effects of fault slip distribution on the geometry and kinematics of the southern junggar fold and thrust belt northern tian shan abstract at the foreland edge of fold and thrust belts ftbs tectonic shortening could either be accommodated by thick skinned faulting and or structural wedges developed near range fronts or be transferred along detachment layers further into basins forming thin skinned structures although the geometry and kinematics of each structure have been well investigated studies that characterize slip distribution along a specific fault as well as the effects of variations in magnitude of fault displacement on the development of fault related folds are still lacking in this study we present a case study of the southern junggar thrust sjt a seismically active fault developed in the southern junggar ftb northern tian shan with an overall vergence to the north the results of structural interpretations of seismic reflection profiles combined with the age constraints provided by previous magnetostratigraphic studies demonstrate that 1 the kinematics of the sjt vary along strike from purely structural wedging to classical fault bend folding besides these end member models intermediate cases exist between them in which fault slip is partitioned by two stage structural deformation i e fault bend folding subsequent to structural wedging at the range front as a result part of the displacement is transferred northward forming the tugulu anticline 2 along strike variations in displacement along the tugulu fault frontal fault of the sjt also affect the geometry and kinematics of the tugulu anticline varying from detachment folding trishear fault propagation folding with a pure shear fault bend folding back limb and classical trishear fault propagation folding to fault bend folding with increasing displacement 3 the sjt has an average quaternary slip rate of 3 9 0 4 mm yr serving as a principal structure accommodating tectonic shortening in the southern junggar ftb the results of this study are helpful for seismic hazard assessments of the study area which may also shed light on structural evolution of fault related folds in other ftbs

patterns of imbricate thrusting through the use of seismic reflection profiles satellite images and balanced kinematic models we describe patterns that help to identify imbricate structures and define the sequence of thrusting in fold and thrust belts measures of folding shear strains are employed to define break forward systems in which younger deeper faults refold overlying thrust sheets in contrast break backward sequences form a wide range of viable geometries that are not expected to conserve these folding strains thus measures of folding shear strains provide a means to define thrusting sequence we also explore map view patterns of imbricate thrusting by using three dimensional models and stereoscopic satellite images we present an example from the peruvian andes in which these map patterns are combined with seismic reflection profiles to define a complex imbricate system with components of both break forward and break backward thrusting these integrated methods provide new tools for understanding the deformational histories of fold and thrust belts including the definition of complex structural closures with opportunities for hydrocarbon reservoir duplication

practical and efficient three dimensional structural restoration using an adaptation of the geochron model we document a novel approach to balanced three dimensional structural restoration based on an adaptation of the geochron model conventionally the geochron model defines a transformation of a geological model to a flattened space u v t with paleogeographic coordinates defined by the horizontal axes u v and geologic time on the vertical axis t in our new balanced structural restoration scheme the complete stratigraphy is restored using a transformation constrained only by the datum horizon scaling the vertical t axis to depth in a manner that preserves volume or layer thickness results in a geometric restoration that approximately minimizes strain globally this restoration provides a geometrically plausible representation of the geologic structure at the time when the datum horizon was deposited restoration is independent of mechanical rock properties and is thus most applicable to regions in which mechanical rock properties are approximately homogeneous restoration kinematics may be constrained by growth strata if present we validate the method with kinematic forward models and a laboratory sandbox model and apply it to two natural examples to demonstrate its capabilities for model validation and palinspastic restoration we identify four criteria for assessing the validity of a structural model using the results of restoration 1 anomalous fault throw 2 timing of fault activity 3 fault compliance and 4 restoration strain analysis of the sandbox results and limitations of volume conservation derived from uncertainties in compaction states suggest accuracy of the method to be in the 5 20 range

modelling growth stratal architectures associated with double edge fault propagation folding abstract fault related folds in fold and thrust belts and accretionary prisms are commonly simulated by three end member classes of geometric models decollement folding fault propagation folding and fault bend folding a given model produces a fold shape that depends on the amount of shortening the fault shape and eventually the fault propagation history the great variety of geometric solutions implies that the final fold shape is adequate to distinguish among different folding mechanisms only in a limited suite of cases additional information to better constrain fold kinematics is provided by the analysis of growth strata patterns which passively register the progressive evolution of deformation in the substratum availability of growth strata pattern templates associated with different geometric and kinematic solutions provides a useful tool for inferring the dominant kinematic pathways of natural thrust related structures in this paper we present growth strata patterns associated with double edge fault propagation folding the influence of the sedimentation rate the fault shape and the fault s p ratio i e slip versus ramp propagation rate on growth strata architectures are investigated geometrical modelling and application to natural examples indicate that double edge fault propagation anticlines are characterised by growth triangles on both limbs their position and geometry relate to the ramp shape and propagation history and on the sedimentation rate

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

geomorphic constraints on listric thrust faulting implications for active deformation in the mackenzie basin south island new zealand 1 deformed fluvial terraces preserved over active thrust related folds record the kinematics of folding as fault slip accumulates on the underlying thrust in the mackenzie basin of southern new zealand the kinematics revealed by folded fluvial terraces along the active ostler and irishman creek fault zones are inconsistent with traditional models for thrust related folding in which spatially uniform rock uplift typically occurs over planar fault ramps instead warped and tilted terraces in the mackenzie are characterized by broad continuous backlimbs and abrupt forelimbs and suggest folding through progressive limb rotation by relating this pattern of surface deformation to the underlying thrust with a newly developed simple geometric and kinematic model we interpret both faults as listric thrusts rooted at depth into gently dipping planar fault ramps constraints on the model from detailed topographic surveying of deformed terraces ground penetrating radar over active fault scarps and luminescence dating of terrace surfaces suggest slip rates for the ostler and irishman creek faults of 1 1 1 7 mm yr and 0 5 0 7 mm yr respectively the predicted depth of listric faulting for the ostler fault 0 7 0 2 0 1 km and the irishman creek fault 1 3 0 5 0 1 km generally agrees with geophysical estimates of basin depth in the mackenzie and suggests control of preexisting basin architecture on the geometry of active thrusting despite the potential effects of changes in fault curvature and hanging wall internal deformation the methodology presented here provides a simple tool for approximating the kinematics of surface deformation associated with slip along listric or curviplanar thrust faults

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

active fault related folding in the epicentral area of the december 25 1222 io ix mcs brescia earthquake northern italy seismotectonic implications abstract a dense grid of petroleum industry seismic reflection profiles coupled with field mapping exploratory trenching and geomorphic and structural analysis are used to characterize the quaternary growth history of the capriano del colle fault system one of several inferred active buried thrusts that extend across the po plain in northern italy shortening is characterized here by a deeply buried south vergent forethrust and an associated north vergent backthrust whose upward propagation is expressed by fault propagation folding near the surface structural interpretation based on seismic data suggests that strain is accommodated at very shallow levels by secondary flexural slip thrusts and reverse faults developed on synclinal flanks that emanate from active axial surfaces analysis of syntectonic growth strata document maximum rates of dip slip of 3 45 0 66 mm yr 1 6 myr 1 2 myr and 0 47 0 22 mm yr during a more recent time period 0 89 myr present a quarry excavation at capriano del colle allows a preliminary paleoseismologic analysis of coseismic surface faulting and liquefaction exposed near the core of an active mid pleistocene to holocene anticline these features are interpreted to be generated during strong local earthquakes consistent with the environmental effects and ground motions of an event similar to the december 25 1222 brescia earthquake io ix mcs this indicates for the first time that compressive folds and blind thrusts in the po plain are currently accommodating slow rates of modern contraction in an active zone of the southern alps that extends from lake garda to varese we thus argue that earthquakes similar to the december 25 1222 brescia event are likely to occur in this region and pose a direct threat to such a densely populated and developed area

multistage structural deformations of a superimposed basin system and its tectonic response to regional geological evolution a case study from the late jurassic early cretaceous tanan depression hailar tamtsag basin abstract the spatial temporal extent and influence of the mongol okhotsk and paleo pacific tectonic regimes in northeast ne china and adjacent areas during late mesozoic times have long been controversial as a superimposed rift system which formed due to extensive intracontinental extension during the late jurassic to early cretaceous periods the hailar tamtsag basin is a key area to study the relationship between the mongol okhotsk and paleo pacific tectonic regimes and their superposition with the aim of constraining the evolution of those two regimes in this paper the tanan depression which is a second order structural unit in the western part of the hailar tamtsag basin has been chosen as the research object on the basis of structural analysis of three dimensional 3d seismic data in the tanan depression and taking into account the controlling effect and influence of the pre existing facies on the basin evolution the deformation events in the early cretaceous can be subdivided into four periods 1 a nw se trending extension during the deposition of the tongbomiao formation to the upper part of the second member of the nantun formation 2 a nw se trending compression during the deposition of the upper part of the second member of the nantun formation to the first member of the yimin formation 3 a near ew trending extension during the deposition of the second member to the lower part of third member of the yimin formation 4 a near ew trending compression during the deposition of the upper part of the third member of the yimin formation additionally we identify compressional structures in the basement in the southeast part of the depression which is a key study that resulted from the mongol okhotsk collisional orogeny during the late jurassic the above five major deformational events make up a relatively complete tectonic deformation sequence of the hailar tamtsag basin moreover the deformation sequence together with other available information from the literature in ne china and adjacent areas including petrology geochemistry and geochronology data also record the whole process from the orogenic stage after the closure of the mongol okhotsk ocean over the post orogenic collapse of the mongol okhotsk orogen to the weakening of the influence of the mongol okhotsk regime and eventually to be replaced by the paleo pacific tectonic regime considering that the superposition and transformation of the two tectonic regimes involves almost all the geological process in ne china and adjacent area during the late mesozoic the complete geological record in the tanan depression during this period provides new constraints on the research of regional tectonic evolution and the model of multiphase deformation is also expected to have useful implications for future studies of complex basin systems

fold evolution matrices and axial surface analysis of fault bend folds application to the medina anticline eastern cordillera colombia the medina anticline is a fault bend fold located in the hanging wall of the aguaclara fault along the southeastern thrust front of the eastern cordillera of colombia a petroleum province with giant fields we employ a modified technique of axial surface analysis using fold evolution matrices which helps define the subsurface geometry and thereby provides important constraints on trap geometry modeling of hydrocarbon migration pathways and prediction of reservoir quality

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

the distribution of deformation in parallel fault related folds with migrating axial surfaces comparison between fault propagation and fault bend folding abstract in fault related folds that form by axial surface migration rocks undergo deformation as they pass through axial surfaces the distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration upon fold initiation unique dip panels develop each with a characteristic deformation intensity depending on their history during fold growth rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation by tracking the pattern of axial surface migration in model folds we predict the distribution of relative deformation intensity in simple step parallel fault bend and fault propagation anticlines in both cases the deformation is partitioned into unique domains we call deformation panels for a given rheology of the folded multilayer deformation intensity will be homogeneously distributed in each deformation panel fold limbs are always deformed the flat crests of fault propagation anticlines are always undeformed two asymmetric deformation panels develop in fault propagation folds above ramp angles exceeding 29 for lower ramp angles an additional more intensely deformed panel develops at the transition between the crest and the forelimb deformation in the flat crests of fault bend anticlines occurs when fault displacement exceeds the length of the footwall ramp but is never found immediately hinterland of the crest to forelimb transition in environments dominated by brittle deformation our models may serve as a first order approximation of the distribution of fractures in fault related folds

subsurface structural interpretation by applying trishear algorithm an example from the lenghu5 fold and thrust belt qaidam basin northern tibetan plateau abstract the application of trishear algorithm in which deformation occurs in a triangle zone in front of a propagating fault tip is often used to understand fault related folding in comparison to kink band methods a key characteristic of trishear algorithm is that non uniform deformation within the triangle zone allows the layer thickness and horizon length to change during deformation which is commonly observed in natural structures an example from the lenghu5 fold and thrust belt qaidam basin northern tibetan plateau is interpreted to help understand how to employ trishear forward modelling to improve the accuracy of seismic interpretation high resolution fieldwork data including high angle dips dragging structures thinning hanging wall and thickening footwall are used to determined best fit trishear model to explain the deformation happened to the lenghu5 fold and thrust belt we also consider the factors that increase the complexity of trishear models including a fault dip changes and b pre existing faults we integrate fault dip change and pre existing faults to predict subsurface structures that are apparently under seismic resolution the analogue analysis by trishear models indicates that the lenghu5 fold and thrust belt is controlled by an upward steepening reverse fault above a pre existing opposite thrusting fault in deeper subsurface the validity of the trishear model is confirmed by the high accordance between the model and the high resolution fieldwork the validated trishear forward model provides geometric constraints to the faults and horizons in the seismic section e g fault cutoffs and fault tip position faults intersecting relationship and horizon fault cross cutting relationship the subsurface prediction using trishear algorithm can significantly increase the accuracy of seismic interpretation particularly in seismic sections with low signal noise ratio

active thrust sheet deformation over multiple rupture cycles a quantitative basis for relating terrace folds to fault slip rates many recent thrust fault earthquakes have involved coseismic surface faulting and folding revealing the multifaceted nature of active thrust sheet deformation we integrate records of surface deformation subsurface structure and geochronology to investigate active surface deformation over multiple rupture cycles across the southern junggar thrust sjt in the southern junggar basin nw china fluvial terrace geometries extracted from a 1 m digital elevation model reveal records of surface faulting across a prominent fault scarp in addition terraces exhibit progressive folding across fold scarps fault and fold scarps are spatially coincident with a surface emergent sjt splay and subsurface fault bends along the sjt respectively constrained by seismic reflection data we quantify the magnitude of fault slip at depth implied by fold scarps along holocene aged terraces our method yields results consistent with independent estimates of slip implied by fault scarp relief for the same terraces four late quaternary terrace records are less continuous preserved only as fold scarps that suggest folding kinematics involving a component of limb rotation we develop a new method for quantifying fault slip at depth from terrace folds using a mechanical forward modeling approach our analysis yields quantitative relations between fold dip and fault slip allowing us to quantify sjt fault slip from terrace folds from 250 ka present sjt fault slip rate has decelerated from 7 0 mm yr in the late quaternary to 1 3 mm yr throughout the holocene these results provide new insight into the kinematics of fault bend folding for natural structures and define new methods to accurately estimate fault slip and slip rates from terrace folds in active thrust sheets

restoration of the cretaceous uplift of the harz mountains north germany evidence for the geometry of a thick skinned thrust reverse movement on the harz northern boundary fault was responsible for the late cretaceous uplift of the harz mountains in northern germany using the known geometry of the surface position and dip of the fault and a published cross section of the base permian horizon we show that it is possible to predict the probable shape of the fault at depth down to a detachment level we use the inclined shear method with constant heave and argue that a shear angle of 30 was most likely in this case the detachment level is at a depth of ca 25 km kinematic restoration of the harz mountains using this fault geometry does not produce a flat horizon rather it results in a ca 4 km depression airy heiskanen isostatic equilibrium adjustment of the harz mountains restores the base permian horizon to the horizontal as well as raising the moho to a depth of 32 km a typical value for northern germany restoration also causes a rotation of tectonic fabrics within the harz mountains of about 11 clockwise we show that this model geometry is very good fit to the interpreted dekorp basin 9601 deep seismic profile

structural evolution of the frontal fold thrust belt nw himalayas from sequential restoration of balanced cross sections and its hydrocarbon potential abstract two sedimentary lithotectonic zones are traditionally recognized in the northwestern himalayan frontal fold thrust belt in the nahan salient the lesser himalaya zone lhz and the sub himalaya zone shz the lhz is made up of a sequence of proterozoic to early cambrian rocks and the shz is made up of cenozoic rock sequences which were deposited subsequent to the india asia collision serial balanced cross sections show that the structural geometries become increasingly complex from independent ramp anticlines near the foreland through imbricate fan duplex to stacked up horses towards the hinterland sequential restoration suggests a structural evolution in which a foreland propagating in sequence thrusting event was followed by out of sequence thrusting in an approximately break back style during the out of sequence movement some of the ramps formed during in sequence thrusting were repeatedly reactivated leading to very complex structural geometries particularly in the lhz in such a complexly deformed terrain a rigorous structural modelling approach combined with a robust geochemical and geochronological database should be used to carry out calibrated petroleum system modelling and thus reduce exploration risk

deformation and kinematic evolution of the subsurface structures zagros foreland fold and thrust belt northern dezful embayment iran the dezful embayment is located in the foreland part of the zagros fold and thrust belt structural style of folding and thrusting vary in the dezful embayment in this study balanced cross sections and subsurface data including 2d seismic profiles and wells data decoded structural style of the subsurface structures in the northern dezful embayment presence of the multiple decollement horizons is the main controlling factor of the structural style in this area the subsurface anticlines have been formed between two main decollement horizons which include the miocene gachsaran formation as upper decollement and permian dashtak evaporites and lower cretaceous garau shales as the middle decollement horizons geometry of the subsurface anticlines differs much vertically and horizontally growth strata indicate folding is started in middle miocene time in this region anticlines formed as open wide and disharmonic structures active processes in the evolution of anticlines are limb rotation and hinge migration which was resulted in increase of inhomogeneous shortening rate more shortening rate indicates more structural relief in anticlines these anticlines are formed as a detachment folds in initiation and then during their evolution converted to fault propagation fold and fault bend fold final geometric shape of these anticlines depends on the geometry of thrusts propagation that formed in the forelimb

map view interference of monoclinal folds abstract outcrop observations and laboratory experiments show that many small chevron folds form by interference of monoclinal kink bands in multilayer buckling kink band interference has also been proposed for some map scale folds furthermore fault related folding provides additional mechanisms of monoclinal fold generation other than buckling and thus makes kink band interference all the more conceptually plausible as a significant large scale process in this paper we document several relatively simple examples of map scale monoclinal fold interference including three interfering monoclines of the colorado plateau a seismically imaged example in the perdido foldbelt of the gulf of mexico and a more complex example from seismic mapping in the santa barbara channel california kink band interference has normally been analyzed in cross section here we emphasize the map view phenomena and present a simple balanced three dimensional model of the interference geometry treating the monoclines as two independent kink bands which does not depend of the kink band folding mechanism this model predicts the shape of the jog produced by crossing monoclines and is used to help evaluate the role of interference in the map view geometry of our examples the documentation of these simple examples supports the concept that more complex monoclinal fold interference could be a significant phenomenon in the upper crust

approach and application of industry software to structural investigations in the subsurface of mercury s thrust fault related landforms abstract historical efforts to model structures underlying planetary tectonic landforms have prioritized characterizing the dips depths and orientations of faults vertical displacement of rock along faults has been assumed to produce observed positive topography model derived fault parameters and values for fault displacement and strain have been estimated and these estimates have then been used to describe strain accumulated within regions of a planet or within entire planetary lithospheres previous modeling efforts have used finite element methods to reproduce topography associated with structure related landforms with acceptable models being determined through statistical best fit testing the approach presented in this work describes how software originally designed for industrial applications can be used in combination with the interpretation of topography and imagery to inform our understanding of the subsurface complexity of structures including faults and folds through a case study of ten structures in a smooth plains unit on mercury a detailed approach is provided for three dimensional modeling of subsurface faults and folds working with qualitative and semi quantitative criteria for acceptable or successful models and using those models to determine the relative importance of faulting and folding on topographic development through these details this work seeks to break through the black box often associated with modeling with the potential to support genuinely reproducible research

aspects of the three dimensional structure of the alberta foothills and front ranges ever more detailed subsurface images of the alberta foothills and front ranges obtained from improving seismic techniques coupled with an ever expanding base of information from deep wells and improved structural analysis techniques have produced an understanding of fold thrust deformation that is probably applicable to other fold thrust belts comprehensive subsurface data obtained by the petroleum industry are used to outline and analyze the three dimensional configuration of fold thrust deformation of paleozoic carbonate strata these data indicate that displacement changes smoothly along individual thrusts but displacement changes along strike may be large marked by considerable horizontal rotation 20 30 or more of hanging wall stratigraphic cutoffs relative to the footwalls stacking of thrusts with varying displacements has produced summed horizontal rotations of hanging wall cutoffs of as much as 45 50 the three dimensional trajectories of the thrusts through the stratigraphy are smooth for large distances interrupted by abrupt offsets at lateral and oblique ramps these are more common than previously realized the intersections of these ramps with other thrusts produce complex three dimensional links between thrusts with concomitant abrupt displacement changes some simple examples of these linkages are examined with a three dimensional geometric analysis the predictions of the analysis are consistent with structural geometries observed in two case studies of subsurface structures the links at lateral ramps imply simultaneous displacement on parts of the thrusts connected by the ramps since the ramps extend downdip 20 km or more displacement occurred simultaneously on structures occupying relatively interior and exterior positions in the thrust belt the smooth and long radius of curvature folding of many upper detachments indicated by reflection seismic data also is consistent with simultaneous or overlapping periods of motion on groups of thrusts distributed along regional dip most major alberta foothills thrust sheets terminate southward at lateral ramps at the paleozoic level the abrupt southwest northeast offsets at these features are most clearly apparent on a palinspastic reconstruction these offsets cause the paleozoic deformation front to step out east and northeast around the southern and eastern margins of the main arc of the foothills in contrast northward thrust terminations at the paleozoic level commonly occur at both tip lines and lateral ramps subsurface data reveal that there have been some misconceptions regarding large scale structural relationships for example the mcconnell and livingstone sheets are actually portions of the same thrust sheet as are the bighorn and nikanassin sheets when corrected for these misconceptions the data from the alberta foothills suggest that maximum displacement has a nonlinear relationship to thrust length although a linear relationship cannot be ruled out

mobile hinge kinking in layered rocks and models abstract an unresolved question in structural geology is whether kink folds grow by the gradual rotation of the fold limbs about a fixed hinge by the nucleation of kink bands that grow by fold hinge migration or by some combination of these mechanisms the importance of mobile hinge kinking has previously been recognized in experimentally deformed slate and phyllite as well as decks of paper cards but its importance in the folding of multilayers consisting of alternating competent and incompetent layers has been uncertain this study shows that mobile hinge kinking can be an important folding mechanism in both natural and experimental multilayers the natural folds are in pelagic limestones from the umbria marche apennines of italy the geometrical properties of these folds as well as the small scale structures in the rocks indicate that these folds formed by the nucleation and expansion of kink bands with mobile hinges not by a fixed hinge folding mechanism the experimental folds were produced by the deformation of multilayered models consisting of layers of lead separated by layers of wax impregnated cloth the progressive growth of these folds by the nucleation and expansion of kink bands was directly observable a rough estimate of the rate at which fold hinges migrated through the apennine limestones was obtained indirectly using the displacement history recorded by calcite fibers on a fault which cuts a kink fold and was active during the formation of the fold it appears that the rate at which fold hinges migrated was approximately 100 times greater than the displacement rate along a fault that was moving by pressure solution slip

fault propagation folds above thrusts with constant dip abstract previous models of fault propagation folds have been extended to include the case where folding initiates above a thrust ramp of constant dip the model may be useful in analyses of fold thrust structures in thin and thick skinned compressional terrains it may be most applicable to fault propagation folds that develop as a fault propagates from a thick massive brittle unit into a thinly layered anisotropic unit

a geometric model to estimate slip rates from terrace rotation above an offshore listric thrust fault kaikōura new zealand abstract the kaik ura peninsula lies at the transition from subduction to continental collision at the southern end of the hikurangi subduction system this study uses a 2012 lidar survey over the kaik ura peninsula to re map a flight of four uplifted late pleistocene marine terraces at high resolution the lidar shows that the terraces are being progressively tilted landwards in a manner consistent with listric thrust faulting offshore the fault known as the kaik ura peninsula fault dips shallowly at c 30 to the northwest at depth and probably truncates the seaward segment of the hope fault in the footwall of the jordan thrust geometric analysis of the tilt using ages based on previous dating and a regional sea level curve suggests that slip rates on the kaik ura peninsula fault have ranged between 2 3 1 5 mm yr and 4 1 1 3 mm yr over the late pleistocene the elevations of late holocene fringing beaches track regional sea level changes apart from a departure indicating a single uplift event penultimate earthquake in the late 18th to earliest 19th century 1702 1838 ce followed by uplift in the 2016 kaik ura earthquake the slip rate calculated from beach uplift including the kaik ura earthquake is consistent with longer term rates the accumulation of the slip over only c 220 years following 2000 years of quiescence suggests that the offshore thrust and associated faults exhibit clustered behavior possibly as a result of keystone faulting

geomorphology kinematic history and earthquake behavior of the active kuwana wedge thrust anticline central japan 1 we combine surface mapping of fault and fold scarps that deform late quaternary alluvial strata with interpretation of a high resolution seismic reflection profile to develop a kinematic model and determine fault slip rates for an active blind wedge thrust system that underlies kuwana anticline in central japan surface fold scarps on kuwana anticline are closely correlated with narrow fold limbs and angular hinges on the seismic profile that suggest at least 1 3 km of fault slip completely consumed by folding in the upper 4 km of the crust the close coincidence and kinematic link between folded terraces and the underlying thrust geometry indicate that kuwana anticline has accommodated slip at an average rate of 2 2 0 5 mm yr on a 27 west dipping thrust fault since early middle pleistocene time in contrast to classical fault bend folds the fault slip budget in the stacked wedge thrusts also indicates that 1 the fault tip propagated upward at a low rate relative to the accrual of fault slip and 2 fault slip is partly absorbed by numerous bedding plane flexural slip faults above the tips of wedge thrusts an historic earthquake that occurred on the kuwana blind thrust system possibly in a d 1586 is shown to have produced coseismic surface deformation above the doubly vergent wedge tip structural analyses of kuwana anticline coupled with tectonic geomorphology at 10 3 10 5 years timescales illustrate the significance of active folds as indicators of slip on underlying blind thrust faults and thus their otherwise inaccessible seismic hazards

sandbox models of fault bend folding a new investigation with a pre existing fault ramp abstract this study presents the results of analogue models of fault bend folds fbfs developed over a pre existing fault dip ramp with a non outcropping upper fault flat to determine the boundary conditions that control the formation of fbfs experiments were performed with quartz sand and glass microbeads both with and without intercalations of thin horizons of mica flakes we varied the initial thickness the ramp dip angle and the basal friction coefficient of the lower fault flat the analogue models revealed that the most important factor for the formation of fbfs was the rheological behaviour of the analogue material the elasto plastic frictional behaviour of the glass microbeads is fundamental for the formation of mode i fbfs with interlimb angles higher than 90 which is independent of the angle of the pre existing fault ramp and the basal friction along the lower fault flat in the sand models the formation of fbfs requires a high initial stratigraphic thickness resulting in a significant increase in the normal stress and or in the cohesion strength in glass microbeads the models developed structures very similar to the fbfs described in the carbonates of the maracaibo basin venezuela as well as those within the appalachian thrust belt usa

evidence for three cenozoic phases of upper crustal shortening of the xiongpo structure in the longmen shan fold and thrust belt china implications for the eastward growth of the eastern tibetan plateau abstract cenozoic crustal shortening across the longmen shan lms fold and thrust belt records the eastward growth of the tibetan plateau although the structural geometries of individual structures in the region have been studied the kinematics and rates of deformation across these structures remain unclear in this study we construct a geological cross section to derive the subsurface structural architecture of the xiongpo structure in the lms piedmont using one seismic reflection profile and data from two boreholes the structure displays a superimposed deep fault bend fold and shallow structural wedge with three splay thrust faults using two dimensional kinematic models based on fault bend folding algorithm we reconstruct three episodes of upper crustal shortening with 7 0 0 3 km of total shortening combining with previously published low temperature thermochronology data we further estimate that the structure has experienced an average shortening rate of 0 2 mm yr since 40 25 ma we infer that the structure acted as the deformation front of the lms fold and thrust belt between 40 and 25 ma and 15 10 ma driven by the eastward growth of the tibetan plateau finally we review the shortening rates of other five structures within the lms piedmont and find that these six structures including the xiongpo structure individually have undergone an average shortening rate

fault related fold styles and progressions in fold thrust belts insights from sandbox modeling fault related folds of variable structural styles and assemblages commonly coexist in orogenic belts with competent incompetent interlayered sequences despite their commonality the kinematic evolution of these structural styles and assemblages are often loosely constrained because multiple solutions exist in their structural progression during tectonic restoration we use a sandbox modeling instrument with a particle image velocimetry monitor to test four designed sandbox models with multilayer competent incompetent materials test results reveal that decollement folds initiate along selected incompetent layers with decreasing velocity difference and constant vorticity difference between the hanging wall and footwall of the initial fault tips the decollement folds are progressively converted to fault propagation folds and fault bend folds through development of fault ramps breaking across competent layers and are followed by propagation into fault flats within an upper incompetent layer thick skinned thrust is produced by initiating a decollement fault within the metamorphic basement progressive thrusting and uplifting of the thick skinned thrust trigger initiation of the uppermost incompetent decollement with formation of a decollement fold and subsequent converting to fault propagation and fault bend folds which combine together to form imbricate thrust breakouts at the base of the early formed fault ramps along the lowest incompetent layers which may correspond to basement cover contacts domes the upmost decollement and imbricate thrusts to form passive roof duplexes and constitute the thin skinned thrust belt structural styles and assemblages in each of tectonic stages are similar to that in the representative orogenic belts in the south china southern appalachians and alpine orogenic belts

ramp initiation in fold thrust belts insight from piv analysis of sandbox models abstract do forethrust ramps propagate up section from the tip line of a detachment or do they initiate within the deforming strata connecting later with the detachment to address this question we acquired cross sectional digital images of a sand layer undergoing shortening in a sandbox analog model analysis of a succession of images using particle image velocimetry piv defines spatial and temporal variations in strain and vorticity in the sand layer during shortening results show that the foreland edge of layer parallel shortening in the sand layer defines the location of the detachment s tip line and that initiation of a new forethrust ramp begins within the layer above the detachment well to the hinterland of the detachment tip once initiated the ramp grows both up dip and down dip until it links to the detachment to define a new branch line as the forethrust ramp grows the position of the tip line of the active detachment migrates to the hinterland so that previously active portions of the detachment stop slipping once the ramp intersects the detachment displacement on the detachment to the foreland of the new branch line ceases temporarily while slip on the ramp accommodates all shortening

growth fault bend folding at southeast lost hills san joaquin valley california synsedimentary deformation has created complex structural and stratigraphic relationships along the west side of the san joaquin valley california this case study of lost hills anticline documents how a simple structural process fault bend folding results in complex growth stratigraphy lost hills anticline is a fault bend fold caused by a step in the lost hills thrust the thrust steps up to the northeast at 27 from a detachment at the base of the tertiary to an upper detachment in the reef ridge formation the lower and upper detachments are at 20 000 ft 6 km and 13 000 ft 4 km displacement on the lower detachment is approximately 4 mi 6 5 km folding consumes 1 2 mi 2 km and the remaining 2 8 mi 4 5 km continues northeast beneath the san joaquin va ley forward and back limb dips of 42 and 27 respectively are consistent with fault bend fold theory pliocene pleistocene sediments onlap a time transgressive unconformity on the northeast front limb but have uniform dip and thickness on the southwest back limb this characteristic growth fault bend fold geometry indicates basinal sediments rolled through an axial surface onto the back limb whereas contemporaneous sediments deposited above the front limb are undeformed basinal sediments onlapping the fold crest indicates fault slip is greater than ramp length onlapping growth sediments indicate folding began during deposition of the etchegoin formation 8 ma and continued to the late pleistocene or holocene corresponding to an average displacement rate on the lost hills thrust of 2 700 ft m y 820 m m y continuous burial of the fold during growth caused each material e physical point in the fold to be at its maximum depth of burial contours of equal density and seismic velocity are relatively flat so that the anticline causes little or no gravity anomaly and less than expected pullup in seismic time sections the geometry of growth sediments imaged on seismic lines indicates lost hills and adjacent anticlines grew by uniform displacement to the northeast with no significant rotation oblique convergence between the pacific and north american plates is manifested as synchronous but spatially separate transcurrent and compressive displacements thus lost hills anticline and perhaps other folds in the area are more appropriately described as compressive folds in a transpressive region than as transpressive folds duplicated lower tertiary strata beneath the lost hills kettleman hills trend are potential targets for petroleum exploration

coseismic fault related fold model growth structure and the historic multisegment blind thrust earthquake on the basement involved yoro thrust central japan 1 we use high resolution seismic reflection profiles boring transects and mapping of fold scarps that deform late quaternary and holocene sediments to define the kinematic evolution subsurface geometry coseismic behavior and fault slip rates for an active basement involved blind thrust system in central japan coseismic fold scarps on the yoro basement involved fold are defined by narrow fold limbs and angular hinges on seismic profiles suggesting that at least 3 9 km of fault slip is consumed by wedge thrust folding in the upper 10 km of the crust the close coincidence and kinematic link between folded horizons and the underlying thrust geometry indicate that the yoro basement involved fold has accommodated slip at an average rate of 3 2 0 1 mm yr on a shallowly west dipping thrust fault since early pleistocene time past large magnitude earthquakes including an historic m 7 7 event in a d 1586 that occurred on the yoro blind thrust are shown to have produced discrete folding by curved hinge kink band migration above the eastward propagating tip of the wedge thrust coseismic fold scarps formed during the a d 1586 earthquake can be traced along the en echelon active folds that extend for at least 60 km in spite of different styles of folding along the apparently hard linked nobi ise blind thrust system we thus emphasize the importance of this multisegment earthquake rupture across these structures and the potential risk for similar future events in en echelon active fold and thrust belts

formation and inversion of salt detached ramp syncline basins results from analog modeling and application to the columbrets basin western mediterranean abstract the widespread extensional deformation that took place during jurassic to cretaceous times in western europe and the north atlantic margin resulted in the formation of several rift systems some of the resulting basins associated with these rifts show broad synclines detached on pre or syn kinematic permian or triassic salts and are filled by thick sedimentary successions the development of these salt detached ramp syncline basins has been associated to the extensional motion of ramp flat extensional sub salt faults the shape and kinematics of such faults have usually been established using the architecture of syn kinematic units and by assuming complete coupling of the hanging wall rocks therefore there are fault interpretations that do not consider the role played by the deep salt layers which clearly act as an effective detachment decoupling sub and supra salt deformations moreover the complexity of these scenarios further increases due to some of these basins which during latest cretaceous and cenozoic times were partially inverted and were often incorporated into fold and thrust belts based on analog models and using the mesozoic columbrets basin western mediterranean as a case study the aim of this research is to decipher the influence of the ramp flat extensional fault during the syncline development and the interaction with a pre kinematic salt and to infer how salt detached ramp syncline basins are subsequently inverted to achieve this goal we carried out an experimental program consisting of eight different sandbox models our results show that the main structure formed at the end of the extension is a salt detached ramp syncline and that its geometry not only depends on the dip and length of the fault panels but also on the fault displacement and salt thickness the inversion of these salt detached ramp synclines resulted in a major thick skinned fault bend anticline with minor thin skinned contractional structures

extensional fault related folding of the north west shelf western australia the occurrence of fault related folds in extensional settings has been gaining increased recognition during the past 20 yr passive margins and rift basins often present intriguing structural complexities that are potential sites for the development of extensional fault related folds fault related folds are important anticlinal traps for hydrocarbon exploration and understanding their evolution is critical for derisking the timing of trap formation and hydrocarbon generation this study presents folds from three areas across the north west shelf nws of western australia and aims to determine their relationship to associated extensional faults a series of kinematic forward models are presented as well as detailed structural and stratigraphic interpretation of folding at the three locations the models suggest each of the three examples have formed under extension that impacted the region during the mesozoic the modeling also highlights different characteristics of folding that are caused by fault geometry ramp flat and a propagating fault tip trishear that can be used as diagnostic features to distinguish different fold mechanisms historical exploration across the nws has targeted a relatively small number of these anticlinal traps some of which have been successful e g marina 1 well petrel subbasin and some have not e g candace 1 sholl island fault anticline this paper suggests that the prospectivity of anticlinal structures should be more carefully assessed to determine whether or not they are related to extensional activity and hence likely to have formed prior to the bulk of the hydrocarbon charge similar structures undoubtedly exist in other basins that have experienced repeated extension

rounding hinges to fault bend folding geometric and kinematic implications fault bend folding is a common folding mechanism in thrust and fold belts worldwide the widely used kink band geometric model of fault bend folding necessitates complex ramp segmentations to reproduce the rounded shape of many natural thrust related anticlines curvilinear hinge sectors provide a geometric and kinematic alternative solution to kink bands for modelling curved hinge folds we developed an analytical solution for modelling fault bend folding using circular hinge sectors the velocity field of this kinematic solution is different from that associated with the classical kink style model our solution predicts the development of curvilinear anticlines above staircase fault geometries the occurrence of limb rotation and consequently the development of rotational syngrowth wedges on both the forelimb and the crest conversely to the kink style kinematics curvilinear hinge sectors imply a dependence of deformation intensity from the fold shape and stratigraphic position of the folded layer application to natural thrust related anticlines validates the effectiveness of curvilinear fault bend folding

a balanced cross section across the himalayan frontal fold thrust belt subathu area himachal pradesh india thrust sequence structural evolution and shortening abstract the structural evolution of the frontal fold thrust belt in the nw himalayas has been deciphered through the construction of a balanced cross section which incorporates all the tertiary and the precambrian sedimentary rock units belonging to the sub himalaya zone and the lesser himalaya zone respectively towards the foreland the structural geometry is rather simple with widely spaced thrust ramps and simple fault bend folds in the hangingwall in the central sector the structural geometry seen at the surface is essentially controlled by a thrust system that can be approximately described as a buried hinterland dipping duplex the structural geometry becomes extremely complex in the northeastern sector i e towards the hinterland owing to out of sequence thrusting low ramp spacing leading to dislocation of older thrusts and related structures by younger thrusts folded thrusts and breached horses stacked up horses occupied by lesser himalaya zone formations dominate the structural geometry in this sector an in sequence thrusting event followed by out of sequence thrusting in an approximately break back style best describe the structural evolution of the fold thrust belt in this area a total slip of about 96 km occurred along the detachment and the shortening partitioned within the fold thrust belt is about 72 km or about 71

the zagros hinterland fold and thrust belt in sequence thrusting iran abstract the collision of the iranian microcontinent with the afro arabian continent resulted in the deformation of the zagros orogenic belt the foreland of this belt in the persian gulf and arabian platform has been investigated for its petroleum and gas resource potentials but the zagros hinterland is poorly investigated and our knowledge about its deformation is much less than other parts of this orogen therefore this work presents a new geological map stratigraphic column and two detailed geological cross sections this study indicates the presence of a hinterland fold and thrust belt on northeastern side of the zagros orogenic core that consists of in sequence thrusting and basement involvement in this important part of the zagros hinterland the in sequence thrusting resulted in first and second order duplex systems mode i fault bend folding fault propagation folding and asymmetric detachment folding which indicate close relationships between folding and thrusting study of fault bend folds shows that layer parallel simple shear has the same role in the southeastern and northwestern parts of the study area e 23 4 9 1 a major lateral ramp in the basement beneath the talaee plain with about one kilometer of vertical offset formed parallel to the sw movement direction and perpendicular to the major folding and thrusting

origin of basin scale syn extensional synclines on the southern margin of the northern carnarvon basin western australia fault geometry exerts a dominant structural control on the deformation of hanging wall sequences during extension and contraction numerical kinematic and sandbox modelling studies have demonstrated that characteristic anticline syncline pairs are produced during the extension of ramp flat faults these features are commonly recognized in smaller fault scale structures but remain underappreciated in larger basin scale settings the lewis trough situated within the northern carnarvon basin western australia is a basin scale largely unfaulted syncline with an associated anticline along its western flank rather than the fault related graben typical of the region we present kinematic models demonstrating that a se dipping ramp flat fault geometry can produce relative highs and lows in jurassic strata as well as honouring the asymmetrical onlap pattern within the lewis trough this study indicates that the lewis trough formed during the early jurassic a period typically associated with high rates of extension and not during the late triassic fitzroy compression event this study also highlights the importance of the locker shale in partitioning deformation of the permian and mesozoic fault systems and as a diffuse zone that variably partitions displacement between stacked permian and mesozoic fault systems

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

the suckling hills fault kayak island zone and accretion of the yakutat microplate alaska 1 the suckling hills and kayak island are isolated mountain blocks located along strike from each other within the foreland of the st elias orogen in southern alaska these blocks preserve an erosional surface that was deformed by slip on northwest dipping reverse faults in the pleistocene we suggest that the suckling hills fault and kayak island zone form a segmented fault network that links with the bering glacier structure to the north this fault network separates the central yakataga fold and thrust belt from complex multiply deformed structures in the western syntaxis ongoing accretion of the yakutat microplate to north america results in translation of structures of the fold and thrust belt into the western syntaxis the composite suckling hills fault kayak island zone and bering glacier structure may have formed because the older structures of the fold and thrust belt were unfavorably oriented within the western syntaxis region this pattern of deformation provides a template for understanding the complex deformation within the core of the western syntaxis and predicts refolding and straightening of the western syntaxis margin with continued accretion this study provides an analog for structural overprinting and changing deformation patterns through time in orogenic corners

the near source ground motion of the 6 august 1979 coyote lake california earthquake a finite fault striking n24 w and extending to a depth of 10 km is proposed to explain the strong ground motion data for the 6 august 1979 coyote lake california earthquake m l 5 9 our source model suggests that right lateral faulting initiated at a depth of 8 km and ruptured toward the south with a velocity of 2 8 km sec this unilateral rupture can explain the large displacement recorded south of the epicenter however the waveform coherency across an array south and southwest of the epicenter suggests that the rupture length is less than 6 km the maximum dislocation is about 120 cm in a small area near the hypocenter and the total moment is estimated to be 3 5 10 24 dyne cm an abrupt stopping phase which corresponds to a deceleration of right lateral motion can explain the high peak acceleration recorded at array station 6 the stress drop in the hypocentral area is about 140 bars the average stress drop over the entire rupture surface is 30 bars the preferred finite source model can predict the p n1 waveforms and the beginning features in the teleseismic seismograms no clear arrivals can be observed in the near source data for the possible second and third smaller events suggested by nabelek personal communication

seismic stratigraphy of a neogene piggyback basin argentina depositional sequences composed of neogene nonmarine strata are imaged on seismic reflection data from the iglesia piggyback basin argentina the strata accumulated in an internally drained basin located between the frontal cordillera the high andes and the precordillera thrust belt two reflection geometries onlap and truncation are observed along four unconformities within the neogene section onlap of reflections onto unconformities defines five distinct intervals of basin growth local truncation of reflections beneath unconformities defines four intervening intervals of nondeposition or erosion along strike variation in the amount of truncation suggests that erosion was limited to zones through which major streams entered the basin postdepositional thrusting o the east side of the basin produced field exposures of the five sequences and allowed examination of the nature of the sequence boundaries the iglesia depositional sequences are interpreted to result from neogene crustal shortening within the central andes the iglesia basin has been passively transported above a horizontal decollement that links mid crustal deformation beneath the frontal cordillera with surface thrusting in the precordillera deposition resulting generally from simultaneous uplift of the frontal cordillera and the precordillera can be explained by two scenarios thrust controlled accumulation where space for deposition was created only during faulting or drainage controlled accumulation where deposition occurred only when thrusting cut off through going drainages linking the iglesia basin with the foreland

earthquake hazards of active blind thrust faults under the central los angeles basin california we document several blind thrust faults under the los angeles basin that if active and seismogenic are capable of generating large earthquakes m 6 3 to 7 3 pliocene to quaternary growth folds imaged in seismic reflection profiles record the existence size and slip rates of these blind faults the growth structures have shapes characteristic of fault bend folds above blind thrusts as demonstrated by balanced kinematic models geologic cross sections and axial surface maps we interpret the compton los alamitos trend as a growth fold above the compton ramp which extends along strike from west los angeles to at least the santa ana river the compton thrust is part of a larger fault system including a decollement and ramps beneath the elysian park and palos verdes trends the cienegas and coyote hills growth folds overlie additional blind thrusts in the elysian park trend that are not closely linked to the compton ramp analysis of folded pliocene to quaternary strata yields slip rates of 1 4 0 4 mm yr on the compton thrust and 1 7 0 4 mm yr on a ramp beneath the elysian park trend assuming that slip is released in large earthquakes we estimate magnitudes of 6 3 to 6 8 for earthquakes on individual ramp segments based on geometric segment sizes derived from axial surface maps multiple segment ruptures could yield larger earthquakes m 6 9 to 7 3 relations among magnitude coseismic displacement and slip rate yield an average recurrence interval of 380 years for single segment earthquakes and a range of 400 to 1300 years for multiple segment events if these newly documented blind thrust faults are active they will contribute substantially to the seismic hazards in los angeles because of their locations directly beneath the metropolitan area

self determining numerical modeling of compressional fault bend folding we present the application of the hca hybrid cellular automata numerical modeling technique to the evolution of compressional fault bend anticlines involving layers that have competency contrasts and a mechanical stratigraphy the new modeling results show that for competent hanging wall layers 1 the fault style is not preserved in the overlying fold 2 fold development is not self similar and rotational growth wedges develop in the forelimb when syntectonic sedimentation occurs and 3 balanced fault bend anticlines can develop for ramp cutoff angles as high as 60 these results compare favorably with field examples and laboratory analogues and dramatically broaden the applicability of fault bend folding to model the evolution of thrust related anticlines

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

fold style inversion placing probabilistic constraints on the predicted shape of blind thrust faults we develop a new methodology which compares quantitatively styles of folding from seismic reflection data the goal of the fold style inversion fsi method is to provide an objective choice of the most appropriate model used when solving for the shape of an unimaged blind fault from folded layer geometry fsi is a discretization of the dip isogon fold classification scheme reformulated as simple vector transformations a data set s goodness of fit to parallel class 1c or similar class 2 fold geometry is assessed by calculating misfit between the predicted and observed bed geometries through a grid search of the parameter space specific to each transformation the two fold types correspond to the constant bed length and arbitrarily inclined simple shear aiss fault solution routines respectively for seismic reflection data confidence estimates may be placed on the preference of fold style and its corresponding fault solution by monte carlo simulations of depth correlative spatially limited depth conversion errors for synthetic geometric examples fsi determines fold style preference and parameters exactly at low fold limb dips 15 the actual geometric difference between parallel and similar folds is very small and the difference between fold styles cannot be resolved highlighting a general difficulty in the analyses of young blind thrust structures for a synthetic seismic line of an aiss fault related fold the method chooses the correct folding style and leads to the correct fault geometry at depth in examples of real data from the barrancas lunlunta carrizal anticlinal complex in mendoza argentina fsi analysis determines 71 and 54 probability of similar preference for two seismic lines on separate structures the corresponding fault solutions for the first example are well constrained whereas for the second example the solutions are widely variant this analysis helps to quantify the relationship between the predicted sub surface fault trajectories and hypocenter and aftershock data of the 1985 mw 5 9 mendoza earthquake showing that the earthquake and the fault causing the barrancas lunlunta carrizal anticlinorium are most likely unrelated

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

multibend fault bend folding this paper shows how slightly complex but angular fault shapes with only a few bends lead to broadly curved and or highly complex folds a common perception exists that simple angular fold geometries are a necessary consequence of the normal assumptions of fault bend fold theory namely angular fault bends straight faults and flexural slip to the contrary it is shown here that exact application of these low level assumptions produces great complexity from simple fault shapes this complexity is caused by the combination of 1 generation of new axial surfaces by displacement of hangingwall cut offs past successive fault bends and 2 fragmentation of axial surfaces by mutual interference the result is entwined arrays of fold axial surfaces that produce quasi curved and or complex folds from discrete angular fault bends fold complexity grows in a highly non linear way in the most extreme case the number of fold axial surface segments grows as the fourth power of the number of fault bends this paper presents examples of the immense variety of complex fold geometries that are thus generated 0 1997 elsevier science ltd all rights reserved

deciphering cumulative fault slip vectors from fold scarps relationships between long term and coseismic deformations in central western taiwan we document the 30 ka cumulative slip history and long term slip vector azimuth on the northern chelungpu fault based on a series of fault bend folded alluvial terraces and draw quantitative relationships between geological structure deformation observed from the geomorphology and coseismic displacements during the 1999 mw 7 6 chi chi earthquake in our study area three main terrace levels show progressive folding by kink band migration in relation to the underlying fault geometry forming a main n s fold scarp up to 193 m high and secondary e w scarps detailed analysis using 5 m resolution digital elevation model allows us to characterize the scarp morphology and quantify the deformation parameters namely terrace heights fold scarp relief and fold limb width and slope angle the 3 d deformation of the highest terrace dated by optically stimulated luminescence at 30 2 4 0 ka enables to simultaneously determine amplitude and azimuth of the long term slip vector based on scarp relief the long term slip vector oriented n338 6 is found to parallel the chi chi coseismic displacements in this area cumulative slip and dating results yield a constant slip rate of 17 7 2 2 mm a in the direction n338 6 late quaternary shortening rates observed at four sites vary along strike in a similar way to chi chi coseismic displacements together with the collinearity of long term and coseismic slip vectors at our study site this suggests that chi chi earthquake is a characteristic earthquake for the chelungpu thrust with recurrence interval 470 years we also discuss implications for the regional and long term distribution of shortening in the central western foothills

structures and active tectonics of compressionally reactivated back arc failed rift across the toyama trough in the sea of japan revealed by multiscale seismic profiling abstract compressional reactivation of back arc failed rifts in the sea of japan and its mechanism that mobilizes active tectonics based on the crustal structures remains poorly understood here we show new results and interpretations of onshore offshore deep seismic reflection profiles across the toyama trough and its southern extension located in the sea of japan back arc rift to reveal their deep to shallow structures of the crust and reactivated active faults we observed 1 approximately 5 km thick syn and post rift neogene sediments underlain by pre neogene basement rocks characterized by high velocity anomalies and 2 crustal thrust wedges adjacent to the rift axis shallower high resolution seismic reflection profiles also suggest quaternary structural growth of the reactivated thrusts and thrust wedges consistent with tectonic geomorphology of the middle to late pleistocene marine and fluvial terraces these findings demonstrate that the mechanical contrasts between the crustal thrust wedges primarily composed of the pre rift continental crust and high velocity lower crust caused by mafic intrusions in the rifting stage have fundamentally controlled the styles of active deformation during the post rift quaternary compressional stress regime these results also contribute to the construction of the seismic source fault models for tsunamis and seismic hazard estimations of this region in addition we emphasize that combining multi scale seismic reflection profiles with tectonic geomorphology sheds light on complicated structural characteristics and recent activities of reactivated normal faults that are mostly blind because of the dynamic subsidence of failed rift structures

a forward modeling strategy for balancing cross sections 1 a strategy to balance cross sections of complex structures is documented and illustrated by the interpretation of a compressional structure in the deep water gulf of mexico the strategy is applicable to structures formed in sedimentary rocks under low temperatures in both compressional and extensional environments and involves the comparison of the observed structure with simple balanced forward models forward models generated using fault related fold theory help in understanding the processes and kinematics involved in the deformation further forward models are completely constrained and easy to balance whereas it is difficult to balance data therefore forward models are useful in evaluating ideas without completely solving the structure models are constructed assuming parallel behavior preservation of layer thickness no net distortion where layers are horizontal and conservation of bed length unmetamorphosed sedimentary rocks are generally observed to deform obeying the assumptions of parallel behavior in field map well and seismic data

late cenozoic east west crustal shortening in southern longmen shan eastern tibet implications for regional stress field changes abstract the co seismic slip sense of the 2008 wenchuan earthquake mw 7 9 has resulted in the present east west e w crustal shortening and oblique thrusting across longmen shan which are inconsistent with southeast directed thrusting that occurred during the late triassic although the two major periods of compressional deformations in longmen shan have long been recognized the fault slip rate of the late cenozoic deformation and the initial e w crustal shortening remain poorly investigated this study confirms the fault slip rate in the dayi thrust fault system dyfs based on data from the petroleum industry and shallow seismic reflection profiles and well data folded late pliocene to present strata are analyzed and yield with an average slip rate of 0 2 mm yr on the dyfs an average fault slip rate of 0 25 mm yr is then obtained from the late pliocene to present for the range front thrust of longmen shan the e w crustal shortening is investigated by using 3 d seismic reflection data interpreting satellite image and conducting a field investigation in the dyfs to determine stress field changes during the late cenozoic two period tectonic deformations during the late cenozoic are found in the dyfs which correspond to the ne and ns trending structures respectively the activities of the dyfs may reflect a change in the field direction of the regional stress from nw se during the oligocene to early pliocene to e w during the late pliocene to holocene which is consistent with the present stress measurements the 120 km ns trending structures in the southern longmen shan range front as well as the wenchuan earthquake co seismic ruptures are assumed to reflect the active e w crustal shortening in longmen shan