University of Azad Jammu and Kashmir

Raja Saad Qamar

TOPIC FAULTS

FAULT CLASSIFICATION AND FAULT CLASSIFICATION AND TERMINALOGYTERMINALOGY

Faults:Faults: Are fractures that have appreciable Are fractures that have appreciable

movement parallel to their plane. movement parallel to their plane. They produced usually by seismic They produced usually by seismic activity.activity.

Understanding faults is useful in Understanding faults is useful in design for long-term stability of design for long-term stability of dams, bridges, buildings and power dams, bridges, buildings and power plants. The study of fault helps plants. The study of fault helps understand mountain building.understand mountain building.

Parts of the FaultParts of the Fault Fault planeFault plane: Surface that the movement has Surface that the movement has

taken place within the fault.On this surface taken place within the fault.On this surface the dip and strike of the fault is measured.the dip and strike of the fault is measured.

Hanging wall:Hanging wall: The rock mass resting on the The rock mass resting on the fault plane.fault plane.

Footwall:Footwall: The rock mass beneath the fault The rock mass beneath the fault plane.plane.

Slip:Slip: Describes the movement parallel to the Describes the movement parallel to the fault plane.fault plane.

Dip slip: Describes the up and down Dip slip: Describes the up and down movement parallel to the dip direction of the movement parallel to the dip direction of the fault.fault.

Strike slip:Strike slip: Applies where movement is Applies where movement is parallel to strike of the fault plane.parallel to strike of the fault plane.

Oblique slip:Oblique slip: Is a combination of strike slip Is a combination of strike slip and dip slip.and dip slip.

Net slip (true displacement): Is the total Net slip (true displacement): Is the total amount of motion measured parallel to the amount of motion measured parallel to the direction of motion direction of motion

Separation:Separation: The amount of The amount of apparent offset of a faulted apparent offset of a faulted surface, measured in specified surface, measured in specified direction. There are strike direction. There are strike separation, dip separation, and separation, dip separation, and net separation. net separation.

Heave:Heave: The horizontal The horizontal component of dip separation component of dip separation measured perpendicular to strike measured perpendicular to strike of the fault.of the fault.

Throw:Throw: The vertical component The vertical component measured in vertical plane measured in vertical plane containing the dip.containing the dip.

Features on the fault surface Features on the fault surface Grooves Grooves (parallel to the (parallel to the

movement direction)movement direction) Growth of fibrous mineralsGrowth of fibrous minerals

(parallel to the movement (parallel to the movement direction)direction)

SlickensidesSlickensides are the polished are the polished fault surfaces.fault surfaces.

Small steps.Small steps.All are considered a kind of All are considered a kind of

lineation. They indicate the lineation. They indicate the movement relative trend NW, movement relative trend NW, NE … etc. NE … etc.

Small steps may also be used to Small steps may also be used to determine the movement determine the movement direction and direction of direction and direction of movement of the opposing movement of the opposing wall. Slicklines usually wall. Slicklines usually record only the last moment record only the last moment event on the fault.event on the fault.

ANDERSON FAULTS CLASSIFICATION ANDERSON FAULTS CLASSIFICATION

Anderson (1942) defined Anderson (1942) defined three types of faults:three types of faults:

Normal FaultsNormal Faults Thrust FaultsThrust Faults Wrench Faults Wrench Faults

(strike slip)(strike slip)

Different Type of Faults

Normal FaultNormal FaultNormal Fault: The hanging wall has moved down

relative to the footwall.Graben:Graben: consists of a block that has dropped down consists of a block that has dropped down

between two subparllel normal faults that dip towards between two subparllel normal faults that dip towards each other.each other.

HorstHorst : : consists of two subparallel normal faults that dip consists of two subparallel normal faults that dip away from each other so that the block between the two away from each other so that the block between the two faults remains high. faults remains high.

Listric:Listric: are normal faults that frequently exhibit (concave- are normal faults that frequently exhibit (concave-up) geometry so that they exhibit steep dip near surface up) geometry so that they exhibit steep dip near surface and flatten with depth. and flatten with depth.

Normal faults usually found in areas where extensional stress is Normal faults usually found in areas where extensional stress is presentpresent..

Normal FaultsNormal Faults

Thrust FaultThrust FaultThrust Faults: In the thrust

faults the hanging wall has moved up relative to the footwall (dip angle 30º or less)

Reverse Faults: Are similar to the thrust faults regarding the sense of motion but the dip angle of the fault plane is 45º or more

Thrust faults usually Thrust faults usually formed in areas of formed in areas of comperssional stress. comperssional stress.

Thrust FaultThrust Fault

Thrust FaultsThrust Faults

Strike-Slip FaultStrike-Slip FaultStrike-slip Faults: Are faults

that have movement along strikes.

There are two types of strike slip faults:

A] Right lateral strike-slip fault (dextral): Where the side opposite the observer moves to the right.

B] Left lateral strike-slip fault (sinistral): Where the side opposite the observer moves to the left.

Note that the same sense of Note that the same sense of movement will also be movement will also be observed from the other side observed from the other side of the fault.of the fault.

Strike-Slip Strike-Slip FaultsFaults

Transform FaultsTransform FaultsTransform Faults:Transform Faults: Are a Are a

type of strike-slip faulttype of strike-slip fault (defined by Wilson 1965). (defined by Wilson 1965). They form due to They form due to the the differences in motion differences in motion between lithospheric between lithospheric plates.plates. They are They are basically occur where basically occur where type of plate boundary type of plate boundary is transformed into is transformed into anotheranother..

Main types of transform Main types of transform faults arefaults are::

Ridge-RidgeRidge-Ridge Ridge-ArcRidge-Arc Arc-ArcArc-Arc

Other types of faultOther types of fault en-echelon faults:en-echelon faults: Faults that Faults that

are approximately parallel one are approximately parallel one another but occur in short another but occur in short unconnected segments, and unconnected segments, and sometimes overlapping.sometimes overlapping.

Radial faults:Radial faults: faults that are faults that are converge toward one pointconverge toward one point

Concentric faults:Concentric faults: faults that are faults that are concentric to a point.concentric to a point.

Bedding faults (bedding plane Bedding faults (bedding plane faults):faults): follow bedding or occur follow bedding or occur parallel to the orientation of parallel to the orientation of bedding planes.bedding planes.

CRITERIA FOR FAULTINGCRITERIA FOR FAULTING Repetition or omissionRepetition or omission of stratigraphic units asymmetrical of stratigraphic units asymmetrical

repetitionrepetition Displacement of recognizable markerDisplacement of recognizable marker such as fossils, such as fossils,

color, composition, texture ..etc.)color, composition, texture ..etc.).. Truncation of structuresTruncation of structures, beds or rock units., beds or rock units. Occurrence of fault rocksOccurrence of fault rocks (mylonite or cataclastic or both) (mylonite or cataclastic or both) Presence of S or C structuresPresence of S or C structures or both, rotated porphyry or both, rotated porphyry

clasts and other evidence of shear zone.clasts and other evidence of shear zone. Abundant veinsAbundant veins, silicification or other mineralization along , silicification or other mineralization along

fracture may indicate faulting.fracture may indicate faulting. Drag UnitsDrag Units appear to be pulled into a fault during appear to be pulled into a fault during

movement (usually within the drag fold and the result is movement (usually within the drag fold and the result is thrust fault)thrust fault)

Reverse dragReverse drag occurs along listric normal faults. occurs along listric normal faults. SlickensidesSlickensides and slickenlines along a fault surface and slickenlines along a fault surface Topographic characteristicsTopographic characteristics such as drainges that are such as drainges that are

controlled by faults and fault scarps.controlled by faults and fault scarps.

conclusion

Faults are the geological structure which sometimes causes serious damaging along the fault line.

Fault may causes the earthquakes which disturbs constructions ,dams, bridges, buildings and even the whole communities

Government must have to stop and banned the construction along the fault line, to save the precious life loses.

References

www.eeescience.utoledo.edu

Web.njcu.edu/sites

Faculty.kfump.edu.sa