
		Multichannel seismic reflection profiles are acquired by means of an acoustic source (usually compressed air discharged via an air gun or water gun), and a hydrophone array.
		The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), and detected at the hydrophone.
	geo-nsdi.er.usgs.gov /metadata/open-file/02-368/metadata.html (1405 words)

	Seismic Methods: Refraction and Reflection (Site not responding. Last check: 2007-10-24)
		In seismic surveying, ground movement caused by some source* is measured at a variety of distances from the source.
		One of the first active seismic experiments was conducted in 1845 by Robert Mallet, considered by many to be the father of instrumental seismology.
		The seismic reflection method, now the most commonly used seismic method in the oil industry, was first demonstrated in Oklahoma in 1921.
	www.geo.ucalgary.ca /~maillol/goph365/SEIS/sintro.html (621 words)

	Seismic Waves Inside Earth
		The amount of time that it takes for a seismic wave to pass through the earth is dependent on the material that it encounters along its path.
		Diagram of Simultaneous Reflection and Refraction showing how part of the light from the fisher is refracted through the air-water interface to the fish and how, simultaneously, the remainder of the light from the fisher is reflected by the air-water interface into the "roving eye".
		A lower angle of incidence promotes more reflection at the expense of refraction (if the fisher looks across the water he/she is more likely to see a reflection, but if looking down directly into the water, he/she is more likely to see into the water (a refraction).
	faculty.weber.edu /bdattilo/shknbk/Notes/insdearth.htm (1182 words)

	Seismic Reflection and Refraction (Site not responding. Last check: 2007-10-24)
		Seismic methods of subsurface evaluation involve directing an intense sound source into the ground and spreading receivers called geophones, analogous to microphones, across the ground.
		Seismic refraction surveys are more suitable for shallow exploration and definition of geologic surfaces, such as bedrock or the water table.
		Seismic methods of subsurface evaluation involve the generation of pulses of energy, usually at the ground surface, consisting of compression, shear and surface waves that propagate through the ground and either dissipate, are reflected back toward the surface, or are refracted at and travel along lithologic boundaries.
	www.epsci.ameslab.gov /etd/technologies/projects/esc/technologies/seismicrefraction.html (635 words)

	Seismic Reflection Data: Revealing Locations And Potentials For Mega Earthquakes -- The Earth Institute at Columbia ... (Site not responding. Last check: 2007-10-24)
		From the reflection data, Nedimovic and his coauthors mapped the locked zone on the megathrust along the northern Cascadia margin, which hosts the populous cities of Vancouver and Seattle.
		Seismic and aseismic slip occurs on different parts of a megathrust, at different depths, temperatures, and pressures, and due to different types of rock deformation.
		Seismic reflection imaging reveals the variations in structures along the megathrust and can be used for detailed mapping of locked and slow-slipping zones.
	www.earthinstitute.columbia.edu /news/2003/story08-08-03.html (832 words)

	Seismic imaging of active faults
		Seismic reflection profiling, which uses sound waves to look into the Earth, is a valuable tool for examining faults beneath the surface.
		The paper has important implications for seismic hazard estimates, such as revising estimates of the total area of the faults in the region and the structural interpretation of those faults.
		In this project we examined seismic reflection data donated by ARCO, Alaska, to examine the geometry of faults in the region and to determine whether they cut young geologic strata.
	faculty.washington.edu /tpratt/high-res-imaging.htm (982 words)

	High-resolution seismic-reflection surveys in the nearshore of outer Cape Cod, Massachusetts, Open-File Report 03-235, ... (Site not responding. Last check: 2007-10-24)
		Based on this, the similarities of the seismic facies, and their position beneath the Eastham plain deposit, we infer that they are of the same unit.
		East of outer Cape Cod, the regressive unconformity (ru) is not observed in the seismic profiles because much of the upper stratigraphic record east of our seismic profiles was removed by marine erosion during the Holocene transgression.
		The Holocene transgressive unconformity is the surface (tu) mapped by Oldale and O'Hara (1990) in the deeper water of Cape Cod Bay.
	pubs.usgs.gov /of/2003/of03-235/html/inter.html (1259 words)

	Seismic Reflection
		The physical process of reflection is illustrated in FIGURE 1 where raypaths for successive layers are shown.
		Thus, seismic reflection data are more complex than refraction data because it is these later arrivals that yield information about the deeper layers.
		It is possible to obtain seismic reflections from very shallow depths, perhaps as shallow as 3 to 5 m (10-16 ft).
	www.microgeo.com /dm2.htm (1429 words)

	The University of Melbourne - 625-304 Applied Geophysics - Seismic
		Seismic exploration is the conduit for most expenditure in geophysical exploration by a wide margin.
		This is a response to the recognition of the highly effective way seismic data images the geometry of subsurface rocks, especially in sedimentary provinces, over almost all scales and in most environments on and off shore.
		Processing of seismic data enables the recognition of even details of past depositional environments from the features preserved as differences in the elastic properties of rocks.
	www.earthsci.unimelb.edu.au /Thomas/lt304/es304seis.html (949 words)

	LAB 4: Subsurface Information from Interpretation of Seismic Reflection Data (Site not responding. Last check: 2007-10-24)
		Generally, reflection seismic data are used after extensive data processing manipulations.
		Seismic waves were recorded on magnetic tape using a 48 channel system with geophones at 35 meter intervals in a line extending from 70 meters to 1715 meters from the vibroseis energy source.
		The large amplitude reflections at about 700 milliseconds on the trace with 105 meters offset are from the basalt flow.
	basalt.geol.vt.edu /mgi/3104/node8.html (455 words)

	GEOWARN - Sea Floor Seismic Reflection Soundings (Generation of a Local Velocity Model)
		Deep seismic soundings and active tomography provided the data needed for developing a velocity-depth model of the volcanic structure, the crust and the upper mantle.
		Tomographic inversion and modeling of the magmatic intrusions and the sedimentary and crustal structures in 2-D and 3-D has resolved the velocity structures at shallow depth and provided the means for a 3-D block presentation of the subvolcanic intrusions and their spatial distribution.
		They record seismic signals using three geophones and one hydrophone and already have been widely deployed for marine seismological observations as well as active seismic experiments.
	www.geowarn.ethz.ch /index.asp?ID=5&cat=121 (610 words)

	Seismic Plugin by Jay Lieske Jr. (Site not responding. Last check: 2007-10-24)
		But much seismic reflection data is not corrected for the seismic velocities within the profile-- so the profile displays time, not true depths.
		Although the depth correction of digital seismic data is straightforward, there are situations where traditional techniques cannot be applied-- for example, when only printouts of the profiles exist, or when the software for processing digital seismic data is inconvenient to use.
		Seismic Plugin provides an alternative tool for analysis: the geologist can scan the printout of a seismic profile and perform calculations on the scanned image to simulate seismic processing, such as depth correction and reflector unfolding.
	home.earthlink.net /~jayjude/seismic (366 words)

	LAB 6: Interpretation of Seismic Reflection Data by Modeling (Site not responding. Last check: 2007-10-24)
		As you shall see during the demonstration, actual recorded paths of seismic waves are too complicated to be plotted for examination.
		This complexity of the seismic sections can be reduced by relocating the recorded waves in the profile-time plane.
		Migration processing of seismic waves from a complex subsurface can be done by the wave equation extrapolations which are all computer intensive jobs.
	basalt.geol.vt.edu /mgi/3104/node10.html (708 words)

	Hasbrouck Geophysics, Inc.: Contaminant Pathway (Shallow 3D Reflection Seismic)
		Seismic energy was generated at 13 source points along line A and received by 24 geophones along line C.
		Reflection midpoints are highlighted for geophone numbers 1 and 24 and for sources 1 through 13.
		Compressional-wave (P-wave) and shear-wave seismic time sections for common geophone midpoints 4 through 15 were converted to depth by applying velocities and static corrections, and the predominant reflectors were digitized.
	www.hasgeo.com /3dseis.htm (628 words)

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