Dip-slip faults

1
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.
2
Part-I Normal-fault systems
Seismic-reflection profile of a large normal fault
3
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

4
Interpreting the profile

• Look for offsets and truncations of layers
• Concentrate on finding the large fault first

5

• 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.

6
Basic interpretation
7

• 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?

8
Different normal-fault styles
9
Symmetric and asymmetric normal-fault systems
Nonrotational
Rotational
10
Growth strata
Growth strata Sed rocks deposited during
faulting. Thickest next to fault

• Watch Allmendingers movie
• www.geo.cornell.edu/geology/faculty/RWA/movies

11
What do normal-fault systems really look like?
The Tetons are a rotated fault block
12
(No Transcript)
13
(No Transcript)
14
Part-II Thrust-fault systems
Seismic-reflection profile of a thrust fault
15

• 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.

16
Basic interpretation
17

• What do you notice about

• Any systematic changes in fault dip
• The orientations of layers approaching the thrust
  fault

18
(No Transcript)
19
Ramp
Flat
Ramp Dipping segment of the fault. Fault cuts up
section Flat Subhorizontal segment of the
fault. Fault follows beds.
20
Frontal ramp 90 to transport direction Lateral
ramp parallel with transport direction Oblique
ramp oblique to transport direction
21
Fault-related folds
Fold due to faulting
22
Ramp anticlines
23
(No Transcript)
24
Fault-propagation folds
Moderately dipping limb
Steeply dipping overturned limb
25
(No Transcript)
26
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
27
(No Transcript)
28
(No Transcript)