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Dipping Interfaces - Seismology - Lecture Slides, Slides of Geology

Jaypee University of Engineering & TechnologyGeology

Lecturer has explained the following key points in these Lecture Slides : Dipping Interfaces, Diagram, Underestimates Velocity, Underestimate Layer, Shoot Up-Dip, Intercepts, Different, Survey, Hidden Layer, Low Velocity Layer

Typology: Slides

2012/2013

Uploaded on 07/19/2013

baber
baber 🇮🇳

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Dipping Interfaces
•If you shoot down-dip
–Slopes on t-x diagram are
too steep
•Underestimates velocity
–May underestimate layer
thickness
•Converse is true if you
shoot up-dip
•In both cases the
calculated direct ray
velocity is the same.
•The intercepts tint will
also be different at
both ends of survey
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Download Dipping Interfaces - Seismology - Lecture Slides and more Slides Geology in PDF only on Docsity!

Dipping Interfaces

  • If you shoot down-dip
    • Slopes on t-x diagram are too steep - Underestimates velocity
    • May underestimate layer thickness
  • Converse is true if you shoot up-dip
  • In both cases the calculated direct ray velocity is the same.
  • The intercepts t (^) int will also be different at both ends of survey

The Hidden Layer

  • There are two cases where a seismic interface will not

be revealed by a refraction survey.

  • The Hidden Layer (book calls it “Hidden Layer Proper”)
  • The Low Velocity Layer This one is straightforward,so we will look at it first.

The Low Velocity Layer

  • Causes:
    • Sand below clay
    • Sedimentary rock below igneous rock
    • (sometimes) sandstone below limestone
  • How Can you Know?
    • Consult geologic data!
      • Boreholes / Logs
      • Geologic sections
      • Geologic maps

The Hidden Layer

  • Recall that the refracted ray eventually overtakes the direct ray (cross over distance).
  • The second refracted ray may overtake the direct ray first if:
    • The second layer is thin
    • The third layer has a much faster velocity

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Undulating Interfaces

  • Undulating interfaces produce non-linear t-x diagrams
  • There are techniques that can deal with this
    • delay times & plus minus method
    • We won’t cover these techniques…