sediment resuspension by surface wave action an examination of possible mechanisms abstract detailed spectral and coherence analyses of both nephelometer data and near bottom acoustic concentration profiles support the conclusion of lesht et al 1980 that surfacewave activity is the most important input to the sediment resuspension process the sand sized fraction is suspended primarily by bursts of turbulence which are related to peak values of the envelope of surface waves two mechanisms for the resuspension of fine sediment are considered when the bed is bimodal sand and silt pore water motion induced by wave pressure fluctuations may carry fine particles into the boundary layer where they are suspended motion of the sand matrix as bedload will also expose fine particles to the flow so that they become suspended the combination of these two mechanisms accounts for the observed quasi linear relation between wave orbital velocity and suspended sediment concentration for the long island data the second mechanism is also consistent with observations of near bottom fluid velocity and suspended sediment concentration in norton sound alaska

vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter vertical profiles of suspended sand concentration and size are obtained from multifrequency acoustic profiling data collected in 1989 during a nearshore experiment at stanhope lane beach prince edward island the data were acquired with acoustic sounders operating at 1 2 25 and 5 mhz independent estimates of concentration were made using optical backscatter sensors obss the algorithm for inversion of the three frequency backscatter data to particle size and concentration based on the ratios of the different signals was tested in laboratory experiments with an unconfined high reynolds number suspended sediment jet results from the stanhope beach experiment are presented for three different surface wave energy regimes with significant wave orbital velocities ranging from 0 3 to 0 8 m s and peak wave periods of 4 6 s the acoustic estimates of mean concentration are shown to be within 10 on average of those determined with the obs nearest the bottom at 5 to 10 cm height over time scales ranging from 6 5 min to 4 6 s one wave period the acoustic estimates of suspended sediment size near the bottom are within 5 20 of the bottom sediment mean size the statistical variability of the size estimates is high with standard deviations in the estimates ranging between 30 and 50 of the mean the time averaged concentration profiles exhibit an exponential decrease with height above an o 10 cm thick near bottom region of nonexpo nential decrease in contrast the time averaged mean size profiles decrease approximately linearly with height and rather slowly about 25 in 0 5 m

thrust fault mechanics and origin of a frontal ramp several features of thrust sheets in nonmetamorphic and relatively low grade metamorphic terrains indicate that the modes of faulting included both gradual and stick slip types of motion a first order quantitative analysis is made of the mechanics of this type of faulting in the analysis part of a wedge shaped thrust belt slips forward over a fault area of length l and unit width w producing a strain concentration in subhorizontal strata at the front of the growing thrust where a frontal ramp develops by shear fracturing equations for net slip x and the conditions for ramping are evaluated with limit equilibrium principles and coupled oscillator theory the quantitative analysis takes into account anisotropy resulting from contrasts in competency and facies changes a special case solution for maximum net slip associated with stick slip is lw ki 1 cos ot o 12 1 cos 1t where is the stress drop ki are spring constants of the strata 0 and 1 are natural frequencies of the system and t evaluated from another equation is the time for net slip the spring constants and natural frequencies can be evaluated from seismic and stratigraphic data a preliminary solution for piggy back thrusting indicates that ramp spacing can be systematic and that it depends upon the thickness of the deforming package the elastic parameters of the deforming package the slope of the topographic surface and the stresses along the trailing edge of the package

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

acoustic inversions for measuring boundary layer suspended sediment processes although sound has been applied to the study of sediment transport processes for a number of years it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters in particular when the attenuation due to the suspension becomes significant the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension to study this attenuation propagation problem numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters the results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters which become increasingly erroneous with range as the sound propagates through the suspension to address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion this approach is not subject to the accumulation of errors and has an explicit solution here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion

strain on the san andreas fault near palmdale california rapid aseismic change frequently repeated strain measurements near palmdale california during the period from 1971 through 1980 indicate that in addition to a uniform accumulation of right lateral shear strain engineering shear 0 35 microradian per year across the san andreas fault a 1 microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between february and november 1979 subsequently november 1979 to march 1980 about half of the contraction was recovered this sequence of strain changes can be explained in terms of south southwestward migration of a slip event consisting of the south southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers the large strain change in 1979 corresponds to the passage of the slip event beneath the san andreas fault

temporal variability of suspended particulate concentrations in the new york bight abstract temporal variability observed in several time series of suspended matter measurements obtained by light scattering and conventional water sampling has been examined to identify significant time scales with respect to synoptic characterization of regional suspended matter distributions in the inner new york bight processes with periods corresponding to surface waves seconds and storms days apparently make the strongest contributions to overall concentration variability and tidal motions appear to have only a weak influence on near bottom suspended load an empirical model is proposed which assumes that concentration variance is linearly related to the mean concentration both increasing in response to such processes as wind wave mixing and boundary layer interactions with the b ttom data obtained during the study support the model this model is used in a numerical experiment which suggests that fair weather variability in processes affecting near bottom concentrations is probably not sufficient to cause serious errors in suspended matter studies in the new york bight

a potentially new instrument for measuring the in situ concentration of fine sediments in suspension abstract there is at present an instrumentation gap for the accurate measurement of suspended cohesive material over the concentration range between approximately 20 and 200 g l 1 to bridge this gap a laboratory feasibility study on a new process control instrument has been conducted to examine the application of such an instrument for measuring the in situ concentration of fine marine solids in suspension the technique provides a very accurate measurement of fluid bulk density from which the solids concentration can be derived the present study shows the instrument to be capable of accurately measuring the mass of fine sediments in suspension from 3 to beyond 200 g l 1

acoustic detection of seabed gravel movement in turbulent tidal currents abstract the measurement of sediment transport rates in the sea remains one of the most elusive goals for oceanographers sedimentologists and coastal engineers such measurements are required to test and validate sediment transport theories progress in this direction is greatly restricted by the lack of suitable field data and is dependent on progress with new instrumental techniques developments investigated in recent years have included the use of active and passive acoustic devices to detect sediment transport in this letter we describe the measurement of seabed gravel movement using a passive acoustic system for the first time using an underwater tv camera it has been possible to simultaneously observe sediment transport and take acoustic measurements thereby gaining independent assessment of the sensors performance further support has been provided by measurements of the turbulent fluctuations in the nearbed reynolds stresses

broadband acoustic quantification of stratified turbulence high frequency broadband acoustic scattering techniques have enabled the remote high resolution imaging and quantification of highly salt stratified turbulence in an estuary turbulent salinity spectra in the stratified shear layer have been measured acoustically and by in situ turbulence sensors the acoustic frequencies used span 120 600 khz which for the highly stratified and dynamic estuarine environment correspond to wavenumbers in the viscous convective subrange 500 2500 m 1 the acoustically measured spectral levels are in close agreement with spectral levels measured with closely co located micro conductivity probes the acoustically measured spectral shapes allow discrimination between scattering dominated by turbulent salinity microstructure and suspended sediments or swim bladdered fish the two primary sources of scattering observed in the estuary in addition to turbulent salinity microstructure the direct comparison of salinity spectra inferred acoustically and by the in situ turbulence sensors provides a test of both the acoustic scattering model and the quantitative skill of acoustical remote sensing of turbulence dissipation in a strongly sheared and salt stratified estuary

on the remote acoustic detection of suspended sediment at long wavelengths experimental results are presented which indicate a linear relation between the time averaged amplitude of the envelope of the backscattered acoustic pulse at 192 khz and the square root of suspended sediment concentration in the 10 to 103 mg 1 1 range particle sizes ranged from 2 to 140 m the measurements were made in a negatively buoyant mine tailing discharge plume in a submarine channel at depths of 60 to 90 m in rupert inlet british columbia from the theory of acoustic backscatter from a solid elastic sphere in the rayleigh region it is shown that if the pressure amplitude of the backscattered wave is rayleigh distributed then such a linear relation is to be expected expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background the possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes

a strategy for short term prediction of earthquakes abstract physical processes leading to laboratory rupture have a nonlinear character which justifies optimism that earthquakes are predictable however nonlinear effects at the source of a smaller earthquake may be an insufficient basis for the prediction of an earthquake with rupture lengths tens to hundreds of kilometers thus a strategy for predicting such major or great events must depend on knowing the state of readiness of the entire length of the suspect fault the two most promising avenues are 1 to search for variations in shear and dilatational strains within the fault zone and in the bordering regions that signify the onset of a stuart instability and 2 to follow in detail the seismicity in response to the temporal variations of shear and normal strains as a measure of what parts of a long fault are at the point of failure an observational strategy based on these physical models requires detailed and frequent to continuous observation of strain within the fault and border zones focal mechanisms and accurate locations of earthquakes m 2 are needed to relate seismicity to a given configuration of the strain field with the exception of observations such as levels in water wells which carry information on the strain field a purely empirical search for earthquake precursors needs to be deemphasized

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

radon content of groundwater as an earthquake precursor evaluation of worldwide data and physical basis the properties of a worldwide data set of 91 radon 222 rn anomalies the frequency of occurrence the precursor time interval and the distribution of peak amplitudes are correlated with earthquake data such as the respective magnitude and epicentral distance these anomalies were reported as precursors to earthquakes in the united states ussr china japan and iceland although the data set is incomplete and limited by experimental deficiencies several consistent patterns emerge radon anomalies from different tectonic regions show similar patterns the radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude anomalies preceding large earthquakes m 6 are frequently observed at a distance of 100 to 500 km these distances are larger than several times the rupture dimensions of the future earthquakes the time from the onset of an anomaly to the time of the earthquake the precursor time increases with magnitude but decreases with distance between epicenter and radon station in addition radon anomalies are observed more frequently prior to large earthquakes than prior to small ones indicating that the preparation zone increases in size as magnitude increases the peak amplitude does not scale with magnitude but forms a consistent pattern with epicentral distance in that the larger the earthquake magnitude the farther away the largest amplitudes tend to occur the preparation zone of the earthquake where the anomalies occur forms an almost continuous annulus that expands with time away from the future rupture zone the outer radius of this annulus scales with the earthquake magnitude model calculations indicate that strain fields of at most 10 6 to 10 8 strain caused the radon anomalies if these strains are divided by the appropriate precursor time minimum strain rates from 10 7 day 1 to 10 10 day 1 are obtained such small strains and strain rates suggest that in most cases neither mechanical crack growth induced by dilatancy nor mechanical coupling between pore pressure and the rock matrix caused the anomalies large changes in the orientation of the local strain field however could occur and affect the local stress intensity factor since changes in the stress intensity factor can result in stress corrosion the occurrence of radon anomalies is attributed to slow crack growth controlled by stress corrosion in a rock matrix saturated by groundwater

identification of intense intermittent coherent motions under shoaling and breaking waves laboratory measurements of the instantaneous horizontal and vertical turbulent velocities u and w induced by regular waves spilling on a rough impermeable slope were analyzed to elucidate the nature of turbulence generated in the bottom boundary layer and by wave breaking the analyses focused on the instantaneous turbulent events such as the absolute shear stress u w and turbulent kinetic energy k u 2 w 2 2 below trough level inside the surf zone the horizontal and vertical velocity records showed intense intermittent turbulent events that did not occur with the passing of each wave and the instantaneous quantities of and k could not be explained in terms of the phase averaged quantities the intermittent turbulent events extended into the bottom boundary layer inside the surf zone and in this region the infrequent but intense turbulence generated by wave breaking was an order of magnitude larger than the turbulence generated locally at the boundary two techniques were used to analyze the turbulent motions a quadrant analysis technique showed that although the large turbulent motions did not occur with each wave they were phase dependent near trough level and less so near the bottom a conditional sampling technique quantified the intensity and duration of the turbulent motions indicating that coherent events intense events occurred for 10 2 of the record and accounted for approximately 50 20 of the turbulent motion it is likely that the exactitude of these statistics will differ depending on breaker type nevertheless these statistics indicated that large turbulent motions are infrequent but contribute significantly to the turbulence intensity and possibly the suspension of bottom sediments

stiffness method for anticipating earthquakes in strain softening earthquake models the single variable r kf ks measures the nearness to earthquake instability kf and ks are stiffnesses of the fault zone and elastic surroundings instability occurs when increasing r reaches unity for a simple two dimensional antiplane model r is a function of d e du and h where e is shear strain at the ground surface and u is remote displacement observed at a distance h from the fault r is independent of the fault zone constitutive law crustal rigidity and shear stress magnitude

acoustic profiling of suspended sediments in the marine bottom boundary layer an acoustic 3 mhz backscattering profilometer has been developed for study of sediment transport in the bottom boundary layer laboratory experiments indicate reasonable correlations between backscattering intensity and mass concentrations for well sorted fine to coarse quartz sands typical of those found in marine sediments departure of the calibration curves from their expected values is thought to be due to the non spherical shape of the quartz grains field experiments on the inner shelf using the profilometer combined with velocity profiles show individual profiles taken at 1 hz during erosion events are characterized by highly variable concentrations surface wave groups rather than individual waves appear to be correlated with groups of profiles with high concentrations extending 25 100 cm above bottom averaging produces smooth profiles which fit well log normal distributions predicted by steady flow suspended load theories

acoustic imaging of sea bed geometry a high resolution remote tracking sonar hrrts ii abstract a high resolution remote tracking sonar hrrts ii is described which is capable of measuring a 2 d profile of the sea bed over a maximum distance of 5 m under conditions of significant sediment transport the backscattered signal from a pulsed 30 s 5 mhz sonar provides acoustic range measurements of the small scale topography generated by bedforms at any point in time as well as changes in this small scale topography and the average elevation of sections of the sea bed over time bedform height and spacing can be determined accurately although bedform shape is distorted by smoothing of large slope changes as a result of the finite size of the footprint of this narrow beamed 0 74 sonar the system operates on command from a shore based micro computer and topographic resolution of the order of a few millimetres is possible resolution deteriorates as wave energy increases to levels where vibration of the transducer and large concentrations of sediment in the water column result in signal attenuation and a decrease in the signal to noise ratio

spatially correlated depth changes in the nearshore zone during autumn storms acoustic reflection measurements of seabed elevation were made at stanhope beach prince edward island during three successive storms in october november 1989 the instruments were located approximately 200 m offshore on the seaward face of a shore parallel bar in a mean water depth of 2 2 m bed elevation measurements were made at 30 min intervals with a range resolution of 1 mm at horizontal spacings between 22 cm and 1 5 m using an array of four acoustic sounders operating at 1 2 25 and 5 mhz it is shown that such an array can be used as 1 an interferometer to determine bedform properties and migration rates 2 a leveling device to determine changes in local bottom slope and 3 an erosion deposition gauge in the interferometric mode time domain autocorrelation and cross correlation analyses of the bottom elevations are used to estimate the wavelengths migration rates and migration directions of sand ripples and megaripples the ripple wavelengths 10 15 cm and heights 3 5 cm are comparable to measurements made by divers ripple migration rates were 1 6 cm h 1 directed offshore in the direction of the mean shore normal near bottom current and increased with increasing mean current speed evidence of megaripple like features 2 5 cm height 1 5 3 m length is found also migrating in the direction of the mean shore normal near bottom drift at speeds of about 20 cm h 1 bedload transport rates in the onshoreoffshore direction are estimated from the bedform migration rates the ripple transport rate was small an order of magnitude smaller than the transport of sediments in suspension by the mean offshore drift in contrast the large scale bedform transport appears to have been comparable to the mean current transport of suspended sediment interestingly it appears that the total bedform transport was comparable to that predicted by watanabe s 1981 net bedload transport formula provided a coefficient appropriate to irregular wave conditions is used during the third and highest energy storm event the measurements indicate transition to flat bed and generalized local erosion at a maximum rate of 8 cm h 1 this erosion event was associated with a general shoreward migration of the bar

sediment transport in the mouth of the eden estuary abstract observations of water movement and sediment transport were made from a fixed platform at an intertidal location in the mouth of the eden estuary the effects of wave activity on water movement and suspended sediment fluxes were evaluated and an empirical relationship between suspended sediment concentrations and near bed water movement is described the circulation of water in st andrews bay indicates a residual movement onshore near to the bed onshore movement of sediment in the mouth of the estuary is indicated by suspended sediment fluxes and bedload transport determined from bedform migration the relative roles of suspended sediment and bedload transport are discussed morphological changes in the estuary mouth over the three year survey period are relatively small and indicate a stable environment

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

vertical suspension profile in the changjiang estuary abstract by using an acoustic suspended sediment monitor assm four patterns of vertical suspension profile have been obtained at spring tide 28 29 may 1994 in the changjiang estuary type i is l shaped at flood tide the vertical gradients in suspended sediment concentration ssc were small

comparison of measurements and models of bed stress bedforms and suspended sediments under combined currents and waves abstract this study presents an analysis of data collected in an embayment off a sandy beach protected by shore parallel breakwaters observations were carried out over a forty day period including spring and neap tidal cycles and low and high wave activity measurements were collected on the waves currents bedforms and suspended sediments and these were used to derive estimates of the bed shear stresses ripple dimensions reference concentrations and suspended sediment profiles the aim of the present study was to use the measurements to assess commonly employed empirical formulations applied to sediment modelling in the coastal marine environment assessments are made of four ripple predictors two formulations of reference concentration and power law and exponential suspended sediment shape functions in some cases predicted parameters are well represented during low wave conditions whilst other parameters are better predicted under high wave events the outcome from the work is an evaluation of the predictive capability of the selected empirical formulae at the sandy location and discussions on the comparison between the observations and predictions

cenozoic erosion and the preglacial uplift of the svalbard barents sea region abstract the creation of the huge fans observed in the western barents sea margin can only be explained by assuming extremely high glacial erosion rates in the barents sea area glacial processes capable of producing such high erosion rates have been proposed but require the largest part of the preglacial barents sea to be subaerial to investigate the validity of these proposals we have attempted to reconstruct the western preglacial barents sea our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western barents sea and consequently use it together with a simple airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western barents sea margin the mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western barents sea margin areas and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information by comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1 2 to 2 3 of the total cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western barents sea could be obtained the results show a subaerial preglacial barents sea thus during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm y while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge sediments have been evacuated and deposited at the margins at high rates the interplay between erosion and uplift represents a typical chicken and egg problem initial uplift is followed by intensive glacial erosion compensated by isostatic uplift which in turn leads to the maintenance of an elevated and glaciated terrain the information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the barents sea is a thermal mechanism

the benthic boundary layer and sediment transport the major problems facing scientists studying marine boundary layer fluid mechanics in 1979 concerned the specific mechanismic operating in the regions of the top and the bottom of the boundary layer at the top the mechanisms of fluid escapement from the boundary layer and mixing into the ocean interior could only be postulated approximations of diffusivity across the top of the layer were being debated the values of which were more articles of faith than physically validated estimates cf armi 1979 garrett 1979 at the bottom the intermittent generation of stress cf gordon 1975 heathershaw and simpson 1979 was held responsible for the wide variability observed in the drag coefficient and the thickness of the viscous sub layer was claimed to be greater than that traditionally found from laboratory studies caldwell and chriss 1979

relationship of the 1979 southern california radon anomaly to a possible regional strain event during the second half of 1979 anomalously high emanation of radon was recorded at two stations of the automated radon thoron monitoring network operated by the w k kellogg radiation laboratory of the california institute of technology the two stations exhibiting major anomalies kresge and dalton canyon are located approximately 30 km apart on the frontal fault system of the transverse ranges of southern california at kresge the anomaly began on june 21 1979 and continued through december 1979 at dalton canyon the anomaly started about 3 weeks later and also continued through december 1979 at both sites the anomalous levels of radon decreased but did not return entirely to normal values shortly before october 15 1979 during the week of october 15 1979 a 6 6 m earthquake occurred about 290 km to the southeast of the two stations and later in that week earthquakes of magnitude 4 2 and 4 1 occurred at malibu and lytle creek the latter two events were within 60 km of the monitors a radon thoron monitor at lytle creek recorded no long term anomaly but did record a sharp spikelike decrease in the radon level on october 13 1979 coincident with our observations of anomalous radon levels other investigators have reported anomalies or suspected anomalies in several other geodetic geophysical and geochemical signals from the same general region the rapid temporal development of several of the anomalies together with the large area over which they were observed suggests that a large scale strain event took place which may have been responsible both for the widespread anomalies and for the seismicity that occurred in the region subsequent to the onset of the anomalies

in situ fluid pressure measurements for earthquake prediction an example from a deep well at hi vista california short term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur and it is now recognized that even to have the possibility of a reliable earthquake prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals we are conducting experiments to determine the maximum signal to noise improvement that can be obtained in drill holes in a 592 m well in the mojave desert near hi vista california we measured water level changes with amplitudes greater than 10 cm induced by earth tides by removing the effects of barometric pressure and the stress related to earth tides we have achieved a sensitivity to volumetric strain rates of 10 9 to 10 10 per day further improvement may be possible and it appears that a successful earthquake prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km assuming that the premonitory strain signals are in fact present

acoustic measurements of suspended sand concentration in the c2s2 experiment at stanhope lane prince edward island abstract a 3 mhz acoustic concentration meter acm was deployed with electromagnetic flowmeters in the nearshore region in october 1984 at stanhope lane prince edward island canada as a component of the canadian coastal sediment study the acm measured the backscatter of acoustic energy in a vertical beam pattern within approximately 1 m of the seabed laboratory calibration experiments were conducted to verify a method for converting acoustic backscatter into suspended sand concentration profiles the acm functioned well when there were no air bubbles in the water both the suspended sand concentration profiles and the bottom location were measured with an approximately 1 s time resolution and a 1 cm vertical spatial resolution the suspension of sand is related to the wave and current forcing and is dominated by events of short duration

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

field measurements of the suspended sand concentration profiles and fluxes and of the resuspension coefficient γ0 over a rippled bed measurements of the acoustic backscatter from suspended sand over a rippled bed and of currents were made near the crest of a ridge and runnel beach on the macrotidal north norfolk coast of the united kingdom two 12 min records were taken close to high water in a depth of 1 7 0 2 m visual inspection of the data shows that sand was intermittently suspended to heights of 20 30 cm but that these events were not always correlated with strong wave induced currents the structure of some of the suspension events suggest that they are due to vortex shedding from a rippled bed the observed time averaged concentration profiles were compared with predictions generated using glenn and grant s 1987 combined flow model the nondimensionalised concentrations showed good correspondence in the first 8 to 10 cm above the wave boundary layer supporting the use of a value of 0 74 drawn from atmospheric data for the constant of proportionality between sediment and momentum diffusivity above this height observed values of the proportionality constant tended to approach 1 0 which may have been due to a decrease in sediment settling velocity with height which is consistent with finer sand being suspended higher in the flow or alternatively to nonuniform turbulence in the vicinity of the wave ripples absolute concentrations measured 2 cm above the bed were consistent with values of o 10 4 for the empirical constant 0 in smith and mclean s 1977 pickup function concentrations within the wave boundary layer were observed to decrease much more rapidly than predicted by the model sand transport fluxes were computed for both the cross shore and alongshore components of the flow using a current profile based on the combined flow model of glenn and grant 1987 for the two records vertically integrated fluxes of 1 5 mg s cm width and 0 89 mg s cm width directed towards the shore were calculated for the wave oscillatory component of the transport the mean flow produced shoreward vertically integrated fluxes of 5 1 and 10 5 mg s cm width the uncertainty associated with these estimates is considerable 50 the vertical profile of the total flux wave oscillatory and mean for both records showed a strong shoreward transport close to the bed an offshore transport between 5 and 15 cm above the bed and a further weak onshore flux above this demonstrating the necessity for measurements of the whole concentration profile rather than a few point samples for the calculation of sand transport over a rippled bed in a wave dominated environment

on the relationship between bedload and suspended sand transport on the inner shelf long island new york data obtained by a near bottom profiling concentration and velocity system pcv deployed in 10 m water depth at a site 1 km from the long island coastline are used to examine links between bedload and suspended sand concentrations calculations of bedload areal concentration c are based on the empirical results of vincent et al 1981 and use the theoretical formulations of grant and madsen 1978 1979 to describe the interaction between wave and current boundary layers suspended sand concentrations were obtained directly from an acoustic concentration meter acm average suspended sand profiles cz were found to fit closely to a log linear profile cz c1 1 a loge z z1 where c1 is the sand concentration at a height z1 1 cm from the bed and a is empirically determined as 0 22 0 005 a linear correlation is observed between the areal bedload concentration c the volume of bedload per unit area of the bed and the suspended sand concentration 1 cm above the bed c1 with a correlation coefficient of 0 82 significant at the 1 level and supports the hypothesis of einstein 1950 that bedload and suspended load are related through bedload concentration it is also shown that the sedment threshold criterion of komar and miller 1973 when expressed as a ratio here called the komar ratio can be used as a useful predictor for c1 under conditions where the wave orbital currents are much greater than the mean flow these relationships offer the opportunity for the calculation of both bedload and suspended sand transport rates from measurements of the steady current velocity and wave parameters combined with information defining the surficial sediments and local bottom topography