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The research on the ultimate crushing state of coarse aggregates is beneficial to analyze and predict the evolutionary process of crushing. The Growing Path method uses the two-dimensional fractal geometry structure to simulate the size variation of particle size fraction during the particle breakage of coarse aggregates and it serves to investigate the ultimate fractal dimension corresponding to the ultimate crushing state of coarse aggregates. This method manifests the self-growing characteristics of particle size distribution in the process of particle crushing. This study found that the two-dimensional image of ultimate fractal model was precisely similar to that of the Sierpinski gasket of fractal theory when the ultimate crushing state was reached. The results from the model analysis show that the theoretically ultimate fractal dimension is about 2.585, which is consistent with the existing results calculated from the three-dimensional ultimate fragmentation model of cataclastic rock located in the fault zones. The relationship between two fractal models was analyzed. Furthermore, the application of fractal geometry presented in this study will also serve as a reference for the analysis of the other chaos phenomena observed in geotechnical engineering. [ABSTRACT FROM AUTHOR]

Vein networks of pseudotachylytes and ultracataclastic rocks are composed mainly of ultrafine-to fine-grained materials, including fault gouge and microbreccia, and are widely considered indicators of past seismic faulting events. I show that such vein networks of pseudotachylyte with both melt and crush origins, as well as ultracataclastic rocks, form by the rapid injection of ultrafine-to fine-grained material sourced from pulverized ultracataclastic rocks in seismogenic fault zones under thermal pressurization and fluidization during seismic events. The thermal expansion of seismic slip zones caused by frictional heating results in the rapid fluidization of ultrafine-to fine-grained materials along with expanded fluids and gases (e.g., water vapor and melt) that are injected under pressure into fracture void spaces within fault zones in a gas–solid–liquid system during large earthquakes. I propose that the thermal expansion of water vapor and ultrafine-to fine-grained materials caused by frictional heating in the fault slip zone is the main mechanism responsible for the dramatic increase in pore pressure that results in the dynamic coseismic weakening of faults. • Vein networks of pseudotachylyte (Pt) are indicators of seismic faulting. • Pt veins are sourced from by pulverized ultracataclastic rocks in seismic fault zones. • Thermal pressurization and fluidization occurred in fault zone during seismic faulting. • Thermal expansion of seismic slip zones caused by frictional heating in fault zones. • Thermal expansion is a main mechanism of dynamic coseismic weakening of faults. [ABSTRACT FROM AUTHOR]

Abstract Structures, lithofacies and semi-quantitative sedimentological analysis of volcanic debris-avalanche deposits are essential to constrain syn-emplacement processes along avalanche fault zones in the setting of mass-flow runout distances. At a distance of 28 km from the extinct Pichu Pichu compound volcano, we show how internal structures of thrust lobes, faulted as to form horst- and graben-like structures, have recorded the brecciation with granular segregations. Cataclastic gradients have been recognized in more than eleven breccia structures with statistical grain-size parameters, among them fractal D -values between 1.96 and 2.53 related to an extensional fracturing in DADs with fractal D -values between 2 and 2.5 leading to granular disaggregation with fractal D -values between 2.13 and 2.22. Primary fractures related to transport processes and the secondary cataclasis produced during emplacement are quantified as having <50% matrix, while the avalanche transformations into lahar deposits occur with >50% matrix. The hybrid lithofacies in graben-like structures may be the precursory stages of the matrix transformation into lahar deposits. Volcanic debris-avalanche structures of eleven worldwide volcanoes that belong to the Central Andes and the Cascades volcanic arc have been compared using sedimentary and statistical methods (156 sieved samples and Shape Preferred Orientation measured on 30,342 clasts). Median diameter, sorting index, skewness and kurtosis values help differentiate four deposits and processes: (1) the proximal gravitational collapse deposits; (2) the avalanche thrust lobes, located in inverted extensional fault zones, and (3) the hybrid and mixed deposits with polymodal distributions; and (4) the bimodal, transformed matrix with clast sorting. The fractal D -values of avalanche matrix range between 2.3 and 2.7, suggesting that extensional fractures have led to granular disaggregation. From the available statistical dataset, a few equations have been developed that help pointing to a syn-emplacement cataclastic gradient along avalanche fault zone. Three textural classes of avalanche fault zones have been identified based on the ellipse/ a / b values of ~2.14 for the planar collapse in fault zone, 1.75 to 2 for the crushing of volcanic avalanche breccias, and <1.7 due to the thermal effect of clast fragmentation. Inherited clast shapes with a / b = 2.5 and ellipse = 4 suggests a co-evolution of avalanche lithofacies. A sedimentological classification of avalanche fault zones proposed here has been related to the syn-emplacement processes of DAD structural units. As a result, the semi-quantitative texture dataset helps constrain the different stages of avalanche runout and the transformation steps into lahar deposits. Highlights • We study internal structures of the Pichu Pichu thrust lobe in extensional fault. • Cataclastic gradient is correlated to granular segregations in transformed matrix. • Precursory stages of the avalanche transformations include the mixed lithofacies. • We compare Pichu Pichu DAD with avalanche textures of eleven worldwide volcanoes. • Semi-quantitative textural classes of avalanche fault zone are established. [ABSTRACT FROM AUTHOR]

This study presents a comparative, field-based hydrogeological characterization of exhumed, inactive fault zones in low-porosity Triassic dolostones and limestones of the Hochschwab massif, a carbonate unit of high economic importance supplying 60 % of the drinking water of Austria's capital, Vienna. Cataclastic rocks and sheared, strongly cemented breccias form low-permeability (<1 mD) domains along faults. Fractured rocks with fracture densities varying by a factor of 10 and fracture porosities varying by a factor of 3, and dilation breccias with average porosities >3 % and permeabilities >1,000 mD form high-permeability domains. With respect to fault-zone architecture and rock content, which is demonstrated to be different for dolostone and limestone, four types of faults are presented. Faults with single-stranded minor fault cores, faults with single-stranded permeable fault cores, and faults with multiple-stranded fault cores are seen as conduits. Faults with single-stranded impermeable fault cores are seen as conduit-barrier systems. Karstic carbonate dissolution occurs along fault cores in limestones and, to a lesser degree, dolostones and creates superposed high-permeability conduits. On a regional scale, faults of a particular deformation event have to be viewed as forming a network of flow conduits directing recharge more or less rapidly towards the water table and the springs. Sections of impermeable fault cores only very locally have the potential to create barriers. [ABSTRACT FROM AUTHOR]

Brittle fault rock samples from carbonate shear zones along the Salzach-Ennstal-Mariazell-Puchberg fault system (SEMP) have been analysed using cathodoluminescence microscopy (CL), microprobe analysis and stable isotope composition. The combination of these analytical methods provides an insight into comminution processes and fluid chemistry. The reconstruction of the evolution of fluid chemistry leads to a chronological classification of five fluid phases with respect to fluid chemistry, CL behavior and related structural processes. Initial cataclasis is accompanied by dedolomitization processes along crystal borders and intragranular fractures (Phase P1). Subsequent fluid precipitation phases (P2-P5) are characterized by variable Fe- (and Si-content) and therefore variable CL behavior. Microprobe element mappings support the discrimination of Fe-bearing, non luminescent phases and Ca- and Mn- bearing fluids with bright luminescent calcite precipitations. Fe-bearing carbonates and Fe-hydroxide precipitation indicates fluid circulation in deeper parts of the stratigraphic sequence. These fluids are assumed to be derived from underlying clastic sequences of the Werfen Formation. Stable isotope signatures (d13C and d18O) indicate mainly meteoric origin of penetrating fluids and variable amounts of fluids in the fault zone. [ABSTRACT FROM AUTHOR]

Slip along faults generates wear products such as gouge layers and cataclasite zones that range in thickness from sub-millimeter to tens of meters. The properties of these zones apparently control fault strength and slip stability. Here we present a new model of wear in a three-body configuration that utilizes the damage rheology approach and considers the process as a microfracturing or damage front propagating from the gouge zone into the solid rock. The derivations for steady-state conditions lead to a scaling relation for the damage front velocity considered as the wear-rate. The model predicts that the wear-rate is a function of the shear-stress and may vanish when the shear-stress drops below the microfracturing strength of the fault host rock. The simulated results successfully fit the measured friction and wear during shear experiments along faults made of carbonate and tonalite. The model is also valid for relatively large confining pressures, small damage-induced change of the bulk modulus and significant degradation of the shear modulus, which are assumed for seismogenic zones of earthquake faults. The presented formulation indicates that wear dynamics in brittle materials in general and in natural faults in particular can be understood by the concept of a 'propagating damage front' and the evolution of a third-body layer. [ABSTRACT FROM AUTHOR]

Shear zones in outcrops and core drillings on active faults commonly reveal two scales of localization, with centimeter to tens of meters thick deformation zones embedding much narrower zones of mm-scale to cm-scale. The narrow zones are often attributed to some form of fast instability such as earthquakes or slow slip events. Surprisingly, the double localisation phenomenon seem to be independent of the mode of failure, as it is observed in brittle cataclastic fault zones as well as ductile mylonitic shear zones. In both, a very thin layer of chemically altered, ultra fine grained ultracataclasite or ultramylonite is noted. We present an extension to the classical solid mechanical theory where both length scales emerge as part of the same evolutionary process of shearing the host rock. We highlight the important role of any type of solid-fluid phase transitions that govern the second degree localisation process in the core of the shear zone. In both brittle and ductile shear zones, chemistry stops the localisation process caused by a multiphysics feedback loop leading to an unstable slip. The microstructural evolutionary processes govern the time-scale of the transition between slow background shear and fast, intermittent instabilities in the fault zone core. The fast cataclastic fragmentation processes are limiting the rates of forming the ultracataclasites in the brittle domain, while the slow dynamic recrystallisation prolongs the transition to ultramylonites into a slow slip instability in the ductile realm. [ABSTRACT FROM AUTHOR]

Abstract: Field investigations reveal spatial variations in fault zone width along strike-slip active faults of the Arima–Takatsuki Tectonic Line (ATTL) and the Rokko–Awaji Fault Zone (RAFZ) of southwest Japan, which together form a left-stepping geometric pattern. The fault zones are composed of damage zones dominated by fractured host rocks, non-foliated and foliated cataclasites, and a fault core zone that consists of cataclastic rocks including fault gouge and fault breccia. The fault damage zones of the ATTL are characterized by subsidiary faults and fractures that are asymmetrically developed on each side of the main fault. The width of the damage zone varies along faults developed within granitic rocks of the ATTL and RAFZ, from ∼50 to ∼1000 m. In contrast, the width of the damage zone within rhyolitic tuff on the northwestern side of the ATTL varies from ∼30 to ∼100 m. The fault core zone is generally concentrated in a narrow zone of ∼0.5–∼5 m in width, consisting mainly of pulverized cataclastic rocks that lack the primary cohesion of the host rocks, including a narrow zone of fault gouge (<0.5 m) and fault-breccia zones either side of the fault. The present results indicate that spatial variations in the width of damage zone and the asymmetric distribution of damage zones across the studied strike-slip faults are mainly caused by local concentrations in compressive stress within an overstep area between left-stepping strike-slip faults of the ATTL and RAFZ. The findings demonstrate that fault zone structures and the spatial distribution in the width of damage zone are strongly affected by the geometric patterns of strike-slip faults. [Copyright &y& Elsevier]

Abstract: Field investigations, combined with meso- and microstructural analyses, reveal that numerous ultracataclastic veins are widely developed within a fault zone (<150 m wide) as simple veins, complex lenses, and networks, along active faults of the Arima–Takatsuki Tectonic Line, southwest Japan. These veins comprise mainly pseudotachylyte-like vein and weakly consolidated to unconsolidated fault gouge that is black, dark-brown, brown, gray, and brownish-red in color. Meso- and microstructural features show that these pseudotachylyte-like and fault gouge veins and networks formed during multiple stages, as earlier veins are generally cut and overprinted by younger veins, indicating that the vein-forming events occurred repeatedly and that ultracataclastic material was injected into networks of faults and fractures in the fault zone. The pseudotachylyte-like and fault gouge veins are characterized by an ultrafine- to fine-grained matrix and angular to subangular fragments of host granitic rocks of various sizes, ranging from submicron to millimeters. SEM–EDS (Scanning Electronic Microscope-Energy Dispersive X-ray) and powder X-ray diffraction analyses show that all the ultracataclastic veins are characterized by crystalline materials composed mainly of quartz and feldspar, similar to the host granitic rocks. The present results support the existing hypothesis that ultrafine- to fine-grained materials formed by comminution can be fluidized and injected rapidly into fracture networks located far from the source fault plane in a solid–fluid–gas system during seismic slip; therefore, such materials provide a record of paleoseismic faulting events that occurred repeatedly within the seismogenic fault zone. [Copyright &y& Elsevier]

Abstract: The internal structure of the Median Tectonic Line (MTL) fault zone and the processes that prevailed at depths are described based on an analysis of a borehole. The fault plane which defines the boundary between the Ryoke- and Sanbagawa-derived rocks dips at 56° to the north. Immediately beneath the boundary, approximately 40m thick fractured rocks form the major strand of the MTL fault zone. The hanging wall above the boundary comprises variably deformed Ryoke granitoids, including several mylonite zones and cataclasite zones. The fault zone has evolved through a series of faulting events under temperatures ranging from 400 to 200°C. The mineral assemblages of the mylonites and cataclasites immediately above the boundary indicate that these fault rocks were formed at temperatures of about 300°C. These mylonites and cataclasites represent, therefore, fault rocks that formed immediately below and above the brittle–plastic transition, respectively. Development of dissolution seams in these cataclasites suggests that the cataclasite has low strength. The presence of pseudotachylytes in the cataclasite indicates the occurrence of seismicity immediately above the brittle–plastic transition. On the other hand, the very fine grain size of recrystallised quartz in the mylonites indicates high differential stress immediately below the brittle–plastic transition. It is therefore likely that the differential stresses immediately below the brittle–plastic transition are much higher than those immediately above the transition. Formation of laumontite in the major strand of the MTL fault zone occurred at temperatures of around 200°C. The central slip zone of the major strand is about 30-cm thick, and is surrounded by thick gouge zones. This situation is favourable for thermal pressurisation during earthquake slips. [Copyright &y& Elsevier]

Geological and geophysical evidence suggests that some crustal faults are weak compared to laboratory measurements of frictional strength. Explanations for fault weakness include the presence of weak minerals, high fluid pressures within the fault core and dynamic processes such as normal stress reduction, acoustic fluidization or extreme weakening at high slip velocity. Dynamic weakening mechanisms can explain some observations; however, creep and aseismic slip are thought to occur on weak faults, and quasi-static weakening mechanisms are required to initiate frictional slip on mis-oriented faults, at high angles to the tectonic stress field. Moreover, the maintenance of high fluid pressures requires specialized conditions and weak mineral phases are not present in sufficient abundance to satisfy weak fault models, so weak faults remain largely unexplained. Here we provide laboratory evidence for a brittle, frictional weakening mechanism based on common fault zone fabrics. We report on the frictional strength of intact fault rocks sheared in their in situ geometry. Samples with well-developed foliation are extremely weak compared to their powdered equivalents. Micro- and nano-structural studies show that frictional sliding occurs along very fine-grained foliations composed of phyllosilicates (talc and smectite). When the same rocks are powdered, frictional strength is high, consistent with cataclastic processes. Our data show that fault weakness can occur in cases where weak mineral phases constitute only a small percentage of the total fault rock and that low friction results from slip on a network of weak phyllosilicate-rich surfaces that define the rock fabric. The widespread documentation of foliated fault rocks along mature faults in different tectonic settings and from many different protoliths suggests that this mechanism could be a viable explanation for fault weakening in the brittle crust. [ABSTRACT FROM AUTHOR]

Abstract: The factors controlling the development of different types of fault rock assemblages and, more specifically, the formation of friction melts are still not fully understood. In this study we compared two exhumed strike–slip faults in the Adamello batholith (Southern Alps): the Gole Larghe and the Passo Cercen fault zones, active at 9–11km depth and temperatures of 250–300°C. Each fault zone consists of hundreds of sub-parallel strands exploiting pre-existing joints. The Gole Larghe fault strikes N105±5° and is dextral; the fault rocks are cataclasites and widespread, centimetre-thick pseudotachylytes. The Passo Cercen fault strikes on average N130° and is formed by multiple fault horizons: fault segments striking N105°–N130° are mainly dextral, whereas faults striking N135°–N140° are mainly sinistral. Microstructural, mineralogical and geochemical investigations show that the fault rocks are cataclasites associated with thick epidote+K-feldspar+quartz veins and rare, millimetre-thick pseudotachylytes. Field evidence suggests that in both fault zones, the direction of the maximum horizontal stress σ 1 was N135°. The Gole Larghe fault strikes at about 30° to σ 1 and is favourably oriented for reactivation. By contrast, the Passo Cercen fault strikes at low angles to σ 1 and is unfavourably oriented for reactivation, therefore requiring the development of high pore pressures, as suggested by the occurrence of extensive epidote veining and hydraulic breccias. It is proposed that frictional melting in the Passo Cercen fault zone was inhibited by the development of high pore pressures and low effective normal stresses. [Copyright &y& Elsevier]

Cataclastic rocks, as clay-rich fault gouges, are commonly present in brittle rock masses when fault zones appear during geological engineering projects. Highly deformed rocks that are of poor mechanical quality can lead to technical, safety, and economic problems in rock engineering. The aim of this study is to characterise the resistant behaviour of a highly deformed clay-rich gouge >40 m wide with a marked tectonic fabric that indicates strength anisotropy. We present the results of consolidated-undrained (CU) triaxial tests that were performed at low confining pressures (50, 150, and 300 kPa) on several sets of foliated gouge specimens with four different orientations in the tectonic fabric. Specimens were collected from the encapsulated rock cores of two research boreholes drilled through the Alhama de Murcia Fault (AMF), a main regional fault located in SE Spain. The strain–stress relationships and failure modes were established, indicating that the gouge behaves as hard soil or very soft rock. The test results were adjusted at each orientation using the non-linear Hoek and Brown criteria by considering the fault gouge as an intact material or as a tectonised rockmass. Here, we use the Geological Strength Index (GSI) as an indicator of the rockmass strength that depends on the direction of the tectonic fabric. However, the results from specimens with tectonic fabric that is oriented most favourably for failure were not the weakest in terms of rock strength. Such an anomalous result could be the result of asymmetry in the roughness of the weakness planes that is related to the original gouge microstructure characterised by the strong reorientation of clays in an S-C′ like tectonic fabric. Our results will be useful for practical applications that are related to the stability of slopes and/or shallow underground excavations in brittle fault zones, and provide an inexpensive and easy way to preliminarily evaluate the anisotropic behaviour of this type of brittle fault zones for future engineering projects. • Strength of a foliated clay-rich fault gouge is controlled by roughness within the weak planes. • Gouge microstructure defined by strong reorientation of clays in a S-C' fabric controls the roughness of the weakness planes • Strength of clay gouges shows a medium to low anisotropy. • GSI is a sensitive index with which the strength anisotropy of tectonised rocks can be investigated. [ABSTRACT FROM AUTHOR]

Fault zone structure and permeability data from the Median Tectonic Line (MTL) in Mie Prefecture, Southwest Japan suggest that fault permeability models are currently too simplistic for such large structurally complex fault zones. Ryoke Belt mylonites are cut by mineralised brittle structures up to 300 m North of the MTL that show evidence of fluid circulation. The Sambagawa schist on the south side of the MTL is deformed into foliated quartz/phyllosilicate gouge across a 15-m-wide zone. The complex fault contact area has foliated cataclasite up to 4 m wide, and is cut by a narrow central planar slip zone that probably represents the most recent seismogenic principal displacement zone. Laboratory-determined permeability data show wide variation with fault rock microstructure (e.g. gouge microclast size), controlled by structural position in the fault zone and slip zone intersections. Central slip zone gouges have the lowest permeabilities of all of the fault rocks studied. Fault permeability models should take into account asymmetry where widely contrasting protolith lithologies exist and large permeability variations within a complex central fault zone ‘core’. Pore pressure evolution during rupture propagation may vary greatly because of this complexity, but thermal pressurisation is feasible above certain pressures if the slip remains within fine-grained gouge. The different deformation behaviours of contrasting protolith lithologies control the fault zone fabrics and hence final permeability structure. [Copyright &y& Elsevier]

Abstract Cataclastic rocks found in the Disaster Prevention Research Institute, Kyoto University (DPRI) 500 m drill core and outcrops along the Nojima Fault zone on Awaji Island, southwest Japan, were examined at mesoscopic and microscopic scales. The damaged zone of this fault in granitic rocks, observed on the southeast side of the fault, is 50–60 m wide and is composed of fractured host rocks and cataclastic rocks including cataclasite, fault breccia, and fault gouge. The fault breccia and gouge of small scales are scattered in the damaged zone. Fault core (zone of extremely concentrated shearing deformation along a fault) consists of fault gouge measuring several tens to approximately 150 mm in width, as recognized both in the drill core and at outcrops of the Nojima Fault along which surface ruptures formed during the 1995 Kobe earthquake. Fault breccia, measuring a few meters wide, has developed pervasively in the damaged zone, just next to the fault core. Pseudotachylyte has been found interlayered with fault gouge within the fault core only at outcrops at Hirabarashi, not in the DPRI 500 m core. Petrological studies and powder X-ray diffraction analysis show that the pseudotachylyte and fault gouge are composed mainly of fine-grained angular clasts of the host granitic rocks, suggesting the pseudotachylyte is of ‘crush origin’. Foliated cataclasite is characterized by the preferred orientation of elongated biotite clasts and granular aggregates of quartz and feldspar clasts, and by the development of cataclastic shear bands. Unlike cataclastically deformed quartz and feldspar in the cataclasite, biotite in the foliated cataclasite shows combinations of brittle and plastic deformation, such as biotite ‘fish’, cleavage steps, bending and kinking. These textures suggest that the foliated cataclasite formed at a deeper level than the cataclasite, fault breccia and gouge, possibly before the Quaternary period during which... [ABSTRACT FROM AUTHOR]

Low-porosity carbonates in San Vito lo Capo underwent two episodes of faulting: extensional faulting in the late Miocene and strike-slip faulting in the Plio-Pleistocene. Limestones and dolostones reacted differently to these faulting events. The first extensional faulting event within the limestone formed localized faults with a single fault core surrounded by a damage zone. The fault rock was either dolomitized as deformation proceeded or resealed by calcite cement after brecciation. The dolomitized fault rocks were reactivated during the following strike-slip faulting, forming polyphase breccias. On the other hand, strain was distributed in dolostones throughout a wider area during the extensional faulting forming a pulverized fault zone. The pulverized rock experienced cataclastic deformation during the following strike-slip faulting forming anastomosing networks of cataclastic shear bands. Fault cores hosted in the limestone appear to have acted as flow conduits until they were cemented or hardened due to evolving cataclasis. The cataclastic shear bands in the dolostone are likely to form baffles to flow, at least on a local scale. The fracture spacing in the damage zone also varies significantly between the lithologies. In particular, damage zones in the limestone have a 5–10 cm fracture spacing whereas fracture spacing is 0.5–3 cm in the dolostone. It is likely that the differing mechanical and chemical properties of the dolostone and limestone were responsible for creating contrasting fault zone architectures. • Displacement in tight limestone tends to be localized along a single fault core. • Cemented fault rock is unlikely to be reactivated. • Non-cemented fault rock acts as a conduit to fluid flow and hence is often dolomitized. • Fault zones in tight dolostone often comprise a network of cataclasite shear bands. • Fractures often abut against the cemented fault cores and cataclasite shear bands. [ABSTRACT FROM AUTHOR]

• We establish that strain can be quantified from rocks deformed by cataclastic flow. • Strain pattern in the trishear model of fault propagation folding is validated. • Balanced cross sections in the frontal Himalaya are improved by strain inclusion. • Our methodology can be used in external thrust sheets in all fold-thrust belts. Pure strain is an important component of the total displacement vector in fold-thrust belts like the Himalayan orogenic belt. We describe a methodology to compute cataclastic strain from external thrust sheets using the Bootstrapped Modified Normalized Fry Method and validate it in two different structural settings in the frontal Himalaya. In the frontal imbricate zone of the Dharan salient in the Darjiling Himalaya we measured the highest strain from a central imbricate thrust (T3) and found that strain decreased away from the fault zones within individual thrust sheets. Modelling of our results indicated that there was significant layer-perpendicular flattening in the fault zones while layer parallel shortening related strain dominated the thrust sheets. Also, fault parallel shear decreased away from the fault zones. In contrast, layer-perpendicular flattening was largely absent in the fault zone associated with the Main Frontal thrust (MFT) and the MFT sheet in the Mohand Range of the Dehradun recess. Here the strain distribution pattern was consistent with a trishear fault propagation monocline which is our preferred model for the structure of the MFT sheet in the recess. Modelling of our results suggested that fault parallel shear decreased away from the MFT fault zone like in the thrust sheets from the Dharan salient and that the fault propagation folding was accomplished by flexural slip folding. We contend that our methodology can be effectively used to quantify and study the pure strain part of the total displacement vector in external thrust sheets from fold-thrust belts worldwide. [ABSTRACT FROM AUTHOR]