least squares reverse time migration with a wavefield separation imaging condition and updated source wavefields abstractdirectly imaging steeply dipping fault zones is difficult for conventional migration including reverse time migration rtm we developed a new least squares rtm lsrtm method to directly image steeply dipping fault zones the method uses a wavefield separation imaging condition and updated source wavefields during each iteration our new imaging method produces horizontal looking images that show mostly steeply dipping fault zones conventional least squares rtm does not update source wavefields and cannot directly image vertical fault zones we numerically determined that it is crucial to update source wavefields to image steeply dipping fault zones using synthetic seismic data we proved that our new lsrtm method can directly image steeply dipping fault zones with dipping angles up to 90 compared with conventional lsrtm our lsrtm method was less sensitive to the smoothness and the velocity error of the initial migration velocity model

power law statistics of cliff failures scaling and percolation large cliff failures have often been characterized by their size in terms of the horizontal eroded area at the cliff top and the maximum local retreat of the coastline field studies suggest that the frequencies of these two quantities decrease as power laws of their respective magnitudes defining two different decay exponents moreover the horizontal area increases as a power law of the maximum local retreat identifying a third exponent this observation indicates that the geometry of cliff failures are similar for different magnitudes it is shown that under a scaling hypothesis the exponents satisfy a precise mathematical relation that relates the exponent of the distributions of magnitudes of events and their geometry a relation that could be useful to validate the analysis of field catalogs in order to understand the observed scenario a numerical model of rocky coast erosion is developed despite its minimal character it reproduces the observed cliff failure statistics strikingly the model precisely reproduces the geometric similarity of cliff failures observed in the field these results suggest that the theory of percolation which underlies the erosion model can possibly be used as a guide to decipher the physics of rocky coast erosion and could provide precise predictions of the statistics of cliff collapses copyright 2015 john wiley sons ltd

kinematics of shot geophone migration recent analysis and synthetic examples have shown that many prestack depth migration methods produce nonflat image gathers containing spurious events even when provided with a kinematically correct migration velocity field if this velocityfieldishighlyrefractive thispathologyoccursinall migration methods that produce partial images as independent migrations of data bins shot geophone prestack depth migration is an exception to this pattern each point in the prestack image volume depends explicitly on all traces within the migration aperture using a ray theoretical analysis we have found that shot geophone migration produces focusedsubsurface offsetdomainorflatscattering angledomain image gathers provided there is a curvilinear coordinate system defining pseudodepth with respect to which the rays carrying significant energy do not turn and that the acquisitioncoverageissufficienttodetermineallsuchrays although the analysis is theoretical and idealized a synthetic example suggests that its implications remain valid for practical implementations and that shot geophone prestack depth migration could be a particularly appropriate tool for velocityanalysisinacomplexstructure

the temporal and spatial scales of rocky coast geomorphology a commentary rocky shores are complex landforms that result from marine erosion and subaerial weathering they are time integrated features where their present day form is the result of instantaneous erosion often on the millimetre to sub metre scale occurring for centuries to millennia as a result research on rocky coasts focuses on a range of temporal and spatial scales from granular scale swelling of a rock surface and instantaneous wave impact to modelling millennial scale sea level drivers the challenge for rocky coast researchers is either to upscale or to downscale their results to the human timescales of greatest interest to managers the research presented in earth surface processes and landforms over the past 3 years highlights the range of spatial and temporal approaches to the study of coastal cliffs and shore platforms we identify a key temporal and spatial gap in current research seasonal annual timeframes over hundreds of metres to kilometre scale studies appear to be lacking and are likely critical in understanding the future evolution of rocky coasts especially their response to climate change copyright 2017 john wiley sons ltd

characterisation of erosional features associated with tsunami terrains on rocky coasts of the maltese islands in recent years there has been a growing body of literature on depositional signatures associated with historic extreme waves on rocky coasts here in the context of the maltese islands we place an innovative focus on evidence of erosional forms the field evidence is concentrated along the ne flank of the islands at a topographically varied range of sites and up to an altitude of 13 m asl a range of forms is broadly classified in terms of their morphologies and the forces responsible for their formation sockets eroded scarps scoured terrains clifftop erosion scars swept terrains and spillways are interpreted as consequences of overwashing of the landscape by an extreme wave or waves these forms are shown to be controlled by flow intensity topography and lithology and especially rock bedding and jointing they comprise the source areas for associated depositional evidence allowing transport paths to be estimated and may significantly enhance the reconstruction of extreme wave events it is likely that similar and additional erosional forms are present elsewhere in the mediterranean domain where comparable lithological and topographic situations are exposed to extreme waves

least squares reverse time migration in a matrix based formulation this paper describes least squares reverse time migration the method provides the exact adjoint operator pair for solving the linear inverse problem thereby enhancing the convergence of gradient based iterative linear inversion methods in this formulation modified source wavelets are used to correct the source signature imprint in the predicted data moreover a roughness constraint is applied to stabilise the inversion and reduce high wavenumber artefacts it is also shown that least squares migration implicitly applies a deconvolution imaging condition three numerical experiments illustrate that this method is able to produce seismic reflectivity images with higher resolution more accurate amplitudes and fewer artefacts than conventional reverse time migration the methodology is currently feasible in 2 d and can naturally be extended to 3 d when computational resources become more powerful

fission track analysis of uranium distribution in granitic rocks abstract the natural uranium concentration and distribution in three granitoids from australia has been used to develop an understanding of the geochemical processes which control its behaviour in the natural environment and the potential behaviour of some analogue elements within a crystalline high level radioactive waste hlw repository environment in the coles bay granite olympic dam granite and the kambalda granodiorite fission track micromapping has been used to identify primary and secondary distribution between four main mineralogical locales 1 background u 2 resistate u 3 secondary u and 4 fracture u minor concentrations of total u are present as background u in the major rock forming minerals whereas resistate u contributed by the accessory minerals comprises up to 60 of total u two modes of redistribution of primary u are evident 1 in the secondary minerals particularly fe and ti hydroxides and 2 on alteration minerals which infill microfractures the association of u with these secondary and fracture infilling minerals indicates that it has been redistributed during post magmatic hydrothermal alteration and possibly by recent groundwater rock interaction the most important geochemical processes involved in this u redistribution include mobilisation and fixation through complex decoupling and redox reactions and retention by secondary minerals through adsorption and ionic exchange the effect of these processes upon natural u redistribution may be considered as an analogue of geochemical processes around a hlw repository this work shows that a degree of post magmatic alteration of a granite increases the proportion of secondary minerals of high sorption capacity present which may thus enhance the radionuclide retardation capability of the granitoids

hydrodynamic constraints and storm wave characteristics on a sub horizontal shore platform few studies of wave processes on shore platforms have addressed the hydrodynamic thresholds that control wave transformation and energy dissipation especially under storm conditions we present results of a field experiment conducted during a storm on a sub horizontal shore platform on the east coast of auckland new zealand small 2 5 times the gravity wave height 0 05 0 33 hz is necessary for waves to propagate onto the platform without breaking on the platform surface the wave height is a direct function of water depth with limiting maximum wave height to water depth ratios of 0 55 and 0 78 at the centre of the platform and cliff toe respectively a relative platform edge submergence water depth water height ratio threshold of 1 1 is identified below which infragravity 0 05 hz wave energy dominates the platform energy spectra and above which gravity waves are dominant infragravity wave height transformation across the platform is governed by the relative platform edge submergence finally the paper describes the first observations of wave setup on a shore platform during the peak of the storm wave setup on the platform at low tide 0 21 m is consistent with measurements from planar sandy beaches but at higher tidal stages the ratio between incident wave height and maximum setup was lower than expected copyright 2014 john wiley sons ltd

radioactive disequilibria in mineralised fracture samples from two uranium occurrences in northern sweden abstract mineralised fractures from two uranium occurrences in northern sweden were examined mineralogically and isotopically to establish the presence or absence of radioactive equilibrium that may indicate recent rock water interaction processes based on the natural mobility of uranium i e during the last 0 5 ma the results show evidence of radioactive disequilibrium in six of the nine samples investigated disequilibria are attributable to solution to solid 234 u recoil gain weakly mineralised zones adjacent to the main mineralisation and solid to solution 234 u recoil loss moderate to highly mineralised zones the absence of significant 238 u loss in the samples emphasises the reducing conditions at the sampled depths

kinematic artifacts in prestack depth migration strong refraction of waves in the migration velocity model introduces kinematic artifacts coherent events not corresponding to actual reflectors into the image volumes produced by prestack depth migration applied to individual data bins because individual bins are migrated independently the migration has no access to the bin component of slowness this loss of slowness information permits events to migrate along multiple incident reflected ray pairs thus introducing spurious coherent events into the image volume this pathology occurs for all common binning strategies including common source common offset and common scattering angle since the artifacts move out with bin parameter their effect on the final stacked image is minimal provided that the migration velocity model is kinematically correct however common image gathers may exhibit energetic primary events with substantial residual moveout even with the kinematically accurate migration velocity model

sea stack formation and the role of abrasion on beach mantled headlands sea stacks are common and striking coastal landforms but few details are known about how how quickly and under what conditions they form we present numerical and analytical models of sea stack formation due to preferential erosion along a pre existing headland to address these basic questions on sediment rich rocky coasts as sea cliffs erode and retreat they produce beach sediment that is distributed by alongshore sediment transport and controls future sea cliff retreat rates depending on their width beaches can encourage or discourage sea cliff erosion by acting either as an abrasive tool or a protective cover that dissipates wave energy seaward of the cliff along the flanks of rocky headlands where pocket beaches are often curved and narrow due to wave field variability abrasion can accelerate alongshore directed sea cliff erosion eventually abrasion induced preferential erosion can cut a channel through a headland separating it from the mainland to become a sea stack under a symmetrical wave climate i e equal influence of waves approaching the coastline from the right and from the left numerical and analytical model results suggest that sea stack formation time and plan view size are proportional to preferential erosion intensity caused by for example abrasion and or local rock weakness from joints faults or fractures and initial headland aspect ratio and that sea stack formation is discouraged when the sediment input from sea cliff retreat is too high i e sea cliffs retreat quickly or are sand rich when initial headland aspect ratio is too small and the headland is rounded much wider in the alongshore direction at its base than at its seaward apex the headland is less conducive to sea stack formation on top of these geomorphic and morphologic controls a highly asymmetrical wave climate decreases sea stack size and discourages stack formation through rock sediment interactions copyright 2014 john wiley sons ltd

lithological controls on soft cliff planshape evolution under high and low sediment availability this paper addresses a series of geomorphic questions relating to large scale 1 km long term 100 1 000 years coastal planshape evolution previous research on soft cliff coasts has recognised the role of protective fronting beach volumes on reducing rates of cliff toe retreat however it is the maintenance of this critical threshold that ultimately determines two contrasting modes of shoreline behaviour mode a in which there is little beach sediment and shoreline evolution is controlled by material strength and mode b when ample beach sediment means that shoreline evolution is controlled by longshore sediment transport here we use a numerical model scape to investigate temporal and spatial changes in beach volume on a broader range of feedbacks than considered in previous models the transition between mode a and mode b coasts is defined by relative sediment inputs to outputs and used to explore how these contrasting modes control the evolution of an initial linear frontage exhibiting longshore changes in cliff lithology material resistance and the proportion of beach grade material in the eroded bedrock under mode a relative changes in material resistance result in long term heterogeneous rates of retreat which result in the development of persistent headland and embayment features however under mode b feedbacks between coastal planshape longshore sediment transport beach volume and wave energy result in steady state retreat rates regardless of longshore variations in resistance results are compared and contrasted to previous simulations and site specific examples and a conceptual model of mode a and mode b interactions presented copyright 2015 john wiley sons ltd

towards an improved understanding of erosion rates and tidal notch development on limestone coasts in the tropics 10 years of micro erosion meter measurements phang nga bay thailand knowledge and understanding of shore platform erosion and tidal notch development in the tropics and subtropics relies mainly on short term studies conducted on recently deposited carbonate rocks predominantly holocene and quaternary reef limestones and aeolianites this paper presents erosion rates measured over a 10 year period on notches and platforms developed on the permian ratburi limestone at phang nga bay thailand in so doing it contributes to informing a particular knowledge gap in our understanding of the erosion dynamics of shore platform and tidal notch development in the tropics and subtropics notch erosion rates on relatively hard ancient limestones measured directly on the rock surface using a micro erosion meter mem over time periods of a decade or more the average intertidal erosion rate of 0 231 mm yr is lower than erosion rates measured over 2 3 years on recent weaker carbonate rocks average erosion rates at phang nga vary according to location and site and are in rank order from highest to lowest mid platform 0 324 mm yr notch floor 0 289 mm yr rear notch wall 0 228 mm yr lower platform 0 140 mm yr notch roof 0 107 mm yr and supratidal 0 095 mm yr the micro relief of the eroding rock surfaces in each of these positions exhibits marked differences that are seemingly associated with differences in dominant physical and bio erosion processes the results begin to help inform knowledge of longer term shore platform erosion dynamics models of marine notch development and have implications for the use of marine notches as indicators of changes in sea level and the duration of past sea levels copyright 2014 john wiley sons ltd

shore platform lowering due to frost shattering during the 2009 winter at mesnil val english channel coast nw france in 2008 2009 a severe cold snap affected the otherwise temperate mid latitude coasts of the english channel of france in march 2009 we gathered rock spalling observations at mesnil val nw france to document the effect of frost on platform lowering in macro tidal environments six epochs of frost were recorded in two months the two longest lasted 16 and 8 days with minimum air temperature dropping to 9 5 c semi diurnal tides flood the entire platform imposing up to 25 freeze thaw cycles below 2 5 c the freezing temperature of seawater 19 cycles occurred at neap tidal elevation lasting at most 3 5 hrs our integrated observations indicate that these frost cycles were responsible for a platform lowering of about 0 8 0 5 mm during a single winter no clear spatial trend appears nor do macroscopic chalk types clearly stand out as being more susceptible to erosion assuming that the long term platform retreat model preserves a constant slope frost shattering would then account for 10 to 20 of the expected annual platform erosion rate under more contrasted climates frost is thus likely to be a prominent shaping process for rocky coastal platforms

hydrological and reactive processes during rapid recharge to fracture zones the aspo large scale redox experiment abstract the hydrochemical response of fracture zones to enhanced recharge into the upper bedrock environment has been studied during a 3 a project at the aspo hard rock laboratory hrl in southeastern sweden hydrochemical data obtained during the experiment provides a basis for development of a model for the impact of accelerated recharge on groundwater composition and reactive processes during repository construction and operation tunnel construction at the hrl resulted in a 50 fold increase in recharge rates and a 30 fold decrease in groundwater residence times in the fracture zone studied up to 80 dilution of the native groundwater created the greatest impact on groundwater composition in addition comparison of mass balances for solutes with known conservative behaviour and reactive solutes indicates a significant source of hco 3 so 2 4 and na ions and a significant sink for ca 2 ions within the fracture zone these trends are explained by ion exchange processes and microbial degradation of organic c transported from the soil with recharge the increased microbial activity helps maintain anoxic conditions within the fracture zone the enhanced recharge favours the performance of the geological barrier since anoxic conditions help to protect against corrosion of engineered barriers and because long lived isotopes of np tc and u are less soluble under reducing conditions a secondary impact is the strong dilution which affects trace element speciation and also the stability and possible transport of colloids through ion strength effects results from this experiment are primarily significant for national radioactive waste disposal programs that consider potential repository sites in granite geology and for other programs considering disposal in fractured rock

an initial evaluation of drone based monitoring of boulder beaches in galicia north western spain low altitude flights by a micro drone were made in 2012 and 2013 over two boulder beaches in north western spain geographical information system software was used to map the data boulder outlines from the first flight were recorded on 4796 clasts at laxe brava and 2508 clasts at oia changes in location were identified by overlaying these outlines on the 2013 images about 17 5 of the boulders mean surface area 0 32 m2 moved at laxe brava and about 53 mean surface area 0 23 m2 at oia most movement on both beaches was between the mid tide to about 2 m above the high tidal level the location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at laxe brava and 3324 boulders at oia these elevations were compared with the elevations at the same locations in 2013 the occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines the study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution micro drone technology copyright 2014 john wiley sons ltd

emergent characteristics of rockfall inventories captured at a regional scale high resolution rockfall inventories captured at a regional scale are scarce this is partly owing to difficulties in measuring the range of possible rockfall volumes with sufficient accuracy and completeness and at a scale exceeding the influence of localised controls this paucity of data restricts our ability to abstract patterns of erosion identify longterm changes in behaviour and assess how rockfalls respond to changes in rock mass structural and environmental conditions we have addressed this by developing a workflow that is tailored to monitoring rockfalls and the resulting cliff retreat continuously in space in 3d and over large spatial scales 10 4 m we tested our approach by analysing rockfall activity along 20 5 km of coastal cliffs in north yorkshire uk in what we understand to be the first multi temporal detection of rockfalls at a regional scale we show that rockfall magnitude frequency relationships which often underpin predictive models of erosion are highly sensitive to the spatial extent of monitoring variations in rockfall shape with volume also imply a systemic shift in the underlying mechanisms of detachment with scale leading us to question the validity of applying a single probabilistic model to the full range of rockfalls observed here finally our data emphasise the importance of cliff retreat as an episodic process going forwards there will a pressing need to understand and model the erosional response of such coastlines to rising global sea levels as well as projected changes to winds tides wave climates precipitation and storm events the methodologies and data presented here are fundamental to achieving this marking a step change in our ability to understand the competing effects of different processes in determining the magnitude and frequency of rockfall activity and ultimately meaning that we are better placed to investigate relationships between process and form erosion at critical regional scales

abrasive notches along the atlantic patagonian coast and their potential use as sea level markers the case of puerto deseado santa cruz argentina patagonia argentina is a key area for the study of sea level changes in the southern hemisphere but the availability of reliable sea level markers in this area is still problematic in fact the storm deposits beach ridge commonly used here to reconstruct past sea level oscillations introduce a wide error along the puerto deseado coast santa cruz morphometric analyses of 11 features were carried out using traditional measurement tools and a digital software based method tested on one selected feature with the aim to investigate the possibility of their use as sea level markers by undertaking accurate topographic profiles we identified the relationship between notches and current sea level in detail we identified two clusters of notch retreat point elevations with a very low internal variability the lower was located a little below the mean high tide level mht and the upper located at least 0 5 m above the maximum high tide level mht field observations of tidal levels and the position of notches suggest that the lower notches are active and the upper are inactive this study on the abrasive notches attests their quality as sea level markers and opens up the use of fossil abrasive notches as palaeo sea level markers because the error linked to these features is substantially smaller than that introduced by beach ridges commonly used in the study area copyright 2014 john wiley sons ltd

offset and angle domain common image point gathers for shot profile migration prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost effective for sparse shot wide azimuth geometries the interpretation of offset as the displacement between the downward propagating shot wavefield and upward propagating receiver wavefield enables us to extract offset domain common image point cip gathers during shot profile migration the offset domain gathers can then be transformed to the angle domain with a radial trace mapping originally introduced for shot geophone migration the computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot geophone to midpoint offset coordinates although this algorithm provides a mechanism for imaging angle dependent reflectivity via shot profile migration for sparse shot geometries the fundamental problem of shot aliasing may severely impact the quality of cip gathers

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

adaptive least squares rtm with applications to subsalt imaging least squares reverse time migration lsrtm refines the seismic image toward true reflectivity by inversion its iterative nature and modeling capability enable the use of synthetic data to guide the preconditioning of input data when the velocity contains errors dynamic warping can be used to shift the input data and force the traveltime to be consistent with the imperfect migration velocity a crosscorrelation based confidence level is introduced to control the quality of dynamic warping for field data the confidence level also is used as an inverse weighting to adaptively precondition the data residual the adaptive preconditioning automatically balances data fitting in the shallow and deep and speeds up convergence in subsalt both synthetic and field data experiments based in the gulf of mexico show that the adaptive lsrtm can improve the image quality in subsalt effectively and efficiently within only a few iterations the adaptive lsrtm suppresses the salt halo artifacts and increases the signal to noise ratio in poorly illuminated areas it also improves the termination of sediments against salt boundaries and enhances subsalt image coherency compared with conventional rtm the adaptive lsrtm image is more favorable to geologic interpretation

modelling the effect of pliocene quaternary changes in sea level on stable and tectonically active land masses a mathematical model was used to examine the effect of pliocene and quaternary changes in sea level on the development of tectonically active and inactive rock coasts the model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime bottom topography and surface roughness and the resistance of the rocks subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations especially on steeply sloping landmasses experiencing slow rates of uplift submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action on slowly subsiding landmasses submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive on rapidly rising or subsiding 5 mm yr 1 landmasses terraces that formed during interglacial stages alternated above and below present sea level with terraces formed during glacial stages despite some differences in terrace occurrence and elevational distribution it may be difficult to distinguish profiles cut during accelerating or decelerating uplift the amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late quaternary were therefore more conducive to erosion than the smaller oscillations of the pliocene and early quaternary the effect of oscillation amplitude may have been countered during the earlier stages of profile development however by steeper submarine gradients and reduced rates of wave attenuation copyright 2014 john wiley sons ltd

some uses for natural analogues in assessing the function of a hlw repository abstract radionuclides migrating with water in a fractured rock may diffuse into the porous matrix of the rock and have access to a very large surface for sorption this will retard their movement very much in excess of what only sorption on the fissure surfaces would do there are some potential natural systems which might be used to show that this process has been active over very long times the transport of u in the bulk rock the salt water content of the micropores of the rock and the interaction of oxygenated water with ferrous minerals in the rock are potential systems to study further a simplified analysis shows that the observed leaching of u in surficial rocks and the observed oxidizing waters in surficial rock is consistent with the assumed diffusion of oxygen into the rock matrix the analysis also shows that the values of observed reducing waters in deeper rock are consistent with the matrix diffusion data oxygenated waters cannot penetrate more than a few meters or tens of meters into rock with the hydraulic properties prevailing at depths below a few hundred meters during several million years of exposure

rock protecting seaweed experimental evidence of bioprotection in the intertidal zone biogeomorphological processes are an important component of dynamic intertidal systems on rocky shores the direct contribution of microorganisms plants and animals to weathering and erosion is well known there is also increasing evidence that organisms can alter rock breakdown indirectly by moderating temperature and moisture regimes at the rock air interface these influences have been purported to represent mechanisms of bioprotection by buffering microclimatic fluctuations associated with weathering processes such as wetting and drying and salt crystallization however virtually nothing has been done to test whether microclimatic buffering translates to differences in actual rock breakdown rates here we report a preliminary laboratory experiment to assess how an artificial canopy chosen to represent seaweed affects mechanical rock breakdown using a simplified and accelerated thermal regime based on field data from a rocky shore platform in southern england uk we find that breakdown mineral debris release of mudstone covered with a canopy is reduced by as much as 79 relative to bare rock after around 100 thermal cycles reduction in rock surface hardness measured using an equotip device was also greater for bare rock 17 compared to covered rock 10 over this period measurements of salt crystal formation indicate that the mechanism driving these differences was a reduction in the frequency of crystallization events via moisture retention and shading of the rock surface copyright 2015 john wiley sons ltd

granitic coastal geomorphology applying integrated terrestrial and bathymetric lidar with multibeam sonar to examine coastal landscape evolution coasts composed of resistant lithologies such as granite are generally highly resistant to erosion they tend to evolve over multiple sea level cycles with highstands acting to remove subaerially weathered material this often results in a landscape dominated by plunging cliffs with shore platforms rarely occurring the long term evolution of these landforms means that throughout the quaternary these coasts have been variably exposed to different sea level elevations which means erosion may have been concentrated at different elevations from today investigations of the submarine landscape of granitic coasts have however been hindered by an inability to accurately image the nearshore morphology only with the advent of multibeam sonar and aerial laser surveying can topographic data now be seamlessly collected from above and below sea level this study tests the utility of these techniques and finds that very accurate measurements can be made of the nearshore thereby allowing researchers to study the submarine profile with the same accuracy as the subaerial profile from a combination of terrestrial and marine lidar data with multibeam sonar data it is found that the morphology of granite domes is virtually unaffected by erosion at sea level it appears that evolution of these landscapes on the coast is a very slow process with modern sea level acting only to remove subaerially weathered debris the size and orientation of the joints determines the erosional potential of the granite where joints are densely spaced 2 m apart or the bedrock is highly weathered can semi horizontal surfaces form copyright 2014 john wiley sons ltd

statistical and empirical analyses of the triggers of coastal chalk cliff failure the triggering factors of rock falls remain unknown due to a lack of exhaustive regular and accurate surveys based on an inventory of 331 rock falls collected weekly between 2002 and 2009 from veules les roses to le treport upper normandy the relationships between coastal chalk cliff rock falls dates and geomorphological features and external factors commonly agreed as triggering rainfall temperature variations tide and wind are studied the combination of multivariate statistical and empirical analyses indicates that 1 cold and dry weather and high rainfall and high wind are the conditions most likely to trigger rock falls 2 the main triggering factors of rock falls are effective rainfall for rock falls mostly between 200 and 1400 m3 or larger than 10 000 m3 and coming from the whole cliff face freeze thaw cycles especially for rock falls smaller than 200 m3 and coming from the foot and top of the cliff face and marine roughness rock falls mainly smaller than 200 m3 and coming from the cliff foot however the contribution of each factor to triggering is difficult to determine because of combinations of factors 85 of 331 cases relays of processes and hysteresis phenomena in view of these first results it is still presumptuous to predict the location and time of triggering of rock falls however the statistical and naturalistic approaches adopted and the observations made in this study are from an original database and constitute a real starting point for the prediction and prevention of the hazard of coastal chalk cliff rock falls in upper normandy copyright 2015 john wiley sons ltd

noise removal by migration of time shift images abstractwhen using seismic data to image complex structures the reverse time migration rtm algorithm generally provides the best results when the velocity model is accurate with an inexact model moveouts appear in common image gathers cigs which are either in the surface offset domain or in subsurface angle domain thus the stacked image is not well focused in extended image gathers the strongest energy of a seismic event may occur at non zero lag in time shift or offset shift gathers based on the operation of rtm images produced by the time shift imaging condition the non zero lag time shift images exhibit a spatial shift we propose an approach to correct them by a second pass of migration similar to zero offset depth migration the proposed approach is based on the local poststack depth migration assumption after the proposed second pass migration the time shift cigs appear to be flat and can be stacked the stack enhances the energy of seismic events that are defocused at zero time lag

attenuation compensation for least squares reverse time migration using the viscoacoustic wave equation strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth conventional acoustic reverse time migration rtm and least squares reverse time migration lsrtm do not account for this distortion which can lead to defocusing of migration images in highly attenuative geologic environments to correct for this distortion we used a linearized inversion method denoted as qp lsrtm during the leastsquares iterations we used a linearized viscoacoustic modeling operator for forward modeling the adjoint equations were derived using the adjoint state method for back propagating the residual wavefields the merit of this approach compared with conventional rtm and lsrtm was that qp lsrtm compensated for the amplitude loss due to attenuation and could produce images with better balanced amplitudes and more resolution below highly attenuative layers numerical tests on synthetic and field data illustrated the advantages of qp lsrtm over rtm and lsrtm when the recorded data had strong attenuation effects similar to standard lsrtm the sensitivity tests for background velocity and qp errors revealed that the liability of this method is the requirement for smooth and accurate migration velocity and attenuation models

observations of coastal cliff base waves sand levels and cliff top shaking concurrent observations of waves at the base of a southern california coastal cliff and seismic cliff motion were used to explore wave cliff interaction and test proxies for wave forcing on coastal cliffs time series of waves and sand levels at the cliff base were extracted from pressure sensor observations programmatically and used to compute various wave impact metrics e g significant cliff base wave height wave cliff interaction was controlled by tide incident waves and beach sand levels and varied from low tides with no wave cliff impacts to high tides with continuous wave cliff interaction observed cliff base wave heights differed from standard normal and rayleigh distributions cliff base wave spectra levels were elevated at sea swell and infragravity frequencies coastal cliff top response to wave impacts was characterized using microseismic shaking in a frequency band 20 45 hz sensitive to wave breaking and cliff impacts response in the 20 45 hz band was well correlated with wave cliff impact metrics including cliff base significant wave height and hourly maximum water depth at the cliff base r2 0 75 with site specific calibration relating wave impacts and shaking and acceptable anthropogenic traffic noise levels cliff top seismic observations are a viable proxy for cliff base wave conditions the methods presented here are applicable to other coastal settings and can provide coastal managers with real time coastal conditions copyright 2016 john wiley sons ltd

efficient amplitude encoding least squares reverse time migration using cosine basis least squares reverse time migration provides better imaging result than conventional reverse time migration by reducing the migration artefacts improving the resolution of the image and balancing the amplitudes of the reflectors however it is computationally intensive to reduce its computational cost we propose an efficient amplitude encoding least squares reverse time migration scheme in the time domain although the encoding scheme is effective in increasing the computational efficiency it also introduces the well known crosstalk noise in the gradient that degrades the quality of the imaging result we analyse the cause of the crosstalk noise using an encoding correlation matrix and then develop two numerical schemes to suppress the crosstalk noise during the inversion process we test the proposed method with synthetic and field data numerical examples show that the proposed scheme can provide better imaging result than reverse time migration and it also generates images comparable with those from common shot least squares reverse time migration but with less computational cost

integrating observational targets and instrumental data on rock coasts through snorkel surveys a methodological approach abstract this work deals with recent advances in scientific snorkel surveying starting from the results of several case studies in the mediterranean between 2012 and 2018 for a total survey length of 531 4 km with the aim of illustrating the pros and cons the snorkel survey method described here also called geoswim allows rough and ready surveys of long sectors of rocky coasts in particular it is able to collect time lapse images perpendicularly to the coastline and observe long sectors of rocky coastline with particular reference to the tidal zone in addition to the photographic survey along the coast rough measures lateral variations in geomorphological geological biological and ecological parameters and the collection of hydrological data are usually performed during the work the expeditions also provide the opportunity to produce large databases of coastal landforms such as coastal sea caves and tidal notches the data collected can be improved by additional on the spot observations the evaluation of the methodology here proposed was based on the results of swot analysis starting from the results and the experience of previous expeditions geoswim is the first snorkel approach that allows the collection of large amount of multidisciplinary data along wide sectors of rocky coastline at the moment this approach is the best and probably the only technique for characterizing the tidal and nearshore zone but also to collect observational data of prominent objects along rocky coasts however snorkel observations are affected by limitations similar to those of terrestrial field surveys the ability to observe specific forms or phenomena increases through the practice of field observation and are strongly observer influenced sheltered sea basins are better suited than ocean basins where tides and wave energy are generally higher data collection is also affected by weather and sea conditions the quality of time lapse images and videos may be reduced as a result of breakers at the cliffs producing images that cannot be used for subsequent analysis as for external factors some sectors of the coast may be closed due to local restrictions on field activities