an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey abstract this paper presents an attenuation relationship of peak ground acceleration pga derived from turkish strong motion data for rock soil and soft soil sites and an iso acceleration map of turkey based on this relationship for the purpose among all the three component accessible records 221 records from 122 earthquakes that occurred in turkey between 1976 and november 2003 were selected the database was compiled for earthquakes with moment magnitudes m w and pga values ranging between 4 1 and 7 5 and 20 and 806 gal and distances to epicenter considered in the database were between 5 and 100 km from the regression analysis of the data an attenuation equation of pga considering rock soil and soft soil conditions was developed the pga values predicted from the equation suggested in this study and those both from a few domestic equations and some imported equations were compared in addition an iso acceleration map of turkey was constructed using the suggested attenuation equation and considering both known active faults and epicenter locations of the earthquakes that have occurred in turkey

river behaviour and holocene alluviation the river severn at welshpool mid wales u k a combination of archaeological evidence 14c dates terrace mapping heavy metal analysis grain size analysis and historical maps is used in a detailed analysis of the alluvial history of the river severn floodplain around welshpool in mid wales u k welshpool gravels underlie a higher terrace surface up to 6 7 m above the present channel they form a sequence of gravels at least 30 m in thickness the upper surface is characterized by a series of braided palaeochannel patterns these sediments were probably deposited at the end of the last glaciation as outwash and are contemporaneous with other high gravelly terrace deposits found in the severn and other mid wales basins overlying the welshpool gravels on the contemporary floodplain are a variable thickness of finer sediments the leighton silts morphological mapping and dating of two cut offs to 2850 60 a bp and 1190 70 a bp indicates that a channel pattern similar to the present planform had formed by the mid to late holocene from this period floodplain development has been dominated by a single thread meandering channel with fine vertical sedimentation and limited lateral gravel accretion abandonment of extended lengths of channel formed by an avulsion mechanism is apparent a combination of historical map data 14c dates and the analysis for heavy metals in fine sediments which were washed into the river system during mining indicates that there has been at least 4 m of sedimentation since the early 17th century but only in a central belt of varying width metal rich waste identified in the fine sediments of this zone of trehelig silts indicates those areas which were most heavily sedimented during the peak of metalliferous mining in the 18th and 19th centuries although the near channel margins appear to be superficially similar to the older floodplain the spatial and vertical pattern of historic sedimentation is complex and is not reflected in marked elevation differences the division of sedimentation periods into these three broad time spans late quaternary terraces late holocene alluviation and avulsion and the historical metal mining period shows that an apparently simple planar floodplain is in reality underlain by complex sedimentation units floodplain construction has involved the development of inset units in cut offs and adjacent to migrating channels as well as the expected contrasts between in channel and overbank environments this has implications both for alluvial sedimentation modelling and for the identification of high pollution zones on the floodplain these cannot be predicted on the basis of simple in channel and overbank environments given the historically complex evolution

residual circulations due to bottom roughness variability under tidal flows abstract tidal flows over irregular bathymetry are known to produce residual circulation flows due to nonlinear interaction with gradients of depth using the depth averaged vorticity equations the generation of residual vorticity and residual flows due to variation of the frictional coefficient are examined the authors find that the contribution due to bottom roughness variations can be as large as that arising from gradients of depth and velocity specific cases are considered on the northern california shelf georges bank and the u s south atlantic bight the generation of residual vorticity is a strong function of the length scales at which roughness or depth vary length scales of bottom roughness variation are commonly within the range of greatest effect e g sand patchiness cobbly outcrops etc the site specific cases show that the bottom roughness variability can generate as much residual circulation as that expected from depth variability the implication for numerical modeling studies

discussion of an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey by ulusay et al eng geol 74 265 291 2004

residual sediment transport paths on a tidal sand bank a comparison between the modified mclaren model and bedform analysis abstract in order to evaluate the validity of the modified mclaren model for sand transport on a tidal sand bank 42 grab samples taken from the northern part of the kwintebank were decalcified sieved and analyzed for statistical parameters the areal distribution of mean grain size standard deviation and skewness were defined and used to determine the residual transport directions the grain size trends taken into consideration were that the sediment becomes finer better sorted and more negatively skewed along the transport pathways f b and the sediment becomes coarser better sorted and more positively skewed along the transport pathways c b these were compared with the transport paths inferred from bedform asymmetries obtained by side scan sonar records there were major differences between the sediment transport paths resulting from the two techniques when the f b trend and small dune asymmetries are compared only 5 out of 24 cases showed agreement 30 whereas in 9 cases the trends were 180 30 different there was even less agreement between the c b trend and the asymmetry of the small dunes only 1 out of 24 cases agreed 30 and almost half of the cases were 90 30 different the sediment transport directions deduced from the morphological analysis of the large dunes all point in the direction of the peak flood current the large dunes seem to be more suitable indicators of the sediment transport paths than the small ones however they conflict with the vectors resulting from the f b trend only one out of 20 cases agrees 30 while in 13 cases the vectors are 180 30 different and in three cases 90 30 neither do the transport directions from the c b trend agree with those deduced from the large dunes only one case agrees 30 while in four out of 20 cases the vectors point in opposite directions in four cases the vectors are 90 30 different the asymmetric cross section of the sand bank suggests sediment transport in a northwest direction it does not seem probable however that sediment transport occurs by migration of the whole sand bank the transport directions inferred from the bank morphology are quite different from the f b trend in 12 out of 42 cases the vectors agree 30 in four cases the vectors point in opposite directions and in 15 cases they are 90 30 different there is slightly more agreement between the c b trend and the transport directions deduced from the sand bank 16 out of 42 cases agree 30 in nine cases the vectors point in opposite directions and three cases are 90 30 different from this study it seems that the residual sediment transport directions can best be deduced from the morphological characteristics of the large dunes the departures between the results of the sediment trend analysis according to the modified mclaren model and the morphology of the subaqueous bedforms are partly explained by the location of the study area near the edge of the sand bank probably better results of the sediment trend analysis would be obtained if samples over the whole length of the sand bank were analyzed and compared perhaps a smaller spacing between the samples would improve the results as well and maybe the samples should not have been decalcified possibly the different transport patterns are attributed to different sediment transport processes which makes a comparison virtually impossible

the cross sectional shape of tidal sandbanks modeling and observations to improve our understanding of tidal sandbank dynamics we have developed a nonlinear morphodynamic model a crucial property of the model is that it fully resolves the dynamics on the fast tidal timescale allowing for asymmetric tidal flow with an m0 m2 and m4 component this approach extending earlier research on the formation of tidal sandbanks leads to equilibrium profiles their heights 60 90 of the water depth and shapes are controlled by the mode of sediment transport and the hydrodynamic conditions bed load transport under symmetrical tidal conditions leads to high spiky banks several mechanisms tend to lower and smooth these profiles such as the relaxation of suspended sediment wind wave stirring and tidal asymmetry this last causes the profiles to be asymmetric as well the morphodynamic equilibrium expresses a tidally averaged balance between a destabilizing flux due to fluid drag and the downslope transport induced by both tidal flow and wind wave stirring the modeled profiles are in fair agreement with observations from the north sea

high resolution temperature observations of a trapped nonlinear diurnal tide influencing cold water corals on the logachev mounds abstract a high resolution thermistor string mooring of 120 m length was used to measure turbulence processes in the water layer above the foot of a densely populated cold water coral mound at 919 m depth at the southeast slope of rockall bank in the logachev area north east atlantic ocean as expected from previous current observations the temperature data reveal a dominant diurnal tidal periodicity associated with topography trapped weakly bottom intensified waves these baroclinic diurnal waves are driven to near resonance around the mound and have vertical amplitudes exceeding the mooring line their horizontal excursion length matches the size of the mound which causes a residual current around and flux up the mound as their particle velocities also match the phase speed of the wave traveling around the mound these waves can become highly nonlinear and show largest turbulence due to wave breaking at the transition from warming downslope to cooling upslope tidal phase averaged over the entire 9 day time series and the 120 m vertical range mean turbulent kinetic energy dissipation amounts to 2 2 1 1 10 7 w kg 1 and mean vertical eddy diffusivity to 9 5 10 3 m2 s 1 with short term variations over four orders of magnitude such large turbulence more than 100 times larger than open ocean values and comparable with that observed in tidally energetic shelf break shallow sea areas will affect the nutrient replenishment of the cold water corals

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

a mechanism for the formation and maintenance of shore oblique sand ridges on storm dominated shelves a remarkable set of shore oblique sand ridges occupies the inner portion of the storm dominated middle atlantic and south atlantic bights off the east coast of the united states of america a mechanism for present day formation and growth of these distinctive geological features follows from a linearized analysis of the stability of alongshore periodic topographical perturbations based on a depth averaged fluid dynamical model with a simple representation of sediment transport the analysis indicates exponential growth of shore oblique features as a result of offshore deflection of storm driven alongshore flows at ridge crests which leads to a convergence of sediment flux because the effective carrying capacity decreases with increasing distance offshore the analysis indicates a set of conditions required for ridge growth model solutions for topography under conditions favorable for ridge growth are strikingly similar to the observed sand ridges

floodplain evolution in the east midlands united kingdom the lateglacial and flandrian alluvial record from the soar and nene valleys this paper describes and interprets the floodplain stratigraphy of two low energy rivers in the east midlands u k and goes on to present an appropriate model of floodplain evolution that may be applicable to other lowland rivers in temperate mid latitudes work has been undertaken at the reach level to try and characterize the entire system in general only laterally extensive exposures have been used and detailed stratigraphic and microstratigraphic recording has been used to facilitate process interpretations all the sites have been radiocarbon dated the dataset consists of three sites in the soar valley and five sites in the larger nene valley the most common sedimentary architecture is a basal gravel with occasional shallow channels covered by a mixed loam sand silt clay of variable thickness with landsurfaces and evidence of bioturbation this loam is frequently interrupted by palaeochannels and finally all these sediments are buried by a massive silt clay unit most of the palaeochannels were abandoned in the early flandrian or between ca 3500 years bp and 2000 years bp the superficial silty clay is diachronous largely because of the irregular topography of the floodplain onto which it was deposited dates from non palaeochannel sections range from ca 3500 bp to ca 2100 years bp the floodplain stratigraphy has been profoundly influenced by soil development and sub aerial processes especially tree throw which has produced distinctive sedimentary structures the loam unit is interpreted as a soil which developed in between both silting palaeochannels and active channels the landsurfaces are both earlier and contemporaneous with the later phase of channel abandonment there is some evidence ca 5000 4000 bp of a rise in floodplain watertables an evolutionary model is proposed which can account for the stratigraphic evidence reported here it is based upon the development of an anastomosing stable multiple channel system from an initial braided river topography and its eventual conversion to a predominantly single channel system due to floodplain and channel siltation the reduction of channels is compensated for by a change in channel types and capacities while the floodplain aggrades this is the stable bed aggrading banks sbab model which necessitates no changes in discharges it is suggested that the sub meandering or straight to sinuous nature of many lowland u k channels may be due to their evolution from an anastomosing pattern where the least meandering channels survived typically with a box s shape planform and at the edges of the floodplain the sites also show that the lateglacial fluvial history of the two catchments seems to have been very different with incision and subsequent aggradation occurring during the younger dryas in the nene but not in the soar given the proximity and similarity of the two catchments this suggests that relatively minor local factors may have been able to push some catchments across fluvial thresholds in contrast the flandrian history of the two rivers has been broadly similar although there is evidence of greater lateral instability and floodplain reworking in the soar which may be due to hydrogeological factors or a different landuse history this work strongly suggests that new process based interpretations of floodplain stratigraphy and new models of floodplain evolution may be required before alluvial history can be easily related to the changing lateglacial and flandrian climate of lowland u k

an overview of local site effects and the associated building damage in adapazari during the 17 august 1999 izmit earthquake two major earthquakes occurred in turkey along the north anatolian fault in 1999 the first one which occurred on 17 august 1999 had a moment magnitude of 7 4 and ruptured the 140 km segment of the fault in the marmara region adapazari a city with a population of 190 000 which is mostly located on a deep alluvial basin in the near field of the ruptured fault was among the worst affected urban areas in the earthquake affected region the distribution of damage over the city was highly nonuniform indicating the variability of the ground response to the strong motion five to six story buildings located over deep alluvial soils were most adversely affected by the earthquake geotechnical characteristics of the alluvial basin of adapazari are evaluated using the deep and shallow borehole logs and the measured parameters from the field and laboratory this data is used for developing representative one dimensional site response models for various depths of alluvium and for liquefaction assessment in saturated surface soils recorded data from several aftershocks are utilized for model calibration the results of soil response studies are found to be highly correlated with the general trends in the intensity and distribution of building damage based on in situ tests soil liquefaction is determined to have occurred extensively in adapazari which is in conformity with the postearthquake observations of widespread liquefaction induced foundation displacements evidently liquefied soil layers served as passive isolation mechanism for numerous buildings some of which were subjected to excessive foundation displacements of various forms without signs of significant structural damage manuscript received 30 august 2000

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

alongshore momentum balance analysis on a cuspate foreland 1 nearshore measurements of waves and currents off cape hatteras north carolina u s a are used to investigate depth averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation north south vs northwest southeast subjected to the same wind forcing in the nearshore the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal suggesting that cape associated shoals may act as an extension of the coastline alongshore momentum balance analysis incorporating wave current interaction by including vortex and stokes coriolis forces reveals that in deep waters surface and bottom stress are almost in balance in shallower waters the balance is complex as nonlinear advection and vortex force become important furthermore linearized momentum balance analysis suggests that the vortex force can be of the same order as wind and wave forcing farther southwest of cape hatteras point wind and wave forcing alone fail to fully explain subtidal flow variability and it is shown that alongshore pressure gradient as a response to the wind forcing can close the momentum balance adjacent tide gauge data suggest that the magnitude of pressure gradient depends on the relative orientation of local coastline to the wind vector and in a depth averaged sense the pressure gradient generation due to change in coastline orientation even at km length scale is analogous to the effect of alongshore variable winds on a straight coastline

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

tidal asymmetry and residual circulation over linear sandbanks and their implication on sediment transport a process oriented numerical study received 12 january 2007 revised 24 july 2007 accepted 17 september 2007 published 22 december 2007 1 a series of process oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks the idealized bathymetry and forcing are similar to those present in the norfolk sandbanks north sea the importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation and subsequent sediment transport implications are discussed the results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation the magnitude of the generated residual flow is always larger than that of the locally generated overtides also net sediment transport is always dominated by the nonlinear interaction of the residual flow and the semidiurnal tidal currents although cross bank sediment transport can occur even in the absence of a cross shore residual flow on the other hand net sediment divergence convergence increases as the bottom drag decreases and as bank orientation increases the sediment erosion deposition is not symmetric about the crest of the bank suggesting that originally symmetric banks would have the tendency to become asymmetric

prolonged extension and subsidence of the peruvian forearc during the cenozoic abstract ocean continental subduction zones are commonly associated with compressional stress fields which ultimately result in regional uplift of the overriding plate this has particularly been inferred by most studies for the western margin of the peruvian andes however local geological observations have contested this idea here we present a review of existing local and international literature supplemented by new structural and geomorphic observations that suggest that nearly the entire central 15 to 11 s latitude and northern peruvian forearc 11 to 6 s latitude are under extension with a slight tendency to transtension instead of compression and that this region has experienced a prolonged period of subsidence since the middle late eocene interrupted by short pulses of uplift in contrast the southern peruvian forearc 15 to 18 s latitude has experienced trans tension from the middle late eocene until recent in combination with uplift the central and southern peruvian forearc that was influenced by the passage of the nazca ridge experienced transtension and subsidence until the middle late miocene and alternating phases of compressional and transtensional tectonics afterwards these new findings on the geodynamic development of the peruvian forearc need to be considered in future reconstructions of the mechanisms at work within this subduction zone

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

on the formation of sand waves and sand banks a fully three dimensional model is proposed for the generation of tidal sand waves and sand banks from small bottom perturbations of a flat seabed subject to tidal currents the model predicts the conditions leading to the appearance of both tidal sand waves and sand banks and determines their main geometrical characteristics a finite wavelength of both sand waves and sand banks is found around the critical conditions thus opening the possibility of performing a weakly nonlinear stability analysis able to predict the equilibrium amplitude of the bottom forms as shown by previous works on the subject the sand wave crests turn out to be orthogonal to the direction of the main tidal current the present results also show that in the northern hemisphere sand bank crests are clockwise or counter clockwise rotated with respect to the main tidal current depending on the counter clockwise or clockwise rotation of the velocity vector induced by the tide only for unidirectional or quasi unidirectional tidal currents are sand banks always counter clockwise rotated the predictions of the model are supported by comparisons with field data finally the mechanisms leading to the appearance of sand waves and sand banks are discussed in the light of the model findings in particular it is shown that the growth of sand banks is not only induced by the depth averaged residual circulation which is present around the bedforms and is parallel to the crests of the bottom forms a steady drift of the sediment from the troughs towards the crests is also driven by the steady velocity component orthogonal to the crests which is present close to the bottom and can be quantified only by a three dimensional model while the former mechanism appears to trigger the formation of counter clockwise sand banks only the latter mechanism can give rise to both counter clockwise and clockwise rotated sand banks

seafloor response to flow in a southern hemisphere sand ridge field argentine inner shelf abstract the inner continental shelf adjacent to buenos aires province argentina is characterized by a series of sand ridges averaging 4 7 m in relief and spaced about 2 7 km apart the ridges trend north south forming a 20 to 35 southward opening angle with the northeast southwest trending coast although the adjacent coast is of depositional strand plain origin it is presently undergoing erosional retreat and the formation of the ridges appears to be part of the retreat process seafloor grain size distributions and bedform arrays are responses to the same velocity field that has formed the ridges along transects normal to the ridges grain size variation is 90 out of phase with the topography the coarsest sediment is not at ridge crests or trough axes but instead occurs on the landward slope finest sands are on the seaward slope side scan sonar reveals bedforms aligned obliquely to both ridges and the coast these are inferred to be sand waves the grain size and bedform patterns suggest that the formative flows are northward currents with an offshore flow component near the bottom although flows observed during the study period were dominantly north to south the grain size gradients and bedform orientations are equivalent to those characteristic of the atlantic shelf of north america with a north south inversion the comparison suggests that inner shelf transport directions in response to wind events can be predicted from the regional geometry and climate of the shelf

experimental evidence for wall rock pulverization during dynamic rupture at ultra high pressure conditions abstract the mechanisms triggering intermediate and deep earthquakes have puzzled geologists for several decades there is still no consensus concerning whether such earthquakes are triggered by brittle or ductile mechanisms we performed a deformation experiment on a synthetic lawsonite bearing blueschist at a confining pressure of 3 gpa and temperatures from 583 to 1 073 k after deformation the recovered sample reveals conjugated shear fractures garnet crystals are dissected and displaced along these narrow faults and reveal micro and nanostructures that resemble natural pulverization structures as well as partial amorphization formation of such structures at low confining pressures is known to require high tensile stresses and strain rates and is explained by the propagation of a dynamic shear rupture the absence of shearing in the pulverized wall rock is taken as evidence that these structures pre date the subsequent heat producing frictional slip in analogy to observations at low pressure we infer that the garnet structures in our experiment result from rapid propagation of a shear fracture even at the high pressure exerted on the sample and thus suggest that brittle deformation is possible at lower crustal to upper mantle depths

imaging spectroscopy to assess the composition of ice surface materials and their impact on glacier mass balance abstract glacier surfaces are not only composed of ice or snow but are heterogeneous mixtures of different materials the occurrence and dynamics of light absorbing impurities affect ice surface characteristics and strongly influence glacier melt processes however our understanding of the spatial distribution of impurities and their impact on ice surface characteristics and the glacier s energy budget is still limited we use imaging spectroscopy in combination with in situ experiments to assess the composition of ice surface materials and their respective impact on surface albedo and glacier melt rates spectroscopy data were acquired in august 2013 using the airborne prism experiment apex imaging spectrometer and were used to map the abundances of six predominant surface materials on glacier de la plaine morte swiss alps a pixel based classification revealed that about 10 of the ice surface is covered with snow water or debris the remaining 90 of the surface can be divided into three types of glacier ice namely 7 dirty ice 43 pure ice and 39 bright ice spatially distributed spectral albedo derived from apex reflectance data in combination with in situ multi angular spectroscopic measurements was used to analyse albedo patterns present on the glacier surface about 85 of all pixels exhibit a low albedo between 0 1 and 0 4 mean albedo 0 29 0 12 indicating that glacier de la plaine morte is covered with a significant amount of light absorbing impurities resulting in a strong ice albedo feedback during the ablation season using a pixel based albedo map instead of a constant albedo for ice 0 34 as input for a mass balance model revealed that the glacier wide total ablation remained similar 10 difference however the large local variations in mass balance can only be reproduced using the pixel based albedo derived from apex emphasizing the need to quantify spatial albedo differences as an important input for glacier mass balance models

water and sediment movement in the vicinity of linear sandbanks the norfolk banks southern north sea geophysical surveys current meter measurements and fluorescent sand tracer experiments were undertaken in the vicinity of the broken bank the data are used to establish localised and regional patterns of water and sediment movement the results obtained confirm mechanisms proposed previously for sandbank growth with particular reference to the north sea these include the clockwise circulation of water and sand with convergence at the crestline secondary helical water circulations do not appear to be a dominant process influencing sandbank maintenance however such circulation may still be important in the initial formation of linear sandbanks and or at some stages in the bank development on a regional basis residual currents bedform asymmetries and tracer dispersion indicate an offshore sediment transport component this observation supports the hypothesis of other investigators formed on the basis of geomorphological observations and numerical model predictions concerning the movement of sand under extreme conditions moreover these transport pathways may persist under low wave and tidally dominated conditions as opposed to being restricted to storm activity

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it