Studies and its significance

FaultsFaults are fractures in rocks along which

appreciable displacement has taken place.

Sudden movements along faults are the cause of most earthquakes.

Classified by their relative movement which can be Horizontal, vertical, or oblique

Components of faults

Types of FaultsDip Slip Faults.

Normal Faults.Reverse Faults.Horst and Grabben.

Strike Slip Faults. Oblique Slip Faults.

Dip Slip Faults- Movement is mainly parallel to thedip of the fault surfaceNormal Fault- Hanging

wall block moves down relative to the footwall block.

Accommodate lengthening or extension of the crust

Dip Slip FaultsHorst and Graben-

 Horst and graben refer to regions that lie between normal faults and are either higher or lower than the area beyond the faults. A horst represents a block pushed upward by the faulting, and a graben is a block that has dropped due to the faulting.

Horst and Graben are formed when normal fault of opposite dip occur in pair with parallel strike lines

Dip Slip FaultsReverse Faults-Hanging wall

moves up relative to footwall.Reverse faults have dips

greater than 450 and thrust faults have dips less then 450

If the angle of the fault plane is low (generally less than 200 degrees from the horizontal) and the displacement of the overlying block is large (often in the kilometer range) the fault is called an overthrust

Accommodate shortening of the crust

Strike Slip FaultsDominant displacement

is horizontal and parallel to the strike of the fault.

Types of strike slip fault

– Right lateral- as you face the fault, the block on the opposite side of the fault moves to the right.

– Left lateral-as you face the fault, the block on the opposite side of the fault moves to the left.

Oblique Slip FaultsA fault which has a

component of dip-slip and a component of strike-slip is termed an oblique-slip fault

Nearly all faults will have some component of both dip-slip and strike-slip, so defining a fault as oblique requires both dip and strike components to be measurable and significant.

Fault Scarp-It is defined as a tectonic landform coincident or roughly coincident with a fault plane that has dislocated the ground surface.

Fault scarps can range from small ephemeral slopes created by a single increment of displacement to a high bedrock escarpments that formed during repeated slip.

Fig-Simple scarps related to single increments of slip on a newly propagated fault. Modified from Hancock 1988

Types of Normal-Faults ScarpsPiedmont Scarp-Product of single increment of motion.Morphology-(After Wallace,1977)*Steep Free face (>500)*Moderately incline debris slope (300-400)*Gently incline wash slope (50-100)

Multiple Scarp-Related to formation of fault splay during a single faulting event.Producing multiple scarps.

Composite Scarp-Related to Renewed slip on a fault coincident with an older, degraded scarp.*Repeated displacements along the same fault.

Splintered Scarp(Cotton 1949)-Formed as a result of fault displacement being distributed across overlapping en echelon segments

Scarps associated with Reverse Faults

When the near-surface material is strong, the reverse faulting occurs on a single slip plane to form a simple overhanging scarp that collapse or erodes back.

When the surface material is weak, internal warping results in the formation of a topographic flexure called fold limb scarp

Thrust-Front Scarps

*When escarpment rise above a sharp break in slope coincident with the emergent of a thrust-flat trace, the escarpment is not a true fault scarp but rather a margin of a thrust sheet.

*The leading edge of the trust sheet has collapsed and been overridden.

*It is known as trust-front scarps in order to distinguish it from thrust-fault scarps. (Ian S Stewart and Paul L Hancock, 1990)

Strike-Slip Scarps

Faults associated with strike-slip faults are mainly the result of the juxtapositon of formerly separate areas of different height

Fig- Selected geomorphic features associated with the active strike slip faultAbbreviations-S-Sag pond; SR-Shutter Ridge; F-Fault Scarp; B-Beheaded Channel; O-Offset channel(Modified from Seih and Wallce (1987,fig 3)

Effect of repeated increments of normal and reverse faults

Bedrock escarpments can form which are several hundred meters of height in active fault zones.

Figure Spanish Fork Peak area of the Wasatch front, Utah, USA, highlighting the main morphological characteristics of tectonically active range fronts in the Basin and Range provinceAbbrevations- transverse spurs (S) and narrow, V-shaped valleys (V), triangular facets (T), piedmont (P). (from Anderson 1977,fig.17)

Effect of repeated increments of normal and reverse faults

Aegean-type range front showing both step like (S) and ramplike (R) morphologies. Taken from Stewart andHancock (1991, fig. 10)

Product of distributed normal splay faulting.

Geomorphic modification of fault scarpA-Creation of fresh piedmont scarp.B-Debris falling from a free face which results in the rapid retreat of the scarp face and progressive build up of debris slope.C-Free face is completely buried by the by the debris slope, the scarp becomes rounded.(101-102 yrs)D-The scarp decline results in the scarp profile being dominated initially by debris slope.E-In the later stage it is being dominated by wash slope

*Thus. the change from a fault scarp to a residual fault scarp (scarps from which the last remnants of the original tectonic surface has been removed) in a piedmont setting occurs when the free face becomes completely buried* In bedrock fault scarps. the removal by denudation of tectonic lineations on the fault-scarp surface would be diagnostic of a residual morphology

Fault Scarps degradationFactors-LithologyTopography- degradation. as scarps crossing ridges

generally are better preserved than scarps on midslopes or along river channels (Yuming. 1989)

The dip of the ground surface before faulting will greatly affect the preservation potential of a scarp, because scarps that slope in the direction of the ground surface before faulting are generally more degraded than scarps that face against the preexisting slope.

Microclimatic differences, such as variations in slope aspect, also have a large effect on degradation rates. For example, Pierce and Colman（ 1986) demonstrated that south-facing scarps in central Idaho, USA. degrade three times as fast as north-facing scarp.

Disparity in degradation rates became intensified as scarp height increase

Faults Scarp Degradation Fault scarps in consolidated

materials are less susceptible to denudation than those in poorly consolidated sediments, their preservation potential is greater. Thus, they are capable of describing longer, if more approximate, records of tectonic activity (Mayer, 1986)

Wallace (1977, p. 1272) contented that bedrock scarps are characterized by slower rates of change

However degradation of fault scarps follows a similar sequence of degradation despite the variation in lithology as shown in the fig. viz-gravity controlled-debris controlled-wash-controlled with decreasing slope angle with time.

Fig-Limits of maximum slope angle versus age of fault scarp. Fractured bed rock are more modified slowly than in fanglomerate. They follow a similar sequence (Modified from Wallace 1977,fig 12)

Complications in Fault Scarp DegradationIt is mainly controlled by structural heterogenityThey do not progress through a systematic and

predictable sequence of morphologic change.For eg- Pattern of degradation exhibited by normal

faults scarps in carbonate bedrock in the Aegean region.(Stewart and Hancock 1988)

A newly emergent and corrugated fault plane cut by tectonic cavities, such as pluck holes (P), and fractures and underlain by alternating layers of compact breccia (CB) and incohesive breccia (IB)

Localized breaching of the armored compact-breccia carapace occurs at sites of enhanced weathering

Uneven degradation creates a cavitated scarp.

A residual ragged and embayed fault scarp forms following the removal of the uppermost compact breccia sheet.

ConclusionsFault scarps includes diverse range of

tectonic landforms that need to be distinguished from one another.

Contrasting tectonic styles and degradational processes can lead to scarps of similar appearance, and hence, careful tectonic and geomorphic investigation is required before fault-generated landforms can be used to date faulting events.

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