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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.

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Presentation on theme: "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."— Presentation transcript:

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: 1.The messy looking part of the profile is likely where the faults are. 2.Start at right-hand side and pick some prominent reflectors (heavy lines) 3.Follow reflectors to the left; look for truncations and/or offsets. 4.Connect truncations and/or offsets together to outline a fault trace. 5.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: a.The orientations of sedimentary layers approaching the large normal fault? b.The thickness of beds approaching the large normal fault? c.The down-dip geometry of the large normal fault?

8 Different normal-fault styles

9 Symmetric and asymmetric normal- fault systems Rotational Nonrotational

10 Watch Allmendinger’s movie Growth strata Growth strata: Sed rocks deposited during faulting. Thickest next to fault

11 What do normal-fault systems really look like? The Tetons are a rotated fault block

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14 Part-II: Thrust-fault systems Seismic-reflection profile of a thrust fault

15 To interpret the profile: 1.Start at the sides and pick prominent reflectors 2.Follow reflectors towards the middle, looking for truncations and/or offsets. 3.Match up similar reflectors on either side of truncations/offsets. 4.Connect these together truncations/offsets to outline a fault trace. 5.Fault may form a reflector or a series of discontinuous reflectors. 6.This fault will sole into a basal detachment surface.

16 Basic interpretation

17 What do you notice about: a.Any systematic changes in fault dip b.The orientations of layers approaching the thrust fault

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19 Ramp: Dipping segment of the fault. Fault cuts up section Flat: Subhorizontal segment of the fault. Fault follows beds. Ramp Flat

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

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24 Fault-propagation folds Steeply dipping overturned limb Moderately dipping limb

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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

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