deformation history of the high pressure lycian nappes and implications for tectonic evolution of sw turkey 1 in southwestern turkey the lycian nappe complex which overlies the autochthonous menderes massif and bey dag platform consists from base to top of metasediments a melange unit and an ophiolitic sequence fresh fe mg carpholite occurrence in the metasediments attests to a high pressure low temperature metamorphic event we report the distribution of fe mg carpholite and its breakdown products e g pyrophyllite and chloritoid on the bodrum peninsula south of the menderes crystalline massif the distribution of fe mg carpholite and its relics shows that the low grade high pressure metamorphism affected a widespread area in the lower units of the lycian nappes analysis of the ductile deformation in hp lt metasediments indicates shear senses top to the northeast to top to the east most of this deformation is contemporaneous with the retrogression of high pressure low temperature parageneses and is therefore coeval with exhumation from a depth of about 30 km at the top of the menderes massif cover series close to the contact with the lycian nappes similar eastward displacements are observed and trajectories of the stretching lineations are continuous from the lycian nappes to the menderes massif across the contact these observed movements are incompatible with the southward transport of the lycian nappes over the menderes massif we discuss the regional tectonic implications and conclude that the lycian nappes and the southernmost part of the menderes massif were exhumed in two stages 1 eocene top to the ne shear syn orogenic extension 2 miocene deformation contemporaneous with the aegean extension

bed configuration and hydraulic resistance in alluvial channel flows a new approach for predicting alluvial channel resistance in the framework of the familiar manning equation is proposed the new method proposes a relation for the manning coefficient that incorporates directly the role of bed configuration in determining alluvial bed resistance a relation for bed form height is developed which is then used as an independent variable to account for the resistance due to bed form drag the method was applied to a large body 969 flows of river and flume data with satisfactory agreement with the observed values mean normalized errors for predicted flow depths and velocities were about 10 for all 969 flows the procedure can be applied to natural streams with compound channels since variable roughness for the main channel and overbank sections can be computed separately in this approach prediction accuracy was generally better for flows that were clearly in the lower regime ripple or dune or in the upper regime flat bed or antidune but larger errors were associat

statistical properties of sediment movement the downstream dispersion of a sediment bed particle is represented by a stationary point process in space and time domains and plausible forms of the probability density functions of the particle step length and rest duration are derived the space rate parameter proposed in this paper gives step length density functions whose forms vary from the exponential curve to the bell shaped configuration the time rate parameters used were proposed by vukmirovic and wilson theoretical results agree well with laboratory experimental data obtained for dune bed conditions

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

the surface tectonics of mantle lithosphere delamination following ocean lithosphere subduction insights from physical scaled analogue experiments many postulated lithospheric removal events occur in regions with an earlier history of subduction but the relationship between the two processes has not been explored in this work we use physical scaled analogue experiments to investigate the evolution from ocean lithosphere subduction to collision and possible delamination of the mantle lithosphere from the crust we test how varying the magnitude of plate convergence alters the behavior of the subduction delamination model our experiments show that a retreating ocean proplate can evolve to continental mantle lithosphere delamination negative surface topography is supported at the delamination hinge and this migrates back with the peeling lithosphere with high plate convergence delamination is suppressed rather the crust and mantle lithosphere split at the collision zone in a form of flake tectonics as oncoming procrust is accreted on top of the retroplate and the promantle lithosphere subducts below localized high topography develops at this zone of crustal accretion and thickening the results suggest that delamination may be a continental continuation of plate retreat and that lithospheric removal is triggered by the transition from one process to another

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

mesozoic tertiary structural evolution of an extensional gneiss dome the kesebir kardamos dome eastern rhodope bulgaria greece the tectonic evolution of the rhodope massif involves mid cretaceous contractional deformation and protracted oligocene and miocene extension we present structural kinematic and strain data on the kesebir kardamos dome in eastern rhodope which document early tertiary extension the dome consists of three superposed crustal units bounded by a low angle nne dipping detachment on its northern flank in bulgaria the detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall the high grade metamorphic rocks of the footwall have recorded isothermal decompression direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit structural analysis and deformational metamorphic relationships give evidence for several events the earliest event corresponds to top to the sse ductile shearing within the intermediate unit interpreted as reflecting mid late cretaceous crustal thickening and nappe stacking late cretaceous palaeocene eocene late tectonic to post tectonic granitoids that intruded into the intermediate unit between 70 and 53 ma constrain at least pre latest late cretaceous age for the crustal stacking event subsequent extension related deformation caused pervasive mylonitisation of the footwall with top to the nne ductile then brittle shear ductile flow was dominated by non coaxial deformation indicated by quartz c axis fabrics but was nearly coaxial in the dome core latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high angle normal faults and additional movement along strike slip faults radiometric and stratigraphic constraints bracket the ductile then brittle extensional events at the kesebir kardamos dome between 55 and 35 ma extension began in paleocene early eocene time and displacement on the detachment led to unroofing of the intermediate unit which supplied material for the syn detachment deposits in supra detachment basin subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 ma as indicated by mica cooling ages in footwall rocks and extension proceeded at brittle levels with high angle faulting constrained at 35 ma by the age of hydrothermal adularia crystallized in open spaces created along the faults this was followed by late eocene oligocene post detachment overlap successions and volcanic activity crustal extension described herein is contemporaneous with the closure of the vardar ocean to the southwest it has accommodated an earlier hinterland directed unroofing of the rhodope nappe complex and may be pre cursor of and or make a transition to the aegean back arc extension that further contributed to its exhumation during the late miocene this study underlines the importance of crustal extension at the scale of the rhodope massif in particular in the eastern rhodope region as it recognizes an early tertiary extension that should be considered in future tectonic models of the rhodope and north aegean regions

rheology and strength of the lithosphere abstract mechanical properties of lithosphere are of primary importance for interpretation of deformation at all spatial and time scales from local scale to large scale geodynamics and from seismic time scale to billions of years depending on loading conditions and time scale lithosphere exhibits elastic brittle plastic or viscous ductile properties as can be inferred from rock mechanics data a large part of the long term lithospheric strength is supported in the ductile or ductile elastic regime while it also maintains important brittle strength yet at short seismic time scale s the entire lithosphere responds in elastic brittle elastic regime even though rock mechanics experiments provide important insights into the rheological properties of the lithosphere their conditions e g time scales strain rates temperature and loading conditions are too far from those of real earth therefore these data cannot be reliably extended to geological time and spatial scales strain rates 10 17 to 10 13 s 1 without additional parameterization or validation based on geological time scale observations of large scale deformation for the oceanic lithosphere the goetze and evan s brittle elastic ductile yield strength envelopes yses were validated by geodynamic scale observations such as the observations of plate flexure however oceanic lithosphere behavior in subduction zones and passive continental margins is strongly conditioned by the properties of the continental counterpart whose rheology is less well understood for continents and continental margins the uncertainties of available data sources are greater due to the complex structure and history of continental plates for example in a common continental rheology model dubbed jelly sandwich the strength mainly resides in crust and mantle while in some alternative models the mantle is weak and the strength is limited to the upper crust we address the problems related to lithosphere rheology and mechanics by first reviewing the rock mechanics data te flexure and ts earthquake data and long term observations such as folding and subsidence data and then by examining the physical plausibility of various rheological models for the latter we review the results of thermo mechanical numerical experiments aimed at testing the possible tectonic implications of different rheology models in particular it appears that irrespective of the actual crustal strength the models implying weak mantle are unable to explain either the persistence of mountain ranges for long periods of time or the integrity of the subducting slabs although there is certainly no single rheology model for continents the jelly sandwich is a useful first order model with which to parameterize the long term strength of the lithosphere it is concluded that dry olivine rheology laws seem to represent well the long term behavior of mantle lithosphere in oceans margins and continents as to the continent and margin crust rheology analysis of the results of thermo mechanical models and of te data based on the most robust variants of flexural models suggests that continental plates with te 30 50 smaller than their theoretical mechanical thickness hm i e te 20 60 km should be characterized by a weak lower or intermediate crustal rheology enabling mechanical decoupling between crust and mantle older plates such as cratons are strong due to crust mantle coupling and specific properties of the cratonic mantle lithosphere

the somalia plate and the east african rift system present day kinematics summary the motion of the somalia plate relative to the nubia africa arabia and antarctica platcs is re evaluated using a new inversion method based on a monte carlo technique and a least absolute value misfit criterion a subset of the nuvel 1 data set with additional data along the levant fault and in the red sea is used the results confirm that the motion of arabia with respect to africa is significantly different from the motion relative to somalia it is further shown that the data along the sw indian ridge are compatible with a pole of relative motion between africa and somalia located close to the hypothetical diffuse triple junction between the ridge and thc east african rift the resulting africa somalia motion is then compatible with the geological structures and seismological data along the east african rift system assuming a separate somalia plate thus solves kinematic and geological problems around the afar triple junction and along the east african rift

tectonics of the syros blueschists cyclades greece from subduction to aegean extension 1 on syros high pressure metamorphism affects a lithological pile that is composed of from base to top 1 the komito vari granitic basement 2 a margin sedimentary sequence that is predominantly made of marbles and schists the pyrgos and kastri units and 3 the kambos metaophiolitic melange the tectonic history occurred in three main stages during the first stage in the mid eocene the kambos oceanic unit was thrust southward on top of the sedimentary pile top to the south southwest ductile senses of shear are synchronous with prograde high pressure metamorphism and associated with this thrusting event the second stage corresponds to a top to the northeast ductile shear that affects the whole metamorphic pile and is synchronous with the metamorphic retrogression from eclogite to greenschist facies however the kambos oceanic unit remained partly undeformed as shown by significant volumes containing undeformed lawsonite pseudomorphs no major extensional detachment related to this exhumation event outcrops on the island the localized semibrittle to brittle deformation of the third stage is associated with the postmetamorphic development of 1 a ramp flat extensional system at the island scale whose southward minimum displacement is estimated at approximately 7 km and 2 two sets of steeply dipping strike slip faults with a normal component trending either east west or around north south indicating that the mean stretching and shortening directions are trending nne ssw and ese wnw respectively this sequence of major tectonic events and their relationship to metamorphism are interpreted within the framework of the subduction of the pindos ocean and then of the adria continental passive margin

the structures stratigraphy and evolution of the gulf of corinth rift greece summary a multichannel seismic and bathymetry survey of the central and eastern gulf of corinth goc greece reveals the offshore fault geometry seismic stratigraphy and basin evolution of one of earths most active continental rift systems active right stepping en echelon north dipping border faults trend ese along the southern gulf margin significantly overlapping along strike the basement offsets of three akrata derveni sithas and xylocastro are linked the faults are biplanar to listric typically intermediate angle 35 in the centre and 45 48 in the east near the surface but decreasing in dip and or intersecting a low or shallow angle 15 20 in the centre and 19 30 in the east curvi planar reflector in the basement major s dipping border faults were active along the northern margin of the central gulf early in the rift history and remain active in the western gulf and in the subsidiary gulf of lechaio but unlike the southern border faults are without major footwall uplift much of the eastern rift has a classic half graben architecture whereas the central rift has a more symmetric w or u shape the narrower and shallower western gulf that transects the 40 km thick crust of the hellenides is associated with a wider distribution of overlapping high angle normal faults that were formerly active on the peloponnesus peninsula the easternmost sector includes the subsidiary gulfs of lechaio and alkyonides with major faults and basement structures trending ne e w and nw the basement faults that control the rift architecture formed early in the rift history with little evidence other than the vrachonisida fault along the northern margin in the marine data for plan view evolution by subsequent fault linkage several have maximum offsets near one end crestal collapse graben formed where the hanging wall has pulled off the steeper onto the shallower downdip segment of the derveni fault the dominant strikes of the corinth rift faults gradually rotate from 090 120 in the basement and early rift to 090 100 in the latest rift reflecting a 10 rotation of the opening direction to the 005 presently measured by gps the sediments include a locally 1 5 km thick early rift section and a late rift section also locally 1 5 km thick that we subdivide into three sequences and correlate with seven 100 ka glacio eustatic cycles the gulf depocentre has deepened through time currently 700 mbsl as subsidence has outpaced sedimentation we measure the minimum total horizontal extension across the central and eastern gulf as varying along strike between 4 and 10 km and estimate full values of 6 11 km the rift evolution is strongly influenced by the inherited basement fabric the regional nnw structural fabric of the hellenic nappes changes orientation to ese in the parnassos terrane facilitating the focused north south extension observed offshore there the basement penetrating faults lose seismic reflectivity above the 4 14 km deep seismogenic zone multiple generations and dips of normal faults some cross cutting accommodate extension beneath the goc including low angle 15 20 interfaces in the basement nappes the thermally cool forearc setting and cross orogen structures unaccompanied by magmatism make this rift a poor analogue and unlikely precursor for metamorphic core complex formation

from ductile to brittle evolution and localization of deformation below a crustal detachment tinos cyclades greece 1 the cycladic oligo miocene detachment of tinos island is an example of a flat lying extensional shear zone evolving into a low angle brittle detachment a clear continuum of extensional strain from ductile to brittle regime is observed in the footwall the main brittle structures marking extension are shallow and steeply dipping normal faults associated with subvertical extensional joints and veins the earliest brittle structures are low angle normal faults which commonly superimpose on and reactivate earlier precursory ductile shear bands but newly formed low angle normal faults could also be observed low angle normal faults are cut by late steeply dipping normal faults the inversion of fault slip data collected within and away from the main detachment zone shows that the direction of the minimum stress axis is strictly parallel to the ne sw stretching lineation and that the maximum principal stress axis remained subvertical during the whole brittle evolution in agreement with the subvertical attitude of veins throughout the island the high angle of 1 to the main detachment suggests that the detachment was weak this observation together with the presence of a thick layer of cataclasites below the main detachment and the kinematic continuum from ductile to brittle leads us to propose a kinematic model for the formation of the detachment boudinage at the crustal scale induces formation near the brittle ductile transition of ductile shear zones near the edges of boudins shear zones are progressively exhumed and replaced by shallow dipping cataclastic shear zones when they reached the brittle field most of the displacement is achieved through cataclastic flow in the upper crust and only the last increment of strain gives rise to the formation of brittle faults the formation of the low angle brittle detachment is thus prepared by the ductile shear zone and the cataclasites and favored by the circulation of surface derived fluids in the shear zone

dynamics of bedforms in the lower mississippi river abstract the size and roughness characteristics of dunes in the mississippi river are not predicted well by experimental and theoretical relations even though intensive flow measurements were made in the study area although dunes increase in scale with increasing discharge of water and sediment the development of multiple dune sizes and nonuniform flow obscure the relationship of dune geometry to synoptic hydraulic variables some nonuniformity is caused by the development of large bed undulations from kinematic waves that can deform into compound dunes but most of it is related to flow convergence and divergence in pools and riffles varying flow geometry with increasing stage and reach controlled relations between flow and energy loss even though changes of bedform size are not found to lag the flow changes because sand transport is large a considerable volume of sediment is required to initiate and propagate the largest compound dunes this means that they might be profiled in different stages of growth and have a varying effect on the flow during their evolution spatially and temporally

small wavelength geoid and topography anomalies in the south atlantic ocean a clue to new hot spot tracks and lithospheric deformation numerous small wavelength elongated features are visible both on filtered geoid maps on topography maps of the south atlantic ocean a number of them are oriented along the directions of absolute plate motion between 80 ma b p and 30 ma b p n50 degree e for the african plate and n63 degree w for the south american plate magmatic traces left over fixed convective plumes more numerous than the classical hot spots best explain these observations other traces especially in the area of the sandwich subduction zone and on the african plate are oriented in a n50 degree w direction and seem to indicate large scale deformation of the oceanic plates

sediment transport of the blue nile at khartoum the blue nile supplies the nile river with the largest proportion of water and sediment nevertheless very few often contrasting data are reported in the literature about its sediment yield this paper deals with detailed field measurement of suspended sediment transport taken at khartoum during three flood seasons in the late 1960s the pattern of suspended sediment concentration discharge and grain size variation with flow is analysed and suspended sediment yield is calculated and compared with data from different sources no bedload transport measurements are reported in the literature for the blue nile the flow data measured in the field consent to select several dune geometry criteria and to adopt the dune bedforms migration method to calculate bedload transport the same procedure is applied also to the bedload data measured in four reaches of the nile river downstream of the high aswan dam with channel and sediment characteristics comparable with those of the blue nile at khartoum to ascertain which dune geometry criterion provided the most reliable results the bagnold 1980 and martin 2003 equations predict similar values of bedload transport that are compared with the very few bedload data assessed by other authors using different equations and methods finally a good relation between flow velocity and bedload transport rate is found

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

fluvial responses to the weichselian ice sheet advances and retreats implications for understanding river paleohydrology and pattern changes in central poland the evolution of the fluvial systems during the weichselian pleniglacial in the torun basin central poland was investigated through sedimentological investigation and paleohydraulic analysis within the basin three fluvial cycles deposited after successive phases of the ice advance which took place 50 28 and 20 ka ago successions of four fluvial lithotypes characterize each fluvial formation that are related to the paleoenvironmental changes e g climate instability and changes in the river regime which affected the channel hydraulics and morphology the successions comprise river style metamorphosis between high energy sand bed meandering rivers lithotype m1 high energy sand bed braided rivers lithotype b1 and medium energy sand bed braided rivers with either unit bars lithotype b2 or compound bars lithotype b3 reflects the maturity stage of sand bed braided river evolution in the basin the assessment of the fluvial sedimentary environments enabled the construction of a quantitative model of the changes in the river channel pattern in relation to the climate oscillation both the paleohydrological controls and their sedimentary consequences are discussed in the article lithotypes m1 and b1 represent riverbed modeled under supercritical flow condition deposition of lithotype b2 corresponded to the river channel pattern transformation and was manifested by decreasing flow velocity energy losses associated with bedform roughness and with the transportation of coarser particles the flow velocity was generally greater in rivers of lithotype b3 and energy of sedimentary environment was more stable than during the deposition of lithotype b2

underthrusting and exhumation a comparison between the external hellenides and the hot cycladic and cold south aegean core complexes greece 1 after their emplacement in the course of the late mesozoic and the cenozoic the hellenic nappes became fragmented during late orogenic extension since the late eocene here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension to this end we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the tripolitza and ionian nappes which were exhumed in the cycladic and south aegean windows with newly obtained data on the sedimentary stratigraphic and structural development of the part of these nappes in the foreland in front of the subduction thrust the results allow the identification of two major events event 1 took place around the eocene oligocene transition and marks the onset of underthrusting of the tripolitza nappe below the pindos nappe and the ionian nappe below the tripolitza nappe respectively this led to the uplift and erosion of the pindos unit and the onset of deposition of the tripolitza and ionian flysch in front of the pindos thrust together with the formation of mylonites at the base of the metamorphosed portions of the pindos unit related to the underthrusting of the tripolitza unit event 2 occurred in the latest oligocene to earliest miocene and marks the decoupling of the ionian unit from the underthrusting plate the accretion of the tripolitza and ionian units to the overriding plate and the onset of late orogenic extension and exhumation in the overriding plate this led to the formation of the south aegean and cycladic core complexes and the subsidence of the klematia paramythia half graben throughout the early miocene

using both free surface effect and sediment transport mode parameters in defining the morphology of river dunes and their evolution to upper stage plane beds doi 10 1061 asce hy 1943 7900 0000873 dunes are common bed forms in sand bed rivers and are of central interest in water management purposes due to flow separation and associated energy dissipation dunes form the main source of hydraulic roughness a large number of dune dimension data sets was compiled and analyzed in this study 414 experiments from flumes and the field showing a significantly different evolution of dune height and length in flows with low froude numbers negligible free surface effects and flows with high froude numbers large free surface effects for high froude numbers 0 32 0 84 relative dune heights are observed to grow only in the bed load dominant transport regime and start to decay for u w s suspension number exceeding 1 dunes in this case are not observed for suspension numbers greater than 2 5 for low froude numbers 0 05 0 32 relative dune heights continue to grow from the bed load to suspended load dominant transport regime dunes in this case are not observed for suspension numbers greater than 5 it was concluded that for reliable predictions of dune morphology and their evolution to upper stage plane beds it is essential to address both free surface effects and sediment transport mode

quantification of variability in bedform geometry we analyze the variability in bedform geometry in laboratory and field studies even under controlled steady flow conditions in laboratory flumes bedforms are irregular in size shape and spacing also in case of well sorted sediment our purpose is to quantify the variability in bedform geometry we use a bedform tracking tool to determine the geometric variables of the bedforms from measured bed elevation profiles for each flume and field data set we analyze variability in 1 bedform height 2 bedform length 3 crest elevation 4 trough elevation and 5 slope of the bedform lee face each of these stochastic variables is best described by a positively skewed probability density function such as the weibull distribution we find that except for the lee face slope the standard deviation of the geometric variable scales with its mean value as long as the ratio of width to hydraulic radius is sufficiently large if the ratio of width to hydraulic radius is smaller than about ten variability in bedform geometry is reduced an exponential function is then proposed for the coefficients of variation of the five variables to get an estimate of variability in bedform geometry we show that mean lee face slopes in flumes are significantly steeper than those in the field the 95 and 98 values of the geometric variables appear to scale with their standard deviation the above described simple relationships enable us to integrate variability in bedform geometry into engineering studies and models in a convenient way

structural and geochronological evidence for paleogene thrusting in the western rhodopes sw bulgaria elements for a new tectonic model of the rhodope metamorphic province 1 the rhodope metamorphic province in the area around the mesta graben sw bulgaria exposes a structurally lower complex the pangaion pirin complex of variscan continental crust and its cover mostly orthogneiss and marble and a higher complex the rhodope terrane of mixed oceanic and continental origin with metamorphosed jurassic arc magmatites the boundary between the two is the top to the southwest nestos shear zone the regional top to the southwest shearing of the two basement complexes is related to the emplacement of the rhodope terrane over the pangaion pirin complex along this shear zone syntectonic and posttectonic alpine intrusions within the basement can provide age limits for the thrusting zircons from the posttectonic teshovo south pirin granitoid pluton in the pangaion pirin complex yielded crystallization ages of 32 0 2 ma la sf icp ms u pb method zircons from two syntectonic granite plutons in the rhodope terrane dolno dryanovo and spanchevo have circa 143 to 145 ma old inherited magmatic cores and circa 55 to 56 ma old magmatic rims these ages especially the presence of the upper jurassic lower cretaceous cores in the plutons from the rhodope terrane and the structural relations indicate that the southwestward thrusting of the rhodope terrane over the pangaion pirin complex took place in the paleogene a model is proposed in which the pangaion pirin complex represents the margin of apulia and the structure of the rhodopes is explained by a switch of subduction polarity from sw dipping in the jurassic and early cretaceous to ne dipping in the late cretaceous and paleogene

orientation of absolute african plate motion revealed by tomomorphometric analysis of the ethiopian dome the ethiopian dome comprising the ethiopian and yemeni plateaus formed as a result of the uplift of red sea gulf of aden and ethiopian rift shoulders the uplift was essentially due to a mantle plume activity a digital elevation model of this region before rifting constructed by using the rotation of its constituent plates and pulling down the rift shoulders reveals that important high areas existed before rifting these highs are interpreted to be the result of mantle plume activity a fast fourier transform was used to smooth the digital elevation model prerift dome before a tomomorphometric analysis was applied to quantify the orientation of each digital elevation model horizontal slice this procedure allowed us to determine a bearing of n30 e for absolute african plate motion since the paleogene

miocene south directed low angle normal fault evolution on kea island west cycladic detachment system greece 1 new structural petrologic and thermochronologic data from kea west cyclades define a crustal scale ductile shear zone and ductile brittle low angle normal fault lanf system both the greenschist facies shear zone forming the footwall and the overlying lanf zone formed during constrictional strains with a consistent top to sw s shear sense with increasing finite strains toward higher structural levels but decreasing temperatures from footwall to hanging wall the tectonostratigraphy comprises a 450 m thick footwall of shallowly dipping schists and calcite marbles representing the intermediate unit of the attic cycladic crystalline acc above the footwall is a 60 m thick highly strained lanf zone consisting of phyllonites cataclastic schists ultramylonitic calcite marbles proto mylonitic calcite marbles and cohesive cataclasites that arch over the whole island these fault rocks exhibit multistage lanfs evolving from ductile to brittle conditions an up to 50 m thick brecciated limestone and dolostone sequence forms the unmetamorphosed hanging wall which is most probably part of the upper unit of the acc multiequilibrium p t estimates on chlorite white mica pairs in the footwall yield 7 5 5 kbar 360 c 450 c for inclusions in albite and epidote 5 5 3 kbar 400 c 350 c for the main foliation and 3 2 kbar 350 c 280 c in localized shear bands c and c foliations the 40ar 39ar white mica footwall cooling ages demonstrate that greenschist facies retrogression occurred between 21 and 17 ma localized late decimeter thick shear zones were active and dynamically recrystallized before 15 to 13 ma the lanf on kea together with similar structures in south attica and the west cyclades define the west cycladic detachment system characterized by ductile to brittle top sw s shear sense

analytical study on steepness of ripples and dunes the mechanics of the limiting equilibrium profiles of ripples and dunes are presented the analysis is based on low sediment transport rates in which the sediment essentially moves as bedload the sediment transport rate is taken as proportional to some power m of the local velocity a two dimensional flow is assumed in which velocities are computed on the basis of a discontinuous potential flow model and on the basis of an incompressible rotational inviscid flow model a family of curves representing the relationship between the limiting steepness of bedforms and the relative depth of flow for various values of m is presented the analytical results are compared with the observed data and the comparison shows a fair agreement

a new kinematic approach for the danakil block using a digital elevation model representation abstract data from the literature are integrated in a regional digital elevation model dem in order to analyse the motion of the danakil block with regard to the arabian and somalian plates the application of the poles and angles of rotation taken from the literature induces a superposition of the danakil block on the arabian plate and the formation of a gap in the afar region the determination of new poles of rotation using a best fitting procedure allows one to avoid these drawbacks in all cases calculations are carried out keeping the nubian plate stationary the present approach shows that the danakil block is an independent entity and is not related to the nubian and arabian plates between the oligocene and the miocene it has been submitted to a n20 e sinistral strike slip motion anterior to the rotation itself that was started in the middle miocene this rotation is directed by a mechanical couple due to the combination of the red sea and north afar extensions

disruption of the hellenic arc late miocene extensional detachment faults and steep pliocene quaternary normal faults or what happened at corinth 1 extensional faults exposed in the peloponnesus and mainland greece most of which are described here for the first time record a transition from regional extension of the aegean domain to the modern tectonic system the east peloponnesus detachment system trends north northwest from the southern peloponnesus to 30 km north of the gulf of corinth dips gently northeast and is late miocene early pliocene in age it has a minimum displacement of 25 30 km and appears to be the youngest of the regional scale extensional systems with significant displacement that formed parallel to the hellenic arc the partially coeval east sterea extensional system which extends from the gulf of corinth to the aegean sea contains low angle normal faults that both crosscut and trend parallel to older structures of the hellenic arc late miocene to early pliocene displacement within this zone disrupted the arc parallel structures of the hellenides upper pliocene quaternary normal faults which trend approximately east west and generally dip steeply at the surface continue the disruption of the hellenic arc much of the subsidence within the gulf of corinth appears to be unrelated to the younger faults and is instead related to the motion on the east peloponnesus detachment which crosscuts the modern graben

geometry and kinematics of mykonos detachment cyclades greece evidence for slip at shallow dip 1 the eastern part of mykonos island cyclades greece shows the detailed internal structure of a two branch shallow dipping extensional detachment system of miocene age this paper shows that the last stage of slip along the detachment during the deposition of syn rift sediments occurred with a very low dip and proposes that this geometry prevailed since the initiation of extension extensional deformation during and after a 13 ma old granite intrusion is taken up by two main shallow dipping shear zones 1 the lower livada detachment which extends laterally across tinos island is a ductile structure located at the interface between the granite and the upper cycladic nappe metabasites a pervasive top to the ne shearing deformation is observed throughout the granite in this island with a strong gradient toward the intrusive contact later brittle faults shallowly and steeply dipping rework the ductile deformation with the same overall shear sense 2 the upper mykonos detachment is brittle and separates the metabasites from late miocene sandstones and conglomerates the detachment fault dips 12 15 toward the nne and its sense of shear is consistent with that of the livada detachment soft sediment deformation during the time of detachment faulting and the presence of steep normal faults that root into the detachment gouge indicate a shallow depth of deformation rotations about vertical and horizontal axes can be reconstructed within and below the detachment zone indicating that the overall direction of extension is nne ssw with a sense of shear toward the nne and the dip of the fault is throughout very low the two detachments have accommodated several tens of kilometers of horizontal extension during the formation of the aegean sea which emphasizes the importance of low angle extensional faults and shear zones in extensional tectonics

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

a comparison of geodetic and finite strain pattern in the aegean geodynamic implications abstract a comparison of the active strain pattern of the aegean constrained by global positioning system measurements and the oligo miocene finite strain field shows some striking similarities in terms of direction and rates of extension the geometry of extension at crustal scale is also very similar with north dipping normal faults connecting near the brittle ductile transition to shallow north dipping shear zones this pattern of extension is not significantly modified by the recent extrusion of the motion of anatolia and aegea the persistence over more than 25 myr of the same pattern of extension suggests that the cause for extension resides within the aegean lithosphere gravitational collapse allowed by extensional boundary conditions after 30 ma slab retreat is the primary cause for post orogenic extension in the aegean and western anatolia

review of the neotectonics of the eastern turkish armenian plateau by geomorphic analysis of digital elevation model imagery digital elevation model dem images provide synoptic views of the earth s surface allowing the analysis of landforms of still active tectonic and volcanic structures at regional scale a dem at 250 m pixel size constitutes regional scale data particularly efficient to investigate the late miocene quaternary deformation of the eastern turkish armenian plateau in the arabian eurasian area of convergence geomorphic analysis of the dem image associated with review of fault plane solutions of earthquakes show that faults are mostly strike slip with small vertical component here we show that the orientations of the tectonic and volcanic structures fit with a tectonic regime characterized by n s shortening and e w lengthening consistent with westward escape of anatolia perpendicular to the direction of the arabia eurasia shortening the uniform uplift of the plateau the predominance of strike slip faulting the lack of major thrusts and the occurrence of normal faults do not support a model of going on crustal thickening due to intracontinental convergence on the contrary our observations can be better interpreted in terms of lithospheric thinning and mantle upwelling related to gravity escape of anatolia

riffle pool morphometry and stage dependant morphodynamics of a large floodplain river vereinigte mulde sachsen anhalt germany riffle pool sequences are a common feature of gravel bed rivers however mechanisms of their generation and maintenance are still not fully understood in this study a monitoring approach is employed that focuses on analysing cross sectional and longitudinal channel geometry of a large floodplain river vereinigte mulde sachsen anhalt germany with a high temporal and spatial resolution in order to conclude from stage dependant morphometric changes to riffle and pool maintaining processes in accordance with previous authors pool cross sections of the mulde river are narrow and riffle cross sections are wide suggesting that they should rather be addressed as two general types of channel cross sections than solely as bedforms at high flows riffles and pools in the study reaches changed in length and height but not in position pools were scoured and riffles aggraded a development which was reversed during receding flows below the threshold of 0 4qbf 40 bankfull discharge an index for the longitudinal amplitude of riffle pool sequences the bed undulation intensity or bedform amplitude is introduced and proved to be highly significant as a form parameter its first derivative as a process parameter the process of pool scour and riffle fill is addressed as bedform maintenance or bedform accentuation it is indicated by increasing longitudinal bed amplitudes according to the observed dynamics of bed amplitudes maintenance of riffle pool sequences lags behind discharge peaks maximum bed amplitudes may be reached with a delay of several days after peak discharges increasing bed undulation intensity is interpreted to indicate bed mobility post flood decrease of the bed undulation intensity indicates a retrograde phase when transport from pools to riffles has ceased and bed mobility is restricted to riffle tails and heads of pools this type of transport behaviour is referred to as disconnected mobility the comparison of two river reaches one with undisturbed sediment supply the other with sediment deficit suggests that high bed undulation intensity values at low flows indicate sediment deficit and potentially channel degrading conditions it is more generally hypothesized that channel bed undulations constitute a major component of form roughness and that increased bed amplitudes are an important feature of channel bed adjustment to sediment deficit be it temporally during late floods or permanently due to a supply limitation of bedload copyright 2011 john wiley sons ltd

annual regime of bedforms roughness and flow resistance lillooet river british columbia bc a field study to examine the statistical character of dune morphology and the correlation among dune morphology discharge and flow resistance was conducted in a meandering reach of lillooet river near pemberton british columbia canada the field season spanned the 1995 1996 hydrologic year with sample day discharge events ranging between 33 and 425 m3 s 1 surveys of the bed morphology along the thalweg in two dune fields a and b were completed using an echo sounder with chart recorder that enabled the measurement of more than 4000 dunes dune height ranged between 0 08 and 0 96 m length between 2 01 and 20 99 m and steepness between 0 02 and 0 10 histograms of each dune shape height length steepness sample most often displayed positive skewness and non gaussian distributions gamma beta and weibull median sample height and length histograms displayed positive skewness and steepness was nearly gaussian histograms of all dimensionless dunes i e measurement divided by average measurement of sample were gaussian and slightly leptokurtic neither the height nor length of dunes measured in this investigation were successfully predicted by the empirical models of allen allen j r l 1984 developments in sedimentology sedimentary structures their character and physical basis 2nd edn elsevier new york vol 30 a and b 1256 pp fredsoe j hydraul div am soc civ eng 108 hy8 1982 932 or yalin j hydraul div am soc civ eng 90 hy5 1964 105 least squares regression models for dune height relations produced here are similar to models published by other field researchers regression models for dune length only conform to those developed elsewhere if the discharge of the study rivers was similar the energy gradient in dune field a varied within a smaller range than in field b enabling dune size to become more fully equilibrated with respect to flow environment although the average froude numbers were much less than critical dunes appeared to wash out towards a plane bed as discharge increased due to a change from a bedload to suspended load dominated sediment transport regime flow resistance increased most rapidly during changes in base flow and at the beginning and end of the seasonal flood resistance tended to be smaller in field a than b reflecting local differences in energy gradient flow resistance increased until a dune steepness of 0 070 was attained and then decreased the steepness value was considered to be coincident with kolk generation dyer k r 1986 coastal and estuarine sediment dynamics wiley ny 342 pp suggesting that macroturbulent flow structures play an important role in defining the roughness of dunes on a channel bed

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

the afar depression transition between continental rifting and sea floor spreading abstract detailed geophysical and geological studies were undertaken in the 1970 s in the afar depression ethiopia in order to study the processes of continental break up occurring in this unique setting the afar is located between the ethiopian and somali plateaus and the red sea we have re evaluated the available seismic refraction and gravity data using modern interpretation techniques and incorporated new information derived from magnetic gravity seismicity and seismic refraction data the results of the re evaluation indicate that the afar depression is a transition zone between the continental rifts of kenya and the present ongoing sea floor spreading of the red sea and the gulf of aden in the depression itself the crust is greatly attenuated and is underlain by a low velocity 7 4 7 5 km s high temperature upper mantle material however it is still a continental crust which thins to the northeast and east towards the red sea and the gulf of aden it is not a newly formed oceanic crust as has been suggested in the past the trends of the areas of crustal thinning are indicated by the gravity anomalies the trend of the ethiopian rift reaches south afar where the trend of crustal thinning changes and becomes parallel to the red sea trend it is offset en echelon from the spreading area of the red sea which is marked by an alignment of gravity maxima the gulf of aden trend continues west towards the ethiopian rift the gravity trends coincide with areas of maximum crustal thinning and may thus suggest a possible triple junction in development

how much divergence has occurred between africa and arabia as a result of the opening of the red sea large coastline gaps in red sea palinspastic reconstructions are not tenable if interpretations of seismic refraction data from the continental margin of southwest saudi arabia in the southern red sea typify the crustal configuration of most of the basin the composition of the crust beneath 4 6 km of shelf and coastal plain sediment is not certain ely assuming 1 that it is extended continental crust that could be reorganized in a kinematically reconstructed cross section of the prerift continent the minimum possible divergence between the stable parts of africa and arabia can be determined the maximum divergence is derived by assuming 2 that the crust formed from a mantle source by rift related igneous processes i e oceanic crust such crust would disappear during the reconstruction assumption 1 suggests that the widest possible shoreline gap was 30 km at lat 17 n corresponding to a minimum divergence of about 320 km the arabian and african shorelines would overlap by at least 25 40 km if assumption 2 is used this suggests a maximum divergence of about 380 km the buried rocks are probably a mixture of continental and oceanic types thus some amount of coastline overlap is desirable in tectonic reconstructions of the early afro arabian continent

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

a continuum mechanics approach to quantify brittle strain on weak faults application to the extensional reactivation of shallow dipping discontinuities a number of field observations suggest that sliding on fault planes may occur at very shallow dip in the brittle field the existence of active low angle normal faults is much debated because 1 the classical theory of fault mechanics implies that faults are locked when the dip is less than 30 and 2 shallow dipping fault planes do not produce large earthquakes m 5 5 to reconcile observations and theory we propose a new model for fault reactivation by introducing an elasto plastic frictional fault gouge as an alternative to the classical dislocation models with frictional properties contrary to the classical model which implies that the dilation angle equals the friction angle our model accounts for and permits 0 in the fault gouge as deduced from laboratory and field observations whilst the predicted locking angles differ in most cases by less than 10 from the classical model a significant amount of plastic strain strain occurring in elasto plastic regime is predicted to occur on badly oriented faults prior to locking in a strain hardening regime we describe four modes of reactivation which include complete partial reactivation with without tensile failure in the surrounding medium this paper presents analytical solutions to separate those four different modes as well as numerically computed estimates of the amount of plastic strain accumulated before locking we conclude that plastic strain on badly oriented faults is favoured by compaction of the fault gouge and that those faults are probably aseismic because this strain always occurs in a hardening regime

fault structure and related basins of the north aegean sea and its surroundings 1 fault structure and basin evolution in the northern aegean sea and its surroundings have been investigated using bathymetry available onshore and offshore seismic profiles onshore fault patterns from ne greece nw turkey three islands in the aegean sea surface ruptures associated with the 1978 thessaloniki earthquakes gps measurements from north aegean islands and a number of earthquake focal plane solutions and historic seismicity bathymetric and isopach data show that the north aegean trough can be divided into the sporades basin and the saros trough post miocene sediment thickness differences in these basins offset of distinct horizons and frequent seismicity along basin bounding faults indicate that sediment accumulation in the area is fault controlled offshore seismic profiles show that the basin bounding faults are dominantly characterized by apparent normal components as well as strike slip components inferred from typical fault zone profiles additional evidence for existence of strike slip faulting comes from earthquake focal plane solutions we refined the pattern and kinematics of the faults controlling the basins and classified them into two major groups the faults in the first group trend ne sw and ene wsw and are here interpreted to be dominantly right lateral strike slip with normal or reverse components these faults accommodate a similar amount of deformation like the ganos fault and thus represent the westernmost extension of the north anatolian fault zone the faults in the second group trend nw se and are dominantly normal faults with an occasional left lateral component these faults are believed to manifest the termination of the north anatolian fault zone because of the segmentation of the right lateral strike slip faults and the preexisting ne trending tectonic grain the basins are compartmentalized into smaller depocenters basins are orientated with their long axes either parallel to the ne sw to ene wsw trending echelon strike slip faults or in the zone north of the strike slip faults parallel to the nw se trending normal faults the interpretations regarding the kinematics of the faults are consistent with the data compiled from the islands near the faults and from the land in ne greece and nw turkey the northern aegean basins and their spatial relationships to the fault architecture representing the diffused termination of the north anatolian fault system are consistent with the mechanical principles of the strike slip tectonics

interactions between bed forms topography turbulence and transport 1 results are presented examining the interaction between two sandy bed forms under low sediment transport conditions in a small laboratory flume the initial artificially made bed forms were out of equilibrium with the flow field temporal evolution of bed forms was monitored using time lapse photography in order to characterize bed form adjustment to the imposed flow velocity measurements were collected using an acoustic doppler velocimeter to characterize both mean flow and turbulence associated with different bed form geometries sandy bed forms all had identical initial geometries however the initial distance between bed form crests was varied between experiments overall deformation of the bed varied as a function of initial bed form spacing however bed forms evolved unpredictably as periods of relatively slow change were punctuated by periods of rapidly changing geometry subtle changes in bed form trough geometry were found to have a strong influence on turbulence and therefore sediment transport comparison with field studies suggests that the mechanisms described herein are active in natural systems

slab top dips resolved by teleseismic converted waves in the hellenic subduction zone the variations of the arrival times and polarities with backazimuth and distance of teleseismic p to s converted waves at interfaces bounding the slab crust under the upper plate mantle are used to constrain the depth dip angle and azimuth of the slab of the hellenic subduction zone a grid search is designed to estimate the model parameters dip values of 16 18 with an azimuth of 20 to 40 are thus derived at 3 sites aligned over 50 km along the eastern coast of peloponnesus they are consistent with the variation from 54 to 61 km of the slab top depths constrained below each receiver north of the gulfs of corinth and evvia a similar depth for the top of the slab is found at a distance from the subduction at least 100 km larger this suggests flatter subduction of a different slab segment such a variation in slab attitude at depth across the region from south of the eastern gulf of corinth to north of evvia is a candidate for the control of the recent or active localized crustal thinning of the upper plate we documented in earlier work and of the surface deformation

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

northwest to north northwest extension direction in the ethiopian rift deduced from the orientation of extension structures and fault slip analysis northeast to north northeast trends of eruptive centers some of which formed at the termination of faults and en echelon extension fractures the largest one of which is 0 1 km wide up to 1 km long and at least 50 m deep exist between lat 7 n and 9 n in the ethiopian rift on systeme probatoire d9observation de la terre spot imagery the extension fractures form scars in the rift floor border faults of the rift are generally oriented northeast to north northeast two fault systems observed on land sat multi spectral scanner mss cross the rift the bilate weyira fault with a north northwest strike and the wonji fault belt with a north northeast trend north northwest striking faults cutting across the rift are interpreted to be transfer faults that cut the rift into rhomboid shaped basins extension fractures and rows of eruptive centers collectively referred to as extension structures are used in the paper to infer the direction of plate motion in the ethiopian rift northwest to north northwest extension of the rift is deduced by assuming that the direction of opening of extension structures is also the orientation of the minimum principal stress 3 fault slip inversion on faults that cut post miocene volcanic rocks confirms this interpretation

recent 1999 2003 canadian research on contemporary processes of river erosion and sedimentation and river mechanics contributions by canadian fluvial geomorphologists between 1999 and 2003 are discussed under four major themes sediment yield and sediment dynamics of large rivers cohesive sediment transport turbulent flow structure and sediment transport and bed material transport and channel morphology the paper concludes with a section on recent technical advances during the review period substantial progress has been made in investigating the details of fluvial processes at relatively small scales examples of this emphasis are the studies of flow structure turbulence characteristics and bedload transport which continue to form central themes in fluvial research in canada translating the knowledge of small scale process related research to an understanding of the behaviour of large scale fluvial systems however continues to be a formidable challenge models play a prominent role in elucidating the link between small scale processes and large scale fluvial geomorphology and as a result a number of papers describing models and modelling results have been published during the review period in addition a number of investigators are now approaching the problem by directly investigating changes in the system of interest at larger scales e g a channel reach over tens of years and attempting to infer what processes may have led to the result it is to be expected that these complementary approaches will contribute to an increased understanding of fluvial systems at a variety of spatial and temporal scales

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

intrusion age of pan african augen gneisses in the southern menderes massif and the age of cooling after alpine ductile extensional deformation

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

have wet and dry precambrian crust largely governed cenozoic intraplate magmatism from arabia to east africa to explain cenozoic continental volcanism between arabia and east africa the existing model infers that a plume impinged beneath ethiopia between 30 ma and 20 ma and volcanism extruded within a 1000 km radius because relative motion of the afro arabian plate was about northeast in the last 120 ma we infer that at 84 ma a plume originated from the core mantle boundary impinged beneath nubia arabia and is now under the tanzania craton this plume caused uplift afro arabian swell and magma under plating after fyfe s idea 1992 the conceptual model proposed herein suggests that following plume impact there was in nubia arabia only intrusion of mafic dykes because the crust was largely unprocessed wet at about 50 ma the plume was under ethiopia and coeval volcanism extruded because the crust was highly recycled dry in zaire burundi and tanzania volcanism is explained to be coeval with the arrival of the plume because there also the crust is recycled in arabia and yemen ethiopia continental flood basalts younger than 30 ma formed because lithospheric extension along the red sea gulf of aden was the cause of or the result of plume s probably originated from the upper mantle

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

slab segmentation and late cenozoic disruption of the hellenic arc the hellenic subduction zone displays well defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy subduction rate and tectonic deformation in space the active hellenic subduction front is dextrally offset by 100 120 km across the kephalonia transform zone coinciding with the junction of a slowly subducting adriatic continental lithosphere in the north 5 10 mm yr and a rapidly subducting ionian oceanic lithosphere in the south 35 mm yr subduction rates can be shown to have decreased from late eocene time onward reaching 5 12 mm yr by late miocene time before increasing again along the southern portion of the subduction system geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic pindos lithosphere until late eocene time followed by subduction of a broad tract of continental or transitional lithosphere hellenic external carbonate platform and then by miocene entry of high density oceanic ionian lithosphere into the southern hellenic trench model results yield an initiation age for the kephalonia transform of 6 8 ma in good agreement with observations consistency between geodynamic model results and geologic observations suggest that the middle miocene and younger deformation of the hellenic upper plate including formation of the central hellenic shear zone can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab using this assumption we make late eocene middle miocene and pliocene reconstructions of the hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation

thrust or detachment exhumation processes in the aegean insight from a field study on ios cyclades greece 1 whether back arc extension in the aegean is symmetric or asymmetric at the regional scale is a key question to the understanding of the dynamics of back arc extension new field observations structural analysis of finite and instantaneous strain and their relationship with metamorphism on ios island cyclades lead us to investigate the significance of the south cycladic shear zone scsz two successive tectonometamorphic events have been documented in the hanging wall and the footwall of the scsz first penetrative top to the south shearing is observed in the upper cycladic blueschists and the lower cycladic basement close to their contact it is expressed in the hanging wall by shear bands and pressure shadows associated to blueschist facies minerals contemporaneous with overthrusting of the cycladic blueschists over the basement unit second large extensional top to the north shear zones lately crosscut the whole stack these constraints allow us to reinterpret the kinematics of the aegean domain during synorogenic and postorogenic periods when replaced in the reconstructed geometry of the hellenic eocene orogenic wedge the observed top to the south thrusting is coeval with extensional shear zones observed in syros that could represent the roof of the cycladic blueschists an extrusion structure is then proposed for the exhumation of the cycladic blueschists in the subduction zone top to the north asymmetric extension together with the andros tinos mykonos and paros naxos detachments can be correlated to oligo miocene extension in the back arc domain

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

45 m y of aegean crust and mantle flow driven by trench retreat the available seismic anisotropy data in the aegean shallow mantle and their relationship with crustal deformation are used for deciphering the lithosphere scale flow pattern driven by rollback of the hellenic subduction slab in the north and central aegean the directions of mantle seismic anisotropy trend parallel to stretching lineations in core complexes of the overlying crust suggesting that crust and mantle have undergone the same direction of flow at the scale of the entire aegean crustal extension is controlled by dextral rotation around a pole located at scutary pec albania that is related to the hellenic trench retreat the intensity of mantle anisotropy increases as a function of distance from the pole and of amount of rotation surface geology reveals that this rotating flow pattern resulted in strains accumulated since 45 ma a slab tear model is suggested to integrate the observed variations of geological events in time and space to subduction dynamics

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

stratigraphy of upper cretaceous palaeogene sequences in the southern and eastern menderes massif western turkey the stratigraphy of the uppermost levels of the menderes massif is controversial and within its details lie vital constraints to the tectonic evolution of south western turkey our primary study was carried out in four reference areas along the southern and eastern menderes massif these areas lie in the upper part of the menderes metamorphic cover and have a clear stratigraphic relationship and contain datable fossils the first one in the akbuk milas area is located south east of bafa lake where the milas then kizilagac and kazikli formations are well exposed there the milas formation grades upwards into the kizilagac formation the contact between the kizilagac and the overlying kazikli formation is not clearly seen but is interpreted as an unconformity the milas and kizilagac formations are also found north of mugla in the region of yatagan and kavaklidere in these areas the milas formation consists of schists and conformably overlying platform type emery and rudist bearing marbles rudists form the main palaeontological data from which a santonian campanian age is indicated the kizilagac formation is characterized by reddish greyish pelagic marbles with marly pelitic interlayers and coarsening up debris flow deposits pelagic marbles within the formation contain planktonic foraminifera and nanoplankton of late campanian to late maastrichtian age the kazikli formation is of flysch type and includes carbonate blocks planktonic foraminifera of middle palaeocene age are present in carbonate lenses within the formation in the serinhisar tavas area mesozoic platform type marbles yilanli formation belonging to the cover series of the menderes massif exhibit an imbricated internal structure two rudist levels can be distinguished in the uppermost part of the formation the first indicates a middle late cenomanian age and the upper one is santonian to campanian in age these marbles are unconformably covered by the palaeocene early eocene zeybekolentepe formation with polygenetic breccias in the cal denizli area the menderes massif succession consists of cherty marbles and clastic rocks with metavolcanic lenses the lower middle eocene alvan formation lies unconformably on this sequence and is interpreted as equivalent to the marble horizons at serinhisar but with pelagic facies the alvan formation consists of shale mafic volcanic rock lenses of limestone and blocks of recrystallized limestone the alvan formation is dated here for the first time by early middle eocene foraminifera and nanoplankton from the matrix of the formation an angular unconformity exists between the upper cretaceous and lower tertiary sequences suggesting that a phase of deformation affected the southern and eastern part of the menderes massif at this time this deformation may be caused by initial obduction of the lycian ophiolite onto the passive margin to the north of the menderes carbonate platform during the latest cretaceous drowning of the platform led to termination of carbonate deposition and deposition of deep water flysch like clastic sediments

computational modeling of dissipation and regeneration of fluvial sand dunes under variable discharges it is observed during flood events that bed forms initially grow in height and make the riverbed rougher but later under high discharge the bed forms grow longer with the opposite effect of making the riverbed smoother after the discharge drops to a lower value new bed forms regenerate on top of the elongated bed forms this mechanism leads to a significant variation in the bed roughness and the water stage and hence determines the behavior of floods and the risk of flood disasters this work presents detailed modeling of bed forms under discharge hydrographs and simulates the conditions under which the bed is flattened out in the upper plane bed regime the flow was simulated by large eddy simulation and the sediments were considered as rigid spheres and modeled in a lagrangian framework the bed morphodynamics were the result of entrainment and deposition of sediment particles we examined several discharge hydrographs in the first case we increased the discharge linearly and then kept it constant after reaching the upper plane bed condition the dunes were generated and grew during the rising stage of discharge when the flow conditions reached the upper plane bed regime high frequency ripples were generated and helped to flatten the bed the results also showed that in contrast with mechanisms in the dune regime the flattening of the bed was associated with a distinct pattern of sediment transport which deposited sediment mainly in the lee side of the dunes and led to flattening of the bed after flattening the sediments were mainly transported in suspension mode as long as flow conditions stayed in the upper plane bed regime the bed remained flat with small high frequency ripples we also examined two other scenarios one with an immediate falling stage of discharge after the rising stage and the other with a period of constant discharge between the rising and falling stages dunes were regenerated during the falling stage of discharge for both cases in the first case the dunes were regenerated before the bed was flattened because of a time lag between the flow and the bed deformation bed flattening was followed by dune regeneration in the second case moreover a significant reduction in the form drag coefficient was observed after the flattening in the second case the reduction in form drag led to a reduction in the flood intensity the model showed its ability to reproduce the key phenomena of the development of subaqueous dunes under conditions of a passing flood wave

bedform characteristics during falling flood stage and morphodynamic interpretation of the middle lower changjiang yangtze river channel china article a survey was conducted to examine river bedforms using side scan sonar sub bottom profiler and an acous tic doppler profiler in the middle lower mid lower changjiang yangtze river downstream of wuhan china during august 14 20 2003 when the discharge was 27 000 36 000 m 3 s 1 the results show bedforms of a range of sizes occur in the channel and their heights and lengths follow an exponential correlation below flemming s maximum line not all bedforms were formed under the flow conditions experienced during the survey as shown by comparison to three existing models in the literature small scale bedforms with a length b60 m defined as flat bed mega ripple and small dune in the present study are mostly in equilibrium and are probably formed under the existing flowconditions the large dunes witha lengthofn60 m are not in equilibrium and are believed to be the relicts of previous largedischargesnow undergoing adjustment different bedform types occur in the five riverreaches inthis section of the changjiang wuhan tianjiazhen tianjiazhen anqing anqing maanshan maanshan jiangyin and jiangyin estuary downstream in the narrow and single channel reaches above anqing large small dunes are limited to the channel with higher water surface slope where stream power is strong enough for riverbed sediments to be moved frequently in the downstream reaches be tween anqing and jiangyin characterized by anabranching channels small scale bedforms superimposed on large dunes occur widely due to intensive riverbed sediment transport from frequent diverging converging flow during both floods and low flow periods mega ripples and flat beds prevail in the lowermost channel

mechanical basis for slip along low angle normal faults 1 the existence of active low angle normal faults is much debated because 1 the classical theory of fault mechanics implies that normal faults are locked when the dip is less than 30 and 2 shallow dipping extensional fault planes do not produce large earthquakes m 5 5 however a number of field observations suggest that brittle deformation occurs on low angle normal faults at very shallow dip to reconcile observations and theory we use an alternative model of fault reactivation including a thick elasto plastic frictional fault gouge and test it at large strain by the mean of 2d mechanical modeling we show that plastic compaction allows reducing the effective friction of faults sufficiently for low angle normal faults to be active at dip of 20 as the model predicts that these faults must be active in a slip hardening regime it prevents the occurrence of large earthquakes however we also evidence the neoformation of riedel type shear bands within thick fault zone which we believe may be responsible for repeated small earthquakes and we apply the model to the gulf of corinth greece

exploratory models of long term crustal flow and resulting seismicity across the alpine aegean orogen 1 long term crustal flow is computed with a kinematic finite element model based on iterated weighted least squares fits to data and prior constraints data include 773 fault traces 106 fault offset rates 510 geodetic velocities 2566 principal stress azimuths and velocity boundary conditions representing the rigid parts of the eurasia africa and anatolia plates model predictions include long term velocities fault slip rates and distributed permanent strain rates between faults one model assumes that geodetic velocities measured adjacent to the aegean trench reflect a temporarily locked subduction zone in this case long term subduction velocity averages 45 mm yr and rapid crustal extension is predicted in the southern aegean sea another model assumes steady creeping subduction in this case subduction velocity averages only 29 mm yr and the eastern aegean seafloor is predicted to be more nearly rigid long term seismicity maps are computed for each model on the basis of the shift hypotheses and previous global calibrations of plate boundary earthquake production retrospective comparisons to seismic catalogs are encouraging map patterns spatial distribution functions and total earthquake counts are all comparable while neither model accurately predicts earthquake rates at all magnitudes the creeping subduction model is more accurate for strong m6 events which dominate the seismic hazard

the magnetic quiet zone in the eastern gulf of aden implications for the early development of the continental margin summary the magnetic quiet zone in the eastern gulf of aden is located between the oceanic crust of sheba ridge and the continental crust of arabia and somalia and is separated from both by important structural boundaries the seaward boundary is marked by the end of the seafloor spreading magnetic anomaly sequence and by a basement depth discontinuity the landward boundary is marked by escarpments made up of a series of normal faults these escarpments extend from 2 3 km below sea level to 1500 m above sea level and are equivalent of the hinge zone found at mature continental margins the magnetic field in the quiet zone is flat in some areas and in others is characterized by anomalies of up to several hundred gammas which are correlatable over distances of up to about 20 km and which appear related to basement topography the basement lacks the topographic slope characteristic of mid ocean ridge flanks and is characterized by moderately rough relief the crustal structure appears quite heterogeneous and where the crustal thicknesses have been determined they are slightly greater than those of oceanic crust new heat flow measurements show high values 95 7 123 3 mw m 2 in the quiet zone with values decreasing from sheba ridge toward the coast the unusual structure of the quiet zone and the observations that more opening appears to have occurred between arabia and somalia than can be accounted for by the oceanic crust of sheba ridge leads to the suggestion that the magnetic quiet zone was generated by diffuse extension of continental crust through a combination of rotational listric faulting and dyke injection this possibility is investigated using both a stretching or lithospheric attenuation model and a model in which a portion of the extension occurs through dyke injection it is found that these models can adequately match the observed heat flow and basement depths although very large amounts of extension 4 6 are required in the deep seaward portion of the quiet zone this results in more extension than is compatible with the documented motion between arabia and africa however formation of the magnetic quiet zone occurred over a period of 10 15 myr rather than instantaneously as assumed in the simple models when the effects of a finite length rifting episode are considered less extension is required and the observed geophysical data are consistent with a diffuse extension origin for the magnetic quiet zone

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

tomomorphometry of the somma vesuvius volcano italy 1 a tomomorphometric analysis of the somma vesuvius topography is presented this consists in extracting horizontal cross sections at different altitudes and in determining some morphometric parameters radius of the circle with a surface area equal to the cross section circularity ratio between the major and minor axis of the best fitting ellipse orientation of the ellipse major axis and the x y centroid the somma includes three portions the apron zone the flanks and the summit caldera boundary between 225 m and 525 m is 50 60 between 600 m and 775 m is 130 135 these are the preferred strike of the eruptive fissures affecting the northwestern somma flanks the faults affecting the whole edifice the nodal planes from local earthquakes the somma activity developed along a ne sw structural discontinuity whereas the post caldera activity concentrated along a nw se striking structure somma activity migrates from se to nw

the stability of ripples and dunes abstract the stability of ripples and dunes in flows of finite depth are investigated for the linear small amplitude case and also for the more realistic finite amplitude situation for the former perturbation approach is taken leading to the general result that without the inclusion of some lag between the sediment transport rate and the boundary shear stress all wavelengths are unstable this results from an upstream shift in the stress relative to the bedform leading to deposition at the crest by assuming a realistic lag based on the mechanics of bed load transport a fastest growing wave at ripple scales results similarly if suspended sediment were included longer lags result and a dune scale instability could result some investigators have invoked a gravitational effect arguing that sediment transport is enhanced downslope and retarded upslope this creates an effective downstream shift in the transport rate and some argue that both ripple and dune instabilities result however a realistic evaluation of this effect shows that it is much too small to be effective naturally occurring bedforms are of finite amplitude typically they are asymmetrical often causing flow separation this highly non linear process creates a vastly different flow environment from that assumed in the initial stability case a wake like flow structure develops downstream of the separation zone and an internal boundary layer develops beneath the complex interaction of these two different flow regimes as well as the effect induced by the topography of the bedform itself produces a shear stress field that dictates the stability of the feature itself

macroturbulence generated by dunes fraser river canada abstract a selectable frequency acoustic profiler and electromagnetic current meter were deployed in the lower fraser river canada to examine large turbulent structures features were generated on the lower stoss sides of dunes and appeared at the surface tens of metres downstream as strong upwellings boils they were identified with acoustic clouds in the acoustic profile event recurrence periods measured from acoustic time series and from ejection events identified in the current meter record had similar two component frequency distributions but the acoustic values lacked the highest frequencies a comparison of measured periods with predictions from the strouhal law indicate that both dune amplitude and the internal boundary layer developed over the dunes are significant length scales associated with the generation of the macroturbulence our data give no support to the notion that boils develop from microturbulent bursts