westward propagation of latitudinal asymmetry in a coupled ocean atmosphere model abstract hemispheric asymmetries of continental geometry have long been speculated to be the cause of the northern hemisphere position of the intertropical convergence zone over the central and eastern pacific it is unknown however how the effects of continental asymmetries are transmitted to and felt by the central pacific thousands of kilometers away this paper proposes a transmitter mechanism by investigating the response of a coupled ocean atmospheric model to a symmetry breaking force by the american continents the model treats land forcing implicitly as an eastern boundary condition in the absence of oceanic feedback the model response to the eastern boundary forcing is tightly trapped and confined to a small longitudinal extent off the coast whereas the climate over the interior ocean is symmetric about the equator ocean atmosphere coupling greatly enhances the transmissibility of the effects of the land forcing establishing large latitudinal asymmetry over a great zonal extent a westwar

about the role of westerly wind events in the possible development of an el nino in 2014 similarities between early 1997 and 2014 has prompted climate scientists to wonder if an el nino matching the 1997 el nino of the century could develop in 2014 until april 2014 the equatorial pacific exhibited positive heat content anomalies along with an eastward warm pool displacement similar to those found during the onset of strong el nino events yet in july 2014 the warm pool had retreated back to its climatological positions and equatorial temperature anomalies were much weaker than in mid 1997 dedicated oceanic simulations reveal that these weak interannual anomalies can be attributed to differences in westerly wind event wwe sequences in contrast with 1997 the lack of wwes from april to june significantly limited the growth of eastern pacific anomalies and the eastward warm pool displacement in 2014 with the absence of additional wwe activity prospects for a mature el nino in late 2014 are fading

rectification of the madden julian oscillation into the enso cycle an ocean general circulation model forced with idealized purely oscillating wind stresses over the western equatorial pacific similar to those observed during the madden julian oscillation mjo developed rectified low frequency anomalies in sst and zonal currents compared to a run in which the forcing was climatological the rectification in sst resulted from increased evaporation under stronger than normal winds of either sign from correlated intraseasonal oscillations in both vertical temperature gradient and upwelling speed forced by the winds and from zonal advection due to nonlinearly generated equatorial currents the net rectified signature produced by the mjo like wind stresses was sst cooling about 0 48c in the west pacific and warming about 0 18c in the central pacific tending to flatten the background zonal sst gradient it is hypothesized that in a coupled system such a pattern of sst anomalies would spawn additional westerly wind anomalies as a result of sst induced changes in the low level zonal pressure gradient this was tested in an intermediate coupled

westerly wind events in the tropical pacific 1986 95 abstract based on examination of 10 yr of 10 m winds and wind anomalies from european centre for medium range weather forecasts ecwmf analysis definitions for westerly wind events wwes of eight different types are proposed the authors construct a composite for each type of event show that a simple propagating gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event and determine the scales of each composite event by fitting the model to each composite the authors discuss the wwes that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment toga coare intensive observing period iop and show the extent to which these composite events are able to reproduce the major westerly wind features of the iop the frequency of occurrence of each type of wwe for each year of this record and by calendar month are described the authors find several types of events are negatively correlated with the annual mean troup souther

synoptic settings of westerly wind bursts the morphology of westerly wind bursts wwbs during the 1980s is investigated using 1000 mbar winds analyzed by the european center for medium range weather forecasts ecmwf the variety of synoptic situations in which wwbs occur are explored so that the dynamics of wwb generation and maintenance can be studied and so that those interested in short and long term forecasts of conditions over the equatorial pacific will have an increased knowledge of those elements associated with wwbs wwbs are identified by searching for episodes in which the zonal wind was at least 5 m s 1 over at least 10 longitude for two or more days this definition based on surface winds rather than elevated winds or wind anomalies reflects the impact wwbs have on air sea interaction processes the spatial and temporal criteria provide a synoptic scale envelope for such interactions and mitigate against erroneous analyses according to these criteria 131 distinct wwbs occurred during the 1980s a new two dimensional classification scheme has been developed the nine patterns in it describe the near surface flow during 90 of these wwbs a single cyclone or a series of cyclones in one or both hemispheres and several different types of cross equatorial flow are the major components of the patterns only 8 of the bursts were associated with concurrent cyclones in both the northern and southern hemispheres four bursts involving cross equatorial flow are subjected to further study the flow is decomposed into barotropic and baroclinic parts and into rotational and divergent baroclinic components one of the bursts was predominantly barotropic and another predominantly baroclinic the cross equatorial flow in all four cases was predominantly divergent in nature the information from these cases coupled with the typical vertical structures and small meridional length scales associated with the various synoptic patterns suggests that simple baroclinic models of circulations driven by near equatorial heating are not adequate to describe the dynamics during wwbs

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

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

the effects of slope length and slope gradient on the size distributions of loess slides field observations and simulations abstract in this study we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides to carry out this study we employ data on 275 loess slides within zhidan county central loess plateau china these data were collected in the field and supplemented by the interpretation of remote sensing images both the field observations and slope stability analysis show that loess slide size increases with the slope length slide sizes is significantly correlated with slope length showing a power law relationship in both cases however the simulation results show that slope gradient is not associated with loess slide size the main part of the link between slope gradient and slide size seen in the observations is only apparent as indicated by the strong connection between slope gradient and length statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations in addition the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation this analysis shows that slope length controls the rollover of the frequency size distribution of loess slides the scaling exponent increases with slope length

multiple flow regimes in the northern hemisphere winter part i methodology and hemispheric regimes abstract recurrent and persistent flow patterns are identified by examining multivariate probability density functions pdfs in the phase space of large scale atmospheric motions this idea is pursued systematically here in the hope of clarifying the extent to which intraseasonal variability can be described and understood in terms of multiple flow regimes bivariate pdfs of the northern hemisphere nh wintertime anomaly heights at 700 mb are examined in the present paper using a 37 year dataset the two dimensional phase plane is defined by the two leading empirical orthogonal functions eofs of the anomaly fields pdfs on this plane exhibit synoptically intriguing and statistically significant inhomogeneities on the periphery of the distribution it is shown that these inhomogeneities are due to the existence of persistent and recurrent anomaly patterns well known as dominant teleconnection patterns that is the pacific north american pna pattern its reverse and zonal and blocked phases of the

applicability of critical wedge theories to foreland belts applying critical wedge theories to foreland belts in contrast to accretionary wedges of poorly indurated sediments results in basic problems of physics one key distinction between these tectonic regimes is the enormous difference in elastic strain energy that can be stored during deformation another key distinction is that most styles of fault slip occurring in the upper continental crust involve changes of momentum in contrast with the stable sliding invoked in critical wedge theories consequently the mechanics of deformation are fundamentally different for foreland belts as compared with accretionary wedges of sediment

sequential development of selected pyrenean thrust faults new mapping structural analysis and magnetostratigraphy reveal a polyphase deformational history at the leading edge of the spanish pyrenean foreland fold and thrust belt the present structural architecture is the consequence of three discrete periods of deformation map relationships between four syntectonic units and major structures provide tight geometric and age constraints for each deformational period d1 55 to 42 ma d2 30 1 to 28 0 ma d3 27 9 to 25 8 ma most of the shortening in the area accumulated during d2 thrusting at rates which varied from 0 7 mm y 1 to 2 8 mm y 1 along strike from northwest to southeast respectively removal of d2 and d3 displacement on thrust faults restores folds formed during d1 a sequential kinematic history during which an individual structure accommodates shortening by folding tightening of the fold and subsequent truncation by thrust faulting is inferred sequential restoration of three serial cross sections demonstrates that nearly every structure active during d1 was also active during d2 distributed deformation characterizes the temporal and spatial pattern on all time scales from structures active during each individual deformational period to the long term history encompassed by the total deformation

spatial distribution analysis of landslides triggered by 2008 5 12 wenchuan earthquake china abstract the 2008 5 12 wenchuan earthquake seismic magnitude mw 7 9 according to the usgs triggered a great number of landslides a spatial database of landslides is built by interpreting the remote sensing rs data which covers 11 counties severely damaged by the earthquake with area of about 31 686 12 km2 the geological settings of the study area are detailed mapped including geologic structure and lithology the digital elevation model dem of the study area with resolution of 30 m 30 m is presented to address the topographic characteristics correlations between the occurrence of landslides with geological settings i e active faults the coseismic surface ruptures geological unit slope gradient slope elevation as well as slope aspect are analyzed using spatial modeling in gis with the aids of field investigations it can be concluded that the distance to the causative faults and slope gradient are much more important than other factors landslides are clustered distributed along the causative faults of f2 and f3 and landslides incidence are dramatically decreasing with the increasing of the distance to the causative faults the landslides incidence has an obvious increase near the active faults i e f1 landslide concentration lc landslides km2 has an obvious exponent increase with slope gradient however lc has no obvious relationship with geological unit and slope elevation the difference of lc value in each geological unit each slope elevation category maybe have been the result affected by slope gradient for each geological unit each slope elevation category and distance of each geological unit each slope elevation category to causative fault zone isoseismal map reflects the incidence of landslides in some degree and lc increases dramatically with intensity increasing almost all landslides occurred in the region above vi degree statistics result also indicates that in the near field of causative faults landslides tend to have the initial sliding direction similar to the movement of the causative faults and preliminary study shows that landslides incidence varies in different slopes with different structure and consequent slopes and obsequent slopes have a higher landslides incidence than other layered slopes

structural evolution of the cape smith thrust belt and the role of out of sequence faulting in the thickening of mountain belts out of sequence thrusting represents a mechanism capable of heterogeneous internal deformation in thrust belts and was largely responsible for internal thickening in the early proterozoic cape smith belt the south verging thrust belt is marked by a complex history of accretion internal deformation thickening induced metamorphism uplift and erosion an overall chronology for thrust belt evolution is built around the timing of thermal peak metamorphism prethermal peak deformation includes 1 initial piggyback stacking of basalt dominated thrust sheets above a basal decollement localized at the basement cover contact 2 greenschist to amphibolite grade metamorphism accompanied by development of a ductile shear zone at the base of the thrust belt and 3 out of sequence thrusting precipitating the metamorphic thermal peak both above and below these faults synthermal peak out of sequence thrusting was responsible for accretion of autochthonous crystalline basement slices and eventual abandonment of the external basal decollement postthermal peak deformation is characterized by the continued development of out of sequence thrusts which appear to young toward the hinterland north internal thickening by development of flattening cleavages or folding appears to be regionally insignificant when compared to that accomplished by the out of sequence faults this suggests that 1 an eroding and accreting thrust wedge may be able to maintain its critical shape by out of sequence thrusting and 2 this style of internal deformation is favored in belts dominated by relatively strong material e g basalt as in the cape smith belt

centrifuge modelling of thrust faulting structural variation along strike in fold thrust belts abstract the three dimensional geometry and the kinematic evolution of fold thrust structures are investigated by analog modelling using the centrifuge technique we focus on along strike structural variation and transfer of displacement between faults and folds the total horizontal shortening across the model fold thrust belts is constant yet there are systematic variations in shortening by the mechanisms of thrusting folding and layer parallel shortening these along strike changes in structural geometry and strain mechanism are manifestations of displacement transfer the model thrust faults have different amounts of thrust displacement at different points along strike the variation is accommodated by transfer of displacement to over or underlying faults or to en echelon faults by transfer of shortening into folding or by transfer of displacement into layer parallel shortening in the models it is clear that faults nucleate at points that are localized by earlier folding of competent units faults nucleated at different points along a single fold may propagate along the fold and link together to form major thrusts the thrust displacement in such cases varies from smaller values at linkage points to larger values at nucleation points the models have a stratigraphie succession like that of the central appalachian valley and ridge province after an equivalent amount of structural shortening the models exhibit structural features analogous to those of the valley and ridge the lowest competent unit equivalent to the cambro ordovician lithotectonic unit forms a large scale duplex like that of the waynesboro sheet the middle competent unit equivalent to the siluro devonian clastic units forms anticlinoria and synclinoria like those of the martinsburg sheet these structures are spatially associated with underlying culminations and depressions that reflect respectively large and small displacements on thrusts that ramp through the lowest competent unit however in the models it appears that the amplitude of buckling of the middle unit controls the amount of displacement on underlying thrusts whereas in the appalachians the structural culminations of the middle unit are interpreted to have been caused by large displacement on underlying faults

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

westerly wind bursts and their relationship with intraseasonal variations and enso part ii energetics over the western and central pacific abstract the mechanism of synoptic scale eddy development in the generation of westerly wind bursts wwbs over the western central pacific and their relationship with the el nino southern oscillation enso and the madden julian oscillation mjo were examined in the wwb occurrences barotropic structures of equatorial eddy westerlies with cyclonic disturbances were found from the surface to the upper troposphere the dominant contributions to substantial eddy kinetic energy eke were the barotropic energy conversion kmke in the lower and middle tropospheres and the conversion from eddy available potential energy peke in the upper troposphere low frequency environmental westerlies centered near the equator preceded strong zonal convergence and meridional shear resulting in the substantial kmke the activation of synoptic convection also contributed to an increase in eke through peke these energies were redistributed to the lower equatorial troposphere through energy flux convergence gke the

controls on the size and geometry of landslides insights from discrete element numerical simulations abstract we use numerical two dimensional discrete element method dem to study the controls on the size and geometry of an individual landslide this method allows us to analyze the temporal and spatial evolution of slope failure and landsliding from the intact pre failure slope to the restabilized post failure slope the size of our simulated landslides reflects the amount of disintegrated material available for sliding which is controlled by the peak strength of the slope material and to a lesser degree by the pre failure slope angle the observed size of natural landslides therefore reflects mainly the local natural material strengths we hypothesize that the observed global characteristic landslide size is a result of the limited thickness generally up to a few meters of disintegrated and weathered material that exists on hillslopes poised and ready for sliding the primary controls on the landslide geometry quantified as the ratio of their thickness to length t l prove to be the residual friction angle of the slope material and the original slope angle the t l is observed to be unchanged for a given initial slope angle and independent of the slope material peak strength or the slope height we suggest that the narrow range of observed natural t l is a result of narrow ranges of mechanical properties and initial slope geometries involved in natural slope failure

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

strong influence of westerly wind bursts on el nino diversity el nino diversity and its genesis are debated an overview of existing work along with a fuzzy clustering analysis and simulations suggest that the asymmetry irregularity and extremes of el nino result from westerly wind bursts

subseasonal atmospheric variability and el nino waveguide warming observed effects of the madden julian oscillation and westerly wind events abstractwesterly wind events wwes have previously been shown to initiate equatorial pacific waveguide warming the relationship between wwes and madden julian oscillation mjo activity as well as the role of mjo events in initiating waveguide warming is reconsidered here over the 1986 2010 period wwes are identified in observations of near surface zonal winds using an objective scheme mjo events are defined using a widely used index and 64 are identified that occur when the el nino southern oscillation enso is in its neutral state of these mjo events 43 have one or more embedded wwes and 21 do not the evolution of sea surface temperature anomaly over the equatorial pacific waveguide following the westerly surface wind phase of the mjo over the western equatorial pacific is examined waveguide warming is found for the mjo with wwe events in similar magnitudes as following the wwes not embedded in an mjo there is very little statistically significant waveguide warming following mjo events that

the role of material properties and landscape morphology on landslide size distributions abstract it has been observed that landslide size distribution shows power law scaling for large landslide areas with a roll over for landslides below a certain threshold which frequently coincides with the modal peak of the distribution the physical reasons leading to this distribution are not yet fully understood the analysis of non cumulative size distribution of two landslide inventories in the italian alps confirms the existence of a power law scaling with exponent of 2 56 0 02 and demonstrates that the roll over is not due to under sampling since it occurs at landslide sizes significantly larger than mapping resolution the control of topography on landslide size distribution is investigated by a topographic analysis using the virtual tiling method we observe a power law scaling of topography with a roll over for finer scales which is comparable with that of landslide size distribution the control of material properties on landslide size and geometry is examined through deterministic and probabilistic 2d limit equilibrium slope stability analyses incoherent materials favour shallow landslides with no limitation in size cohesive materials favour deep landslides and show a limitation for small sizes multilayered materials with depth dependent strength show a limitation for both small and large landslides the joint probability of 1 the probability that a slope with a given size and slope gradient is unstable i e failure probability from probabilistic stability analysis and 2 the probability that a slope with a given size and slope gradient exists topographic analysis allows to build synthetic size distributions which show both power law scaling and roll over for multilayered materials we obtain a scaling exponent of the power law of 2 58 0 02 we suggest that the power law scaling in landslide size distribution results in the study area from the constraint of topography and the presence of multilayered materials or depth dependent strength the roll over is an intrinsic characteristic of the size distribution due to the contribution of cohesion to slope stability

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

tropical pacific sea surface temperature anomalies el nino and equatorial westerly wind events abstract the authors examine global statistical relationships between westerly wind events wwes and sea surface temperature anomaly ssta variability using a compositing technique for the period 1986 98 the authors describe the extent to which equatorial wwes are associated with central and eastern equatorial pacific waveguide warming and with local ssta changes under the wwe their goal is to quantify the extent to which equatorial wwes are fundamental to the onset and maintenance of warm el nino southern oscillation conditions in order to understand the effect of wwes on ssta evolution they begin by examining how ssta changes in the absence of equatorial wwes they find that ssta tends toward mean climate values in the absence of equatorial wwes whether the eastern equatorial pacific has close to normal ssta or warmer than normal ssta the two equatorial wwe types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling the equatorial wwe type t

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

processes driving intraseasonal displacements of the eastern edge of the warm pool the contribution of westerly wind events we investigate the processes responsible for the intraseasonal displacements of the eastern edge of the western pacific warm pool wpee which appear to play a role in the onset and development of el nino events we use 25 years of output from an ocean general circulation model experiment that is able to accurately capture the observed displacements of the wpee sea level anomalies and upper ocean zonal currents at intraseasonal time scales in the western and central pacific ocean our results confirm that wpee displacements driven by westerly wind events wwes are largely controlled by zonal advection this paper has also two novel findings first the zonal current anomalies responsible for the wpee advection are driven primarily by local wind stress anomalies and not by intraseasonal wind forced kelvin waves as has been shown in most previous studies second we find that intraseasonal wpee fluctuations that are not related to wwes are generally caused by intraseasonal variations in net heat flux in contrast to interannual wpee displacements that are largely driven by zonal advection this study hence raises an interesting question can surface heat flux induced zonal wpee motions contribute to el nino southern oscillation evolution as wwes have been shown to be able to do

critical acceleration as a criterion in seismic landslide susceptibility assessment abstract the 2008 wenchuan earthquake in china triggered approximately 200 000 landslides this study examined a detailed landslide inventory for the event based on newmark s method the correlation between critical acceleration and landslide occurrence was analyzed for the beichuan region in sichuan province where various kinds of geohazards occurred due to the earthquake the results indicate that critical acceleration is a good and reliable criterion to assess slope stability and that slope gradient and material component are important factors influencing landslide occurrences it was found that external forces behave differently in different directions critical acceleration in horizontal direction is more important for assessing the stability of steeper slopes this knowledge will help in the understanding of the mechanism of earthquake triggered landslides and facilitate the combined use of critical acceleration and landslide distribution maps for determining peak ground acceleration in a region without abundant seismic instrument records

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

growth of the south pyrenean orogenic wedge a six step reconstruction of the south pyrenean foreland fold and thrust belt in spain delineates the topographic slope basal dtcollement angie internal deformation and thrust front advance from the early eocene until the end of contractional deformation in the late oligocene style of thrust front advance dip of the basal dtcollement slope of the upper surface and internal deformation are decoupled and not simply related internal deformation increased decreased and maintained surface slope angle at different stages from the onset to the cessation of deformation the basal dtcollement angle decreased overall suggesting translation of the thrust belt onto stronger crust with time taper angle of the pyrenean thrust wedge was fundamentally controlled by the flexural rigidity of the lower plate the relative rate of creation of structural relief in the rear versus the front of the wedge the extent of deposition of eroded material within the deforming wedge and the taper of the pretectonic stratigraphic wedge

thrust tectonics in the south central pyrenees abstract surface structural data and published stratigraphies are combined to construct two balanced and restored sections through the nogueras zone of the south central pyrenees the allochthonous nogueras zone units are interpreted as the foreland dipping margin of a major antiformal stack in the palaeozoic rocks of the pyrenean axial zone their structural evolution is summarized in a hangingwall sequence diagram this reinterpretation of the nogueras zone is incorporated into a new n s balanced and restored section from the centre of the pyrenean axial zone to the ebro basin a classical rocky mountains piggy back thrust model is employed and the resulting section is a significant departure from those previously published it is argued that gravity gliding has never been an important mechanism in the alpine pyrenees section restoration casts doubt on the correlation of the surface expression of the north pyrenean fault and the seismically detected moho step beneath it

eastern equatorial pacific response to three composite westerly wind types it has been suggested recently that episodes of westerly wind near the international date line in the western pacific tend to fall into one of four types three of the types have enough equatorial zonal wind variation to be able to induce an eastern pacific response by forcing equatorial waves in this note we examine the central and eastern pacific waveguide response to idealized representations of these three types of westerly wind episodes using a combination of linear theory and results from an ocean general circulation model the idealized westerly wind types are the c type maximum anomalies centered on the equator the n type maximum anomalies just north of the equator and the s type maximum anomalies just south of the equator the composite c type event excites equatorially trapped kelvin pulses that alter sea surface temperature in the central and eastern pacific warm anomalies caused by the c type episode have approximately equal contributions from a zonal advection of heat by the kelvin pulses and a meridional advection of heat by an altered instability wave field because the center of forcing of the s type event is displaced off of the equator the kelvin pulses excited by the s type episode have smaller amplitude than those of the c type episode even though the maximum wind anomaly is the same in the two cases the s type anomaly also excites weak rossby gravity waves that can propagate into the eastern pacific because the rossby gravity waves are dispersive their amplitude diminishes as the waves propagate into the eastern pacific the n type episode as observed in winds from the western tropical pacific is much weaker and of shorter duration than the c and s types and therefore excites only a very weak eastern pacific response although all types of westerly wind excite a local western pacific response only the c and s type events excite a significant eastern pacific response

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

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

seasonal dependence of the mjo enso relationship abstract observations of the development of recent el nino events suggest a pivotal role for the madden julian oscillation mjo previous attempts to uncover a systematic relationship between mjo activity and the el nino southern oscillation enso however have yielded conflicting results in this study the mjo enso relationship is stratified by season and the focus is on mjo activity in the equatorial western pacific the results demonstrate that mjo activity in late boreal spring leads el nino in the subsequent autumn winter for the period 1979 2005 spring is the season when mjo activity is least asymmetric with respect to the equator and displays the most sensitivity to sst variations at the eastern edge of the warm pool enhanced mjo activity in the western pacific in spring is associated with an eastward expanded warm pool and low frequency westerly surface zonal wind anomalies these sustained westerly anomalies in the western pacific are hypothesized to project favorably onto a developing el n

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

the continental collision zone south island new zealand comparison of geodynamical models and observations the south island zone of oblique continent continent convergence occurs along a 400 km long section of the modern australia pacific plate boundary zone across which about 50 km of shortening has been accommodated since about 10 ma the orogen comprises a central mountain range southern alps flanked on both sides by what are interpreted to be foreland basins two essential features that characterize the orogen are 1 the degree of denudation that accompanied deformation and 2 a fundamental structural asymmetry the architectural asymmetry of the orogen can be explained by plane strain finite element models of continental convergence incorporating mantle subduction comparison of model and orogen polarity implies that pacific plate mantle subducts the models predict two crustal scale dipping shear zones that form above the point where the pacific mantle subducts the localized one more distant from the incoming plate retro step up shear zone corresponds to the alpine fault whereas its conjugate pro step up shear zone corresponds to the distributed strain and thrusting along the eastern margin of the mountain belt parameters that modify the model boundary conditions top surface degree of denudation basal zone subduction load crust mantle velocity discontinuity subduction of lower crust mantle retreat and distributed decrease in mantle velocity and the internal strength of the crust two layer crust with moderate coupling temperature distribution strain weakening are varied in a series of numerical model calculations that establish the combination of material properties and boundary conditions that lead to different cross sectional architectures of the modeled collision zone in turn these are compared with observations about the south island orogen the calculations show how the style and extent of deformation across the whole orogen depend on the rheological properties of the crustal layer and on the balance between its internal strength and the combined effects of the boundary and gravitational stresses north to south along strike differences in the width and two dimensional architecture of the orogen simulated in the experiments by varying the model parameters can be explained by a combination of southward increases in preconvergent crustal thickness geothermal gradient convergence and potentially subduction retreat with the added possibility of a southward decrease in the component of lower crustal subduction

modulation of westerly wind bursts by sea surface temperature a semistochastic feedback for enso abstract westerly wind bursts wwbs in the equatorial pacific are known to play a significant role in the development of el nino events they have typically been treated as a purely stochastic external forcing of enso recent observations however show that wwb characteristics depend upon the large scale sst field the consequences of such a wwb modulation by sst are examined using an ocean general circulation model coupled to a statistical atmosphere model i e a hybrid coupled model an explicit wwb component is added to the model with guidance from a 23 yr observational record the wwb parameterization scheme is constructed such that the likelihood of wwb occurrence increases as the western pacific warm pool extends a semistochastic formulation which has both deterministic and stochastic elements the location of the wwbs is parameterized to migrate with the edge of the warm pool it is found that modulation of wwbs by sst strongly affects the characteristics of enso in particular coupled fe

the march 1997 westerly wind event and the onset of the 1997 98 el nino understanding the role of the atmospheric response in a previous study the effect of the march 1997 westerly wind event wwe on the evolution of the tropical pacific ocean was studied using an ocean general circulation model gcm the response was characterized by i a cooling of the far western pacific 0 88c ii a rapid eastward displacement of the warm pool 2000 km in a month and iii a weak warming of the central eastern pacific along the path of the oceanic kelvin wave excited by the wwe 0 58c in this study the atmospheric response to these aspects of the sea surface temperature sst response are investigated using an atmospheric gcm forced with the sst anomalies from the ocean only experiments the results have demonstrated that the three aspects of the sst anomaly field generated by the wwe

the mechanical paradox of large overthrusts the mechanical paradox of large overthrusts originates with a fallacious assumption in the conceptual model upon which mechanical analyses of overthrust faulting have been based the notion that the maximum width of a sheet of rock that may be displaced along an overthrust fault can be determined by using the mohr coulomb failure criterion to compare the strength of the rocks with the stress required to overcome the total frictional resistance to slip and the total cohesion or adhesion over the entire fault surface tacitly assumes that slip is initiated and occurs simultaneously over the entire fault surface this unstated and untenable assumption which is incompatible with what is known about real faults is the real explanation for the mechanical paradox a realistic model for overthrust faulting must be compatible with the nature of real overthrust faults and particularly with the way in which displacements including earthquake displacements occur on real faults most large overthrusts are discrete shear surfaces within a coherent mass of rock that is physically continuous around their ends total displacement clearly varies from place to place over these discrete shear surfaces and moreover must be the cumulative result of many relatively small incremental displacements that also varied from place to place over the finite part of the fault surface on which they occurred each increment began as a local shear failure and propagated along the fault as a smeared out somigliana dislocation at a velocity that was small considering the time required for propagation over the total area of the fault during any individual displacement event whether a megathrust earthquake or a creep event only a small part of the fault surface was in relative motion at any one time fault displacements may appear to occur simultaneously across laboratory specimens that are very small relative to the velocity of propagation of displacement because the transit time is so short when the linear scale is expanded over six orders of magnitude to encompass an entire surface of a large overthrust fault however the transit time is much longer because the velocity of propagation is very small relative to the area of the fault surface and the displacement clearly involves only a very small part of the fault surface at any one time the shape and size of overthrust faults result from the propagation of dislocations and this process is controlled by the strength heterogeneity and anisotropy of the rock mass as well as by variations in the regional stress field but not by the frictional resistance to sliding integrated over the entire fault surface

source characteristics of long runout rock avalanches triggered by the 2008 wenchuan earthquake china the may 12 2008 wenchuan china earthquake which measured m w 8 3 according to chinese earthquake administration cea m w 7 9 according to the usgs directly triggered many landslides which caused about 20 000 deaths a quarter of the total rock avalanches were among the most destructive landslides triggered by this seismic event and have killed more people than any other type of landslide in this earthquake the donghekou rock avalanche one example of a catastrophic avalanche triggered by the wenchuan earthquake occurred in qingchuan and buried one primary school and 184 houses resulting in more than 780 deaths and in addition caused the formation of two landslide dams which formed barrier lakes combining aerial images resolution of 0 5 m with field investigations this paper lists some parameters of 66 cases in one table and details source characteristics of six typical cases it has been found that most of the long runout rock avalanches have source areas with high relief and steep inclination causing the debris in the travel courses to accelerate there was also a large amount of saturated holocene age loose deposits formed by a river or gully that existed in the travel courses comparison studies indicate that saturated holocene loose deposits in the travel courses could be the most important factor for the causes of the long runout characteristic of the rock avalanches especially when they traveled over gentle or even flat ground surfaces furthermore the relationships among the relief slope gradient runout and covered area are investigated and a threshold line for predicting the maximum horizontal runout distance under certain change in elevation is presented c 2010 elsevier ltd all rights reserved

effects of westerly wind bursts on el nino a new perspective daily observations from 1971 to 2010 reveal that every el nino during this period was accompanied by congregated westerly wind bursts suggesting a close relationship of these bursts with both cold tongue and warm pool el nino events with the addition of burst like multiplicative noise to an intermediate ocean atmosphere coupled model it is shown that westerly wind bursts by generating eastward equatorial surface currents and downwelling kelvin waves could be responsible for the existence of the warm pool el nino and for the irregularity and extremes of the cold tongue el nino whether these bursts give rise to one type of el nino or the other depends on the timing of their occurrence relative to the phase of the recharge discharge cycle of the equatorial upper ocean heat content

mechanics of the salt range potwar plateau pakistan a fold and thrust belt underlain by evaporites the salt range and potwar plateau are part of the active foreland fold and thrust belt of the himalaya in northern pakistan in this region the distance from the main boundary thrust mbt to the front of the fold and thrust belt is very wide 100 150 km because a thick evaporite sequence forms the zone of decollement recent studies have combined seismic reflection profiles petroleum exploration wells bouguer gravity anomalies and surface geology to construct cross sections in the eastern central and western salt range potwar plateau areas in this study the sections are compared with a model that considers the mechanics of a fold and thrust belt to be analogous to that of a wedge of snow or soil pushed in front of a bulldozer chapple 1978 davis et al 1983 dahlen et al 1984 dahlen 1984 models which include the effects of evaporites at the base chapple 1978 davis and engelder 1985 suggest that these thrust belts will have 1 narrow 1 cross sectional tapers 2 larger widths than areas not underlain by evaporites 3 symmetrical structures and 4 changes in deformational style at the edge of the evaporite basin the section across the eastern potwar plateau most closely resembles this latter model having 1 a taper of 0 8 0 1 2 a width of 100 150 km 3 thrust faults that verge both to the north and south and 4 structures rotated 30 counterclockwise with respect to the salt range from the observed taper and pore fluid pressures of the eastern potwar plateau estimates of the values for the yield strength of the evaporites o and the coefficient of internal friction of the overlying wedge are calculated as o 1 33 1 50 mpa and 0 95 1 04 which are then applied to the other cross sections in the central and western sections a basement uplift the sargodha high interferes with the front of the fold and thrust belt this feature causes the ramping of the salt range thrust and produces a relatively steep basement slope 2 4 beneath the potwar plateau this dip in the presence of the weak evaporite decollement is sufficient to provide critical taper no topographic slope is necessary and the thrust wedge of the southern potwar plateau is pushed over the decollement without significant internal deformation the northern potwar plateau is strongly folded and faulted yet the topographic slope remains flat although the deformation suggests that evaporites are not present there the observed taper in the northern potwar plateau is best fitted by the model with evaporites at the decollement combining this with published paleomagnetic and geologic constraints a model for the evolution of the northern potwar plateau suggests that the area deformed as a steeply tapered 3 5 5 5 thrust wedge until approximately 2 million years ago when the southward propagating decollement encountered the evaporites between 2 ma and the present the northern potwar plateau has been pushed along the salt decollement without deformation and erosion has reduced its original steep topographic slope to a nearly level surface

enso asymmetry in cmip5 models abstractthe el nino la nina asymmetry is evaluated in 14 coupled models from phase 5 of the coupled model intercomparison project cmip5 the results show that an underestimate of enso asymmetry a common problem noted in cmip3 models remains a common problem in cmip5 coupled models the weaker enso asymmetry in the models primarily results from a weaker sst warm anomaly over the eastern pacific and a westward shift of the center of the anomaly in contrast sst anomalies for the la nina phase are close to observations corresponding atmospheric model intercomparison project amip runs are analyzed to understand the causes of the underestimate of enso asymmetry in coupled models the analysis reveals that during the warm phase precipitation anomalies are weaker over the eastern pacific and westerly wind anomalies are confined more to the west in most models the time mean zonal winds are stronger over the equatorial central and eastern pacific for most models wind forced ocean gcm experiments suggest

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

triggering of el nino by westerly wind events in a coupled general circulation model two ten members ensemble experiments using a coupled ocean atmosphere general circulation model are performed to study the dynamical response to a strong westerly wind event wwe when the tropical pacific has initial conditions favourable to the development of a warm event in the reference ensemble cref no wind perturbation is introduced whereas a strong westerly wind event anomaly is introduced in boreal winter over the western pacific in the perturbed ensemble cwwe our results demonstrate that an intense wwe is capable of establishing the conditions under which a strong el nino event can occur first it generates a strong downwelling kelvin wave that generates a positive sea surface temperature sst anomaly in the central eastern pacific amplified through a coupled ocean atmosphere interaction this anomaly can be as large as 2 5 c 60 days after the wwe secondly this wwe also initiates an eastward displacement of the warm pool that promotes the occurrence of subsequent wwes in the following months these events reinforce the initial warming through the generation of additional kelvin waves and generate intense surface jets at the eastern edge of the warm pool that act to further shift warm waters eastward the use of a ten members ensemble however reveals substantial differences in the coupled response to a wwe whereas four members of cwwe ensemble develop into intense el nino warming as described above four others display a moderate warming and two remains in neutral conditions this diversity between the members appears to be due to the internal atmospheric variability during and following the inserted wwe in the four moderate warm cases the warm pool is initially shifted eastward following the inserted wwe but the subsequent weak wwe activity when compared to the strong warming cases prevents to further shift the warm pool eastwards the seasonal strengthening of trade winds in june july can therefore act to shift warm waters back into the western pacific reducing the central eastern pacific warming this strong sensitivity of the coupled response to wwes may therefore limit the predictability of el nino events as the high frequency wind variability over the warm pool region remains largely unpredictable even at short time lead

kinematic history of the meade thrust based on provenance of the bechler conglomerate at red mountain idaho sevier thrust belt with up to 45 km of slip the meade thrust fault in southeastern idaho is one of the major thrusts in the sevier thrust belt yet its age of displacement has remained enigmatic because of the lack of a derivative synorogenic deposit we propose that the synorogenic conglomerate produced by initial meade thrusting crops out on red mountain in southeastern idaho 1 5 km east of the present trace of the meade thrust this conglomerate historically has been considered part of the ephraim formation of the lower cretaceous gannett group but we suggest that it is a conglomeratic facies of the bechler formation localized to the area of red mountain regional stratigraphic considerations and paleontological dates from underlying and overlying strata indicate that the bechler conglomerate facies bcf is aptian in age the bcf is 850 m thick and consists of pebble to boulder conglomerate sandstone and mudrock deposited by fluvial and mass flow processes on medial to distal parts of an alluvial fan paleocurrent data indicate an eastward fan shaped dispersal pattern the bcf contains clasts of micritic limestone chert pebble conglomerate and cherty litharenite that were derived from the ephraim formation in addition the conglomerate contains abundant clasts of ordovician carboniferous and lower mesozoic rocks that crop out on both the meade thrust sheet and the paris thrust sheet 25 30 km to the west the base of the bcf is marked by a local 27 angular unconformity on top of the ephraim formation the bcf contains intraformational progressively rotated angular unconformities internal growth folds and minor dip discontinuities that were produced by simultaneous folding and sediment accumulation on the proximal footwall of the meade thrust provenance modeling indicates that the bcf was derived from mesozoic strata that were exposed along the frontal part of the meade thrust sheet and from paleozoic strata that were coevally exposed in the hindward located paris thrust sheet topography on the paris sheet was rejuvenated as it was carried passively over a major ramp in the meade thrust provenance and structural data are combined to produce an incremental bulk rock retrodeformation of initial meade displacement clasts of jurassic twin creek limestone with pressure solution cleavage in the lower part of the bcf indicate that an episode of layer parallel shortening occurred in the meade hanging wall prior to meade displacement this may have been related to emplacement of the paris thrust sheet the bcf recorded 6 km of initial meade related shortening by thrust slip and fault propagation folding during aptian time illite crystallinity systematic fracture sets in the ephraim formation and bcf finite strain in meade footwall and hanging wall rocks and thermal models by previous workers indicate that the meade thrust sheet ultimately overrode the bcf and other footwall rocks probably during albian cenomanian time the bcf and the meade thrust were folded during slip on thrust faults related to the northern crawford thrust during coniacian time a revised interpretation of gannett group provenance throughout the thrust belt suggests that the ephraim formation was derived from both the paris thrust sheet and an older hindward located thrust sheet the bechler was derived from the meade and paris sheets

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

influence of inherited taper on structural variability and conglomerate distribution cordilleran fold and thrust belt western united states north south changes in thickness of the prethrust stratigraphy of the north american cordillera within the united states controlled kinematic development of the late mesozoic sevier fold and thrust belt variation in stratigraphic thickness determined the initial slope o of the basal decollement beneath the thrust wedge as predicted by critical wedge theory segments of the sevier thrust belt with initially thick precambrian and paleozoic stratigraphic sections are structurally simple and are composed of few thrust sheets segments with thin prethrust stratigraphy and comparably low values of o are intensely imbricated the difference in structural style resulted because wedge segments with higher values of o required less internal deformation to build and maintain the critical taper required for thrust wedge advance transverse structural zones across which kinematic style differed formed at the terminations of thrust belt segments and controlled the locations of long lived antecedent drainage systems that transported gravel to the foreland therefore along strike changes in prethrust stratigraphic thickness resulted in an observed disjunct distribution of conglomerate in synorogenic deposits of the thrust wedge and foreland basin

dynamic analysis of a slope failure from the 6 august 1979 coyote lake california earthquake abstract the coyote lake california earthquake of 6 august 1979 m l 5 7 provided a rare opportunity to perform a dynamic numerical analysis of a seismically induced slope failure using actual strong motion records the earthquake displaced a preexisting slump on the northeast shore of lake anderson and formed a fissure 20 m long offsets of 9 mm vertically and 18 mm horizontally were measured across the fissure the slump is 9 km northwest of the located epicenter but within 100 m of the mapped trace of the calaveras fault two strong motion records were written in the vicinity of the slump coyote creek 5 km to the southeast and gilroy 6 15 km to the southeast these records combined with field measurements of the slope estimates of the material properties and a dynamic numerical model based on the newmark analysis of seismic slope stability to calculate a predicted displacement for the landslide a displacement of 27 mm calculated using the n50 e component of the gilroy 6 record is in excellent agreement with the displacement measured in the field 21 mm however displacements of only 0 12 mm calculated using the 250 component of the coyote creek strong motion record reflect significant local variations in seismic shaking intensity because strong motion records and slope failures rarely coincide this landslide provides an important test case for our understanding of the dynamics of seismically induced landslides as well as a warning that local seismologic variations need to be considered in any design applications

landward vergence in accretionary prisms the role of the backstop and thermal history the accretionary histories recorded along the convergent margins in southwest alaska and southwest japan are punctuated by two anomalous events near trench magmatism closely associated in time and space with landward structural vergence in both areas the near trench magmatism is believed to be related to the subduction of an active spreading center it is postulated that these anomalous thermal events caused the backstop i e mechanical boundary within the prism to be reoriented to a seaward instead of a landward dip this seaward dipping backstop resulted in the development of landward verging structures for the only time in the almost 100 m y history of these two margins a modern analog may be the washington convergent margin these examples illustrate the potential importance of thermal history and the dip of the backstop in controlling the style of accretion in submarine wedges

importance of background seasonality over the eastern equatorial pacific in a coupled atmosphere ocean response to westerly wind events coupled atmosphere ocean response to westerly wind events wwes which sometimes trigger el ninos was investigated using a coupled general circulation model to clarify its dependence on the timing and location of wwes twelve sets of 20 member ensembles were made with an idealized single wwe imposed in different months from january to july and at different longitudes from 160 circ e to 160 circ w the initial ocean states are set to be near neutral to el nino la nina so that the lagged response to wwes can be isolated the results show that sea surface temperature sst in the nino3 4 region increases largely and persistently favorable for el nino growth when a wwe is imposed in may whereas a wwe in march increases sst only in the easternmost pacific in both cases an oceanic kelvin wave propagates eastward to warm the eastern pacific when forced by the wwe in may a positive nino3 4 sst anomaly appears in boreal summer according to the seasonal outcrop of the equatorial thermocline and it can strongly interact with seasonally active tropical rain belt to amplify the sst response further a favorable combination of timing and location that maximize the impact of wwes on el ninos in the subsequent winter is suggested albeit its relevance to nature should severely be tested another experiment with initial ocean states in el nino la nina years showed that the wwes in may are efficient to amplify el nino similar to the neutral case but are not efficient to suppress la nina

the relationship between the slope angle and the landslide size derived from limit equilibrium simulations abstract katz et al 2014 carried out a study of controls on the size and geometry of landslides using two dimensional discrete element numerical simulations one of their conclusions is that in addition to the peak strength of the slope material the initial slope angle is another factor that controls the amount of material available for landslides thus the size of the resultant landslide it means that in steeper slopes more material disintegrates for a given material strength and consequently the produced landslide is larger however in our studies based on limit equilibrium simulations the sliding mass volume decreases with the increasing slope angle for a given material strength just contrary to the result of katz et al one possible explanation is that when the slope angle in our model increases the geometry of the potential critical slip surface changes leading to a decrease of the amount of material available for potential sliding that compensates the increasing gravity effect owing to the enlargement of the slope angle it suggests that there exist different controls of the slope angle on the landslide size for given material strength