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1 GY 305: Geophysics GY 305: Geophysics Lecture 12: Lecture 12: Seismic Stratigraphy Seismic Stratigraphy UNIVERSITY OF SOUTH ALABAMA Last Time Last Time Introduction to Seismology Seismology (resolution versus penetration) Techniques (marine versus terrestrial) Seismology http://www.oceansatlas.com/unatlas/-ATLAS-/IMAGES/HIGH/i156-1.jpg Seismology uses acoustic waves (sound or “shock” waves) to resolve subsurface stratigraphy and is related to depth sounders in marine transducer-transceiver systems. Seismology (Marine Surveys) Marine seismic vessels are typically about 75 m [246 ft] long and travel about 5 knots [9.3 km/hr or 5.75 statute miles/hr] while towing arrays of air guns and streamers containing hydrophones a few meters below the surface of the water. The tail buoy helps the crew locate the end of the streamers. The air guns are activated periodically, such as every 25 m (about 10 seconds), and the resulting sound wave travels into the Earth, is reflected back by the underlying rock layers to hydrophones on the streamer and then relayed to the recording vessel. http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236 Seismology Marine seismic data can be acquired using single streamers (second vessel) or multiple streamers (first vessel) of various lengths or ocean bottom cable. 3D seismic data of various footprints, or areas covered by an array of multiple towed streamers, are also routinely acquired (four vessels on the right). http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=236 Other Other “ Seismic Seismic” Techniques Techniques
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2 Side Scan Sonar Side Scan Sonar http://www.abc.se/~m10354/mar/img/sture/system2.jpg
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