bison and deer bone mineral densities comparisons and implications for the interpretation of archaeological faunas abstract volume bone mineral densities are derived for modern bison skeletal parts using dual energy x ray densitometry these density measurements are compared to those published by lyman 1984 journal of anthropological archaeology3 259 299 for small cervids differences that exist can be explained in terms of body size and patterns of locomotion density data then are compared to skeletal part frequencies from two great plains bison assemblages bison bone mineral densities provide a more appropriate model than do cervid densities for examining variability in large bovid bone assemblages and point to the need for constructing similar data bases for other taxa

structural reactivation in plate tectonics controlled by olivine crystal anisotropy structures formed during ancient tectonic events are commonly reactivated during subsequent tectonism numerical models point to mechanical anisotropy arising from the inherited orientation of crystals of the mineral olivine in the lithospheric mantle as the cause of this behaviour

formation and maintenance of shear zones the processes that initiate and maintain prograde ductile shear zones are not well understood we have performed shear experiments 1 to 3 on a fine grained 100 150 m gneiss 59 quartz 28 plagioclase 13 aligned but not interconnected biotite to determine the evolution of deformation mechanisms that produce dramatic strain weakening and localization at conditions 1 5 gpa 800 c dot gamma 2 10 5 s where pure quartz aggregates deform homogeneously by dislocation creep initial yield occurs where stress concentrations at the tips of weak biotite grains produce semibrittle deformation in intervening quartz or plagioclase allowing local biotite interconnection by slip on 001 and initiating strain weakening after yield the interconnected biotites kink and thus strengthen but the highly strained parts of grains react to a fine grained mixed phase assemblage which deforms by grain size sensitive creep allowing further strain weakening and localization at 3 3 the strain and strain rate in the 100 m thick shear zone are 100 times that of the enclosing host rock similar to the localization observed in natural shear zones thus the processes that initiate strain localization are not necessarily the same as those that preserve the weak shear zone and once formed a shear zone may be permanently weakened

weak faults rotten cores earthquakes are triggered when crustal deformation produces displacements along fault zones the rock in these zones is found to be weaker than adjacent material but what are the mechanisms of this loss of strength in his perspective holdsworth 1 discusses how recent studies of exposed ancient fault zones combined with laboratory analyses are revealing that rock properties at the grain scale can determine the large scale behavior of crustal deformation 1 http www sciencemag org cgi content full 303 5655 181

oriented grain growth and modification of frozen anisotropy in the lithospheric mantle abstract seismic anisotropy throughout the oceanic lithosphere is often assumed to be generated by fossilized texture formed during deformation at asthenospheric temperatures close to the ridge here we investigate the effect of high temperature and high pressure static annealing on the texture of previously deformed olivine aggregates to simulate residence of deformed peridotite in the lithosphere our experiments indicate that the orientation and magnitude of crystallographic preferred orientation cpo will evolve due to the preferential growth of grains with low dislocation densities these observations suggest that texture and stored elastic strain energy promote a style of grain growth that modifies the cpo of a deformed aggregate we demonstrate that these microstructural changes alter the orientation distributions and magnitudes of seismic wave velocities and anisotropy therefore static annealing may complicate the inference of past deformation kinematics from seismic anisotropy in the lithosphere

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

epicenter distribution and magnitude of earthquakes in fold thrust belts insights from sandbox models scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth quakes in the sedimentary cover of active fold thrust belts model results suggest that in fold thrust belts shortenedabove low friction ductile decollements rock salt or over pressured mudstone low to moderate magnitude earth quakes mw 5 3 5 6 distributed over a wide area occuralong several long lived thrust faults conversely in areasshortened above high friction decollements large magnitudeearthquakes mw 6 6 6 8 distributed over a narrowzone are likely to occur along few short lived thrust ramps calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat tern from the zagros mountain belt which is partially short ened above a ductile decollement of hormuz salt formation model results also showed that erosion reactivates older in active thrusts and promotes formation of out of sequencethrusts

evolution of the triangle zone in the rocky mountain foothills near coalspur central alberta a triangle zone which commonly occurs along the external margin of a foreland thrust and fold belt with a buried thrust front is underlain by a subhorizontal blind foreland verging thrust that ends against a foreland dipping hinterland verging thrust these contemporaneous thrusts active towards the end of orogenesis enclose an intercutaneous wedge that moved towards the foreland during orogenesis a triangle zone evolves through periodic replacement of faults bounding the active wedge replacements occur in cycles during each of which a lower fault tends to be replaced by one in a lower stratigraphic horizon an upper fault by one farther away from the foreland each cycle ends with the lower fault moving to a younger horizon where it joins a new more external upper fault near coalspur the triangle zone exposes the remnants of several wedges involving upper cretaceous and paleocene molasse most of these wedges developed during the last cycle but one and have a combined displacement of about 5

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

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

ten million year history of a thrust sheet the final deformed state of a fold and thrust belt may be reached by an infinite number of kinematic paths two end member kinematic paths are due to continuous or discontinuous rates of deformation we have used a new magnetostratigraphic section from the spanish pyrenees to calibrate the emplacement history over 10 m y of a major thrust sheet the sierras marginales thrust sheet and the deformation of both its hanging wall and footwall six time windows from before 36 5 ma until after 24 7 ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures footwall deformation of the sierras marginales thrust sheet occurred continuously on a detachment within the foreland basin sequence 4 5 km net shortening shortening rates steadily increased from 0 14 to 1 5 mm yr with time although the detachments at the base of the foreland and the detachment at the base of the sierras marginales thrust sheet were active coevally the rate of displacement on the sierras marginales detachment decayed with time and shows considerable variability emplacement of the thrust sheet may be divided into three distinct periods a rapid 13 8 km translation from 37 0 to 36 5 ma 27 6 mm yr a gradual climb of the toe of the thrust sheet up a 4 3 km long ramp across the foreland basin succession from 36 5 to 32 0 ma 0 95 mm yr and a final 8 9 km translation from 32 0 to 29 5 ma 3 56 mm yr internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29 5 ma shortening rates steadily decreased from 0 6 mm yr between 29 5 and 27 8 ma to 0 26 mm yr from 27 8 until after 24 7 ma only 1 km of shortening accumulated during each of the two periods the last shortening localized on the most northerly thrust in the study area folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation in contrast translation followed by internal deformation on the hinterland side of the toe of the sierras marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time rate of deformation on both detachments was discontinuous and shows substantial variability about the mean in general the spatial and temporal pattern of deformation was distributed and continuous in detail however shortening was spatially and temporally discontinuous above each detachment and structures related to each one display distinctly different deformational patterns rates and styles

basal slip and mechanical anisotropy of biotite the basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on 001 samples loaded at 45 to 001 exhibit gentle external rotations associated with dislocation glide high angle kink bands in these samples unlike those developed in micas loaded parallel to 001 are limited to sample corners samples shortened perpendicular to 001 show no evidence of nonbasal slip and fail by fracture over all conditions tested the mechanical response of biotite shortened at 45 to 001 is nearly perfectly elastic plastic stress strain curves are characterized by a steep elastic slope a sharply defined yield point and continued deformation at low mostly 1 stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 mpa and exhibit weak dependencies upon strain rate and temperature assuming an exponential relationship between differential stress d and strain rate e of the form e cexp d exp q rt the data collected over strain rates and temperatures of 10 7 to 10 4 s 1 and 20 to 400 c respectively are best fit by an exponential constant of 0 41 0 08 mpa 1 and an activation energy q of 82 13 kj mol a power law fits the data equally well with n 18 4 and q 51 9 kj mol samples oriented favorably for slip in directions 100 and 110 are measurably weaker than those shortened at 45 to 010 and 310 consistent with the reported burgers vectors 100 1 2 110 and 1 2 110 the anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to 001 previous studies have shown that biotite loaded in the 001 plane is strong prior to the nucleation of kink bands the strength of biotite shortened perpendicular to 001 exceeds that measured parallel to 001 and is pressure dependent application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions its presence within foliated rocks and shear zones may limit locally the stresses that can be supported

chemical investigation of mineralisation categories used to assess taphonomy abstract a recent case study from the geelbek dunes archaeological site in western cape province south africa revealed that counter to prevailing notions long term bone survivorship is not always linked to estimates of bone density porosity differences between modern cancellous and compact bones of different animals and skeletal parts provided density estimates for fossil bones taphonomic history was inferred from the physical condition and mineral burden of the fossil bones and represented by five mineralisation categories bones in mineralisation category one had the lowest secondary mineral burden whereas samples with very high secondary mineral contents were considered category five here we examine the proposed link between mineralisation category and taphonomic history by analysing fossils with non destructive energy dispersive x ray fluorescence spectroscopy we hypothesised that higher mineralisation categories should be evident as higher concentrations of elements associated with secondary minerals however chemical measurements could not distinguish fossil bones in mineralisation category one from those in category three furthermore bones in categories four and five could not be distinguished from one another a control of modern bone specimens and fossils in mineralisation category two formed separate and distinct clusters of principal component score values spectra from the geelbek dunes specimens were subsequently used to predict mineralisation categories for fossils from a nearby archaeological locality named anyskop blowout based on the surface chemistry anyskop fossils clustered in two principal groups low mineralisation categories one two and three and high mineralisation categories four and five energy dispersive x ray fluorescence spectroscopy provided useful taphonomic information for fossils from both the geelbek dunes and anyskop blowout although this surface biased technique was not well correlated with the five mineralisation categories

formation of orogen perpendicular thrusts due to mechanical contrasts in the basal decollement in the central external sierras southern pyrenees spain two series of analogue models are used to explore the effect of ductile frictional contrasts of the basal decollement on the development of oblique and transverse structures during thin skinned shortening these models simulate the evolution of the central external sierras ces southern pyrenees spain which constitute the frontal emerging part of the southernmost pyrenean thrust the ces are characterised by the presence of n s to nw se anticlines perpendicular to the pyrenean structural trend and developed in the hanging wall of the thrust system they detach on unevenly distributed triassic materials evaporitic dolomitic interfingering the models simulated the effect of adjacent ductile versus frictional decollements during shortening model series a tests the thickness ratio between overburden and the ductile layer whereas model series b tests the width perpendicular to the shortening direction of frictional decollement model results confirms that deformation reaches further in areas detached on a ductile layer whereas above frictional decollement areas shortening is accommodated by additional uplift and penetrative strain this replicates the structural style of the ces higher structural relief of n s anticlines with regard to orogen parallel structures absence of a representative ductile decollement in the core plunging towards the hinterland and foreland side closure not thrusted by the south pyrenean thrust

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

kinematic analysis of faults in a physical model of growth faulting above a viscous salt analogue abstract syn sedimentary faults overlying an extended ductile layer within a sand model provide an analogue for studying some aspects of the geometry and kinematics of basin scale extensional listric faults associated with salt rollers the displacement analysis techniques used to examine displacement variations over fault surfaces within the sand model show that displacement varies in a regular and predictable manner deviations from simple fault displacement patterns are due to transfers of displacement onto adjacent synthetic faults aggregation of the displacements on adjacent synthetic faults produces more regular patterns of displacement distribution and demonstrates the geometric coherence of the aggregated faults rapid upward decreases in displacement on the model faults are due to fault growth during sedimentation elsewhere in the model post sedimentary faulting is associated with very low upward displacement gradients and pre and syn faulting sedimentation are readily distinguished on cross sectional fault traces in three dimensions a non horizontal line separating the pre faulting and syn faulting sequences tracks the lateral extent of a fault through time backstripping of fault displacements by subtracting the fault displacement of a sedimentary horizon from the displacements of underlying horizons gives the displacement distribution on a fault surface at the time of deposition of the backstripped horizon backstripped fault displacement distributions also allow examination of the general fault structure through time backstripping of fault displacements on one of the larger faults within the model and on an associated hanging wall synthetic splay shows that the two structures originated as a relay zone which was breached by lateral propagation of one of the overlapping faults which form the relay zone the backstripping technique allows determination of the geometrical changes during growth of a fault system

analogue modelling of inclined brittle ductile transpression testing analytical models through natural shear zones external betics abstract the combination of analytical and analogue models gives new opportunities to better understand the kinematic parameters controlling the evolution of transpression zones in this work we carried out a set of analogue models using the kinematic parameters of transpressional deformation obtained by applying a general triclinic transpression analytical model to a tabular shaped shear zone in the external betic chain torcal de antequera massif according to the results of the analytical model we used two oblique convergence angles to reproduce the main structural and kinematic features of structural domains observed within the torcal de antequera massif 15 for the outer domains and 30 for the inner domain two parallel inclined backstops one fixed and the other mobile reproduce the geometry of the shear zone walls of the natural case additionally we applied digital particle image velocimetry piv method to calculate the velocity field of the incremental deformation our results suggest that the spatial distribution of the main structures observed in the torcal de antequera massif reflects different modes of strain partitioning and strain localization between two domain types which are related to the variation in the oblique convergence angle and the presence of steep planar velocity and rheological discontinuities the shear zone walls in the natural case in the 15 model strain partitioning is simple and strain localization is high a single narrow shear zone is developed close and parallel to the fixed backstop bounded by strike slip faults and internally deformed by r and p shears in the 30 model strain partitioning is strong generating regularly spaced oblique to the backstops thrusts and strike slip faults at final stages of the 30 experiment deformation affects the entire model box our results show that the application of analytical modelling to natural transpressive zones related to upper crustal deformation facilitates to constrain the geometrical parameters of analogue models

reconstructing depositional histories through bone taphonomy extending the potential of faunal data reconstructing the sequences of deposition of archaeological material is central to the interpretation of archaeological sites and provides the foundations for how site chronology is understood generally stratigraphy provides the most direct evidence for understanding depositional histories however in certain instances stratigraphic relationships may be obscured or unobservable and therefore other sources of evidence must be drawn upon for defining deposits and reconstructing sequences of deposition this is a particular problem at dark earth sites which are homogeneous in terms of the colour and texture of deposits and also in artefact rich samples which have little sedimentary matrix this paper explores the potential of a new approach to the analysis of bone taphonomic data for the purposes of deciphering depositional histories when stratigraphy is unobservable integral to this method is rigorous statistical analysis of modification data combined with an assessment of the taxonomic and anatomical composition of deposits in terms of their susceptibility to modification this facilitates more confident interpretation of modification patterns as deposit composition can be discounted from responsibility for significant differences the approach is tested on a sample area of the later prehistoric midden of potterne wiltshire uk through detailed recording and statistical analysis of bone modifications weathering gnawing and trampling this research demonstrates that bone taphonomy is not only useful for identifying distinct depositional events in apparently homogeneous strata but can also provide detail on the nature of processes responsible for the formation of the deposit

how heating and cooling and wetting and drying can destroy dense faunal elements and lead to differential preservation abstract recent taphonomic research has demonstrated that bulk bone density significantly determines survivability in many archaeological and paleontological contexts researchers often assume that higher density skeletal elements invariably preserve better than lower density skeletal elements this assumption however is not universally valid here we present data on the taphonomy and preservation of assemblages from the geelbek dunes of the western cape province south africa these data indicate that skeletal preservation of fossil assemblages from deflation hollows can reflect an unexpectedly high proportion of porous low density skeletal parts high density skeletal parts including teeth and the shafts of long bones often shatter as a result of the repeated thermal shock and wetting and drying of the kind observed at geelbek this effect is greatest for highly mineralized bones from large mammals the data from geelbek demonstrate that survivability is affected by the size of the animal small mammals are represented by high proportions of non mineralized dense skeletal parts especially long bones

structural significance of an evaporite formation with lateral stratigraphic heterogeneities southeastern pyrenean basin ne spain we run a series of analogue models to study the effect of stratigraphic heterogeneities of an evaporite formation on thin skinned deformation of the southeastern pyrenean basin spb ne spain thi

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

effect of plastic viscous layering and strain softening on mode selection during lithospheric extension 1 factors controlling the selection of deformation modes during continental extension are investigated using analytical and numerical methods we view the lithosphere as a laminate and examine a simple system with a uniform plastic layer overlying a uniform linear viscous layer the rate of energy dissipation is analyzed for pure shear ps symmetric plug sp and asymmetric plug ap extension modes and the analysis reveals that the primary control is the relative rate of dissipation in the two layers a basic difference is that the plastic layer yield strength is independent of the strain rate whereas the viscous stress depends on strain rate therefore dissipation scales linearly and quadratically with extension velocity for these respective layers when other parameters e g extension velocity and properties are held constant minimum dissipation predicts that the modes ap sp and ps will be selected in this order with increasing viscosity of the lower layer transition viscosities between modes t1 and t2 are 4 1021 pa s and 8 1022 pa s respectively for our parameters values numerical models confirm the analysis results inferred mode controls and order of mode selection when strain softening of the plastic layer occurs during extension implications for lithosphere that acts as a bonded plastic viscous laminate include the following 1 asymmetric extension ap mode is preferred when the extension rate and or effective viscosity is low or the viscous region temperature is high 2 symmetric sp mode extension is preferred for intermediate combinations of parameters and 3 overall pure shear ps mode may occur for opposite end member parameter combinations

intraplate seismicity of a recently deglaciated shield terrane a case study from northern ontario canada the economy of northern ontario canada is heavily dependent on mining so accurate knowledge of seismicity is important for the safe design and op eration of mines and other critical facilities including a proposed underground repos itory for nuclear waste in this study we analyzed 537 cataloged earthquakes that occurred from 1980 to 2006 seismicity is mainly concentrated in topographically elevated archean terranes northwest of lake superior and in the james bay and ka puskasing regions we analyzed waveforms to determine the focal depth for 331 re corded events using the regional depth phase modeling rdpm method coupled with surface wave relative amplitude analysis the majority of events are shallow 350 m although in the east ern part this pattern breaks down and some deeper earthquakes 12 km are ob served based on a moving window event counting technique we show that distinct spatial clusters of seismicity can be delineated that are statistically significant relative to background seismicity levels a particularly active cluster is located within james bay where focal depths range from a few kilometers to more than 20 km another cluster near kapuskasing contains deep focus events and may occur along a hot spot track that runs through western quebec near dryden a shallow 1 km earthquake swarm concentrated in a 1 1 km region commenced in may 2002 faded and then started up again in february 2003 shallow mining induced events are also common around sudbury a major world center for nickel mining the overall pattern of seis micity appears to correlate with upper mantle p wave velocity anomalies suggesting that lateral variations in mantle rheology may play a significant role in controlling intraplate seismicity of shield areas it is also likely that crustal stresses caused by glacial isostatic adjustment are an important factor although the correlation of seis micity with uplift rate is not as clear online material focal depth solutions for earthquakes in northern ontario canada

intermediate decollement activation in response to the basal friction variation and its effect on folding style in the zagros fold thrust belt an analogue modeling approach although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains the interaction between basal and intermediate de

the plate tectonic approximation plate nonrigidity diffuse plate boundaries and global plate reconstructions the central assumption of plate tectonics that plate interiors are rigid remains a useful but uncertain approximation strain rates of stable plate interiors are bounded between 10 i12 10 i11 year i1 and 4 10 i10 year i1 the narrowness of all plate boundaries the other main assumption of plate tectonics as originally conceived is contradicted by many observations both in the continents and in the oceans some diffuse plate boundaries in both continents and oceans exceed dimensions of 1000 km on a side diffuse plate boundaries cover 15 of earth s surface the maximum speed of relative plate motion across any one diffuse plate boundary ranges from 2t o 15 mm year which is faster than some upper bounds on intraplate motion across stable plate interiors 2m m year i1 strain rates in diffuse plate boundaries can be as high as 10 i8 year i1 25 times higher than the upper bound on strain rates of stable plate interiors but 600 times lower than the lowest strain rates across typical narrow plate boundaries the poles of rotation of the plates flanking a diffuse oceanic plate boundary tend to be located in the diffuse boundary which is a consequence of the strong coupling across the boundary

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

significant motions between gps sites in the new madrid region implications for seismic hazard position time series from global positioning system gps stations in the new madrid region were differenced to determine the relative motions between sta tions uncertainties in rates were estimated using a three component noise model con sisting of white flicker and random walk noise following the methodology of langbein 2004 significant motions of 0 37 0 07 one standard error mm yr were found between sites ptgvand stle for which the baseline crosses the inferred deep portion of the reelfoot fault baselines between stle and three other sites also show significant motion site mcty adjacent to stle also exhibits significant motion with respect to ptgv these motions are consistent with a model of interseismic slip of about 4 mm yr on the reelfoot fault at depths between 12 and 20 km if constant over time this rate of slip produces sufficient slip for an m 7 3 earthquake on the shallow portion of the reelfoot fault using the geologically derived recurrence time of 500 years this model assumes that the shallow portion of the fault has been pre viously loaded by the intraplate stress a gps site near little rock arkansas shows significant southward motion of 0 3 0 4 mm yr 0 08 mm yr relative to three sites to the north indicating strain consistent with focal mechanisms of earthquake swarms in northern arkansas

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

rates and uncertainties on seismic moment and deformation in eastern canada 1 on the basis of earthquake statistics from the canadian earthquake hazard model we estimate the rates of seismic moment and deformation in seismic zones of eastern canada we use a logic tree approach to derive median values and 66 confidence intervals for models based on earthquake cluster distributions and geological and tectonic structures typical moment rates are low 0 1 1 1017 n m yr 1 equivalent to a magnitude mw 7 earthquake every 350 3500 years in each seismic zone in a few zones such as baffin bay moment rates reach 2 10 1017 n m yr 1 expressed in terms of relative velocity between zone boundaries seismic deformation rates are typically 0 2 0 5 mm yr 1 for a few regions of high seismicity such as baffin bay charlevoix or grand banks the relative velocities reach 1 2 mm yr 1 strain rates are typical of the intraplate environment 10 13 10 10 yr 1 with values locally as high as 10 8 yr 1 these rates give some insight into geodynamic aspects of the northeastern north america plate assuming that the seismic deformation rates represent long term deformation of the lithosphere they provide some constraint to the amplitude and variability of intraplate strain on a shorter timescale seismic strain rates can be compared with postglacial rebound predictions and might help constrain some aspects of these models because they reflect the seismic energy released over the last few hundred years our estimates in combination with geodetic measurements can also help constrain models of earthquake dynamics in eastern north america

deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone

late cenozoic structural deformation and evolution of the central southern longmen shan fold and thrust belt china insights from numerical simulations abstract since the late cenozoic the central southern longmen shan lms region is characterized by a two decollement thrust fold system with a localized upper evaporite weaker layer just beneath the sichuan basin and the lower stronger decollement beneath the lms to date the role of upper decollement and erosion in shaping the structural deformation of the lms remains unknown the investigation of this question may shed lights on the assessment of the structural evolution and the further discrimination of mountain building mechanism in this work a 2d finite difference method is applied with regards to the variations of viscosity friction angle and lengths of upper decollement under different erosion rates two types of numerical models are setup with purely lower upper frictional ff decollements and lower frictional upper viscous fv decollements tectonic evolution with ff models exhibits large similarity with that of fv models meanwhile our results underline the presence of in sequence fault propagation procedures during most of the stages the development of the boundary ramp the range frontal blind fault is strongly induced by a prerequisite with upper decollement of necessary length the activation of beichuan pengguan faults or blind ramp piercing to the surface is extremely mechanically sensitive to the viscosity of the salt decollement erosion rate and the length of the upper decollement out of sequence thrusting shallow and possible basal accretion processes beneath the sichuan basin are found when deformation transfers from the thick skinned lms to the thin skinned sichuan basin at the very late stage supporting upper crustal shortening dominates the mountain building mechanism

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

the caribbean plate pulled pushed or dragged 1 mechanical coupling between the lithosphere and the asthenosphere remains a controversial topic in the geosciences beneath the caribbean plate shear wave splitting measurements indicate ew strain in the asthenosphere which can be interpreted as mantle flow driving or resisting motion of the overlying lithosphere here we constrain the average shear traction on the base of the caribbean plate by balancing all torques these torques result from body forces that act on the caribbean slab pull ridge push lateral density variations from plate boundary friction and from basal shear tractions we obtain a range of physically realistic torque solutions which we examine further by computing the corresponding stresses and rotations within the caribbean plate for comparison with observations the deformation field for the caribbean is particularly sensitive to the amount of friction on intraplate faults representative models have a good fit with observations and are characterized by 1 a near zero basal shear traction 0 3 mpa 2 lithosphere averaged plate boundary friction 10 mpa 3 local forces due to indenters and trench pull 4 a net pull by the caribbean slab and 5 intraplate fault shear stresses on the order of tens of megapascals we conclude that the mechanical coupling of the caribbean plate to the underlying asthenosphere is small

time variable deformation in the new madrid seismic zone new geodetic measurements show that the new madrid is currently deforming too slowly if at all to account for large earthquakes in the region over the past 5000 years this result together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicates that either tectonic loading rates or fault properties vary over a few thousand years

micromammal taphonomy of el wad terrace mount carmel israel distinguishing cultural from natural depositional agents in the late natufian a taphonomic analysis of micromammal remains from the late natufian deposits of el wad terrace mount carmel israel was conducted in order to test the long standing premise of owl deposition as the primary accumulating agent the inferred taphonomic sequence was modeled within an actualistic recent comparative framework incorporating a locally derived barn owl pellet collection and an off site control assemblage of micromammal remains from the cliff overhanging the terrace the sequence was reconstructed based on multiple types of recorded taphonomic data comprising skeletal modifications breakage digestion weathering gnawing and charring and age structure evidence for post depositional processes including fluvial transport trampling and weathering was isolated and consequently the typical owl imprints were traced through the two actualistic and the archaeological assemblages based on the extent of breakage and patterning in skeletal element frequencies it was also possible to scale the preservation potential of primary data in el wad terrace as a discrete site type intermediate between true cave and open air depositional environments verifying the role of owls as principal agents of accumulation of the el wad terrace micromammal remains enabled the detection of two minor superimposed cultural patterns consumption of mole rats spalax sp by the natufians and commensalism of mice mus spp

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

the chronology of the eocene tectonic and stratigraphic development of the eastern pyrenean foreland basin northeast spain abundant and clearly exposed relationships between structures and syntectonic sedimentary rocks in the southern pyrenees make this area particularly suitable for detailed studies of the sequential development of a collisional orogenic belt during the pyrenean orogeny major shortening occurred in the eastern pyrenees in eocene and early oligocene times until now individual tectonic and depositional events have been only loosely defined temporally by biostratigraphic data in order to provide a more precise chronological framework four new magnetostratigraphic sections spanning 8 km of eocene strata and encompassing 18 m y have been developed in the eastern pyrenees of northern spain the ages of nine major depositional sequences in the eastern pyrenean foreland have been specified within the context of these chronologic data beginning with the early eocene transgression that commenced at 58 ma the timing of numerous tectonic events that occurred during the subsequent 16 m y can also be delineated including the initial emplacement of the pedraforca thrust sheet 58 54 ma the development of the pedraforca breakback thrusts 47 5 40 ma at a mean shortening rate of 2 4 mm yr rotation of the pedraforca footwall three intervals of motion along the vallfogona thrust 42 5 44 0 40 5 41 5 and

stress induced by topography and crustal density heterogeneities implication for the seismicity of southeastern canada abstract the stress induced by the topography and density heterogeneities in the lithosphere has been calculated for a large region covering most of southeastern canada the calculations assume that the lithosphere consists of a three dimensional layered elastic slab overlaying an inviscid fluid the calculations show that the deviatoric stress difference induced by density heterogeneities and the topographic load is of the same order as the regional tectonic stress tens of mpa stresses appear largest along the saint lawrence valley where most of the seismicity is located e g the charlevoix and the lower saint lawrence areas the charlevoix seismic zone was analyzed in greater detail and theoretical focal mechanisms were computed this analysis shows that the stress induced by surface and internal loading is compressional in this area and the principal stress orientation is consistent with earthquake focal mechanisms and in situ measurements

bone frequencies differential transport in situ destruction and the mgui abstract human transport of bones with high food values and destruction of bones with low density values are the traditionally invoked explanations of the frequencies of bones in archeological contexts the manner in which these two explanations have been used suggests archaeologists assume the explanations to be independent of one another the transport explanation is operationalized as the modified general utility index mgui of binford and the destruction explanation is operationalized with measures of bone density statistical correlation of the mgui with bone density while weak indicates that many high utility bones have low density values while many low utility bones have high density values because low density bones tend to be destroyed more readily than high density bones inferences of human utility strategies derived from bone frequencies and based on the mgui may be inaccurate the utility strategies suggested by three archaeofaunas are compared to bone density and two of these faunas are shown to potentially be the result of differential destruction and not human transport as measured by the mgui

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

far field strain transmission and contractional step overs abstract in contractional subduction collisional settings convergence is accommodated by the formation of thin and thick skinned thrust and fold belts the transmission of such deformation over larger distances into orogenic foreland areas is influenced by the inherited rheological characteristics of continental lithosphere lateral rheological variations parallel to the strike of continental foreland areas creates contrasting geometries and sequences of deformation that interact during orogenic build up we investigate the far field transmission of strain within a continental lithosphere characterized by a laterally variable rheology through physical analogue modelling rheological weak crustal zones were introduced at distance from an advancing backstop to study the progressive along strike linkage and interference of structures during contraction the results reveal that rheologically weak crustal zones localise far field contractional deformation when the size of weak zones by means of their horizontal extend to depth ratio is large deformation localises at the boundaries of the weak zone where they lead to the formation of large offset faults subsequently the faults migrate along strike into areas that are rheologically stronger when the size of the weak zone is reduced a large scale contractional step over forms in orogenic forelands where rheologically contrasting domains transmit out of sequence deformation by a gradual migration of thrust offsets and fold amplitudes along their strike these results show that crustal scale orogenic step overs do not always reflect variations in the geometry of the plate boundary indenter or along strike gradients in shortening rates such features may also form in response to variations in rheology as the ones created by inherited extensional basins situated at large distances from plate boundaries in the orogenic foreland

bone density studies in zooarchaeology abstract accurate bone density data are essential for assessing the influence of destructive processes in archaeological faunal assemblages unfortunately the diversity of methods employed by different researchers to derive density values has resulted in recent confusion two recent publications in this journal j archaeol sci 29 2002 883 j archaeol sci 29 2002 979 exemplify this state of misunderstanding both studies argued that the role of bone density in shaping archaeological faunal assemblages has been largely overrated but both based their conclusions on density values that were inaccurately derived the former employed a method of calculating bone density that has been largely discredited over the past decade j archaeol sci 29 2002 883 within a larger discussion of zooarchaeological methodology the latter provided an assessment of the current state of bone density research that inappropriately characterized the discrepancies between available sets of density data as a reflection of the differences between two technologies photon densitometry and computed tomography j archaeol sci 29 2002 979 the actual dichotomy exists irrespective of the technology employed between studies that account for variation in the shape of bone cross sections and those that do not the different sets of density data currently available to zooarchaeologists vary tremendously in their accuracy we review and evaluate the different techniques employed in the research of bone density patterns of mammalian fauna computed tomography produces the most accurate density data for elements without medullary cavities photon densitometry may provide density values of similar accuracy but only if a method of cross sectional shape adjustment is applied

measuring the post depositional destruction of bone in archaeological assemblages abstract post depositional processes have affected most archaeozoological assemblages often causing fragmentation or destruction of bone which can vary by assemblage and hamper interpretations of the original element representation klein cruz uribe 1984 the analysis of animal bones from archaeological sites chicago university of chicago press prior to performing interassemblage comparisons analysts must first assess the post depositional destruction for each assemblage hammerstone breakage and hyaena ravaging experiments show that compact bones carpals tarsals fibulae are rarely fragmented therefore fragmentation of these bones in archaeozoological assemblages should be the result of post depositional destruction a completeness index for compact bones provides a description of the magnitude of post depositional destruction because the completeness index is independent of differential fragmentation and transport by bone collectors and quantification variation between researchers the efficacy of the completeness index for showing varing completeness of archaeological bone is demonstrated by comparing two late pleistocene archaeological sites in kenya when guided by experimental results the completeness index allows an evaluation of the impact of post depositional destruction on the two kenyan assemblages published archaeozoological reports must provide a measure of post depositional destruction or else the usefulness of the data for comparative analysis is compromised

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

long bone fragmentation and interpretation of faunal assemblages approaches to comparative analysis abstract fragmentation of archaeological faunal assemblages has served as the basis for inferring a wide range of human behaviours however relationships between long bone breakage and past behaviours have often been expressed in terms of a direct equivalence between bone breakage and intensity of processing that is the greater the fragmentation the more intense the processing more refined interpretations based on bone breakage require a development of techniques to examine variability within the archaeological record data from western north american archaeological sites and several recent alaskan collections are used as the basis for documentation of assemblage variability in terms of 1 frequencies of complete bones 2 percentage difference values of proximal and distal articular ends 3 length of shaft attached to articular ends and 4 use of ratios of articular ends to shaft splinters and long bone shaft fragments in the development of minimum number of elements counts

stress channelling and partitioning of seismicity in the charlevoix seismic zone quebec canada summary the charlevoix seismic zone csz in the st lawrence valley of quebec is historically the most active in eastern canada the structurally complex region comprises rift faults formed during the opening of the iapetus ocean superimposed by a 350 ma meteorite impact structure resulting in a circular highly fractured zone although seismicity is localized along two steeply dipping planar rift parallel zones previous work indicates that most of the large scale rift faults bound the low magnitude background seismicity rather than generate earthquakes themselves in order to gain insight into the mechanics of the partitioning of this seismicity a 2 d model of the csz was built using the stress analysis code flac the rift faults are represented by frictional discontinuities the heavily fractured impact structure is represented by an elastic continuum of reduced modulus boundary displacements are used to generate a regional stress field with the major horizontal component in the direction of tectonic loading given a high strength the rift faults have little effect on the stress patterns stress trajectories naturally flow around the crater of reduced elastic modulus leaving the fractured area with lower stresses than the background level however when the rift faults have low strength they are unable to support stress trajectories inclined to them due to the resolved shear stress exceeding their strength this prevents trajectories from flowing out of the rift effectively channelling higher magnitude stresses into the region of the impact structure between the faults low strength bounding faults can thus explain the localization of seismicity into linear bands rather than distributed seismicity throughout the impact structure it also explains how the rift faults act as boundaries to regions of low magnitude seismicity these results indicate that the interplay between faults of varying strength and zones of differing elastic modulus can give rise to complicated stress patterns and can explain many of the seismicity patterns observed in the csz this has implications for other intraplate seismic zones as it shows an example of how regional weak faults can modify stress conditions around local structures and drive seismicity the results are particularly relevant for other regions located within rifted crust such as the new madrid seismic zone which possibly display evidence of stress channelling

structural inheritance control on intraplate present day deformation gps strain rate variations in the saint lawrence valley eastern canada structural inheritance is one of the key factors commonly proposed to control the localization of strain and seismicity in continental intraplate regions primarily on the basis of a first order spatial correlation between seismicity and inherited tectonic structures in this paper we present new gps global positioning system velocity and strain rate analyses that provide strong constraints on the magnitude and style of present day strain localization associated with the inherited tectonic structures of the saint lawrence valley eastern canada we analyze 143 continuous and campaign gps stations to calculate velocity and strain rate patterns with specific emphases on the combination of continuous and campaign velocity uncertainties and on the definition of robustness categories for the strain rate estimations within the structural inheritance area strain rates are on average 2 11 times higher than surrounding regions and display strong lateral variations of the style of deformation these gps velocity and strain rate fields primarily reflect ongoing glacial isostatic adjustment gia their comparison with gia model predictions allows us to quantify the impact of the structural inheritance and the associated lithosphere rheology weakening outside of the major tectonic inheritance area gps and gia model strain rates agree to first order both in style and magnitude in contrast the saint lawrence valley displays strong strain amplification with gps strain rates 6 28 times higher than model predicted gia strain rates our results provide the first quantitative constraints on the impact of lithospheric scale structural inheritance on strain localization in intraplate domains

measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures abstract simple laboratory tests have been made on dry quartz sand and on mixtures of sand and clay and sand and cement tests were made on both low and high density specimens of each mixture as determined by physical handling techniques the tests included measurements of density estimates of the coefficient of internal friction based on fault orientation and estimates of the friction coefficients and cohesion values for fault initiation and reactivation in a shear frame apparatus which was also used to test artificial fault zones made from pure clay glass microspheres and wheat flour the results suggest that density is determined more by handling technique than by composition and that friction coefficients and perhaps cohesion both increase with increasing density the shear testing revealed a consistent drop in cohesion for fault reactivation in all densely packed mixtures tested although small this drop may be significant for some types of laboratory models

an updated global earthquake catalogue for stable continental regions reassessing the correlation with ancient rifts summary we present an updated global earthquake catalogue for stable continental regions scrs i e intraplate earthquakes that is available on the internet our database contains information on location magnitude seismic moment and focal mechanisms for over 1300 m moment magnitude 4 5 historic and instrumentally recorded crustal events using this updated earthquake database in combination with a recently published global catalogue of rifts we assess the correlation of intraplate seismicity with ancient rifts on a global scale each tectonic event is put into one of five categories based on location i interior rifts taphrogens ii rifted continental margins iii non rifted crust iv possible interior rifts and v possible rifted margins we find that approximately 27 per cent of all events are classified as interior rifts i 25 per cent are rifted continental margins ii 36 per cent are within non rifted crust iii and 12 per cent iv and v remain uncertain thus over half 52 per cent of all events are associated with rifted crust although within the continental interiors i e away from continental margins non rifted crust has experienced more earthquakes than interior rifts no major change in distribution is found if only large m 6 0 earthquakes are considered the largest events m 7 0 however have occurred predominantly within rifts 50 per cent and continental margins 43 per cent intraplate seismicity is not distributed evenly instead several zones of concentrated seismicity seem to exist this is especially true for interior rifts taphrogens where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category of the four rifts taphrogens that have experienced the largest earthquakes seismicity within the kutch rift india and the east china rift system may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves the st lawrence depression canada besides being an ancient rift is also the site of a major collisional suture thus only at the reelfoot rift new madrid seismic zone nmsz usa is the presence of features associated with rifting itself the sole candidate for causing seismicity our results suggest that on a global scale the correlation of seismicity within scrs and ancient rifts has been overestimated in the past because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts we conclude that a shift in attention more towards non rifted as well as rifted crust is in order

strain weakening enables continental plate tectonics much debate exists concerning the strength distribution of the continental lithosphere how it controls lithosphere scale strain localization and hence enables plate tectonics no rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid like behaviour of plate interiors here we show that the duality of strength of the lithosphere corresponds to different stages of microstructural evolution geological constraints on lithospheric strength and large strain numerical experiments reveal that the development of layers containing weak minerals and the onset of grain boundary sliding upon grain size reduction in olivine cause strain localisation and reduce strength in the crust and subcontinental mantle respectively the positive feedback between weakening and strain localization leads to the progressive development of weak plate boundaries while plate interiors remain

jabal hafit anticline uae and oman formed by decollement folding followed by trishear fault propagation folding abstract creating three dimensional 3d models to replicate geological structures is crucial in discerning the geometry and kinematics of an orogen the jabal hafit anticline in the foreland of the al hajar mountains extends through oman and the united arab emirates and is a relatively simple and well exposed structure surprisingly previous studies of this anticline have presented conflicting interpretations regarding the strain field and the timing of deformation in this study a structural 3d geological model of the jabal hafit anticline is constructed and demonstrates that the anticlines geometry can be reproduced by a two phase model 1 flexural slip folding followed by 2 trishear fault propagation folding the trishear mode occurred due to a west dipping backthrust that propagated from the decollement to accommodate wsw directed shortening the different geometries of the various biostratigraphic layers indicate that anticline growth occurred during the late oligocene to early middle miocene this timing supports the recently established age for uplift of the al hajar mountains

the relationship between surface kinematics and deformation of the whole lithosphere the variation of mechanical properties with depth in the lithosphere determines the relationship between surface deformation and whole lithosphere deformation hence between surface deformation and whole lithosphere dynamics where viscosity or elastic strength is a continuous function with depth surface deformation can be used to constrain both force balance and rheological parameters where viscosity is discontinuous but the upper crust and mantle lithosphere have comparable maximum values surface deformation can be used to approximate force balance and rheological parameters but tradeoffs mean that estimates of stress and viscosity are effective equivalent values rather than actual values where viscosity is both discontinuous and differs by much more than an order of magnitude between the upper crust and mantle lithosphere information about both force balance and rheology are absent from the surface deformation so surface observations alone are insufficient to estimate either the dynamic or mechanical state of the lithosphere

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

taphonomic evaluation of the degree of historical representation of the archaeological bone samples in anaerobic versus aerobic environments the neolithic site of la draga banyoles spain abstract the site of la draga is located in the central part of the eastern shore of lake banyoles 172 m a s l archaeological work began in 1990 it is the only early neolithic lakeshore site in the western mediterranean currently being excavated two different occupations have been documented within a timeline of 5430 4796 cal bc an extent of about 800 m2 has been excavated out of the minimum surface area of 8000 m2 an added peculiarity is that different excavated sectors have distinct characteristics regarding their condition due to the changing water levels of the lake in historic times sector a 328 m2 is the emerged land sector sectors b and d 132 m2 and 48 m2 respectively are located in the perennial phreatic level and sector c 310 m2 is completely underwater the analysis of more than 20 000 retrieved faunal remains evidences the exploitation of at least 51 different animal species 46 wild and 5 domestic comparative taphonomic analyses performed on assemblages in the terrestrial and phreatic sectors have focused on evaluating how the different conditions at the site influence the composition and characteristics of samples both quantitatively and qualitatively emphasis is placed on the specific and anatomical variability documented in each sector the proportions of mature and immature animal bone remains and on the animal carcass integrity the estimation of the degree of historical representation of the faunal assemblages in each of the excavation sectors shows important differences between peat anaerobic and dry aerobic environments documenting significant biases in sector a these results demonstrate that the identification of taphonomic processes that operate at intrasite level and their effects are crucial data with important implications for the understanding of past social and economic dynamics

modes of continental rifting as a function of ductile strain localization in the lithospheric mantle analogue and numerical models have shown that the strength of the lithospheric mantle controls the mode of lithosphere deformation in extension the presence or absence of a high strength brittle mantle respectively leads to localized or distributed rifting however first order geophysical data question the existence of such a brittle mantle here we use 2 d finite element large strain modelling to quantify the impact of a ductile localizing mantle instead of brittle in triggering continental rifting as a novelty the mantle rheology considers the effect of grain boundary sliding during strain induced grain size reduction which may promote a significant strength drop and subsequent strain localization at low mantle temperature 700 800 c our results reveal that such ductile localizing mantle implies varying modes of continental rifting that mainly depend on both the amount of weakening in the ductile mantle and the strength of the lower ductile crust a medium to strong lower crust implies coupling between the upper crust and ductile localizing mantle yielding to narrow continental rifting in contrast a weak lower crust implies decoupling between the upper crust and ductile localizing mantle giving rise to a switch from distributed faulting at incipient strain to localized faulting at large strain ductile strain localization in the lithospheric mantle is therefore sufficient to trigger continental rifting although a critical amount of weakening is required such ductile localizing mantle provides a relevant geological and mechanical alternative to the brittle mantle it moreover provides a wider variety of modes of upper crustal faulting that are commonly observed in nature

quantitative impact of structural inheritance on present day deformation and seismicity concentration in intraplate deformation zones abstract structural inheritance i e paleo tectonic areas acting as weakened domains appear to be a key element localizing the seismicity in intraplate deformation zones however the impact of structural inheritance on the observed present day seismicity and strain rate concentration remains to be quantified in this study we quantify through 2d numerical modeling the localization and amplification factor of upper crustal strain rates induced by structural inheritance our 2d models are constrained by intraplate velocity boundary conditions and include rheology laws that accounts for inherited strain weakening in both the brittle and ductile layers of the lithosphere the role of structural inheritance is investigated for different localization of the weakened domain in the lithosphere for an average intraplate geotherm moho temperature ca 500 c brittle weakening i e inherited faults alone induces a limited amplification factor of upper crustal strain rates of ca 4 ductile weakening can increase the amplification factor to ca 7 when localized in the lower crust but has no effect when localized in the lithospheric mantle overall the amplification factors of upper crustal strain rates vary between 1 and 27 depending on the location of the weakened area in the lithosphere and on the different possible net driving forces crustal strengths amounts of weakening and geotherms these model amplification factors are in reasonable agreement with those derived from gps and seismicity data over large spatial scale several hundreds of kilometers in north america

descent of the ancient farallon slab drives localized mantle flow below the new madrid seismic zone 1 the great earthquake sequence that occurred in the central mississippi river valley during the winter of 1811 1812 is unprecedented in the historical record of seismicity within stable continental plate interiors we show using viscous flow models based on high resolution seismic tomography that the descent of the ancient farallon slab into the deep mantle beneath central north america induces a highly localized flow directly below the new madrid seismic zone nmsz this localization arises because of structural variability in the farallon slab and the low viscosity of the sub lithospheric upper mantle and it represents a heretofore unrecognized and possibly significant driving mechanism for the enigmatic intraplate seismicity

an evaluation of nitrogen porosimetry as a technique for predicting taphonomic durability in animal bone to date direct measurements of bone porosity have been used primarily to quantify the degree of diagenetic alteration qualitative zooarchaeological observations over many years have suggested that for equivalent burial conditions the bones of different taxa degrade at different rates and that even within a single skeleton systematic variation often occurs given that freedom of access of water to the internal bone surface is likely to be an important factor in controlling the rate of chemical alteration we postulate that the initial porosity of a bone may be an important factor in predicting the rate of degradation to test this we have used nitrogen porosimetry as a technique for comparing the total pore volume and size distribution of pores between a selection of anatomical elements taken from a range of modern animals commonly represented on european archaeological sites we show that the bones of modern domestic pig are on average more porous than those of other ungulates and should therefore be likely to degrade faster after burial systematic differences in porosity are also shown between different anatomical elements from a single individual and between adult and juvenile bone however we also show that porosity measurements are affected by sample storage and preparation methodology particularly freezing variations in bone porosity between different skeletal elements and taxa necessitate careful sample selection and matching in order to minimize variation we conclude that despite these restrictions direct measurement of variations in bone porosity shows good potential for contributing to a predictive model for bone diagenesis

india asia collision and the cenozoic slowdown of the indian plate implications for the forces driving plate motions the plate motion of india changed dramatically between 50 and 35 ma with the rate of convergence between india and asia dropping from 15 to 4 cm yr this change is coincident with the onset of the india asia collision and with a rearrangement of plate boundaries in the indian ocean on the basis of a simple model for the forces exerted upon the edges of the plate and the tractions on the base of the plate we perform force balance calculations for the precollision and postcollision configurations we show that the observed euler poles for the indian plate are well explained in terms of their locations and magnitudes if 1 the resistive force induced by mountain building in the himalaya tibet area is 5 6 10 12 n m 2 the net force exerted upon the indian plate by subduction zones is similar in magnitude to the ridge push force 2 5 10 12 n m and 3 basal tractions exert a resisting force that is linearly proportional to the plate velocity in the hot spot reference frame the third point implies an asthenospheric viscosity of 2 5 10 19 pa s assuming a thickness of 100 150 km synthetic euler poles show that crustal thickening in the tibetan plateau was the dominant cause of the cenozoic slowdown of the indian plate

a model of composite seismic sources for the lower rhine graben northwest europe abstract the lower rhine graben lrg straddling the border zone of belgium the netherlands and germany is an active tectonic structure in continental northwest europe it is characterized by northwest southeast oriented normal faults and moderate but rather continuous seismic activity many faults have been mapped in the lrg but so far a model of fault hierarchy or fault segmentation has been lacking in the frame of a european database of seismogenic sources we have devised a seismic source model for the lrg consisting of so called composite seismic sources each composite seismic source may encompass one or more segments but it is unlikely that a segment would extend across more than one source we distinguish 15 seismic sources based on major stepovers bifurcations gaps and important changes in strike dip direction or slip rate the sources are partitioned into one or more informal fault sections each with an associated surface trace for each source we describe the limits and the composing fault sections and present the geological arguments for their existence we have compiled all relevant data concerning the seismic source parameters required for the database putting lower and upper bounds on strike dip rake slip rate and depth and an upper bound on earthquake magnitude this source model should provide a new basis for modeling seismic hazard as well as for guiding further paleoseismic studies in the lrg online material detailed maps of the composite sources in the lower rhine graben 3d views of the fault model and a table with parameters of earthquake focal mechanisms and detailed information sheets for each composite seismic source

numerical modelling of strain localisation during extension of the continental lithosphere dipping reflectors in the upper mantle are observed on reflection seismic data and in some cases have been interpreted to represent mantle shear zones it is not clear however how these shear zones develop and under what circumstances previous attempts to model strain localisation by strain softening in the ductile regime have failed to show the development of mantle shear zones we present here results from a numerical model of lithospheric extension the model uses an elasto visco plastic rheology dependent on temperature pressure deviatoric stress and composition strain softening is incorporated into the mechanical model via a simple ad hoc strain viscosity relationship the results demonstrate that strain localisation can dominate lithospheric deformation in an extensional regime we illustrate the effects of varying the parameters which define the strain viscosity relationship on the geometry of lithospheric scale shear zones and the rift basin we also investigate the effects on shear zone development of introducing a variety of pre extension weak zones in the crust and or mantle our results suggest that if dipping reflectors observed on deep seismic data around the world are evidence of the existence of mantle shear zones there is a need to review our conceptual models of strain strength evolution during the development of continental rifts

the effect of structural density on marmot skeletal part representation in archaeological sites abstract volume bone mineral densities for two species of marmota are more similar to each other than their average is to previously published volume densities for small cervids and large bovids marmot bone density values do not correlate with frequencies of marmot bones reported by grayson journal of archaeological science 1989 16 643 652 for the white mountains of california suggesting that bone assemblage has not undergone density mediated attrition marmot bone density values are correlated with frequencies of marmot bones recovered from the salishan mesa site in washington and those specimens appear to be relatively larger and less fragmented than those from the white mountains these multiple lines of evidence suggest frequencies of salishan mesa marmot remains are the result of density mediated attrition and frequencies of white mountains marmot remains may be either the result of differential recovery or the influence of differential fragmentation on identifiability

geological interpretation and numerical modelling of salt movement in the barbastro balaguer anticline southern pyrenees abstract the barbastro balaguer salt anticline located in the south pyrenean foreland basin was characterised with seismic reflection profiles and well logs interpretation to be the result of a combination of thrusting buoyancy and differential loading mechanisms these mechanisms were responsible for the formation and the evolution of the structure from the late oligocene to the present seismic reflection interpretation indicates that alpine compressional tectonics played the major role in the early stages of the formation of the anticline a numerical model based on the finite difference involving thrusting buoyancy and differential loading mechanisms was developed and applied to the modelling of the development of the salt structure the results of our modelling suggest that buoyancy and differential loading have played an important role in the subsequent growth of the barbastro balaguer anticline

control of tectonic inheritance on continental intraplate strain rate and seismicity abstract present day deformation and seismicity of continental lithosphere are characterized by a first order dichotomy between plate boundary zones pbz and stable continental regions scr whereas the former are associated with high strain and seismicity rates the latter tend to remain un deformed except in localized regions of higher strain and seismicity commonly related to fossilized paleo pbz acting as locally weaker domains because of their low amplitudes these intraplate strain and seismicity rates are particularly difficult to measure and characterize in this study we propose a simple model to explain and quantify first order continental strain rate variations focusing on intraplate regions assuming near failure equilibrium on 1d lithosphere profiles we derive steady state strain rates driven by tectonic forces as a function of rheological models that include new strain weakening rheologies in order to simulate tectonic inheritance within this framework inherited strain weakening plays a fundamental role in allowing for and explaining strain and seismicity concentration in intraplate weak zones our model predicts strain rates in intraplate weak zones up to two to three orders of magnitude higher compared to stable cratons due to the effect of tectonic inheritance on rheology weakening these model predictions are in agreement with empirical estimations in intraplate regions and can provide a conceptual framework for characterization of scr strain and seismicity rates

analysis of continental midcrustal strain localization induced by microfracturing and reaction softening 1 low angle extensional shear zones which often characterize the brittle ductile transition of the continental crust are seen here to result from strain localization the potentially destabilizing deformation mechanism is assumed to be the progressive transformation of fractured coarse feldspar grains into white mica as observed in the east tenda shear zone alpine corsica the coupling between microfracturing and feldspar to mica reaction is coeval with strain localization that occurred in that field case at a depth close to 15 km this reaction is proposed as the main destabilizing factor responsible for the onset of localization with feldspar having a stationary dislocation creep flow stress larger than mica to test this hypothesis a rheological model is constructed based on the field observations for a mixture of three phases mica quartz and feldspar deforming at a common strain rate the phase concentrations change with time according to the feldspar to mica reaction which takes place only if feldspar grains are fractured a condition detected with the mohr coulomb criterion the tendency for the strain to localize is assessed by numerical means for the structure composed of an upper crust gliding rigidly over the lower crust which sustains an overall simple shear the onset of strain localization is defined by an increase of at least two orders of magnitude in strain rate over part of the lower crust the upper crust gliding velocity has to be increased by at least a factor of 5 for localization to occur the time lapse for this velocity change determines the depth of the shear zone 15 17 km the kinetics of the metamorphic reaction and the final amount of white mica control its width 1 4 km the time of the shear zone formation is less than half a million years