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Seismic Interpretation Image showing marine transgressive surface and eroded channels
Seismic Interpretation Image showing an unconformity and a younger channel
Examples of interpreted seismic profiles. Click on the images above to
view an enlarged version. Note: The above images are taken from Cross and others, 1998.

The interpretation of features mapped using a seismic data set is based on acoustic impedance differences of subsurface material. A towed seismic source emits acoustic energy at regular intervals. The transmitted acoustic energy is reflected from boundaries between mediums of different acoustic impedances (e.g. the water-sediment interface). The interface between different materials is displayed graphically in a seismic record, based on the time it takes the transmitted acoustic energy to travel from the source to each interface and back to the receiver, termed two-way travel time. If the speed of sound within the material is known, depth to each interface can be calculated.

Graphical depiction of two-way travel time
Graphical depiction of two-way travel time. Two-way travel time is the amount of time required to travel the outgoing and returning acoustic pathways, shown in purple in the figure above.

Chart showing the progress of acquired data into interpreted maps and seismic line displays The Sea-floor Mapping Group at the USGS Woods Hole Science Center interprets high-resolution seismic data to delineate the shallow geologic framework of a survey area. Processing, interpretation, and analysis of the seismic stratigraphy are performed within a suite of programs designed for this task. The Landmark SeisWorks interpretation software enables the visualization, interpretation, and to some extent the modeling of a large quantity of data within a study area. Stratigraphic data and surface models are displayed within a GIS and can be integrated with other data types, such as sidescan-sonar and sediment samples.

SeisWorks

SeisWorks 2D, a seismic data interpretation and analysis package from Landmark Graphics Corp. (LGC), allows us to display and interpret seismic data in a graphical, on-screen interface. This greatly reduces the time involved in generating seismic interpretations, in that interpretations no longer need to be digitized from paper records. In SeisWorks, the interpretation process is interactive and digital. Examples of two windows typically open during a session are shown to the left (labeled Screen Shot 1 and 2), along with two interpretive images derived from the data imaged in the screen shots. The interpretations can be exported from SeisWorks and imported into various display or archival applications, for example, ESRI ArcView GIS for spatial layout and referencing (see image derived from screen shot 1). Interpreted seismic lines are also selected to display certain features of scientific interest, such as that displayed in the image derived from Screen Shot 2. Note: Derived figures are modified with permission from Foster and others, 1999.

SeisWorks 2D Screen Shot
Screen Shot 1 -This window displays a composite trackline map drawn from the shotpoint navigation data stored in the headers of the SEG-Y files. It demonstrates how interpreted horizons can be geographically referenced in the trackline map.
SeisWorks 2D image showing thickness of modern sand
Image Derived from Screen Shot 1 -This image shows a figure of sand thickness derived from interpretations of seismic lines in the survey area.
SeisWorks screen shot
Screen Shot 2 - A trace display of the seismic line is shown and is active during interpretation. From this window, interpreted horizons can be screen digitized and linked to the trackline map, referenced by shotpoint.
Image showing derived figure of sand thickness
Image Derived from Screen Shot 2 - Example of a seismic line interpretation from the data set shown in screen shot 2, exported from SeisWorks for use in publications.>
Click on the images above to view an enlarged version.

SeisVision

This Windows-based seismic interpretation package has the seismic interpretation functionality of SeisWorks, but a more limited capability in terms of tools available for geologic analyses and applications.

In the screen shot displayed below, there are three nested images: the track chart of seismic lines on the left; on the right there are two images atop one another, the seismic line undergoing interpretation is on the bottom and a display of additional physical property information, in this case resistivity, is displayed on the top right, to additionally aid interpretation of the seismic data.

Screen shot of SeisVision
SeisVision screen shot

WHSC utilizes these seismic interpretation software systems in the field, in the lab, and at professional meetings/conferences/workshops. The flexibility inherent in such a setup allows for multiple users to access and manage the projects and databases, rather than be limited to a single user on a devoted system.

References

Cross, V., Twichell, D., Parolski, K., and Harrison, S. 1998. Archive of boomer seismic-reflection data collected aboard RV Corliss cruise CRLS97007 off Northern Oregon and Southern Washington inner continental shelf: U.S. Geological Survey Open-File Report 98-351.

Foster D.S., Swift B.A., and Schwab W.C. 1999. Stratigraphic Framework Maps of the Nearshore Area of Southern Long Island from Fire Island to Montauk Point, New York: U.S. Geological Survey Open File Report 99-559.


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