observations of wave induced set up on a natural beach a new technique has been used to make field measurements of wave induced set up the technique is reliable and accurate and the results presented show the variation of mean set up at the shoreline with incident wave height the amount of set up is well predicted by a linear function of incident wave height and is found to be in good agreement with theoretical predictions based on the observed decay of wave height across the surf zone the maximum set up observed was about 40 cm

layer formation in sedimentary fingering convection author s reali jf garaud p alsinan a meiburg e abstract when particles settle through a stable temperature or salinity gradient they can drive an instability known as sedimentary fingering convection this phenomenon is thought to occur beneath sediment rich river plumes in lakes and oceans in the context of marine snow where decaying organic materials serve as the suspended particles or in the atmosphere in the presence of aerosols or volcanic ash laboratory experiments of houk a green deep sea res vol 20 1973 pp 757 761 and green sedimentology vol 34 2 1987 pp 319 331 have shown sedimentary fingering convection to be similar to the more commonly known thermohaline fingering convection in many ways here we study the phenomenon using three dimensional direct numerical simulations we find evidence for layer formation in sedimentary fingering convection in regions of parameter space where it does not occur for non sedimentary systems this is due to two complementary effects sedimentation affects the turbulent fluxes and broadens the region of parameter space unstable to the unicode stix x1d6fe instability radko j fluid mech vol 497 2003 pp 365 380 to include systems at larger density ratios it also gives rise to a new layering instability that exists in unicode stix x1d6fe stable regimes the former is likely quite ubiquitous in geophysical systems for sufficiently large settling velocities while the latter probably grows too slowly to be relevant at least in the context of sediments in water

evaluation of various satellite sensors for waterline extraction in a coral reef environment majuro atoll marshall islands abstract the ability of five satellite sensor bands ikonos band 4 terra aster bands 3 and 4 and landsat etm bands 4 and 5 was examined to extract the waterline at coral reef coasts majuro atoll marshall islands using different wavelength regions near infrared nir and shortwave infrared swir and different spatial resolutions 4 15 and 30 m after performing georeferencing and normalization of the images density slicing was used to extract the waterline comparisons of extracted waterline positions with ground level data for eight transects and global positioning system gps tracks of the island shorelines showed that nir bands were superior to swir bands because of the characteristics of the coral reef coasts including a lack of foam and suspended sediments which can affect the nir wavelength region if present and the presence of remnant water on reef flats during low tide which can affect the swir wavelength region a linear relationship was found between the estimation errors of waterline positions and the spatial resolutions of the nir sensors analysis on estimation errors and image costs showed that terra aster band 3 was the most cost effective sensor for extracting waterlines with reasonable accuracy the results serve as general guidelines for using satellite derived data to estimate intertidal topography and detect and monitor shorelines in coral reef environments

continuous monitoring of coastline dynamics in western florida with a 30 year time series of landsat imagery abstract continuous monitoring of coastline dynamics is of crucial importance to the understanding of relative contributions of various potential driving factors behind the long term coastline change while a large number of efforts have been made to extract coastline and detect coastline change with remotely sensed data the temporal frequency and spatial resolution of coastline datasets obtained are generally not fine enough to reflect the detailed process of coastline retreat and or advance particularly in coastlines with subtle variability to overcome these limitations we developed a method to continuously monitor the dynamics of a muddy coastline with subtle variability in western florida at annual and subpixel scales using time series landsat data 1984 2013 first robust indicators were used to indicate the annual average location of the dynamic coastline due to the complexity of muddy coast morphology the annual average location is represented not by the coast line but by the fractional inundated area of coastline pixels pixels where the coastline is located namely annually inundated area second the annually inundated area of coastline pixels was estimated with a model proposed in this study and the uncertainty was estimated with the monte carlo method the retrievals were validated at 10 sites with aerial imagery and the overall rmse root mean square error is 11 48 third the long term trend for the time series of annually inundated area was derived with a statistical model the results indicate that the muddy coast in western florida continues to shrink with an average rate of 0 42 0 05 km2 year during the three decades this study demonstrates the feasibility of time series landsat data in continuous monitoring of coastline dynamics

interpolation of an intertidal digital elevation model from heighted shorelines a case study in the western wash abstract a method of interpolating a spatiotemporal digital elevation model dem of an intertidal zone from a set of heighted shorelines is described the heighted shorelines are obtained by the water line method using remote sensing and hydrodynamic modelling this enables an intertidal dem to be constructed over a large area relatively quickly as well as frequent subsequent updating of the dem to detect changes the dem may be used for studying sediment transport in the intertidal zone and for the development of improved hydrodynamic models the spatiotemporal interpolator is based on universal block kriging and its results are illustrated using data from the wrangle flats area of the western wash u k for a kriging block size of 50 m 50 m 1100 days an average block height estimation standard deviation of 14 3 cm is achieved using shorelines from 33 images collected over the period 1992 1994 this height accuracy is compared with those obtained from dems constructed from beach transect data and is shown to be an improvement over the transect dem accuracies away from transects the construction of dems of improved accuracy 13 cm from combined shoreline and beach transect data using cokriging is discussed ways in which the shoreline accuracies may be improved are also considered

the importance of double diffusion to the settling of suspended material the vertical fingering motions which can occur when warm salty water overlies colder fresher water are important to the vertical flux of salt in the ocean an analogous and not uncommon situation is that where turbid water overlies clearer and denser water for the case of an originally sharp horizontal interface between the two water layers associated as an example with an interflow due to a warm muddy river entering a stratified lake the resulting downward sediment flux is compared with that occurring by way of gravitational settling rules are proposed to ascertain when the fingering effect could be important to sedimentation for example it seems that fingering could be of consequence in the situation where the sediment has a diameter of 2 m and the upper layer is about 1 c warmer than the clear lower layer when the upper layer concentration is 1 ppm the effect of fingering on the residence time of a gravitationally stable turbid layer is calculated such layers may be more short lived than commonly thought

floor subsidence and rebound of large venus craters the topography and geology of large craters on venus reveal no evidence for floor rebound or relaxation rather the floors have subsided depressions of the floor centers relative to the margins are evident in topography and floor faulting is interpreted as contractional failure of the likely processes responsible only subsolidus thermal contraction applies to craters that both have and have not been infilled by lavas assuming volcanism occurred within a few tens of millions of years after the impact thermal subsidence satisfies the measured floor depressions for reasonable scaling of impact energies and temperature distributions in the lithosphere further the predicted stresses are generally consistent with observed floor fracturing we constrain the impact heat deposited in the lithosphere to be less than roughly 5 1023 j for diameters of 100 km the absence of perceptible floor subsidence at craters this size on the moon and icy satellites is readily explained by the scaling dependence of impact energy not only on transient crater diameter but also on gravity and target density the unfractured melt sheets of three large young bright floored craters imply sufficient lithospheric rigidity to support the crater cavities an elastic flexural rebound model restricts the elastic plate thickness to at least 10 15 km for the three craters corresponding to maximum geotherms of 20 30 k km 1 structural evidence for early rebound in older dark floored craters may have been buried by subsequent volcanism

olivine friction at the base of oceanic seismogenic zones 1 we investigate the strength and frictional behavior of olivine aggregates at temperatures and effective confining pressures similar to those at the base of the seismogenic zone on a typical ridge transform fault triaxial compression tests were conducted on dry olivine powder grain size 60 m at effective confining pressures between 50 and 300 mpa using argon as a pore fluid temperatures between 600 c and 1000 c and axial displacement rates from 0 06 to 60 m s axial strain rates from 3 10 6 to 3 10 3 s 1 yielding shows a negative pressure dependence consistent with predictions for shear enhanced compaction and with the observation that samples exhibit compaction during the initial stages of the experiments a combination of mechanical data and microstructural observations demonstrate that deformation was accommodated by frictional processes sample strengths were pressure dependent and nearly independent of temperature localized shear zones formed in initially homogeneous aggregates early in the experiments the frictional response to changes in loading rate is well described by rate and state constitutive laws with a transition from velocity weakening to velocity strengthening at 1000 c microstructural observations and physical models indicate that plastic yielding of asperities at high temperatures and low axial strain rates stabilizes frictional sliding extrapolation of our experimental data to geologic strain rates indicates that a transition from velocity weakening to velocity strengthening occurs at approximately 600 c consistent with the focal depths of earthquakes in the oceanic lithosphere

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

the effects of pressure and porosity on the micromechanics of the brittle ductile transition in quartzite room temperature experiments on a quartzite with 7 porosity show that with increasing pressure there is a transition from brittle faulting to ductile cataclastic flow at about 600 mpa in contrast experiments on nonporous quartzite show only faulting up to 1000 mpa the transition to cataclastic flow in the porous quartzite is due to the changing influence of the pores microstructural observations and elastic theory suggest that the transition occurs at the pressure where the differential stress producing a compressive stress concentration sufficient to initiate pore collapse becomes less than that producing a tensile stress concentration sufficient to nucleate axial microcracks at the tops and bottoms of pores cataclastic flow of the porous quartzite is only transient deformation remains distributed and accompanied by work hardening only as long as pore collapse continues to 16 strain at higher strains microcracking produces a net dilatancy which causes strain weakening that leads to faulting at 26 strain at a confining pressure of 750 mpa the faults are stable whereas at 1000 mpa they are unstable the results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust but higher strains will cause deformation to localize

the influence of diffusive convection on sedimentation from buoyant plumes abstract diffusive convection driven by the differential diffusion of density altering fluid properties may enhance the scavenging of particles from natural buoyant plumes for single phase fluid solute heat systems this phenomenon has been extensively studied because salt fingering generated at the oceanic thermocline is a major mechanism of salt transport in the oceans however the influence of this process on particle laden plumes for example fluvial plumes in lakes and estuaries volcanic clouds and seafloor hydrothermal plumes is largely unknown in this paper we present direct experimental measurements of the interfacial particle flux at the plume base which can be applied to predict particle scavenging from natural buoyant plumes particle flux is measured using a light attenuation technique employing a chain of photodiodes which average concentration over a large number of fingers the results are in good general agreement with earlier studies based on finger velocity flux measurements cover a wide range of conditions from those where diffusive convection dominates to those where settling and diffusive convection are of a similar magnitude for very small particles double diffusive salt finger theory is applicable to two component particulate systems as suggested by earlier studies green t 1987 the importance of double diffusion to the settling of suspended material sedimentology 34 319 331 two component diffusive convection theory is extended to three components in order to predict particle scavenging from marine fluvial plumes which involve the diffusion of sediment salt and heat for larger particles which settle significantly the flux can be approximated by adding the double diffusive and settling fluxes a theory to predict particle transport through the lower layer and sedimentation at the bed is developed based on the observation of strong convection below the plume application of our theory and experimental results indicates that while double diffusion may significantly influence the longitudinal distribution and vertical sorting of deposits from lacustrine plumes the diffusive convection process is generally insignificant in marine plumes observational evidence for lacustrine double diffusion based on water column measurements is presented

automatic extraction of shorelines from landsat tm and etm multi temporal images with subpixel precision abstract a high precision geometric method for automated shoreline detection from landsat tm and etm imagery is presented the methodology is based on the application of an algorithm that ensures accurate image geometric registration and the use of a new algorithm for sub pixel shoreline extraction both at the sub pixel level the analysis of the initial errors shows the influence that differences in reflectance of land cover types have over shoreline detection allowing us to create a model to substantially reduce these errors three correction models were defined according to the type of gain used in the acquisition of the original landsat images error assessment tests were applied on three artificially stabilised coastal segments that have a constant and well defined land water boundary a testing set of 45 images 28 tm 10 etm high gain and 7 etm low gain was used the mean error obtained in shoreline location ranges from 1 22 to 1 63 m and the rmse from 4 69 to 5 47 m since the errors follow a normal distribution then the maximum error at a given probability can be estimated the results confirm that the use of landsat imagery for detection of instantaneous coastlines yields accuracy comparable to high resolution techniques showing the potential of landsat tm and etm images in those applications where the instantaneous lines are a good geomorphological descriptor

measurement of recent intertidal sediment transport in morecambe bay using the waterline method abstract an illustration of how sediment transport may be measured over a large dynamic intertidal area at reasonable cost and spatiotemporal resolution using the waterline method employing remote sensing and hydrodynamic modelling is presented areas and volumes of accretion and erosion were measured in the study area of morecambe bay in north west england over the period 1992 97 tidal asymmetry is considered to be the dominant agent of sediment movement in the bay with waves being of secondary importance waterlines i e land sea boundaries were extracted from 31 synthetic aperture radar images of the bay covering a substantial fraction of the tidal range heights were attached to the waterlines using water elevations from nested hydrodynamic tide surge models interpolation in space and time was carried out to produce a continuous spatiotemporal height map of the intertidal zone height maps with a spatial resolution of about 50 m and height accuracy of about 40 cm were constructed over an area of about 350 km 2 strong temporal decorrelation in the bay limited the height accuracy achievable differences between height maps for 1992 94 and 1995 97 allowed sediment volume changes to be extracted the intertidal region showed a loss of 16 1 4 5 10 6 m 3 over the period almost all the change being due to a significant decrease between mean sea level and the low water mark changes were also measured in three of the main river estuaries within the bay the leven kent and lune these included movement of the leven north east by about 2 km cutting into cartmel wharf accretion seaward of grange over sands and changes in the low water channels at the mouth of the lune these changes could be used to validate sediment transport models of the bay

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

calibration of a two dimensional finite element flood flow model using satellite radar imagery the application of numerical models of free surface flow to fluvial flood prediction is currently hampered by the lack of distributed calibration and validation data we address this shortcoming by the use of satellite borne synthetic aperture radar imagery to map a flood on a 15 km reach of the river thames england a finite element numerical model of shallow water flow is constructed over the reach and analysis shows that floodplain friction is the dominant factor affecting inundation extent when compared to channel friction turbulence parameterization and downstream boundary conditions the area of the domain correctly classified by the model is maximized with the constraint of uniform floodplain friction 77 at maximum compared with 70 for a simple planar model of the water free surface a simple distributed calibration scheme is also tested with a minor improvement over the uniform parameterization

lithosphere strength inferred from fracture strength of rocks at high confining pressures and temperatures abstract a model is proposed for the strength of the crust or lithosphere in which the peak strength is in the brittle regime but not on the brittle ductile transition the model is based on experimental evidence which suggests that the fracture mechanism changes from ordinary brittle fracture to a high pressure type when the compressive strength equals the frictional strength the model assumes that a high pressure type of fracture is dominant in the earth s lower crust except where very high pore pressures exist it takes account of the scale effect on the strength of rocks the strength of the high pressure regime is estimated as a function of depth or pressure and temperature using experimental results derived at high confining pressures and temperatures in the upper part of the brittle zone where the frictional strength is lower than the compressive strength byerlee s friction law is used in the ductile regime the steady state creep law is used two cases of lithospheric strength dry and wet hydrostatic water pressure respectively are evaluated for thrust strike slip and normal faulting mechanisms with the exception of a wet lithosphere and a normal faulting mechanism the strength between the frictional and creep regimes is approximately constant with depth although the peak strength is in this part

investigating the onset of multi ring impact basin formation multi ring basins represent some of the largest oldest rarest and therefore least understood impact crater structures various theories have been put forward to explain their formation there is currently however no consensus here numerical modeling is used to investigate the onset of multi ring basin formation on the moon using two thermal profiles suitable for the lunar basin forming epoch various multi ring basin formation hypotheses are discussed compared and evaluated against target deformation and strain distribution in the models as well as geological and geophysical observations the mechanism that most closely resembles the numerical models in terms of basin formation and structure as well as observations appears to be the ring tectonic theory whereby ring formation is dependent on transient cavities penetrating entirely through the moon s lithosphere into the asthenosphere below the numerical models suggest that all lunar basins larger than schrodinger 320 km diameter should be capable of forming multiple rings as their transient cavities penetrate into the asthenosphere for both thermal profiles additionally the models demonstrate that the target s thermal profile starts to influence basin formation and structure when impact energy exceeds that of the schrodinger event

observational and laboratory insights into salt finger convection improving observational capabilities in the ocean are revealing a substantial body of evidence that the double diffusive instability known as salt fingers is widely present and plays a significant role in oceanic mixing this evidence includes unique fine and microstructure features in particular regions and distinct patterns in the temperature and salinity variations over large areas laboratory experiments have also advanced our understanding of salt fingers the insights gleaned from both laboratory and ocean are reviewed and related to large scale ocean structure and climate modeling

mechanism of deformation in a dry porous basalt at high pressures abstract the deformation behavior of a dry fine grained porous basalt with 7 porosity has been studied up to a confining pressure of 2 5 gpa at room temperature microscopic observations for triaxially compressed specimens have been compared with the results on the measurements of strain and activity of acoustic emission ae for the same rock initial pores of 100 200 m size begin to collapse and the compaction starts at a mean pressure of about 400 mpa as confining pressure and differential stress increase compaction is followed by crystals colliding with each other undergoing deformation with microcracks crushing and finally granulation during compaction the rock is compressed beyond the hydrostat and the ae activity is relatively high as confining pressure and differential stress increase to much higher levels e g above 1 5 gpa confining pressure or above 1 5 gpa differential stress at 1 gpa confining pressure most pores collapse areas where the crystals are deformed with numerous microcracks crushed and granulated begin to pervade the specimen further deformation is due to the pervasion of such areas and to the closure of pores or voids a few m in size among granulated grains in this stage of deformation the rock is compressed in the same way as in hydrostatic compression in spite of the uniaxial compression and the ae activity is very low and almost constant the deformation at lower confining pressures is also discussed for a brittle fractured specimen and a bulged specimen with luders bands in the ductile regime cataclastic flow is predominant during the compaction whereas intragranular flow and grain sliding and or a combination of both with cataclastic flow seem to govern the behavior in the post compaction state at higher stress levels the results have interesting implications on studies of the structures of aseismic zones and fault zones in the crust and the upper mantle although further work is necessary to examine whether the governing processes producing ductile flow correspond between the present experimental conditions and those in the earth s interior

convective instability in sedimentation linear stability analysis 1 convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis convective sedimentation is known to occur due to the double diffusive mechanism and the settling driven mechanism in this study a semi empirical closure of sediment diffusivity based on the long range hydrodynamics effect is adopted the sediment phase can act as either the slow or fast diffusing agent in the double diffusive system for the given salt diffusivity moreover the settling driven effect is proportional to the square of the sediment diameter via stoke settling law we consider sediment concentration grain size in the upper freshwater layer to be in the range of 0 1 to 39 4 g l 2 to 60 m which is on top of a saltwater layer with salinity 35 ppt linear stability analysis allows us to identify the dominant mechanism that triggers the instability the growth rate and the resulting characteristic finger width model results suggest that for fine sediment with grain diameter smaller than 10 m settling velocity 0 09 mm s double diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale for the given threshold of growth rate of o 0 01 s 1 the minimum sediment concentration is about 8 15 g l for grain size greater than or around 10 m the settling driven mechanism dominates and instabilities occur at sediment concentration as low as o 0 1 g l with centimeter scale fingers our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers

numerical experiments on salt finger convection salt finger convection is now widely recognized as an important mechanism for mixing heat and salt both vertically and laterally in the ocean this article reviews numerical simulations of salt finger salt fingers were first produced in the laboratory in the mid 1960s when their structure and transport mechanisms were partially described however rapid diffusion of heat in the laboratory frustrates exact or conclusive understanding of many aspects of salt fingers numerical simulation of salt finger began in the 1980s the rapid development of computational technology has brought great improvements in our understanding of salt fingers however fully 3 d simulations that resolve all the scales present in salt fingering particularly in an oceanic environment where internal waves and turbulence are confounding influences pose many more challenges for the future

a review of oceanic salt fingering theory salt fingering is a potentially important mechanism for mixing different water masses in those parts of the ocean where warm salty waters overlie cooler fresher this review surveys advances in salt fingering theory as they pertain to ocean mixing basic equations are presented along with steady maximum buoyancy flux and fastest growing finger solutions attempts to quantify theoretically finger induced fluxes of heat salt and buoyancy and to understand staircase formation and maintenance are described also considered are the confounding influences of internal wave shear and strain and intermittent internal wave shear driven turbulence which are present in the ocean but in few theories finally outstanding theoretical questions about the role of salt fingers in the ocean are raised

multitemporal backscattering logistic analysis for intertidal bathymetry a new methodology for the mapping of intertidal terrain morphology is presented it is based on the use of synthetic aperture radar sar images and the temporal correlation between the sar backscatter intensity and the water level on the intertidal zone the proposed methodology does not require manual editing providing a set of geolocated pixels that can be used to generate a digital elevation model of the intertidal zone the methodology is validated using terrasar x sar images acquired over tagus estuary this methodology can be useful for the regular updating of intertidal bathymetric models useful for both flood hazard mitigation and morphodynamics modeling

two types of brittle fracture of silicate rocks under confining pressure and their implications in the earth s crust abstract four silicate rocks granite gabbro dunite and eclogite were triaxially compressed up to a confining pressure of 3 gpa at room temperature and were found to exhibit brittle fracture behaviour from the measurements of the compressive and frictional strengths and the activity of acoustic emission ae and the observations of the microstructure of fractured specimens the pattern of fracture was found to change when the compressive strength became equal to the frictional strength two types of fracture mechanism low pressure and high pressure types were inferred the low pressure type fracture exhibits features of brittle fracture equivalent to those recorded by previous workers the features of high pressure type fracture are similar to those observed between brittle fracture and ductile creep in high temperature triaxial experiments microcracks are not concentrated close to the main fault and the main fault is sharp and oriented at approximately 45 to the stress direction this suggests that the high pressure type fracture might correspond to the transitional fracture type between the brittle and ductile regimes at room temperature for granite and gabbro samples of a few centimeters size high pressure type fracturing begins at 0 8 gpa confining pressure while for dunite and eclogite it begins at 1 0 and 2 0 gpa respectively the size effect on compressive strength under confining pressure was estimated based on the suggestion that the uniaxial strength decreases with increasing specimen size and ceases to decrease for specimens 1 m this estimation suggests that the compressive strength for a granite specimen a few meters in size would become equal to the frictional strength at confining pressures as low as 60 mpa the significance of this is that it may be necessary to model earthquakes using the high pressure type fracturing because in the absence of pore pressure 60 mpa confining pressure corresponds to a depth of 3 km faulting processes in the crust including both the initial faulting and the movement of existing faults were inferred using the experimental results and the estimated size effect on strength

the apollo peak ring impact basin insights into the structure and evolution of the south pole aitken basin abstract the 492 km diameter apollo impact basin post dates and is located at the inner edge of the 2240 km diameter south pole aitken spa basin providing an opportunity to assess the spa substructure and lateral heterogeneity gravity recovery and interior laboratory gravity data suggest an average crustal thickness on the floor of spa of 20 km and within the apollo basin of 5 km yet remote sensing data reveal no conclusive evidence for the presence of exposed mantle material we use the isale shock physics code to model the formation of the apollo basin and find that the observational data are best fit by the impact of a 40 km diameter body traveling at 15 km s into 20 40 km thick crustal material these results strongly suggest that the apollo impact occurred on ejecta deposits and collapsed crustal material of the spa basin and could help place constraints on the location size and geometry of the spa transient cavity the peak ring in the interior of apollo basin is plausibly interpreted to be composed of inwardly collapsed lower crustal material that experienced peak shock pressures in excess of 35 gpa consistent with remote sensing observations that suggest shocked plagioclase proposed robotic and or human missions to spa and apollo would present an excellent opportunity to test the predictions of this work and address many scientific questions about spa basin evolution and structure

estimating transient crater size using the crustal annular bulge insights from numerical modeling of lunar basin scale impacts 1 the transient crater is an important impact cratering concept its volume and diameter can be used to predict impact energy and momentum impact melt volume and maximum depth and volume of ejected material transient crater sizes are often estimated using scaling laws based on final crater rim diameters however crater rim estimates especially for lunar basins can be controversial here we use numerical modeling of lunar basin scale impacts to produce a new alternative method for estimating transient crater radius using the annular bulge of crust observed beneath most lunar basins using target thermal conditions appropriate for the lunar imbrian and nectarian periods we find this relationship to be dependent on lunar crust and upper mantle temperatures this result is potentially important when analyzing lunar basin subsurface structures inferred from the grail mission

sediment transport dynamics near a river inflow in a large alpine lake sediment dynamics were investigated in lake maggiore italy with field observations from october to mid december 2012 three moorings were deployed in pallanza bay a small embayment on the western side of the lake near the toce river inflow to measure temperature and currents throughout the water column and suspended sediment concentration ssc was estimated with acoustic instrumentation river intrusions are shown to dominate observed ssc although a small amount of sediment resuspension was observed at the site of the shallowest mooring during a large wind event that produced strong upwelling of the thermocline followed by downwelling although vertical turbulent sediment flux is typically assumed to indicate resuspension and the upward transport of sediment w c 0 downward turbulent sediment flux was observed w c 0 near the bed during the largest observed intrusion event the downward turbulent sediment flux significantly contributes to net deposition rates which are one order of magnitude larger than rates of erosion measured during the two major events observed horizontal transport of sediment occurs in vertically confined layers due to buoyancy driven intrusions beneath the intrusions sediment settles out of the water column at settling rates that appear to be constant with depth based on acoustic doppler current profiler backscatter measurements the effective settling velocities needed to produce the observed vertical transport of ssc during an inflow intrusion are one order of magnitude larger than those due to the stokes settling velocity ws alone particle flocculation and possible convective instabilities may play a role in generating the large observed effective settling rates

a coastline detection method in polarimetric sar images mixing the region based and edge based active contour models this paper proposes a coastline detection method for polarimetric synthetic aperture radar sar images based on region based and edge based active contour models it can be used to detect coastline accurately and fast in this method the region based and edge based active contour models are effectively combined by an important property of the likelihood ratio edge detector in polarimetric sar images which is proved by theory using low resolution image obtained by multilook processing we detect accurate and continued coarse coastlines by a region based level set method the property of the likelihood ratio edge detector of polarimetric sar images along the coastline region is then analyzed the coarse detection result is finally refined using a fast snake active contour model based on the edge property polarimetric sar data acquired by radarsat 2 over a singapore region and terrasar x over a berkeley region are both used to test the proposed algorithm the experimental results show that the coastline is fast and accurately detected in different initial scales the proposed method greatly reduces the data processing time compared with the coastline detection method based on a single scale

low temperature plasticity of olivine during high stress deformation of peridotite at lithospheric conditions an experimental study abstract deformation experiments on natural peridotite from the almklovdalen complex norway were carried out in a griggs type apparatus at temperatures of 20 300 and 600 c confining pressures of 1 0 to 2 5 gpa and strain rates of 3 10 6 to 8 10 5 s 1 the experiments yield maximum differential stresses in the range of 1 0 to 2 9 gpa falling mostly between byerlee s law and goetze s criterion and thus indicating semi brittle behaviour whereas strength of samples deformed at 20 c increases significantly with increasing confining pressure a systematic pressure dependence of strength is not obvious at 300 and 600 c the intracrystalline deformation features of the main constituent olivine were analysed by light and electron microscopic techniques sem ebsd tem deformation microstructures systematically vary with temperature but are insensitive to confining pressure samples deformed at 20 c reflect predominantly brittle failure by intragranular microcracks and shear zones microstructures from samples deformed at higher temperatures show evidence of low temperature plasticity of olivine in the form of pronounced undulatory extinction associated with high dislocation densities pile up of dislocations leads to the formation of either fracture arrays at 300 c or deformation lamellae parallel 100 and cellular structures at 600 c indicating intragranular work hardening a gradual increase in glide controlled crystal plastic deformation of olivine at increasing temperature is interpreted to be responsible for the variation in mechanical behaviour and microstructural characteristics the mechanical data and microstructural observations consistently suggest a temperature for the transition from the strength controlling dominance of brittle to crystal plastic deformation mechanisms close to 600 c the tested peridotite samples show a lower strength than quartzite samples at comparable experimental conditions possibly related to crystallographic differences of olivine and quartz the agreement between microfabrics of experimentally and naturally deformed peridotites demonstrates the importance of low temperature plasticity of olivine during high stress deformation at lithospheric conditions related in particular to seismic activity in the mantle

convective instability in sedimentation 3 d numerical study to provide a probable explanation on the field observed rapid sedimentation process near river mouths we investigate the convective sedimentation in stably stratified saltwater using 3 d numerical simulations guided by the linear stability analysis this study focuses on the nonlinear interactions of several mechanisms which lead to various sediment finger patterns and the effective settling velocity for sediment ranging from clay single particle settling velocity v0 0 0036 and 0 0144 mm s or particle diameter d 2 and 4 m to silt v0 0 36 mm s or d 20 m for very fine sediment with v0 0 0036 mm s the convective instability is dominated by double diffusion characterized by millimeter scale fingers gravitational settling slightly increases the growth rate however it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface for sediment with v0 0 0144 mm s rayleigh taylor instabilities become dominant before double diffusive modes grow sufficiently large centimeter scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes for sediment with v0 0 36 mm s rayleigh taylor mechanism dominates and the resulting centimeter scale sediment fingers show a plume like structure the flow pattern is similar to that without ambient salt stratification rapid sedimentation with effective settling velocity on the order of 1 cm s is likely driven by convective sedimentation for sediment with v0 greater than 0 1 mm s at concentration greater than 10 20 g l

constraining the size of the south pole aitken basin impact abstract the south pole aitken spa basin is the largest and oldest definitive impact structure on the moon to understand how this immense basin formed we conducted a suite of spa scale numerical impact simulations varying impactor size impact velocity and lithospheric thermal gradient we compared our model results to observational spa basin data to constrain a best fit scenario for the spa basin forming impact our results show that the excavation depth to diameter ratio for spa scale impacts is constant for all impact scenarios and is consistent with analytical and geological estimates of excavation depth in smaller craters suggesting that spa scale impacts follow proportional scaling steep near surface thermal gradients and high internal temperatures greatly affected the basin forming process basin structure and impact generated melt volume in agreement with previous numerical studies of spa scale impacts crustal material is entirely removed from the basin center which is instead occupied by a large melt pool of predominantly mantle composition differentiation of the melt pool is needed to be consistent with observational data assuming differentiation of the thick impact generated melt sheet occurred and using observational basin data as constraints we find the best fit impact scenario for the formation of the south pole aitken basin to be an impact with an energy of 4 1026 j our specific model considered an impactor 170 km in diameter striking at 10 km s

crack location in granitic samples submitted to heating low confining pressure and axial loading summary until now observations of mechanically and thermally induced microcracks in rocks could only be carried out by indirect measurements or destructive observations on samples brought back to atmospheric pressure conditions a special triaxial test cell was designed in order to perform direct observations during loading the use of a cell in tomography apparatus involves new devices 1 a movable horizontal load frame around a scanner and 2 a test cell transparent to x rays able to withstand up to 28 mpa maximum confining pressure and temperatures of up to 180 c volumetric strains are compared with radiological density measurements the first processed x ray images locating microcracks during propagation are also presented mineralogical evects on the crack location can be demonstrated strain inferred from ct density measurement is clearly correlated with the strain usually measured by a strain gauge diverent phases of mechanical behaviour are described contracted phase and failure by macrocrack formation the principal results obtained with this tool are the description of the porosity formation and macrocracking results show two principal factors localizing the porosity first the divused porosity volume is controlled by mineralogical parameters quartz and plagioclase grains and boundaries of biotite grains during the thermal and mechanical loading second macrocracking begins at the perimeter of the central section of core and grows towards the sample piston interface it seems that the first macrocracking is not located in the high porosity zone formed during the loading phase but in a relatively low porosity zone

fracturing process of granite inferred from measurements of spatial and temporal variations in velocity during triaxial deformations fracturing in fine grained homogeneous granite during triaxial deformation was investigated by measuring the spatial and temporal variations of elastic wave velocities velocities along 20 ray paths were measured with 12 piezoelectric transducers attached to a sample under confining pressures up to 400 mpa systematic velocity differences observed among the 20 paths apparently indicate the formation of a dilatant region near the surface of a sample the damaged region formed near the surface due to asymmetric development of dilatancy seemed to play an important role in controlling ultimate failure no evidence of the formation of a crack concentration zone adjacent to the ultimate fracture plane could be found before failure insofar as could be estimated from the velocity variations of elastic waves propagating along its plane however a highly concentrated region of cracks in which the fracture nucleated was generated in the damaged region at stresses of more than 97 99 of the ultimate strength in all the specimens based on tomographic images computed using an algebraic reconstruction technique the elastic waves were strongly affected by the damaged region even under the high confining pressures at which cracks are considered to close

laboratory constraints on the rheology of the upper mantle the dynamics of convection and the mechanical behavior of the lithosphere are controlled by the rheology of upper mantle rocks for this reason experimental and theoretical studies on the rheology of olivine aggregates have been fields of active research for at least the last 35 years in this short course paper i briefly review some experimental and theoretical constraints on the rheology of upper mantle rocks and minerals and then discuss the application of these data for understanding the rheology of the upper mantle in different tectonic environments there is an expansive literature on the subject of mantle rheology extensive reviews and background can be found in several recent articles and books poirier 1985 ranalli 1995 karato and wu 1993 kohlstedt et al 1995 drury and fitzgerald 1998 hirth and kohlstedt 2003 as well as numerous references made throughout this chapter i focus the discussion of this chapter on the application of experimental data for constraining the rheology of the oceanic lithosphere and mantle constraints on mantle rheology based on extrapolation of laboratory experiments to deformation conditions in the oceanic lithosphere and asthenosphere are illuminating for several reasons first the composition of the mantle is relatively well constrained by analyses of peridotites from ophiolites and mid ocean ridges as well as chemical analyses of basalts second the oceanic lithosphere is comprised of rock that cooled from high temperature conditions at high pressure and is therefore not previously fractured in this way the lithosphere is similar to the ideal rocks we use in our experiments third the temperature of the lithosphere is constrained by a number of geophysical observations fourth microstructural observations on naturally deformed mantle rocks justify applying experimental flow laws at geologic conditions finally several independent geophysical observations such as constraints on viscosity based on analysis

enhanced diapycnal mixing by salt fingers in the thermocline of the tropical atlantic diapycnal mixing plays a significant role in the ocean s circulation and uptake of heat and carbon dioxide but has not been quantified in salt finger driven thermohaline staircases we recently performed a tracer release experiment in the western tropical atlantic staircase at approximately 400 m depth the observed dispersion implies an effective diapycnal diffusivity for tracer and salt of 0 8 to 0 9 x 10 4 m2 s temperature microstructure data interpreted in terms of a vertical production dissipation balance yields a smaller effective diffusivity for heat of 0 45 0 2 x 10 4 m2 s consistent with salt fingers and well above the mixing ascribable to mechanical turbulence

semi automated procedures for shoreline extraction using single radarsat 1 sar image coastline identification is important for surveying and mapping reasons coastline serves as the basic point of reference and is used on nautical charts for navigation purposes its delineation has become crucial and more important in the wake of the many recent earthquakes and tsunamis resulting in complete change and redraw of some shorelines in a tropical country like malaysia presence of cloud cover hinders the application of optical remote sensing data in this study a semi automated technique and procedures are presented for shoreline delineation from radarsat 1 image a scene of radarsat 1 satellite image was processed using enhanced filtering technique to identify and extract the shoreline coast of kuala terengganu malaysia radsarsat image has many advantages over the optical data because of its ability to penetrate cloud cover and its night sensing capabilities at first speckles were removed from the image by using lee sigma filter which was used to reduce random noise and to enhance the image and discriminate the boundary between land and water the results showed an accurate and improved extraction and delineation of the entire coastline of kuala terrenganu the study demonstrated the reliability of the image averaging filter in reducing random noise over the sea surface especially near the shoreline it enhanced land water boundary differentiation enabling better delineation of the shoreline overall the developed techniques showed the potential of radar imagery for accurate shoreline mapping and will be useful for monitoring shoreline changes during high and low tides as well as shoreline erosion in a tropical country like malaysia

quantifying the attenuation of structural uplift beneath large lunar craters 1 terrestrial crater observations and laboratory experiments demonstrate that target material beneath complex impact craters is uplifted relative to its preimpact position current estimates suggest maximum uplift is one tenth of the final crater diameter for terrestrial complex craters and one tenth to one fifth for lunar central peak craters these latter values are derived from an analytical model constrained by observations from small craters and may not be applicable to larger complex craters and basins here using numerical modeling we produce a set of relatively simple analytical equations that estimate the maximum amount of structural uplift and quantify the attenuation of uplift with depth beneath large lunar craters

dynamics of fingering convection part 1 small scale fluxes and large scale instabilities received and in revised form double diffusive instabilities are often invoked to explain enhanced transport in stablystratified fluids the most studied natural manifestation of this process fingering convection commonly occurs in the ocean s thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion fingering convection is also often associated with structures on much larger scales such as thermohaline intrusions gravity waves and thermohaline staircases in this paper we present an exhaustive study of the phenomenon from small to large scales we perform the first three dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions we then develop a generalized mean field theory to study the stability of fingering systems to large scale perturbations using our calculated turbulent fluxes to parameterize small scale transport the theory recovers the intrusive instability the collective instability and the instability as limiting cases we find that the fastest growing large scale mode depends sensitively on the ratio of the background gradients of temperature and salinity the density ratio while only intrusive modes exist at high density ratios the collective and instabilities dominate the system at the low density ratios where staircases are typically observed we conclude by discussing our findings in the context of staircase formation theory

heat salt and momentum transport in a laboratory thermohaline staircase flow characteristics and fluxes in thermohaline staircases are measured in two tanks differing in aspect ratio a where a is the ratio of tank width to fluid depth in one tank the 1 x 1 tank which is 30 cm deep and 30 cm wide a staircase of one salt finger layer and one convecting layer develops for a certain setting of the control parameters the convecting layer has a 2 shadowgraphs show convecting plumes that appear disorganized and a large scale flow never develops instead the finger layer grows in height overtakes the convecting layer and within a few days becomes one finger layer the second tank the 1 x 5 tank is also 30 cm deep but is 150 cm wide for the same control parameter setting a similar staircase with a finger layer 20 cm deep and a convecting layer 10 cm deep develop the convecting layer with a 15 has quite a different character a large scale flow develops so that the convecting layer has one cell 10 cm deep and 150 cm wide in this flow are large plumes which are transient and tilted particle image velocimetry measurements of reynolds stresses show they help to maintain the large scale flow against viscous dissipation shadowgraphs show all the finger tips swept in the direction of the large scale flow adjacent to the finger layer measurements show that the large scale flow collects the salt delivered by the many fingers so that the accumulated negative buoyancy leads to deep convection this is a more stable arrangement with the configuration lasting to the order of 10 2 days

fracture strength of dry silicate rocks at high confining pressures and activity of acoustic emission abstract three dry silicate rocks gabbro dunite and eclogite were triaxially compressed up to a confining pressure of 3 gpa at room temperature these rocks exhibited brittle fracture behavior up to the highest confining pressure the change of the mechanism of fracture in the brittle region is suggested from the measurement of the compressive fracture strength and the activity of acoustic emission the existence of the high pressure brittle fracture phase is proposed the fracture strength increased with increase of confining pressure the increasing rate of strength was lowered at a value of confining pressure at about 0 8 gpa on gabbro at about 1 0 gpa on dunite and at about 1 5 gpa on eclogite at lower confining pressures than the above value the acoustic emission rate began to increase at the onset of dilatancy and increased rapidly followed by fracture as the axial stress was increased at the higher confining pressures however the acoustic emission rate did not increase rapidly before final fracture and stayed constant to the fracture the similar behavior was shown on the granite studied previously it is interesting that the frictional strength forms the boundary between low and high pressure brittle fracture phases

the method of compression test under high pressures in a cubic press and the strength of granite abstract a cubic press was used for the triaxial test on rocks under very high confining pressures up to 4 gpa for a specimen of 16 mm length and 8 mm diameter in a silver chloride sleeve with a pressure medium of pyrophyllite the axial and the confining pressures were calibrated by means of the phase transitions in bismuth thallium and barium the compressive strength of granite was determined up to 3 gpa of confining pressure in the cubic press the results were compared with those from the ordinary triaxial testing machine with a pressure medium of oil up to 450 mpa for the whole pressure range the compressive strength was expressed by c c0 1 4 33 p c0 0 47 where c is the differential compressive strength p is the confining pressure and 0 is the uniaxial compressive strength which was 180 mpa for the man nari granite used in this work

relationships between the microstructural evolution and the rheology of talc at elevated pressures and temperatures abstract we conducted triaxial compression experiments to investigate the effects of pressure temperature and strain rate on the rheology of talc rocks the tests were carried out at t from 25 to 860 c p from 0 1 to 300 mpa and e from 0 3 to 30 10 5 s 1 in addition to being very weak there are other important differences between the mechanical behavior of talc and that of most other silicates deformation at all temperatures up to dehydration was accommodated by a combination of crystal plasticity frictional sliding and cataclasis a transition from localized to distributed deformation occurred at p 300 mpa and t 400 c but this transition is ill defined as both distributed and localized deformation were observed at p 300 mpa and t 600 c unlike most silicates both the coefficient of internal friction and the coefficient of sliding friction are very low and nearly equal to each other temperature enhances plastic deformation kinking and inter and intra granular microcracks are observed parallel to the 001 planes at all conditions voids are created by delamination along 001 planes at kink band boundaries full crystal plasticity was not achieved under any of the conditions tested i e the von mises criterion was never satisfied however the strength of the aggregates remained much less than the confining pressure these unusual properties are likely a manifestation of the pronounced mechanical anisotropy of talc at the grain scale at t 750 c dehydration is observed but only along shear zones these results suggest that feedbacks between deformation and reaction kinetics could control fluid flow in fault zones the presence of talc can promote significant weakening and strain localization in the oceanic lithosphere the subducting plate and the overlying mantle wedge

the origin of lunar mascon basins high resolution gravity data from the gravity recovery and interior laboratory spacecraft have clarified the origin of lunar mass concentrations mascons free air gravity anomalies over lunar impact basins display bull s eye patterns consisting of a central positive mascon anomaly a surrounding negative collar and a positive outer annulus we show that this pattern results from impact basin excavation and collapse followed by isostatic adjustment and cooling and contraction of a voluminous melt pool we used a hydrocode to simulate the impact and a self consistent finite element model to simulate the subsequent viscoelastic relaxation and cooling the primary parameters controlling the modeled gravity signatures of mascon basins are the impactor energy the lunar thermal gradient at the time of impact the crustal thickness and the extent of volcanic fill

strength of slightly serpentinized peridotites implications for the tectonics of oceanic lithosphere we deformed cores of peridotite with 10 15 lizardite and chrysotile serpentine to determine the influence of serpentine content on the strength and the style of deformation the strength the pressure dependence of strength and the nominally nondilatant mode of brittle deformation of slightly serpentinized peridotites are comparable to those of pure serpentinites these results indicate that deformation is accommodated primarily by serpentine while olivine despite being the more abundant component remains nominally undeformed on the basis of these data and previous work we determine that the transition from a strong dilatant dunite rheology to a weak nondilatant serpentinite rheology is not a linear function of the degree of serpentinization instead an abrupt transition in strength is observed at low degrees of serpentinization the pressure of the transition from localized to distributed deformation also decreases abruptly from 1000 mpa to 150 350 mpa the change in rheological behavior occurs at a serpentine content of 10 15 or less which corresponds to published compressional seismic velocity of 7 8 7 5 km s at a pressure of 200 mpa the seismic velocity of the oceanic lithosphere particularly of that formed at slow spreading ridges can thus provide constraints on its mechanical properties at depth because slightly serpentinized peridotites have a rheology similar to that of pure serpentinite significant lithospheric weakening may occur after the onset of alteration near or at the ridge axis

seismicity and shallow slab geometry in the central vanuatu subduction zone the vanuatu arc in the southwest pacific ocean is one of the world s most seismically active regions with almost 39 magnitude 7 earthquakes in the past 43 years convergence rates are around 90 120 mm yr along most of the arc but drop to 25 43 mm yr in the central section probably due to the subduction of the d entrecasteaux ridge we characterize the slab geometry and tectonic state in this central section by analyzing data from a 10 month deployment of 30 seismometers over this section we located more than 30 000 events all less than magnitude 5 5 constructed an improved 1 d velocity model calculated focal mechanisms and cluster geometries and determined the 3 d geometry of the interplate seismogenic zone the seismogenic zone has a shallow bulge in front of the d entrecasteaux ridge which could be explained by the ridge s buoyancy contributing to the uplift of the fore arc islands the seismogenic zone extends to 45 km depth significantly below the 26 27 km depth of the fore arc moho indicating that the upper mantle wedge is not significantly serpentinized which is consistent with the relatively high thermal parameter of the subducting plate the maximum width of the seismogenic zone is 80 km indicating an upper earthquake magnitude limit of mw 7 85 0 4 assuming standard rupture zone aspect ratios the data also reveal a double seismic zone 20 to 30 km below the seismogenic zone which is presumably caused by flexure of the downgoing plate

a sensitivity analysis of the waterline method of constructing a digital elevation model for intertidal areas in ers sar scene of eastern england abstract a sensitivity analysis of the waterline method of constructing a digital elevation model dem of an intertidal zone using remote sensing and hydrodynamic modelling is described variation in vertical height accuracy as a function of beach slope is investigated using a set of nine ers synthetic aperture radar sar images of the humber wash area on the english east coast acquired between 1992 and 1994 waterlines from these images are heighted using a hydrodynamic tide surge model and interpolated using block kriging on 1 500 slope beaches an average block height estimation standard deviation of 18 22 cm is achieved this rises to 27 cm on 1 100 slope beaches and 32 cm on 1 30 slope beaches the average heighting error at different slopes is decomposed into components due to waterline heighting error inadequate sensor resolution and interpolation inaccuracy it is shown that at 1 500 slope waterline heighting error and interpolation inaccuracy are the main error sources whilst at 1 30 slope errors due to inadequate sensor resolution become dominant the ability of the technique to generate intertidal dems for almost the entire coastal zone in a complete ers sar scene covering 100 100 km is demonstrated

confirmation of two types of fracture in granite deformed at temperatures to 300 c abstract shimada m 1992 confirmation of two types of fracture in granite deformed at temperatures to 300 c in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 259 268 dry granite samples were triaxially compressed at confining pressures of up to 2 gpa at temperatures to 300 c the existence of two types of fracture previously observed in room temperature experiments was confirmed the low pressure type occurs when the compressive strength is higher than the frictional strength and the high pressure type occurs when the compressive strength is equal to the frictional strength the rate of increase of strength with confining pressure in the high pressure type regime is lowered as temperature increases as if an ideal coulomb fracture criterion at a fracture angle of 45 might be applicable with increasing temperature near the boundary between the low and high pressure type regimes unusually high values of strength were measured the specimens after such runs gave the suggestion that both low and high pressure types of fracture coexist there are some discrepancies in the values of strength from room temperature and those performed previously which are considered to be due to the experimental variability however the present experimental results to 300 c confirmed that two types of brittle fracture exist and that the fracture type changes when the compressive strength becomes equal to the frictional strength this tends to confirm previous speculations that many crustal fractures are of the high pressure type if so the low pressure type of fracture in which precursory ae acoustic emission activity before final fracturing is observed would be anticipated only at very shallow depth at ordinary pore pressure conditions it would occur at the depth of seismogenic zones only in the case of very high pore pressure

effect of brittle fracture on the rheological structure of the lithosphere and its application in the ordos abstract an empirical formula for the fracture strength of the principal rock type in the lithosphere is obtained based on the experimental data from previous studies in which the effects of the confining pressure size of the rock sample temperature strain rate and the pore pressure are taken into account the empirical formulae for the effects of them are also presented by comparing the frictional strength to the fracture strength calculated using the new empirical formula it is shown that frictional sliding is dominant in the upper crust but brittle fracture is dominant in the lower part of the crust and the lithosphere beneath the crust therefore the fracture mechanism must be taken into account in the study of the rheological structure of the lithosphere the empirical formula for the fracture strength is applied to study the rheological structure of the lithosphere in the ordos block brittle regime in the rheological structure can be divided into two sub regions in one of which brittle fracture and in the other frictional sliding are dominant respectively unlike previous conventional studies in which frictional sliding is assumed to be the only factor the magnitude of the rheological strength of the lithosphere calculated by the empirical formula is also lower than that obtained in previous conventional studies

numerical modeling of the formation and structure of the orientale impact basin 1 the orientale impact basin is the youngest and best preserved lunar multi ring basin and has thus been the focus of studies investigating basin forming processes and final structures a consensus about how multi ring basins form however remains elusive here we numerically model the orientale basin forming impact with the aim of resolving some of the uncertainties associated with this basin by using two thermal profiles estimating lunar conditions at the time of orientale s formation and constraining the numerical models with crustal structures inferred from gravity data we provide estimates for orientale s impact energy 2 9 1025 j impactor size 50 80 km diameter transient crater size 320 480 km excavation depth 40 55 km and impact melt volume 106 km3 we also analyze the distribution and deformation of target material and compare our model results and orientale observations with the chicxulub crater to investigate similarities between these two impact structures

compressive failure of rocks by shear faulting a model for the compressive failure of rocks via the process of shear faulting is presented the model addresses the progressive growth of damage that leads to the formation of a critical fault nucleus which grows unstably in its own plane by fracturing the grain boundaries in an increasingly rapid succession the model uses a two parameter weibull type shear strength distribution for defining the nucleation of initial damage followed by the use of stress enhancement factors for addressing the increased probability of failure in the vicinity of already cracked grain boundaries these factors essentially involve surface averaging of enhanced stresses in the neighboring grains with the appropriate strength distribution as the weighting function as the stress is further increased similar correlated fracturing events get preferentially aligned to the crack cluster resulting in en echelon of cracks this crack cluster is modeled as an elliptical inhomogeneity within which the cracks interact and lead to material pulverization the effect of which mechanistically is to lower the shear modulus compared with the uncracked material on the outside the shear stress concentration resulting from this moduli mismatch is calculated and used to compute the stress enhancement factors for defining the nucleation of additional cracking events near the crack cluster eventually the size of the crack cluster becomes sufficiently large that it carries a stress concentration high enough to fracture all grain boundary elements in from of it in an increasingly rapid succession the stress associated with this event is taken as the failure stress since the model allows other cracking events to occur within the material volume in accordance with the assumed strength distribution function formation of other competing but subcritical shear faults naturally occurs besides the faulting stress for a prescribed confinement the model is able to predict the angle of the shear fault fairly well the model is applied to a variety of rock types including granite eclogite gabbro aplite rock salt sandstone dunite limestone and marble and the predicted failure envelopes compare rather well with the failure data available in the literature

lithospheric rheology and flexure at artemis chasma venus artemis chasma is an arcuate 2000 km diameter zone of convergence and lithospheric underthrusting on venus inelastic flexure modeling of the topography at artemis combined with observations of trench tectonics allow us to document local temperature gradients below 4 k km 1 and an immense compressive in plane force at the trench lithospheric rheology on venus may be stronger than would be predicted from conventional extrapolations of rock mechanics experiments in particular the brittle surface strength must reach a few tens of megapascals to satisfy the observed lack of flexurally induced surface faulting elastic plate bending models provide an adequate estimate of the bending moment at artemis but they fail to constrain or even recognize the in plane force the inelastic analysis implies an in plane force of the order of 1 1014 n m 1 a potential driving force is thermal thinning of regionally thick lithosphre in the highlands to the north the low heat flux at artemis which is a comparatively young structure is compatible with the notion that venus has experienced a prolonged period of cooling in the last several hundred million years the inference of such exceptionally low thermal gradients embraces three end member possibilities 1 the surface age is 600 ma 2 the lithospheric thermal age is greater than the surface age and or 3 the upper mantle temperature is anomalously low 1550 k

multi frequency sar data help improving the monitoring of intertidal flats on the german north sea coast abstract we demonstrate that synthetic apertur radar sar data have great potential to improve an existing monitoring system based on optical data for intertidal flats and to complement the classification of sediments macrophytes and mussels in the german wadden sea multi satellite sar data acquired at different radar bands l c and x band from alos palsar from ers sar radarsat 2 and envisat asar and from terrasar x respectively were used to investigate whether they can be jointly used for crude sediment classification on dry fallen intertidal flats and for detecting benthic fauna such as blue mussel or oyster beds in this respect we show that both multi satellite and multi temporal analyses provide valuable input for the routine monitoring of exposed intertidal flats on the german north sea coast the latter already improving the identification of the spatial extent of mussel oyster beds in addition we demonstrate that high resolution sar is capable of detecting residuals of historical land use in areas that were lost to the sea during major storm surges in the 14th and 17th centuries

a simple waterline approach for tidelands using multi temporal satellite images a case study in the yangtze delta abstract waterline technique based on satellite remote sensing is potentially one of the most effective tools for studying changes in tidal flat environment and coastlines however multi temporal waterlines obtained from satellite images are often difficult to compare directly because fluctuant tidal conditions may produce different elevation of waterlines to overcome the difficulty this study developed a comparable waterline solution to estimate active lateral evolutions using tm satellite images at different tide conditions owing to the dynamic properties the yangtze river mouth was selected as the case example to test the suitability of the approach and totally four time slices were partitioned during 1987 2004 for investigating coastline changes the first step of this technique is to digitize waterlines with various elevations labeling in a time slice in the second step the waterlines were merged to generate dems and contour maps using the linear gridding interpolation method in the last step any interested contour line may be extracted from dems and used for comparison of tideland changes to evaluate the errors in digitizing and interpolation process quantitative checks were examined after the dems were constructed in order to monitoring the rate of coastline spread a proposed approach for estimating mean coastline spread distance between two time spans is developed in this paper to conclude this work demonstrates the importance of tm etm images to provide high frequency historical topography and morphodynamics information for coastal monitoring and evaluation

study of the polarimetric characteristics of mud flats in an intertidal zone using c and x band spaceborne sar data abstract the polarimetric characteristics of a mud flat area in the intertidal zone near jiangsu china are analyzed under different environmental conditions using x band and c band spaceborne synthetic aperture radar sar data from the terrasar x tsx and radarsat 2 r2 satellites the dominant scattering mechanisms of different objects including mud flats and aquaculture facilities in the intertidal zone are studied based on the polarimetric target decomposition of fully polarimetric r2 data the polarimetric characteristics of different objects in the intertidal zone are quantitatively compared using the depolarization parameters derived from the r2 data which indicate that tides have different effects on the dominant scattering mechanisms of the mud flats and aquaculture farms furthermore comparisons of the c band and x band polarimetric characteristics of the mud flats and aquaculture farms in the intertidal zone are analyzed by combining the tsx and r2 data the results show that surface scattering is the dominant mechanism of the mud flats whereas different dominant mechanisms occur in the aquaculture areas present during different tides interestingly strikingly similar polarimetric characteristics of mud flats and aquaculture in x band and c band sar are observed and these novel results were achieved through a depolarization analysis based on the tsx and r2 data in synergy

accurate and efficient determination of the shoreline in ers 1 sar images extraction of the shoreline in sar images is a difficult task to perform using simple image processing operations such as grey value thresholding due to the presence of speckle and because the signal returned from the sea surface may be similar to that from the land a semiautomatic method for detecting the shoreline accurately and efficiently in ers 1 sar images is presented this is aimed primarily at a particular application namely the construction of a digital elevation model of an intertidal zone using sar images and hydrodynamic model output but could be carried over to other applications a coarse fine resolution processing approach is employed in which sea regions are first detected as regions of low edge density in a low resolution image then image areas near the shoreline are subjected to more elaborate processing at high resolution using an active contour model over 90 of the shoreline detected by the automatic delineation process appear visually correct

sediment laden fresh water above salt water nonlinear simulations when a layer of particle laden fresh water is placed above clear saline water both double diffusive and rayleigh taylor instabilities may arise the present investigation extends the linear stability analysis of burns meiburg j fluid mech vol 691 2012 pp 279 314 into the nonlinear regime by means of two and three dimensional direct numerical simulations dns the initial instability growth in the dns is seen to be consistent with the dominant modes predicted by the linear stability analysis the subsequent vigorous growth of individual fingers gives rise to a secondary instability and eventually to the formation of intense plumes that become detached from the interfacial region the simulations show that the presence of particles with a stokes settling velocity modifies the traditional double diffusive fingering by creating an unstable nose region in the horizontally averaged profiles located between the upward moving salinity and the downward moving sediment interface the effective thickness l s l c of the salinity sediment interface grows diffusively as does the height h of the nose region the ratio h l s initially grows and then plateaus at a value that is determined by the balance between the flux of sediment into the rose region from above the double diffusive rayleigh taylor flux out of the nose region below and the rate of sediment accumulation within the nose region for small values of h l s leqslant o 0 1 double diffusive fingering dominates while for larger values h l s geqslant o 0 1 the sediment and salinity interfaces become increasingly separated in space and the dominant instability mode becomes rayleigh taylor like a scaling analysis based on the results of a parametric study indicates that h l s is a linear function of a single dimensionless grouping that can be interpreted as the ratio of inflow and outflow of sediment into the nose region the simulation results furthermore indicate that double diffusive and rayleigh taylor instability mechanisms cause the effective settling velocity of the sediment to scale with the overall buoyancy velocity of the system which can be orders of magnitude larger than the stokes settling velocity while the power spectra of double diffusive and rayleigh taylor dominated flows are qualitatively similar the difference between flows dominated by fingering and leaking is clearly seen when analysing the spectral phase shift for leaking dominated flows a phase locking mechanism is observed which intensifies with time hence the leaking mode can be interpreted as a fingering mode which has become phase locked due to large scale overturning events in the nose region as a result of a rayleigh taylor instability

compressive failure of rocks abstract a model for the compressive failure of rocks via the process of shear faulting is presented the model addresses the progressive growth of damage that leads to the formation of a critical fault nucleus which grows unstably in its own plane by fracturing the grain boundaries in an increasingly rapid succession the model uses a two parameter weibull type shear strength distribution for the defining nucleation of initial damage followed by the use of stress enhancement factors for addressing the increased probability of failure in the vicinity of already cracked grain boundaries as the stress is further increased similar correlated fracturing events gets preferentially aligned to the crack cluster resulting in an echelon of cracks this crack cluster is modeled as an elliptical inhomogeneity with a lower shear modulus compared with the uncracked material on the outside the shear stress concentration resulting from this moduli mismatch was calculated and used to compute the stress enhancement factors for defining the nucleation of additional cracking events near the crack cluster eventually the size of the crack cluster becomes sufficiently large such that it carries a stress concentration high enough to fracture all grain boundary elements in front of it in an increasingly rapid succession the stress associated with this event is taken as the failure stress the model is applied to a variety of rocks including granite eclogite gabbro aplite rocksalt sandstone dunite limestone and marble and the results compare rather well with the failure data from the literature

holderness coast erosion and the significance of ords a sample ord a low section of beach characteristic of the holderness coast is examined as it moved southwards between 1977 and 1983 and its significant role in coast erosion is demonstrated the reduction in beach level at the cliff foot by up to 3 9 m enabled most hwn tides to reach it as compared with only some hws tides along the inter ord beach and the volume of till eroded from the cliffs increased by eight times to an annual mean of 72m3m 1 the holderness tills are shown to be composed of 31 per cent sand and coarser sediment which is the sediment range of the beaches where an ord is sited the massive injection of beach sediment goes to form the ord s most prominent constructional feature the lower beach ridge which extends southwards from the centre of the ord analysis of 12 months observer wave data collected at withernsea in 1969 70 indicates that a net southward sand movement of 144 000 m3 occurred comparison of this rate with beach sediment input rates along the whole coast backed by till cliffs suggests a sediment deficit at the northern end and a surplus towards the southern end this conclusion is supported by an overall increase in beach sediment volume southwards from barmston within this longshore sediment transport system the ords migrate southwards from their point of origin in the barmston skipsea area without losing their identity until reaching the tip of spurn head

topographic mapping of the german tidal flats analyzing sar images with the waterline method the waterline method is used to derive the topography of the tidal flats along the german coast by evaluation of synthetic aperture radar sar images a series of about 70 european remote sensing satellites sar images of the german bight taken at different water levels within four years is analyzed to detect the borderline between tidal flats and adjacent water areas using a wavelet based edge detection algorithm after geocoding the waterlines are combined with the corresponding water levels to represent the topography on an irregularly spaced grid the water levels are taken from a numerical tide model and corrected with the measured gauge data interpolation of these data into a regular grid yields a topographic map of the intertidal zone while the general practicability of this method has been demonstrated in previous studies for smaller test areas this paper is the first attempt to generate maps of a large area on a yearly basis