balanced section in thrust belts part 1 construction balanced geological cross sections are an important aid to understanding thrust belt structures and to estimating their hydrocarbon bearing potential two approaches to section balancing have been taken in the past construction of retrodeformable sections from raw data and modification of previous interpretations after an evaluation procedure these approaches may be unified by use of a langrangian grid projection of datum locations dips and stratigraphic thicknesses onto the section plane is performed directly by calculation or graphically using plunge lines spline interpolation and parallel fold modeling are the simplest ways of filling gaps in the sectional data but isogon interpolation yields rheologically more realistic results faults are interpolated using cutoff geometries as constraints fault tips are located from distance displacement plots whereas the depth to detachment is obtained by a modified chamberlin construction interpolations made on the section are directed back to the geologic map via plunge lines although these techniques of section construction do not guarantee a balance especially when complexities such as growth structures diapirs or strike slip faults are present they eliminate many potential errors

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

a new high precision 40ar 39ar age for the rochechouart impact structure at least 5 ma older than the triassic jurassic boundary the rochechourt impact structure in south central france with maximum diameter of 40 50 km has previously been dated to within 1 uncertainty of the triassic jurassic boundary at which time 30 of global genera became extinct to evaluate the temporal relationship between the impact and the triassic jurassic boundary at high precision we have re examined the structure s age using multicollector argus v 40ar 39ar mass spectrometry results from four aliquots of impact melt are highly reproducible and yield an age of 206 92 0 20 0 32 ma 2 full analytical external uncertainties thus the rochechouart impact structure predates the triassic jurassic boundary by 5 6 0 4 ma and so is not temporally linked to the mass extinction rochechouart has formerly been proposed to be part of a multiple impact event but when compared with new ages from the other purported paired structures the results provide no evidence for synchronous impacts in the late triassic the widespread central atlantic magmatic province flood basalts remain the most likely cause of the triassic jurassic mass extinction

three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

structural interpretation of thrust fault related landforms on mercury using earth analogue fault models abstract the yakima fold province has often been referenced as an earth analogue to thrust fault related landforms on many solar system bodies including mars the moon and mercury the asymmetric ridges of deformed flood basalts in this region evoke the morphology and topographic expression of the landforms observed in the smooth plains units of mercury observed similarities have supported the interpretation that thrust faults and folds comprise both sets of landforms however this is an incomplete analogy recent modeling efforts have revealed that the terrestrial landforms developed over millions of years with vertical uplift associated with each landform accumulating on multiple faults and accommodated by large folds these studies highlight the important role that folding plays in accommodating crustal shortening work presented here uses the structural geometries and folding styles from the yakima fold province as a framework for constructing ten three dimensional models of thrust fault related landforms in smooth plains units near suisei planitia on mercury which traditionally would have been classified as wrinkle ridges based on appearance and some aspects of morphology forward modeling of topography revealed that multiple faults and folds are necessary to reproduce complex topographic features folding was found to account for 50 of vertical uplift associated with the landforms and without considering folding shortening accommodated by the landforms was underestimated by 61 to 88 studies which use thrust fault related landforms as proxies for stress and strain must therefore consider the effect of folding on these estimates and their associated effect on tectonic and thermal histories

geometrical modeling of fault related folds a pseudo three dimensional approach abstract area balanced cross sections of ramp anticlines and tip line folds in thin skinned fold thrust belts can be quantitatively constructed using plane strain fault bend and fault propagation fold models cross sections alone however are somewhat inadequate for interpreting along strike changes in thrust related fold geometry complex interplay between along strike changes in fault slip and fault shape determines a range of geometric configurations which are difficult to visualize without the aid of quantitative three dimensional models we extend conventional two dimensional folding theories into the third dimension by allowing for continuous variations in fault slip and fault shape along strike geometric equations relating map view angles between fold axial surface traces are derived for a case assuming a uniform fault geometry and an along strike displacement gradient the resulting folds possess no unique fold axis but rather are characterized by multiple fold hingelines each corresponding to bends in the fault for typical displacement gradients observed in the field analysis of the models suggests that discernible differences exist between map patterns of fault bend folds and fault propagation folds whereas little difference exists between map patterns of similar and parallel fault bend folds map view angles between axial surface traces for parallel fault bend folds and fault propagation folds are a function of both ramp cutoff angle and fault slip whereas these same angles for similar fault bend folds are solely a manifestation of fault slip examples assuming uniform shortening and continuously varying fault geometry along strike are also presented fault geometry is varied along strike to simulate oblique and lateral ramps depending upon model type and fault shape parameter modified resulting folds exhibit either cylindrical or non cylindrical fold geometries closure is generated by a decrease in fold amplitude where there is a decrease in ramp cutoff angle along strike or where a fault laterally cuts up section in either instance closure develops without varying shortening along strike model map patterns resemble actual thrust related fold geometries and can be compared to maps of real structures to help predict subsurface geology

structural styles in the deep water fold and thrust belts of the niger delta the deep water niger delta includes two large fold and thrust belts products of contraction caused by gravity driven extension on the shelf that exhibit complex styles of thrusting these contractional structures formed above multiple detachment levels in the overpressured shales of the akata formation using the patterns of growth sedimentation fold shapes fault plane seismic reflections and combined conventional and shear fault bend folding theories we describe and model the structural styles and kinematics of the fault related folds and imbricate thrust systems that compose these belts individual fault related folds involving both forethrusts and backthrusts are characterized by long planar backlimbs that dip less than the associated fault ramps with upward shallowing of dips in growth strata above the backlimbs suggesting components of progressive limb rotation forelimbs are short compared to backlimbs but growth strata show more consistent dips that suggest a component of folding by kink band migration thus we employ a combination of classic and shear fault bend fold theories to describe these structures including the influence of a weak basal detachment zone in the overpressured shales we expand upon these theories to model the kinematics of imbricate thrust systems which display a complex history of thrusting related to spatial and temporal variations in deposition across the delta regional patterns of folded growth strata are used to define break forward break backward and coeval thrusting involving single and multiple detachment levels we define two main types of imbricate thrust systems type i system with a single basal detachment level and type ii imbricate system with multiple basal detachment levels which cause massive structural thickening of the akata formation and refolding of shallow thrust sheets through the sequential restoration of two regional cross sections across these systems we resolve the structural styles the timing and sequences of thrusting as well as the regional amounts of shortening all of which have important implications for hydrocarbon maturation and charge in the deep water niger delta

deep water niger delta fold and thrust belt modeled as a critical taper wedge the influence of elevated basal fluid pressure on structural styles we use critical taper wedge mechanics theory to show that the niger delta toe thrust system deforms above a very weak basal detachment induced by high pore fluid pressure the niger delta exhibits similar rock properties but an anomalously low taper sum of the bathymetric slope and dip of the basal detachment compared with most orogenic fold belts this low taper implies that the niger delta has a very weak basal detachment which we interpret to reflect elevated pore fluid pressure 0 90 within the akata formation a prodelta marine shale that contains the basal detachment horizon the weak basal detachment zone has a significant influence on the structural styles in the deep water niger delta fold belts the overpressured and thereby weak akata shales ductilely deform within the cores of anticlines and in the hanging walls of toe thrust structures leading to the development of shear fault bend folds and detachment anticlines that form the main structural trap types in the deep water fold belts moreover the low taper shape leads to the widespread development of backthrust zones as well as the presence of large relatively undeformed regions that separate the deep water fold and thrust belts this study expands the use of critical taper wedge mechanics concepts to passive margin settings while documenting the influence of elevated basal fluid pressures on the structure and tectonics of the deep water niger delta

structural trend analysis by axial surface mapping we present a new method of structural trend analysis in which axial surfaces fold hinges are mapped through grids of seismic reflection profiles and balanced forward models axial surface maps 1 define fold trends lateral terminations and closure in structure 2 constrain underlying fault geometry and slip and 3 highlight and connect regions that can be interpreted by a series of balanced models or cross sections maps of folds in southern california and northeastern pennsylvania are compared with forward model solutions and used to construct balanced three dimensional structural interpretations using fault bend fold theory axial surface maps generated from balanced fault bend fold models define theoretical relationships between map patterns and structural geo etry and fault slip kink band widths between paired axial surfaces in map view are related to underlying fault slip lateral variations in fault slip which can be identified on axial surface maps may cause fold plunge and provide lateral closure lateral changes in subsurface fault geometry which include lateral and oblique ramps are also reflected by terminations bends or offsets of axial surfaces in map view based on these relationships between folding and faulting we develop map view interpretations and balanced cross sections across structures that are consistent with the geology along trend

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

fluviodeltaic response to sea level perturbations amplitude and timing of shoreline translation and coastal onlap 1 alluvial river systems respond to changing sea level by adjusting channel length through shoreline translation and coastal onlap offlap at the alluvial basement transition the magnitude and timing of shoreline translation and coastal onlap offlap relative to the driving sea level signal depend on the dynamics of the fluvial system and have important implications for interpreting ancient fluviodeltaic deposits i obtain analytical solutions to a diffusive geometric model of fluviodeltaic response to sea level perturbations that treats the shoreline and alluvial basement transition as moving boundaries fluviodeltaic behavior is most sensitive to the ratio of the period of eustatic cycling to the fluvial response time which varies with the length and water discharge of the fluvial system the square root of this ratio provides a first order estimate of the fraction of the fluvial long profile affected by eustatic forcing the fluviodeltaic system behaves as a low pass filter with respect to eustatic cycling the amplitude of both shoreline translation and coastal onlap offlap increase with increasing cycle period within a relatively narrow bandwidth in which the fluvial response time is comparable to the cycle period only small time lags develop between shoreline response and eustatic forcing the time lag between maximum coastal onlap and maximum sea level increases without bound as the forcing period decreases relative to the fluvial response time model predictions agree with experimental data and differ considerably from the model predictions of pitman 1978 and angevine 1989 which suggest that fluviodeltaic systems are strong high pass filters to sea level cycling

geologic stereo mapping of geologic structures with spot satellite data reply the spot imaging system launched in 1986 by the french national space agency cnes provides two significant advances for mapping geological structures from satellite imagery increased spatial resolution of key structural and stratigraphic elements and stereoscopic capabilities for making strike and dip measurements quantitative stereo mapping with spot data may be done using hard copy images and conventional equipment such as stereo plotters or by displaying images on a video monitor in stereo viewing format the latter method is a new remote sensing technique particularly relevant to the exploration community this technique allows development with minor expenditure and training of an effective stereo mapping capability on existing image processing systems or on stand alone personal computers spot stereo data is particularly useful for mapping low amplitude and highly deformed structures surface structure maps generated from stereo imagery data can be applied to exploration at two levels at early stages such maps can be used to establish the style trend size and spatial distribution of structures in a basin and to investigate key tectonic elements at more advanced prospecting stages these maps can be used to constrain subsurface mapping of structures located in areas of poor seismic data quality this latter technique however may require the support of highermore resolution stereo aerial photography less

a scenario for late neogene andean shortening transfer in the camisea subandean zone peru 12 s implications for growth of the northern andean plateau precise knowledge of the timing of deformation in the subandean zone of the andean plateau is a prerequisite for deciphering the late neogene growth of the andean plateau in this paper we report new apatite fission track aft and vitrinite reflectance ro data for a regional balanced cross section of the camisea basin in the central peruvian subandean zone adjacent to the northern andean plateau the balanced cross section shows that the structure of this basin is characterized by a broad internal passive roof duplex and external thrust related anticlines the balanced cross section restoration shows 53 km 39 of total horizontal shortening we sampled paleozoic to cenozoic sedimentary strata for aft and ro analyses along the 4 km thick vertical profile of the mainique back thrust passive roof thrust the innermost preserved subandean structure young components of aft ages are spread between ca 6 ma and ca 24 ma a break in the slope in the aft ages determines the geometry of the miocene partial annealing zone and the exhumation of the mainique back thrust at ca 6 ma sequential restoration calibrated by aft and ro data indicates that the last 23 km horizontal shortening were accommodated by the camisea thrust system over the past 6 m y giving a mean shortening rate of 3 8 mm yr using this shortening rate for the first 30 km horizontal shortening we calculate that the andean shortening transfer into the peruvian subandean zone initially started at ca 14 ma this result suggests that the transfer of shortening from the northern andean plateau to the subandean zone occurred prior to the removal of dense lithosphere previously reported to have occurred between ca 10 ma and ca 7 ma we rather propose that the late neogene growth of the northern andean plateau mostly resulted from a continuous crustal shortening combined with lower crustal flow

structural evolution of backthrusting in the mentawai fault zone offshore sumatran forearc 1 we present the interpretation of newly acquired high quality industry standard deep seismic reflection and swath bathymetry data to provide insight into the structural style and evolution of the mentawai fault zone mfz the mfz lies along the boundary between the accretionary wedge and the proposed continental backstop this zone exhibits arcuate ridges on the seafloor convex toward the east beneath these ridges the structures developed as landward vergent imbricated backthrusts in the inner part of the accretionary wedge and higher angle backthrusts that deformed the forearc basin sediments in the forearc high anticlines were developed due to the seaward vergent forearc high thrusts originating in the accretionary wedge the imbricated backthrusts may have initiated during the early middle miocene contemporaneously with the slide and back rotation of forearc high thrusts in the late miocene the higher angle backthrusts were initiated continuous contraction induced the frontal higher angle backthrusts and formed a fold thrust belt toward the east during the pliocene the folds and thrusts were disturbed by diapirs and mud volcanoes backthrusting and fold thrust belts developed in the mfz may explain the compressional features observed at the boundary between the accretionary wedge and continental backstop along the southern sumatra margin the backthrusts along the mfz are waning in activity and hence the risk of a large earthquake and associated tsunami at the present time should be small

quantitative structural analysis with stereoscopic remote sensing imagery we employ powerful stereoscopic methods with satellite imagery to obtain surface bedding attitude measurements these data are used to constrain geologic structures in three dimensions using quantitative structural models we document a numerical method for measuring the strike and dip of bedding using stereoscopic pairs of air photos as well as landsat thematic mapper and spot images in examples from the north american and andean cordilleras these remote measurements prove consistent with direct surface control and subsurface structures imaged in seismic reflection profiles remotely derived measurements are combined with subsurface data to generate balanced structural interpretations that define complex structural traps using fault related folding theory these remote sensing methods can provide a low cost and rapid means of delineating prospects and leads

development and growth of basement involved structural wedges in the northwestern qaidam basin china structural wedges contain two connected fault segments a fore thrust and back thrust that bound a triangular or wedge shaped fault block coeval displacements on both faults drive the wedge into surrounding rock causing distinctive patterns of uplift and folding we identified a series of thick skinned structural wedges in northwestern qaidam basin china where syntectonic strata record deformation timing and kinematics the qaidam basin is located at the northern margin of the tibetan plateau and contains more than 100 large anticlinal structures many of which exhibit characteristics of structural wedges we interpreted and modeled these structures using seismic reflection data well logs surface geological exposures remote sensing images and digital elevation data these wedge structures are distinguished by having elevated and deformed strata in the footwalls of the back thrusts and synclinal folds that extend upward from the wedge tips with the constraints of fold shape growth strata structural relief and shallow fault geometry we developed a series of forward models that describe the geometry and kinematic evolution of these wedge structures the analysis suggests that some of the wedge structures reactivate preexisting normal faults our results provide a better understanding of how to identify thick skinned wedge systems and model their geometry and kinematic evolution which has implications for studying the tectonic history of the basin understanding the geometry and kinematics of the wedge structures is also crucial for petroleum exploration because both hanging wall and footwall traps constitute an important component of current exploration targets

stress determination in active thrust belts an alternative leak off pressure interpretation abstract in thrust belts fluid flow through critically stressed fractures will occur at pressures less than the overburden stress which is the minimum stress we propose that low leak off pressures obtained in active thrust belts may result from this mechanism leading workers to infer that apparent minimum stresses are 30 60 less than the overburden stress in some compressional settings traditionally leak off pressure data have been used to constrain the magnitude of minimum stress assuming that the rock is dilating against the minimum stress during a leak off test in our new interpretation we constrain the stress state by assuming that the leak off test causes shear failure along pre existing weaknesses rather than tensile opening while this mechanism has been discussed in a small number of borehole stability and hydraulic fracture papers it has not been directly applied to leak off tests we considered this interpretation because we observed that some leak off tests imply an apparent contradiction between the stress states from the standard interpretation of leak off tests versus the stress state inferred from geologic and geophysical evidence in tectonically active thrust belts we present two examples with one in an onshore fold thrust belt and one in a deepwater fold thrust belt our new interpretation of stresses based on shear failure resolves the contradiction and also provides a constraint on the maximum horizontal stress in the fold thrust belts

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

geomechanical restoration as a tool for fractured reservoir characterization application to the permian basin west texas we present a three dimensional 3 d geomechanical restoration method as a reservoir characterization tool in the permian basin west texas the oates sw field produces gas from the lower devonian thirtyone formation within structural traps the thirtyone is a brittle chert with characteristics of a fractured reservoir field development has experienced variable production trends for decades to assess the impact of deformation on reservoir properties we employ 3 d geomechanical restorations to model strain patterns associated with fault displacement and fold growth we correlate these model strains with independent measures of natural rock strain to assess the viability of the restoration results a semblance volume generated from 3 d seismic reflection data illuminates secondary faults and fracture zones that are not incorporated in the geomechanical restorations our analysis yields strong correlations between low semblance and elevated strain throughout the thirtyone reservoir these correlations indicate that restoration strains may be used to describe the distribution of secondary faults and fractures that are not represented in our models providing predictive capabilities for defining fractured reservoir properties we integrate strain and semblance with production data to evaluate these correlations at the borehole scale in the study area we describe how tectonic strain likely enhanced permeability directly impacting observed production trends our characterization of the thirtyone reservoir demonstrates the ability to accurately predict strain distributions with geomechanical restorations where structure has been a significant factor in the development of reservoir permeability we suggest that these methods show promise as a reservoir characterization tool for conventional and unconventional development operations

hydromechanical modeling of stress pore pressure and porosity evolution in fold and thrust belt systems we present coupled critical state geomechanical fluid flow simulations of the evolution of a fold and thrust belt in nw borneo our modelling is the first to include the effects of both syntectonic sedimentation and transient pore pressure on the development of a fold and thrust belt the present day structure predicted by the model contains the key first order structural features observed in the field in terms of thrust fault and anticline architectures stress predictions in the sediments show two compressive zones aligned with the shortening direction located at the thrust front and back limb between the compressive zones near to the axial plane of the anticline the modelled stress field represents an extensional regime the predicted overpressure distribution is strongly influenced by tectonic compaction with the maximum values located in the two laterally compressive regions we compared the results at three notional well locations with their corresponding uniaxial strain models the 2d thrust model predicted porosities which are as much as 7 5 lower at 2 5 km depth and overpressures which are up to 6 4 mpa higher at 3 km depth these results show that one dimensional methods are not sufficient to model the evolution of pore pressure and porosity in contractional settings finally we performed a drained simulation during which pore pressures were kept hydrostatic the predicted geological structures differ substantially from those of the coupled simulation with no thrust faulting these results demonstrate that pore pressure is a key control on structural development

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

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