Riddle - Seismology - Lecture Slides, Slides of Geology

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A Riddle…

What do these things have in common?

Reflection Seismology

Chapter :: 7

Images Courtesy John Shaw, Harvard University

The Seismic Reflection Method:

A dynamic geophysical technique of generating a

sound wave at a source and recording the time it

takes for components of that seismic energy to

return to the surface and be recorded by receivers

Ground Penetrating Radar:

Utilizes similar theory, but the source is

electromagnetic waves

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Reflection Seismology

• 1920’s - 1930’s, seismic reflection developed for oil/gas exploration in sedimentary basins.
• Since 1970’s, valuable in understanding structure of mid-lower crust.
• Popular for three main reasons:
  • Reflection data is commonly portrayed as profile resembling “geologic cross sections”.
  • Offers high resolution of subsurface data.
  • Cheaper than blindly drilling

Refraction vs. Reflection

• So, what are the main take-home differences between these two seismic techniques? Refraction Reflection

Resolves gross crustal velocities

Resolves fine subsurface details critical refraction requires large v gradient

requires a change in v or density X=5-10x the depth of interest

X=1x the depth of interest

Processing is relatively easy

Processing can be very CPU intensive ~30% of global CPU time is spent on processing seismic reflection data http://pangea.stanford.edu/~sklemp/bering_chukchi/reflection.html