STRUCTURAL GEOLOGY SEMINAR

A PRESENTATION

ON

STRIKE-SLIP FAULTS, ASSOCIATED

STRUCTURES , AND HYDROCARBON TRAPS.

BY Fiona Haldane Chinedu AmadiTom Johnson

Ildiko Vass -Talmage

AIMS

1. Descriptive overview of strike slip faults.a. Identify major features and related structures.

2. Discuss basic mechanisms for SS faults to form.

3. Show relationship of strike slip faults as hydrocarbon traps.

4. Provide illustrative examples of strike slip faults in major basins.

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.

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.

REGIONALREGIONAL TECTONICSTECTONICSAreas of continental strike slip faultsAreas of continental strike slip faults Plate boundaries: continental counter part to transform Plate boundaries: continental counter part to transform

faults faults

e.g San Andreas Fault, California e.g San Andreas Fault, California

Escape tectonics associated with compressional orogens,Escape tectonics associated with compressional orogens,

e.g. (Himalayas)e.g. (Himalayas)

Non regional settings: Tear faults in thrust systems Non regional settings: Tear faults in thrust systems

(Pine Mountain thrust sheet in Appalachians)(Pine Mountain thrust sheet in Appalachians)

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.

For strike slip faulting : σ1> σ2> σ3

σ1, σ3 = horizontal stress σ2 = vertical stress

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.

DEXTRAL OR RIGHT SLIP FAULT

To an observer standing on one side of the fault, if the motion on the otherside is to the left, we have Sinistral strike slip fault.

SINISTRAL OR LEFT LATERAL

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

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.

FAULT-BEND BASINS

STEPOVER BASINS

TRANSROTATIONAL BASINS

TRANSPRESSIONAL BASINS

POLYGENETIC BASINS

POLYHISTORY BASINS

BASIN TYPES

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

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.

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.

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

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

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.

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.

FLOWER STRUCTURES

Positive Flower Structure Ardmore basin , Oklahoma.

Example 1 – San Andreas Fault Example 1 – San Andreas Fault System, CaliforniaSystem, California

Dextral fault systemDextral fault system Large amount of different basin Large amount of different basin

structures form along it’s length.structures form along it’s length. Hydrocarbon reserves Hydrocarbon reserves

accumulate in transcurrent fault accumulate in transcurrent fault systems.systems.

The trap in flower structure The trap in flower structure formed by faulted anticlines.formed by faulted anticlines.

Estimated oil reserves in Estimated oil reserves in Californian basins is >15 billion Californian basins is >15 billion BOE BOE (Selley, 1998)(Selley, 1998)..

Unrecoverable at this time due Unrecoverable at this time due to large earthquake hazard that to large earthquake hazard that is prevalent in the region.is prevalent in the region.

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

Dextral faultDextral fault

1500km long, extending from eastern Turkey to mainland Greece1500km long, extending from eastern Turkey to mainland Greece

Extremely seismically active, with seven M>7.0 earthquakes since 1939Extremely seismically active, with seven M>7.0 earthquakes since 1939

Area of hypothesised remote earthquake triggeringArea of hypothesised remote earthquake triggering

Example 2 – North and East Anatolian fault system

Simulated model of the Anatolian Fault Simulated model of the Anatolian Fault SystemSystem

Location map of the Anatolian Fault Location map of the Anatolian Fault SystemSystem

Nekkor and Jebha faultsNekkor and Jebha faults

Nekkor fault is sinistral, 300 km longNekkor fault is sinistral, 300 km long

Structures formed by strike-slip faulting provide HC traps.Structures formed by strike-slip faulting provide HC traps.

Shallow features overlie heavily faulted anticlines.Shallow features overlie heavily faulted anticlines.

These structures have formed several small oil fields in the area.These structures have formed several small oil fields in the area.

Example 3 – Moroccan Rif System

Jebha fault is also sinistralJebha fault is also sinistral

The large displacement on this has produced structural highs The large displacement on this has produced structural highs and lows, which in turn have become heavily faulted themselvesand lows, which in turn have become heavily faulted themselves

Oil seeps have been found along this fault, showing the potential Oil seeps have been found along this fault, showing the potential for future hydrocarbon explorationfor future hydrocarbon exploration

Geology of this Rif is very similar to the strike-slip fault system of Geology of this Rif is very similar to the strike-slip fault system of Venezuela and Trinidad, where hydrocarbons have been foundVenezuela and Trinidad, where hydrocarbons have been found

This area hasn’t been explored, but has very good hydrocarbon This area hasn’t been explored, but has very good hydrocarbon potentialpotential

Location map of the Moroccan Rif SystemLocation map of the Moroccan Rif System

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.

TABLE OF CLASSIFICATIONSylvester’s (1988)

Interpolate Transforms (deep seated, delimiting plate)

Interpolate “transcurrent” faults(confined to crust)

Ridge transform fault: displaces segmentsof oceanic crust with similar spreading vectorse.g Romanche fracture zone (Atlantic ocean)

Boundary transform faultsSeparate different plates parallel to the plate boundary. Eg San andreas (california), alpine fault (New Zealand)

Trench-linked strike-slip faultsAccommodate horizontal component of oblique subduction. Eg Atacama fault (chile), Median Tectonic line (Japan)

Indent-linked strike slip faultsBound continental blocks in collission Zones. Eg North Anatolian (Turkey)

Intercontinental strike slip faults .Separate allochthons of different tectonicStyles eg Garlock fault (California)

Tear faultsAccommodate different displacement within a given allochthon or between the Allochthon and adjacent structural units Eg Asiak fold thrust belt (Canada)

Transfer FaultsLiving overstepping or en echelon strike Slip faults eg Southern and Northern Diagonal faults (eastern Sinai, Isreal)

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.

Donald L. Turcotte and Gerald Schubert: Geodynamics,ch1 52, ch 8, pg 341

Twiss R J & Moores E M: Structural Geology ch 7, pg 113-127.

Price N J & Cosgrove J W: Analysis of Geological Structures, ch 6 pg 139-159.

Engelder T: Stress Regimes in the Lithosphere, pg 14-15.

http://www.geo.wvu.edu/~jtoro/Structure/ppt/13StrikeSlipFaults.pdf http://www.glossary.oilfield.slb.comhttp://www.emsc-csem.org/Doc/TURKEY_bingol.pdfhttp://neic.usgs.gov/neis/world/turkey/tec_setting.htmlStrike-slip faults in the Moroccan Rif: Their geophysical signatures and hydrocarbonpotential, Jobidon, G.P., SEG, 2005Elements of Petroleum Geology, 2nd ed, Selley, R. C., 1998, Academic Press

REFERENCES