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Unformatted text preview: 1 MAS 603: Geological Oceanography MAS 603: Geological Oceanography Lecture 21: Lecture 21: Geophysics 1: Gravity Geophysics 1: Gravity UNIVERSITY OF SOUTH ALABAMA Last Time Last Time Extinctions ht p:/ www.cartoonstock.com/newscartoons/cartoonists/for/lowres/forn441l.jpg Geophysics Introduction (various techniques) Gravity Gravity anomalies Today Today s Agenda s Agenda Geophysical analysis is done when 1) you cant get direct access to the rocks 2) you want to model a large area quickly 3) you know what you are looking for Geophysics Geophysics Geophysical analysis is done when 1) you cant get direct access to the rocks 2) you want to model a large area quickly 3) you know what you are looking for but every geophysical technique only estimates geology (lots of interpretation) Geophysics Geophysics There are 2 scales of geophysical analysis: 1) small-scale (single well; shallow penetration seismic etc.) Geophysics Geophysics ht p:/ www.spwla.org/library_info/glossary/reference/glossd/images/glsp32f1.gif htp:/www.encapgroup.com/driling/images/oil-driling-wel.jpg 2 There are 2 scales of geophysical analysis: 1) large-scale (basin wide surveys) Geophysics Geophysics ht p:/ www.seadolby.com/images/the-seafarer-images/seismic-boat.jpg ht p:/ www.ucmp.berkeley.edu/fosrec/images/ONeil Fig8.jpg Proposed well Ultimately what geophysics do Ultimately what geophysics do is to measure the intensity of is to measure the intensity of waves waves or force or force fields as they fields as they pass through geological pass through geological materials. materials. They are looking for They are looking for unpredicted variations or unpredicted variations or deviations from normal (i.e., deviations from normal (i.e., anomalies anomalies ) Geophysics Geophysics ht p:/ miac.uqac.ca/MIAC/grav-1.jpg Geological interpretations are Geological interpretations are made on the basis of these made on the basis of these anomalies anomalies Geophysics Geophysics ht p:/ www.geos.ed.ac.uk/homes/jru/Silverpitseismic.jpg An incredible 3D seismic line across a structurally complex area of the North Sea (once thought to be an impact site, now thought to be a collapse structure) So what kind of geophysics is So what kind of geophysics is there? there? Geophysics Geophysics Seismology Seismology- Study of natural [from Study of natural [from earthquakes] and man earthquakes] and man-induced seismic induced seismic waves waves Gravity Gravity- Study of variations in earth's Study of variations in earth's gravitational field gravitational field Electrical Methods Electrical Methods- Use of electrical Use of electrical conductivity / resistance of earth conductivity / resistance of earth Electromagnetics Electromagnetics- Study of induced Study of induced electromagnetic fields electromagnetic fields Magnetics Magnetics- Analysis of variations in Analysis of variations in earth's magnetic field earth's magnetic field...
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- Fall '11