crustal deformation along the altyn tagh fault system western china from gps we collected gps data from the southern tarim basin the qaidam basin and the western kunlun shan region between 1993 and 1998 to determine crustal deformation along the altyn tagh fault system at the northern margin of the tibetan plateau we conclude from these data that the altyn tagh is a left lateral strike slip fault with a current slip rate of 9 mm yr in sharp contrast with geological estimates of 20 30 mm yr this contrast poses an enigma because the gps data cover a wider region than the geologic data they might be expected to reveal somewhat more slip we also find that the tarim and qaidam basins behave as rigid blocks within the uncertainty of our measurements rotating clockwise at a rate of 11 and 4 5 nrad yr respectively with respect to the eurasia plate the rotation of the tarim basin causes convergence across the tian shan increasing progressively westward from 6 mm yr at 87 e to 18 mm yr at 77 e our data and other gps data suggest that the indo asia collision is mainly accommodated by crustal shortening along the main himalayan thrust system 53 and the tian shan contractional belt 19 eastward extrusion of the tibetan plateau along the altyn tagh and kunlun faults accommodates only 23 of the indo asia convergence

minimum age of initiation of collision between india and asia north of everest based on the subsidence history of the zhepure mountain section the collision of india with asia one of the most profound tectonic events to have occurred in past 100 m y is thought to have had geological geochemical and climatological consequences of global extent surprisingly the age of initiation of this collision remains poorly constrained estimates range from the late cretaceous 65 ma to latest eocene 40 ma with little consensus in between this paper reviews the stratigraphic section preserved on zhepure mountain on the north flank of everest mount qomolongma and its implied subsidence history zhepure mountain lies about 65 km south of the indus yarlung zangbo suture and contains the most complete and youngest passive margin shelf sediments in the tethyan himalayas on the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks therefore collision related loading and accelerated subsidence must post date the youngest sediments preserved which date from the earl

a two phase model for compaction and damage 3 applications to shear localization and plate boundary formation a new two phase theory employing a nonequilibrium relation between interfacial surface energy pressure and viscous deformation bercovici et al this issue provides a model for damage void generation and microcracking and thus a continuum description of weakening failure and shear localization here we demonstrate applications of the theory to shear localization with simple shear flow calculations in which one phase the matrix representing for example silicate is much stronger more viscous than the other phase the fluid this calculation is motivated as a simple model of plate boundary formation in a shear zone even without shear the two phases eventually separate due to gradients in surface tension however the influence of shear on phase separation is manifest in several ways as shear velocity increases the separation rate of the phases increases demonstrating a basic feedback mechanism accumulation of the fluid phase causes focused weak zones on which shear concentrates causing more damage and void generation and thus greater accumulation of fluid beyond a critical shear velocity phase separation undergoes intense acceleration and focusing leading to a tear localization in which the porosity becomes nearly singular in space and grows rapidly like a tear or crack at an even higher value of shear velocity phase separation is inhibited such that shear localization gives way to defocusing of weak zones suggestive of uniform microcracking and failure throughout the layer our two phase damage theory thus predicts a wide variety of shear localization and failure behavior with a continuum model applications of the theory to various fields such as granular dynamics metallurgy and tectonic plate boundary formation are numerous

intersite comparison of interannual nearshore bar behavior 1 long term years bathymetric data sets collected in six multiple near shore sandbar systems were analyzed with complex empirical orthogonal function analysis to quantify intersite differences and similarities in cyclic offshore progressive bar behavior the observations came from a 37 year annually sampled data set of four regions along the dutch coast spanning 70 km of coastline an 18 year fortnightly to monthly sampled data set at duck north carolina alongshore extent 1 km and a 7 year daily sampled data set of a single cross shore profile at the hasaki coast of japan the first complex mode typically representing 50 70 of the total depth variance described the long term offshore progressive behavior and allowed for an objective separation of the barred part of the profile from the shoreward and seaward located nonbarred parts by considering a threshold bar amplitude below which the spatial results from the first mode were not considered reliable the sandbars at the six examined sites share common lengths and nondimensional amplitude characteristics which can be described by a negatively skewed gaussian function the absolute amplitude dimensions and the cycle return intervals differ however considerably between the sites the key geometric parameters that steer this intersite variation are the time averaged mean depths at the shoreward and seaward side of the bar zone shore and sea respectively as well as their difference bz the degree to which intersite differences in shore sea and bz are related linearly to intersite differences in bulk statistics of external forcings wave tide sediment and bed profile characteristics is inconclusive

the influence of tides wind and waves on the redistribution of nourished sediment at terschelling the netherlands abstract a calibrated morphodynamic model of the barrier island of terschelling the netherlands grunnet n m walstra d j r ruessink b g 2004 process based modelling of a shoreface nourishment coastal eng 51 7 581 607 comprising the island and its two adjacent tidal inlet systems is applied to identify the relative contribution of tides wind and waves to the cross shore and alongshore redistribution of a 2 mm3 nourishment supplied to the nearshore zone along the island several model simulations with varying combinations of horizontal and vertical tide wind and wave forcing were designed to investigate the effect of each individual forcing on a large spatio temporal scale order of kilometres and months respectively as expected stirring and transport by waves and wave induced currents are predicted to be by far the dominant contributor to the net sediment transport along the coast of terschelling because of the strong obliquity of the winds and the relatively small tidal currents in front of the island 0 5 m s alongshore wind driven currents increase sediment transport rates and horizontal tides virtually have no net transport capacity this motivated a local model of the study area along the closed coast of terschelling not including tidal inlets and further simplifying tidal boundary definitions by omitting the horizontal tides morphodynamic simulations of the local model show virtually identical results as the larger model predictions the reduction in complexity in setting up a local model instead of a regional model coupled with the corresponding significant reduction in computational time points to an increasing applicability of complex process based models

coupling and decoupling of crust and mantle in convergent orogens implications for strain partitioning in the crust topographic relief strain partitioning and crust mantle coupling within convergent orogens may be systematically related to the distribution of strength as a function of depth within continental crust this result is obtained by solving analytically for basally driven three dimensional flow within an idealized crust with a laterally invariant depth dependent newtonian viscosity two end member flow states are shown to occur in the first crustal flow is directly coupled to the underlying mantle and is controlled by stresses transmitted vertically through the crust in the second upper crustal to midcrustal flow is decoupled from the underlying mantle and is controlled by stresses transmitted horizontally through the crust this model is applied to deformation of continental crust above plate like mantle that undergoes oblique convergence across a narrow suture if no significant low viscosity zone develops within the crust crustal deformation is coupled to motion of the underlying mantle and a triangular mountain range develops surface shortening occurs at the foot of the mountains normal to the trend of the range while strike slip and extension are partitioned along the axis of the orogen if a low viscosity zone is initially absent but develops during crustal thickening a steep sided flat topped plateau forms crustal deformation is coupled to mantle motions on the plateau flanks but may be strongly decoupled beneath the plateau surface shortening normal to the plateau occurs at the foot of the plateau while surface extension normal to the plateau occurs at the plateau edge if a low viscosity zone is present in the lower crust prior to convergence a wide orogen with low topographic relief develops crustal deformation is decoupled from the mantle except at the edges of the deforming region and surface shortening is partitioned uniformly across the belt this study shows that horizontal and vertical partitioning of strain occur even in the absence of lateral strength variations and that shortening and extension may exist simultaneously in different parts of an orogen similar morphology and strain partitioning can be observed in many real orogenic belts including the eastern alps the tibetan plateau and the lachlan tasman fold belt

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

on the accuracy of automated shoreline detection derived from satellite imagery a case study of the sand motor mega scale nourishment measured trends and variability in shoreline position are used by coastal managers scientists and engineers to understand and monitor coastal systems this paper presents a new and generic method for automated shoreline detection from the largely unexplored collection of publicly available satellite imagery the position of the obtained satellite derived shoreline sds is tested for accuracy for 143 images against high resolution in situ data along a coastal stretch near the sand motor a well documented mega scale nourishment along the dutch coast in this assessment we quantify the effects of potential inaccuracy drivers such as the presence of clouds and wave induced foam the overall aim of this study is to verify whether the sds is suitable to study structural coastline trends for coastal engineering practice in the ideal case of a cloud free satellite image without the presence of waves with limited morphological changes between the time of image acquisition and the date of the in situ measurement the accuracy of the sds is with subpixel precision smaller than 10 30 m depending on the satellite mission and depends on intertidal beach slope and image pixel resolution for the highest resolution images we find an average offset of 1 m between the sds position and the in situ shoreline in the considered domain the accuracy deteriorates in the presence of clouds and or waves on the image satellite sensor corrections and georeferencing errors the case study showed that especially the presence of clouds can lead to a considerable seaward offset of the sds of multiple pixels e g order 200 m wave induced foam results in seaward offsets in the order of 40 m these effects can largely be overcome by creating composite images which results in a continuous dataset with subpixel precision 10 30 m depending on the satellite mission this implies that structural trends can be detected for coastlines that have changed with at least the pixel resolution within the considered timespan given the accuracy of composite images along the sand motor in combination with the worldwide availability of public satellite imagery covering the last decades this technique can potentially be applied at other locations with large structural coastline trends

oligocene miocene tectonics and sedimentation along the altyn tagh fault northern tibetan plateau analysis of the xorkol subei and aksay basins abstract tertiary basins adjacent to the northern edge of the tibetan plateau include both giant intracontinental sedimentary basins such as tarim and qaidam and smaller basins directly related to the evolution of the altyn tagh strike slip fault system and nearby fold thrust belts three examples of these smaller basins that formed during early evolution of the altyn tagh fault system are the xorkol aksay and subei basins the xorkol basin was the site of nonmarine siliciclastic sedimentation in alluvial fan playa and fluvial environments from at least the mid oligocene through the miocene sediment was delivered to the basin from source areas uplifted by basin bounding thrust faults and from the opposite side of the altyn tagh fault the age of the aksay basin is more poorly constrained but it also contains oligocene miocene nonmarine clastic strata that were derived from the southern side of the altyn tagh fault and adjacent thrust fault bounded uplifts the subei basin is characterized by s

overview of 20 years of field measurements in the coastal zone and at the petten sea dike in the netherlands abstract this paper intends to give an overview of almost 20 years 1994 2013 of field measurements at the petten site in the netherlands and to list the main research findings derived from these measurements the main objectives of the petten site were to obtain field data of i wave propagation from deep water through the surf zone to the dike ii wave run up against the dike and iii since 2006 wave overtopping the paper describes the evolution of the site lay out during its existence and discusses the data collection processing and dissemination the most important research findings based on petten site data have been obtained in research projects like opticrest 1998 2001 clash 2002 2004 and wti 2003 2013 the results of the wti project on wave overtopping wave run up redundant wave measurements and rapid bathymetric changes are described here in more detail because these results have not gained widespread attention yet

nourishing the shoreface observations and hindcasting of the egmond case the netherlands abstract although beach nourishment policy in the netherlands is generally successful in maintaining the 1990 shoreline the efficiency of nourishments at several locations along the north sea coast is unacceptably low these locations are identified as erosion hotspots egmond aan zee is such a hotspot the bathymetric longshore irregularities make this coastal stretch highly susceptible to rip currents and horizontal circulations which transport large volumes of nourished sand to the sea in 1999 an alternative nourishment design was implemented this consisted of a shoreface nourishment at the outer bar at 7 5 m depth combined with a nourishment of the beach behind it high resolution bathymetric surveys carried out with the wesp revealed that the shoreface nourishment resulted in a significant shoreward migration of the outer bar during 1999 2001 after 2 years the system started to return to its natural dynamic equilibrium and lost the positive influence of the shoreface nourishment area shoreward movement of bars and increase of bar height which forms the first defense line of the mainland against the sea and positive contribution to the sand budget which increased as a result of the nourishment after 3 years may 1999 to april 2002 the sediment volume still had an increase of 477 500 m3 45 of the applied sand relative to may 1999 the shoreface nourishment area did not have a direct effect on the beach the shoreface nourishment area probably will have to be maintained to retain the sediment on the beach in the long run in egmond the shoreface nourishment started to disappear before the sediment could reach the beach the time scale of sediment feed to the beach zone probably is of the order of 5 10 years the shoreface nourishment seems to function as a reef creating a lee side effect that influences both cross shore and longshore sediment transport resulting in two main hypotheses firstly the longshore effect in which large waves break at the shoreface nourishment cause a calmer wave climate shoreward of the shoreface nourishment area and a reduction of the longshore current the shoreface nourishment partially blocks the wave driven longshore current secondly the cross shore effect in which shoaling waves generate onshore transport these hypotheses are supported by generated model results with both a process based profile model unibest tc and a process based coastal area model delft3d mor the unibest tc model was able to predict the detachment of the outer bar from the shoreface nourishment and to some extent the shoreward bar movements in the lee of the shoreface nourishment area the model found an increase in sediment confirming the shielding effect of the shoreface nourishment area the delft3d model found as a result of the shoreface nourishment area a decrease of the flow velocity and the wave height just shoreward of the shoreface nourishment area the model was able to predict the similar trend in sedimentation erosion pattern although the intensities were smaller in the lee of the shoreface nourishment area a clear sedimentation was found erosion was found south and seaward of the shoreface nourishment area the modeled profiles did not follow the measured profile changes the separation of the shoreface nourishment from the outer bar and the shoreward migration of the bars could not be accurately modeled because the cross shore transport caused by wave asymmetry is not taken into account in the standard version of delft3d these results were in line with the expectations

the role of a heterogeneous inclusion during continental collision abstract we study a simple model of the deformation due to collision between two continental plates the model is patterned after the geometry of the india asia collision but it may be applicable to more general situations the collision is modelled by the indentation of a viscoplastic plate asia by a rigid punch india a finite element approach capable of dealing with finite deformation heterogeneity and non linear rheologies is used to study the role of an inclusion of increased rigidity on the viscoplastic flow of the plate the heterogeneous zone was chosen to approximate the shape and position of the tarim basin behind tibet the lateral boundaries of the plate were defined so as to approximate those that are believed to apply for the asian plate i e fixed boundaries to the west and north free boundaries to the west and south several geometries and contrasts of rheology were analyzed to verify the general validity of our results the purpose was to determine the main kinematic features of the flow not to model the particular case of tarim it is found that the heterogeneity affects the flow in a drastic way even for small contrasts of rigidity and for small size heterogeneities the main effect of the heterogeneity is to create two important shear zones or internal boundary layers the most important is in front of the inclusion separating the main flow from the inclusion as the flow proceeds the inclusion rotates and the shear zone progressively bends in qualitative agreement with the bending of the large strike slip faults like the altyn tagh that separates the tarim from tiber our model of continuous deformation does not allow for the formation of faults or fractures but the shear zones may be understood as the initial stages for the generation of fractures or velocity discontinuities another shear zone develops to the left of the inhomogeneity near the fixed boundary and in the wake of the punch the role of these shear zones is to isolate the heterogeneity from the main flow to facilitate its rigid rotation inside the flow of the softer plate a final observation is that in the presence of the heterogeneity the lower left hand corner rotates almost like a rigid block producing a sharp bend on the left hand side of the plate as the inclusion rotates pushed by the punch this rigid block rotates clockwise to open up the space necessary for the homogeneity

cross shore stratified tidal flow seaward of a mega nourishment abstract the sand engine is a 21 5 million m 3 experimental mega nourishment project that was built in 2011 along the dutch coast this intervention created a discontinuity in the previous straight sandy coastline altering the local hydrodynamics in a region that is influenced by the buoyant plume generated by the rhine river this work investigates the response of the cross shore stratified tidal flow to the coastal protrusion created by the sand engine emplacement by using a 13 h velocity and density survey observations document the development of strong baroclinic induced cross shore exchange currents dictated by the intrusion of the river plume fronts as well as the classic tidal straining which are found to extend further into the nearshore from 12 to 6 m depth otherwise believed to be a mixed zone estimates of the centrifugal acceleration directly after construction of the sand engine showed that the curvature effects were approximately 2 times stronger suggesting that the sand engine might have played a role in controlling the cross shore exchange currents during the first three years after the completion of the nourishment presently the curvature effects are minute

geodynamics of the tarim basin and the tian shan in central asia the india asia collision has caused crustal thickening in tibet by at least a factor of 2 in the last 20 30 myr of this collision the tian shan mountain range has also been reactivated the tarim basin however shows little internal deformation we describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the tarim basin and the tian shan in the context of a thin viscous sheet model we use a finite element representation of the thin viscous sheet model to approximate the deformation field in the india asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography the experiments show that a strong tarim basin while undergoing little internal deformation transfers strain to the tian shan producing significant crustal thickening in the tian shan region based only on diagnostic parameters such as the maximum thickening in the tian shan and the minimum in the tarim basin the principal features of the topography can be approximately reproduced using models in which either the tarim basin is strong or the tian shan is weak or both for a rheological model in which the stress versus strain rate exponent is n 3 the strength coefficient for the strong tarim basin model vtarim is between about 1 7 and 2 for the weak tian shan model the relative strength coefficient vtian is between about 0 65 and 0 75 if both strong tarim and weak tian shan are included there is a trade off between the required values of vtarim and vtian and the shape of the predicted crustal thickness profiles better matches the observed profiles the steep topographic slope on the southern margin of the tarim basin requires that it is anomalously strong while the rapid decrease of topographic height to the north of the tian shan requires that it is anomalously weak similar conclusions are obtained with a rheological model based on n 10 simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the moho temperature of the order of 10 to 30 c

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

is the north altyn fault part of a strike slip duplex along the altyn tagh fault system although the altyn tagh fault system has played an important role in the indo asian collision its geometry and tectonic evolution remain poorly known between 86 and 92 e this system is at least 100 km wide and is bounded to the north and south by the north altyn and altyn tagh faults respectively mapping along the jianglisai reach of the north altyn fault indicates that miocene to pliocene motion was predominantly left to left reverse slip with transport vectors trending n45 60 e map relationships suggest that total offset on the fault is 120 km these results are inconsistent with previous models of the altyn tagh fault system in which oblique convergence along the northern margin of the tibetan plateau is partitioned into thrusting on the north altyn fault and left slip on the altyn tagh fault an alternative hypothesis is that the north altyn fault is the northern boundary of a transpressional strike slip duplex within which the structurally elevated altyn mountains were created our model suggests that transpressional deformation may be restricted to this strike slip duplex and need not characterize the entire margin

protecting natural landforms and habitats by nourishing an eroding estuarine beach an important issue facing coastal managers is how natural coastal habitats can be protected against wave erosion by human action an assessment is made of attempts to protect a rare maritime forest on the bay side of a barrier island at fire island new york usa using artificial beach fill the sediment deficit is caused by human attempts to stabilize the island by restricting inlet formation overwash and dune migration and it is exacerbated by a nearby marina bulkhead a total of 1099 m3 of sand dredged from the navigation channel was placed near the bulkhead loss of fill was 5 54 7 87 m3 m 1 in the first 6 months the fill was gone 18 months after placement sediment moving out of the fill area caused almost 4 m of shoreline advance 40 m downdrift after 6 months gain of 3 28 m3 m 1 followed by retreat of about 5 m at that location over the next 12 months loss of 5 51 m3 m 1 these results reveal how small changes in volume of microtidal estuarine beaches can cause great shoreline displacement rates the amount of fill from maintenance dredging is insufficient to replenish erosion losses placing additional fill sediment on the bayside to create artificial washover fans can mimic natural landforms and overcome loss of sediment inputs caused by stabilizing the ocean shore mechanical placement may be preferable to natural processes which would deliver sediment across the island and through pre existing stable habitat eliminating some of the features that take long to form

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

four year performance and associated controlling factors of several beach nourishment projects along three adjacent barrier islands west central florida usa abstract to quantify the performance of several beach nourishment projects on three adjacent barrier islands located in west central florida a total of 5200 beach and nearshore profiles spaced at 300 m were surveyed monthly to bi monthly from 2006 to 2010 beach nourishment performance at annual temporal and kilometer spatial scales within the microtidal low wave energy barrier island coast is most significantly influenced by the interruption of longshore sediment transport by complex tidal inlet processes the inlet processes directly influencing adjacent beach nourishment performance include longshore transport interruption resulting from divergence induced by wave refraction over an ebb tidal shoal flood tidal currents along the beach and total littoral blockage by structured inlets secondary factors controlling the nourishment performance include project length and width shoreline orientation and antecedent geology a morphologic indicator of a large longshore transport gradient within the study area is the absence of a nearshore sandbar these non barred beaches are characterized by persistent shoreline erosion the presence of a sandbar indicates the dominance of cross shore processes with bar migration in response to wave condition variations and a relatively stable shoreline the entirety of a barrier island system should be considered when evaluating the performance of a nourishment

behaviour of subtidal sandbars in response to nourishments the behaviour of subtidal sandbars can be strongly influenced by the introduction of sand nourishments in the coastal system this study focuses on the impact of nourishments on subtidal bar behaviour at spatio temporal scales beyond a single nourishment project it aims to determine the long term behaviour of subtidal sandbars along an entire coastal cell taking into account both the unnourished and nourished regime and covering various types of nourishments the analysis is based on over 50 years of sandbar evolution along the delfland coast a 17 km long coastal cell at the dutch north sea coastline protected by groynes and maintained with frequent sand nourishments observations reveal clearly different sandbar behaviour during the unnourished first 20 years and nourished periods of the dataset introduction of the first beach nourishments nourished sand primarily placed at the subaerial beach was found to stimulate sandbar development along previously unbarred sections of the coast shoreface nourishments nourished sand placed at the seaward face of the pre existing subtidal sandbar tended to migrate shoreward rapidly at a rate of 20 to 60 m year at this coast thereby forcing the pre existing sandbar to weld to the dry beach an abrupt transition of sandbar dynamics was observed following a major nourishment operation 37 5 mm3 of nourished sand that covered the entire coastal cell a new shallow sandbar formed with a degree of alongshore variability that was unprecedented at the delfland coast over the full study period these results imply that individual nourishments can influence the formation and migration of individual sandbars while continued nourishments can fundamentally change long term sandbar dynamics along an entire coastal cell

monitoring and simulation of salinity changes in response to tide and storm surges in a sandy coastal aquifer system tidal dynamics and especially storm surges can have an extensive impact on coastal fresh groundwater resources combined with the prospect of sea level rise and the reliance of many people on these resources this demonstrates the need to assess the vulnerability of coastal areas to these threats in this study we investigated the impact of tides and storm surges on coastal groundwater at a pilot location on the dutch coast viz the sand engine to monitor changes in groundwater salinity under a variety of conditions we performed automated measurements with electrical resistivity tomography for a period of 2 months between november 2014 and january 2015 the obtained resistivity images were converted to salinity images and these images served effectively as observations of the impact of tidal fluctuations salt water overwash during storm surges and the recovery of the freshwater lens after land surface inundations most of the observed changes in groundwater head and salinity could be reproduced with a two dimensional variable density groundwater flow and salt transport model this shows that groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh ground water resources given a thorough understanding of the local system comparisons of measurements and model simulations also showed that morphological changes and wave run up can have a strong impact on the extent of land surface inundations in low elevation dynamic coastal environments and can therefore substantially affect coastal fresh groundwater resources

the application of a radar based depth inversion method to monitor near shore nourishments on an open sandy coast and an ebb tidal delta abstract coastal management in the netherlands has the aim to defend coastal zones by preventing flooding and mitigating erosion to that end large scale nourishments are placed in the nearshore which are supposed to dynamically preserve the coastal zone over a timescale of years to assess their effectiveness these nourishments are monitored over large areas and long durations as repetitive in situ measurements become too expensive remote sensing offers an attractive alternative mapping depth and near surface current fields via depth inversion algorithms dia however the information that can be derived from remotely sensed data is subject to improvement in this study a 3d fft based dia named xmfit x band matlab fitting is introduced which is robust accurate and fast enough for operational use focusing on depth estimates the algorithm was validated for two case studies in the netherlands 1 the sand engine a beach mega nourishment at a uniform open coast and 2 the tidal inlet of the dutch wadden sea island ameland characterizing a more complex coast considering both sites the algorithm performance was characterized by a spatially averaged depth bias of 0 9 m at the sand engine and a time varying bias of approximately 2 0 m at the ameland inlet when compared to in situ depth surveys the accuracy was lower but the time resolution higher depth estimates from the ameland tidal inlet were produced every 50 min by an operational system using a navigational x band radar to monitor the placement of a 5 million m3 ebb tidal delta nourishment a pilot measure for coastal management volumetric changes in the nourishment area over the year 2018 occurring at 7 km distance from the radar were estimated with an error of 7 depth errors statistically correlated with the direction and magnitude of simultaneous near surface current estimates additional experiments on sand engine data demonstrated that depth errors may be significantly reduced using an alternative spectral approach and or by using a kalman filter

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

beach nourishments at coolangatta bay over the period 1987 2005 impacts and lessons abstract erosion of the southern gold coast beaches se queensland australia was exacerbated after the extension of the tweed river training walls in the early 1960s to achieve the objective of restoring and maintaining beach amenity significant nourishment works have been undertaken in coolangatta bay over the past 30 years particularly under the tweed river entrance sand bypassing project tresbp since 1995 a number of nourishment campaigns and the implementation of a permanent sand bypass system in 2001 have resulted in significant changes of coolangatta bay morphology the present case study investigates the influence of both wave climate and nourishment works on the area extending from the updrift snapper rocks area to downdrift kirra beach swan spectral wave model is implemented at coolangatta bay area and forced by the global wave model ww3 to estimate wave forcing and the potential natural longshore drift entering in coolangatta specific transects extracted from accurate bathymetric surveys are used to investigate and quantify coolangatta bay sedimentation for the period 1987 2005 a network of argus video stations provides high sample rate information on the shoreline evolution results show that over the past 10 years coolangatta bay has infilled rapidly sedimentation reached up to 6 m in some areas between 1995 and 2005 with beach width increasing by 200 m at kirra beach rapid seaward shoreline migration is consistent with the intense over pumping of sand relative to the natural potential to move sand alongshore the nourishment strategy used during this project has successfully delivered large amounts of sand to the southern gold coast embayment although it has been up to now controversial from many community perspectives the artificial sand bypassing process proved to be much more efficient than depositing the dredged sand in the nearshore area which requires a significant period of low energy condition in order for the deposited sediment to migrate shoreward and weld to the shore this case study confirms that when carefully undertaken sand bypassing is a sustainable and flexible soft engineering approach which can work in concert with natural processes

observations of bedform migration and bedload sediment transport in combined wave current flows bedload transport is an important mechanism for sediment flux in the nearshore yet few studies examine the relationship between bedform evolution and net sediment transport our work contributes concurrent observations of bedform mobility and bedload transport in response to wave dominant current dominant and combined wave current flows in the nearshore bedload sediment flux from migrating bedforms during combined wave current conditions accounted for at least 20 more bedload transport when compared with wave dominant flows and at least 80 more than current dominant flows bedforms were observed to transport the most sediment during periods with strong currents with high energy skewed waves and while bedform orientation and transport direction were aligned regardless of flow type bedform migration rates were directly proportional to the total kinetic energy contained in the flow field eleven bedload transport models formulated to be used in combined flows both shear and energetics based were compared with sediment flux estimated from measured bedform migration an energetics based sediment transport model was most representative for our data

identifying the plane of slip for a fault plane solution from clustering of locations of nearby earthquakes numerous methods have been proposed recently to analyze the spatial pattern of locations of earthquakes to infer planes along which earthquakes cluster these planes are considered to be earthquake slip planes the application of such methods is to find major planes passing through a set of earthquake locations when the fault plane solutions of the events are unusual or when locating planes would contribute to understanding the structural setting in which an earthquake occurred a modification to one of these methods the three point method allows one to study anomalous or otherwise interesting events and to choose which nodal plane in the fault plane solution for the event is the plane of slip to be successful the method requires that a sufficient number of other events had the same or similar slip plane the modified three point method consists of finding the orientations of planes formed by combinations of the location of the earthquake under study and all other locations in the remainder of the earthquake catalog taken two at a time a test to determine which orientations occur more often then expected is used to identify statistically significant planes along which earthquakes cluster each plane identified passes through the earthquake beingmore studied if one of these planes is parallel or nearly parallel to one of the nodal planes of the fault plane solution that nodal plane is assumed to be the slip plane the method is demonstrated by investigating ten earthquakes that occurred during 1983 1984 near coalinga california using the method significant alignments of events along planes that are nearly parallel to one of the nodal planes for eight of the ten events were found less

mid el nino erosion at nourished and unnourished southern california beaches wave conditions in southern california during the 2015 2016 el nino were similar to the 2009 2010 el nino previously the most erosive minimum beach widths and subaerial sand levels in a 7 year record as of february 2016 torrey pines beach had eroded slightly below 2009 2010 levels threatening the shoulder of a major highway however cardiff solana and imperial beaches nourished with imported sand in 2012 were on average 1 2 m more elevated and more than 10 m wider than in 2009 2010 monthly subaerial sand elevation observations showed that the nourished beaches remained consistently wider than unnourished beaches under similar wave conditions in contrast to a 2001 nourishment at torrey pines built with native sized sand that was removed from the beach face during a single storm these relatively coarse grained nourishments protected shorelines for several years and during the significant wave attack of the 2015 2016 el nino as of february 2016

modeling the influence of horizontal advection deformation and late uplift on the drainage development in the india asia collision zone 1 we present results of a new model in which we couple a mechanical model to describe continental indentation in plan view with a landscape evolution model to describe drainage development we apply the model to investigate aspects of the development of drainage systems erosion and exhumation in the india asia collision zone it is shown that the orogen scale distribution of erosion and exhumation can be well matched by the model however the elevation of the tibetan plateau and the steep topographic gradients at its margins are difficult to reproduce they appear to require an additional cause of uplift we show that some of the major observed river capture events can be reproduced by invoking such a late uplift in much of the orogen except the region of the sichuan basin this includes the inferred capture of the yarlong tsangpo by the brahmaputra and that of the upper yangtze by the lower yangtze thereby deserting the red river

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

seasonal scale nearshore morphological evolution field observations and numerical modeling abstract a coupled waves currents bathymetric evolution model delft 3d is compared with field measurements to test hypotheses regarding the processes responsible for alongshore varying nearshore morphological changes at seasonal time scales a 2001 field experiment along the beaches adjacent to grays harbor washington usa captured the transition between the high energy erosive conditions of winter and the low energy beach building conditions typical of summer the experiment documented shoreline progradation on the order of 10 20 m and on average approximately 70 m of onshore sandbar migration during a four month period significant alongshore variability was observed in the morphological response of the sandbar over a 4 km reach of coast with sandbar movement ranging from 20 m of offshore migration to over 175 m of onshore bar migration the largest seasonal scale onshore migration event observed in a natural setting both observations and model results suggest that in the case investigated here alongshore variations in initial bathymetry are primarily responsible for the observed alongshore variable morphological changes alongshore varying incident hydrodynamic forcing occasionally significant in this region due to a tidal inlet and associated ebb tidal delta was relatively minor during the study period and appears to play an insignificant role in the observed alongshore variability in sandbar behavior at kilometer scale the role of fully three dimensional cell circulation patterns in explaining the observed morphological variability also appears to be minor at least in the case investigated here

ductile shear zones beneath strike slip faults implications for the thermomechanics of the san andreas fault zone we have carried out two dimensional 2 d numerical experiments on the bulk flow of a layer of fluid that is driven in a strike slip sense by constant velocities applied at its boundaries the fluid has the linearized conventional rheology assumed to apply to lower crust upper mantle rocks the temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations as has thermal conduction in an overlying crustal layer two end member boundary conditions have been considered corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive weak crust in many cases of practical interest shear heating is concentrated close to the axial plane of the shear zone for either boundary condition for these cases the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half space at a depth corresponding to the top of the fluid layer this approximation along with the application of a theoretical result for one dimensional shear zones permits us to obtain simple analytical approximations to the thermal effects of 2 d ductile shear zones for a range of assumed rheologies and crustal geotherms making complex numerical calculations unnecessary results are compared with observable effects on heat flux near the san andreas fault using constraints on the slip distribution across the entire fault system ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the mendocino triple junction and match the amplitude of the regional heat flux anomaly in the california coast ranges because ductile dissipation depends only weakly on slip rate faults moving only a few millimeters per year can be important heat sources and the superposition of effects of localized ductile shearing on both currently active and now inactive strands of the san andreas system can explain the breadth of the heat flux anomaly across central california

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

extracting decadal morphological behaviour from high resolution long term bathymetric surveys along the holland coast using eigenfunction analysis abstract the understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management the controlling variables for coastal behaviour on these scales are yet unknown it is hypothesised that regions exhibiting different large scale coastal behaviour lscb regions are controlled by different hydrodynamic forcings or by different sedimentological or morphological constraints or by some combination of these factors the objective of this study is to elaborate a method that effectively quantifies large scale morphological changes from a large bathymetric data set large temporal and spatial extent combined with a high resolution such to define lscb regions the method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach the method has been applied on a data set of over 14 000 nearshore profiles the data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length the holland coast the alongshore profile spacing is generally 250 m all profiles surveyed in the period 1963 1990 are included in the analysis application of the method on the dutch data set reveals that lscb regions indeed can be identified the sizes of the lscb regions are 5 km 15 km 20 km 32 km and 42 km differences in behaviour of the secondary morphology i e morphology other than the mean profile shape e g nearshore bars are most pronounced the change in behaviour between lscb regions generally occurs over distances as short as about 2 km the boundaries between the regions are therefore surprisingly sharp in general no clear long term trends in the development of the shape of the sub aqueous profile have been observed along the holland coast along certain stretches trends in cross shore shifting of the sub aqueous profile occurred the average shape of the sub aqueous profile seems to have no relation with the trend in cross shore shifting of the shoreline the 1 m contour the sub decadal shoreline fluctuations however are possibly related to the largescale dynamics of multiple bar systems

tidal flow separation at protruding beach nourishments in recent years the application of large scale beach nourishments has been discussed with the sand motor in the netherlands as the first real world example such protruding beach nourishments have an impact on tidal currents potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself the present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions based on extensive field observations and numerical flow simulations observations of the flow field around the sand motor obtained with a ship mounted current profiler and a set of fixed current profilers show that a tidal eddy develops along the northern edge of the mega nourishment every flood period the eddy is generated around peak tidal flow and gradually gains size and strength growing much larger than the cross shore dimension of the coastline perturbation based on a 3 week measurement period it is shown that the intensity of the eddy modulates with the spring neap tidal cycle depth averaged tidal currents around coastline perturbations are simulated and compared to the field observations the occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape results show that several different types of behavior exist characterized by different combinations of the nourishment aspect ratio the size of the nourishment relative to the tidal excursion length and the influence of bed friction

morphodynamic response of nearshore bars to a shoreface nourishment abstract the autonomous nearshore bar behaviour along the barrier island of terschelling the netherlands is characterised by the presence of net seaward cyclic migrating sand bars generated near the shoreline in 1993 a perturbation of the cyclic bar system was introduced by the implementation of a 2 mm 3 shoreface nourishment supplied to the nearshore bar zone filling up the trough between the middle and outer bar the morphodynamic response of the nearshore bars to the nourishment perturbation is investigated using a bathymetric data set with an alongshore extent of 12 km and sampled for 10 years bar behaviour is quantified in terms of bar crest position in relation to morphometric parameters such as bar depth height width and volume along with a pronounced development of a three dimensional bar system unseen in the autonomous behaviour the nearshore bars exhibited a 6 7 year arrest in their migrational behaviour during which bar morphology remained stable at immediate pre nourishment morphometric values at the subsequent onset of bar movement bars resumed their migration at a rate predicted by autonomous behaviour in parallel development with morphometric parameters along their predicted trends it is shown that the observed onshore transport of nourished sediment in the 6 7 year arrest results from a gradual deepening of troughs cross shore sediment transport modelling is used to assess the effect of the nourishment on yearly averaged onshore short wave nonlinearity and offshore undertow sediment transport rates the gradual reappearance of the pre nourishment bar trough morphology is shown to engender a normalisation in the cross shore distribution of sediment transport rates to pre nourishment rates

beach scarp dynamics at nourished beaches abstract beach scarps are nearly vertical seaward facing sandy cliffs within the cross shore beach profile these features are often associated with eroding nourished coastlines and can reach heights of o 2 3 m an analysis of a six year dataset of beach scarp presence at the nourished sand engine beach shows that the formation of beach scarps at the nourishment is linked to mildly erosive summer storm conditions whereas destruction is often related to extremely erosive winter storm conditions additional experiments were carried out showing the formation migration and destruction of scarps from artificially constructed mounds with linear slopes the field experiments show that steep initial slopes are more susceptible to beach scarp formation video observations at these experiments show that the scarp toe level where the vertical slope meets the gently sloping beach is related to the high wave runup events the commonly used 2 exceedance wave runup estimates can therefore be used to predict the final elevation of the scarp toe the strong connection of maximum runup elevation with the scarp toe elevation provides a direct relation between the final scarp height through nourishment platform height and hydrodynamic conditions high platform nourishments will promote the formation of beach scarps and steep initial profiles increase the speed at which scarps form this study suggests that by adjusting the design of beach nourishments beach scarp formation and persistency can be limited by regulating the natural destruction of these features

heat sources of cretaceous metamorphism in the eastern alps a discussion abstract the alpine orogenic cycle is characterised by a series of early metamorphic events that occurred in the cretaceous the eoalpine events a collection of data on peak metamorphic conditions pt paths and on relationships between structure and metamorphism for these events in the eastern alps shows that 1 eoalpine metamorphism occurred largely simultaneously with pervasive deformation 2 the eoalpine thermal peak was reached near the pressure peak 3 lower grade structurally higher rocks reached their metamorphic peak earlier than higher grade structurally lower rocks and there is a wide spread of metamorphic ages 4 low grade metamorphic conditions are probably more perturbed than high grade conditions and 5 there is a conspicuous regional distribution of metamorphic grade with amphibolite and eclogite facies metamorphism occurring predominantly in two regions located symmetrically west and east of the tauern window possible heating mechanisms are discussed that can satisfy these observations and a review of previous thermal models is provided it is shown that models which rely on conductive heat transfer cannot account for all of these observations in order to assess other heat sources the effects of shear heating are evaluated here with simple model calculations and a straightforward comparison of length and time scales of dissipative heat production the results suggest that shear heat episodically released during the stacking of the austroalpine nappe pile may be a significant contributor to the observed thermal perturbation

shorerise and bar berm profiles on ocean beaches a beach equilibrium model is developed that treats the outer shorerise portion of the profile independently from that of the inner bar berm portion the two portions are matched at the breakpoint bar the partitioning of the profile in this way is consistent with the different forcing modes on either side of the breakpoint this formulation utilizes beach profile data not previously available it is shown that both portions of the profile are well fitted by curves of the form h axm where h is positive downward and x is the positive offshore coordinate surprisingly the value of m 0 4 is nearly the same for shorerise and bar berm and does not change significantly with seasonal beach changes summer winter the principal difference between seasonal profiles is that in winter higher waves the breakpoint bar is deeper and farther offshore while the berm crest is displaced landward thus the changes in seasonal equilibria are manifested by simple self similar displacements of the bar berm and shorerise curves as a consequence of changes in surf zone width and o 1 variations in the factor a

sediment sorting at the sand motor at storm and annual time scales bed sediment composition with a focus on the median grain size d50 was investigated at a large scale nourishment the sand motor at the dutch coast 21 5 million m3 sand considerable alongshore heterogeneity of the bed composition d50 was observed as the sand motor evolved over time with 1 coarsening of the exposed part of the sand motor 90 to 150 m and 2 a depositional area with relatively fine material 50 m finer just north and south of the sand motor the alongshore heterogeneity of the measured d50 values was most evident outside the surfzone i e seaward of msl 4 m coarsening of the bed after construction of the sand motor was attributed to hydrodynamic sorting processes because the alongshore heterogeneity of the d50 showed a similar spatial pattern as the mean bed shear stresses the observed alongshore heterogeneity of the d50 and correlation of d50 with modelled mean bed shear stresses suggest that preferential erosion of the finer sand fractions has taken place the selective transport of finer sand fractions results in a coarser top layer of the bed at the sand motor the preferential transport is most dominant during mild and moderate conditions when hydrodynamic forcing conditions are close to the critical bed shear stresses for transport the measurements also show the impact of a storm which consists of a 40 m finer d50 of the offshore bed composition in front of the sand motor i e where a considerably coarser bed was in place additionally storms may generate a temporary zone with fine bed material at the toe of the deposition profile this means that the coarsening of the bed is reduced by storms as a result of the mobilization of both coarse and fine sediment and mixing of the bed with the relatively finer substrate

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

the initial morphological response of the sand engine a process based modelling study abstract sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width over the last decades global sand nourishment volumes have increased greatly and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise with the increase in nourishment size and the request for more complex nourishment shapes an adequate prediction of the morphodynamic evolution is of major importance yet neither the skill of current state of the art models for such predictions nor the primary drivers that control the evolution are known this article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the sand engine and the adjacent coastline the process based model delft3d is used to hindcast the first year after completion of the mega nourishment the model reproduces measured water levels velocities and nearshore waves well the prediction of the morphological evolution is consistent with the measured evolution during the study period with brier skill scores in the excellent range the model results clearly indicate that the sand eroded from the main peninsular section of the sand engine is deposited along adjacent north and south coastlines accreting up to 6 km of coastline within just one year analysis of model results further show that the erosional behaviour of the sand engine is linearly dependent on the cumulative wave energy of individual high energy wave events with the duration of a storm event being more dominant than the maximum wave height occurring during the storm the integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60 of the total eroded volume of the peninsula indicating that the less energetic wave events with a higher probability of occurrence are also important for the initial response of the sand engine a structured model experiment using the verified delft3d model indicates that wave forcing dominates the initial morphological response of the sand engine accounting for approximately 75 of the total erosion volume in the first year the vertical tide is the second most important factor accounting for nearly 17 of the total erosion volume with surge wind and horizontal tide playing only a minor role

continental collision with finite indenter strength 1 concept and model formulation 1 the partitioning of deformation during continental collision is modeled in plan view using a thin viscous sheet simulation in contrast to many previous models an indenter is defined here as a zone of finite viscosity contrast to the foreland and aspect ratio deformation is enforced by pushing the southern boundary into the model region it is shown that deformation is equally partitioned between indenter and foreland if the aspect ratio of the indenter is about 1 2 and it is about twice as viscous as the foreland for higher viscosity contrasts between the two plates the partitioning of deformation between indenter and foreland depends more strongly on argand number the process of lateral extrusion is investigated by separating the lateral velocity field into a component that is due to lateral escape and a component that is due to gravitational extensional collapse it is shown that lateral escape is roughly constant over time and is controlled by the convergence velocity and the obliquity of indentation

modelling of bed sediment composition changes at the lower shoreface of the sand motor abstract large perturbations in the coastline such as the sand motor nourishment 21 million m3 at the holland coast can initiate considerable spatial and temporal changes in the median grain size d 50 of the sea bed on the lower shoreface the relevance of hydrodynamic conditions for the development of the heterogeneity in d 50 at large scale nourishments was assessed with a numerical model delft3d which required a validation against 2 5 years of d 50 measurements a good representation of the observed spatial pattern of d 50 was obtained independent of a 2dh or 3d approach and initial condition for the d 50 of the bed five sediment size fractions and a multi layer administration of the bed composition were used the extent and magnitude of the coarsening of the bed is related to the velocity of the horizontal tide while a far less pronounced coarsening takes place during energetic conditions i e h m 0 3 m differential suspension behaviour between the size fractions which are all mobilized at the bed causes a preferential transport of fine sediment in alongshore direction away from the sand motor at the lower shoreface i e seaward of msl 6 m storm conditions may induce a partial removal of the coarse top layer due to mobilization of all of the size fractions and mixing with the relatively fine substrate material simulations also show that transport of the fine sand fraction extents to much deeper water than for the medium and coarse sand fractions models with multiple sediment fractions are therefore required for the assessment of environmental impacts of large scale coastal structures or land reclamation s and sediment transport on the lower shoreface

scarping of artificially nourished mixed sand and gravel beaches sedimentological characteristics of hayling island beach southern england abstract beach cliffing is a wide spread characteristic of artificially replenished beaches which has many undesirable engineering environmental and economic consequences a sedimentological study undertaken on the replenished mixed gravel and sand beach of hayling island southern england has shown that the persisting beach cliff consists typically of three distinct layers the textural geochemical and mineralogical analyses of the deposit showed that the development of the cliff and particularly the formation of the intermediate densely packed layer could be attributed to a series of processes firstly the techniques used to emplace the recharge material on the beach i e placement by heavy dumper trucks bulldozers result in a compaction and grain fracture of the recharge material and therefore a denser packing arrangement than that expected by its textural characteristics alone secondly percolating water transfers medium and fine grained material to deeper parts of the deposit resulting in the clogging of the interstices between the gravels and the formation of a densely packed poorly sorted layer the above processes promote the interactions between the clay minerals of the deposit with ca2 cations resulting in the formation of particular cementing materials such as calcium silicate hydrates csh

nourishment evolution and impacts at four southern california beaches a sand volume analysis abstract four southern california beaches were nourished with offshore sand placed as subaerial pads several meters thick 50 m wide and spanning between 500 and 1500 m alongshore three nourishments constructed with coarser than native sand placed in 2012 at imperial cardiff and solana beaches elevated subaerial sand volumes for several years even when exposed to the energetic winter waves of the 2015 16 el nino followed by a stormy 2016 17 winter as these relatively resilient pads were overwashed landward tilted subaerial profiles accretionary crowns formed at the eroding front face of the originally flat topped pads and pooling occurred in the backbeach at imperial beach nourishment sand helped prevent waves from directly impacting riprap fronting houses while groundwater flooding behind the pad was observed at a location where the pad was elevated 1 6 m above the street as the nourishments retreated alongshore oriented spits grew downdrift from the eroding face the alongshore displacement of the subaerial center of mass of the 2012 nourishments is positively correlated with the seasonally varying s x y the alongshore radiation stress component after four years the net southward drift of the imperial beach nourishment contributed to the winter 2016 closure of the tijuana river mouth and the associated hyper polluted and anoxic estuary conditions nourishment impacts on sand levels on rocky reefs were not unambiguously detectable in the background of natural variability over several years gains or losses in the total sand volume integrated from the back beach to 8 m depth over the few km alongshore survey spans are sometimes comparable to nourishment volumes suggesting relatively large interannual sediment fluxes across the control volume boundaries the clearest trend in total volume is at torrey pines during 16 years since the 2001 nourishment about 300 000 m3 of sand has been lost if the trend continues the thinning veneer of sand will be removed more often from the subaerial winter beach exposing rocks and cobbles

the impact of storms and stratification on sediment transport in the rhine region of freshwater influence we present measurements of along and across shore sediment transport in a region of the dutch coast 10 km north of the rhine river mouth this section of the coast is characterized by strong vertical density stratification because it is within the midfield region of the rhine region of freshwater influence where processes typical of the far field such as tidal straining are modified by the passage of distinct freshwater lenses at the surface the experiment captured two storms and a wide range of wind wave tidal and stratification conditions we focus primarily on the mechanisms leading to cross shore sediment flux at a mooring location in 12 m of water which are responsible for the exchange of sediment between the nearshore and the inner shelf net transport during storms was directed offshore and influenced by cross shelf winds while net transport during spring tides was determined by the mean state of stratification tidal straining dominated during neap tides however cross shore transport was negligible due to small sediment concentrations the passage of freshwater lenses manifested as strong pulses of offshore transport primarily during spring tides we observe that both barotropic and baroclinic processes are relevant for cross shore transport at depth and since transport rates due to these competing processes were similar the net transport direction will be determined by the frequency and sequencing of these modes of transport based on our observations we find that wind and wave driven transport during storms tends move fine sediment offshore while calmer more stratified conditions move it back onshore

a possible middle paleozoic suture in the altyn tagh nw china preliminary 40ar 39ar thermochronologic results from two transects across the altyn tagh at range allow new interpretations for the genesis of the range and provide constraints for its subsequent displacement recent reports of middle to upper ordovician pillow lavas in the ne portion of the range as well as the first reports of high pressure metamorphic rocks within the range are interpreted as the remnants of a lower paleozoic ocean subducted within the at muscovite and biotite ages from schist gneiss and granodiorite document a significant metamorphic and intrusive event throughout the range at 435 20 ma this fabric is crosscut by undeformed postorogenic microgranite plutons dated at 383 7 ma by muscovite these data suggest that an ocean basin closed after the early silurian and prior to the middle devonian forming the herein named lapeiquan suture the lack of similary aged plutons to the north and the suggestion of a synchronous arc to the south implies that subduction was south dipping present geography if the altyn tagh contains a middle paleozoic suture lateral continuations should be identifiable possibilities to the west include the kudi suture in the western kunlun shan comparisons of lithologies and radiometric data reveal significant similarities between the kudi suture and the altyn tagh suggesting that the at originated as part of the same middle paleozoic orogenic belt reconstruction of the paleozoic structure of northern tibet is complicated by cenozoic deformation particularly along the altyn tagh fault although this could be used as a measure of the finite post devonian deformation a more thorough understanding of paleozoic geodynamics is a prerequisite to unraveling subsequent displacements

environmental controls on decadal morphologic behaviour of the holland coast a detailed comparison of alongshore variation in environmental variables along the holland coast with the observed marked regional differences in decadal nearshore morphologic behaviour reveals that neither offshore hydrodynamic parameters nor grain size are discriminating factors rather the abrupt alongshore changes in decadal behaviour coincide with sharp changes in shoreface morphology and the location of large man made structures these structures such as jetties and a protruding seawall appear to act as artificial headlands once they are built the coastal stretches on either side of the structure can develop independently of each other initially small differences in the development of the regions potentially may evolve into larger differences with time consequently on the long term large man made structures may affect the behaviour of coastal stretches over far larger distances than was previously known

slowing extrusion tectonics lowered estimate of post early miocene slip rate for the altyn tagh fault abstract determination of long term slip rate for the altyn tagh fault is essential for testing whether asian tectonics is dominated by lateral extrusion or distributed crustal shortening previous slip history studies focused on either quaternary slip rate measurements or pre early miocene total offset estimates and do not allow a clear distinction between rates based on the two the magmatic and metamorphic history revealed by shrimp zircon dating of clasts from miocene conglomerate in the xorkol basin north of the altyn tagh fault strikingly matches that of basement in the southern qilian shan and northern qaidam regions south of the fault this match requires that the post early miocene long term slip rate along the altyn tagh fault cannot exceed 10 mm year supporting the hypothesis of distributed crustal thickening for post early miocene times this low long term slip rate and recently documented large pre early miocene cumulative offset across the fault support a two stage evolution wherein asian tectonics was dominated by lateral extrusion before the end of early miocene and since then has been dominated by distributed crustal thickening and rapid plateau uplift

aeolian sediment supply at a mega nourishment abstract mega nourishments are intended to enhance growth and resilience of coastal dunes on medium to long time scales by stimulation of natural sediment transport processes the growth and resilience of coastal dunes largely depends on the presence of a continuous supply of aeolian sediment a recent example of a mega nourishment is the 21 mm 3 mega nourishment known as the sand motor the sand motor is intended to nourish the entire holland coast over a period of two decades four years of bi monthly topographic measurements of the sand motor domain provide an opportunity to analyze spatiotemporal variations in aeolian sediment supply using an aeolian sediment budget analysis it appears that more than 58 of all aeolian sediment deposits originate from the low lying beaches that are regularly reworked by waves aeolian sediment supply from higher beaches diminished after half a year after construction of the sand motor likely due to the formation of deflation lag deposits that constitute a beach armor layer the compartmentalization of the sand motor in armored and unarmored surfaces suggests that the construction height is an important design criterion that influences the lifetime and region of influence for any mega nourishment

morphodynamic response of a two barred beach to a shoreface nourishment abstract the response to a shoreface nourishment of the two bar system at noordwijk the netherlands is analyzed based on a daily data set of time exposure video images collected during about 6 years complemented with topographic and bathymetric surveys the 1 7 mm 3 nourishment implemented as a 3 km alongshore bump seaward of the outer bar migrated more than 300 m onshore in 4 years before losing its integrity furthermore the nourishment interrupted the autonomous seaward migration of both bars for the entire duration of the study period and allaying earlier fears did not intensify the three dimensional patterns in the bars such as the crescentic plan shape and rip channels the nourishment did result in clear head effects on both flanks with the bar becoming discontinuous and the flank section decaying or becoming attached to an offshore located bar while the section of bar landward of the nourishment became attached to a landward located bar this sequence of morphologies is known as bar switching each switching episode took almost one year to complete and can therefore not be ascribed to individual wave events we suspect that shoreface nourishments enhance the possibility of bar switching by creating alongshore variability in the position and depth of the outer bar and in its cross shore migration rate and direction the noordwijk nourishment did not influence the shoreline position as its trend did not undergo distinctive variations after 1998 differences in the response of the noordwijk sandbars to the shoreface nourishment compared with other dutch nourishments are attributed to the location and size volume per unit length of the nourishment with respect to the sandbars and to the median grain size of the nourished material

constraints on extension of continental lithosphere the extension of the continental lithosphere is considered in terms of the deformation of a thin viscous sheet with a temperature dependent rheology which is governed primarily by the strength of the upper mantle the lithosphere is subjected either to a constant strain rate or to a strain rate decreasing with time corresponding to the stretching of a region of fixed volume with a constant velocity boundary condition the progress of the extension is influenced by the decrease in strength of the lithosphere owing to its attenuation and by an increase in strength resulting from cooling the relative importance of these two effects depends on two parameters a dimensionless strain rate and the total strain for a given strain rate the extending lithosphere goes through two phases as the strain increases in the first the effect of thinning the lithosphere is predominant and the average strength of the lithosphere remains close to and perhaps slightly below its original strength in the second the effect of cooling of the lithosphere leads to very rapid increase in strength as a function of strain resulting presumably in an effective limit on the degree of stretching that the lithosphere experiences for the case of strain rate decreasing with time when the initial strain rates are of order 10 15s 1 this maximum extension is between 100 and 150 for a strain rate of 10 l4 s 1 the maximum lies around 400 to 500 at higher strain rates than this very large extension may occur before cooling significantly affects the strength of the lithosphere this model accords well with the constraints available from the continental margins of the north atlantic

teleseismic shear wave splitting and lithospheric anisotropy beneath and across the altyn tagh fault sixteen 3 component 5 sec stations along a profile crossing the altyn tagh fault atf at 90 e were used to measure shear wave splitting beneath tibet s northern edge splitting delay times t of 0 3 to 1 3 sec show a marked increase in a narrow zone centered on the fault implying anisotropy in the lithospheric mantle fast polarization directions fpd swing counterclockwise from a mean azimuth of 110 e in the qaidam basin south of the fault to a mean azimuth of 60 e in the altyn mountains this swing occurs in less than 40 km both the t increase and fpd swing are consistent with ductile sinistral shear along the 40 km wide low p wave velocity anomaly 6 8 imaged to a depth of 140 km beneath the fault by teleseismic tomography this confirms that the atf guides the northeastwards extrusion of the tibet qaidam s lithosphere relative to the tarim s

seasonal accretion and erosion patterns of a microtidal sandy beach monthly elevation surveys of a 1 5 km stretch of coast at noordwijk the netherlands were made 1 to quantify seasonal variability in the cross shore position of high mean and low tide contours beach width and beach volume and 2 to examine the dependence of the variability on the offshore wave characteristics additionally daily cross shore positions of contours obtained from video images were used to examine daily beach response to wave characteristics between successive surveys the more intense and frequent storm events in winter than in summer resulted in a seasonal change from a wide beach with a small volume at the end of winter to a narrow large volume beach in summer the seasonal pattern in beach width resulted from the cross shore sediment exchange between the supratidal and lower intertidal part of the beach in contrast to the coupling between beach behaviour and wave characteristics on a seasonal scale beach variability between successive surveys was unrelated to day to week averages of the preceding offshore wave conditions partly due to the precise timing of a storm relative to the two survey moments moreover daily variability determined from the video images showed that differing antecedent morphology to storms and alongshore variations in beach morphology contributed to spatially and temporally variable beach response

sediment transport and budget of the central coastal zone of holland abstract based on the available short term morphological data 1964 1992 the net yearly averaged sand volume change in the surfzone 3 8 m nap to local datum approximately mean sea level along the coast of holland was found to be 125 000 m 3 year sedimentation including beach nourishments a sand budget model has been developed which describes the sand volume change in m 3 year in each compartment of the coastal area given known gradients of the computed longshore and cross shore transport rates and known source sink terms nourishment dumping and dredging the model area extends in cross shore direction from the 3 m nap contour to the 20 m nap contour the sand budget model has been calibrated hindcast study using the yearly averaged sand volume changes derived from bathymetry data jarkus data base collected during the period 1964 1992 input data are the gradients of the yearly averaged longshore and cross shore transport rates at the boundaries of the compartments and the available data of beach nourishment dumping and dredging in the same period a 2dv mathematical model representing the hydrodynamic waves and currents and sand transport processes in a cross shore profile was applied to compute the yearly averaged transport rates in various profiles along the coast at depths of 20 and 8 m and in the surf zone a detailed sensitivity study was performed to determine the variation ranges of the transport rates

cross shore sand transport by infragravity waves as a function of beach steepness two field data sets of near bed velocity pressure and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross shore transport on the moderately sloping sand motor beach 1 35 the local ratio of infragravity wave height to sea swell wave height is relatively small hig hsw 0 4 most sand is suspended during negative infragravity velocities and qig is offshore directed the infragravity contribution to the total sand flux is considerably larger and reaches up to 60 during energetic conditions on the whole hig hsw is a good indicator for the infragravity related sand suspension mechanism and the resulting infragravity sand transport direction and relative importance

length scales for continental deformation in convergent divergent and strike slip environments analytical and approximate solutions for a thin viscous sheet model the deformation of a thin viscous layer that has a moving boundary is investigated for comparison with zones of deformation in the continental lithosphere exact analytical solutions for the case of a newtonian fluid and approximate solutions for the case of fluid with power law rheology show that when the imposed velocity vector is normal to the boundary congressional or extensional regime the deformation field decays away from the boundary with a characteristic length scale 1 3 to 1 10 the wavelength of the imposed boundary velocity distribution for n between 1 and 10 where n is the stress strain exponent in the rheology in contrast when the imposed velocity vector is parallel to the boundary transcurrent regime the length scale of the deformation field is approximately 4 times smaller in each case these length scales decrease approximately as n the difference in length scales arises even in the absence of any buoyancy forces acting on thickened or thinned crust such forces would modify the ratio of length scales but not sufficiently to affect this result

laboratory investigation of nourishment options to mitigate sea level rise induced erosion abstract the response of nourished beaches to sea level rise is investigated experimentally with random waves in a laboratory wave flume 20 m 1 m 1 m following on from a previous investigation of the response of non nourished beaches atkinson et al 2018 the nourishments are placed on beach profiles previously exposed to sufficient durations of waves to have approached a near equilibrium state i e with stable shoreline bars and berms nourishment was placed in three different locations on the berm within the bar trough and as a shoreline placement in the latter case and following bruun rule concepts bruun 1962 the volume of sediment placed was estimated a priori to lead to zero recession under the chosen water level rise the nourished beaches were then exposed again to sufficient durations of waves to reach a near equilibrium state at the raised water level the shoreline recession and the mean recession of the profile following a rise in water level are compared for both the nourished and non nourished beaches and to theoretical estimates based on bruun rule concepts and a previously developed profile translation model ptm quantitative agreement is found with the variants of the bruun rule that account for nourishment and with the ptm and the predicted recession is within an order of 30 of the observed recession overall the ptm provides the best estimate of the recession the mean recession of the profile is found to be in better agreement with the model predictions than the recession measured at the shoreline because the latter is affected by changes in profile shape around the still water line the efficacy of the nourishment was investigated from the reduction in the observed recession the efficacy depends on how the recession is measured for the mean recession highest efficacy was observed when all the nourishment is added into the active profile conversely for the shoreline recession highest efficacy was observed with the nourishment placed on the upper beach because it prevents additional recession through wave overtopping

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

analysis of nourished profile stability following the fifth hunting island sc beach nourishment project a comparison of the geotechnical properties of beach fill vs borrow area sediments for the fifth hunting island sc beach nourishment project is presented in this paper sediment samples were taken from the beach and borrow area to characterize pre nourishment 1990 and post nourishment 1993 conditions grain size frequency curves were developed for these samples which were then used to perform the geotechnical analyses the results indicate that post nourishment profile stability can be improved measurably by variations in grain size distribution specifically where a coarse fraction is present i e negative skewness in other words by using borrow sediments that are coarser than native the nourished profile will adjust to a steeper configuration producing a wider dry beach other factors influencing profile durability include fill placement techniques and environmental factors waves currents storms etc

localization of shear along a lithospheric strength discontinuity application of a continuous deformation model to the boundary between tibet and the tarim basin 1 a marked contrast in strength or viscosity within a continuously deforming zone can lead to concentration of shear strain in the weaker material adjacent to the boundary between them but localization comparable to the width of the altyn tagh shear zone requires an additional weakening process during numerical experiments on a thin viscous sheet indented by a rigid object a shear zone develops adjacent to a strong region mimicking the tarim basin when the boundary between the weak and strong regions is oblique to the orientation of convergence the width of this shear zone narrows with increased strain and for comparable penetration by the indenter the strain is more concentrated for larger values of n the exponent that relates strain rate to a power of stress and for smaller values of the argand number ar a measure of buoyancy induced stress relative to viscous stress increasing concentration of shear occurs as the indentation develops without weakening because of a change in material properties additional localization develops with the inclusion of strain dependent weakening associated with for instance a temperature increase due to shear heating for such localization to scale to the width of the altyn tagh fault zone of tibet the initial temperature near the moho must be relatively low 600 c and a large value of n 10 is required this suggests that deformation there is described by a high strength flow law such as that proposed by evans and goetze 1979 in which the lithosphere would deform approximately plastically

immediate profile and planform evolution of a beach nourishment project with hurricane influences abstract in this study planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration weekly beach profiles shoreline surveys and nearshore wave measurements were conducted before during and immediately after construction of the 1100 m long upham beach nourishment project on the low energy west coast of florida this project was constructed in three segments the wide north segment the central segment and the narrow south segment with the exception of the relatively distant passage of hurricane charley calm weather prevailed for 45 days following completion of the south and central segments construction of the wide north segment was completed on august 27 2004 substantial planform diffusion occurred prior to construction completion via formation of a 300 m long spit extending from the wide north segment the shoreline orientation was changed abruptly due to this diffusion spit formation as opposed to the gradual adjustment predicted by most long term models planform adjustment was initiated prior to profile equilibration and it did not require high energy conditions a simple vector sum model for determining the orientation of a potential diffusion spit was developed this study recommends designing end transitions at the predicted diffusion spit orientation to avoid post nourishment spit formation during future projects profile equilibration occurred rapidly due to the passage of three hurricanes soon after nourishment was complete nine days after completion hurricane frances passed by the project area generating high wave conditions h sig 1 7 m for this region the steep post nourishment beach slope of 0 078 was reduced to 0 036 nearly to the equilibrium slope 0 034 due to this storm hurricanes ivan and jeanne which were nearly as energetic passed by the project area within 1 month after frances and resulted in much less profile slope change examination of the ratio of total volume to plan area remaining in the project area also suggested that a substantial portion of the total profile equilibration occurred as a result of hurricane frances this study indicates that profile equilibration can be an event driven process which contradicts the concept of longer term gradual profile equilibration both profile and planform adjustment can occur rapidly given the appropriate site conditions and energy levels

modeling the long term diffusion and feeding capability of a mega nourishment a morphodynamic model based on the wave driven alongshore sediment transport including cross shore transport in a simplified way and neglecting tides is presented and applied to the zandmotor mega nourishment on the dutch delfland coast the model is calibrated with the bathymetric data surveyed from january 2012 to march 2013 using measured offshore wave forcing the calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until march 2015 according to the long term modeling using different wave climate scenarios based on historical data for the next 30 yr period the zandmotor will display diffusive behavior asymmetric feeding to the adjacent beaches and slow migration to the ne specifically the zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability the modeled coastline diffusivity during the 3 yr period is 0 0021 m2 s close to the observed value of 0 0022 m2 s in contrast the coefficient of the classical one line diffusion equation is 0 0052 m2 s thus the lifetime prediction here defined as the time needed to reduce the initial amplitude by a factor 5 would be 90 yr instead of the classical diffusivity prediction of 35 yr the resulting asymmetric feeding to adjacent beaches produces 100 m seaward shift at the ne section and 80 m seaward shift at the sw section looking at the variability associated to the different wave climates the migration rate and the slight shape asymmetry correlate with the wave power asymmetry w vs n waves while the coastline diffusivity correlates with the proportion of high angle waves suggesting that the dutch coast is near the high angle wave instability threshold

numerical modelling of erosion rates life span and maintenance volumes of mega nourishments mega nourishments aiming at providing long term coastal safety nature qualities and recreational space have been applied recently at the holland coast and are considered at various other places in the world methods to quickly evaluate the potential and lifetime of these coastal mega nourishments are therefore very much desired which is the main objective of this research two types of mega nourishments can be distinguished feeder type mega nourishments may erode freely to feed adjacent coasts for a more natural dynamic dune growth while permanent mega nourishments are designed to preserve safety levels and need to maintain their size and shape and thus needs to be nourished themselves the design and impact assessment studies for both types of mega nourishments require detailed morphological studies to determine the morphological evolution in this paper 2dh delft3d and 1d unibest cl and longmor numerical models were calibrated using data of the sand motor mega nourishment and were then applied to model a series of mega nourishments with various width over length ratios and volumes in order to derive relations and design graphs for erosion rates life span and maintenance volumes these relations and design graphs can be used in project initiation phases and feasibility studies the magnitude of the modelled wave driven longshore sediment transport rates in 1d coastline models depend on the representation of wave refraction on the lower shoreface since a distinction should be made between the non rotating lower shoreface and active surfzone it was shown that the life time of nourishments is mainly determined by the dimensions of the nourishment and incoming wave energy

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

observations on sandbar behaviour along a man made curved coast sandbars submerged ridges of sand parallel to the shoreline affect surfzone circulation beach topography and beach width under time varying wave forcing sandbars may migrate onshore and offshore referred to as two dimensional 2d behaviour and vary in planshape from alongshore uniform ridges to alongshore non uniform ridges through the growth and decay of three dimensional 3d patterns referred to as 3d behaviour although 2d and 3d sandbar behaviour is reasonably well understood along straight coasts this is not the case for curved coasts where the curvature can invoke spatial variability in wave forcing here we analyse sandbar behaviour along the 3000 m man made curved coastline of the sand engine netherlands and determine the wave conditions governing this behaviour 2d and 3d behaviour was quantified within a box north and west of the sand engine s tip respectively using a 2 4 year dataset of daily low tide video images and a sparser bathymetric dataset the northern and western sides behaved similarly in terms of 2d behaviour with seasonal onshore and offshore migration resulting in a stable position on inter annual timescales however both sandbar geometry and 3d behaviour differed substantially between both sides the geometric differences bar shape bar crest depth and wavelength of 3d patterns are consistent with computed alongshore differences in breaker height due to refraction the differences in the timing in growth decay and morphological coupling of 3d patterns in the sandbar and shoreline are likely related to differences in the local wave angle imposed by the curved coast similar dependency of bar behaviour on local wave height and angle may be expected elsewhere along curved coasts e g shoreline sandwaves cuspate forelands or embayed beaches copyright 2017 john wiley sons ltd

seasonal persistence of a small southern california beach fill abstract torrey pines state beach a site with large seasonal fluctuations in sand level received a small shoreface beach fill about 160 000 m3 in april 2001 the 600 m long flat topped nourishment pad extended from a highway riprap revetment seaward about 60 m terminating in a 2 m tall vertical scarp a 2 7 km alongshore span centered on the nourishment region was monitored prior to the nourishment and biweekly to monthly for the following 2 years for the first 7 months after the nourishment through fall 2001 significant wave heights were small and the elevated beach fill remained in place with little change near and above mean sea level msl in contrast the shoreline accreted on nearby control beaches following a seasonal pattern common in southern california reducing the elevation difference between the nourished and adjacent beaches during the first winter storm 3 m significant wave height the shoreline retreated rapidly over the entire 2 7 km survey reach forming an alongshore oriented sandbar in 3 to 4 m water depth seymour r j guza r t o reilly w elgar s 2004 rapid erosion of a southern california beach fill coastal engineering 52 2 151 158 we show that the winter sandbar most pronounced offshore of the nourishment moved back onto the beach face during summer 2002 following the usual seasonal pattern and formed a wider beach above msl at the site of the original nourishment than on the control beaches thus the april 2001 shoreline nourishment was detectable until late fall 2002 persisting locally over a full seasonal cycle in an extended 7 year time series total sand volumes summed between the back beach and 8 m water depth over the entire 2 7 km reach exhibit multi year fluctuations of unknown origin that are twice as large as the nourishment volume

sensitivity of rip current forecasts to errors in remotely sensed bathymetry operational nearshore current forecasts based on numerical model simulations are gaining popularity as a measure to increase the safety of swimmers applying remotely sensed bathymetry in these model simulations is often proposed in order to cope with rapidly changing nearshore bathymetry errors in the remotely sensed bathymetry may negatively affect performance of the hydrodynamic model hence this study aims to determine the sensitivity of modelled nearshore currents with a strong focus on rip currents to errors in remotely sensed bathymetries the errors in the remotely sensed bathymetries depth inversion algorithm applied to video stream were quantified with a length scale aware validation technique providing useful insights in the contribution of pattern and amplitude errors to the total error throughout the analysis domain and over a range of bathymetric length scales subsequently simulations with a nearshore hydrodynamic model were performed using both in situ and remotely sensed bathymetries as an input a comparison of predicted rip currents on either bathymetry yielded performance statistics for operational current forecasts on remotely sensed bathymetries taking the model with in situ bathymetry as a reference linking these performance statistics back to the quantified errors in the remotely sensed bathymetry finally revealed the relation between errors in flow and bathymetry of all rip currents generated on an in situ bathymetry 55 were reproduced on the remotely sensed bathymetry showing that models predicting nearshore currents on remotely sensed bathymetry have predictive value positive rip current predictions were promoted significantly by accurate reproduction of the pattern and amplitude of nearshore bars at length scales between 200 and 400 m in contrast to the length scale aware validation technique applied here commonly used domain wide bulk error metrics lack important information about spatial variations in the quality of remotely sensed bathymetry

late quaternary and present day rates of slip along the altyn tagh fault northern margin of the tibetan plateau 1 both global positioning system gps measurements and studies of late quaternary faulting are consistent with a slip rate of 10 mm yr along the central segment of the altyn tagh fault and a systematic decrease in that rate toward the eastern end of the fault dates of terraces above and below laterally offset terrace risers yield bounds on quaternary slip rates that range from those that agree with gps measurements to values as much as three times faster we argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace in some cases valleys upstream of the fault have been incised into bedrock and few if any terrace risers can be seen within the valleys such streams debouch onto alluviated floodplains or fans that become incised presumably during climate changes to create terrace risers the terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault and thus the risers become protected from further incision in such cases dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces such dates yield slip rates of 10 mm yr in the central segment of the fault and decreasing rates eastward although we cannot with certainty rule out the higher slip rates along the altyn tagh fault our analysis does show that viable interpretations consistent with gps measurements are more likely at least along some segments of the fault not only do these rates support the view that the tibetan plateau deforms internally by slip on a distributed network of faults in the shallow brittle crust and hence behaves as a continuum at depth but the gradual decrease toward the east also shows that the altyn tagh fault does not separate two effectively rigid lithospheric plates correspondingly the relatively low slip rate and the eastward decrease in slip rate suggest that the altyn tagh fault does not transfer a significant portion of the convergence between india and asia into northeastward extrusion of the tibetan plateau thus large scale extrusion of crustal material in india s path into eurasia seems to be limited largely to the confines of the tibetan plateau