fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

deformation and fault activity in space and time in high resolution numerical models of doubly vergent thrust wedges a discrete element model is used to investigate the manner in which deformation and fault activity change in space and time during the development of a doubly vergent thrust wedge in the upper crust deformation is a result of shortening at a subduction slot in the base of the model a configuration which produces a dynamic backstop within the cohesionless frictional cover material a series of experiments with differing basal decollement friction are performed the distinct manners in which thrust wedges grow and the variability of fault development and activity in space and time are then examined both predicted large scale wedge geometries and individual fault fold structures are similar to those observed in sandbox models and show the complex manner in which shortening is accommodated and localized during the development of the thrust wedge when compared to a sandbox model with similar boundary conditions model results are strikingly similar in all cases deformation initiates above the subduction slot with the formation of an axial zone the wedge is then developed by displacement on a retro wedge thrust and propagation of deformation into the pro wedge region models with low coefficients of basal friction typically develop wide shallow wedges with distributed spaced deformation and rather symmetric box like structures whereas those with high coefficients of basal friction develop narrower steeper wedges consisting of a series of stacked pro wedge thrust sheets and a high displacement retro wedge thrust in general fault initiation and linkage is extremely complex in our models with several smaller faults operating until linkage occurs to form a major through going structure of particular interest is the observation that many of the faults do not develop at the basal decollement and propagate upwards through the cover but rather initiate at high levels in the cover and propagate link downwards with other deeper structures results also indicate the utility of the discrete element approach in modelling large displacement complex deformation of geological materials

optimal dip based on dissipation of back thrusts and hinges in fold and thrust belts 1 back thrusts and hinges are two types of transition between rigid sections of hanging walls observed in fold and thrust belts back thrusts are typical of frictional and homogeneous solids and hinges of creeping and layered materials our objective is to study the orientation of these transitions for the special case of a lower flat ramp transition in a fault bend fold with the following general two step methodology in the first step the forces acting on the transition are determined using equilibrium of each rigid section in the second step the optimal dip of the transition is obtained by minimizing the total dissipation of the structure the three sources of dissipation of comparable magnitude are at the transition on the flat and on the ramp for frictional material flows the back thrusts are velocity discontinuities with optimal dips always less than half the complementary ramp angle leading to hanging wall thickening the optimal dip agrees well with the results of physical analogue and numerical experiments for creeping and layered materials it is shown that a destabilizing deformation mechanism selected to be flexural slip is necessary for the strain to localize and the existence of hinges to be justified activation of flexural slip reduces dissipation at the transition and affects the optimal transition dip the two step methodology proposed here could be seen as a first attempt in producing mechanically balanced cross sections accounting for material rheology this approach should complement the now classical kinematic models of folding

a new strategy for discrete element numerical models 2 sandbox applications 1 here we present a series of numerical experiments using a new formulation of the discrete element method dem that improves performance in modeling faults and shear zones in the new method named the stress based discrete element method sdem which is introduced in the companion paper by egholm stress tensors are stored at each circular particle further sdem includes rotational resistivity of particles and elastoplastic constitutive rules for governing particle deformation when combining these new features the sdem is capable of reproducing the friction properties of rocks and soils without the need for the ad hoc calibration routines normally associated with dem in contrast to the conventional dem the friction properties of a sdem particle system are in agreement with the mohr coulomb constitutive model with friction angles specified on a particle level benchmark sandbox models show that unlike most commonly used numerical methods sdem faults and shear zones develop at angles in agreement with general observations from structural geology and analogue modeling studies citation egholm d l m sandiford o r clausen and s b nielsen 2007 a new strategy for discrete element numerical models 2 sandbox applications j geophys res 112 b05204 doi 10 1029 2006jb004558

decollement tectonics in the jura forelandfold and thrust belt abstract interpretation of more than 1500 km of industry seismic reflection lines from theswiss and french jura mountains and the western swiss molasse basin demonstrates that themesozoic and cenozoic cover of the jura fold and thrust belt has been deformed over a veryweak basal decollement and displaced for many kilometers toward the nw and that thebasement is not involved a depth to the basement map derived from depth conversion of theseismic lines shows a rather smooth flat basement dipping 1 3 to the s se the low amplitudebroad folds of the molasse basin and the external plateau jura are controlled by evaporitepillows or anticlines of middle triassic age the high amplitude folds of the haute chaine jura however are related to nw or se vergent thrusts with at least kilometric dipslip displacementthat has doubled the entire jurassic sequence the plateau jura evaporite related folds located in the foreland are interpreted as early stage buckle folds with further deformation afault ramp nucleates and develops into thrust related folds as observed in the haute chaine thus within the fold and thrust belt deformation increases toward the hinterland in the molassebasin however low amplitude folds represent an early deformation stage which could notdevelop further owing to the load of the overlying thick tertiary clastic wedge

prediction of thrusting sequences in accretionary wedges 1 the main objective is to determine the three stages of the life of a thrust in an accretionary wedge which are the onset of thrusting along its ramp the development with the construction of the relief and the arrest because of the onset of another thrusting event a simple kinematics is proposed for the geometry of the developing thrust fold based on rigid regions separated by velocity discontinuities along which work is dissipated according to the coulomb criterion the evolution of the thrust fold satisfies mechanical equilibrium and is optimized at every time of the three stages to provide the least upper bound in tectonic force according to the maximum strength theorem the development of the thrust or its arrest because of the initiation of another thrust is decided by selecting the event which leads to the least upper bound in tectonic force the approach is first validated by proving that the critical slope angle c for the classical triangular wedge is properly captured it is shown that a perturbation in the form of an extra relief in this perfectly triangular geometry leads to the onset of thrusting with the ramp or the back thrust outcropping either at the back or to the front of the perturbation respectively for a range of slope dip close to the critical angle c the study of normal thrust sequences from the rear to the front in the wedge toe reveals that weakening of the ramp accounted for by changing its friction angle from an initial to a smaller final value is necessary for each thrust to have a finite life span this life span is longer with a larger relief buildup for more pronounced weakening decreasing the decollement friction angle results in an increase in the number of thrusts in the sequence each thrust creating milder relief the normal sequence is ended with the first out of sequence thrust which occurs earlier for smaller weakening over the ramp the proposed methodology is partly used to construct an inverse method proposed to assess the likeliness for the transfer of activity from the active to the incipient thrust in a section of nankai s accretionary wedge the inverse method provides the initial friction angle over the incipient ramp and the final friction angle over the fully active ramp from the geometry of the corresponding thrusts and the topography it is shown that the friction angle over the incipient ramp is most likely to be larger then the one over the active ramp justifying a key hypothesis needed to predict discrete sequences of thrusting

predicting orogenic wedge styles as a function of analogue erosion law and material softening 1 the evolution of a compressive frictional wedge on a weak frictional and planar decollement subjected to frontal accretion is predicted with a two step method called sequential limit analysis the first step consists in finding with the kinematic approach of limit analysis the length of the active decollement and the dips of the emerging ramp and of the conjugate shear plane composing the emerging thrust fold the second step leads to a modification of the geometry first because of the thrust fold development due to compression and second because of erosion erosion consists in removing periodically any material above a fictitious line at a selected slope as done in analogue experiments this application of sequential limit analysis generalizes the critical coulomb wedge theory since it follows the internal deformation development with constant frictional properties the deformation is mostly diffuse a succession of thrust folds being activated so that the topographic slope reaches exactly the theoretical critical value frictional weakening on the ramps results in a deformation style composed of thrust sheets and horses applying an erosion slope at the critical topographic value leads to exhumation in the frontal central or rear region of the wedge depending on the erosion period and the weakening erosion at slopes slightly above or below the critical value results in exhumation toward the foreland or the hinterland respectively regardless of the erosion period exhumation is associated with duplexes imbricate fans antiformal stacks and major backthrusting comparisons with sandbox experiments confirm that the thickness dips vergence and exhumation of thrust sheets can be reproduced with friction and erosion parameters within realistic ranges of values

a glacial lake outburst flood associated with recent mountain glacier retreat patagonian andes harrison s glasser n f winchester v haresign e warren c jansson k 2006 a glacial lake outburst flood associated with recent mountain glacier retreat patagonian andes the holocene 16 4 pp 611 620 sponsorship nerc grant ner b s 2002 00282 carnegie trust for the universities of scotland

thrust dip and thrust refraction in fault bend folds analogue models and theoretical predictions analogue models made of two layers of loose sand separated by a thin layer of micro glass beads were shortened by a rigid emerging ramp dipping at either 30 or 45 and possessing a high intermediate or null surface friction shortening resulted in formation of closely spaced back thrusts in the sand layers the dips of the back thrusts vary within a range of 30 depending on the ramp friction and 7 depending on its dip an increase in ramp friction or to a lesser extent in ramp dip decreases the thrust dips in the model the second important observation is that when friction is greater along the ramp than along the layer of glass beads then the glass beads layer acts as a separate upper ramp above which the back thrusts steepen the theory proposed to explain these observations predicts the thrust dips through a two step procedure first global equilibrium of forces in the two layers is required to yield the mean forces at stake along the ramps and thrusts second the total dissipation is minimized with respect to the dips of the back thrusts the relevant frictional properties of our analogue materials have been measured in stress conditions as close as possible to the experimental ones below 1 kpa and used with the theory to yield optimal back thrust dips that are all within 3 of the measured dips this is a surprisingly good fit when considering that we did not take into account geometric changes strain softening and dilatancy or compaction due to slip on the thrusts we conclude that this general two step theoretical procedure is validated in the context of analogue frictional materials we also propose a possible mechanism for thrust refraction and top to the foreland sense of shear observed in the hanging walls of lower flat to ramp transition in sedimentary piles that is based on the triggering of secondary upper ramps finally this mechanical approach can also be seen as complementary to the kinematic models of fold thrust structures which by definition cannot grasp the strong effects of friction on the kinematics

the mont terri rock laboratory a new international research project in a mesozoic shale formation in switzerland abstract in many countries argillaceous formations are being considered as potential host rocks for repositories of radioactive waste therefore in 1995 several organisations decided to start an international research project in the reconnaissance gallery of the mont terri motorway tunnel in north western switzerland in a mesozoic shale formation the opalinus clay aalenian this project is under the patronage of the swiss national hydrological and geological survey the following organisations are also partners in the project andra and ipsn france bgr germany enresa spain nagra switzerland jnc and obayashi japan sckcen belgium the aims of the project are to analyse the hydrogeological geochemical and rock mechanical properties of an argillaceous formation the changes of these properties induced by the excavation of galleries and to evaluate and improve appropriate investigation techniques in january 1996 eight niches were excavated for the project and 15 experiments were started in boreholes of no more than 30 m in length in the winter of 1997 1998 a new research gallery was excavated to host further experiments different excavation drilling and investigation techniques have been tested and improved significant results of the different experiments are already available some of those dealing with hydrochemistry porewater pressure measurements and the evolution of the excavation disturbed zone edz are reported in this paper

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

the influence of intrabasinal faults on the development of a linked thrust system the mesozoic and cenozoic rocks exposed in the arve valley region of the external french alps are used to assess the role of early intrabasinal faults on later thrust fault evolution the early intrabasinal faults produced at some time from latest upper cretaceous to tertiary strike parallel or subparallel to later neo alpine thrusts where early faults dip away from the thrusts they are generally cut through and occasionally are overturned during this process in one example extreme overturning has allowed partial reactivation early faults dipping in the same direction as thrusts may a be reactivated b initiate ramping of the thrust ahead of the preexisting fault c be cut through by the thrust d cause pinning of the thrust at the footwall of the fault and folding against the fault as displacement continues buttressing from this work it is evident that intrabasinal faults exerted a major influence on the distribution of mechanical heterogeneities these heterogeneities include variations of stratigraphic thickness and type across faults fault related unconformities and the presence of the fault itself during the period of contraction such features strongly controlled the development of the stress field produced ahead of an advancing thrust and hence influenced the position of thrust fault propagation within the stratigraphy

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

analogue benchmarks of shortening and extension experiments we report a direct comparison of scaled analogue experiments to test thereproducibility of model results among ten different experimental modelling laboratories we present results for two experimen

simultaneous normal faulting and extensional flexuring during rifting an example from the southernmost upper rhine graben the southern end of the upper rhine graben urg is formed by a major continental transfer zone which was localised by the reactivation of ene oriented basement faults of late palaeozoic origin a combination of subcrop data derived from exploration wells and reflection seismic lines and palaeostress analysis provided new constraints on the timing and kinematics of interacting basement faults rifting in the southern urg began in the upper priabonian under regional wnw ese directed extension oriented roughly perpendicular to the graben axis in the study area this led to the formation of nne trending half grabens simultaneously ene trending basement faults situated in the area of the future rhine bresse transfer zone rbtz were reactivated in a sinistrally transtensive mode in the sedimentary cover the strike slip component was accommodated by the development of en echelon aligned extensional flexures flexuring and interference between the differently oriented basement faults imposed additional but locally confined extension in the sedimentary cover which deviated by as much as 90 from the regional wnw ese extension the interference of regional and local stresses led to a regime approaching radial extension at the intersection between the urg and rbtz

area length and thickness conservation dogma or reality abstract the basic assumption of quantitative structural geology is the preservation of material during deformation however the hypothesis of volume conservation alone does not help to predict past or future geometries and so this assumption is usually translated into bed length in 2d or area in 3d and thickness conservation when subsurface data are missing geologists may extrapolate surface data to depth using the kink band approach these extrapolations preserving both thicknesses and dips lead to geometries which are restorable but often erroneous due to both disharmonic deformation and internal deformation of layers first the bolivian sub andean zone case is presented to highlight the evolution of the concepts on which balancing is based and the important role played by a decoupling level in enhancing disharmony second analogue models are analyzed to test the validity of the balancing techniques chamberlin s excess area approach is shown to be on average valid however neither the length nor the thicknesses are preserved we propose that in real cases the length preservation hypothesis during shortening could also be a wrong assumption if the data are good enough to image the decollement level the chamberlin excess area method could be used to compute the bed length changes

deep crustal structure of the rhine graben from dekorp ecors seismic reflection data a summary abstract results of two deep reflection seismic lines crossing the northern and southern part of the rhine graben which were recorded in 1988 by the french ecors and the german dekorp teams indicate that the asymmetry of this rift persists to the base of the crust the brittle ductile transition zone approximately coincides with the top of the lower crust ductile shear zones appear to affect the crust mantle boundary upper crustal extension by faulting accounts for a divergence of the graben flanks by 5 7 km whereas the crustal configuration of the rhine graben suggest an extension value of some 17 km

basin inversion and fault reactivation in laboratory experiments abstract a series of analogue models have been performed to get insights into the relationships between the reactivation of pre existing normal faults and the orientation of a successive compressive stress field the models were deformed in two phases 1 a first extension phase h 3 generating a graben and 2 a successive compressive phase with the orientation of the shortening direction h 1 trending between 0 and 90 obliquity angle to the faults bounding the graben the deepening of this graben was accompanied by syn tectonic sedimentation that included a basal ductile layer simulating salt in nature overlain by a brittle sand pack the experimental results suggest that the development of compressive structures is strongly controlled by the pre existing normal faults and by the obliquity angle the experiments have invariably shown that the extensional faults were reactivated during shortening whatever the value of the angle whereas strike slip reactivation of major normal faults is favoured by low obliquity angles mostly dip slip reactivation of pre existing structures is instead promoted for high obliquity angles the analysis of model results highlights the important role played by a ductile layer at the base of the basin fill and the obliquity angle in controlling both strain partitioning and brittle ductile decoupling

mechanical validation of balanced cross sections the case of the mont terri anticline at the jura front nw switzerland abstract close to north west front of the jura thrust belt in switzerland the mont terri anticline is located at a disruption of the muschelkalk decollement due to a former normal fault numerous geological data are available thanks to a motorway tunnel cross cutting the fold and an underground laboratory original field data two geological maps a borehole and a highway tunnel constrain the inner structure the anticline is characterized by an overturned frontal limb a steep back limb and a ramp cross cutting older normal faults three geological cross sections and three 2d kinematic models are proposed as various combinations of fault bend folding fault propagation folding and detachment folding the main motivation of this study is to illustrate how geometrical constructions can be constrained by the kinematic approach of limit analysis which determines the optimal deformation including faults that verifies mechanical equilibrium and the coulomb criterion matching some of the important kinematic steps assumed in each three interpretations to the optimal deformation leads us to define the compatible ranges of values of the frictional parameters these ranges allow us to assess the likeliness of the important kinematic steps of each kinematic model the present analysis provides a quantitative link between the assumed evolution of the internal structure and the concomitant evolutions of the topography and of the frictional parameters

hydro meteorological drivers and sources of suspended sediment flux in the pro glacial zone of the retreating castle creek glacier cariboo mountains british columbia canada glaciers are major agents of erosion that increase sediment load to the downstream fluvial system the castle creek glacier british columbia canada has retreated 1 0 km in the past 70 years suspended sediment concentration ssc and streamflow q were monitored independently at five sites within its pro glacial zone over a 60 day period from july to september 2011 representing part of the ablation season meteorological data were collected from two automatic weather stations proximal to the glacier the time series were divided into hydrologic days and the shape and magnitude of the ssc response to hydro meteorological conditions cold and wet hot and dry warm and damp and storm were categorized using principal component analysis pca and cluster analysis ca suspended sediment load ssl was computed and summarized for the categories the distribution of monitoring sites and results of the multivariate statistical analyses describe the temporal and spatial variability of suspended sediment flux and the relative importance of glacial and para glacial sediment sources in the pro glacial zone during the 2011 study period 60 of the total ssl was derived from the glacial stream and sediment deposits proximal to the terminus of the glacier during storm events that contribution dropped to 40 as the contribution from diffuse and point sources of sediment throughout the pro glacial zone and within the meltwater channels increased while storm events accounted for just 3 of the study period ssl was 600 higher than the average over the monitoring period and 20 of the total ssl was generated in that time determining how hydro meteorological conditions and sediment sources control sediment fluxes will assist attempts to predict how pro glacial zones respond to future climate changes copyright 2015 john wiley sons ltd