influence of a pre existing basement weakness on normal fault growth during oblique extension insights from discrete element modeling abstract we use discrete element modeling to investigate three dimensional fault geometry and the three dimensional evolution of a fault network that develops above a 60 dipping planar pre existing weakness striking 60 relative to the extension direction the evolution of the fault network comprises three stages i reactivation of pre existing structure and nucleation of new faults 0 10 extension ii radial propagation and interaction between reactivated structure and new faults 15 20 extension and iii linkage between reactivated structure and adjacent faults 20 25 extension during the first stage the pre existing structure mostly reactivates forming a long and under displaced fault new faults are mainly extension perpendicular and dip at 60 during the second stage saw tooth fringes grow upwards from the upper tip of the reactivated structure which becomes the major fault and influence the density and orientation of surrounding faults during the third stage the reactivated structure links laterally and vertically with adjacent faults creating non planar fault geometries following linkage the reactivated structure enhances the displacement of linked faults along branch lines our study demonstrates that pre existing weak faults can be reactivated propagating upwards in an irregular saw tooth pattern and affecting fault density orientation dip and displacement and providing the nucleation site of new faults

duplex style and triangle zone formation insights from physical modeling duplexes are a common feature in thrust belts at many scales their geometries vary significantly from antiformal stacks with significant forethrusting in the cover e g southern pyrennes spain to triangle zones e g foreland canadian rockies to low displacement individually spaced ramp anticlines e g sub andean thrust belt bolivia we present a series of physical experiments demonstrating that the strength of the decollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style the models comprise brittle layers made of dry quartz sand and decollements made of two types of viscous silicone polymers the strength of the decollements in the models is a function of the shortening rate applied to the model the relative strength of the decollements and surrounding rocks affects the development of active or passive roof duplexes triangle zones it also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp anticlines model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions the presence of relatively strong decollements promotes local underthrusting of the cover individual ramp anticlines internal deformation of thrust sheets low early layer parallel shortening and sequential towards the foreland propagation of structures weak decollements promote forethrusting of the cover antiformal stacks coeval growth of structures and low internal strain with the exception of significant early layer parallel shortening no underthrusting at a regional scale occurred in any model

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

seismotectonic and seismicity of makran a bimodal subduction zone se iran abstract the present study combined spatial distribution and mechanism of seismicity seismicity parameters geomorphology in satellite imagery and tectonic features in makran inland to show that the makran low angle thrust fault is divided into two separate segments depth dispersal of earthquakes especially relocated events shows that the sinking plate is steeper in the west than in the east of makran significant facts were identified from the variation of moho depth between west and east slip rates of the inland faults and crustal shortenings in the north of makran the sistan suture zone plays a significant role in dividing the overriding plate into a non deforming helmand block and a less deforming lut block these blocks have different resistances against the northward subduction large and great events such as the 1989 chabahar mw 5 5 and 1945 gwadur mw 8 1 occurred in the south of subduction fronts of the western and eastern makran respectively they occurred in shallow depth and were the pieces of evidence of weak and strong coupling between the oceanic and continental crusts on a low angle and a very low angle reverse faults respectively spectral analysis and depth determination of the instrumental and pre instrumental earthquakes respectively helped to separate some plate boundary and intraplate events this separation geometry and non characteristic behavior of the subduction zone revealed from spatial and temporal distribution of the earthquakes probably dedicate a mature aleutian type for the subduction zone in the east missing great m 6 1 earthquakes less slip rate of the continental faults and steeper dipping of the sinking plate in the west probably indicate a kurile type for the iranian part of subduction makran is a bimodal subduction because geomorphological and seismic pieces of evidence indicate a nnw surficial and right lateral fracture zone in the continental crust and a nw deep and left lateral fracture zone in the oceanic crust respectively the fractures and geometry of subductions showed that the eastern makran has seismotectonically a wider area for potential coupling of a larger earthquake than the western makran

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

double evaporitic decollements influence of pinch out overlapping in experimental thrust wedges abstract this article focuses on how deformation and displacements are transferred between two decollements located at different stratigraphic levels by means of analogue modeling using brittle viscous sand silicone systems we present results from ten analogue models in which we varied key parameters such as the amount of horizontal offset or overlap between the pinch outs of the upper and lower decollements the total amount of shortening and the planform geometry of the upper decollement results indicate that i structures root onto the basal and upper decollement defining an inner and an outer domain and ii the offset overlap of the decollements controls the geometry of the transition zone located between the two decollements the propagation of deformation into the foreland both in space and time and the deformation style and kinematics in the different domains of the model when the pinch out of the upper decollement is at an angle with the backstop oblique structures form and the geometry and propagation mode of the structures change progressively along strike we compare our experimental results with other silicone sand analogue models and with the natural examples of the southern pyrenees where upper triassic and eocene oligocene syn tectonic evaporites acted as basal and upper decollements respectively

the effect of decollement dip on geometry and kinematics of model accretionary wedges we conducted a series of sand box models shortened asymmetrically above a frictional plastic decollement to study the influence of amount and sense of the decollement dip on the geometry and kinematics of accretionary wedges model results illustrate that the amount and direction of decollement dip strongly influence the geometry and mode of deformation of the resulting wedge in general for models having similar decollement frictional parameters the resulting wedge is steeper grows higher and is shorter when shortened above a decollement that dips toward the hinterland at 42 bulk shortening the length height ratio of wedges formed above a 5 dipping decollement was equal to 2 4 whereas this ratio was equal to 3 for wedges shortened above a horizontal decollement moreover models with a hinterland dipping decollement undergo larger amounts of layer parallel compaction lpc and area loss than models shortened above a non dipping decollement the effect of decollement dip on wedge deformation is most pronounced when basal friction is relatively high b 0 55 whereas its effect is less significant in models where the basal decollement has a lower friction b 0 37 model results also show that increasing basal slope has a similar effect to that of increasing basal friction the wedge grows taller and its critical taper steepens

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

viscous accretionary prisms viscoelastic relaxation of the makran accretionary prism following the 2013 baluchistan pakistan earthquake

the interaction of two indenters in analogue experiments and implications for curved fold and thrust belts abstract scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold and thrust belt the experimental set up has two adjacent indenters moving in parallel with a velocity difference the slow indenter moves with a relative velocity ranging from 40 to 80 of that of the fast one in a first experimental series quartz sand and low friction glass beads represent the sediment stack and its basal detachment respectively silicone oil simulates a viscous detachment in the second series of experiments the surface evolution and the spatio temporal strain distribution are derived from particle image velocimetry piv together with the 3d finite structure derived by cutting the models at the end of each experiment this allows the analysis of the structural evolution of the experimental wedges thrusting wedge development depends crucially on the relative velocity when the slow indenter moves with a velocity of more than 55 of the fast indenter a single curved thrust wedge develops the wedge becomes decoupled along strike slip zone at large velocity differences i e when the slow indenter moves slower than 55 of the faster indenter consequently the thrust front is strongly curved at high 55 60 and smoothly curved at low velocity differences 70 80 in all cases curvature increases during indentation along the most strongly curved portion of the thrust wedge the transfer zone rises particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front this implies distant effects of wedge growth active hundreds of kilometres along strike of orogens silicone oil as a detachment induces a low angle wedge which is less curved than in the glass beads experiments and shows variable thrust vergence with fore and back thrusts we compare our experimental results with the curved fold and thrust belts of the tajik basin in front of the hindu kush and pamir indenters our results are able to explain several first order features

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

internal dynamics of a paleoaccretionary wedge insights from combined isotope tectonochronology and sandbox modelling of the south central chilean forearc forearc accretionary wedges are cyclic systems in which material is frontally and or basally accreted material cycling involves underthrusting subduction underplating exhumation erosion transfer to the trench and underthrusting again in this study we present a novel tectonochronologic approach to constrain long term exhumation rates of basally accreted wedge complexes based on isotopic dating of structural features on petrological data and sandbox analogue simulations congruence between the structural inventory in nature and structures generated in scaled sandbox experiments allows detailed insights into wedge dynamics for the present day surface material of the paleoaccretionary wedge of south central chile valdivia area 40 s published u pb ages of detrital zircon place a maximum age of 278 ma for subduction prograde metamorphism at transitional greenschist to blueschist facies conditions 420 c 8 9 kbar was immediately followed by progressive penetrative deformation associated with basal accretion dated at 250 245 ma using rb sr internal mineral isochrons the accretion process involved duplex tectonics and antiformal stacking with formation of near horizontal mylonitic shear zones at around 241 ma continuous basal accretion at depth gave rise to an extensional tectonic regime at higher structural levels both semi ductile small scale extensional shear zones and post kinematic vein mineralizations yield rb sr ages of 235 ma tension gashes representing the latest isotopically dateable stage of structural evolution were formed at 210 ma at conditions of 230 c at 1 5 3 kbar as constrained by fluid inclusion data zircon fission track data indicate final cooling to below 200 c at 186 24 ma the results suggest continuous basal accretion for at least 50 ma with long term average exhumation rates of 0 6 0 2 mm a most probably outbalanced by similar long term average erosion rates changing plate boundary conditions at about 210 200 ma terminated the accretion process as evident from a dramatic decrease of exhumation rates at that time since then the paleoaccretionary wedge remained stably in place despite its delicate geotectonic position within the andean active margin the tectonochronologic approach complements thermochronologic and geomorphologic methods of exhumation research as it provides direct constraints on mass flux rates even for high temperature increments of p t trajectories

mineral composition and seal condition implicated in pore structure development of organic rich longmaxi shales sichuan basin china abstract shale pore structure morphology type size distribution and porosity is important in controlling the storage and movement of oil and gas characterization of pore structure is one of the main research foci for unconventional resources however factors influencing its heterogeneity are poorly understood with total organic carbon ranging at 0 52 4 23 23 core samples from three wells jy2 wy1 and yz1 in different tectonic units of the longmaxi shale in sichuan basin were studied using a combination of petrographic geochemical and pore structure characterization techniques the shale porosity shows positive relationships with quartz and total organic carbon contents in jy2 and wy1 but not in yz1 because of its different pore structure pore structure differences are primarily attributed to the different contributions of organic matter om hosted nanopores which are controlled by preservation conditions due to the differences in the duration and intensity of tectonic activities the jy2 and wy1 areas are characterized by over pressured conditions with respective pressure coefficients of about 1 5 and 1 4 conversely the yz1 area has a normal pressure condition with a pressure coefficient of about 1 0 indicating a poor seal condition under good seal conditions generated hydrocarbons cannot escape easily thus the accumulation and expansion of shale gas trapped within organic pores increase the pore pressure to abnormally high levels which in turn protect the shale reservoir from compaction and support om hosted pore development the om pore evolution of the longmaxi shale in the sichuan basin during burial was generally uniform thus the differences in pore structure reflect subsequent tectonic uplift the siliceous shales of yz1 did not develop many om hosted pores because of the lack of seal conditions during the high maturity stage before uplift most of the pores shrink or close due to an escape of hydrocarbons mineral composition thermal maturity and seal conditions are identified to influence pore development and preservation in fine grained sedimentary rocks

numerical simulations of waves over large crater topography in the atmosphere abstractnumerical simulations are used to investigate waves generated by flow over crater topography of diameter 100 km in an idealized atmosphere the atmosphere is stratified with a constant buoyancy frequency profile and the background wind is constant this study describes the development of a low level jet along the upstream crater slope and its interaction with the cooler air within the crater valley this interaction results in a hydraulic jump like structure that acts as a modified topography forcing a beam of secondary waves the hydraulic jump is formed by a retreating gravity current as the cool air within the crater readjusts after the initial tilting of potential temperature contours a two dimensional simulation is used to compare features such as wave overturning in two and three dimensions several variations on the atmosphere s profile are considered including an atmosphere with reduced constant stratification and an atmosphere that is unstratified within the crater these results indic

the impact of analogue material properties on the geometry kinematics and dynamics of convergent sand wedges abstract simulation of geodynamic processes in sandbox experiments requires analogue materials with a deformation behaviour that reproduces the deformation mechanisms of typical crustal rocks we present data on the frictional strength of different sand types employing static and dynamic shear tests the sand types analysed are characterised by an elastic frictional plastic mechanical behaviour with a transient strain hardening and strain softening phase prior to transition to stable sliding this is in conflict with the standard assumption of an ideal cohesionless coulomb material with constant frictional properties the influence of the identified transient material properties on the kinematics growth mechanisms and internal deformation patterns of convergent sand wedges results in characteristic wedge segments which vary depending on material compaction between wedges with well defined segments i e frontal deformation zone frontal imbrication zone and internal accumulation zone with straight slopes and wedges with a continuous convex topographic profile for most materials only the frontal part of the wedge is critical during experimental runs taper and strength of the wedge segments can be shown to be controlled by the frictional properties of active faults wedge segmentation is controlled by a bulk strength increase toward the rear of the wedge due to fault rotation in mechanically less favourable orientations and plastic material hardening the limit between the frontal critical parts of a wedge and internal stable parts is largely controlled by a critical state of stress upon which either renewed failure or fault inactivation occurs on this basis we suggest that critical taper analysis of wedges must be restricted to specific kinematic segments comparison of the experimental results with the nankai accretionary wedge suggests that our interpretation also applies to natural convergent wedges moreover we provide constraints for the selection of adequate granular analogue materials to simulate typical crustal rocks in natural convergent wedges

gravity wave drag on two mountains the generation of linear internal gravity waves by the flow over two idealized mountains whose summits are aligned in the same direction as the mean wind is studied in particular the sensitivity of the wave drag to the downwind distance between the mountains is examined by using a three dimensional numerical model based on the linearized steady state boussinesq equations of motion both two and three dimensional orography is considered when the upstream conditions are such that the wind and buoyancy frequency do not vary with height and the mountains are wide enough for non hydrostatic effects to be unimportant the model predicts the same drag dependence on two dimensional ridge spacing as was derived analytically by grisogono et al the corresponding three dimensional numerical result predicted by the model is qualitatively very similar to the two dimensional result when the mountains are narrow and the waves are non hydrostatic the drag dependence on mountain spacing is more complicated maxima and minima in the drag can occur when the distance between the two mountains is such that waves generated by the mountain furthest upstream are in phase maxima in the drag or out of phase minima in the drag with the waves generated by the downstream mountain it is shown that this is an important effect when the waves are trapped by upstream profiles whose wind speed varies with height

work optimization predicts accretionary faulting an integration of physical and numerical experiments we employ work optimization to predict the geometry of frontal thrusts at two stages of an evolving physical accretion experiment faults that produce the largest gains in efficiency or change in external work per new fault area wext a are considered most likely to develop the predicted thrust geometry matches within 1 mm of the observed position and within a few degrees of the observed fault dip for both the first forethrust and backthrust when the observed forethrust is active the positions of the second backthrust and forethrust that produce 90 of the maximum wext a also overlap the observed thrusts the work optimal fault dips are within a few degrees of the fault dips that maximize the average coulomb stress slip gradients along the detachment produce local elevated shear stresses and high strain energy density regions that promote thrust initiation near the detachment the mechanical efficiency wext of the system decreases at each of the two simulated stages of faulting and resembles the evolution of experimental force the higher wext a due to the development of the first pair relative to the second pair indicates that the development of new thrusts may lead to diminishing efficiency gains as the wedge evolves the numerical estimates of work consumed by fault propagation overlap the range calculated from experimental force data and crustal faults the integration of numerical and physical experiments provides a powerful approach that demonstrates the utility of work optimization to predict the development of faults

the impact of mountain wakes on the drag exerted on downstream mountains the pressure drag exerted on two identical high idealised mountain ridges aligned perpendicular to the mean flow with the second mountain lying directly downstream of the first is investigated using a numerical model the drag is measured for a variety of different distances between the two peaks mountain heights and lengths and incident flows each two mountain simulation has a companion single mountain simulation with an identical mountain and identical upstream flow with which to compare the drag the maximum modelled drag in the two mountain simulations is close to two times the drag in the single mountain case while the minimum two mountain drag is similar to that exerted on the single mountain this change in drag is a result of the wake behind the first mountain reducing the speed of the flow impacting on the second mountain a parametrization of this effect is suggested which combines the distance between the two mountain peaks a measure of the velocity deficit in the wake of the first mountain and the wake decay scale a measure of the length scale over which the flow perturbation generated by the first mountain decays downwind copyright 2008 royal meteorological society and crown copyright 2008 published by john wiley sons ltd

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

crustal investigation of the hellenic subduction zone using wide aperture seismic data abstract we present the results of a wide aperture seismic onshore offshore study crete seismic experiment in the cretan region as part of the hellenic arc compressional system three seismic lines were carried out on and around the island of crete in order to investigate the crustal structure of the region up to 119 three component recording stations were deployed on each profile that observed seismic energy generated by a 48 l airgun array and eight 20 kg landshots a total of 6208 shots were fired upon completing the fieldwork the vertical components of all stations were evaluated 300 common receiver gather crg sections of the ocean bottom seismographs obs and land stations as well as 100 common source gather csg sections of the land shots and selected airgun shots were compiled and modeled in order to generate a 2d p wave velocity depth model for each profile the accuracy of the model depends on the depth and position along the profiles and does not exceed 5 for both depth and p wave velocity we identified strong lateral variations in crustal and sedimentary thickness mainly in a north south direction but also along strike east west the crust is continental and has a maximum thickness of 32 5 km below northern central crete its subdivision in an upper v p 5 8 6 3 km s locally up to 6 5 km s and a lower v p 6 4 6 9 km s part is justified by a first order discontinuity with v p velocity a contrast of up to 0 6 km s the eastern part of crete shows a significantly thinner crust of 24 to 26 km to the north the crustal thickness decreases to 15 km below the central cretan sea the prominent decrease of the moho depth north of central crete is interpreted to represent the northern end of a microcontinent that was subducted in oligocene times and later surfaced by buoyant escape stockhert et al 1999 thomson et al 1999 the p t t d history of the high pressure rocks of crete greece denudation by buoyant escape in exhumation processes normal faulting ductile flow and erosion ring u lister g willet s brandon m eds spec publ of the geol soc of london p 154 to the south and southwest of the island the continental crust gradually thins to a minimum of 17 km and at approximately 100 km off the southern coast of crete it is in contact with oceanic crust below the mediterranean ridge upper mantle velocities were determined to be 7 7 km s below the cretan sea and 8 0 km s south of crete below the continental cretan crust a 6 to 7 km thick layer with v p velocities between 6 6 and 7 1 km s was identified on each line and could be followed by reflections to a depth of 42 km it is decoupled from the overlying continental crust at central crete and is interpreted as oceanic crust presently under subduction towards the nne below the aegean sea

deformation patterns and structural vergence in brittle ductile thrust wedges an additional analogue modelling perspective abstract scaled physical models of brittle ductile thrust wedges investigated the causes leading to the development of the various structural styles observed in fold and thrust belts and accretionary prisms this study focused on some potential controlling factors such as 1 relative strength between the brittle overburden and the viscous decollement layer brittle ductile coupling 2 the effect of very low basal friction and 3 pre shortening rheological stratigraphy including decollement strength type 1 models had a single basal decollement whereas in type 2 models the decollement was embedded in brittle material simulating an upper roof sequence and a lower floor sequence other models investigated the effects produced by an horizon of mechanical weakness at the base of the viscous decollement type 1a and the role of decollement offset type 3 the experiments suggest the occurrence of a genetic relationship between the absolute values of shear stresses and the development of dominating hinterland or foreland verging thrust faults or dually verging thrusts by controlling the orientation of the 1 axis basal friction and decollement offset is found to effectively influence the deformation pattern and structural vergence and could explain the development of dominating backthrusts in cascadian type margins the decoupling of a frontal monocline via the upper decollement type 2 models produced passive roof duplex structures termed composite roof duplex when the frontal monocline coexists with outward fold propagation

dynamic constraints on the crustal scale rheology of the zagros fold belt iran thin skinned fold and thrust belts are generally considered as the result of contractional deformation of a sedimentary succession over a weak decollement layer the resulting surface expression frequently consists of anticlines and synclines spaced in a fairly regular manner it is thus tempting to use this spacing along with other geological constraints to obtain insights into the dynamics and rheology of the crust on geological time scales here we use the zagros mountains of iran as a case study as it is one of the most spectacular well studied thin skinned fold and thrust belts in the world both analytical and numerical models are employed to study what con trols fold spacing and under what conditions folding dominates over thrusting the models show that if only a single basal decollement layer is present underneath a brittle sedimentary cover deformation is dominated by thrusting which is inconsistent with the data of the zagros fold belt if we instead take into account additional decollement layers that have been documented in the fi eld a switch in deformation mode occurs and crustal scale folding is obtained with the correct spacing and time scales we show that fold spacing can be used to constrain the friction angle of the crust which is 5 the zagros fold belt this implies that on geological time scales the upper crust is signifi cantly weaker than previously thought possibly due to the effect of fl

gigantic low gradient landslides in the northern periphery of the crimean mountains ukraine abstract large scale low gradient ancient landslides estimated at 5 4 18 9 km 2 in area and 0 2 1 2 km 3 in volume have been studied in the northern hilly periphery of the crimean mountains ukraine they originated on slopes along wide water gaps of rivers belbek kacha alma and biyuk karasu crossing the cuestas of the northern foothills the slopes generally consist of slightly northward tilting miocene mainly sarmatian limestones overlying weak clay rich lower neogene palaeogene substratum with a significant content of smectite although the region is characterised by the least active contemporary morphodynamics within the crimean mountains the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula the landslides are generally a spreading type but the sliding mechanics were probably very complex involving toppling rotational slides gravitational folding and translational block slides all the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults a common feature is also a location close within several km to the mesozoic suture zone which is the most important tectonic feature in the northern periphery of the crimean orogene this suture was formerly classified as aseismic however evidence of strong low frequency palaeoearthquakes was collected during the last decade within both the mesozoic suture and the low lying northern part of the crimean peninsula radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide activity during the late glacial chronozone and holocene epoch the main landslide phase presumably took place at some time between the late glacial and atlantic chronozones minor reactivation of landslide toes occurred during the subatlantic chronozone and some of them have been active up to recent times the first major landslide phase was possibly triggered by an earthquake whereas late holocene activity can be attributed both to seismic and hydroclimatic factors

internal deformation and compaction of the makran accretionary wedge the makran accretionary wedge is one of the largest on earth a 7 km thick column of sands and quartzolithic turbidites are incorporated into this wedge in a series of deformed thrust sheets we present the results of prestack depth migration and focusing error analysis migration velocity analysis performed on a profile across the makran wedge the depth section shows the deformation style of the accreted sediments and the migration velocities allow us to estimate porosity variations in the sediments the thrust sheets show evidence of fault propagation folding with a long wavelength of deformation 12 km and secondary thrusting in the kink bands of the folds such that the central part of each thrust sheet is elevated to form an additional ridge this deformation style and the 15 steep surface slope of the first ridge suggest a high degree of consolidation porosities were calculated from the seismic migration velocities and the ratio of fluid pressure to lithostatic pressure was estimated for 5 locations along the profile rather than being undercompacted and overpressured as in most accretionary wedges the sedimentary input is normally compacted exponential porosity decay throughout almost the whole wedge however a slight increase in porosity and at depth with respect to the normal compaction curve indicates that the turbiditic sequence might be overpressured landward of the deformation front

mechanical decoupling and basal duplex formation observed in sandbox experiments with application to the western mediterranean ridge accretionary complex sandbox experiments of accretionary wedges were performed incorporating a thin weak layer of micro glass beads the impact of heterogeneous sedimentary input on wedge mechanics evolution and mass transfer was investigated we report the first experimentally documented growth of basal duplexes these occurred for high basal friction conditions with restricted output of the lower section the upper and lower sections were completely decoupled due to the intervening layer of glass beads with frontal accretion occurring in the upper section simultaneously with basal duplex formation and underplating of subsequent generations of duplexes imerse multichannel seismic reflection data from the western mediterranean ridge wmr image tertiary clastics beneath a thick section of messinian evaporites the base of the evaporites is identified as the primary decollement for deformation in the frontal part of the accretionary complex constriction of the channel of subducting tertiary sediments as well as internal deformation observed as arcward dipping reflectors argue for basal underplating and or two different active decollements we propose an evolution of the wmr in accordance with the sandbox experimental results a weak mid level detachment base of evaporites combined with a strong basal detachment produce mechanical decoupling and basal accretion of toeward verging duplexes

numerical models of the evolution of accretionary wedges and fold and thrust belts using the distinct element method a 2 d numerical model is used to investigate the evolution of accretionary wedges and fold and thrust belts the numerical method is based on the distinct element method dem unlike many continuum numerical models demallows localization to occur even after substantial amounts of deformation the method is used to study the evolution of simple accretionary wedges and thrust belts with a rigid backstop and base experiments are done with a large range of coefficients of interelement friction e and element wall friction b two modes of deformation which depend mainly on b are observed for the weak base case low b the dominant mode is frontal accretion by pop up structures at or near the toe of the wedge for the strong base case high b uplift is concentrated near the back of the wedge and is accompanied by underthrusting along a flat ramp flat or staircase thrust fault structure at intermediate values of b the wedge oscillates between the two modes of deformation during periods of frontal accretion normal faulting sometimes occurs in regions where the material has thickened considerably the transition between the two modes of deformation is found to be a strong function of b but a weak function of e a simple explanation of the experimental results is made using the principle of work minimization comparisons between the results and some accretionary wedges fold and thrust belts are also made

coulomb theory applied to accretionary and nonaccretionary wedges possible causes for tectonic erosion and or frontal accretion based on observations from both modem convergent margins and sandbox modeling we examine the possible conditions favoring frontal accretion and or frontal and basal tectonic erosion mean characteristic parameters t t and are used to discuss the mechanical stability of 28 transects across the frontal part of convergent margins where the coulomb theory is applicable natural observations reveal that typical accretionary wedges are characterized by low tapers with smooth surface slope and subducting plate low convergence rates and thick trench sediment while nonaccretionary wedges display large tapers with irregular surface slopes and rough subducting plate high convergence rates and almost no trench fill sandbox experiments were performed to illustrate the effects of seamounts ridges in the subduction zone on the deformation of an accretionary wedge these experiments show that a wedge of sand is first trapped and pushed in front of the seamount which acts as a moving bulldozer this is followed by a tunnelling effect of the subducting seamount through the frontal wedge material which results in considerable sand reworking at an advanced subduction stage the d6collement jumps back from a high level in the wedge to its former basal position we conclude that a high trench sedimentation rate relative to the convergence rate leads to frontal accretion in contrast several conditions may favor tectonic erosion of the upper plate first oceanic features such as grabens seamounts or ridges may trap upper plate material during their subduction process second destabilization of the upper plate material by internal fluid overpressuring causing hydrofracturing is probably another important mechanism

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

evolution of the calabrian accretionary wedge central mediterranean 1 the neogene tectonics of the central mediterranean are related to the subduction and trench rollback of the ionian basin under eurasia causing the opening of the liguro provencal and tyrrhenian back arc basins and the formation of the calabrian accretionary wedge the calabrian accretionary wedge is a partially submerged accretionary complex located in the ionian offshore and laterally bounded by the apulia and malta escarpments while the history of the back arc extension process is fairly well defined the structure and evolution of the wedge are still poorly known we have analyzed and interpreted the available reflection multichannel and single channel seismic profiles in the ionian offshore and integrated them with other geological and geophysical data acquired in the last 40 years here we present unpublished seismic profiles to provide a new map of the tectonic structure of the ionian offshore and to define the structure of the wedge and its evolution during the last 15 myr our reconstruction points out that the messinian salinity crisis represents an important break in the evolution of the wedge as the basal decollement ramps up onto the messinian salt deposits producing a dramatic and fast forward propagation of the frontal thrust and resulting underplating of the underlying crustal ionian sequence during progressive trench rollback our results provide new insight into the style of accretion in a weakly converging setting which is typical for the mediterranean region

variation in geometries and displacement along thrust faults a quantitative analysis from sandbox models the present work combines theoretical analysis laboratory experiments and field examples together with quantitative analysis to understand displacement variation along fault surfaces with varying dip angle two sandbox experiments are described to quantitatively analyze the interactions between shortening and sedimentation during late stages of deformation the two models consisted of sand layers with single and two microbeads layer s within the sandpack sieved over horizontal frictional detachment the models demonstrate that the overlying sediment load bears a major role on kinematic of developing structures fault displacement varied along imbricate thrusts due to variation in fault dip angle in the listric geometry maximum displacement occurred in the up dip direction up section or near fault tip along the faults where fault dip angles were shallower and favourable for thrust displacement in contrast the displacement was limited in the down dip direction down section or near basal detachment where fault dip angles were steeper the variation in fault displacement with fault dip along the fault surfaces made it possible to establish an inverse relationship between the fault dip and related displacement values i e lower is the dip angle greater the displacement and vice versa despite the inherent limitations and assumptions of laboratory experiments application of results to natural examples sheds new light on the mechanics and geometry of thrust faults from the deep to shallow structural levels as well as structural patterns that could appear as anomalous at a first sight

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

dating late pleistocene pluvial events and tephras by correlating paleomagnetic secular variation records from the western great basin abstract paleomagnetic records are used to correlate sedimentary sequences from pluvial lakes chewaucan and russell in the western great basin this correlation is the basis for age control in the relatively poorly dated sequence from lake chewaucan the resulting chronology supports a lack of sedimentation in lake chewaucan during the interval 27 400 to 23 200 yr b p an assertion supported by the presence of a lag deposit at the corresponding stratigraphic horizon because the lake chewaucan outcrop near summer lake oregon is near the bottom of the lake basin we conclude that lake chewaucan was at a lowstand during this time interval the chewaucan lowstand is coeval with the lowstand accompanying the wizard s beach recession isotope stage 3 previously seen in the geologic record from nearby pluvial lake lahontan the ages of six tephra layers including the trego hot springs tephra were also estimated using the paleomagnetic correlation together the new age of the trego hot springs tephra 21 800 yr b p and the lake surface level prehistory of lake chewaucan imply a revised model for the lake surface level prehistory of lake lahontan the revised model includes a longer duration for the wizard s beach recession and the occurrence of a younger lowstand of short duration soon after the lowstand corresponding to the wizard s beach recession

the influence of an embedded viscoelastic plastic layer on kinematics and mass transport pattern within accretionary wedges abstract the major aim of this study was to examine the influence of an embedded viscoelastic plastic layer at different viscosity values on accretionary wedges at subduction zones to quantify the effects of the layer viscosity we analysed the wedge geometry accretion mode thrust systems and mass transport pattern therefore we developed a numerical 2d sandbox model utilising the discrete element method starting with a simple pure mohr coulomb sequence we added an embedded viscoelastic plastic layer within the brittle undeformed sediment package this layer followed burger s rheology which simulates the creep behaviour of natural rocks such as evaporites this layer got thrusted and folded during the subduction process the testing of different bulk viscosity values from 1 1013 to 1 1014 pa s revealed a certain range where an active detachment evolved within the viscoelastic plastic layer that decoupled the over and the underlying brittle strata this mid level detachment caused the evolution of a frontally accreted wedge above it and a long underthrusted and subsequently basally accreted sequence beneath it both sequences were characterised by specific mass transport patterns depending on the used viscosity value with decreasing bulk viscosities thrust systems above this weak mid level detachment became increasingly symmetrical and the particle uplift was reduced as would be expected for a salt controlled forearc in nature simultaneously antiformal stacking was favoured over hinterland dipping in the lower brittle layer and overturning of the uplifted material increased hence we validated that the viscosity of an embedded detachment strongly influences the whole wedge mechanics both the respective lower slope and the upper slope duplex shown by e g the mass transport pattern

interaction between accretionary thrust faulting and slope sedimentation at the frontal makran accretionary prism and its implications for hydrocarbon fluid seepage 1 using high resolution seismic profiles and other geophysical data collected during r v meteor cruise m74 2 we investigate the distribution patterns of shallow sediments their structure and deformation processes and their role in the migration accumulation and seepage of hydrocarbon rich fluids here we show that rapid syn kinematic sedimentation at the frontal makran accretionary prism provides a mechanism by which emerging imbricated thrust packets override the footwall at the seafloor without significant mass wasting and destruction of fault related anticline in the hanging wall these anticlines may rise high above the seafloor to form plate boundary parallel ridges and distinguish from simple thrust blocks seen at convergent margins elsewhere with the fast burial of many thrust faults by the syn kinematic sediments anticlinal growth structures form in these syn kinematic sediments by continuous thrust activity the anticlinal structures preserved within the cores of the ridges or formed from these syn kinematic sediments act as structural traps for migrating hydrocarbon rich fluids above which fluid escape structures are generated leading to seafloor seeps most of the discovered hydrocarbon seeps around sixth ridge are sourced from these traps despite the compressional environment and the rapid syn kinematic sedimentation rates shallow subsurface of the frontal makran is a normally pressured regime in which the buoyancy of hydrocarbons may account for the fluid migration in this important respect the makran accretionary prism differs from many other convergent margins and accretionary prisms where fluid flow is largely driven by tectonically induced overpressure

syntectonic sedimentation effects on the growth of fold and thrust belts we use two dimensional mechanical models to investigate the effects of syntectonic sedimentation on fold and thrust belt development testing variable syntectonic wedge top and foredeep sediment thicknesses and flexural rigidities model results indicate a first order control of syntectonic sedimentation on thrust sheet length and thrust spacing thrust sheets are longer when syntectonic sediment thickness and or flexural rigidity increase comparison with observations from several fold and thrust belts confirms this first order control of syntectonic sedimentation

first time landslides in vashon advance glaciolacustrine deposits puget lowland u s a abstract advance glaciolacustrine qglv deposits from the last continental glaciation are widespread in the densely populated puget lowland and are prone to shallow landsliding much less frequently in historic time new landslides propagate deeply within intact qglv deposits the exceptional volume and highly mobile nature of the 22 march 2014 state route 530 oso landslide generated considerable uncertainty and public concern about the likelihood for similar deep seated failures initiating from most any slope where these deposits crop out the primary study objectives are to utilize geotechnical data from the small data set of available published and public domain investigations to characterize in general terms hydrogeologic geotechnical and geomorphic factors and their relative contribution to initiating deep seated landslides within intact qglv deposits and to inform future hazard and risk assessments for first time landslides within these deposits qglv deposits are overconsolidated very stiff to hard laminated to massive silt and clay shear strength is anisotropic with cohesion being a significant component of bedding parallel strength and friction dominating strength perpendicular to bedding hydraulic conductivity is likely also anisotropic multi year records of pore pressures within qglv deposits show no to minor seasonal flux only minor pore pressure responses to multi day to multi week episodes of heavy precipitation have been detected back analyses using limit equilibrium methods and peak anisotropic strength under drained conditions demonstrate initial stability of the slopes instability occurs near the fully softened strength we conclude that over the long term loss of cohesive strength rather than hydroclimatic pore pressure response is the more important contributor to diminishing stability and in some cases initiation of first time landslides in qglv deposits the shape and location of the slide surface is strongly influenced by strength anisotropy and stress state sliding surfaces developed near the basal contact of the qglv deposits in all of the five studied landslides higher stress states associated with increasing sequence thickness of the landslide masses decrease stability the length of the basal slide surface and thus the aspect ratio of the landslide mass appears to increase proportionally with sequence thickness of the landslide mass

a mass movement origin for cirques the glacial process of cirque initiation whereby small initial hillslope hollows grow by nivation until snow can form glacier ice and ice motion then enlarges the hollow to a fully developed cirque appears to have difficulty explaining the creation of large cirques in the time available during quaternary glaciations at the rates at which glaciers are reported to erode rock and in rapidly uplifting mountain ranges it also has difficulty explaining the striking proliferation of cirques in fiordland south island new zealand an area of harder rock and less glaciation than the nearby cirque poor area of south westland here we show that cirques can be initiated as large deep seated often coseismic rock slope failure source area depressions in which snow may accumulate to form cirque glaciers which can then remove detritus from smooth and enlarge the cirque we present an example of a classically shaped cirque that has never held a glacier we show that many similarities between the locations sizes and shapes of rock slope failure source area depressions and cirques are understandable on this basis as is the occurrence of cirques in presently aseismic intraplate locations and their relative paucity in actively uplifting ranges the extent to which cirques may be of mass movement origin has implications for their value as palaeoclimatic indicators copyright 2006 john wiley sons ltd

effect of increased shear stress along a plate boundary fault on the formation of an out of sequence thrust and a break in surface slope within an accretionary wedge based on numerical simulations abstract we investigated the effect on accretionary wedge structure of increased shear stress which describes the frictional sliding resistance along a decollement arising from an increase in material friction or reduction in pore pressure to clarify the nature of the effect we performed numerical simulations using two models a stable friction model and an increased friction model the stable friction model produced a low angle smooth surface slope and an in sequence thrust whereas the increased friction model produced a break in surface slope scarp and an out of sequence thrust ost that cuts through the thrust sheet the ost formed via the connection of segments of two adjacent thrusts and its formation resulted in a change in the thickening mode of the wedge from thrust sheet rotation and back thrust activity to underplating this contrast in thickening mode between the landward high friction zone and seaward low friction zone resulted in the formation of a clear break in slope as the landward zone is steeper than the seaward zone consistent with critical taper theory the subduction of a basement slice or seamount can produce similar structures arising from an increase in resistance to basal shear sliding however the distinctive structures arising in an accretionary wedge as a result of increased shear sliding resistance include a flat basal plane and absence of slope failure sediments beneath the ost these structural features are observed in accretionary wedges of the nankai trough off muroto japan the sunda strait and the barbados ridge

distinct element modeling of structures formed in sedimentary overburden by extensional reactivation of basement normal faults fault and fold patterns in sedimentary rocks have been modeled using a computer code based on the distinct element method dem this numerical method considers the relative motion of disconnected elastic elements governed by newton s laws and frictional sliding criteria forces are transmitted between elements at contact points by changing element size ratios assemblages of elements can simulate different kinematic behavior from localized faulting to distributed flow as an application of the method we investigate folding and faulting patterns that develop in the sedimentary overburden above basement normal faults the number position orientation and sense of slip on faults as well as the fold geometry depend on the basement fault dip and basement rotation the dem model results have practical implications for predicting the evolving characteristics of structural traps and their petroleum potential

mechanical role of backstops in the growth of forearcs we use numerical and laboratory modeling to analyze the mechanical role of backstops in the overriding plate at subduction zones a backstop is defined as a region within a forearc that has significantly greater shear strength than the sediment lying farther trenchward it can be thought of as the bulldozer behind an accretionary wedge we calculate the stress and displacement fields within forearcs for various backstop models using the finite element method and we simulate deformation over a backstop using a small scale laboratory model in this way we model the effects of the mechanical properties and geometry of a backstop on forearc structures we find that the growth of an outer arc high the development of an inner deformation belt with landward vergence and the seemingly paradoxical presence of an undeformed forearc basin within an otherwise highly deformed forearc can be explained by assuming the existence of a geometrically simple backstop with geologically reasonable contrasts in mechanical properties compared to the sediments just trenchward of it the structures produced in our numerical models are quite insensitive to the rheology boundary conditions and exact mesh geometry employed the general types of structures observed in the laboratory models depend only weakly upon the strength and the geometry of the backstop these results suggest that a detailed picture of an underlying backstop cannot be determined from surface information alone backstops in which the contact with the accretionary wedge dips arcward rather than trenchward however should produce only slightly different forearc structures with less development of both the outer arc high and the landward vergent inner deformation belt although natural forearcs are far more complex than our simple models they exhibit many of the same features indicating that relatively simple backstop mechanics may be a very important factor in the overall growth of forearcs

deformation of brittle ductile thrust wedges in experiments and nature 1 even though the rheology of thrust wedges is mostly frictional a basal ductile decollement is often involved by comparison with purely frictional wedges such brittle ductile wedges generally display anomalous structures such as backward vergence widely spaced thrust units and nonfrontward sequences of thrust development laboratory experiments are used here to study the deformation of brittle ductile thrust wedges results are compared with natural systems in the jura mountains and the northern pakistan salt range and potwar plateau two series of three models are used to illustrate the effects of varying the basal wedge angle and shortening rate v these two parameters directly control variations in relative strength between brittle and ductile layers bd coupling wedges with strong bd coupling low and high v give almost regular frontward sequences with closely spaced thrust units and as such are not significantly different from purely frictional wedges weak bd coupling high and low v gives dominantly backward thrusting sequences intermediate bd coupling produces frontward backward oscillating sequences the spacing of thrust units increases as coupling decreases back thrusts develop in parts of a wedge where bd coupling is weak regardless of the thrust sequence wedges with weak bd coupling need large amounts of bulk shortening more than 30 to attain a state of equilibrium at which stable sliding along the base occurs on this basis we argue that a state of equilibrium has not yet been attained in at least some parts of the jura mountains and eastern salt range and potwar plateau thrust systems

effect of overburden thickness on thrust belt geometry and development laboratory sand models simulating development of thrust belts indicate that 1 distance between the backstop and the first formed thrust is a linear function of initial sand layer thickness 2 spacing between the first two thrusts is most likely a nonlinear function of initial sand layer thickness 3 initial dip of successive ramps decreases progressively toward the foreland because of variations in principal stress directions with depth and or changes of mechanical properties of sand with increasing overburden 4 faults to the hinterland steepen and become less active as hinterland thrust sheets undergo penetrative shear during sand wedge growth and 5 new ramp initiation occurs to the hinterland of the basal detachment tip line these observations can be interpreted both in context of area balance considerations and soil mechanics theory if initial sand layer thicknesses in our models represent syntectonic overburden in natural thrust belts i e distance between the ground surface and the detachment then our results suggest that locations of some thrust belt salients are controlled by along strike variations in stratigraphic thicknesses and that initial thrust spacing decreases progressively to the foreland if the thrust belt involves a foreland tapering basin furthermore our sand model observations suggest that the concept of a fixed rigid backstop in the hinterland of thrust belts may be misleading as a consequence of thickening the hinterland portion of the thrust belt becomes stabilized and effectively becomes the backstop itself

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

duplex accretion and underplating in an ancient accretionary complex kodiak islands alaska the landward belt of the kodiak formation represents a sequence of lower maastrichtian turbidites that was underplated to the kodiak accretionary complex by duplex accretion evidence for duplexes exists on the mesoscopic and map scale at the microscopic scale incremental strain histories are consistent with early shear during underthrusting abrupt landward rotation of individual thrust slices over fault ramps and locking of thrust packets in steeper orientations duplex geometries at the mesoscopic scale are represented by high angle reverse faults bounded either above or below by low angle southeast verging detachments at the map scale different structural belts can be related to a low angle detachment zone central belt flooring a more landward duplex landward belt duplex underplating can result in the uplift and thickening of accretionary prisms without necessarily deforming the overlying previously accreted material and slope sediments

lee wave resonances over double bell shaped obstacles lee wave resonance over double bell shaped obstacles is investigated through a series of idealized highresolution numerical simulations with the nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps model using a free slip lower boundary condition the profiles of wind speed and stability as well as terrain derive from observations of lee wave events over the sierra nevada and inyo mountains from the recently completed terrain induced rotor experiment t rex numerical experiments show that double bell shaped obstacles promote trapped lee waves that are in general shorter than those excited by an isolated ridge while the permissible trapped lee wave modes are determined by the upstream atmospheric structure primarily vertical wind shear the selected lee wave wavelengths for two obstacles that are close or equal in height are dictated by the discrete terrain spectrum and correspond to higher harmonics of the primary orographic wavelength which is equal to the ridge separation distance the exception is the smallest ridge separation distance examined one that corresponds to the owens valley width and is closest to the wavelength determined by the given upstream atmospheric structure for which the primary lee wave and orographic wavelengths were found to nearly coincide the influence two mountains exert on the overall lee wave field is found to persist at very large ridge separation distances for the nonlinear nonhydrostatic waves examined the ridge separation distance is found to exert a much stronger control over the lee wave wavelengths than the mountain half width positive and negative interferences of lee waves which can be detected through their imprint on wave drag and wave amplitudes were found to produce appreciable differences in the flow structure mainly over the downstream peak with negative interference characterized by a highly symmetric flow pattern leading to a low drag state

viscosity estimates of salt in the hormuz and namakdan salt diapirs persian gulf the parabolic surface profiles of the hormuz and namakdan salt diapirs in the persian gulf suggest that they have been extruding with newtonian viscous rheologies for the last 10 4 years we derive velocity profiles for these diapirs neglecting gravitational spreading and erosion dissolution while assuming incompressible newtonian rheology of the salt fitting known rates of extrusion at specific points in its elliptical cross section the dynamic viscosity of the salt of the hormuz diapir is found to range between 10 18 and 10 21 pa s approximating its sub circular cross section to a perfect circle the range of viscosity of the salt of the namakdan diapir is obtained as 10 17 10 21 pa s these calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt diapirs but are broader than those for salts with newtonian rheology deforming at room temperatures the salts of the hormuz and namakdan diapirs are expected to exhibit a broader range of grain size which matches the limited existing data

sensitivity of shear zones in orogenic wedges to surface processes and strain softening abstract we investigate the internal deformation of orogenic wedges growing by frontal accretion with a two dimensional numerical model our models are limited to crustal deformation and assume a horizontal detachment as observed for various natural orogens e g alaska and costa rica the model wedges develop as a result of convergence of a brittle sediment layer in front of a strong backstop we find that our reference model develops in sequence forward thrusts which propagate upward from the basal detachment for this reference model we investigate the sensitivity of shear zone activity to surface processes and strain softening model results show that diffusive or slope dependent erosion enhances material transport across the wedge and slows down forward propagation of the deformation front frictional strain softening focuses deformation into narrow shear zones and enhances displacement along them this has also been postulated for natural thrusts such as the glarus thrust in the swiss alps and the moine thrust in the scottish caledonides a second series of models investigates the effects of regularly spaced weak inclusions within the sediment layer which simulate remnants of previous deformation phases these inclusions facilitate and focus internal deformation influence the thrust dip and thrust vergence and enable thrust reactivation in the internal part of the wedge our results show that inactive thrusts in the internal part of the wedges may be reactivated in models with diffusive surface processes strain softening or weak inclusions thrust reactivation occurs as models seek to maintain their critical taper angle first order characteristics of our numerical models agree well with natural orogenic wedges and results from other numerical and analogue models

a discrete element model for orogenesis and accretionary wedge growth 1 we develop a two dimensional discrete element model to investigate the evolution of doubly vergent orogenic and accretionary wedges this generates the localization of deformation across persistent structures as emergent phenomena unlike many continuum models that require predefined weaknesses to localize strain the model is used to study how deformation processes evolve for two different boundary conditions drawing strong comparisons with previous sandbox analogues and computational approaches the deformational history of the modeled wedges is characterized by three stages defined by an evolution in the mechanisms available to accommodate shortening the first stage develops a strong retrovergent thrust that initiates at the subduction point the second stage shows a change in vergence of deformation as thin skinned thrusting propagates into material carried on the subducting plate thus evolving a folded and thrusted prowedge finally a second shallower retrowedge develops in the overriding plate through accretion this final stage is not present in all sand analogue modeling approaches and defines a difference in the deformation style thresholds in geometry and size regulate the localization and style of deformation and hence the progression through the three stages the wedges produced show periodicity in the modes of accretion to maintain a geometric form with deformation localizing across structures that are internally reactivated thus prowedges and retrowedges are seen to oscillate about constant taper angles

the use of glass for dating volcanic ash by thermoluminescence the development of a new physical dating method for late pleistocene tephrochronometry is described here tests of laboratory procedures applied to glass from independently dated samples show that the thermoluminescence tl additive dose dating method can yield accurate ages for both proximal and distal tephra from a few hundred years to at least 400 ka the technique involves purification of 4 to 11 m glass by heavy liquid centrifugation pre tl readout heating at 50 75 c for 8 days and careful regression analysis of tl growth curves several unknown age tephra are dated directly by this method for the first time these include five ash beds from summer lake oregon 67 200 ka a sheep creek valley ash from alaska 81 9 ka an ash from nevada 200 50 ka correlated to the wadsworth tephra an unknown ash 210 30 ka from rye patch dam in nevada previously correlated to the 400 to 600 ka dibekulewe tephra and ash 9m from washtucna in eastern washington 250 30 ka

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

a controlled source seismic and gravity study of the high lava plains hlp of eastern oregon 1 this study employs data collected during the high lava plains hlp controlled source seismic experiment conducted in september 2008 in this experiment 2612 short period seismic recorders and 120 3 component recorders were deployed across eastern oregon and adjacent parts of nevada and idaho to record 15 seismic sources seismic and gravity data were integrated to create 2 d crustal scale p wave velocity and density models for the 400 km long nw se and n s profiles to provide a better understanding of the crustal and upper mantle structure and ultimately the magmatic and tectonic evolution of the region these models are the first high resolution images beneath the path of migratory bi modal volcanism that dotted the high lava plains beginning at 16 ma our models show that the crustal structure across the hlp region is similar to that of the northern basin and range which has experienced extension since 35 ma but with moderate magmatic modification of the crust a thick layer 5 7 km of sediments and volcanics extends over most of the area and is thickest in the harney basin area we interpret denser faster material in the lower to middle crust under the southern harney basin area to be mafic intraplating we have also identified a region of denser faster material in the upper crust in the vicinity of oregon idaho border the crust thickens from 34 to 37 km and the lower crust increases in density 2 8 2 85 g cm3 from west to east across eastern oregon in close proximity to the interpreted position of the 0 706 sr isotope line suggesting a decrease in extension in the lowermost crust below the southeastern hlp there is relatively high velocity 7 2 7 4 km s and density 2 95 g cm3 that suggests the presence of underplating the hlp region has undergone moderate extension and the average crustal velocity is somewhat higher than in the adjacent basin and range suggesting some magmatic modification in the lower crust but not as much as might be expected given the voluminous surface volcanism

megathrust and accretionary wedge properties and behaviour in the makran subduction zone this work forms part of the nerc and esrc funded project earthquakes without frontiers and was partially supported by the nerc large grant looking inside the continents from space cp is funded by an nerc studentship the facilities of iris data services and specifically the iris data management center were used for access to waveforms related metadata and or derived products used in this study iris data services are funded through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation under cooperative agreement ear 1261681

mechanism of decollement formation in subduction zones summary the mechanism of decollement formation was investigated through a particle based simulation model assuming homogeneity e g no weak layer or pore fluid a decollement like structure appeared as a spontaneously localized shear deformation near the bottom of the sediment when the thickness of the sediment was sufficient to balance the gravitational force and tectonic loading in contrast no such decollement like structure was formed when the sediment was too thin in this case the entire prism was deformed because of plate motion these results are consistent with various observations in real subduction zones a precise analysis of the stress state evolution during accretion reveals that the formation of a decollement like structure is controlled by the spatio temporal distribution of isotropic compression states

frontal accretion along the western mediterranean ridge the effect of messinian evaporites on wedge mechanics and structural style in the context of the imerse project several crossings of the deformation front of the western mediterranean ridge were made in the region of the sirte abyssal plain the messina abyssal plain and the intervening region in this paper we present seismic images and interpretations across the deformation front with particular emphasis on the role the messinian evaporites have played in controlling the accretionary tectonics of the thin frontal portion of the wedge the seismic images show that the basal detachment generally is located at the base of the evaporites from a consideration of the mechanics of the wedge for both coulomb and plastic rheologies we show that the low wedge taper c 2 requires that the detachment is characterised by extreme fluid overpressuring within 2 of lithostatic in places and that the basal yield stress less than 1 mpa is lower than that of a wet salt decollement zone this supports the seismic interpretation that the detachment occurs in overpressured sediments beneath the impermeable evaporites lateral variations in the accretionary style can be related to lateral variations in evaporite thickness the effectiveness of the evaporite as an impermeable seal and to local relief on the subducting plate these factors control the escape of fluids from beneath the evaporites and hence fluid pressure and basal yield stresses

accretion structural style and syn contractional sedimentation in the eastern mediterranean sea we analyse four multichannel seismic profiles collected by ogs from 1971 to 1979 along the outer part of the mediterranean ridge accretionary complex in order to understand the nature of the deformation affecting african plate sediments as they approach the africa europe plate boundary tectonic style as revealed by our data and previous studies varies considerably along the plate boundary and this variation suggests the division of the margin in three provinces characterised by different structural patterns and deformation rates 1 near orthogonal terminal subduction initial collision ionian and sirte foredeeps 2 incipient continental collision collision of continental promontories of the african margin off the cyrenaica peninsula 3 oblique terminal subduction initial collision herodotus foredeep this work aims to relate the tectonic features revealed by the seismic profiles to the geodynamic and stratigraphic parameters of the convergent margin these are essentially related to the geometry of subduction rate of convergence and obliquity and to the lithology of the incoming sedimentary section as well as the accumulation rate in the foredeep in the sirte province accumulation rate in the foredeep is relatively low and deformation is related to thrusting and folding which accounts for sediment shortening and uplift at the outer deformation front in the provinces of oblique terminal subduction the rate of normal convergence is lower the sedimentary section is thicker and the foredeep fed by the nile river has an higher syn tectonic sedimentation rate here deformation produces a broad band of large wavelength and high amplitude folds folding in this area is produced both by plate convergence related shortening and by movement of salt triggered by differential loading of the prograding nile deep sea fan in the area of incipient continental collision the foredeep is a v shaped trough as the abyssal plain has been completely subducted and the folded sediments of the accretionary complex rest directly on the african continental slope such differences in structural style are explained by great differences in strain rate that in the herodotus foredeep province has been calculated as at least four times weaker than in the western sector two factors contribute to decrease strain rate syn contractional accumulation and normal component of the effective convergence rate the former increases from west to east and possibly causes overpressuring on the decollement level salt mobilisation landward and seaward vergent folding and a very low surface taper in the herodotus foredeep the latter decreases from west to east and favours thrusting in the western sector

influence of particle shape on the frictional strength of sediments a numerical case study abstract numerous direct and ring shear tests supply that composition and texture of sediments are crucial for shear and frictional strength we simulate particle interactions on a micro scale level during shearing with a numerical shear box using the discrete element method dem based on the granular model approach detailed information about slip localisation and rates forces at particle contacts as well as particle rotation can be quantified as function of particle shape stress conditions and shear rate our numerical experiments show that the deformation behaviour of clay is largely controlled by their particle shape two key factors sphericity and roughness could be identified as relevant for frictional strength shear zone development and particle rotation with sphericity dominating over roughness decreasing sphericity leads to complex initial microfabrics whose breakdown with increasing strain is caused by particle rotation preferred particle orientation favours low friction decreasing volume strain and the evolution of particle domains of similar orientation decreasing roughness results in particle interlocking of different degrees which obstructs slip and rotation to preferred orientations so that friction is high and volume strain positive spatial and temporal shear zone development depends on the roughness of particles increasing roughness precludes shear zone development and particle domain evolution shear zone localisation depends on particle sphericity increasing sphericity leads to more localised but vertically dilated deformation

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

the control of salt supply on entrainment of an anhydrite layer within a salt diapir the influence of four parameters sedimentation rate viscosity of salt stratigraphic location of the anhydrite layer within the salt layer and the perturbation width on salt supply to down built diapirs and its entrainment capacity are studied systematically in numerical models model results show that these four parameters affect salt supply and the evolution history of a salt diapir as such these parameters strongly influence the style and the amount of entrainment of dense inclusions into a diapir in active diapirs i e unburied diapirs salt supply increases with increasing sedimentation rate whereas it decreases with an increase in salt viscosity diapirs initiating from wide perturbation provide more salt supply to feed the diapir presence and initial stratigraphic location of any denser layer e g an anhydrite layer within a salt layer also affects salt supply when lateral forces are negligible salt supply into a diapir depends on these four parameters which directly control the entrainment of any embedded anhydrite layer into the diapir

thrust geometry controlled by erosion and sedimentation a view from analogue models analogue sandbox models have been set up to study thrust systems formed above two decollements and affected by erosion and sedimentation the deformation was imaged by x ray scanner three erosion sedimentation conditions were tested for all the experiments a duplex develops between the two decollement levels for the experiment without erosion and without sedimentation ramp anticlines form in the upper series for the model with syntectonic sedimentation and without erosion the shortening in the upper series is first characterized by fault related folds and then by a forward propagation of the decollement that induces the development of a piggy back basin for the experiment with erosion and sedimentation a passive roof duplex is formed relationships between structural style and syntectonic superficial conditions in classical thin skinned thrust belts are similar to those found in the analogue models the ramp anticlines of the jura developed with low erosion and low sedimentation and the large sub andean thrust belt is controlled by syntectonic sedimentation whereas the passive roof duplex of pakistan is synchronized with intense erosion this study outlines the crucial effect of the superficial mass transport phenomena in the tectonic style of thrust belts

geology of the onshore makran accretionary wedge synthesis and tectonic interpretation abstract this contribution is a synthesis of studies carried out since 2004 in the makran accretionary wedge exposed in se iran these studies were intended to improve our understanding of the behaviour of accretionary wedges and of the significance of the makran wedge in the frame of tethys tectonics reassessing the stratigraphy and structure of the iranian makran has allowed distinguishing four main litho tectonic units the lithological content of these four units is briefly described to discuss the sedimentary environments which record the general filling of an oceanic basin with clastic sediments derived from the north the petrology of ophiolites exposed in the backstop region to the north of the accretionary wedge itself demonstrates the existence of an oceanic basin formed in the jurassic late cretaceous to the north of continental slivers which had separated from central iran there is petrological evidence for a subduction related magmatic arc during the late cretaceous which sourced much of the clastic material in the cretaceous lower miocene turbidites present throughout the wedge the literature survey shows that the late cretaceous to present evolution of the pakistan part of the makran fold and trust belt is in its major attributes similar to that of the iranian makran these observations and results are discussed in a tectonic model that integrates knowledge on the oman mountains on the other side of the current oman subduction

controls on large landslide distribution and implications for the geomorphic evolution of the southern interior columbia river basin large landslides 0 1 km 2 are important agents of geomorphic change while most common in rugged mountain ranges large landslides can also be widespread in relatively low relief several 100 m terrain where their distribution has been relatively little studied a fuller understanding of the role of large landslides in landscape evolution requires addressing this gap since the distribution of large landslides may affect broad regions through interactions with channel processes and since the dominant controls on landslide distribution might be expected to vary with tectonic setting we documented 400 landslides between 0 1 and 40 km 2 across 140 000 km 2 of eastern oregon in the semiarid southern interior columbia river basin the mapped landslides cluster in a nw se trending band that is 50 100 km wide landslides predominantly occur where even modest local relief 100 m exists near key contacts between weak sedimentary or volcaniclastic rock and coherent cap rock fault density exerts no control on landslide distribution while 10 of mapped landslides cluster within 3 10 km of mapped fold axes landslide occurrence is curtailed to the ne by thick packages of coherent basalt and to the sw by limited local relief our results suggest that future mass movements will localize in areas stratigraphically preconditioned for landsliding by a geologic history of fluviolacustrine and volcaniclastic sedimentation and episodic capping by coherent lava flows in such areas episodic landsliding may persist for hundreds of thousands of years or more producing valley wall slopes of 7 13 and impacting local channels with an evolving array of mass movement styles

gigantic seismogenic landslides of summer lake basin south central oregon subsidence of summer lake basin situated in the northwestern basin and range province in south central oregon has exposed a kilometer thick neogene sequence of dense volcanic flow rocks overlying very weak tuffaceous sedimentary rocks in the bounding winter ridge slide mountain escarpment subsidence occurs along the active 40 km long winter ridge slide mountain fault which is capable of producing mw 7 earthquakes with near field maximum horizontal acceleration approaching 1 g gigantic landslides cubic kilometers in volume scallop the southwestern part of the escarpment and the deposits run out several kilometers characteristic of rock avalanches geotechnical rock mass characterization and slope stability analyses confirm observations that these landslides were initiated within the weak tuffaceous sedimentary rocks along shallow east dipping planar failure surfaces are insensitive to groundwater fluctuations and are stable under static conditions pseudostatic analyses reveal that strong shaking is required to trigger landsliding the bennett flat landslide failed as a single event between 900 270 ka and 16 8 ka the landslide has a depletion zone volume of 1 1 km3 but only 0 3 km3 of debris is discernible in the accumulation zone the foster creek landslide also appears to have failed as a single event between 180 and 16 8 ka the landslide has a depletion zone volume of 2 9 km3 but only 0 3 km3 of debris is discernible in the accumulation zone the punchbowl landslide evidences multiple events the most recent of which failed in the holocene and had a volume of 0 4 km3 0 5 km3 of debris is found in the accumulation zone

modeling deformation and salt tectonics in the eastern mediterranean ridge accretionary wedge this study addresses some aspects of the kinematics and structural setting of the mediterranean ridge accretionary complex particularly those aspects related to the occurrence and distribution of messinian evaporites the approach is by 1 identification of the geometry of deformation through reprocessing of existing multichannel seismic reflection data from the levantine basin aimed at the definition of the velocity field and depth imaging 2 physical modeling in the laboratory aimed at the study of the kinematics of shortening of sedimentary sequences detaching on viscous decollements and 3 comparison between the results of the two approaches we conclude that the thick messinian sequence of the levantine basin is composed primarily of salt so that the entire evaporitic sequence can be expected to behave as a viscous material it follows that the main detachment of the post messinian wedge is located at the base of the messinian salt layer a viscous salt decollement would produce thrusting trending normal to the shortening direction but boundary conditions affect structural trends even more than stress and or movement direction both strain partitioning and the formation of major strike slip faults within the post messinian wedge are prevented by the high angle of convergence between the african and aegean plates as well as by the low intraplate friction in addition we show that curved and anastomosing thrust fronts are reflected in the cobblestone topography of the mediterranean ridge we finally postulate that extension may occur in the central mediterranean ridge as a result of the geometry of the plate boundaries this extension is considered as a possible cause of mud volcanism and mud diapirism

episodic imbricate thrusting and underthrusting analog experiments and mechanical analysis applied to the alaskan accretionary wedge seismic reflection profiles from the sediment rich alaska subduction zone image short frontally accreted imbricate thrust slices and repeated sequences of long underthrust sheets rapid landward increases in wedge thickness backthrusting and uplift of the forearc are observed suggesting underthrusting beneath the wedge these features and a widely varying frontal wedge morphology are interpreted to be caused by different modes of accretion active concurrently along the trench at different locations episodic wedge growth is observed in high basal friction experiments using sand as an analog material two phases of an accretionary cycle can be distinguished frontal accretion of short imbricate thrust slices alternating with underthrusting of long undeformed sheets the phase is shown experimentally to depend upon the surface slope of the wedge mechanical analysis of the forces at work predicts these two modes of deformation due to the varying frictional forces and yield strengths for a temporally varying wedge geometry maximum length of thrust slices is calculated for experimental conditions and confirmed by the observations for a steep frontal slope at the upper limit of the mohr coulomb taper stability field the overburden is too great to permit underthrusting and failure occurs repeatedly at the wedge front producing short imbricate slices the wedge grows forward lowering the surface angle to the minimum critical taper for a shallow frontal slope the reduced overburden along an active roof thrust permits sustained underthrusting causing frontal erosion and backthrusting steepening the wedge and thus completing the cycle

evolution of experimental thrust wedges accreted from along strike tapered silicone floored multilayers the possible effect of pre deformational along strike sedimentary tapers on the structural architecture of thrust wedges accreted above viscous materials has been commonly underestimated or neglected we illustrate results of an experimental programme specifically designed to study the impact of this parameter on thrust wedge evolution using sandbox analogue modelling two series of experiments were performed the first series was designed to investigate the sensitivity of wedge growth to the along strike sedimentary taper variability the second was designed to investigate the sensitivity of a growing along strike tapered wedge to the convergence rate our experimental results indicate that even gentle pre deformational along strike thickness variations in foredeep clastic sequences overlying viscous materials such as evaporites or overpressured shales can produce dramatic changes in the first order structural architecture and kinematic evolution of accreting thrust wedges

a fragmentation spreading model for long runout rock avalanches based on the observation that deposits of large rock avalanches consist predominantly of intensely fragmented rock debris it is proposed that the processes of rock fragmentation are significant ca

coastal cliffs rock slope failures and late quaternary transgressions of the black sea along southern crimea abstract rock slope failures represent a significant hazard along global coastlines but their chronology remains poorly documented here we focus on the geomorphology and chronology of giant rockslides affecting the crimean mountains along the black sea coast geomorphic evidence suggests that high 100 m limestone cliffs flanking the southern slopes of the crimean mountains are scarps of rockslides nested within larger deep seated gravitational slope deformations dsgsds such pervasive slope failures originated due to lateral spreading of intensively faulted late jurassic carbonate blocks moving atop weak plastic late triassic flysch and tuff layers by introducing a dating strategy relying on the combination of the uranium thorium dating u th of exposed calcareous speleothems covering the landslide scarps with the 36cl exposure dating of rock walls we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces for the three representative large scale rockslides between the towns of foros and yalta the initiation of the dsgsds as evidenced by the widening of crevices and the onset of speleothem accumulation was 300 ka bp but the recent cliff morphology along the coast is the result of late pleistocene holocene failures spanning 20 0 5 ka bp the exposures of rockslide scarps occurred mostly at 20 15 8 5 4 and 2 0 5 ka which substantially coincide with the last major black sea transgressions and or more humid holocene intervals our study suggests that before ultimate fast and or catastrophic slope failures the relaxation of rock massifs correlative with karstification cracks opening and incipient sliding lasted on the order of 104 105 years rapid late glacial holocene transgressions of the black sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides simultaneously affecting the majority of the sw coast of the crimean peninsula

late holocene catastrophic slope collapse affected by deep seated gravitational deformation in flysch ropice mountain czech republic the region of the flysch western carpathians is characterized by abundant deep seated gravitational slope deformations dsgsds this study deals with a detailed analysis of late holocene catastrophic collapse of a fault created slope of mountain ropice in the moravskoslezske beskydy mountains eastern czech republic the catastrophic collapse was initialized by huge compound rotational slide toppling deformation which occurs on the upper part of the studied slope and affects tectonically weakened subhorizontally inclined sandstone beds detailed geomorphological mapping accompanied by morphotectonic analysis and geophysical sounding revealed at least two historic flowslides the older event f1 affected 0 5 0 8 mm3 of bedrock and created a 1000 m long and up to 150 m wide accumulation with abundant transverse steps and a carapace like surface the landslide toe blocked an adjacent valley which led to the development of a small impoundment with 4 m thick deposits containing lacustrine peat bog floodplain and alluvial fan facies radiocarbon dating and pollen analysis indicate the valley blockage at 1 5 ka bp the other flowslide f2 of much smaller dimensions 10 000 12 000 m3 overlaid the main landslide body and according to the dating of minerogenic horizon in the impoundment may have taken place 0 3 ka bp the organisation of landforms character of slope failures and dynamic back modelling point to a likely rock avalanche or combined rock slide debris avalanche mechanism of movement this case study shows that rapid rock avalanches can operate also in mountainous terrain with moderate relief if toppling together with deep seated gravitational deformation of slopes modifies the original stable position of bedding planes