mantle reflections beneath the montana great plains on consortium for continental reflection profiling seismic reflection data a systematic search for reflections from the upper mantle has been carried out on 2000 km of consortium for continental reflection profiling seismic reflection data from 14 different sites across the united states the general observation from these data is the striking contrast between the generally pervasive reflectivity of the crust and the relative lack of coherent reflectivity in the upper mantle a contrast that cannot always be attributed to lack of signal penetration in order to image more of the upper mantle section on the seismic data seismic field files were increased from 16 to 28 s two way travel time by extended correlation processing while the results reveal an upper mantle generally devoid of laterally continuous coherent energy pronounced local reflections called here the lonesome lake complex are observed at upper mantle travel times beneath the montana plains reflections at mantle travel times do not ensure mantle reflectors as other mechanisms operating at shallower levels in the crust may be responsible for the observed reflections however multiple reflections and converted waves from the crust are unlikely explanations for the lonesome lake complex although energy from outside the plane of profile cannot be ruled out circumstantial evidence suggests that these reflections are likely due to intramantle heterogeneity the lonesome lake complex joins examples of upper mantle reflectivity observed on other deep seismic data worldwide in establishing the mantle as an productive target for future deep seismic surveys

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

morphological and morphometric approach to the study of the structural arrangement of northeastern abruzzo central italy abstract the morphotectonic research at the dipartimento di scienze della terra of the universita di roma la sapienza aims to define the role of tectonics and neotectonics in the morphological evolution of central italy in this context the relationships between morphology and tectonics have been investigated in an area of northern abruzzo extending from the apennine chain to the adriatic sea morphological and morphometric analyses carried out show that the geomorphological evolution of the study area was strongly affected by tectonics especially recently the most recent extensional tectonics intersect the previous compressive structures overthrust reverse faults folds strike slip faults determining the structural arrangement characterized by uplifted and downthrown blocks morphological analysis shows that extentional tectonics occurred with the following alignments nw se nnw sse ne sw ene wsw n s and e w the spatial variability of amplitude of relief values corroborated the observations obtained from previous analyses in particular the existence of different blocks differentially uplifted along the alignments mentioned above finally data obtained through the statistical analysis of preferred stream orientations confirm the previous considerations showing that the same tectonic directions markedly influenced the drainage network development streams of lower order preferentially follow the n s and e w directions which suggests that these tectonic trends were active until very recent times at least up to the late pleistocene the results obtained testify both to the effectiveness of the methodological approach and the likelihood of the proposed morphotectonic arrangement of the study area

fluvial origin of the valley system in northern victoria land antarctica from quantitative geomorphic analysis a network of sinuous valleys with typical dendritic pattern characterizes northern victoria land nvl in antarctica subparallel to parallel and angular to rectangular patterns are also present quantitative geomorphic analysis of the valley network has been carried out utilizing gis spatial analysis while drainage densities and drainage frequencies show low values segments of the nvl valley network are substantially well organized as indicated by bifurcation ratio r b and direct bifurcation ratio r bd parameters all basins faithfully adhere to horton s laws of drainage network composition quantitative geomorphic analysis suggests that the valley system can be ascribed to fl uvial origin and that consequently a morphoclimatic system completely different from that of present day must have driven its carving the resulting data provide indications about the origin of the valley network and this invaluable information can be used for the reconstruction of earlier phases of glacial history and climatic and tectonic evolution of this signifi cant antarctic region fluvial erosion enhanced the denudation of the transantarctic mountains from at least 55 ma to at least the eocene oligocene boundary ca 34 ma fluvial basins adapted to the tectonic structure following the main regional fault systems a well developed alpine topography postdates the fl uvial morphology temperate glaciers were responsible for denudation until the late miocene parasitic glaciers presently mantle the previously sculpted topography present day glacial erosion is negligible and denudation has been exceedingly slow since 7 5 ma

morphometric and landsliding analyses in chain domain the roccella basin ne sicily italy the dynamic interaction of endogenic and exogenic processes in active geodynamic context leads to the deterioration of the physico mechanical characteristics of the rocks inducing slopes instability in such context the morphometric parameters and the analysis of landslide distribution contribute to appraise the evolutive state of hydrographic basins the aim of the study is the morphometric characterization of the roccella torrent basin rtb located in south italy landsliding and tectonic structure dynamically interact with the drainage pattern that records these effects and permits the definition of the evolutive geomorphic stage of the basin the air photograph investigation and field surveys permitted to draw the main geomorphic features the drainage pattern of the rtb to calculate the morphometric parameters and to delimit the landslides bodies detailed analysis about the landslide distribution within a test site 17 km2 wide were carried out to elaborate indicative indexes of the landslides type and to single out the lithotypes that are more involved in slope instability phenomena the morphometric parameters indicate the rejuvenation state within the rtb where the stream reaches show the effects of increased energy relief in agreement with the geological settings of this sector of the apennine maghrebian chain

analytical study of an isotropic viscoplastic sea ice model in idealized configurations abstractanalytic solutions of a mechanical sea ice model are computed in idealized configurations they are then used to study the properties of this model it classically assumes that the ice behaves at large scale as an isotropic viscoplastic medium the plastic regime is characterized by a mohr coulomb yield curve the flow rule corresponds to the one used in granular mediums and depends on a parameter that characterizes the expansion properties of the medium using simple model configurations this study first shows that a sliding of the ice along the coast must be permitted otherwise the model generally has no solution when the plastic regime is active this study then shows that the viscous regime is reached only if the stress remains nearly uniform over a large area for a stress having no particular properties the plastic regime acts everywhere in this case the compressive stress may reach the maximum value allowed by the model close to the coastline the extension of the domain where the c

geomorphological response of fluvial and coastal terraces to quaternary tectonics and climate as revealed by geostatistical topographic analysis geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces this work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the late quaternary we chose the major valleys of the adriatic foothills central italy affected since late miocene by a differential tectonic uplift which is still active in particular i we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the metauro river and cesano river mouths ii we performed correlations between the height distribution of the alluvial terrace sequences and the quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the metauro cesano misa and esino rivers the obtained averaged incision rates have been interpreted also in the light of the stream length gradient index sl index steepness index ks and concavity index as proxies of the stream power per unit length results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers in particular we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the metauro and cesano rivers already recognized in previous works through sedimentological morphostratigraphic and chronological data moreover we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late quaternary glacial periods despite the slope area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration we observed some space and time variability of averaged incision rates for adjacent valleys mainly explained by physiographic configuration and dynamics of drainage network copyright 2011 john wiley sons ltd

variability of sea ice simulations assessed with rgps kinematics 1 sea ice drift and deformation from coupled ice ocean models are compared with high resolution ice motion from the radarsat geophysical processor system rgps in contrast to buoy drift the density and extent of the rgps coverage allows a more extensive assessment and understanding of model simulations at spatial scales from 10 km to near basin scales and from days to seasonal timescales this work illustrates the strengths of the rgps data set as a basis for examining model ice drift and its gradients as it is not our intent to assess relative performance we have selected four models with a range of attributes and grid resolution model fields are examined in terms of ice drift export deformation deformation related ice production and spatial deformation patterns even though the models are capable of reproducing large scale drift patterns variability among model behavior is high when compared to the rgps kinematics the characteristics shared by the models are 1 ice drift along coastal alaska and siberia is slower 2 the skill in explaining the time series of regional divergence of the ice cover is poor and 3 the deformation related volume production is consistently lower attribution of some of these features to specific causes is beyond our current scope because of the complex interplay between model processes parameters and forcing the present work suggests that high resolution ice drift observations like those from the rgps would be essential for future model developments improvements intercomparisons and especially for evaluation of the small scale behavior of models with finer grid spacing

morphostructural elements of central eastern abruzzi contributions to the study of the role of tectonics on the morphogenesis of the apennine chain abstract the relief features of the apennine chain have been developed in a complex geomorphological and geological evolution from neogene to quaternary in order to define regional geomorphological characteristics of the central and eastern part of the abruzzi region central italy between the fucino plane and the adriatic coast a schematic map of morphostructural elements structural landforms and erosional landforms was constructed the results point out the clear coherence of present landforms with the tectonic framework in the abruzzi area in the chain area exhumed thrust ridges and faulted homocline ridges are present generally nw se nnw sse n s separated by tectonic valleys fault line valleys tectonic basins and tectonic karstic basins partially filled up with continental deposits in the piedmont periadriatic area the most important morphological elements are represented by homocline relief gently ne dipping mesa relief dip stream valleys sw ne and alluvial plains the latter grade eastwards towards the coastal plain

contrasts in sea ice deformation and production in the arctic seasonal and perennial ice zones 1 four years 1997 2000 of radarsat geophysical processor system rgps data are used to contrast the sea ice deformation and production regionally and in the seasonal siz and perennial piz ice zones ice production is of seasonal ice in openings during the winter three day estimates of these quantities are provided within lagrangian elements initially 10 km on a side a distinct seasonal cycle is seen in both zones with these estimates highest in the late fall and with seasonal minimums in the midwinter regional divergence over the winter could be up to 30 spatially the highest deformation is seen in the siz north of coastal alaska both ice deformation and production are higher in the siz deformation related ice production in the siz 0 5 m is 1 5 2 3 times that of the piz 0 3 m this is connected to ice strength and thickness atmospheric forcing and boundary layer structure contribute to only the seasonal and interannual variability seasonal ice growth in ice fractures accounts for 25 40 of the total ice production of the arctic ocean uncertainties in these estimates are discussed by itself this deformation ice production relationship could be considered a negative feedback when thickness is perturbed however the overall effect on ice production in the face of increasing seasonal and thinner weaker ice coverage could be modified by local destabilization of the water column promoting overturning of warmer water due to increased brine rejection and the upwelling of the pynocline associated with increased occurrence of large shear motion in sea ice divergence is shown to be negligibly correlated to cyclonic motion in summer and winter in both ice zones

phase change and thermal subsidence of the williston basin summary a mechanism of subsidence for the williston basin is proposed and tested the mechanism combines cooling and thermal contraction of the lithosphere with a phase transformation in the lower crust the cooling and the phase boundary movement following a sudden change in the thermal boundary condition at the base of the lithosphere are calculated isostatic adjustments and sea level variations are included to determine subsidence and sediment accumulation at the basin s centre which are compared with the data the subsidence record could not be explained by temperature boundary conditions the calculations show that 1 the heat flow boundary condition explains the long duration more than 350 myrs of subsidence of the williston basin and 2 the delay of the phase change subsidence about 40myrs explains an acceleration of subsidence in the early stages of the basin s evolution when isostatic adjustments and the effect of sea level variations are included the calculated sediment accumulation history fits well the sediment record of the williston basin

active tectonics of ne gujarat india by morphometric and morphostructural studies of vatrak river basin abstract landscape owes its shape to the combination of tectonic and climatic forces differential displacement of land by tectonic processes changes the elevation of earth s surface locally and in turn affects the rate of geomorphic processes which are altitude dependent the tectonic and geomorphic processes are very tightly coupled and their results are intertwined to extract the tectonic signal the numerical modelling of the landscape of the vatrak river basin part of which falls in the northern part of the gujarat alluvial plains of western india has been undertaken applying morphometric and morphostructural approach the study helped in understanding the role of tectonic elements in the evolution of the basin demarcation of geomorphic indicators of active tectonics which include the analyses of asymmetry factor valley floor ratio gradient basin elongation ratio long profile and related parameters pseudo hypsometric integral drainage basin asymmetry drainage pattern analysis and azimuthal distribution of stream channels have been performed for each drainage network and associated basin the morphological field evidence of tectonics combined with the results of morphometric analysis has been used to obtain information about the orientation of tectonic elements and the possible reconstruction of their activity in recent times the analyses indicate eastward tilting of the drainage systems strong asymmetry in some reaches pronounced elongation of certain tributaries long profiles indicating base level lowering poor organisation of the hydrographic network and close alignment between lower order streams and active faults all these analyses point towards the active tectonism in the area data obtained through the statistical analysis of preferred stream orientations confirm that the old tectonic directions markedly influenced the drainage network development of the older order streams whereas streams of lower order which preferentially follow the n s and ne sw directions suggest that these tectonic trends were active until very recent times

anisotropic internal thermal stress in sea ice from the canadian arctic archipelago results from an ice stress buoy deployed near the center of a multi year floe in the viscount melville sound of the canadian arctic archipelago between 10 october 2010 and 17 august 2011 are presented the position record indicates the landlocked season was approximately 5 months from 18 january to 22 june when the sea ice was fast to melville island and victoria island thermal stresses ranging from 84 to 66 kpa dominate the internal stress record with only a few dynamic stress events 50 kpa recorded before the landlocked season intriguingly the thermal stresses are isotropic before the landlocked ice onset and anisotropic during the landlocked season two possible causes to explain anisotropy in thermal stresses are considered preferred c axis alignment of the ice crystal and land confinement associated with the nearby coastline the orientation of the principal stresses indicates that land confinement is responsible for the anisotropy the stress record also clearly shows the presence of residual compressive stresses at the melt onset suggesting a viscous creep relaxation time constant of several days finally results show an interesting reversal in the sign of the correlation from negative to positive between surface air temperature and thermal stress after the onset of surface melt we attribute this to the onset of water infiltration within sea ice after which colder night temperature leads to refreezing and compressive stresses to the best of the authors knowledge this is the first time that anisotropic thermal stresses have been reported in sea ice

evaluation of high resolution sea ice models on the basis of statistical and scaling properties of arctic sea ice drift and deformation sea ice drift and deformation from models are evaluated on the basis of statistical and scaling properties these properties are derived from two observation data sets the radarsat geophysical processor system rgps and buoy trajectories from the international arctic buoy program iabp two simulations obtained with the louvain la neuve ice model lim coupled to a high resolution ocean model and a simulation obtained with the los alamos sea ice model cice were analyzed model ice drift compares well with observations in terms of large scale velocity field and distributions of velocity fluctuations although a significant bias on the mean ice speed is noted on the other hand the statistical properties of ice deformation are not well simulated by the models 1 the distributions of strain rates are incorrect rgps distributions of strain rates are power law tailed i e exhibit wild randomness whereas models distributions remain in the gaussian attraction basin i e exhibit mild randomness 2 the models are unable to reproduce the spatial and temporal correlations of the deformation fields in the observations ice deformation follows spatial and temporal scaling laws that express the heterogeneity and the intermittency of deformation these relations do not appear in simulated ice deformation mean deformation in models is almost scale independent the statistical properties of ice deformation are a signature of the ice mechanical behavior the present work therefore suggests that the mechanical framework currently used by models is inappropriate a different modeling framework based on elastic interactions could improve the representation of the statistical and scaling properties of ice deformation

the architecture of an anisotropic elastic plastic sea ice mechanics constitutive law the architecture for a new large scale anisotropic constitutive law intended for use in a sea ice dynamics model is presented here this architecture accounts directly for refrozen lead systems in the pack ice strength with an anisotropic failure surface and in the ice thickness distribution with an oriented thickness distribution the lower limit 5 km of the model resolution is controlled by the fracture spacing of old thicker ice and the maximum lead width the upper limit of the model resolution 100 km is controlled by curvature in the lead directions and variations in the lead width these in turn are controlled by the variations in internal ice stress due to driving forces winds and currents which set the time resolution this architecture features abrupt changes in the failure surface and the associated flow rule that cannot be averaged over a time step in addition the principal stress normal to a new lead must be zero as it opens this model has subscale simulations that allow for the inclusion of phenomena such as ridging rafting buckling and fracture on the behavior of the ice with this new ice constitutive law it is possible to test directly the ice failure strength plastic flow rule and ice thickness distribution the data most useful for this testing come from ice stress and position buoys together with synthetic aperture radar deformation data some data comparisons have already been made

cocorp profiles from the montana plains the archean cratonic crust and a lower crustal anomaly beneath the williston basin new cocorp deep seismic reflection profiles from the montana plains between the rocky mountains and the williston basin image the crystalline continental basement of the archean wyoming cratonic province on a regional scale the crust is in general reflective throughout its entire thickness west of the williston basin the crust mantle boundary is at the base of the reflective zone and is not marked by the presence of any distinctive reflections the lowermost crust beneath the williston basin is in contrast characterized by a prominent laterally extensive zone of relatively high amplitude reflections if as the spatial correlation suggest the anomalously reflective lower crustal zone is causally related to the subsidence of the basin then the data place constraints in addition to those of the sedimentary record on physical models for the evolution of the williston basin

morphotectonic evolution of the adriatic piedmont of the apennines an advancement in the knowledge of the marche abruzzo border area abstract this study focuses on the morphotectonic evolution of the apennines central adriatic piedmont and in particular on the region along the marche abruzzo border stratigraphically the rocks of this area are typical of a marine environment which characterised the central periadriatic basin up to the early pleistocene a differential regional uplift produced a north eastward tilting of the area this led to the development of a parallel drainage network across the emerged coastal plain during the middle pleistocene these tectonic events along with a series of climatic changes during the quaternary caused alternating phases of fluvial incision and deposition which eventually produced four levels of fluvial terraces as outcropping lithologies seldom display a full record of significant tectonic deformation we carried out morphometric analysis along with a geomorphological survey in order to enhance our morphotectonic understanding of the area and to better define the role of neotectonics in the morphological evolution of the area we also analysed the morphological evidence of tectonics including field surveys focusing on fluvial and alluvial fan terraces as they are valuable indicators of neotectonic evolution finally we employed geostatistical analysis to facilitate the detection of fluvial terraces even when affected by neotectonics our results indicate an active control on drainage evolution by nw se to wnw ese tectonic lineaments intersected by sw ne and wsw ene ones these tectonic lines continued to be active up to the formation of the third level of terraces late pleistocene river captures and diversions followed during the late pleistocene and the holocene in some cases favoured by passive tectonic control

the statistical relationship between unconfined compressive strengths and the frequency distributions of slope gradients a case study in northern hungary this paper focuses on the question of whether there is a deterministic connection between the slope gradient and unconfined compression strength ucs as a lithological factor and on describing the nature of this connection moreover the authors determined the sensitive statistical parameters in the statistical surface analyses the surface analyses were carried out in an area extending over 1500 km 2 in northern hungary and containing parts of the uplifted palaeozoic and mesozoic basement and the semi consolidated material of the palaeogene and neogene molasse sediments the 67 geological formations of the area were grouped into 10 petrophysical categories characterised by unconfined compressive strength as a petrophysical parameter the geological database was the digitalized geological map of north hungarian region 1 100000 the digital topographic database was based on 10 m contour lines of 1 50000 maps the digital elevation model was generated by kriging interpolation three topographic models were created with resolutions of 25 25 50 50 and 100 100 m per pixels evident correlation can be shown between the ucs and the relative frequency of the slope gradient the adequate regression procedure is the power regression for low slope category values while logarithmic regression is applicable at high slope angles based on the characteristic of the relationship and the value of r 2 slope category intervals can be identified the relative frequency of which is proven to be determined by the ucs these intervals are found to be between 4 10 10 16 16 22 22 44 and over 44 using the determination equations of slope gradient between 4 10 and over 44 the ucs of the bedrock can be calculated approximately as the average value of the two calculated results so the quotient of the frequency of these two category intervals can be regarded as an important morphometric index for a given bedrock

impact of a new anisotropic rheology on simulations of arctic sea ice 1 a new rheology that explicitly accounts for the subcontinuum anisotropy of the sea ice cover is implemented into the los alamos sea ice model this is in contrast to all models of sea ice included in global circulation models that use an isotropic rheology the model contains one new prognostic variable the local structure tensor which quantifies the degree of anisotropy of the sea ice and two parameters that set the time scale of the evolution of this tensor the anisotropic rheology provides a subcontinuum description of the mechanical behavior of sea ice and accounts for a continuum scale stress with large shear to compression ratio and tensile stress component results over the arctic of a stand alone version of the model are presented and anisotropic model sensitivity runs are compared with a reference elasto visco plastic simulation under realistic forcing sea ice quickly becomes highly anisotropic over large length scales as is observed from satellite imagery the influence of the new rheology on the state and dynamics of the sea ice cover is discussed our reference anisotropic run reveals that the new rheology leads to a substantial change of the spatial distribution of ice thickness and ice drift relative to the reference standard visco plastic isotropic run with ice thickness regionally increased by more than 1 m and ice speed reduced by up to 50

geomorphic response to neotectonic instability in the deccan volcanic province shetrunji river western india insights from quantitative geomorphology abstract the saurashtra peninsula a deccan trap terrain in western india lacks the studies that document on land information of tectonically active faults in the present paper the tectonogeomorphology of the shetrunji river basin is investigated to identify the neotectonic signatures of the buried structural element by detailed analyses of the landforms and drainage pattern using quantitative geomorphic analysis morphostructural studies and gradient length analysis gla along with field investigation the basin has been divided into three segments based on channel orientation a segment 1 upper reach oriented in ne sw direction b segment 2 middle reach oriented in an e w direction and c segment 3 lower reach oriented in nw se direction the tectono geomorphic analysis suggests the neotectonic deformation is mainly demonstrated by the ne sw oriented girnar fault gf in segment 1 and e w oriented shetrunji fault sf in segment 2 the segment 3 interestingly shows least or no tectonic deformation signatures for the first time we report the geomorphic evidence of the two main faults 1 the girnar fault gf a left lateral strike slip fault and 2 the shetrunji fault zone sfz a right lateral strike slip fault the interplay between drainage pattern and buried structures are observed in the form of offset channel offset ridges deflection in stream and linear valleys the sfz is characterized by an anastomosing drainage pattern offsetting deflection of streams and development of linear valleys in zone which is 52 km in length and 2 km wide the sl index and ksn show high values along the fault zone which is also supported by the presence of incised river channel entrenched mender and incised ravine surfaces the study reveals the prevalent neotectonic activity in the shetrunji river basin along with the gf and the sfz the findings are consistent with the geomorphic structural setup of the region and coincide with the historical as well as current seismicity distribution

l aquila earthquake april 6th 2009 central apennine italy site effect coseismic evidence and historical development of the collebrincioni area the village of collebrincioni is located right at the center of the most damaged area of the april 6th 2009 l aquila earthquake it is known from historical data that this site had been heavily affected by the 1461 and 1703 seismic events and for that reason remained abandoned for a long time the area has been settled again at the end of the 18th century with the rebuilding of the present conurbation in a new safer location after the april 6th 2009 earthquake many evidences of coseismic effects have been found around the collebrincioni surroundings even though the macroseismic intensity calculated in the new settlement was found to be moderate 6 mcs the aim of this work is to verify whether the cause of the migration from the old location can be linked to site effects for this purpose several measurements of horizontal to vertical spectral ratio hvsr have been carried out at various locations to obtain information on amplification phenomena to allow a quick evaluation of site seismic response without requesting any information about stratigraphical and geotechnical properties of the foundation soils the nakamura s technique was adopted in this paper measurements of hv spectral ratio carried out in the area show relevant differences between the new and the ancient settlements confirming the hypothesis that the abandonment of the old collebrincioni settlement can be related to the site effects which have amplified the destructive effects of the earthquakes

neotectonic evolution of the northern laborec drainage basin northeastern part of slovakia this study investigates the influence of neotectonic activity on river and basin patterns in a mountainous area located in the northeastern part of the carpathian belt the laborecka vrchovina and bukovske vrchy mts in eastern slovakia this area evolved within the accretionary wedge of the carpathians during the neogene and it was alsowas affected by middle to late miocene thrusting of the external carpathians morphometric analysis longitudinal and transverse river valley profiles analysis of basin and valley symmetries and investigation of alluvial terraces were carried out on the northern laborec river and its tributaries this was done to detect a possible relationship between their river courses and any ongoing neotectonic activity which is otherwise difficult to detect by methods of structural geology because of the poorly exposed area the general topography of the basin is characterized by a stepwise inclination to the sw as a result of differential uplift and subsidence the reorganization of the river network in the laborec drainage basin was influenced by tectonic activity along the ne sw up to n s fault structures during the neotectonic phase pliocene quaternary the movement along these fault structures is predominantly normal to transtensive the obtained data assumes that the region is under approximately ne sw oriented sh compression and nw se trending sh tension the laborec drainage basin is characterized by a very high degree of asymmetry that sharply increases from the upper to the lower courses of the river the right bank tributaries of the laborec river are 12 km in length however the left bank tributaries such as vydra ka ol sava v rava udava and cirocha streams are up to 50 km long with a high potential of headward erosion and capturing the valley asymmetry is also very variable in the upper and lower portions of the basin based on these presented results the ancient river thalweg was located along the axis of the hostovice habura depression and it was captured by the ol sava v rava and udava streams the asymmetric pattern of the drainage basin is the result of active tectonics the continual subsidence of the transcarpathian basin and by the uplift of the laborecka vrchovina and bukovske vrchy mts these events caused rejuvenation of the headward erosion of streams in the southern part favorable lithology was also essential in the process of river capture

the use of the stream length gradient index in morphotectonic analysis of small catchments a case study from central italy abstract the aim of this work is to test an integrated quantitative geomorphic approach based on stream length gradient index sl index analysis within the small catchment of the tarugo river in the northern marchean apennines central italy the tarugo river basin 92 km 2 wide strikes sw ne across the marchean ridge and the western sector of marchean piedmont the area is characterized by a series of nw se trending ne verging thrust folds affecting the meso cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks the area investigated has been affected since the pliocene by extensional tectonics accompanying a regional uplift decreasing in rate north eastwards in this work the sl index analysis has been integrated with the spatial analysis of the amplitude of relief a r and compared to geological and geomorphological field data results of this work indicate that the sl index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes i e regional uplift that is often undetectable by other morphotectonic parameters in contrast the sl index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one

a new map of crustal terranes in the united states from cocorp deep seismic reflection profiling a new map has been constructed to summarize major systematic variations in seismic reflection character observed by over 10000 km of cocorp profiling in the us among the seismic characteristics represented on this map are crustal scale detachments which can be traced as relatively low angle reflectors over large areas deeply penetrating dipping reflection zones some of which mark major shear zones perhaps even crustal sutures moho reflectivity which appears to vary from craton to phanerozoic periphery seismic transparency which can sometimes be interpreted as geologic homogeneity seismic layering prominent in the lower crust in many areas and now known to dominate the upper basement in other regions and unusually strong reflections or bright spots at mid crustal levels that may mark deep crustal fluids

elastic decohesive constitutive model for sea ice 1 one of the dominant characteristics of arctic ice is the development and persistence of leads leads are critically important for climate modeling since they are a source for new ice and an avenue for heat exchange between the atmosphere and ocean therefore a specific representation for leads in a constitutive model for pack ice is considered essential presented here is an elastic decohesive constitutive model whose purpose is to specifically indicate when a lead is initiated to provide the orientation of the lead to give the mode of failure and to allow for the numerical determination of the width of leads both laboratory and in situ data of sea ice provide the motivation for the basic structure of the model sample paths in stress and strain space are used to illustrate how the model can simulate failure the model can predict multiple failure planes a feature that is necessary to simulate crack branching preexisting planes of weakness such as those formed from previous leads can also be accommodated

moho reflectivity and seismic signal penetration abstract analysis of amplitude decay and frequency change is applied to determine limits of seismic signal penetration on deep seismic reflection data collected by lithoprobe and the consortium for continental reflection profiling cocorp changes in spectral frequency content are efficiently monitored with averaged instantaneous frequency and bandwidth results from montana show pronounced increases in average frequency and slight drops in amplitude associated with a die out of reflections at the moho results from quebec show amplitude and frequency change occurring through the moho on lines with and without moho reflections these contrasting observations confirm both adequate signal penetration and that the differences in moho reflectivity are representative of geologic differences

arctic ice dynamics joint experiment aidjex assumptions revisited and found inadequate 1 this paper revisits the arctic ice dynamics joint experiment aidjex assumptions about pack ice behavior with an eye to modeling sea ice dynamics the aidjex assumptions were that 1 enough leads were present in a 100 km by 100 km region to make the ice isotropic on that scale 2 the ice had no tensile strength and 3 the ice behavior could be approximated by an isotropic yield surface these assumptions were made during the development of the aidjex model in the 1970s and are now found inadequate the assumptions were made in part because of insufficient large scale 10 km deformation and stress data and in part because of computer capability limitations upon reviewing deformation and stress data it is clear that a model including deformation on discontinuities and an anisotropic failure surface with tension would better describe the behavior of pack ice a model based on these assumptions is needed to represent the deformation and stress in pack ice on scales from 10 to 100 km and would need to explicitly resolve discontinuities such a model would require a different class of metrics to validate discontinuities against observations

crustal structure and evolution of the trans hudson orogen results from seismic reflection profiling a 400 km long deep seismic reflection transect across northeastern montana and northern north dakota reveals the crustal scale structural fabric of the early proterozoic trans hudson orogen beneath the williston basin comparison with deep seismic reflection data across the canadian portion of the same orogen 700 km to the north reveals first order similarities in crustal architecture but documents significant along strike variation in orogenic evolution both transects display a broad crustal scale antiform axial to the orogen in the north geologic data suggest that this antiform is cored by an archean microcontinent in the south west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the archean wyoming craton within the wyoming craton the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the early proterozoic trans hudson orogen as interpreted from potential field and drill core data on the basis of subsurface geochronologic data from the crystalline basement and by analogy with the glennie domain within the exposed trans hudson orogen in canada we suggest that the southern antiform is cored by an archean crustal fragment that was caught up in the terminal collision of the wyoming and superior cratons during hudsonian orogeny the eastern side of the trans hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections we interpret the easterly dip of these reflections as evidence that the superior province was thrust westward over the interludes of the orogen during terminal collision although juvenile early proterozoic terranes characterize the exposed segment of the trans hudson orogen in canada limited drill core information within the dakota segment of the orogen shows a predominance of granulitic archean age crust this difference in basement lithologies along strike within the orogen may indicate the following either juvenile crust comparable to that exposed in the northern trans hudson was never present in the south or it was removed by progressive over thickening erosion and or faulting postorogenic extensional collapse may be responsible for preservation of juvenile terranes in the north

a new modeling framework for sea ice mechanics based on elasto brittle rheology we present a new modeling framework for sea ice mechanics based on elasto brittle eb behavior the eb framework considers sea ice as a continuous elastic plate encountering progressive damage simulating the opening of cracks and leads as a result of long range elastic interactions the stress relaxation following a damage event can induce an avalanche of damage damage propagates in narrow linear features resulting in a very heterogeneous strain field idealized simulations of the arctic sea ice cover are analyzed in terms of ice strain rates and contrasted to observations and simulations performed with the classical viscous plastic vp rheology the statistical and scaling properties of ice strain rates are used as the evaluation metric we show that eb simulations give a good representation of the shear faulting mechanism that accommodates most sea ice deformation the distributions of strain rates and the scaling laws of ice deformation are well captured by the eb framework which is not the case for vp simulations these results suggest that the properties of ice deformation emerge from elasto brittle ice mechanical behavior and motivate the implementation of the eb framework in a global sea ice model

trans hudson orogen and williston basin in montana and north dakota new cocorp deep profiling results cocorp consortium for continental reflection profiling deep reflection profiling across the williston basin and underlying trans hudson orogen shows the following 1 there is no evidence for a precursor rift basin beneath the axis of the williston basin with the exception of small scale structures e g nesson and cedar creek anticlines the basement surface beneath the williston basin is smooth and has a dish shaped geometry 2 crustal penetrating reflections within the eastern trans hudson orogen dip eastward in apparent contradiction to the conventional view that the superior province underthrusts the eastern side of the orogen 3 basement reflections beneath the center of the orogen define a broad crustal scale antiform the axis of which coincides approximately with the depocenter of the overlying williston basin midcrustal reflections defining the crest and western flank of this antiform also coincide generally with the location and shape of the source of the north american central plains conductivity anomaly 4 crustal penetrating reflections beneath the western side of the orogen dip westward supporting the current view that subduction polarity was to the west beneath the wyoming province 5 the eastern edge of the wyoming province is marked by east dipping upper crustal reflections and subhorizontal lower crustal reflections that are truncated by the west dipping reflectivity of the trans hudson orogen

formation of sea ice bridges in narrow straits in response to wind and water stresses ice bridges are rigid structures composed of sea ice that form seasonally in the many straits and channels of the canadian arctic archipelago driven primarily by atmospheric stresses these ice bridges are formed when sufficiently thick ice jams during the course of its flow between land masses resulting in a region of stationary compacted ice that is separated from a region of flowing open water a polynya by a static arch using a continuum description of sea ice that is widely used in climate modeling we present an asymptotic theory of the process of formation of such bridges in slender channels when the motion of the ice is driven by external wind and water stresses we show that for an arbitrary channel shape ice bridges can only form within a range of ice properties that is determined by the channel geometry and the external stress we then compare the results of our theory with direct numerical simulations and observational evidence finally we provide simple analytical expressions for the mean velocity of the ice flow as a function of the channel shape the properties of the ice and the wind and water stresses along the channel

seismic studies in the limpopo belt abstract the structure of the archaean limpopo belt of southern africa has been investigated by means of a deep seismic reflection profile and the recording of the traveltimes of mining induced tremors at regional distances interpretation of the traveltimes suggests that a seismic low velocity zone exists in the upper mantle of the northern kaapvaal craton and limpopo belt beginning at a depth of about 42 km the seismic reflection profile provides evidence for a northward dip of the contact between the kaapvaal craton and the southern marginal zone of the limpopo belt no mid crustal decollement zone is detected the tectonic model of van reenen et al 1990 is in accord with these observations the lower crust is essentially seismically transparent and no reflection moho is observed

late quaternary geomorphic scenario due to changing depositional regimes in the tangtse valley trans himalaya nw india abstract records from the tangtse valley in the trans himalaya reveal depositional history since 48 ka with fluvial aggradation followed by incision lacustrine sediment fill and later incision varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses flood events colluvial and glacial activity are preserved the valley is located west of the pangong tso bangong co one of the largest lakes in tibet which has served as a spillway flooding and damming the entire tangtse valley resulting in the formation of a lake today pangong tso consists of five basins separated by shallow sills and is fed by snow melt documentation based on 14 c and osl chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of pangong tso toward west occupying the present day tangtse valley between 9 6 5 1 ka this event coincides with periods of high lake levels in tibet china as well as intensified monsoon periods over the indian subcontinent a fluvial regime around 48 ka and 30 21 ka with comparatively arid conditions and dry phases interspersed by flooding is documented the valley has been incised to depths of 40 50 m in the upper part and to 130 m in the lower part the incision rate ranges from 0 3 to 1 2 mm yr 1 in the upper part and reaches as high as 10 8 mm yr 1 in the lower valley much of the incision took place between 22 and 9 6 ka although repeated sediment fill incision cycles in the valley from 30 22 ka 22 9 6 ka 9 6 5 1 ka 5 1 ka and even to present time were observed

morphotectonic study of the lower sangro river valley abruzzi central italy abstract this work analyses the morphotectonic setting of the adriatic piedmont of central italy in order to outline the role of tectonics in the development of the fluvial landscape in this area particularly it focuses on the sangro river which flows in the southern abruzzi from the apennines through the piedmont to the adriatic coast the piedmont area developed in a marine environment from the pliocene to the early pleistocene resulting in the deposition of a clayey sandy sequence afterwards regional uplift processes with ne tilting led to the deposition of a regressive conglomeratic sequence as the area evolved into a continental environment this work is based on the qualitative and quantitative study of drainage patterns and on the analysis and correlation of selected morphological evidence of tectonics on fluvial terraces in order to define the role of tectonics in the geomorphological evolution of the lower sangro river valley the drainage network and its statistical azimuthal distributions are analysed the distribution and the transverse and longitudinal profiles of fluvial terraces are investigated and the morphological evidence for tectonics is then assessed river bends linear valleys beheaded and hanging valleys counterflow confluences of streams space and time correlation of these features allows us to highlight the effects of regional uplift tilting and local tectonics on drainage development following the emergence of the piedmont area middle pleistocene uplift and tilting determined a sw ne consequent and parallel drainage progressive incision shaped the sangro valley as a consequent valley local tectonics along nnw sse and wnw ese faults and fractures resulted in the incision of linear valleys beheading the previous sw ne drainage and controlled the development of a rectangular drainage network late middle pleistocene the drainage network was then rearranged by selective erosion processes maintaining a strong inheritance from of its middle pleistocene configuration

the effects of late alpine tectonics in the morphology of the argentera massif western alps italy france several swath profiles drainage morphometric parameters slope and drainage density maps were obtained by dtm analysis of the argentera massif western alps the spatial distribution of the analysed parameters indicates that the central southern sector is characterized by orographic and drainage characteristics very different from the rest of the massif two main systems of nw and wnw trending faults the orgials fault and valletta fault bound this area both faults belong to large scale fault zones the dextral strike slip bersezio fault and the south facing colle del sabbione thrust the orientations and kinematics of both faults indicate a late alpine pliocene to recent sw verging thrusting coupled with a dextral strike slip movement the central southern sector of the massif corresponds to the hanging wall of a sw verging late alpine thrust zone and underwent the highest post pliocene tectonic uplift in the argentera massif the uplift occurred in a transpressive setting with an n s shortening direction which is consistent with the post pliocene tectonics in the southern portion of the western alps r 2002 elsevier science ltd and inqua all rights reserved

using the material point method to model sea ice dynamics 1 the material point method mpm is a numerical method for continuum mechanics that combines the best aspects of lagrangian and eulerian discretizations the material points provide a lagrangian description of the ice that models convection naturally thus properties such as ice thickness and compactness are computed in a lagrangian frame and do not suffer from errors associated with eulerian advection schemes such as artificial diffusion dispersion or oscillations near discontinuities this desirable property is illustrated by solving transport of ice in uniform rotational and convergent velocity fields moreover the ice geometry is represented by unconnected material points rather than a grid this representation facilitates modeling the large deformations observed in the arctic as well as localized deformation along leads and admits a sharp representation of the ice edge mpm also easily allows the use of any ice constitutive model the versatility of mpm is demonstrated by using two constitutive models for simulations of wind driven ice the first model is a standard viscous plastic model with two thickness categories the mpm solution to the viscous plastic model agrees with previously published results using finite elements the second model is a new elastic decohesive model that explicitly represents leads the model includes a mechanism to initiate leads and to predict their orientation and width the elastic decohesion model can provide similar overall deformation as the viscous plastic model however explicit regions of opening and shear are predicted furthermore the efficiency of mpm with the elastic decohesive model is competitive with the current best methods for sea ice dynamics

pds receiver function evidence for crustal scale thrusting relic subduction and mafic underplating in the trans hudson orogen and yavapai province a b s t r a c t article history the trans hudson orogen tho in the north central united states represents a major suturing event between the wyoming and superior archean provinces it is bounded to the south by the ne sw striking yavapai province which was accreted along the southeastern margin of north america between 1 71 and 1 68 ga and was one of a series of major collisional events responsible for the assembly of laurentia in this study pds teleseismic receiver functions were used to investigate the deep crustal structure associated with these collisions using data from over 800 broadband seismic stations distributed throughout the great plains midcontinent region we calculated 0 5 hz receiver functions using 245 m 6 0 teleseismic events the receiver functions were then ccp common conversion point stacked to create a 3d image volume profiles through this image volume show evidence of crustal scale thrusting of the wyoming province in the west over the superior province in the east and a relic subduction zone associated with the yavapai superior boundary we also performed a density analysis of the region using relative amplitude of the 2p1s and 0p1s receiver function phases from 233 stations these data indicate a relatively low moho density contrast throughout the tho and northern yavapai province associated with a region of thickened crust 50 km which we interpret to be evidence of a dense lower crustal layer that is the result of mafic underplating

four stages of pressure ridging the pressure ridging process is simulated using a two dimensional particle model blocks are broken from an intact sheet of relatively thin lead ice pushed against a thick multiyear floe at a constant speed the blocks of ice rubble accumulate to form the ridge sail and keel during the simulations the energy consumed in ridge growth including dissipation is explicitly calculated on the basis of the results of simulations performed with the model the ridging process can be divided into four distinct stages the first stage begins with an intact sheet of lead ice impacting a floe and ends when the sail reaches its maximum height in the second stage the ridge keel deepens and widens the stage ends when the maximum keel draft is reached in the third stage the direction of growth is leadward creating a rubble field of more or less uniform thickness the third stage ends when the supply of thin ice is exhausted in the fourth stage the rubble field is compressed between converging floes the results of simulations establish the dependence of ridging energetics in the first and second stages on the thickness of the ice sheet and the amount of ice pushed into the ridge the average profiles of the simulated ridges delineate the growth process in the first second and third stages the energetics and profiles of the fourth stage were described by hopkins et al 1991 lead ice extents of up to 1300 m are pushed into ridges to determine maximum sail heights keel drafts and ridging forces

discrimination of fluvial eolian and neotectonic features in a low hilly landscape a dem based morphotectonic analysis in the central pannonian basin hungary abstract the godoll hills a low relief terrain within the central pannonian basin in hungary is characterised by moderate tectonic deformation rates although typical tectonic landforms are not clearly recognisable in the study area this paper succeeded in discriminating between tectonically controlled landforms and features shaped by fluvial erosion or deflation with no tectonic control dem based morphometric parameters including elevation slope and surface roughness enabled the delineation of two nw se trending spearhead shaped ridges separated by a wide rectilinear valley of the same strike although directional statistics suggested possible tectonic control of nw se striking landforms precise morphometry completed with an analysis of subsurface structures rejected their tectonic preformation deflation plays a significant role in shaping the area and the presence of two large scale yardangs separated by a wind channel is proposed in temperate continental areas of europe no deflational landforms of such scale have been described so far suggesting that pleistocene wind power in periglacial areas was more significant than it was previously thought characteristic drainage patterns and longitudinal valley profiles enabled the recognition of areas probably affected by neotectonic deformation a good agreement was observed between locations of quaternary warping predicted by the morphometric study and subsurface structures revealed by the tectonic analysis zones of surface uplift and subsidence corresponded to anticlinal and synclinal hinges of fault related folds in low relief and slowly deforming areas where exogenous forces may override tectonic deformation only the integrated application of morphometric and subsurface structural indications could assure correct interpretation of the origin of various landforms while a morphometric study alone could have led to misinterpretation of some morphometric indices apparently suggesting tectonic preformation on the other hand the described morphological expression of subsurface structures could verify quaternary age of the deformation