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Dip-slip faults. Goal : To interpret dip-slip faults on seismic sections and to build on your interpretations to understand normal-fault and thrust-fault systems. Part-I : Normal-fault systems. Seismic-reflection profile of a large normal fault. Seismic-reflection profiles.

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Presentation Transcript
dip slip faults
Dip-slip faults

Goal: To interpret dip-slip faults on seismic sections and to build on your interpretations to understand normal-fault and thrust-fault systems.

part i normal fault systems
Part-I: Normal-fault systems

Seismic-reflection profile of a large normal fault

seismic reflection profiles
Seismic-reflection profiles
  • The squiggly lines on these profiles are reflectors
    • Recorded by sound waves reflected off of density contrasts (geologic contacts)
    • Represent different rock layers.
  • Seismic reflection profile = sound-based impressionist picture of earth.
  • Number-one tool in oil-and-gas exploration
interpreting the profile
Interpreting the profile
  • Look for offsets and truncations of layers
  • Concentrate on finding the large fault first
slide5
To interpret the profile:
  • The messy looking part of the profile is likely where the faults are.
  • Start at right-hand side and pick some prominent reflectors (heavy lines)
  • Follow reflectors to the left; look for truncations and/or offsets.
  • Connect truncations and/or offsets together to outline a fault trace.
  • If fault is large enough and at sufficiently low angle, it may form a reflector or a series of discontinuous reflectors.
slide7
What do you notice about:
  • The orientations of sedimentary layers approaching the large normal fault?
  • The thickness of beds approaching the large normal fault?
  • The down-dip geometry of the large normal fault?
slide10
Watch Allmendinger’s movie

www.geo.cornell.edu/geology/faculty/RWA/movies

Growth strata

Growth strata: Sed rocks deposited during faulting. Thickest next to fault

what do normal fault systems really look like
What do normal-fault systems really look like?

The Tetons are a rotated fault block

part ii thrust fault systems
Part-II: Thrust-fault systems

Seismic-reflection profile of a thrust fault

slide15
To interpret the profile:
  • Start at the sides and pick prominent reflectors
  • Follow reflectors towards the middle, looking for truncations and/or offsets.
  • Match up similar reflectors on either side of truncations/offsets.
  • Connect these together truncations/offsets to outline a fault trace.
  • Fault may form a reflector or a series of discontinuous reflectors.
  • This fault will sole into a basal detachment surface.
slide17
What do you notice about:
  • Any systematic changes in fault dip
  • The orientations of layers approaching the thrust fault
slide19

Ramp

Flat

Ramp: Dipping segment of the fault. Fault cuts up section

Flat: Subhorizontal segment of the fault. Fault follows beds.

slide20

Frontal ramp: 90° to transport direction

Lateral ramp: parallel with transport direction

Oblique ramp: oblique to transport direction

fault related folds
Fault-related folds

Fold due to faulting

fault propagation folds
Fault-propagation folds

Moderately dipping limb

Steeply dipping overturned limb

dissected thrust belts
Dissected thrust belts

Window: Hole eroded through hanging wall of a thrust fault that exposes footwall rocks

Klippe: Isolated remnant of thrust sheet. Typically topographic highs