rapid water exchange between the lagoon and the open ocean at majuro atoll due to wind waves and tide current measurements and conductivity temperature depth surveys of the lagoon and ocean at majuro atoll the republic of the marshall islands were made from january 10 to 24 1997 a vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements by fourier transform a three dimensional robust diagnostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles we used the diagnostic model to examine the effects of wind stress radiation stress density gradients and tidal stress on the exchange of water between the lagoon and the ocean wind effectively mixes the lagoon water in approximately 2 weeks tidal flushing appears to be restricted to a small area near the main channels connecting the lagoon to the ocean cross reef flat currents induced by radiation stress and flowing to the deep channels in the center of the northern boundary form the dominant mechanism for exchange between the lagoon and the open ocean causing water to exchange completely with the ocean in about 15 days computer generated particles tracked through the lagoon showed that radiation stress is also the main forcing mechanism for particle export from the lagoon however the coupling of tidal exchange through the calalin channel and wind stress induced mixing in the lagoon could also provide a significant export mechanism particularly for particles originating uniformly inside the lagoon

forcing of resonant modes on a fringing reef during tropical storm man yi 1 open basin resonant modes have been observed at tidal frequencies on coastal shelves but their excitation on coral reef platforms has only been suggested the topography of and water depth over most fringing reefs correspond to resonant periods that are the order of tens of minutes and fall outside of the energetic part of the wave spectrum during tropical storm man yi low frequency near resonant oscillations dominated the variance of the sea surface elevation at the shoreline of ipan reef guam the excitation of the resonant modes resulted both from a large increase in water level over the reef due to wave setup which increased the resonant frequencies and the occurrence of wave group forcing with time scales commensurate with these increased resonant frequencies

postglacial uplift neotectonics and seismicity in fennoscandia abstract fennoscandia has experienced major uplift in postglacial time which is assumed to reflect a glacial isostatic process connected to the melting of the last ice sheets extensive modelling of the isostatic movements show that the applied deglaciation and uplift model fit the observations well there are however areas with significant deviations between uplift measurements and regional model predictions the misfit between observations and the isostatic uplift modelling is interpreted here to reflect a tectonic component of the uplift the objective of the present investigation is to isolate this tectonic uplift component interestingly enough the areas found partly correspond to areas with pronounced seismic activity and the assumption that the postglacial rebound is responsible for much of the observed onshore seismicity is substantiated we conclude that there seems to be present day deformation along the shoreline of mid norway southern norway shoreline and mountain areas and along the swedish east coast with the centre northeast of the gulf of bothnia that cannot be explained by glacial isostasy not all of the deformations in these areas are necessarily co seismic the study suggests that such vertical deformations are small in magnitude and overprint the glacial rebound the deformations may be a consequence of the plio pleistocene erosional pattern which is of glacial origin

azimuthal anomalies of short period p wave arrivals from nahanni aftershocks northwest territories canada and effects of surface topography abstract following two large earthquakes in the northwest territories of canada in 1985 and one in 1988 four field surveys were undertaken to study the extensive aftershock activity some of the seismographs employed recorded three component digital data which allowed the directions of approach of short period p wave arrivals to be analyzed at three stations observed azimuthal deviations reached as much as 40 from theoretically expected azimuths as computed from the inferred hypocenters for the events theoretical results are presented that support the hypothesis that the observed azimuthal deviations are caused principally by local topographic slopes in the vicinity of the recording instruments similar theoretical results indicate that effects of local surface topography on arrival azimuths of sh and sv waves are nearly an order of magnitude less than for p waves so that such effects will generally be unimportant in shear wave splitting studies

the use of instantaneous polarization attributes for seismic signal detection and image enhancement this research has been supported by the spanish ministry of education culture and sport through grant sb2000 0120 and by a marie curie fellowship of the european community programme ihp hpmf ct 2001 01322

an automated rayleigh wave detection algorithm abstract the desire to operate denser networks in order to monitor seismic activity at lower thresholds leads to greater emphasis on automated data processing an algorithm for detecting and characterizing long period rayleigh wave arrivals has been developed and tested the routine continuously monitors all directions of approach to a station in a manner similar to beamforming the detector is based on cro ss powers between the hilbert transformed vertical and rotated horizontal signals so it is sensitive to both the power and polarization properties of the three component wavefield elliptically polarized rayleigh arrivals are enhanced while linearly polarized love waves and body phases are suppressed a test using one month of data from station anmo demonstrated that this technique can with high reliability detect rayleigh arrivals which would be visible to an analyst the measured arrival times and azimuths are accurate enough to permit automated association of the detections to events in a bulletin

wave transformation over coral reefs ocean wave attenuation on coral reefs is discussed using data obtained from a preliminary field experiment and from the seasat altimeter marked attenuation of the waves is observed the rate being consistent with existing theories of bottom friction and wave breaking decay in addition there is a significant broadening of the spectrum during propagation across reefs three dimensional effects such as refraction and defraction can also lead to substantial wave height reduction for significant distances adjacent to coral reefs as a result a matrix of such reefs provides significantly more wave attenuation than may initially be expected

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

seismic waves estimation and wavefield decomposition application to ambient vibrations summary passive seismic surveying methods represent a valuable tool in local seismic hazard assessment oil and gas prospection and in geotechnical investigations array processing techniques are used in order to estimate wavefield properties such as dispersion curves of surface waves and ellipticity of rayleigh waves however techniques presently in use often fail to properly merge information from three components sensors and do not account for the presence of multiple waves in this paper a technique for maximum likelihood estimation of wavefield parameters including direction of propagation velocity of love waves and rayleigh waves and ellipticity of rayleigh waves is described this technique models jointly all the measurements and all the wavefield parameters furthermore it is possible to model the simultaneous presence of multiple waves the performance of this technique is evaluated on a high fidelity synthetic data set and on real data it is shown that the joint modelling of all the sensor components decreases the variance of wavenumber estimates and allows the retrieval of the ellipticity value together with an estimate of the prograde retrograde motion

studies of coda using array and three component processing the application of standard array processing techniques to the study of coda presents difficulties due to the design criteria of these techniques typically the techniques are designed to analyze isolated short arrivals with definite phase velocity and azimuth and have been useful in the frequency range around 1 hz coda is long in time and may contain waves of different types phase velocities and azimuths nonetheless it has proved possible to use or adapt array methods to answer two questions what types of waves are present in coda and where are they scattered most work has been carried out on teleseismicp coda work on local coda has lagged due to lack of suitable data and the difficulties of dealing with high frequencies the time domain methods of beamforming and vespagram analysis have shown that there is coherent energy with a high phase velocity comparable top orpp in teleseismicp coda these methods can detect this coherent coda because it has a fairly definite phase velocity and the same or close to azimuth as firstp orpp this component must consist ofp waves and is either scattered near the source or reflected in the mantle path as apdpp or precursorpp reflection the fourier transform method of the frequency wavenumber spectrum has been adapted by integrating around circles of constant phase velocity constant total wavenumber to produce the wavenumber spectrum which shows power as a function of wavenumber or phase velocity for teleseismicp coda wavenumber spectra demonstrate that there is a diffuse coda of shear lg or surface waves scattered from teleseismicp near the receiver wavenumber spectra also suggest that the coherent coda is produced by near source scattering in the crust not mantle reflection since it is absent or weak for deep focus events crustal earthquakes have a very strong coherent component of teleseismic coda suggesting scattering from shear to teleseismicp near the source three component analysis of single station data has shown the presence of off azimuth arrivals and may lead to the identification of waves scattered from a single scatterer

automated phase picker and source location algorithm for local distances using a single three component seismic station abstract procedures for automatic location of local events by using single site three component seismogram records are described epicentral distance is determined from the time difference between p and s onsets for onset times estimates a special phase picker algorithm is introduced onset detection is accomplished by comparing short term average with long term average after multiplication of north east and vertical components of recording for epicentral distances up to 100 km errors seldom exceed 5 km the slowness vector essentially the azimuth is estimated independently by using the christoffersson et al polarization technique although a priori knowledge of the p onset time gives the best results differences between true and observed azimuths are generally less than 12 practical examples are given by demonstrating the viability of the procedures for automated three component seismogram analysis the results obtained compare favourably with those achieved by a miniarray of three stations

modeling bottom roughness in the presence of wave generated ripples 1 near bottom wave current and microtopography measurements have been obtained at the leo 15 site off the southern coast of new jersey the measurements are used in conjunction with a recently calibrated continental shelf bottom boundary layer model to refine estimates of bottom roughness for a rippled bed under combined wave and current flows in the presence of nearly two dimensional wave generated ripples application of the grant and madsen 1979 type bottom boundary layer model produces estimates of the bottom roughness felt by the current that are several times greater than established formulations for rippled beds under waves modifying one of the primary length scales in the eddy viscosity profiles returns estimates that are more consistent with the wave roughness results application of the roughness model in conjunction with a refined empirical ripple geometry model produces highly accurate estimates of measured shear velocities and apparent roughnesses during a moderate storm the demonstrated accuracy of this simple combined roughness and ripple geometry formulation reveals its utility when considering applications of coupled bottom boundary layer shelf circulation models

regional seismic event location with a sparse network application to eastern kazakhstan ussr three component data from a sparse three station seismic network in eastern kazakhstan surrounding the soviet nuclear test site have been analyzed to determine location estimates for regional events recorded by two or three stations included among these events are the september 1987 chemical explosions whose locations are known locations are calculated using arrival times of p and s phases and arrival azimuths from first p location uncertainties are estimated using a combination of a priori and a posteriori data uncertainties a layered p wave velocity model adapted from soviet deep seismic sounding surveys is employed for calculating travel times and two s models are tried location results for the chemical explosions are excellent even if only two stations are used absolute location errors are less than 10 km and estimated 90 confidence uncertainties are only a few kilometers the data are also adequate to determine correctly their depth i e focus at the surface the other regional events include numerous suspected mine blasts and two earthquakes from the tien shan the calculated locations of the latter events agree well with a teleseismic location for one of them falling within a belt of regular seismic activity nearly all of the presumed blasts can be associated with mapped mines and we have been able to identify the source areas for two sets of blasts in high resolution satellite images before and after photographs allow us to identify specific active mines our location estimates agree quite well with the observed active mines

surface topographic effects at arrays and three component stations abstract a unified method of slowness analysis has been applied to the noress and arcess arrays and to the three component stations within these arrays with the following results 1 there is a relatively large scatter in the three component solutions for events from the same source region and 2 there are significant differences between the solutions at the different three component stations evidence is presented that a uniform half space model is inadequate to derive slowness solutions from three component data layering of the crust and upper mantle affect the surface response at long periods and surface topography and near surface structure perturb the surface particle motion and slowness solutions especially at short periods topographic effects are evaluated by means of numerical simulations based on a newly developed multiple scattering method the theoretical results explain up to about half of the observed anomalies in the three component solutions on the other hand the array solutions based on vertical component phase delays are relatively stable since the nongeometrical phase perturbations are negligible

shear wave splitting and anisotropy in the charlevoix seismic zone quebec during the month of august 1984 an experiment was undertaken in the charlevoix seismic zone to test the hypothesis that shear wave splitting could be observed in a seismically active region seismograms recorded by digital 3 component seismographs located very close to the epicentres of three earthquakes showed shear wave splitting the amount of splitting was estimated to be 1 6 to 2 of the shear wave velocity from particle motion diagrams the average azimuth of the direction of polarization was 30 these observations can be explained by the presence of vertical cracks striking 30 east of north with a minimum crack density of e 0 03

microearthquakes and seismotectonic analysis for a nuclear plant area in southeastern finland abstract microearthquake observations are used to study the local seismicity and seismotectonics in the precambrian rapakivi granite in the loviisa area se fi around the nuclear power plant in loviisa is limited to a radius of 100 km the results from a local microearthquake network in the loviisa area showed that during 6 years of measuring there were 29 micro and ultra microearth 0 1 1 2 in the area the events identify active faults in the area the estimated value of the peak slip is an important parameter connecting microearthquakes to geodynamical processes the peak slip gives an approximat and aseismic movement on a certain fault and thus an indication of ongoing tectonic processes the movements on the active fault may continue for thous source parameters were computed for a simple circular source model giving peak slips less than 0 25 mm stress drop values less than 2 105n m2 and source radii generally less than 50 m the earthquakes occurred at depths of less than 5 km

spectral wave modeling in fringing reef environments abstract this study examines the implementation and validity of phase averaged spectral models in describing wave transformation over fringing reefs the wave breaking mechanism over the abrupt reef crest dissipation due to bottom friction and nonlinear energy transfer over the reef flat set the problem apart from general applications in non tropical settings the simulating wave nearshore swan model which is widely used in coastal engineering applications has embedded parameterizations of these surf zone processes for examination in addition we extend the model to include a recently implemented bottom friction source term for tropical reefs comparisons of model predictions with laboratory and field observations over fringing reefs identify promising wave breaking and bottom friction parameterizations for calibration the calibrated parameterizations enable swan to reproduce the observed wave height and setup and extend the applicability of spectral models to fringing reef environments swan however lacks the parameterization to describe the nonlinear energy transfer toward the infra gravity band that was observed in the laboratory and field studies

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

depth and current induced effects on wave propagation into the altamaha river estuary georgia abstract a study of sea surface wave propagation and its energy deformation was carried out using field observations and numerical experiments over a region spanning the midshelf of the south atlantic bight sab to the altamaha river estuary ga wave heights on the shelf region correlate with the wind observations and directional observations show that most of the wave energy is incident from the easterly direction comparing midshelf and inner shelf wave heights during a time when there was no wind and hence no wave development led to an estimation of wave energy dissipation due to bottom friction with corresponding wave dissipation factor of 0 07 for the gently sloping continental shelf of the sab after interacting with the shoaling region of the altamaha river the wave energy within the estuary becomes periodic in time showing wave energy during flood to high water phase of the tide and very little wave energy during ebb to low water this periodic modulation inside the estuary is a direct result of enhanced depth and current induced wave breaking that occurs at the ebb shoaling region surrounding the altamaha river mouth at longitude 81 23 w modelling results with stwave showed that depth induced wave breaking is more important during the low water phase of the tide than current induced wave breaking during the ebb phase of the tide during the flood to high water phase of the tide wave energy propagates into the estuary measurements of the significant wave height within the estuary showed a maximum wave height difference of 0 4 m between the slack high water shw and slack low water slw in this shallow environment these wave current interactions lead to an apparent bottom roughness that is increased from typical hydraulic roughness values leading to an enhanced bottom friction coefficient

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

estimation of ancient and future shoreline positions in the vicinity of olkiluoto an island on the western coast of finland the difference between grid and tin based gis approaches abstract the rise of gis data and spatial modelling techniques has brought new insights into shore displacement and palaeogeographical studies during recent years the aim of this study was to compare the capabilities of a raster data and map algebra based technique with those of a vector data triangulated irregular network tin based technique in the reconstruction of ancient and future shoreline positions in the vicinity of olkiluoto an island on the rapidly uplifting western coast of finland the first two models were carried out using a raster subtraction technique with grid cell sizes of 200 m and 30 m and a third model utilised a tin intersection technique where the shoreline is derived from the intersection of the tin representing the modern topography and the tin representing the water plane of the reconstructed phase the results show that the raster based technique has limited capability in recognition of important landscape features common to glacially sculptured coastal areas subject to glacial isostatic adjustment gia whereas the tin intersection technique provides more detailed information about the shoreline features comparison of the results reveals that the advantage of the tin intersection technique is more obvious the finer the scale is novel spatial modelling techniques improve the reconstructions of palaeolandscapes and shoreline positions of different time periods

polarization analysis of high frequency three component seismic data abstract we present a method to determine the polarization of body waves from three component high frequency data and examples of its application the method is based on the principal component approach one advantage of this approach is that the polarization state can be determined for small time windows compared with the predominant period of the wave this is particularly useful for identifying converted waves within the crust the stability of the result is analyzed with synthetic cases by adding simultaneous arrivals from waves and random noise the method works well with both synthetic and local data in the detection of the polarization of the wave by separating arrivals from different directions from the local data some seismic phases related to crustal conversions are observed that require strong lateral variations

tide effects on wave attenuation and wave set up on a caribbean coral reef abstract the effects of tides on wave attenuation and wave set up were investigated at great pond bay a caribbean reef located in st croix u s virgin islands measurements of wave pressure fluctuations were made at three stations across the reef profile total wave set up was measured between the forereef and the reef crest or backreef lagoon wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef the energy dissipation calculations imply an average energy reduction of 62 between the forereef and reef crest mean energy reduction between the forereef and lagoon was 90 energy dissipation between the forereef and reef crest increased 15 between high and low tide and 6 between forereef and lagoon tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation measurements of wave set up ranged from 0 8 to 1 5 cm calculations of wave set up using tait s 1972 model showed good agreement with observations

spatial and temporal variations in wave characteristics across a reef platform warraber island torres strait australia a field experiment was conducted at warraber island torres strait australia to investigate spatial and temporal variations in wave characteristics and energy across a mesotidal coral reef platform measurements of water depth were obtained using five pressure sensors deployed across a 2 7 km section of reef flat from july 3 5 2001 the reef surface was uneven and consisted of an outer reef flat a central reef flat depression an inner reef ramp a palaeo reef surface and the shoreline water levels decreased landward across the platform with tide ranges at the shoreline being almost 50 lower than at the outer reef flat rising and falling tides were characterised by a bimodal energy distribution with both short period 0 3 s and wind 3 8 s waves present higher water levels were dominated by wind waves the highest waves occurred at high tides associated with nocturnal tidal cycles with hs decreasing from 0 5 to 0 2 m from the outer reef flat to the shoreline wave energy at swell 8 20 s and infragravity 20 s frequencies was negligible across the reef platform although there was evidence of wave groups at higher water levels reef geometry and changes in water level determine the magnitude of wave energy on the reef platform up to 85 95 of incident wave energy is attenuated by the central reef flat depression at high and low tide respectively and strong linear relationships exist between hs and h at all locations both wave height and wave type are strongly depth dependent critical reef rim depths required to produce hs of a given size vary spatially across the reef rim due to variations in reef topography a distinct depth related threshold exists at which short period and wind wave dominance reverses over a 14 day spring neap tidal cycle the time of occurrence of wave action diminishes across the reef platform to the shoreline larger waves hs 0 2 m occur for only 9 of time at the outer reef flat and for less than 0 5 over the remaining reef platform this implies that on mesotidal reef platforms sediment entrainment and transport are severely constrained under normal wave energy conditions and significant change is likely restricted to extreme events

oscillatory flow across an irregular boundary 1 laboratory experiments examining oscillatory flow along a coastline or isobath with a series of headlands or ridges reveal a mechanism for transfer of momentum and mass from the boundary into the interior flow through the establishment of organized residual flow patterns particle imaging velocimetry is used to visualize the vorticity field and to quantify large scale residual circulations generated near the region of roughness two flow regimes are observed for differing ratios of along coast tidal excursion l to the length of the roughness region d for l d 1 a weak inflow is produced in the vicinity of the roughness region with a corresponding alongshore flow away from the region for l d 1 a strong outflow jet is established near the center of the roughness region the two flow regimes result from different residual vorticity patterns and rely on eddies being long lived relative to the tidal period thus these results are relevant to flows in which dissipation is weak relative to the mean flow kinetic energy such as for tidal flow in deep water flow past a single roughness element is used as an analog to tidal flow past a headland and is represented by the high l d limit

nonhydrostatic and surfbeat model predictions of extreme wave run up in fringing reef environments abstract the accurate prediction of extreme wave run up is important for effective coastal engineering design and coastal hazard management while run up processes on open sandy coasts have been reasonably well studied very few studies have focused on understanding and predicting wave run up at coral reef fronted coastlines this paper applies the short wave resolving nonhydrostatic xb nh and short wave averaged surfbeat xb sb modes of the xbeach numerical model to validate run up using data from two 1d alongshore uniform fringing reef profiles without roughness elements with two objectives i to provide insight into the physical processes governing run up in such environments and ii to evaluate the performance of both modes in accurately predicting run up over a wide range of conditions xbeach was calibrated by optimizing the maximum wave steepness parameter maxbrsteep in xb nh and the dissipation coefficient alpha in xb sb using the first dataset and then applied to the second dataset for validation xb nh and xb sb predictions of extreme wave run up rmax and r2 and its components infragravity and sea swell band swash sig and sss and shoreline setup were compared to observations xb nh more accurately simulated wave transformation but under predicted shoreline setup due to its exclusion of parameterized wave roller dynamics xb sb under predicted sea swell band swash but overestimated shoreline setup due to an over prediction of wave heights on the reef flat run up swash spectra were dominated by infragravity motions allowing the short wave but not wave group averaged model xb sb to perform comparably well to its more complete short wave resolving xb nh counterpart despite their respective limitations both modes were able to accurately predict rmax and r2

the crustal transfer function in seismic 3 component slowness estimation here we present a new approach for estimating the slowness vector of incident p waves from records of a single or an array of 3 component 3c seismometers the slowness vector is extracted by using a maximum likelihood ml inversion scheme where the signal model incorporates the transfer function of the layered crust beneath the receivers the unknown time function of the incident plane wave is excluded from the inversion in the case of array observations both polarization and moveout times are utilized the scheme was tested on records of noress 3 component stations from teleseismic and local events and the obtained slowness estimates are closer to the expected values than estimates derived by conventional methods

boundary layer turbulence and flow structure over a fringing coral reef measurements of velocity and rates of turbulence were made across a fringing coral reef in the gulf of aqaba red sea to determine the effect that the rough topography has on boundary layer mixing and flow dynamics observations were made at two fore reef sites and a nearby sandy slope the friction velocity u and drag coefficient cd were determined directly from turbulent reynolds stresses measured using acoustic doppler velocimeters values of cd for the coral substrates ranged from 0 009 to 0 015 three to five times greater than over the sandy bottom site the turbulence dissipation rate e was determined by fitting spectra of vertical velocity to the theoretical 5 3 law expected for the inertial subrange of turbulence there was a local balance between production and dissipation of turbulent kinetic energy signifying that we could estimate u from either the mean velocity profile turbulence or dissipation rate of turbulent kinetic energy estimates from all three measures agreed well with mean u uo ranging from 0 10 6 0 03 to 0 12 6 0 03 indicating that existing turbulent boundary layer flow theory can be applied to flows over the rough topography of coral reefs the bottom topography by enhancing both reef scale and local drag and mixing levels allows reef biota to more effectively exchange dissolved and particulate matter with oceanic waters

autoregressive segmentation of signal traces with applications to geological dipmeter measurements a general method and algorithm for segmenting data traces according to changes in the shape and scale of their autoregressive frequency structure are discussed the algorithm is based on the least squares principle which is utilized in several iterations and on several levels in the underlying model the transitions from one segment to another take place according to a markov mechanism but the algorithm works for any signal trace where the segmentwise characteristics occur in a repetitive manner the method is illustrated on four track geological dipmeter measurements from an unidentified oil well drilling hole in the north sea how more precise boundaries between geological layers can be determined by using the algorithm is indicated extensive testing of the algorithm on simulated data is discussed

on the wave current interaction during the passage of a tropical cyclone in the bay of bengal abstract the impact of waves on currents and vice versa is an integral part of the complex coastal dynamics the wave current interaction is prominent in the coastal shelf slope regions particularly during the passage of a tropical cyclone in the present study we describe the importance of wave current interaction in the northern bay of bengal bob using a fully coupled three dimensional coupled ocean atmosphere wave sediment transport coawst modelling system the coawst model is applied to the case of a very severe cyclonic storm phailin that passed over the bob basin during 10 15 october 2013 to represent the interaction between waves and currents we utilized the newly implemented vortex force method in the coupled model numerical experiments with different coupling configuration within the coawst modelling framework were performed to separately identify the effects of wind tide and wave current interaction process a comparison of model results with the buoy observations of water elevations currents and wave measurements shows a good agreement between model and observed data various terms of the momentum balance were calculated from the model simulated and diagnosed parameters a comparison of the horizontal momentum balance term identifies the wave breaking induced acceleration as one of the leading terms along the storm affected the east coast of india further an increase in the apparent bed roughness caused by waves found to affect the values and distribution of the bottom shear stress the pressure gradient term showed significant changes to the pure tidal case the study highlights that the changes in the momentum balance caused by waves includes contributions from the variations in the water level and currents the most relevant effect on the coastal hydrodynamics was in the form of a wave induced setup near the location of landfall of the cyclone

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

apparent roughness in wave current flow implication for coastal studies high turbulence intensities generated by waves in the wave bottom boundary layer affect the mean current velocity and should be taken into account for calculation of currents in the presence of waves this influence of the wave induced turbulence on the mean current can be schematized by introducing an apparent bed roughness which is larger than the physical bottom roughness apparent bed roughness is defined here as roughness that provides the same depth mean velocity for current alone configuration as for the wave current flow a one dimensional vertical k l turbulence closure model that allows detailed time dependent flow modeling has been applied for apparent roughness computations the domain of variable parameters is chosen according to the israeli near shore conditions an approximate expression for apparent bed roughness calculations as a function of wave and current parameters based on this turbulence closure model is derived simulation of flow patterns on the tel aviv coast using the three

single station location of seismic events a review and a plea for more research abstract traveltime based location methods are ineffective for locating regional seismic events which are recorded by few stations however the comprehensive test ban treaty ctbt makes it imperative that we monitor sparsely observed events this paper reviews the current status of single station location ssl methods the location of seismic events using records from one three component broadband digital station we argue here that ssl methods may ultimately provide the most effective and economical means for monitoring small magnitude m 3 seismic events over most of the earth potentially station event distance and focal depth may be determined accurately by utilizing broadband three component data and matching observed and synthetic waveforms station event azimuth is determinable from the polarization of the p wave arrival and p coda however more research is required before ssl methods become a practical alternative to traveltime based methods currently the most significant problem is that regional seismograms are strongly dependent on regional crustal structure thus future research efforts should focus both on determining appropriate crustal models in specific regions and also on improved methods for dealing with regional variations in crustal structure a second important problem concerns location errors with ssl they may involve 180 errors in station event azimuth or other highly non gaussian blunders

strategy for automated analysis of passive microseismic data based on s transform otsu s thresholding and higher order statistics small magnitude seismic events either natural or induced microearthquakes have increasingly been used in exploration seismology with applications ranging from hydrocarbon and geothermal reservoir exploration to high resolution passive seismic tomography surveys we developed an automated methodology for processing and analyzing continuously recorded single channel seismic data this method comprised a chi squared based statistical test for microseismic event detection and denoising filtering in the stransform domain based on the otsu thresholding method an automatic p phase picker based on higher order statistics criteria was used the method was used with data from a surface seismic station the performance of the method was tested and evaluated on synthetic and real data from a microseismic network used in a high resolution pst survey and revealed a high level of consistency

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

the effect of wave current interaction on tidally forced estuarine circulation reductions in the velocity and surface elevation of tidal flows that have been observed in the delaware bay a coastal plain estuary on the eastern coast of the united states correlate well with local wind events while there are several mechanisms that could account for this phenomenon we consider hydrodynamic wave current interaction to be a reasonable explanation in order to theoretically model the interaction between tides and surface gravity waves and eliminate the need for a reference velocity required by the grant and madsen 1979 wave current interaction model we propose a process oriented model that couples the mechanism of wave current interaction directly to the current dynamics of the tidal flow the tidal model uses an eddy viscosity concept to parameterize the turbulent stresses and further characterizes the eddy viscosity in terms of a flow dependent shear velocity within the bottom boundary layer of the surface gravity wave the turbulent stresses are also parameterized by an eddy viscosity that is coupled to the shear velocity of the tidal model results of the coupled model indicate that as expected wave current interaction increases the bottom friction felt by the tidal flow and usually reduces the volume flux however if the physical bottom roughness is sufficiently small less than 30 cm then it is possible to enhance the volume flux in a long deep estuary contrary to expectations a simple one dimensional linearized friction model shows this potentially dramatic effect can be attributed to an increase in the bottom friction that then tunes the estuary closer to its natural resonance obviously an estuary at resonance maximizes the volume flux that must pass through the estuary mouth the effect of wave current interaction is to provide a possible means of increasing the bottom friction and enhancing the volume flux

holocene humidity changes in northern finnish lapland inferred from lake sediments and submerged scots pines dated by tree rings conclusive evidence for a rise in water levels has been found in connection with lake sediment studies undertaken partly in collaboration with the pine megafossil sampling and dendrochronological work in northern finnish lapland the change in lake level stands is shown by slow sedimentation rate in the early to mid holocene and an increase thereafter these data indicate a regional rise in water levels during the latter part of the holocene following a relatively dry period between 8000 and 4000 bp synchronous changes also indicating rising water levels have been observed in the diatom and cladoceran assemblages of the sediment cores subfossil scots pines pinus sylvestris l have been preserved in large quantities in small lakes in lapland because in many cases the rising water level has inundated the trunks after death the position of the subfossil trunks and stumps often indicates that the pines have been growing on dry land at the sides of the lakes in which they are now submerged traces of

event location at any distance using seismic data from a single three component station this paper demonstrates the usefulness of a novel technique for analysis of single site three component seismogram records for reliable epicenter determinations for even small seismic events at any distance parameters that may be extracted by this technique are p phase identifications in terms of x 2 probabilities and the associated slowness vectors using data from short period and broadband seismometers installed in the new noress norway array single site event locations are demonstrated azimuth estimates are found directly from the slowness vector while epicenter distance estimates are derived from differential arrival times between pn pg sn and lg sg simultaneous inversion for crustal model and hypocenter data indicate a crustal thickness beneath noress of 33 5 km if sn and or lg are well recorded focal depth estimates are often accurate to within a few kilometers locating teleseisms is problematic since secondary phases are not fully readily identifiable and hence distance can be estimated only by conversion of the measured apparent phase velocity for distances out to approximately 1000 km event location errors as compared to network solutions seldom exceed 50 km and are due mainly to errors in azimuth estimates with sn phases available focal depth errors appear to be of the order of 4 km for teleseismic p waves short period location errors occasionally exceeded 7 and were due mainly to poor distance estimates using broadband records from relatively strong events location errors were about 1 further refinements seem feasible by using seismicity information and or recognition of stationarity in the p wave decomposition pattern for events within the same region at least in certain cases such approaches reflect genuine location refinements as demonstrated

three component analysis of regional seismograms abstract both phased array techniques for single component sensors and vectorial analysis of three component recordings can provide estimates of the azimuth and slowness of seismic phases however a combination of these approaches provides a more powerful tool to estimate the propagation characteristics of different seismic phases at regional distances conventional approaches to the analysis of three component seismic records endeavor to exploit the apparent angles of propagation in horizontal and vertical planes as well as the polarization of the waves the basic assumption is that for a given time window there is a dominant wavetype e g a p wave traveling in a particular direction arriving at the seismic station by testing a range of characteristics of the three component records a set of rules can be established for classifying much of the seismogram in terms of wavetype and direction it is however difficult to recognize sh waves in the presence of other wavetypes problems also arise when more than one signal in either wavetype or direction arrive in the same window the stability and robustness of the classification scheme is much improved when records from an array of three component sensors are combined for a set of three component instruments forming part of a larger array it is possible to estimate the slowness and azimuth of arrivals from the main array and then extract the relative proportions of the current p sv and sh wave contributions to the seismogram this form of wavetype decomposition depends on a model of near surface propagation a convenient choice for hard rock sites is to include just the effect of the free surface which generates a frequency independent operation on the three component seismograms and which is not very sensitive to surface velocities this approach generates good estimates of the character of the s wavefield because the phase distortion of sv induced by the free surface can be removed the method has been successfully applied to regional seismograms recorded at the medium aperture warramunga array in northern australia and the two small arrays noress and arcess in norway which were designed for studies of regional phases the new wavefield decomposition scheme provides results in which the relative proportions of p sv and sh waves as a function of time can be compared without the distortion imposed by free surface amplification such information can provide a useful adjunct to existing measures of signal character used in source discrimination

regional wave propagation in southern california and nevada observations from a three component seismic array we present results from a study conducted to characterize regional wave propagation in southern california and nevada the data are from events whose paths sample the southern coast ranges the southern sierra nevada mountains and the southern basin and range these regional earthquake data were recorded by a small aperture three component seismic array located at the pinon flat observatory southern california the data are analyzed using a statistical array processing algorithm that provides estimates of the propagation direction frequency wavenumber and particle motion polarization characteristics of the coherent arrivals observed at the array perhaps the most striking feature shared by these data is the extent to which the p s and lg wave trains are composed of coherent forward scattered multipathed energy the nature of the p s and lg wave trains suggests that spatially anisotropic scattering plays an important role in regional wave propagation in southern california and nevada and that scattering sources are located not on elliptical shells whose foci are the source and the receiver but instead in a limited volume subparallel to the path of the direct arrivals the high amplitude coherent nature of numerous of the pg and lg coda waves suggests that strong scattering in the source zone plays an important role in shaping the pg and lg wave trains while the p s and lg wave trains for these regional events share some general characteristics they also exhibit fairly significant differences these differences illustrate the important role regional and source zone structure play in shaping the wave field and the need to account for both complex scattering and three dimensional propagation effects in regional waveform modeling the coda for these regional data do not begin to exhibit a character consistent with the random scattering model for coda generation until the arrival of the surface waves the fact that much of the surface wave coda cannot be effectively modeled as plane waves suggests that it is not the product of scattering from distant heterogeneities

modeling flow in coral communities with and without waves a synthesis of porous media and canopy flow approaches both canopy flow and porous media theories have been developed independent of one another to predict flow through submerged porous structures these approaches are very similar albeit with some key differences in how canopy resistance forces are parameterized canopy models provide a means of parameterizing the shear stresses that occur at the top of the canopy whereas porous media models can often provide a simpler and more tractable way of parameterizing turbulent form drag based on simple morphological metrics and empirical relationships already in the hydrology literature we developed a set of equations combining aspects of both models and applied this hybridized model to predict the flow structure within an experimental canopy formed by the branching coral porites compressa using model parameter values obtained from the literature results from the model predictions agreed well with direct measurements of flow speed and flow forces derived from particle image velocimetry under conditions of both unidirectional and wave driven oscillatory flow

the nature of particle motion in regional seismograms and its utilization for phase identification summary the particle motion of regional arrivals is frequently treated in automatic phaserecognition schemes as that appropriate to simple p or s waves incident on an elastic laterally homogeneous half space this model implies that the motion in p type phases can be described in terms of a single generalized signal process and s type phases in terms of two independent processes sv and sh and thus all regional arrivals could be fully characterized by three components of motion in this paper we present anlyses of the particle motion patterns of various regional arrivals recorded at the arcess array from closely spaced events in the kola peninsula we have found that only pn particle motion described in terms of two independent signal processes can be reliably characterized by three component recordings on the other hand the various regional arrivals following pn such as pg sn and lg can only be poorly characterized on the basis of three component recordings alone the reason is that these arrivals must be described in terms of more than two independent generalized signal processes at least three for pg and sn and possibly up to five for lg recognition of these phases will thus require the use of more sensors than signal processes in the observing sensor configuration such as three component sensors combined with a small tripartite array we have investigated the feasibility of adaptive automatic recognition of regional arrivials by a wavefield extrapolation scheme utilizing such a mini array the process which appear to be promising adaptively learns the particle motion patterns of individual arrivals including complex site response functions from examples of closely located regional events

wave transformation on a coral reef wave transformation of regular waves was measured in a laboratory model of a fringing reef with a steep face and an outer reef top slope gradually decreasing in the landward direction data was obtained for various wave conditions and water levels a nonlinearity parameter fco g1 25ho 0 5t2 5 hc 1 75 based upon one proposed by swart and loubser 1979 is proposed as a suitable parameter for classifying wave transformation regimes on this reef in particular when fco 150 waves plunge on the reef edge and the amount of wave energy reaching a shore or structure is small 16 when fin co 100 waves spill on the reef top but the greater part of their energy is transmitted over the reef top the maximum values of the wave height to water depth ratio on the reef top were found to be consistent with nelson s analyses for laboratory and field data which indicate that the maximum stable wave height to depth ratio h d on a horizontal bottom never exceeds 0 55 for shallow water waves fc 500 the experimental data confirms that the maximum value of h d decreases when fc decreases but that it also increases when the bottom slope increases

mass transfer limitation of nutrient uptake by a wave dominated reef flat community maximum rates of phosphate nitrate and ammonium uptake by a reef flat community were estimated from rates of frictional dissipation that were calculated from the attenuation of waves propagating over the kaneohe bay barrier reef flat time averaged flow speeds across the entire study area ranged from 0 08 to 0 22 m s 21 observed decreases in wave energy fluxes and near bottom orbital velocities gave a mean estimate for the bottom friction coefficient cf of 0 22 6 0 03 friction coefficients were used to estimate nutrient mass transfer coefficients of 5 9md 21 for phosphate and 9 16 m d 21 for ammonium and nitrate wave heights offshore of kaneohe bay were also used to estimate an annual phosphate mass transfer coefficient of 8 6 2md that was determined from measured changes in phosphate concentrations across the reef flat we conclude that rates of phosphate uptake by the kaneohe bay barrier reef flat community are occurring near the limits of mass transfer net primary production is a major pathway by which mass and energy flow into coral reef ecosystems the uptake of dissolved nutrients is often the rate limiting step for net pri mary production in marine ecosystems thus a knowledge of the kinetics of nutrient uptake by coral reef communities is necessary for assessing how nutrient loading rates change in response to natural or anthropogenic increases in nutrient concentrations bilger and atkinson 1992 proposed that nutrient uptake by shallow reef communities was limited by mass transfer the physical transfer of nutrients across con centration boundary layers covering the surfaces of reef au totrophs these authors used mass transfer correlations for rough surfaces taken from the engineering literature to cor relate maximum rates of nutrient uptake with the frictional characteristics of experimental reef communities subse quent studies demonstrated the ability of such mass transfer correlations to predict nutrient uptake kinetics for experi mental reef communities within closed recirculating flumes atkinson and bilger 1992 bilger and atkinson 1995 thomas and atkinson 1997 and a large experimental me socosm atkinson et al 2001 the results of these studies made it clear that shallow water reef communities are ca pable of taking up nutrients from the water column at rates that are limited by mass transfer however it had not yet been demonstrated whether in situ rates of nutrient uptake

wave breaking hydrodynamics within coral reef systems and the effect of changing relative sea level this paper considers the hydrodynamics of wave driven flow across a coral reef and the resultant flushing of its lagoon current depth coefficients are introduced that describe the fractional change of across reef and lagoonal current with change in the relative local sea level i e the depth of water over the reef flat the coefficients are derived from an analytical hydrodynamic model and compared with data from two reefs the first is ningaloo reef in northwest australia which is a typical barrier reef with a narrow coastal lagoon and the second is kaneohe bay in oahu hawaii where the reef is both unusually deep and wide the current depth coefficients are shown to be sensitive to the form of the frictional law on the reef flat and can be deduced from measurements of the astronomical tidal currents in the lagoon both quadratic and linear friction laws are considered for the reef flat and good agreement obtained with a linear law based on the high frequency motion due to surface gravity waves

wave driven flow over shallow reefs long term 1 month observations of waves and currents over a natural reef are presented which show a strong correlation between offshore rms incident wave height and cross reef currents at subtidal frequencies the energy spectrum of the cross reef currents shows a significant peak at twice the semidiurnal tidal frequency while the spectrum of sea surface elevation over the reef flat shows no corresponding peak furthermore experimental results reported by gourlay 1993 show setup over the reef occurs in the absence of a beach and the cross reef transport decreases with an increase in the sea surface slope across the reef flat due to an increase in setup at the top of the reef face analytic solutions for flow forced by wave breaking over an idealized reef explain the above features of cross reef flows in the absence of a beach through the surf zone on the reef face the cross reef gradient in the radiation stress due to wave breaking is partitioned between balancing an offshore pressure gradient associated with setup over the reef and forcing a mean flow across the reef over the reef flat where the depth is constant there is no forcing due to wave breaking and the flow is driven by a pressure gradient which results from the setup through the surf zone the magnitude of the setup through the surf zone is such that the transport across the reef flat matches the transport through the surf zone which is forced by the gradient in the radiation stress solutions are presented for general reef geometry defined by the reef width and slope of the seaward reef face and incident wave forcing defined by the depth at the breakpoint and the depth of water over the reef as the depth over the reef goes to zero the solutions converge to the plane beach solutions described by longuet higgins and stewart 1964 wave setup is maximized and the cross reef transport is zero in other cases the relative magnitudes of the setup and the cross reef transport depend on the geometry of the reef and the incident wave forcing

wave height variation across beaches of arbitrary profile an intuitive expression for the spatial change in energy flux associated with waves breaking in the surf zone is developed using shallow water linear wave theory analytical solutions for wave height transformation due to shoaling and breaking on a flat shelf a plane slope and an equilibrium beach profile are derived and then compared to laboratory data with favorable results the effect of beach slope on wave decay is included explicitly while wave steepness effects are included implicitly by specification of the incipient conditions set down set up in the mean water level bottom friction losses and bottom profiles of arbitrary shape are introduced and solutions are obtained numerically the model is calibrated and verified using laboratory data with very good results for the wave decay but not so favorable results for set up a test run on a prototype scale profile containing two bar and trough systems demonstrates the model s ability to describe the shoaling breaking and wave re forming process commonly observed in nature bottom friction is found to play a negligible role in wave decay in the surf zone when compared to shoaling and breaking

surface wave breaking over sheared currents observations from the mouth of the columbia river measurements of waves and currents from freely drifting buoys are used to evaluate wave breaking parameterizations at the mouth of the columbia river where breaking occurs in intermediate depths and in the presence of vertically sheared currents breaking waves are identified using images collected with cameras onboard the buoys and the breaking activity is well correlated with wave steepness vertical shear in the currents produces a frequency dependent effective current that modifies the linear dispersion relation accounting for these sheared currents in the wavenumber spectrum is essential in calculating the correct wave steepness without this wave steepness can be over under estimated on opposing following currents by up to 20 the observed bulk steepness values suggest a limiting value of 0 4 the observed fraction of breaking waves is in good agreement with several existing models each based on wave steepness further a semi spectral model designed for all depth regimes also compares favorably with measured breaking fractions in this model the majority of wave breaking is predicted to occur in the higher frequency bands i e short waves there is a residual dependance on directional spreading in which wave breaking decreases with increasing directional spread this article is protected by copyright all rights reserved

energy saturation and phase speeds measured on a natural beach field measurements of wave height and speed from 7 m depth shoreward are described the experiment plan consisted of a shore normal transect of closely spaced compared to a dominant wave length velocity pressure and elevation sensors on an almost plane profile having an inshore slope of 1 50 as the waves shoal and begin to break the dominant dissipative mechanism is due to turbulence generated at the crest and wave heights become increasingly depth controlled as they progress across the surf zone wave heights in the inner surf zone are strongly depth independent the envelope of the wave heights is described by h sub rms 0 42 h the depth dependence of the breaking wave height is shown to be related to the kinematic instability criterion celerity spectra were measured by using phase spectra calculated between pairs of adjacent sensors inshore of 4 m depth the celerity was found distant over the energetic region of the spectrum a mean celerity was compared with linear theory and was within 20 and 10 showing good agreement for such a nonlinear dissipative region

wave driven along channel subtidal flows in a well mixed ocean inlet observations of waves flows and water levels collected for a month in and near a long narrow shallow 3000 m long 1000 m wide and 5 m deep well mixed ocean inlet are used to evaluate the subtidal periods 30 h along inlet momentum balance maximum tidal flows in the inlet were about 1 5 m s and offshore significant wave heights ranged from about 0 5 to 2 5 m the dominant terms in the local across the km wide ebb shoal along inlet momentum balance are the along inlet pressure gradient the bottom stress and the wave radiation stress gradient estimated nonlinear advective acceleration terms roughly balance in the channel onshore radiation stress gradients owing to breaking waves enhance the flood flows into the inlet especially during storms

field study of wave attenuation on an offshore coral reef a major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef water level data were collected for over 3000 individual time series during a wide range of environmental conditions at the innermost measurement site which is located on the horizontal reef flat after the completion of wave breaking the upper bound of significant and maximum wave heights is limited to less than 40 and 60 of the reef flat water depth respectively as with significant wave height both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth for higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra however the attenuation is greater for both lower frequencies and higher energy portions of the spectra this causes the reef flat spectra to be broader than those measured windward of the reef at lower water levels considerable energy losses due to wave breaking and bottom friction occur most of the energy loss comes from the vicinity of the spectral peak and energy shifts to harmonics of the peak of the spectrum can be seen

integrated array and three component processing using a seismic microarray abstract a microarray as defined in this paper is modeled on a sub geometry of the noress array and comprises a 3 component center seismometer surrounded by 3 closely spaced vertical component sensors deployed over a typical aperture of 0 3 km analysis of five days of continuous data has shown that such a system combines the benefits of array and 3 component processing in providing reliable automatic detection phase identification and azimuth estimation of weak seismic events at local and regional distances using vertical components only broadband f k array analysis enables correct phase identification p type or s type phase in 95 of the cases and gives s wave azimuths with a root mean square rms deviation of 13 9 degrees from the estimates of the full noress array it is particularly significant that the small array eliminates the need for introducing particle motion models which creates ambiguities in 3 component analysis of secondary phases when interfering sh and sv phases occur p phase azimuths are estimated using integrated array and 3 component f k analysis and have an rms deviation relative to noress of only 9 6 degrees compared to the full noress array the p wave detection capability is reduced especially for epicentral distances greater than 500 km the s phase detection capability is enhanced by incoherent beamforming of the horizontal channels and approaches that of noress at all distances a considerable reduction in the detector false alarm rate is achieved by imposing constraints on the estimates of apparent velocity obtained from the f k analysis before accepting a detected phase

a new three component detector and automatic single station bulletin production a new three component 3c seismic signal detector is introduced that has enabled us to produce a preliminary single station bulletin in an automatic mode we consider automatic station bulletins as very important because in the high frequency range local events mostly chemical explosions like quarry blasts are truly numerous say 20 to 50 per day and cannot be handled efficiently by an analyst in the conventional way a short term average long term average sta lta test statistic is used either alone or in combination with 3c signal polarization for p phases which allows a lowered threshold an added advantage with the polarity estimate is that a corresponding slowness vector estimate is obtained the detector is operated in three consecutive steps 1 the detector is run on a suite of bandpass filtered records 2 the initial detection log is compressed while retaining parameters from the best filter and 3 the detected and identified phases are grouped into event families and epicenter parameters are estimated the 3c detector has been tested on 6 days of recordings from the station c4 in the noress array located in se norway and results were compared to the array bulletin for teleseismic signals the array has an advantage in snr of about 15 db for local and regional events distance 1500 km the 3c snr in the frequency range 5 to 15 hz is about 6 to 8 db below that of the array the 3c detector picks practically all s phases detected by the array but occasionally misses the preceding pn however some new events missed by the array were also found at local and regional distances the 3c azimuth and distance estimates are generally within 20 and 20 km respectively of the noress solution and the origin time estimates are within a few seconds the 3c epicenter solutions are less stable than that of the array mainly due to phase identification problems and pn azimuth errors at low snr naturally the benefit of analyst screening and re processing would improve the 3c bulletin quality although the performance is considered satisfactory at the present stage of development

woody vegetation fuel and fire track the melting of the scandinavian ice sheet before 9500 cal yr bp abstract new studies indicate the presence of early holocene ice free areas far north in scandinavia post glacial fire and vegetation were investigated based on sedimentary charcoal and pollen from two small lakes in northern sweden accumulation of organic sediment started around 10 900 and 9200 cal yr bp showing that both lake valleys were ice free extremely early given their northerly location fire events started after 9600 cal yr bp and became less common around the 8 2 ka event woody vegetation provided fuel that contributed to fires the first vegetation in our pollen record consisted of hippophae dryas grasses and sedges subsequently broadleaved trees betula salix increased in abundance and later pinus alnus ferns and lycopodium characterized the vegetation pollen from larix picea and malus were also found the change in vegetation composition was synchronous with the decrease in lake water ph in the region indicating ecosystem scale processes this occurred during a period of net global and regional warming the changes in fire frequency and vegetation appear independent of regional trends in precipitation the reconstructed fire history and vegetation support the scenario of early ice free areas far north in scandinavia during early holocene warming creating favorable conditions for woody plants and wildfires

isostatic land uplift and mesolithic landscapes lake tilting a key to the discovery of mesolithic sites in the interior of northern sweden until recently only a few mesolithic sites were known from the interior of n sweden although extensive archaeological surveys have been carried out since the 1950s the lack of archaeological data made every attempt to interpret the process of pioneer colonization quite fruitless in this paper we present a model of non uniform glacio isostatic uplift and lake tilting used to identify potential areas of mesolithic habitation by reconstructing shoreline displacement of ancient lakes archaeological palaeoecological and geological studies have resulted in the discovery of a significant number of mesolithic sites and of an early post glacial landscape previously unknown

focal depth estimation using pn coda phases including pp sp and pmp abstract we address a classic problem in observational seismology namely the precise estimation of the focal depth of small to moderate earthquakes the data available are three component records including pn onsets and their coda we believe that the pn coda contains p type phases that originate in the source area and lag behind due to longer travel paths phases such as pp and sp are generally not included in seismic bulletins and even cepstrum and array f k techniques have not been successful in extracting such arrivals we use recent developments in polarization analysis roberts and christoffersson 1990 fedorenko et al 2008 to extract secondary p phases in local and regional records from five earthquakes phase characteristics are typically slowness and lag time relative to the preceding pn phase however information is incomplete for confidently deciding whether an arriving wavelet should be classed as pp sp or something else this validation problem is resolved by picking several coda arrivals that can uniquely be fitted to travel time curves for suites of pn coda waves focal depth estimates even for ground truth 05 events are seldom more accurate than to 5 km and therefore we compared our results with those from moment tensor analysis differences in depth estimates were less than 5 km and for h pn arrival is generally spn the dt pn ppn lag time for shallow events is 2 0 s or less and hence difficult to detect in the coda most techniques for focal depth estimation are not user friendly in contrast the polarization schemes tested are easy to use and depth estimates are more accurate than those derived from ground truth studies based exclusively on p wave arrivals

hydrodynamics at a microtidal inlet analysis of propagation of the main wave components abstract the evolution of different wave components as they propagate within a microtidal inlet during a storm occurring from 24 26 january 2014 is analysed in order to improve knowledge on how microtidal river mouths typical of the adriatic sea behave for the first time the low pass filter mechanism previously ascertained at several macrotidal oceanic inlets around the world has been observed in the field with remarkably specific hydrodynamic conditions i e low tide excursion permanent connection with the sea and generally milder wave climate than in the ocean sea swell ss waves were strongly dissipated before entering the river mouth through the combined action of wave breaking due to reducing depths and opposing river currents enhanced by rainfall infragravity ig waves propagated upstream and significant ig wave heights of up to 0 4 m about 13 of the local water depth have been observed 400 m upriver about 10 times the local ss peak wavelength during storm climax the ig wave energy here represented over 4 of the maximum offshore storm energy ig wave components travelled upriver at estimated velocities between 3 6 m s and 5 5 m s comparable with speeds of nonlinear long waves during intense storm stages up to 600 m into the river channel about 15 times the local ss peak wavelength and are enhanced by tide induced increase in water depths it is estimated that tide induced excursion accounted for about 80 of the total mean water elevation at storm peak at about 400 m into the river finally tidal oscillations are detected up to 1 5 km upstream about 40 times the local ss peak wavelength this study highlights the dominance of astronomical tide over both wave setup and storm surge in controlling the upriver propagation of ig waves even in a microtidal environment

the removal of free surface interactions from three component seismograms summary the effect of the free surface can be removed from three component seismic recordings to recover the incident upgoing wavefield if the slowness and azimuth of the current wavefront are known as a function of time for a single threecomponent station it is usually possible to estimate an azimuth for an event from the first arriving p waves but slowness estimates are less reliable when more than one wavetype is presented in the seismic wavetrain however the free surface correction operators are generally slowly varying functions of slowness and so some error in slowness can be tolerated effective approximations for the removal of the free surface effects can be made for hard rock sites to cover slowness bands for the main regional phases pn pg sn and lg by applying these operators in turn over group velocity windows appropriate to the particular phases the relative amplitude of the p sv and sh contributions to the wavefield can be estimated because the free surface amplification effects have been removed the amplitudes can be compared directly and provide useful constraints on the radiation characteristics of the source this procedure is therefore helpful for developing discrimination measures for different classes of sources

optimal backazimuth estimation for three component recordings of regional seismic events augmenting travel time data with backazimuth information can improve regional seismic event locations for which only a few recording stations are available this study examines the achievable accuracy of backazimuths derived from 164 regional short period p waves recorded at regional seismic test network rstn stations the data represent 62 events with a good distribution of distance azimuth and signal to noise ratio snr at each of four rstn stations using preliminary determination of epicenter locations to generate reference backazimuths we examine the effects of computational method signal window length frequency content and snr on rstn backazimuth estimates the variety of geologic environments at the receivers also allows assessment of the effect of receiver structure on backazimuth estimation our results indicate that regional three component recordings can produce useful backazimuths more than 75 per cent of the records yield backazimuths within 20 of the correct value when reasonable parameters are used the accuracy of the calculated backazimuths does vary with the receiver however rstn stations in new york and ontario located in precambrian terranes produce very accurate backazimuths for snrs greater than 5 db at the south dakota and tennessee stations located in sedimentary rocks complicated receiver structure is the controlling factor in backazimuth estimation propagational complexities at the south dakota site preclude recovery of reasonable backazimuth values poor statistics are obtained for all parameter combinations at the tennessee site backazimuth accuracy depends strongly on the computational method used in general the choice of frequency band is important and varies by stations while the length of the signal window is less critical if the problematic south dakota records are excluded we achieve an rms backazimuth error of about 6 for recordings with snr above 10 db while a single optimized choice of parameters produces good results for the 164 record data set a further 5 to 10 per cent improvement can be achieved if the parameters are customized on a station by station basis

wave friction factors in nearshore sands abstract wave friction factors are estimated from vertical profiles of near bed turbulence and horizontal velocity spanning the wave bottom boundary layer measured values are partitioned by bed state which ranged from irregular ripples to flat bed and are examined as a function of two traditionally selected parameters physical bed roughness and outer flow reynolds number the measurements are from two field experiments in very different nearshore environments a relatively protected unbarred pocket beach and a linear barred beach exposed to the open shelf duck measured wave friction factors are remarkably similar for the two beaches and are highest for low energy rippled beds and lowest for the high energy flat bed conditions the reduction in the friction factor for high energy conditions corresponds to a decrease in the physical roughness of the bed as wave energy increases as a function of relative roughness measured friction factors are generally consistent with previous laboratory results and

a case study of wave current bathymetry interactions at the columbia river entrance abstract a unique set of field observations has documented intense wave current bathymetry interactions in a tidal inlet providing a severe test of existing wave theory hourly wave spectral estimates were acquired over ten complete tidal cycles at locations offshore of and on the columbia river bar this site has long been recognized as an extreme hazard to navigation due to the interaction of incident waves with a strong tidal jet typified by ebb currents in excess of 2 m s 1 during the five day observational period offshore significant wave height ranged from 1 to 5 m in contrast the bar wave height oscillated at tidal periods sometimes doubling during a single six hour flood to ebb cycle in one case the bar wave height was 7 0 m with an offshore wave height of 2 9 m a one dimensional model based on linear wave action density conservation and incorporating shoaling refraction and radiation stress fits the data remarkably well 85 of the observed variance in bar swell height and 57 of th

wave transformation in the nearshore zone a review this paper reviews works related to nearshore wave propagation with an emphasis on several aspects related to coastal morphodynamic modelling including randomness and directionality of waves energy transfer and dissipation in the surf zone shallow water non linearities and long period motions the first part briefly reviews four main issues in laboratory experiments and field campaigns the second part is devoted to spectral and probabilistic approaches then recent developments of advanced numerical models based on boussinesq equations are reviewed the last part is devoted to low frequency waves and vortical motions

seismic wavefield separation by multicomponent tau p polarisation filtering abstract this paper presents a modified form of controlled direction reception cdr filter to separate p and s waves in a multi component seismic profile the aim of cdr is to enhance the clarity of the section the essence of the method in seeking s wave extinction is to perform a dot product between the signal vector and the polarisation slowness vector during projection of the section into tau p space using the p wave velocity along the array alternatively s waves can be enhanced and all other wave types including background noise suppressed by using a conjugate rotation operator and the s velocity profile in forming the slant stack a two dimensional gain function based on the rectilinearity of particle motion is then applied in tau p space as a non linear boost function in order to enhance strongly polarised arrivals synthetic and physical model examples are used to demonstrate the noise rejection properties of the cdr process and to show how p and s wave seismic sections can be separately obtained

exploring the upper crystalline crust a combined interpretation of 3d imaging and reflection profiling in the noress array abstract p wavefield complexities are easily seen in the noress array records despite the small aperture of 3 km the siting area is well mapped geologically and is partly sampled by a 2 5 km seismic reflection profile using this information in combination with tomographic mapping ach on the basis of noress p n records we have undertaken structural mapping of the site area down to ca 3 km the major result is that the area is relatively homogeneous rhyolite granite except for the northeast quadrant which is dominated by an intrusive gabbro body the gabbro intrusion appears to be roughly mushroom shaped thinning towards the centre of the array only the upper reflector on the profile ca 1 1 km is accounted for by this model while deeper ones at ca 1 7 and 2 5 km do not have a counterpart in the 3d results the small array aperture excludes mapping of more deep seated structural anomalies

automatic seismogram analysis statistical phase picking and locating methods using one station three component data abstract seismic events at local and regional distances are located using data from the vaasa vaf 63 0 n 22 7 e three component station in western finland the analysis is performed off line after pseudo on line detections the continuous data are first recorded on long disk loops these loops can cover 10 days of data the events are picked using murdock hutt detector and after that they are recorded as separate files for further analysis the direction of approach which estimates the polarization state of the signal is determined by the well established maximum likelihood method the difference between the arrival times of p and s phases is used to estimate the distance phases observed up to 185 km distance from the source are assumed to be pg and sg and beyond that pn and sn the onset times of the phases are estimated by a statistical data adaptive method the onsets calculated in this way are very accurate when compared with earlier methods like sta lta epicenter locations are similar to those of finsa network reported in helsinki bulletins the median of the location differences is about 50 km

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

variability of depth limited waves in coral reef surf zones wave breaking and transformation on coral reef flats is an important process protecting tropical coastlines and regulating the energy regimes of coral reefs however the high hydraulic roughness shallow water and steep bathymetries of coral reefs may confound common surf zone assumptions such as a depth limited and saturated surf zone with a constant wave height to water depth ratio here we examine wave transformation across a coral reef flat during three separate swell events on both a time averaged and a wave by wave basis we use the relationship between significant wave height and water depth to examine the change in surf saturation across the reef flat and compare the measured wave height decay to results of modelled wave energy dissipation in the surf zone our results show that was not cross reef constant and varied according to location on the reef flat and local water depth on average was greatest at the outer reef flat near the reef crest and progressively reduced towards the inner reef flat near the reef lagoon this was most pronounced in shallow water with large values 0 85 at the outer reef flat and small values 0 1 at the inner reef flat this indicates that there is an increase in wave energy dissipation in shallow water most likely due to increased breaker and bed frictional dissipation the measured wave energy dissipation across the entire reef flat could on average be modelled accurately however this required location specific calibration of the free parameters the wave friction factor f and and further suggests that there is no value for either parameter that is universally applicable to coral reef flats despite model calibration inaccuracies were still observed primarily at the outer reef flat these inaccuracies reflected the observed cross reef variation of on the reef flat and potentially the limitations of random wave breaker dissipation models in complex surf zones our results have implications for the use of wave energy dissipation models in predicting breaker dissipation and subsequent benthic community change on coral reef flats and suggest that careful consideration of the free parameters in such models such as f and is required

wavefield decomposition using ml probabilities in modelling single site 3 component records summary this paper presents a new approach to the analysis of three component digital seismograms earlier approaches used techniques such as principal components to estimate particlemotion using models of p and s waves in this paper the maximum likelihood ml estimator is preferred because this allows the use of x2 probabilities to test whether energy of a specific wave type p s love or rayleigh is present in addition this analysis allows the joint estimation of azimuth of approach and in cases of p and sv waves also apparent angle of incidence and hence information on apparent velocity for a single three component seismogram the covariance matrix provides only six independent observations thus restricting analysis to rather simple wave models the technique works satisfactorily for p waves whereas shear and surface wave models sometimes prove cumbersome to handle due to correlation between radial and transverse components reflecting complex propagation characteristics in inhomogeneous media this technique has been tested on synthetic data and in such cases works perfectly for all wave types an important aspect of this work has been the visual display of the probability and velocity information as functions of time and azimuth displaying the data in this form provides information on the ray path in a manner similar to analysis performed by seismic arrays practical examples on a variety of siesmic data are given to illustrate the viability of the technique the data cover a broad spectrum of frequencies and applications from broad band teleseismic data 1 hz regional seismic data 10 40 hz seismic profiling data 125 hz and vsp 500 hz recordings