migrated time
Explanation:
(seismic survey) endorsement of the sismica information migrated in time despues to pile up
Earthquake Terms
Glossary of Earthquake Terms
Aftershock:
An earthquake that occurs after a "mainshock" (or larger earthquake). Aftershocks occur in the same general region as the "mainshock" and result from readjustments of stress at places along the fault zone. For large earthquakes (M=8) aftershocks may occur over hundred's of kilometres. Depending on the size, and depth of the earthquake, aftershocks may occur for many months after the mainshock. However, both the size, and the rate of aftershock activity dies off quickly with time.
Earthquake:
The sudden release of stored elastic energy caused by the sudden fracture and movement of rocks along a fault. Some of the energy released is in the form of seismic waves, that cause the ground to shake.
Earth's crust:
The earth's crust is the layer of rock located immediately below the earth's surface. Beneath continents, it is typically about 35 km thick, and composed of granite. Under the ocean, the crust is about 5-10 kilometres thick and mainly composed of basalt.
Epicentre:
The point on the earth's surface directly above the focus (hypocentre) of an earthquake is called the epicentre.
Foreshock:
An earthquake that is smaller than, and precedes, a "mainshock". Foreshocks tend to occur in the same area as the mainshock. Foreshocks have not been observed before damaging earthquakes in British Columbia.
Fault:
Faults are fractures or breaks between rocks where movements occur. Earthquakes occur along faults because they are weak zones in the rock. The only known seismically active surface faults in British Columbia are beneath the ocean off the west coast.
Hypocentre:
The focus is the subsurface location at which the energy of an earthquake is released. Earthquakes generally occur at depths less than about 30 km, but may occur to a depth of 600 km or more in some areas.
Intensity:
The intensity of an earthquake (how it was felt) is described by the Modified Mercalli Scale. These effects may range from I (not felt except by a very few under a especially favorable conditions) and XII (Damage total).
Mainshock:
The largest earthquake in a "cluster" of earthquakes. Mainshocks are sometimes precede by "foreshocks", and generally followed by aftershocks.
Plates and plate tectonics:
The crust and upper mantle of the earth is made up of about a dozen large plates and several smaller ones that are constantly moving. The movements are very slow - only a few centimetres each year. When the plates rub against one another, strain builds up, especially at the edges. When the strength of the rock is exceeded, the earth's crust may suddenly shift by several metres causing an earthquake.
Richter Scale:
Developed by Charles Richter, this scale is a measure of the size (magnitude) of an earthquake. It is estimated from the amplitude of the seismic waves that are recorded by sensitive instruments called seismographs. This can be used to estimate the energy released at the focus. The Richter scale is logarithmic, so that each whole number represents a tenfold increase in recorded amplitude. A magnitude of 7.0, for example, indicates measured amplitudes that are ten times greater than those of magnitude 6.0 and 100 times greater than those of magnitude 5.0.
Seismic waves:
Seismic waves are vibrations caused by the movement of rock within the earth's crust. When an earthquake occurs, seismic waves travel from the focus through the earth and up to the surface. The speeds at which the waves travel depend on the type of motion, and the type of rock through which they pass, and ranges from 1 to 10 kilometres per second.
Earthquakes create two main types of waves: compression waves (P-waves) and shear waves (S-waves). Only P-waves are able to travel through a liquid. They also travel the fastest, and arrive at the surface first. The S-waves travel more slowly, and arrive later. It is these two wave types that people often notice during an earthquake. The time difference between the P and the S-waves provides an indication of how far away the earthquake was.
Seismograph:
Seismographs are very sensitive instruments used to record and measure earthquakes. During an earthquake, vibrations initiated by fracturing of the earth's crust radiate outward from the point of fracture and are detected by seismographs. The visual record produced is called a "seismogram".
Subduction Zone:
A subduction zone is a region where the earth's plates collide, with one plate sliding beneath the other. The world's largest earthquakes occur along this type of plate boundary. The Cascadia subduction zone, extending from northern California to the north end of Vancouver Island, is one such area. The subducting ocean plate is about 40 km beneath Victoria, BC, and about 70 km beneath Vancouver.
Tsunami:
Tsunamis are huge ocean waves caused by underwater earthquakes. The waves of the tsunami spread in a circular manner from the point of disturbance at speeds that can reach more than 800 kilometres per hour. Tsunamis can travel across the ocean, causing damage many thousands of kilometres from the earthquake epicentre. In deep waters, tsunami are about less than a metre high. However, when they reach shallow waters or narrow inlets (such as Alberni Inlet) the waves pile up into a tall wall of water which causes devastation on the shore.
Earthquake Seismology Home Page
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National Earthquake Hazards Program
Geological Survey of Canada
GSC Pacific - Sidney Subdivision
Pacific Geoscience Centre
P.O. Box 6000
9860 West Saanich Road
Sidney, BC CANADA V8L 4B2 E-Mail: [email protected]
Tel. 1-250-363-6500
Fax. 1-250-363-6565
Home Page: http://www.pgc.nrcan.gc.ca
Copyright Natural Resources Canada, 1998 Disclaimer
November 3, 1999
http://www.pgc.nrcan.gc.ca/seismo/eqinfo/gloss.htm
H-Sense: Newsletter #1 June 1998
... and in good order in time ... bits and pieces: Cruise and seismic ... an initial list of recommended
survey ... same today as 1.5 years after ... Long waves that suddenly pile ...
http://hjs.geol.uib.no/Hsense/publications/public/newsletter...
More Results From: hjs.geol.uib.no
Equipment used in Marine Geology Research
Geophysical surveys provide a more sophisticated means of gathering data about the ocean floor. Information about the nature of sediment-covered bedrock can be obtained by shipboard gravimeters, which measure the rocks' density, and by magnetometers, which measure their magnetic properties. Seismic surveys, using reflected sound waves, give valuable information about submarine topography and the thickness and folding and faulting of rocks that are covered with sediment. Seismic surveys are particularly useful for locating oil and gas deposits commonly found trapped in deep accumulations of sedimentary rocks. Seismic sound waves can be made by releasing compressed air, high voltage spark, mechanical clappers, or electronic pulse to create a spectrum of sonar frequencies. The returning signals,or echoes, are printed on moving chart paper to create a graphic profile, or cross section, revealing the sediment/rock layers. The profiles are recorded with great clarity and in many cases show structures as deep as 6 miles beneath the seafloor.
Side-scan sonar, the latest acoustic system, sends out beams of sound waves sideways from the ship's course to map the seabed topography in broad swaths. Irregularities in the seafloor topog- raphy alter the energy in the signal bounced back to the receiver and these irregularities are used to produce an acoustic picture of the ocean floor. This system is especially useful for mapping large frontier regions, but it also can be used to map features as small as 20 feet across. Intricate patterns of meandering gullies and channels of oceanic canyon systems are transformed by side-scan sonar into a two-dimensional format much like an aerial photograph.
Seismic recorders are used to identify the depth to the ocean floor and the configuration of its sediment and rock layers. In this graphic record, the ship has just transected a submarine canyon.
As in all scientific fields, computers are important tools for marine geologists All large research vessels carry banks of multipurpose computers. Magnetic and gravity data are recorded continuously on computer tape throughout the day and night. Another type of onboard computer system receives signals from navigation satellites and radio beacons and can locate a ship's position to within 300 feet on the often featureless expanse of open ocean. Onshore computers perform statistical analyses, plot maps, and transform seismic data into a clearer form.
The side-scan sonar fish sends out acoustic signals in a broad swath. Inset is a sonograph of a submarine canyon system.
Plate Tectonics
In the 1960's the unifying theory of plate tectonics was proposed to explain many regional and global geologic phenomena, including drifting continents, spreading seafloors, and the worldwide distribution of mountains, earthquakes, and volcanoes. According to the plate tectonic model, the Earth's outer crust is a mosaic of gigantic continental and oceanic crustal plates, all of which are in motion relative to each other. Over hundreds of millions of years, these plates have collided with each other to form deep trenches and they are periodically broken along the rift zones by processes acting deep within the Earth's mantle so that the huge fragments then spread away from each other. Marine geologists are making major contributions to this new explanation of the Earth's history by studying the trenches and spreading zones, most of which lie beneath the oceans.
Tectonic plates of the Earth (below) and idealized cross section (AB) across the continents of South America and Africa (above).
Resources in the Marine Realm
Much of the research in marine geology relates directly or indirectly to assessing the seabed resource potential. With greater demands for certain mineral resources and depleting onland supply, the United States is looking toward the ocean as a new frontier and source of these vital resources. In 1983, the United States extended its exclusive mineral rights outward to a 200 nautical mile limit. The newly designated Exclusive Economic Zone (EEZ) extends from the shoreline and reaches across broad zones of flooded continental rocks known as the continental shelf, as well as deeper oceanic crust. Surprisingly, the area of the EEZ covers 3.9 billion acres, one-and-two-thirds times larger than the onshore area of the United States. In this vast domain lie resources of great importance to the Nation: an estimated 35 percent of the economically recoverable oil and gas yet to be found in the United States;
The United States Exclusive Economic Zone.
major resources of metals like cobalt, manganese, and nickel in seafloor crusts, pavements, and nodules; and major concentrations of heavy minerals such as gold and platinum in nearshore sand bodies. Along continental margins around the world, USGS scientists are discovering areas which may contain large amounts of petroleum. Petroleum and natural gas are generally restricted to ancient basins within the continental crust where thick piles of organic and terrigenous sediments have accumulated. Marine geologists have just learned, however, of the potential for natural gas in deeper water basins such as the Bering Sea in Alaska.
The new mineral deposits in the ocean are among the most exciting geologic discoveries of the past decade. Geologists now believe that most of the valuable mineral deposits mined on land originate at ocean-spreading ridges.
Scientists inspect a just recovered dredge haul (below), which contains samples of volcanic basalt (above left) and a seafloor crust rich in manganese (above right).
Along fractures and faults caused by crustal spreading, molten rock rises from beneath the Earth's surface, is injected in a linear zone along the axis of the ridge, and cools to create new seafloor. As the sea-floor spreading continues, the faults also provide conduits so that cold seawater can circulate downward into the hot crust. The water reacts with the hot rock, leaching from it elements such as manganese, zinc, iron, silver, copper, and cadmium in the form of metallic sulfides. When this hot mineral laden water reaches the seafloor, it shoots upward in a plume of precipitating minerals and forms spectacular, chimney-like columnal vents. These dynamic geysers or "smokers" were photographed from the submersible Alvin along the hydrothermally active Galapagos spreading ridge in 1979. Recently, USGS scientists have discovered these vents along other Pacific spreading ridges, including the Juan de Fuca Ridge off Oregon and Washington. Analyses of photographs, samples, and other data, some obtained by the Alvin, from these vents are giving onland geologists, who study ancient "fossilized" spreading zones, a greater ability to predict the location and extent of important mineral deposits
Scattered along spreading ridges are submarine "hot springs" rich in metallic sulfides. The min- eral-laden hot water shoots upward in a plume ("smoker") from vents on the seafloor.
Predicting Effects of Marine Processes
If people are to live and build along coastlines and out into the sea, they must understand and be able to predict the behavior of coastal geologic processes. Natural erosion along coasts is generally slow. Sea cliffs tend to retreat at moderate rates because they are protected against direct wave attack by natural bulwarks of beach sand. But the construction of a jetty or breakwater interrupts the natural movement of sand along a shore. Sand will tend to pile up on one side of a structure but will be completely stripped away on the other side, exposing sea cliffs to the full vigor of the waves and producing a disastrous increase in the rate of erosion.
Erosion often drastically increases along coastlines where jetties or breakwaters have been con- structed.
These undesirable effects, however, can be minimized if the designs of such structures are guided by detailed studies of coastal erosion processes or if the structures are not built.
Effectively predicting the effects of storms along heavily populated shores is an important part of coastal planning.
Major earthquakes, devastating as they may be in inland areas, are even more destructive along coasts. Buildings that would stand well on bedrock may be shaken to the ground if they are anchored in artificial fills or mud. Seismic seawaves (tsunamis) set off by an earthquake can sweep thousands of miles across the ocean to expend their destructive energies on distant shores. These tsunamis now can be forecasted in time for public warning, but local waves generated by submarine landslides are a more insidious hazard. When submarne landslides are set in motion by seismic vibrations, the water above them may be thrown into sudden violent waves capable of sweeping onto the shore hundreds of feet above sea level. Surveys by marine geologists at the USGS show the location of faults near the coast and nearby unstable seafloors. Information of this kind may help identify, in advance, coastal regions where tsunamis are likely to originate and can aid coastal planners by discouraging development in areas with potential geologic hazards.
Nearshore submarine landslides pose a threat to coastal developers(from a drawing by Tau Rho Alpha, USGS).
earthquake can sweep thousands of miles across the ocean to expend their destructive energies on distant shores. These tsunamis now can be forecasted in time for public warning, but local waves generated by submarine landslides are a more insidious hazard. When submarine landslides are set in motion by seismic vibrations, the water above them may be thrown into sudden violent waves capable of sweeping onto the shore hundreds of feet above sea level. Surveys by marine geologists at the USGS show the location of faults near the coast and nearby unstable seafloors. Information of this kind may help identify, in advance, coastal regions where tsunamis are likely to originate and can aid coastal planners by discouraging development in areas with potential geologic hazards.
http://walrus.wr.usgs.gov/pubinfo/margeol2.html
In hydrocarbon exploration and field appraisal, seismic surveys are the primary source of information about subsurface structures. Because the seismic record is referenced to time, assumptions about the velocity of the signal through the Earth are made in order to connect the time-based interpretation to a depth model. However, current methods for estimating Earth velocity have limited accuracy.
From Prototype to Commercial Software with
PV-WAVE®: Software Used in Oil and Gas Exploration
Oil and gas exploration
Data are analyzed in PV-WAVE using combinations of dynamically linked scatterplots, contour plots, histograms
In hydrocarbon exploration and field appraisal, seismic surveys are the primary source of information about subsurface structures. Because the seismic record is referenced to time, assumptions about the velocity of the signal through the Earth are made in order to connect the time-based interpretation to a depth model. However, current methods for estimating Earth velocity have limited accuracy.
As part of the LINK collaborative research program, funded by the Oil and Gas projects and Supplies Office (OSO) of the UK Department of Trade and Industry and the National Environment Research Council (NERC), Scott Pickford has teamed up with Imperial College, London, to address this problem.
The project has been using PV-WAVE as its development environment because of the system's high-level graphic analysis capabilities. The development team includes petrophysicists and programmers, all of whom use PV-WAVE to differing degrees. But all involved agree that without the use of a 4GL such as PV-WAVE, much of the system development would be impossible. Two systems were completed at the end of 1995: IC2 and Gather Snapper. A further system, Minerva, is under development.
Final Year
When the "IC2" and "Gather Snapper" projects were completed at the end of 1995, the industry sponsors (British Gas, Elf, Enterprise, OMV and Geco-Prakla) received fully engineered software packages based on methodology developed during the project, and a detailed structural interpretation of the North Sea's southern gas basin blocks, which make up the data set. In addition, the software will be sold commercially.
During the project's three-year duration, several significant milestones have been passed.
A two-year research program by Imperial College successfully completed a fully functional prototype Interactive Clustering and Multivariate Attribute Analysis (IC) software package. Although primarily designed for seismic data, the software can handle any multivariate data set.
Data are analyzed in PV-WAVE using combinations of dynamically linked scatterplots, contour plots, histograms, etc. Regions can be highlighted in one window and the corresponding points displayed in other windows; all plots are linked, giving a powerful tool to explore structure in a multivariate data set.
The user can subdivide the seismic data set into time windows corresponding to geological horizons and compute a wide range of attributes ranging from widely used parameters such as trace energy.
A regional well log and seismic database including raw traces, stacks, maximum coherence stacking velocities and migrated data has been established. Routines for handling log data have been completed and will be incorporated into the Log Data Analysis Environment. A link between the well-based and seismic domains via the Discrete Wavelet Transform will be developed.
An understanding of the accuracy and reliability of seismically derived velocities and interval velocities derived from them is crucial to the method. As such, the Gather Snapper has been designed to allow the user to examine the geometry of events observed on seismic gathers and extract velocities from them in various ways. A study has been made of the magnitudes of error and the mathematics of error propagation during the process of extracting interval velocities from the RMS velocities obtained from seismic gathers. This is supported by ray tracing routines that enable the user to transfer data between the unmigrated time, migrated time and depth domains.
PV-WAVE - Oil and Gas Exploration
... surveys are the primary source of information ... from the RMS velocities obtained from
seismic ... transfer data between the unmigrated time, migrated time ...
http://www.vni.com/successes/osonerc.html
Illustrated Glossary of Geologic Terms
... when added to a pile ... Possibly related to the migration ... portions of the Earth migrated ... sedimentary
rock made up ... scale a unit of time ... permafrost table The depth ...
http://www.geology.iastate.edu/new_100/glossary.html
lag time The delay in the response of stream flow between precipitation and flood peak.
P- wave (primary wave, compressional wave) A seismic body wave that involves particle motion, alternating compression and expansion, in the direction of wave propagation. It is the fastest seismic wave. compare S-wave .
period In the geologic time scale a unit of time less than an era and greater than an epoch. Example: The Tertiary period was the earliest period in the Cenozoic era and included, among others, the Eocene epoch.
shock metamorphism Metamorphism induced in rock by the passage of a high-pressure shock wave acting over a period of time from a few microseconds to a fraction of a minute. The only known natural cause of shock metamorphism is the hypervelocity impact of a meteorite.
Illustrated Glossary of Geologic Terms
... pages linked to this glossary ... added to a pile ... related to the migration ... of the Earth
migrated ... sedimentary rock made up ... a unit of time ... permafrost table The depth ...
http://www.ge-at.iastate.edu/courses/Geol_100/glossary.v2.ht...
NSSH - Glossary of Landform and Geologic Terms (Part 629)
... (c) Glossary Terms. ... A fold, at any depth ... no evidence of time ... the stoss end (up ... formed
by lateral migration ... the resulting debris pile ... coarse fragments have migrated ...
http://www.statlab.iastate.edu/soils/nssh/629.htm
Glossary of Geophysical Sciences
Glossary of Geophysical Sciences ... when added to a pile of ... related to the migration ... of
the Earth migrated ... sedimentary rock made up ... a unit of time ... table The depth ...
http://www.istanbul.edu.tr/eng/jfm/geosozluk.htm
PV-WAVE - Oil and Gas Exploration
... from the RMS velocities obtained from seismic ... transfer data between the unmigrated
time, migrated time ... and establishing data connectivity with the oil ...
http://www.vni.com/successes/osonerc.html
GX Technology Solutions - Solutions
... risk and cost associated with drilling for oil ... intelligently, can be instrumental
in identifying seismic ... analysis has been done on prestack time migrated ...
http://www.gxt.com/solutions.htm
More Results From: www.gxt.com
SiteMap
... Seismic Data Example 7. Acquistion Parameters ... Section Migrated Time Section Zoom Interpreted
Migrated Time ... Copyrights © 1999, Saudi Arabian Oil Company ...
http://www.lsif.org/html/sitemap.html
More Results From: www.lsif.org
Locating Geopressured HC Reservoirs in Soft, Clastic Sediments ...
... Geopressured oil and gas fields in the Gulf of ... including: West Cameron Block 66 3D
survey (migrated time ... logs, check shot surveys, and three 2D seismic ...
http://dominoweb.fossil.energy.gov/domino/apps/fred/fred.nsf... 505e2181a105256b0900564d56!OpenDocument
More Results From: dominoweb.fossil.energy.gov
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Note added at 2002-07-05 23:58:58 (GMT)
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sorry - about first sentence, didn\'t realize I hadn\'t deleted it. Inundation of information. Hope some of it is helpful.
| Deb Phillips (X)
PRO pts in pair: 4
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