1. STRUCTURAL GEOLOGY SEMINAR
A PRESENTATION ON
STRIKE-SLIP FAULTS, ASSOCIATED
STRUCTURES , AND HYDROCARBON TRAPS. BY
Fiona Haldane
Chinedu Amadi
Tom Johnson
Ildiko Vass -Talmage

2. Descriptive overview of strike slip faults.
AIMS
Descriptive overview of strike slip faults.
Identify major features and related structures.
Discuss basic mechanisms for SS faults to form.
Show relationship of strike slip faults as hydrocarbon traps.
Provide illustrative examples of strike slip faults in major basins.

3. STRIKE-SLIP FAULTS, ASSOCIATED STRUCTURES AND HYDROCARBON TRAPS.
Definition:
‘Strike slip faults are generally steeply dipping faults along which horizontal slip has occurred.’ (Davis, G.H. and Reynolds, S.J., Structural Geology)
Displacement on a given fault may be either right lateral (dextral) or left lateral (sinistral), and it results in no net addition or subtraction of area to the crust.

4. Characteristics:
Anderson’s Classification: maximum and minimum stresses are
horizontal and orthogonal.
Within strike slip fault systems conjugate Riedel Shears develop.
Strike slip faults give rise to imbricate fans, en echelon faulting
and relay ramp structures.
Where complex regional tectonics and stress regimes exist,
strike slip duplexes form.
Strike slip faults are mainly found at major plate boundaries,
orogenic belts and extensional basins.
Most of the truly large strike slip faults in continental areas
are fundamental plate boundaries, e.g., San Andreas in California,
and the Alpine fault in New Zealand.
Large strike slip faults are marked by prominent continuous
topographic features.
Strike slip faults have been given a number of names, such as tear,
wrench, transcurrent and transform faults.

5. REGIONAL TECTONICS Areas of continental strike slip faults
Plate boundaries: continental counter part to transform faults
e.g San Andreas Fault, California
Escape tectonics associated with compressional orogens,
e.g. (Himalayas)
Non regional settings: Tear faults in thrust systems
(Pine Mountain thrust sheet in Appalachians)

6. MECHANISM:
The state of stress in strike-slip faulting consists of a vertical lithostatic
stress (σ2 = pgz); and two horizontal deviatoric principal stresses that
are compressional (σ 1=push) in one direction and tensional (σ 3=pull) in
the other.
One horizontal stress will be larger, than the other horizontal stress.
σ 1> σ 3.
For strike slip faulting, the vertical stress (σ2) is always the
intermediate stress.
Generally, stress relationship for strike-slip fault are σ1> σ2> σ3.

7. For strike slip faulting : σ1> σ2> σ3
σ1, σ3 = horizontal stress σ2 = vertical stress

8. DEXTRAL OR RIGHT SLIP FAULT
To an observer standing on one side of the fault, if the motion on the other
side is to the right, we have dextral strike slip fault.

9. SINISTRAL OR LEFT LATERAL
To an observer standing on one side of the fault, if the motion on the other
side is to the left, we have Sinistral strike slip fault.

10. STRUCTURAL FRAMEWORK
Four principal factors control the structural patterns that develop
along strike-slip faults
The kinetic framework (transtensional, transpressional, or parallel)
The magnitude of the displacement
The material properties of the rocks and sediments in the deforming zone.
The configuration of pre-existing structures

11. STRIKE SLIP BASINS
Divide into hot and cold types based on whether the mantle has been involved in their formation.
Hot basins: Uniform extension models with modifications for lateral heat loss have been applied with some success.
Cold basins: Thin skinned , post-deformational, thermal subsidence is
Insignificant.

12. BASIN TYPES
FAULT-BEND BASINS
STEPOVER BASINS
TRANSROTATIONAL BASINS
TRANSPRESSIONAL BASINS
POLYGENETIC BASINS
POLYHISTORY BASINS

13. FAULT-BEND BASINS: This typically develop at releasing bends along strike slip faults.

14. STEPOVER BASINS: generally develop from transtension that develops between the unconnected ends of two parallel to sub-parallel strike slip faults or strands of the same fault.

15. TRANSROTATIONAL BASINS: develops between strike slip faults as a result of the rotation of blocks about a sub-vertical axis in the same direction as the principal shear strain, clockwise in right simple shear and counter clock-wise in left simple shear.

16. TRANSPRESSIONAL BASINS: are generally long, narrow structural depression that lie parallel to, but outboard of restraining bends in strike-slip faults.

17. POLYGENETIC BASINS: develop as a result of local strike-slip in larger regions of generally divergent or convergent tectonics.

18. POLYHISTORY BASINS: develop where episodes of strike slip alternate with or are replaced by episodes of extensional rifting, contractile thrusting, or other styles of deformation.

19. FLOWER STRUCTURES
In a strike slip duplex, the shape of the faults on the vertical section normal to the main fault trace is referred to as a flower structure.
If the dip slip component is normal , the faults tend to be concave up, and forms a negative flower structure or Tulip structure.
If the dip slip component is reverse, the faults tend to be convex up and form a positive or palm tree structure.
Examples of these two types of flower structures can be seen in seismic reflection profiles from the southern Andaman sea, and from the Ardmore basin in southern Oklahoma.

20. Positive Flower Structure Ardmore basin , Oklahoma.

23. Example 1 – San Andreas Fault System, California

24. Dextral fault system
Large amount of different basin structures form along it’s length.
Hydrocarbon reserves accumulate in transcurrent fault systems.
The trap in flower structure formed by faulted anticlines.
Estimated oil reserves in Californian basins is >15 billion BOE (Selley, 1998).
Unrecoverable at this time due to large earthquake hazard that is prevalent in the region.

25. Map showing Central Californian strike-slip basins and their associated faults

26. Dextral fault Example 2 – North and East Anatolian fault system
1500km long, extending from eastern Turkey to mainland Greece
Extremely seismically active, with seven M>7.0 earthquakes since 1939
Area of hypothesised remote earthquake triggering

27. Simulated model of the Anatolian Fault System

28. Location map of the Anatolian Fault System

29. Example 3 – Moroccan Rif System
Nekkor and Jebha faults
Nekkor fault is sinistral, 300 km long
Structures formed by strike-slip faulting provide HC traps.
Shallow features overlie heavily faulted anticlines.
These structures have formed several small oil fields in the area.

30. Jebha fault is also sinistral
The large displacement on this has produced structural highs and lows, which in turn have become heavily faulted themselves
Oil seeps have been found along this fault, showing the potential for future hydrocarbon exploration
Geology of this Rif is very similar to the strike-slip fault system of Venezuela and Trinidad, where hydrocarbons have been found
This area hasn’t been explored, but has very good hydrocarbon potential

31. Location map of the Moroccan Rif System

32. DISCUSSTION & CONCLUSION:
Six main type of strike-slip basins can be defined on the basis of their fault patterns and mechanisms of formation.
The basins form in diverse tectonic settings and are commonly deformed and reformed as fault blocks rise, fall, converge, diverge, and are laterally translated in space and time.
Most long-lived strike-slip basins undergo repeated periods of transtensional subsidence and transperssive uplift within complex flower structures.
Strike slip faults are secondary structures commonly associated with
major faults and folds.

33. TABLE OF CLASSIFICATION
Sylvester’s (1988)
Interpolate Transforms
(deep seated, delimiting plate)
Interpolate “transcurrent” faults
(confined to crust)
Ridge transform fault: displaces segments
of oceanic crust with similar spreading vectors
e.g Romanche fracture zone (Atlantic ocean)
Indent-linked strike slip faults
Bound continental blocks in collission
Zones. Eg North Anatolian (Turkey)
Boundary transform faults
Separate different plates parallel to the plate boundary. Eg San andreas (california), alpine fault (New Zealand)
Intercontinental strike slip faults .
Separate allochthons of different tectonic
Styles eg Garlock fault (California)
Trench-linked strike-slip faults
Accommodate horizontal component of oblique subduction. Eg Atacama fault (chile), Median Tectonic line (Japan)
Tear faults
Accommodate different displacement within a given
allochthon or between the Allochthon and adjacent
structural units Eg Asiak fold thrust belt (Canada)
Transfer Faults
Living overstepping or en echelon strike
Slip faults eg Southern and Northern
Diagonal faults (eastern Sinai, Isreal)

34. The Anatolian system along with the San Andreas Fault and the Moroccan Rif are examples of strike-slip faults.
Strike-slip faults cause severe geological hazards along the San Andreas Fault and in the Anatolian mountain range; which affects local population and economy. (i.e. San Francisco, CA 1906, Kocaeli, Turkey 1999)
Hydrocarbon reserves are known to be associated with strike-slip faults despite difficulties with trap preservation and source rocks. Kingston(1983) indicates that about 47% of all wrench cycles studied worldwide were found to produce commercial hydrocarbons.

35. REFERENCES
Donald L. Turcotte and Gerald Schubert: Geodynamics,ch1 52, ch 8, pg 341
Twiss R J & Moores E M: Structural Geology ch 7, pg
Price N J & Cosgrove J W: Analysis of Geological Structures, ch 6 pg
Engelder T: Stress Regimes in the Lithosphere, pg
Strike-slip faults in the Moroccan Rif: Their geophysical signatures and hydrocarbon
potential, Jobidon, G.P., SEG, 2005
Elements of Petroleum Geology, 2nd ed, Selley, R. C., 1998, Academic Press