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

controls on structural styles along the deformation front of the subandean zone of southern bolivia abstract the subandean zone of southern bolivia is a typical thin skinned fold and thrust belt with remarkable regularity in the geometry of the structures however when the structural geometry and evolution are analyzed in detail it is verified that there are many deviations from such regularity in this paper special emphasis has been placed on analyzing those processes that could explain the along strike variations in structural styles of the deformation front particularly the role that played the upper detachment level in the development of the different structural styles observed along the deformation front is analyzed herein this analysis is focused on the development of overpressures which may have been essential for the activation of the detachment level in the devonian shales of the los monos formation to do this we made a series of 1d petroleum system models at different locations along the deformation front this analysis allowed to model primary gas generation and secondary cracking processes that are related to overpressure occurrence and therefore to the efficiency of the upper detachment level the models suggest a close relationship between thermal evolution of the foreland basin and generation of gas with different structural styles observed at the deformation front thus it was possible to divide the deformation front of the southern subandean zone into two distinct segments in the northern segment where models suggest that gas generation and overpressures of the los monos formation would be well developed the existence of composite roof duplexes is verified on the other hand where the models suggest that generation of gas in the los monos formation would be limited the upper detachment level is not involved in the deformation and the existence of fault bend fold structures is verified

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

control of syntectonic erosion and sedimentation on kinematic evolution of a multidecollement fold and thrust zone analogue modeling of folding in the southern subandean of bolivia abstract several analogue modeling studies have been conducted during the past fifteen years with the aim to discuss the effects of sedimentation and erosion on foreland fold and thrust belt among which a few have analyzed these processes at kilometric scale malavieille et al 1993 nalpas et al 1999 barrier et al 2002 pichot and nalpas 2009 the influence of syn deformation sedimentation and erosion on the structural evolution of fftb has been clearly demonstrated here we propose to go further in this approach by the study of a more complex system with a double decollement level the natural study case is the bolivian sub andean thrust and fold belt which present all the required criteria such as the double decollement level a set of analogue models performed under a ct scan have been used to test the influence of several parameters on a fold and thrust belt system among which i the spatial variation of the sediment input ii the spatial variation of the erosion rate iii the relative distribution of sedimentation between foreland and hinterland these experiments led to the following observations 1 the upper decollement level acts as a decoupling level in case of increased sedimentation rate it results in the verticalization of the shallower part above the upper decollement level while the deeper parts are not impacted 2 similarly the increase of the erosion rate involves the uplift of the deeper part below the upper decollement level whereas the shallower parts are not impacted 3 a high sedimentation rate in the foreland involves a fault and fold vergence reversal followed by a back thrusting of the shallower part 4 a high sedimentation rate in the hinterland favours thrust development toward the foreland in the shallower parts

deformation evolution of eastern sichuan xuefeng fold thrust belt in south china insights from analogue modelling abstract the eastern sichuan xuefeng fold thrust belt cxftb located in south china has received wide attention due to its distinctive deformation styles and close relationships with natural gas preservation but its deformation evolution still remains controversial in order to study further this issue we designed three sets of analogue models based on the results of the models we suggest that 1 the deformation in the cxftb may simultaneously initiate along two zones nearby the dayong and qiyueshan faults at 190 ma and then progressively propagate into the interiors of the western hunan hubei and eastern sichuan domains at 140 150 ma and finally reach the front of the huayingshan fault at 120 ma 2 the difference in decollement depth is the main factor determining the patterns of folds in different domains of the cxftb and 3 the eastern sichuan domain may have a basement significantly different from those of the western sichuan and western hunan hubei domains

the 1964 prince william sound earthquake joint inversion of tsunami and geodetic data the 1964 prince william sound alaska earthquake mw 9 2 ruptured a large area beneath the continental margin of alaska from prince william sound to kodiak island a joint inversion of tsunami waveforms and geodetic data consisting of vertical displacements and horizontal vectors gives a detailed slip distribution two areas of high slip correspond to seismologically determined areas of high moment release the prince william sound asperity with average slip of 18 m and the kodiak asperity with average slip of 10 m the average slip on the fault is 8 6 m and the seismic moment is estimated as 6 3 1022 n m or over 75 of the seismic moment determined from long period surface waves

global frequency of magnitude 9 earthquakes for decades seismologists have sought causal relationships between maximum earthquake sizes and other properties of subduction zones with the underlying notion that some subduction zones may never produce a magnitude 9 or larger event the 2004 andaman m w 9 2 earthquake called into question such ideas given multicentury return times of the greatest earthquakes ignorance of those return times and our very limited observation span i suggest that we cannot yet make such determinations present evidence cannot rule out that any subduction zone may produce a magnitude 9 or larger earthquake based on theoretical recurrence times i estimate that one to three m9 earthquakes should occur globally per century and the past half century with five m9 events reflects temporal clustering and not the long term average

crustal deformation along the dead sea transform and the carmel fault inferred from 12 years of gps measurements received 20 february 2012 revised 27 june 2012 accepted 30 june 2012 published 17 august 2012 1 large scale crustal deformation in the levant is mainly related to the dst and the cfs the former is an active left lateral transform bounding the arabian plate and the sinai sub plate and the latter branches out of the former and separates the sinai sub plate into two tectonic domains in this study we obtain the velocities of 33 permanent gps stations and 145 survey stations that were surveyed in three campaigns between 1996 and 2008 we use a simple 1 d elastic dislocation model to infer the slip rate and locking depth along various segments of the dst we infer a 3 1 4 5 mm yr slip rate and a 7 8 16 5 km locking depth along the dst north of the cfs and a slip rate of 4 6 5 9 mm yr and locking depth of 11 8 24 km along the jericho valley south of the cfs further south along the arava valley we obtain a slip rate of 4 7 5 4 mm yr and a locking depth of 12 1 23 km we identify an oblique motion along the carmel fault with 0 7 mm yr left lateral and 0 6 mm yr extension rates resulting in n s extension across the carmel fault this result together with the decrease in dst slip velocity from the jericho valley to the segment north of the cfs confirms previous suggestions according to which part of the slip between arabia and sinai is being transferred from the dst to the cfs

fore arc deformation controls frequency size distribution of megathrust earthquakes in subduction zones 1 seismotectonic deformation in subduction zones seems to follow rather simple spatiotemporal patterns with fore arc basins overlying the areas of large slip during quasiperiodic megathrust earthquakes to study the possible coupling between long term deformation and earthquake behavior we use compressive granular wedges overlying a rate and state dependent frictional interface as analogue models of subduction zone fore arcs overlying a seismogenic megathrust for different seismogenic zone geometries we analyze deformation time series with respect to the accumulation of permanent strain and frequency size distributions of episodic slip events equivalent to great m 8 earthquakes we observe that permanent deformation in the wedges localizes at the periphery of unstable slip at depth over tens of simulated seismic cycles for updip limited seismogenic zone models this leads to structural wedge segmentation characterized by an elastic domain overlying the zone of unstable basal slip along with the evolution of segmentation the frequency size distributions of episodic slip events develop from more random gutenberg richter like events b value 0 6 toward more periodic characteristic events b value 0 1 corresponding coefficients of variation cv of recurrence intervals decrease from cv 0 6 in deforming wedges to cv 0 3 in segmented wedges from the experiments we thus infer a positive feedback between fore arc tectonics and megathrust seismogenesis which brings the system from a stochastic to a more deterministic state our experimental observations imply that the quasiperiodic recurrence of great subduction earthquakes evident from existing earthquake records is a long term feature intrinsically related to the seismotectonic segmentation of the fore arc wedges

tsunami early warning using gps shield arrays 1 the 2004 catastrophic indian ocean tsunami has strongly emphasized the need for reliable tsunami early warning systems another giant tsunamigenic earthquake may occur west of sumatra close to the large city of padang we demonstrate that the presence of islands between the trench and the sumatran coast makes earthquake induced tsunamis especially sensitive to slip distribution on the rupture plane as wave heights at padang may differ by more than a factor of 5 for earthquakes having the same seismic moment magnitude and rupture zone geometry but different slip distribution hence reliable prediction of tsunami wave heights for padang cannot be provided using traditional earthquake magnitude based methods we show however that such a prediction can be issued within 10 minutes of an earthquake by incorporating special types of near field gps arrays gps shield these arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than the seismic moment if placed above the rupture zone or are less than 100 km away of the rupture zone stations in the arrays are located as close as possible to the trench and are aligned perpendicular to the trench i e parallel to the expected gradient of surface coseismic displacement in the case of sumatra and java the gps shield arrays should be placed at mentawai islands located between the trench and sumatra and directly at the sumatra and java western coasts we demonstrate that the gps shield can also be applied to northern chile where giant earthquakes may also occur in the near future moreover this concept may be applied globally to many other tsunamigenic active margins where the land is located above or close to seismogenic zones

opposing gradients of permanent strain in the aseismic zone and elastic strain across the seismogenic zone of the kodiak shelf and slope alaska an industry acquired seismic reflection line from the aleutian arc to the alaska trench was prestack depth migrated and further constrained with wide angle ocean bottom hydrophone seismic velocity data and swath mapping from the seismic reflection image individual thrust slices the backstop and the forearc basin were resolved sufficiently well to balance the section tectonic shortening and age estimates provided rates of permanent contraction in five discrete segments over 150 km during the past 3 myr about 70 of the plate convergence is measured as contraction across the 40 km wide neogene accretionary prism which composes less than 10 of the forearc permanent contraction is minimal above the 1964 alaska earthquake aftershock zone indicating dominently elastic strain since elastic strain is poorly recorded in the geological record it was approximated from the historical record of the 1964 alaska earthquake the 1964 coseismic vertical deformation displays an inverse pattern to the permanent strain consistent with the earthquake cycle concept elastic deformation is dominant beneath the shelf and upper slope rapid permanent deformation is concentrated beneath the lower slope and a transition between them occurs beneath the middle slope

interaction between deformation and sedimentation in a multidecollement thrust zone analogue modelling and application to the sub andean thrust belt of bolivia fold and thrust belts are influenced by the presence of decollement levels as well as the amount of shortening and synkinematic sedimentation these parameters are studied at the scale of a thrust belt using a field approach combined with analogue and numerical modelling in this study we use analogue modelling to test the evolution of a single structure during sedimentation in a domain containing three prekinematic decollement levels the development of this structure in the analogue experiments shows that the expression of the deformation is strongly dependent on sedimentation rate i the structure propagates forward in an overall asymmetric shape if the sedimentation rate is slower than the uplift velocity or ii the structure grows vertically and its vergence changes at the surface if the sedimentation rate is similar to the uplift velocity or iii the structure grows vertically with a double vergence at the surface and at depth if the sedimentation rate is higher than the uplift velocity the results of the experiments are compared with structures in the subandean thrust belt to aid the interpretation of poor seismic data

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

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

enhanced gps inversion technique applied to the 2004 sumatra earthquake and tsunami 1 since the devastating earthquake and tsunami in 2004 offshore sumatra many source models have been put forward recent studies clearly show that modern gps processing could achieve high resolving power for slip in near real time which is crucial for determining tsunami initial conditions provided accurate gps processing and inversion here we propose an inversion technique with improved representation of the subduction zone geometry and physically justified boundary conditions we show that the discrepancy between the inversion of near and far field gps data for the 2004 event which is often explained by postseismic slip can be eliminated by using our inversion method and iasp91 earth model inverted source models including versions with splay faulting are shown to be consistent with satellite altimetry data of offshore tsunami wave height suggesting that displacement at the splay fault might have been present but was likely a second order process

backstop geometry and accretionary mechanics of the sunda margin the convergent sunda margin off indonesia displays all geological features characteristic of an accretion dominated subduction zone a combined interpretation of prestack depth migrated seismic reflection data and velocity information gained from refraction studies is supplemented by high resolution bathymetric data and for the first time allows the exact mapping of backstop regimes initially the outer high evolved as material was pushed against a static rigid arc framework backstop underlying a forearc basin increasing material strength of the outer high due to lithification formed a dynamic backstop which controls accretion today an out of sequence thrust marks the transition from the recent active frontal accretionary prism to the outer high and may be traced in the seismic and bathymetric data over the whole extent of the study area the existence of a static as well as a dynamic backstop controls the forearc geometry and is associated with the segmentation of the forearc which is observed in regimes of frontal as well as of oblique subduction mass balance calculations which account for porosity changes and metamorphism indicate a subduction history dominated by accretionary processes since the late eocene accretion is associated with the low values of basal friction inferred for the sunda margin structural investigations of conjugate fault planes indicate a very weak basal detachment effective stress analyses reveal that intrinsically weak material causes the high strength ratio of the detachment to the overlying sediments whereas overpressuring within the frontal accretionary prism is negligible

influence of synkinematic sedimentation in a thrust system with two decollement levels analogue modelling abstract compressive systems in foreland domains are characterised by fold and thrust belts linked to the presence of one or several ductile layers in depth acting as a decollement level the main parameters controlling the structural evolution are the presence of a decollement level the amount and rate of shortening and the amount of synkinematic sedimentation the effect of these parameters has only been studied on a thrust belt scale furthermore only the effect of synkinematic sedimentation on a simple system with one decollement level has been studied at the scale of a single structure the aim of this study was to use analogue modelling to test the effect of shortening rate velocity and the localization of sedimentation on a single system characterised by the presence of two prekinematic decollement levels the main results showed variations in the structural vergence folding geometry symmetric or asymmetric the evolution of the deformation horizontal propagation versus vertical uplift and the decoupling of the lower and upper brittle structures in relation with the main parameters shortening rate and mass transfer the results of the experiments were then compared to natural examples from the sub andean thrust belt

local tsunamis and distributed slip at the source variations in the local tsunami wave field are examined in relation to heterogeneous slip distributions that are characteristic of many shallow subduction zone earthquakes assumptions inherent in calculating the coseismic vertical displacement field that defines the initial condition for tsunami propagation are examined by comparing the seafloor displacement from uniform slip to that from an ideal static crack we demonstrate that dip directed slip variations significantly affect the initial cross sectional wave profile because of the hydrodynamic stability of tsunami wave forms these effects directly impact estimates of maximum runup from the local tsunami in most cases an assumption of uniform slip in the dip direction significantly underestimates the maximum amplitude and leading wave steepness of the local tsunami whereas dip directed slip variations affect the initial wave profile strike directed slip variations result in wavefront parallel changes in amplitude that are largely preserved during propagation from the source region toward shore owing to the effects of refraction tests of discretizing slip distributions indicate that small fault surface elements of dimensions similar to the source depth can acceptably approximate the vertical displacement field in comparison to continuous slip distributions crack models for tsunamis generated by shallow subduction zone earthquakes indicate that a rupture intersecting the free surface results in approximately twice the average slip therefore the observation of higher slip associated with tsunami earthquakes relative to typical subduction zone earthquakes of the same magnitude suggests that tsunami earthquakes involve rupture of the seafloor whereas rupture of deeper subduction zone earthquakes may be imbedded and not reach the seafloor

the nature of roof thrusts in the moine thrust belt nw scotland implications for the structural evolution of thrust belts buried thrust systems commonly analysed in terms of duplex structures are often interpreted as forming in a particular sequence this model considers that only one thrust is active at a time and the resulting structural geometry is well ordered however a reappraisal of structural geometries from the moine thrust belt in nw scotland has shown that many apparent duplex structures are more complex although the upper roof thrust of some duplexes may be folded and bulged by underlying imbricate slices in accordance with simple duplex models the footwall to these roof thrusts cut up and down stratigraphic section in conflict with the simple duplex models examples include the glencoul thrust with its underlying imbricate system and the foinaven duplex simultaneous slip on an array of imbricate thrusts can bulge duplex roofs relationships classically used to infer piggy back sequences of thrust propagation however activity on more hinterland ward imbricate thrusts can cause the roof onto which they branch to truncate more foreland ward structures in this fashion the duplex roof can cut up and down stratigraphic section mimicking an extensional fault by varying thrust activity in three dimensions within an imbricate system local parts of roof thrusts can generate domains of overstep behaviour that have only local significance existing interpretations of overstep relationships in the moine thrust belt as representing late orogenic low angle extensional faults may need revision the new interpretations of deformation activity where displacements in thrust arrays happen synchronously rather than sequentially are consistent with emergent thrust and fold belts with analogue experiments and with mechanical models of orogenic wedges

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

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

the thrust and shear zones of the moine thrust zone and the nw scottish caledonides the caledonian thrust belts of nw scotland exhibit many features typical of foreland fold and thrust belts the major structures propagated westwards towards the foreland the thin carapace of cambro ordovician sediments being accreted in imbricate and duplex zones beneath the major thrust sheets on a broad scale the rules of thrust geometry are obeyed but many local anomalies are found particularly in the assynt region in assynt several large fault bounded gravity spreading structures surge zones have been identified extensional faults have been traced into strike slip and then contractional faults there are zones of extensional and contractional imbricate faults and extensional and contractional ductile flow similar structures have been found along the length of the moine thrust belt suggesting that gravity spreading was an important mechanism during the later stages of movement within the main caledonian fold belt there are several major tectonic slides which are recognized by a local increase in intensity of deformation the majority are nw verging and were originally gently dipping in the highlands se of the great glen there are early major se verging recumbent folds associated with considerable crustal thickening reflected in high pressure 12kbar metamorphism many of the major slides may have formed by spreading away from this thickened crust the caledonian deformation and metamorphism occurred later in the moines and moine thrust zone than in the dalradian and grampian moines to the se of the great glen this may reflect different levels of deformation alternatively it may argue for a large strike slip displacement on the great glen fault juxtaposing crustal blocks which had experienced different ages of caledonian deformation and metamorphism the late movement on the moine thrust involved spreading from an area of thickened caledonian crust formed either by the stair step trajectory of the basal thrust to the moines and or by thickening due to intrusion of large masses of late caledonian granites

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

basin inversion in tectonic wedges insights from analogue modelling and the alpine carpathian fold and thrust belt abstract this work simulates the inversion and incorporation of sub thrust segmented half graben basins into tectonic wedges by means of sandbox analogue models segmented half graben basins striking at 90 45 and 15 to the extension direction were created first and then shortened using different angles for the basal detachment and topographic slope a shallow viscous polymer layer located above the half graben basin was included in one of the models the experiments were analysed using time lapse photography topography laser scans and image based 3d voxels the results indicate a deformation sequence characterised by layer parallel compaction fault reactivation thrust propagation and related folding fault reactivation was associated with the layer parallel compaction accomplished by slip along the basal detachment prior to and in between pulses of thrusting results reveal the fundamental control imposed by the vertical load of the tectonic wedge and its integrated strength profile in the inversion of sub thrust basins results are compared to the alpine carpathian fold and thrust belt

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

experimental insights into the scaling and variability of local tsunamis triggered by giant subduction megathrust earthquakes 1 giant subduction megathrust earthquakes of magnitude 9 and larger pose a significant tsunami hazard in coastal regions in order to test and improve empirical tsunami forecast models and to explore the susceptibility of different subduction settings we here analyze the scaling of subduction earthquake triggered tsunamis in the near field and their variability related to source heterogeneities we base our analysis on a sequence of 50 experimentally simulated great to giant mw 8 3 9 4 subduction megathrust earthquakes generated using an elastoplastic analog model experimentally observed surface deformation is translated to local tsunami runup using linear wave theory we find that the intrinsic scaling of local tsunami runup is characterized by a linear relationship to peak earthquake slip an exponential relationship to moment magnitude and an inverse power law relationship to fore arc slope tsunami variability is controlled by coseismic slip heterogeneity and strain localization within the fore arc wedge and is characterized by a coefficient of variation cv 0 5 wave breaking modifies the scaling behavior of tsunamis triggered by the largest mw 8 5 events in subduction settings with shallow dipping 1 2 fore arc slopes limits tsunami runup to 30 m and reduces its variability to cv 0 2 the resulting effective scaling relationships are validated against historical events and numerical simulations and reproduce empirical scaling relationships the latter appear as robust and liberal estimates of runup up to magnitude mw 9 5 a global assessment of tsunami susceptibility suggests that accretionary plate margins are more prone to tsunami hazard than erosive margins

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

identifying multiple detachment horizons and an evolving thrust history through cross section restoration and appraisal in the moine thrust belt nw scotland abstract many thrust systems including parts of the moine thrust belt are commonly interpreted as rather simple imbricate fans splaying from a master detachment floor thrust at depth we use field observations and geological map data to construct cross sections through the achnashellach culmination southern moine thrust belt northwest scotland to test this interpretation initially cross sections are constructed by assuming a single lower detachment line length imbalances and thrust trajectory mismatches between deformed and restored state sections indicate an invalid model significant differences in horizon lengths between two rock units are seen indicating the position of a second detachment which when incorporated into the deformed state cross section creates a valid structural model the presence of this second detachment accounts for complex geometries seen at outcrop and indicates that the achnashellach culmination is likely to have formed by the sequential activation of two detachment horizons this new structural model has been derived using an iterative workflow involving cross section construction section balancing and integration of field observations from across the study area ensuring model validity in three dimensions this workflow is applicable to other systems in general

oblique half graben inversion of the mesozoic neuquen rift in the malargue fold and thrust belt mendoza argentina new insights from analogue models abstract the malargue fold and thrust belt located in the andean mountains between 34 s and 36 30 s formed in response to contraction during cenozoic times its structural style and geometry was controlled by the mesozoic rift system that formed the neuquen basin in west central argentina the rift architecture in the southern sector of this belt was previously interpreted in terms of the present n s compressive structural trends assuming the inversion of pre existing normal faults with the same orientation here we propose that the nw se trending el manzano liu cullin lineament located in the northern termination of the sierra azul reflects the presence of a half graben master fault in the subsurface this hypothesis is supported by subsurface data a balanced cross section and it is tested using a series of scaled sandbox analogue models we suggest that the lineament responds to a reactivated nw trending half graben fault hidden by the mainly n s trending andean structures the proposed orientation is in agreement with the ne sw extension developed in the neuquen basin during the triassic early jurassic the modeling of the inverted oblique half graben reveals that the strikes of the main structures of inversion related belts may often be independent of the orientation of the previously developed extensional system providing a new perspective for their interpretation

tsunami generation by horizontal displacement of ocean bottom tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting the effect of horizontal deformation is usually neglected however when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement the effect becomes significant we show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves in the case of the 1994 june 2 java indonesia earthquake the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope in the case of the 1994 nov 14 mindoro philippines earthquake strike slip faulting extended from ocean to land perpendicular to the coast line in both cases we found that the horizontal motion of slope had an important contribution to the tsunami generation

thrust sequences and the significance of low angle out of sequence faults in the northernmost moine nappe and moine thrust zone nw scotland in common with most thrust belts the moine thrust zone scotland preserves a foreland propagating sequence of thrusting however significant examples of local to regional overstep sequences are also recognized and their interpretation remains controversial remapping of the northernmost moine thrust zone has defined a thick belt of mylonites in the centre of which lies the ductile wnw directed moine thrust the base of the mylonite belt however is marked by a regionally significant low angle west directed brittle fault here termed the lochan riabhach thrust that truncates thrust related structures in its footwall comparison of the tectonic stratigraphy of the mylonite belt with that preserved in a downfaulted outlier to the west at durness indicates that the lochan riabhach thrust cuts down section in its footwall and therefore appears to be extensional locally it is unequivocally breached by underlying imbricate thrusts we prefer to interpret the lochan riabhach thrust as an extensional fault that formed during a hiatus in thrust stacking we relate this faulting episode to the changes in the stability of the evolving orogenic wedge and reiterate that such extensional faults may be common although possibly unrecognized features in many other thrust belts

henry cadell s experimental researches in mountain building their lessons for interpreting thrust systems and fold thrust structures funding the fold thrust research group has been funded by interoil santos oilsearch and nagra the original compilation of cadell s researches was part of an outreach programme funded by bp acknowledgements rwhb is indebted to the late john mendum for arranging access to cadell s notebooks and his field maps that were lodged in the then offices of the british geological survey in murchison house edinburgh this formed part of a collaboration with bgs and the development of the assynt s geology website in the early 2000s many of the images from cadell s notebooks including his experimental results were part of this site regrettably it has not been maintained and is no longer accessible rectifying this loss of resource forms the motivation for this contribution we thank juergen adam and an anonymous referee for construct reviews together with james hammerstein for shepherding the manuscript through the editing process although of course the views expressed in this paper remain the responsibility of the authors alone