the bristol mendip foreland thrust belt the thrusts and associated fold structures of the bristol mendip area are interpreted in terms of a thin skinned piggy back foreland thrust belt of variscan age with dominant northward transport strike normal balanced sections and compatible strike parallel sections have been constructed to illustrate the 3 d geometry of the linked thrust system north south shortening of c 20 km 40 is calculated from deformed and restored strike normal sections a thick and extensive thrust wedge of pre old red sandstone basement in the west of the area is responsible for culminations expressed at the surface as the mendip periclines uplifted culminations permit erosion to lower stratigraphic levels in the west and south of the area strike parallel sections and a hanging wall cut off map indicate that the majority of thrusts in the area are mainly oblique ramps rather than simple frontal and lateral ramps or flats the en echelon pattern of the mendip periclines may be related to the oblique ne climb of two of these thrusts the angle of frontal ramp climb through the dinantian stratigraphy is generally low and this explains the presence of numerous klippen of lower on upper carboniferous rocks whilst suggesting that certain thrust sheets were much more extensive than present outcrops indicate early pre thrusting movement on basement lineaments in the variscan foreland created uplifts angular unconformities and a predominance of n s structures in the north of the area

displacement efficiency of faults and fractures abstract faults and fractures evolve kinematically as somigliana dislocations as a result displacement gradients are always present with displacements reducing to zero at fault fracture tips we present a graphical method for the comparison of displacement gradients from fractures of various magnitudes and types displacement efficiency of a fault fracture is defined as its ability to maximise displacement across its surface

thrust fracture network and hydrothermal gold mineralization witwatersrand basin south africa abstract this paper examines the geometry and genesis of a mineralized thrust related fracture system developed at a major rheological interface between witwatersrand sediments and ventersdorp volcanics in the witwatersrand basin of south africa at the elandsrand gold mine the conglomeratic ventersdorp contact reef which separates these successions is imbricated by kilometre wide zones of minor thrusts containing ultracataclastic fault rocks associated with hydrothermal fluid flow several sets of fractures are intimately associated with the imbricates which link to underlying kilometre scale thrusts the fractures provided a linked fluid flow pathway and structural sites for precipitation of gold within the ventersdorp contact reef carrying 900f observed gold with the remaining 100ccupying post diagenetic matrix corrosion spaces within a few 100 m of fractures the relatively rigid volcanics deformed into low amplitude kilometre wavelength flexures centred on the imbricate zones and underlying kilometre scale thrusts these major structures controlled the thrust fracture system formation along the ventersdorp contact reef lava contact three progressive stages of structural evolution were identified 1 layer parallel shear across the contact with stratigraphy focused shallow fracture formation 2 propagation of a kilometre scale thrust towards the contact leading to kilometre scale flexure of the volcanics with layer parallel shearing in the limbs producing steep fractures and minor thrusts 3 propagation of the major thrust along the contact imbricating the sediments with shallow fracture formation in ramps

3 d anatomy of an active fault propagation fold a multidisciplinary case study from tsaishi western caucasus georgia abstract ongoing deformation processes combining fault propagation and folding are the cause of diffuse seismicity in many areas of the world a detailed understanding of the structural evolution of tectonically active folds is crucial for the evaluation of seismic hazard this paper proposes an integrated analysis of an active fold consisting in the development of a 3d model by combination of geomorphological observations field geological structural data and seismic reflection sections our case study is the tsaishi anticline located at the southwestern tip of the rioni basin uplifted area at the foothill of greater caucasus western georgia we recognized that the fold started to form since the beginning of the middle miocene although preliminary data suggest the possibility of initial local uplift in the oligocene folding process continues up to nowadays giving rise to a south vergent anticline as shown by upwarped late quaternary river deposits the fold backlimb is affected by three main back thrusts whereas at the foot of the forelimb a main north dipping thrust comes very close to the surface based on seismic sections here field data show the presence of a 13 km long fault scarp or fold scarp along the scarp is located the epicenter of the strongest earthquake to date the ms 6 0 tsaishi earthquake that struck the area in 1614 ce based on our results we propose that the overall structure can be classified as an active fault propagation fold the recognition of its very recent growing associated with a major underlying active fault represents also a major contribution to the seismic hazard assessment of this populated area

strain variation in the henaux basse normandie duplex northern france abstract a completely exposed section through a miniature duplex developed in carboniferous limestones exists in a disused quarry and an adjacent railway cutting in the boulonnais region of northern france the structure is unique in that the propagating tip of the duplex where the shortening dies to zero is exposed a balanced restored section reveals an overall contraction of 38 7 increasing from zero at the duplex tip to over 70 at the distal end the limestone beds above the roof thrust of the duplex have shortened by 24 5 in a complex of foreland and orogen dipping thrusts which are typically developed above decollements

2 d modelling of the anticlinal structures and structural development of the eastern fold belt of the bengal basin bangladesh abstract structural architecture of the bengal basin has been strongly controlled by the collision pattern of the indian plate with the burma and tibetan plates the eastern fold belt efb of the basin comprising a series of north south trending curvilinear anticlines and synclines represents a fold and thrust belt that constitutes the westward continuation of arakan chin fold system of the indo burman ranges the present study is mainly concerned with the 2 d modelling of the anticlinal structures in order to develop an understanding about the process response relationships between the structural style and tectonic evolution of the eastern fold belt the dominant fold generating mechanism is believed to be the east west directed compressional force arising from oblique subduction of the indian plate beneath the burma plate that resulted in the growth of fault propagation folds above a detachment or decollement at depth giving rise to the neogene accretionary prism complex development a prominent feature of the region is the major east dipping thrusts separating successive accretionary wedges in seismic sections evidence for several phases of compressional deformation suggests that multiphase stress conditions were responsible for the structural expression of the fold belt deep seismic sections reveal that the base of folding is characterized by a low interval velocity horizon that represents a detachment separating the upper folded zone from the lower seismically coherent nearly unfolded zone this detachment coincides with the undercompacted pressured shale unit which is thought to have played an important role in the structural development of the eastern fold belt clay mineralogical analysis reveals the presence of a low density shale horizon within the dense and thick shale sequence that is thought to be an undercompacted pressured shale during the geological past and was responsible for the initiation of decollement and incipient diapirism involving thin skinned tectonics it is suggested that the salient structural features of the eastern fold belt e g multiphase fold development series of east dipping thrusts and a basal zone of detachment or decollement are the products of thin skinned tectonics resulting from the indo burmese plate convergence

lateral and vertical changes of deformation style in the osen roa thrust sheet oslo region abstract changes in deformation style and amounts of shortening in the osen roa thrust sheet of the oslo region occur vertically and laterally approaching the thrust front in the south deformation in the cambromiddle ordovician sequence passes laterally from closely spaced imbricates in the north 50 60 shortening through triangle pop up and imbricate zones toward the south 20 37 shortening to widely spaced zones of deformation up to 20 shortening approaching the thrust front changes in deformation style are attributed to changing boundary conditions across the klekken thrust declining end of orogenic forces and an increase in thickness of competent units in the ordovician rocks to the south vertical changes in deformation style are attributed to the increasing percentage of competent units upward in the cambro silurian sedimentary rocks in the north the accompanying decrease in shortening upwards requires a structurally necessary upper detachment horizon to separate folded late middle ordovician silurian sediments from imbricated early cambro middle ordovician sediments below while southward in the oslo area the upper detachment needs to be placed between silurian and cambro ordovician units finally in eiker with less than 20 shortening the whole cambrosilurian sequence appears to have deformed as a single unit in the northern oslo region the upper detachment probably has a backthrust sense of motion above an imbricate stack passive roof duplex further south the upper detachment is probably directed toward the foreland

nature of thrust zones in deep water sand shale sequences outcrop examples from the champsaur sandstones of se france compressional structures are commonly found in deep water turbidite successions that contain important hydrocarbon reservoirs here we present a field study of deformation in the champsaur sandstones of the french alps to illustrate the geometry of natural thrust zones in weakly lithified turbidites the evolution of these zones results from a combination of faulting and folding a general model for thrust zone evolution is developed where even though there is a tendency to produce localised through going slip surfaces folding can occur at various stages segments of dismembered fold limbs carried up thrust ramps potentially increase the fault zone permeability and fluid communication through the stratigraphic pile the propensity for folding is increased by the presence of thin bedded sand shale successions while imaging these detailed architectures may lie beyond the reach of seismic methods in the sub surface it may be possible to predict the nature of thrust zones from knowledge of the sand shale stratigraphy and vice versa

testing thrust tectonic models at mountain fronts where has the displacement gone the alternative relationships that can exist between a mountain front and the adjacent foreland basin have been recognized for many years however seismic reflection data from such areas are commonly of poor quality and therefore structural models may contain large uncertainties in view of scientific and commercial interest in mountain belts we have reviewed the methods for discriminating between alternative interpretations using a case study from the montagna dei fiori in the central apennines italy in this area mesozoic and tertiary carbonate sediments are juxtaposed with a foredeep basin containing up to 7 km of messinian and plio pleistocene siliciclastic sediments a new structural model for this area demonstrates how the structures in this area form a kinematically closed system in which displacement is transferred from the thrust belt to blind structures beneath the present day foreland growth strata show that pliocene shortening was initially rapid 15 mm a 1 followed by slower rates during the final stages of deformation variations in structural elevation indicate a component of basement involvement during thrusting and this is further supported by magnetic modelling the results illustrate the interaction of thin and thick skinned structures in the central apennines and the methods for discriminating between alternative structural models

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model reply abstract fault planes propagate radially from a point source and this failure propagation process is very similar to the movement of a dislocation through a crystal lattice an elastic strain represented by an extra half plane is necessarily imparted to the lattice at an edge dislocation and this is equivalent to the ductile bead which accompanies the propagating tip of a thrust fault this ductile bead migrates with the fault tip and imparts a characteristic internal strain to the thrust sheet a two dimensional model is presented to illustrate the inter relationship between fault plane slip fault tip propagation and internal strain in multilayered sequences internal strain is usually represented by asymmetric folds verging in the thrust transport direction a simple technique the displacement distance plot utilizes the fact that displacement dies out towards the fault tip this plot can be used to quantify the relative stretch measured parallel to the fault movement which is dependent on the slip propagation rate and it may be used to define exactly the position of the fault tip on a cross section examples of fold thrust structures from devon england and pembrokeshire wales are used to illustrate the technique

origin of a thrust related fold geometric vs kinematic tests abstract geometric tests to determine the origin of fault related folds are common but as is typical in structural geology more than one fold origin may yield the final natural geometry thus the results of geometric tests are usually non unique in contrast kinematic tests of origin which employ both geometry and data about deformation commonly yield more constrained if not unique results unfortunately the necessary data collection requires much more work than for a geometric test in this study the thrust related barclay anticline is analyzed both geometrically and kinematically to determine which test is more effective geometric tests using angular relationships indicate three possible origins fault bend fault arrest and break thrust for the kinematic test predicted deformations for interlayer and flexural slip flexural flow simple shear and bending strains are compared to micro and mesostructural distributions solution strain and finite strain from the anticline strain measurements indicate that microscale deformation is uniformly distributed through the structure and is lithification dominated the microscale deformation does not match kinematic predictions and did not accommodate fold formation fold growth was achieved primarily through layer parallel slip restricted mostly to the forelimb and absent in the hinge which eliminates fault bend and fault arrest origins that require material transport from forelimb to backlimb the barclay anticline is therefore interpreted to be a break thrust structure interestingly a suite of contraction faults in the forelimb and hinge indicates material transport from forelimb to backlimb such transport has been discounted for break thrust folds the most important result of this study is that a kinematic test was a necessary step for distinguishing fold origin geometric testing alone was insufficient given that the barclay anticline has geometric characteristics typical of many thrust related folds kinematic testing appears necessary to determine their structural origin

progressive evolution of a fault related fold pair from growth strata geometries sant llorenc de morunys se pyrenees abstract new structural stratigraphical mapping constrains the three dimensional kinematics and mechanisms of eocene oligocene growth folding at sant llorenc de morunys ne ebro basin spain a 1 km wide sub vertical panel of syntectonic alluvial gravels passes southwards via a highly asymmetrical growth fold pair to shallowlydipping strata the axial surface of the anticline comprises either continuous or en echelon segments while that of the syncline is concave and usually continuous while converging upwards the axial surfaces do not define growth triangles principal and subsidiary growth unconformities and thickness changes occur across both axial surfaces and the common limb dips within the common limb decrease up stratigraphy and up dip mesostructures indicate that internal deformation was ongoing during folding at all stratigraphical levels and concentration of cleavage in the syncline indicates that this hinge was essentially fixed sequential restoration of three profiles shows that folds amplified principally by limb rotation but incorporated minor passive hinge migration particle movement vectors generated by section restoration are arcuate about a hinterland pinpoint a new trishear model of fault propagation folding involving non rigid limb rotation reproduces the rounded hinge forms thickening geometries and limb dip variations observed simple kink band migration models fixed axis and constant thickness theories do not replicate these features

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

thrust tectonics a personal view the structure of fold and thrust belts has been studied for just over one hundred years and has been the subject of a recent international conference at toulouse in may 1984 this article reviews some of the recent advances in thrust tectonics from a personal viewpoint in the light of the toulouse meeting key tools in correctly interpreting thrust systems are the use of balanced restorable cross sections and the resolution of three dimensional fault systems these analytical methods are now being widely developed and applied to numerous orogenic belts with many surprising results while our understanding of foreland thrust belts is now probably better than any other structural environment there is still great uncertainty as to the emplacement driving mechanisms of these belts future work will try to solve these and other outstanding problems and apply the new analytical methods to the interior parts of thrust belts in efforts to restore entire orogens

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

ancient synsedimentary structural control on thrust ramp development an example from the northern apennines italy the umbria marche sabina foreland fold and thrust belt northern apennines italy provides excellent test cases for the hypothesis of ancient syndepositional structural features controlling thrust ramp development the sedimentary cover late triassic to miocene in age is made of platform and pelagic carbonates whose deposition was controlled by significant synsedimentary extension normal faulting mainly during the jurassic and the late cretaceous palaeogene determined sensible lateral thickness variations within the relative sequences by late miocene the sedimentary cover was detached from its basement along a mainly evaporitic horizon and was deformed by means of eastward verging folds and thrusts in order to locate the points where thrust ramps branch off the basal detachment both line length and equal area techniques were used in the construction of a balanced cross section through three major fault related folds in southeastern umbria the nucleation of thrust ramps was controlled by the occurrence of jurassic and cretaceous palaeogene synsedimentary normal faults these interrupted the lateral continuity of the evaporitic unit the late triassic anidriti di burano fm at the base of the sedimentary cover and acted as obstacles to the eastward propagation of the thrust system giving rise to major folds which originated from tip line folding processes therefore the inferred relationships between ancient normal faults and late thrusts indicate that synsedimentary tectonic structures and the related lateral stratigraphic variations can be envisaged as mechanically important perturbations which effectively control the nucleation and development of thrust ramps

magnetic fabric variations along the fault related anticlines of eastern kachchh western india abstract an investigation of the anisotropy of magnetic susceptibility ams along the kachchh mainland fault kmf and south wagad fault swf in the eastern kachchh has been carried out to determine the variation of magnetic fabric in different anticlines 105 cores drilled from 35 jurassic sandstone samples collected from both forelimbs and backlimbs of the anticlines are analyzed the various types of fabrics from the three sites indicate essentially three stages of generation of magnetic fabric the sedimentary fabric type i is affected a initially by layer parallel shortening resulting in the development of type iii fabric with oblique to parallel bedding and magnetic foliation b later by bedding parallel shear associated with the rotation of limbs resulting in the tectonic fabric type iv and c finally by bedding parallel thrusting dominantly in the backlimbs resulting in the imprint of higher tectonic fabric type v vi about 14 of the sampled sites belong to the sedimentary type i fabric 54 to the type iii and 32 show tectonic fabric type iv and v vi the different stages of fabric evolution are not accompanied by linear increase in the degree of anisotropy but show construction and destruction of magnetic fabric during the layer parallel shortening to late stage bedding parallel thrusting the tectonic magnetic lineation orientations are mostly not consistent with the bedding strikes or fold axes the intermediate fabric lineation direction of nne ssw is superimposed by later tectonic lineation with varying orientations of nw se in the western end to nne ssw to nnw sse along the eastern end of kmf we attribute the variations in shortening direction essentially to the transpressional deformation of the basin in general and individual anticlines in particular the variation in slip propagation ratio along individual segmented faults has resulted in the rotation of fold limbs

the displacement distance method for contractional kink bands and its application to fold thrust structures the displacement distance d x method can be modified to study the geometry and development of contractional kink bands by dividing displacements into cartesian component vectors kink bands are idealised as having constant layer lengths enabling simple trigonometry to be used to determine the displacement of one wall of the kink band relative to the other wall in a consideration of several applications of the d x method for kink bands it is shown that displacement is transferred between conjugate and overstepping kink bands in a similar way to displacement transfer between conjugate and overstepping faults and extension fractures the several different models of kink band formation are shown to each have different displacement characteristics the d x method can also be used to study the geometry and evolution of folds related to thrust propagation and ramps which are often modelled as having kink band geometries for instance the d x method can be used to show how fault tip and fault bend folds cause or accommodate thrust displacement variations and to estimate displacement rates from the amounts of deformation in different syn thrust sedimentary layers

use of fault cut offs and bed travel distance in balanced cross sections abstract successful hydrocarbon exploration in foreland fold thrust belts requires the preparation of numerous fully balanced cross sections each section must be compatible with neighboring sections line balancing on many sections is preferable to balancing on single sections a series of balanced sections must also be volume balanced if constructed properly an often overlooked basic principle is that the fault cut off angle on both hangingwall and footwall and the angle and distance that a fault travels within a bed will not change significantly during thrusting under simple shear motion assuming no significant interbed slippage the section must be geometrically correct if it is to have a chance of being geologically correct

thrust surface geometry implications for thrust belt evolution and section balancing techniques abstract the application of modern concepts of thrust tectonics to orogenic belts has yielded many detailed restorable sections thrusts generally restore with a staircase geometry onto the undeformed stratigraphic template since the work of rich 1934 it has been generally assumed that thrusts have propagated with a staircase trajectory and that hangingwall structures result from the movement of the thrust sheet up footwall ramps however thrusts often cut through previously folded strata with a smooth trajectory smooth trajectory thrusts can be identified from footwall geometry and strain state once a smooth trajectory thrust has been identified it is insufficient to produce a balanced deformed section and its restored counterpart sequential balanced sections must be constructed reversing the deformation history the restoration of thrusts to a staircase trajectory has no mechanical significance as the thrust is merely acting as a marker if restored back beyond the time at which it propagated thrust ramps are not necessarily actual steps in the thrust surface they are often just zones where the thrust cuts through bedding in a smoothly curving trajectory ductile deformation in thrust belts can reduce bed length at depth thus removing the need for structures which are necessary to preserve constant bed lengths ductile deformation in the internal zones of orogenic belts renders the construction of balanced sections in these zones highly problematical

trishear for curved faults abstract fault propagation folds form an important trapping element in both onshore and offshore fold thrust belts and as such benefit from reliable interpretation building an accurate geologic interpretation of such structures requires palinspastic restorations which are made more challenging by the interplay between folding and faulting trishear erslev 1991 allmendinger 1998 is a useful tool to unravel this relationship kinematically but is limited by a restriction to planar fault geometries or at least planar fault segments here new methods are presented for trishear along continuously curved reverse faults defining a flat ramp transition in these methods rotation of the hanging wall above a curved fault is coupled to translation along a horizontal detachment including hanging wall rotation allows for investigation of structures with progressive backlimb rotation application of the new algorithms are shown for two fault propagation fold structures the turner valley anticline in southwestern alberta and the alpha structure in the niger delta

fold and thrust systems in mass transport deposits abstract improvements in seismic reflection data from gravity driven fold and thrust systems developed in offshore mass transport deposits mtds reveal a number of significant features relating to displacement along thrusts however the data are still limited by the resolution of the seismic method and are unable to provide detail of local fold and thrust processes investigation of exceptional gravity driven contractional structures forming part of mtds in lacustrine deposits of the dead sea basin enables us to present the first detailed outcrop analysis of fold and thrust systems cutting unlithified soft sediments we employ a range of established geometric techniques to our case study including dip isogons fault propagation fold charts and displacement distance diagrams previously developed for investigation of thrusts and folds in lithified rocks fault propagation folds in unlithified sediments display tighter interlimb angles compared to models developed for lithified sequences values of stretch which compares the relative thickness of equivalent hangingwall and footwall sequences measured along the fault plane may be as low as only 0 3 which is significantly less than the minimum 0 5 values reported from thrusts cutting lithified rocks and reflects the extreme variation in stratigraphic thickness around thrust related folds we suggest that the simple shear component of deformation in unlithified sediments may modify the forelimb thickness and interlimb angles to a greater extent than in lithified rocks the average spacing of thrust ramps and the thickness of the thrust sequence display an approximate 5 1 ratio across a range of scales in mtds in general thicker hangingwall and footwall sequences occur with larger thrust displacements although displacement patterns on thrusts cutting unlithified yet cohesive sediments are more variable than those in lithified rocks line length restoration of thrust systems in mtds reveals 42 shortening which reduces to 35 in overlying beds a 23 reduction in shortening by folding and thrusting along individual thrusts suggests that heterogeneous lateral compaction may increase by 10 towards the sediment surface thrust systems cutting unlithified sediments display distinct steps in cumulative displacement distance plots representing increased rates of slip along the floor thrust while displacement distance plots along individual thrusts also reveal horizontal steps relating to lithological variation competent units cut by thrust ramps may display the greatest displacement which then progressively reduces both upward and sometimes downward along the ramp this relationship demonstrates that ramps do not necessarily propagate upwards from the underlying flat as in some traditional models but rather initiate by offset of competent horizons in the hangingwall of the detachment critical taper angles in mtds may be an order of magnitude less than in accretionary complexes or lithified rocks overall thrusts cutting unlithified sediments in mtds display more variable displacement and more pronounced displacement gradients toward fault tips compared to thrusts cutting lithified sequences

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

displacement and deformation associated with a lateral thrust termination southern golden gate range southern nevada u s a abstract the golden gate thrust offers an excellent opportunity to study displacement and deformation at a lateral thrust tip slip across this e vergent thrust is uniformly about 2 4 km for the southern 2 km of exposed strike length and dies out to zero in the northern 5 km constant displacement and uniform hangingwall structure along the southern one third of exposed strike length suggest that along strike displacement variation and consequent deformation are localized near the lateral tip structures located at and north of the lateral tip are consistent with transpression and later uplift as slip accumulated on the thrust fold and fault orientations and calcite twinning strain record possible transpression north of the lateral tip e w striking normal faults at the thrust tip record extension that is interpreted to be the result of the uplift and translation of a structurally continuous rigid block located north of the normal faults this block is connected to and was uplifted with the crest of the hangingwall anticline and was separated by the normal faults from thrust related folding to the south the main hangingwall structure is an anticline that in southern exposures trends n s parallel to the thrust but bends westward and opens into a box fold to the north the hangingwall anticline superficially resembles a classic fault propagation fold formed by a migrating ductile bead however we are forced to reject the ductile bead hypothesis for the fold because 1 the geometry of the hangingwall anticline far from the thrust tip cannot have evolved from the geometry at the thrust tip and 2 twinned calcite strain data from along the thrust suggest that strain was homogeneous and coaxial rather than inhomogeneous and progressively non coaxial as predicted for a migrating ductile bead the three dimensional structural and kinematic relations at the lateral tip of the golden gate thrust appear to be the result of deformation around a pinned tip although the reason that the tip was pinned at its present location is unclear we interpret the thrust to have propagated relatively quickly to its ultimate extent with little initial displacement indicating that it was easier to fault the rocks than to fold them

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

earthquake slip estimation from the scarp geometry of himalayan frontal thrust western himalaya implications for seismic hazard assessment geometric and kinematic analyses of minor thrusts and folds which record earthquakes between 1200 ad and 1700 ad were performed for two trench sites rampur ghanda and ramnagar located across the himalayan frontal thrust hft in the western indian himalaya the present study aims to re evaluate the slip estimate of these two trench sites by establishing a link between scarp geometry displacements observed very close to the surface and slip at deeper levels as geometry of the active thrust beneath the scarp is unknown we develop a parametric study to understand the origin of the scarp surface and to estimate the influence of ramp dip the shortening estimates of rampur ghanda trench by line length budget and distance displacement d d method show values of 23 and 10 15 respectively the estimate inferred from the later method is less than the line length budget suggesting a small internal deformation ramnagar trench shows 12 shortening by line length budget and 10 25 by the d d method suggesting a large internal deformation a parametric study at the trenched fault zone of rampur ghanda shows a slip of 16 m beneath the trailing edge of the scarp and it is sufficient to raise a 8 m high scarp this implies that the rampur ghanda scarp is balanced with a single event with 7 8 m coseismic slip in the trenched fault zone at the toe of the scarp 8 15 mean deformation within the scarp and 16 m slip at depth along a 30 ramp for a pre 1400 earthquake event a 16 m slip is the most robust estimate of the maximum slip for a single event reported previously by trench studies along the hft in the western indian himalaya that occurred between 1200 ad and 1700 ad however the ramnagar trenched fault zone shows a slip of 23 m which is larger than both line length and d d methods it implies that a 13 m high scarp and 23 m slip beneath the rigid block may be ascribed to multiple events it is for the first time we report that in the south eastern extent of the western indian himalaya ramnagar scarp consists of minimum two events i pre 1400 ad and ii unknown old events of different lateral extents with overlapping ruptures if the more optimistic two seismic events scenario is followed the rupture length would be at least 260 km and would lead to an earthquake greater than mw 8 5

geometric tests and their application to fault related folds in kuqa abstract for brittle rock deformation there are two main types of fault related folds found in foreland thrust belts i e fault bend folds and fault propagation folds the predicted angular function for the quantitative geometric relationships between fault shapes and fold shapes in fault bend folds and fault propagation folds have been tested in seismic profiles i e deep bashijiqike tugeerming kashangtokai east qiulitage deep east qiulitage and yakelike fault bend anticlines and bashijiqike yiqikelike and south yiqikelike fault propagation anticlines in the kuqa rejuvenated foreland thrust belt test results for the transformation from seismic time section into seismic depth section using the seismic velocity spectrum can be used to identify whether the interpreted structures are reasonable with geometric analysis and testing of the subsurface structures it is possible to predict the existence of the fault bend folds and fault propagation folds in the kuqa area this study provides convincing proof that the kuqa basin is a rejuvenated foreland basin

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

local displacement rate cycles in the life of a fold thrust belt the evolution of minor structures during the growth of major folds and thrusts in the chartreuse district of the french subalpine thrust belt shows that each thrust evolved through a phase of distributed faulting major thrust propagation and displacement followed by distributed shear modification of the hanging wall fold microstructural studies suggest that the distributed faulting phases early and late in the history were characterized by strain rates limited by diffusive mass transfer processes c 10 15 10 16 s 1 faulting whose rate is limited by dmt is too slow on its own to accommodate the regional time averaged shortening rates for the thrust belt as a whole implying that the slow thrusts operated in tandem with those major fast thrusts where deformation was primarily cataclastic consequently each thrust anticline experienced a displacement rate cycle and an array of thrust anticlines must amplify simultaneously these interpretations raise important issues for the dynamics of fault populations the evolution of thrust wedges and the history of fluid migration in thrust belts

displacement transfer at thrust terminations the saltville thrust and sinking creek anticline virginia u s a abstract the saltville thrust terminates in the core of the sinking creek anticline changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination consequently thrust displacement would be transferred into the fold we combine newly published maps and new strain and mesostructural data from the tuscarora sandstone to argue that the sinking creek anticline did perform this kinematic role we propose that the anticline developed as a fault propagation fold that experienced both decollement and anticlinal breakthrough by the saltville thrust thrust displacement was accommodated by the development of the modified fault propagation fold and by transfer to a roof flat from the decollement breakthrough new strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding consequently layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough towards the plungeout of the sinking creek anticline the displacement on the saltville thrust is transferred to a floor thrust we apply this interpretation to the termination of the st clair thrust which has a similar surface geometry where the thrust terminates into an anticline a testable implication of this proposed interpretation for the st clair thrust is that the appalachian plateau must absorb over 20 km of thrust displacement as horizontal shortening

a velocity description of constant thickness fault propagation folding abstract the expression of the geometric model of constant thickness fault propagation folding as a velocity description of deformation allows the derivation of rates of displacement uplift and fault propagation the velocity model of fault propagation folding and sedimentation are combined in a finite difference scheme and two examples of growth strata associated with overturned fold forelimbs illustrate the application of the model

aspects of the reconstruction of the stress history of a fold and thrust belt rhenish massif federal republic of germany abstract by use of faults and striations parts of the deviatoric stress tensors and thereby essential aspects of the paleostress history of the rhenish massif can be reconstructed the stress history is unexpectedly complex even on the local scale the region under investigation is subdivided into various areas each of which exhibits somewhat different sequences of stress states several mutual aspects are evident in lower devonian rocks in the north which show only very slight deformation a pre folding stress state is preserved with a preferentially n s trending extension attributed to the stage of basin development the stage of folding itself during the carboniferous shows strong regional and temporal heterogeneity under frequently altering stress states after an initial stage of a semi homogeneous stress field this development occurs simultaneously with partial stress uncoupling at larger thrust zones with diverging deformation histories of hangingwalls and footwalls movement patterns in the north evidence subsequent clockwise rotation of the stress field which is only weakly represented in the south on the other hand there is clear evidence of a still younger counterclockwise rotation of the stress field which only affects the southern massif this is probably due to the superpositioning of orthogonal relative movements on the southern rim of the fold belt by a dextral strike slip component during final deformation thus indicating late dextral transpression succeeded by dextral transtension the final extensional stage is related to late paleozoic uplift and crustal stretching perpendicular to the strike of the fold belt followed by a change of direction of extension this state of stress obviously extends into the present although complex the various stress conditions are clearly correlated with other fabric elements in particular with cleavage fold geometry and mineralization

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

strain accommodation at the lateral margin of an active transpressive zone geological and seismological evidence from the lebanese restraining bend geological geomorphological and seismological data are used to postulate the existence of a lateral domain bounding fault the roum fault zone in sw lebanon the fault zone accommodates transpression at the margins of the lebanese restraining bend abruptly dividing the transpressional mount lebanon jebel barouk uplift from the extension of the tyre nabatiye plateau transpressional deformation at the sw margin of the restraining bend is mainly seen through large scale folding trending parallel to the restraining bend such folding is thought to be accommodated laterally along a 100 km length of fault zone in sw lebanon the roum fault zone mapped lineaments and topographic expression show the fault zone to die out to the south of beirut offsets of incised river valleys decrease northwards from 7 2 km to 0 2 km along the length of the fault zone over a distance of 80 km also inferring a postulated fault tip to the south of beirut strain gradients along both sides of the fault zone wall rocks shows several deformation mechanisms to be involved pressure solution folding distributed shear and normal faulting the postulated fault tip coincides with the extent of transpression of the mount lebanon block a new seismicity catalogue 2100 bc ad 1995 32 35 n 34 37 e 1725 events all magnitudes converted to isn reported m l was compiled from published sources seismicity is apparently sparse around the northern yammouneh fault but concentrates in sw lebanon especially in a diffuse 50 100 km wide zone around the southern roum fault zone epicentral uncertainties are typically 10 25 km for modern reporting although depths are poorly known the seismic b value is 0 75 0 07 for the beirut area compared to 0 88 0 09 for the dead sea transform to the south mapping of b values for the sw lebanon area suggests a gradual reduction northward along the roum fault zone these observations are interpreted as the signature of a fault zone whose tip lies to the south of beirut the transition from transpression to extended crust at the western edge of the lebanese restraining bend is accommodated along a 100 km length of fault zone decreasing seismic activity over the time of the catalogue and seismic b values imply a differing style or mechanism of faulting in the short term along the roum fault zone toward beirut

kinematic evolution of thrust related structures in the umbro romagnan parautochthon northern apennines italy in the internal part of the umbro marchean romagnan apennines the foredeep clastic wedge constituting the neogene part of the sedimentary cover is completely detached from the underlying mesozoic palaeogene succession the resulting umbro romagnan parautochthon consists of tectonostratigraphic units with a general geometry of broad synclinal blocks separated by narrow faulted anticlines thrust related structures observed in the field require thrust ramp propagation to have occurred within already folded rocks therefore they cannot be restored using simple fault bend fold or fault propagation folding models evidence for a passive fold origin in the studied rocks suggests that an early detachment folding episode preceded ramp propagation the latter was facilitated by the enhanced thickness of incompetent material in the cores of detachment anticlines which became the preferential sites where thrust ramps cut up section depending on the trajectory of such thrust ramps different types of fault related structures could develop hanging wall anticlines which give way to monoclinal structures higher up in the section are associated with listric thrust ramps whereas hanging wall monoclines approximately parallel to the underlying fault surface are associated with straight trajectory ramps this kinematic evolution which occurred partly during syn depositional compression also accounts for the observed lithofacies distribution the latter reflects an early differentiation of the foredeep trough into sub basins that are progressively younger towards the foreland the detachment anticlines that originally bounded such sub basins were the site of later thrust propagation leading to a tectonic juxtaposition of different tectonostratigraphic units consisting of broad nw se elongate synclinal blocks

upslope verging back thrusts developed during downslope directed slumping of mass transport deposits acknowledgements sm acknowledges the israel science foundation isf grant no 1436 14 and the ministry of national infrastructures energy and water resources grant 214 17 027 rw was supported by the israel science foundation isf grant no 1245 11

fault displacement distance relationships as indicators of contractional fault related folding style we present a method of using fault displacement distance profiles to distinguish fault bend shear fault bend and fault propagation folds and use these insights to guide balanced and retrodeformable interpretations of these structures we first describe the displacement profiles associated with different end member fault related folding models then provide examples of structures that are consistent with these model based predictions natural examples are imaged in high resolution two and three dimensional seismic reflection data sets from the niger delta sichuan basin sierras pampeanas and cascadia to record variations in displacement with distance updip along faults termed displacement distance profiles fault bend folds exhibit constant displacement along fault segments and changes in displacement associated with bends in faults shear fault bend folds demonstrate an increase in displacement through the shearing interval and fault propagation folds exhibit decreasing displacement toward the fault tip more complex structures are then investigated using this method demonstrating that displacement distance profiles can be used to provide insight into structures that involve multiple fault related folding processes or have changed kinematic behavior over time these interpretations are supported by comparison with the kinematics inferred from the geometry of growth strata overlying these structures collectively these analyses illustrate that the displacement distance approach can provide valuable insights into the styles of fault related folding

distinguishing thrust sequences in gravity driven fold and thrust belts abstract piggyback or foreland propagating thrust sequences where younger thrusts develop in the footwalls of existing thrusts are generally assumed to be the typical order of thrust development in most orogenic settings however overstep or break back sequences where later thrusts develop above and in the hangingwalls of earlier thrusts may potentially form during cessation of movement in gravity driven mass transport deposits mtds in this study we provide a detailed outcrop based analysis of such an overstep thrust sequence developed in an mtd in the southern dead sea basin evidence that may be used to discriminate overstep thrusting from piggyback thrust sequences within the gravity driven fold and thrust belt includes upright folds and forethrusts that are cut by younger overlying thrusts backthrusts form ideal markers that are also clearly offset and cut by overlying younger forethrusts portions of the basal detachment to the thrust system are folded and locally imbricated in footwall synclines below forethrust ramps and these geometries also support an overstep sequence however new short cut basal detachments develop below these synclines indicating that movement continued on the basal detachment rather than it being abandoned as in classic overstep sequences further evidence for synchronous thrusting where movement on more than one thrust occurs at the same time is provided by displacement patterns on sequences of thrust ramp imbricates that systematically increases downslope towards the toe of the mtd older thrusts that initiate downslope in the broadly overstep sequence continue to move and therefore accrue greater displacements during synchronous thrusting our study provides a template to help distinguish different thrust sequences in both orogenic settings and gravity driven surficial systems with displacement patterns potentially being imaged in seismic sections across offshore mtds

extended and revised archaeomagnetic database and secular variation curves from bulgaria for the last eight millennia the efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models on the other hand the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions the accumulation of archaeomagnetic determinations began at the middle of the last century parallel with the progressive development of experimental methodology and acceptance criteria the presence of great number of old determinations requires their critical assessment the important question about the reliability of the associated dating intervals should be also re assessed all this requires the continuous refinement and extension of the accumulated databases this paper presents the last synthesis of bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on bayesian approach rencurve software the rock magnetic characteristics of the newly included non published results are summarized

interpreting structural geometry in fold thrust belts why style matters abstract structural interpretation in fold thrust belts has become reliant on a few idealized geometric models i e fault bend fault propagation and detachment folding and their quantitative methods for section construction and validation we couple historical review with selected outcrops to show that there is a substantially greater range of solutions available for interpreting the geometry and evolution of thrust belt structures than implied by these idealized models examples are documented and lessons drawn from comparing structural interpretations developed in the foothills of the canadian rockies with those in the western alps both show a range of structural geometries with regional variations that reflect variations in the pre kinematic stratigraphic template locally fold thrust development can localize on pre existing structures thus consideration of the precursor geology is essential for structural interpretation using a case study from the papuan fold belt we show that even with seismic data assessing the role of basement in structural development can be uncertain the idealized models offer only a narrow range of possible geometries for constructing cross sections and developing structural understanding in fold thrust systems failure to consider alternatives and the inherent interpretation uncertainty has biased understanding of thrust systems leading in turn to over optimistic risk assessment and repeated drilling surprises

extensional fault propagation folding in mechanically layered rocks the case against the frictional drag mechanism abstract fault drag deflection of beds or other markers into folds that are convex in the direction of relative slip is often interpreted as the product of frictional sliding along a fault and progressive tilting of beds with increased amount of displacement along a fault we analyze two sets of normal faults with throws ranging from 0 5 m to 5 m and associated fault related folds in mechanically layered upper cretaceous carbonate anhydrite and shale in central texas for each fault set we interpret the fault displacement and fault related folds exposed in outcrop to represent different stages in the developmental sequence in both fault sets faults in dolostone or limestone lose displacement and tip into less competent anhydrite or shale where deformation is accommodated by folding and smaller scale deformation fold wavelength is established early and at small displacement

displacement distance methods in the analysis of fold thrust structures and linked fault systems a new method for analysing the internal strain in thrust sheets is described the displacement distance diagram can be used to quantify the relative shortening or relative stretch between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold thrust structures the stretch is a function of the relative rates of thrust propagation and thrust slip the cumulative displacement distance diagram described here can be used to calculate the absolute shortening or extension when this is accommodated above a single decollement in a linked fault system this method offers a useful way of analysing duplex structures and large scale foreland thrust zones as well as extensional fault systems and can be used as an alternative to or in conjunction with balanced cross sections both methods can be used to quantify the variation in shortening above a single detachment zone this variation may be mechanically significant reflecting lithological control on thrust or normal fault growth

fault bend folding as an end member solution of double edge fault propagation folding fault bend folding is the most commonly used kinematic mechanism to interpret the architecture and evolution of thrust related anticlines in thrust wedges however its basic requirement of an instantaneous propagation of the entire fault before hangingwall deformation limits its kinematic effectiveness to overcome this limitation we used the interdependence between fold shape and fault slip vs propagation rate s p ratio implemented in double edge faultpropagation folding we show that very small s p values produce fault propagation anticlines that when transported

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

structural development during flysch basin collapse the fencemaker allochthon east range nevada abstract during mesozoic deformation in north central nevada a thick succession of triassic siliciclastic and hemipelagic carbonate strata that were deposited in a deep water basin shortened against and overrode penecontemporaneous shallow water carbonates and interbedded siliciclastics at the eastern margin of the basin initial rheologic contrasts developed between lithologic units during shallow pretectonic burial localized displacements within fine grained poorly cemented units and along lithologic boundaries changes in theology during low pressure and low temperature deformation led to more brittle conditions possibly due to fluid expulsion and subsequent displacements truncated bedding structures in triassic strata suggest that the w facing slope of the shelf to basin transition localized thrusting collapse of the basinal strata against strata of the basin margin and formation of a thrust at the shelf to basin transition demonstrate the ability of stratigraphic declivities and associated rheologic contrasts to buttress deformation and localize thrusting

strain partitioning across a fold and thrust belt the rhenish massif mid european variscides abstract strain data across the entire western rhenish massif illustrate the pattern of deformation partitioning within a fold and thrust belt from the foreland on the northern front of the european variscides to the suture with the internal zones of higher metamorphic grade shortening perpendicular to cleavage increases from 16 to 27 constant volume assumed in the northern rhenish massif to 51 at the southern border these values correspond to a weak general layer parallel shortening of the basin filling in cross section on the order of about 5 15 and more in the case of volume loss the geometry of apparent finite strain is nearly plane strain except in the venn anticlinorium where strain is apparent prolate and near the southern margin of the massif where it is apparent oblate net orogenic shortening in the upper crust of the fold and thrust belt is approximately 42 it is mainly achieved by folding and tectonic stacking of the deformed basin filling which was apparently detached from the lower crust distribution of strain in the orogenic wedge is controlled by different factors at different scales heterogeneity is caused by changes in lithology and average grain size by the structural position of samples in folds and their distance from thrusts in the hangingwall at deeper crustal levels and by the regional distribution of the metamorphic grade i e by the dominant deformation mechanism this last factor causes an exponential increase of strain with approach to the ductile lower crust the superposition of strain partitioning mechanisms on different scales creates a complex regional strain pattern the southern part of the thrust belt apparently suffered late westward motion in gently dipping imbricates or strike parallel motion in steeply dipping imbricates which is probably due to oblique convergence between the rhenohercynian and saxothuringian microplates

linkage and evolution of conjugate strike slip fault zones in limestones of somerset and northumbria conjugate strike slip fault zones that cover metre scale areas at beadnell northumbria and kilve somerset were initiated as conjugate vein arrays early conjugate faults are linked by the propagation of one fault that eventually by passes the other fault a model for the development of strike slip faults is presented using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction this model includes the evolution of networks from 1 the initial random development of vein arrays to 2 the isolated development of several unconnected conjugate fault segments that pass into vein arrays through 3 the intersection of a conjugate set of master faults and linkage with minor antithetic faults and the formation of new vein arrays with extensional geometries after a linked network of faults is established to 4 breaching of intersection points by dominant faults and finally 5 the propagation towards oversteps that are breached to form a through going fault the geometry of the active structures simplifies with time as strain is localised along the master fault but the complexities are preserved in the fault walls

structural evolution of fold thrust structures in analog models deformed in a large geotechnical centrifuge abstract we investigate the structural evolution of fault propagation folds and fold thrust systems with scaled analog modeling carried out using the 5 5 m radius geotechnical centrifuge at c core st john s nl the experiments presented here are the first of their kind scaled ten times larger than predecessors and deformed using a custom rig with load monitoring and displacement control plane layered models approximately 1 m long and representing 50 km sections are shortened horizontally under an enhanced gravity field of 160 g the large model scale allows for a proportionally large number of bedding laminations that act as strain markers this allows detailed analysis of strain partitioning and interplay both at the scale of a fold thrust system and the individual fold thrust structure layer parallel shortening lps and rotation of fault bounded blocks are revealed by mapping contraction fault populations and bedding contraction fault intersection angles low angle contraction faulting and lps are found to be dominant at early stages of development and rotation of fault bounded blocks occurs during progressive folding of the hanging wall panel during fault propagation folding displacement distance data obtained from major thrusts in the model show relative stretch values and consequently fault slip propagation ratios that are similar to natural structures

slip vectors and fault mechanics in the makran accretionary wedge southwest pakistan the makran is a broadly east west trending arcuate accretionary wedge currently forming where the oceanic floor of the gulf of oman is being subducted north northeastward beneath the south asian margin two traverses across the makran coast ranges extending about 80 km inland from the coastline which lies about 100 km north of the wedge front show that the structure of this region is dominated by large back rotated south directed thrust faults and associated folds related structures include duplexes fault gouge containing reidel shears and melange along fault zones these structures are cut by later north directed backthrusts out of sequence south directed thrusts and apparently conjugate sets of nne trending sinistral and nw trending dextral strike slip faults slip vectors were determined from slickenlines fiber lineations gouge fabrics and riedel shears vectors from early thrusts and bedding parallel slip surfaces corrected for tectonic rotation form a broad south directed concentration lying between the normal to the regional strike varying from 160 to 180 and the present plate convergence vector 200 locally the concentration is bimodal this pattern may represent the interaction between plate forces and body forces in the accretionary wedge the late thrusts have widely variable slip vectors and stair step off the early thrusts they overlap in orientation and slip vector with gently dipping sinistral strike slip faults suggesting that they also stair step in plan off the latter the steep strike slip faults represent the final tectonic stage involving minor n s shortening and longitudinal extension these three stages probably occurred in sequence in any one area but migrated diachronously southward as the wedge grew

strains developed in the hangingwalls of thrusts due to their slip propagation rate a dislocation model discussion abstract modern seismic data indicate that the sole fault of the turner valley thrust sheet does not lose displacement in an up dip direction and that it does not crop out but rather flattens into the triangle zone on the eastern edge of the rocky mountain foothills belt well constrained balanced cross sections drawn through this part of the belt do not incorporate significant folding related to the propagation of thrust faults

active inversion tectonics simple shear folding and back thrusting at rioni basin georgia abstract the rioni basin located between the greater and lesser caucasus in georgia is an outstanding example of ongoing inversion tectonics marine and continental deposits of cretaceous neogene age have been locally uplifted since the end of miocene the uplifted area totals 1300 km 2 and plio quaternary river deposits have been raised up to 200 m above the surrounding plains inversion tectonics has been accompanied by the development of south vergent asymmetrical folds and strike slip faults along the border of the uplifted area the folds have locally an en echelon geometry and microtectonic data indicate rotation of the paleostress direction over time suggesting simple shear deformation in the interiors of the uplifted area there are gentle symmetrical folds and one main active south dipping reverse fault corresponding to a backthrust morphostructural evidence as well as the tilting of quaternary strata the offset of quaternary alluvial deposits and the presence of crustal seismic activity indicate that compressional tectonics is still active the combination of field data with seismic reflection sections shows that inversion tectonics took place through a series of north dipping blind thrusts and a wedge with passive back thrusting uplift and contraction are more developed along the eastern part of the study area suggesting the westward propagation of the closure of the transcaucasian depression

estimation of fault propagation distance from fold shape implications for earthquake hazard assessment a numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault propagation fold the propagation distance defines the initial position of the tip line at the onset of slip in the santa fe springs anticline of the los angeles basin we show that the tip line of the underlying puente hills thrust fault initiated at the same position as the 1987 magnitude 6 0 whittier narrows earthquake

tectonics in the cuddapah fold thrust belt in the indian shield andhra pradesh india and its implication on the crustal amalgamation of india and rayner craton of antarctica during neoproterozoic orogenesis neoproterozoic orogenesis in east antarctica and india led to the amalgamation of northern prince charles mountains rayner complex of antarctica with the krishna province of india along the present eastern coast of india with the development of 990 900 ma old fold thrust belt the frontal part of the fold thrust belt henceforth called the cuddapah fold thrust belt cftb recognized in the intercratonic palaeoproterozoic neoproterozoic cuddapah basin includes two frontal thrust sheets carried by the eastern velikonda and the western nallamalai thrusts along with a part of the undeformed foreland constituting frontal part of a larger fold thrust belt now fragmented and separated in different continents of gondwanaland therefore the intercratonic deformation now preserved in the palaeoproterozoic neoproterozoic cuddapah basin is related to the collision of the indian shield to the antarctic block during the amalgamation of the rodinia supercontinent cftb is dominated by quasi plastic deformational structures representing exhumed deeper level fault propagation folding related to the velikonda thrust while the nallamalai thrust represents the forelandward thrust of the cftb dominated by elastico frictional deformation structures

a rate and state friction law for saline ice sea ice friction models are necessary to predict the nature of interactions between sea ice floes these interactions are of interest on a range of scales for example to predict loads on engineering structures in icy waters or to understand the basin scale motion of sea ice many models use amonton s friction law due to its simplicity more advanced models allow for hydrodynamic lubrication and refreezing of asperities however modeling these processes leads to greatly increased complexity in this paper we propose by analogy with rock physics that a rate and state dependent friction law allows us to incorporate memory and thus the effects of lubrication and bonding into ice friction models without a great increase in complexity we support this proposal with experimental data on both the laboratory 0 1 m and ice tank 1 m scale these experiments show that the effects of static contact under normal load can be incorporated into a friction model we find the parameters for a first order rate and state model to be a 0 310 b 0 382 and m0 0 872 such a model then allows us to make predictions about the nature of memory effects in moving ice ice contacts

duplexes as slip transfer zones application to the himalayan fold thrust belt abstract duplex fault zones and imbricate fans originally termed schuppen schuppenstruktur or imbricate structure were first described in the late 1800s from the alps nw highlands scotland and montana rockies lewis thrust sheet as originally defined duplexes contained shingled imbricate slices bounded above and below by through going thrusts these duplex fault zones commonly occur along the base of major regional thrust sheets or within the body of such sheets accommodating regional bed parallel shortening and transferring slip from a lower stratigraphic horizon to a higher one thereby providing a mechanical advantage to the emplacement of large thrust sheets however faulting is not the only means of layer parallel shortening lps and displacement transfer within duplexes lps cleavage and detachment folds are also common and can play the same role as imbricate faults based on some selected examples we recognize three types of duplexes 1 fault duplex 2 cleavage duplex and 3 fold duplex the style of duplex that forms is likely a function of mechanical stratigraphy and deformation conditions the relationships among the three basic duplex styles can be plotted on a ternary diagram each duplex type constituting an apex given the complexities of most sedimentary sequences hybrid duplexes with a mix of fault fold and cleavage shortening can also form hybrid duplexes plot along the side of the triangle as fault fold fold cleavage and fault cleavage duplexes while those combining all three mechanisms plot in the middle if the partitioning of shortening by the different mechanisms can be quantified the ternary diagram provides a means of representing the contributions of the three mechanisms in shortening and slip transfer along much of the himalayan fold thrust belt a significant portion of the lesser himalayan shortening is taken up by the lesser himalayan duplex a first order fault duplex with subsidiary cleavage and fold development the geometry of and shortening within the duplex varies significantly along the length of the himalaya

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

kinematic modeling of cross sectional deformation sequences by computer simulation we derive a kinematic algorithm which permits simulation of postulated cross sectional deformation sequences in sedimentary rocks affected by faulting fault related folding and simple shear the transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration forward modeling lagrangian description the medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections the displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment as a consequence the deformation path is continuous but not smooth and causes an angular style of parallel folding except at the deformation front where the layer thickness is not conserved the inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains whereas the area of the medium remains constant these strains which are superposed on the externally applied simple shear make the mapping transformation unconformal we define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements evaluate the defined displacement functions for the grid nodes and graph the deformed mesh eventually we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data

application of geometric models to inverted listric fault systems in sandbox experiments paper 1 2d hanging wall deformation and section restoration abstract fault geometry is a primary control on hanging wall deformation in order to examine their geometrical relationships a positive inversion analogue experiment was conducted using a rigid fault surface of listric geometry the hanging wall deformation observed on a representative vertical section was examined with conventional 2d geometric models and was restored to its pre inversion phase with two techniques these results suggest that the deformation can be best approximated by inclined simple shearing iss the iss model can determine the inclination of the apparent shear plane and the amount of apparent horizontal shortening which is equivalent to that calculated with the conventional depth to detachment method this estimated apparent shortening was generally smaller than the actual amount of the experiments probably due to tectonic compaction

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

major miocene exhumation by fault propagation folding within a metamorphosed early paleozoic thrust belt northwestern argentina 1 the central andean retroarc thrust belt is characterized by a southward transition at 22 s in structural style thin skinned in bolivia thick skinned in argentina and apparent magnitude of cenozoic shortening 100 km more in the north with the aim of evaluating the abruptness and cause of this transition we conducted a geological and geo thermochronological study of the cachi range 24 25 s which is a prominent topographic feature at this latitude our u pb detrital zircon results from the oldest exposed rocks puncoviscana formation constrain deposition to mainly cambrian time followed by major cambro ordovician shortening and 484 ma magmatism later cretaceous rift faults were locally inverted during cenozoic shortening coupled with previous work our new u th he zircon results require 8 10 km of miocene exhumation that was likely associated with fault propagation folding within the cachi range after miocene shortening displacement on sinistral strike slip faults demonstrates a change in stress state to a non vertically oriented 3 this change in stress state may result from an increase in gravitational potential energy in response to significant crustal thickening and or lithospheric root removal our finding of localized cenozoic shortening in the cachi range increases the estimate of the local magnitude of shortening but still suggests that significantly less shortening was accommodated south of the thin skinned bolivian fold thrust belt our results also underscore the importance of the pre existing stratigraphic and structural architecture in orogens in influencing the style of subsequent deformation

interpretation of the rupture history of a low slip rate active fault by analysis of progressive displacement accumulation an example from the quaternary eupcheon fault se korea abstract the eupcheon fault one of more than 20 identified quaternary faults recently reported in the area around the yangsan and ulsan faults se korean peninsula was discovered during the construction of a primary school in an area close to a nuclear power plant we analysed a trench excavated across the eupcheon fault with the aim of understanding its movement history and kinematics the eupcheon fault is a reverse fault strike dip n20 e 40 se that records 6 7 m of displacement 3 4 m vertical separation the fault consists of a series of branch faults associated fault related folds and rotated pebbles a previous study reported that the fault originally recorded normal slip but was reactivated during the quaternary as a reverse fault we identified four or five quaternary faulting events upon the fault based on an interpretation of the trench logs including an analysis of colluvial wedges and measurements of displacement distance d x relationships along the fault we used a quantitative analysis of d x relationships commonly used for consolidated sedimentary rocks to interpret the deformation history of the fault from this we estimated the amount of slip in the range of 0 7 1 8 m for each of the five identified faulting events and the earthquake magnitude in the range of m w 5 4 7 4 we propose two ideal d x profiles for syndepositional and post depositional faulting and a tectonic evolution model for the area around this fault this approach may be applicable to analyses of earthquake hazards and studies of fault evolution elsewhere

the corrugation and bifurcation of fault surfaces by cross slip abstract the formation of corrugated and stepped fault surfaces by conservative shear is discussed it is suggested that fault boundaries which lie parallel to the direction of shear are able to deviate from a plane as a fault spreads like dislocations that cross slip in a crystal it is explained how deviations from planar shear can bifurcate fault surfaces and create en echelon faults the residual stresses produced by such deviations are tensions and compressions in the direction of shear

displacement efficiency of faults and fractures discussion abstract higgs and williams present a kinematic classification of one event faults it is our contention that the new terms which they propose are misleading and that the conclusions drawn cannot be reconciled with the findings of earthquake seismologists