microseismic measurement of wave energy delivery to a rocky coast rocky coasts are attacked by waves that drive sea cliff retreat and etch promontories and embayments into the coastline understanding the evolution of such coastlines requires knowledge of the energy supplied by waves which should depend upon both the deep water waves and the coastal bathymetry they cross we employ microseismic measurements of the wave induced shaking of sea cliffs near santa cruz california as a proxy for the temporal pattern of wave energy delivery to the coast during much of the winter 2001 storm season visual inspection of the time series suggests that both deep water wave heights and tide levels exert considerable control on the energy delivered we test this concept quantitatively with two models in which synthetic time series of wave power at the coast are compared with the shaking data in the first model deep water wave power is linearly scaled by a fitting parameter because this model fails to account for the strong tidal signal it fits poorly in the second model the wave transformation associated with shoaling and refraction diminishes the nearshore wave power and dissipation associated with bottom drag and wave breaking is parameterized by exponential dependencies on two length scales this model reduces the variance by 32 45 and captures the essence of the full signal shoaling and refraction greatly modulate the wave power delivered to the coast energy dissipated by bottom drag across the shelf is relatively small the dissipation length scale is many times the path length across the shelf in contrast much energy is dissipated in the surf zone the tidal dissipation depth scale is of the same order as the tidal range 1 2 m which accounts for the strong dependence of the cliff shaking on the tide

break up of the atlantic deep western boundary current into eddies at 8 s the existence in the ocean of deep western boundary currents which connect the high latitude regions where deep water is formed with upwelling regions as part of the global ocean circulation was postulated more than 40 years ago1 these ocean currents have been found adjacent to the continental slopes of all ocean basins and have core depths between 1 500 and 4 000 m in the atlantic ocean the deep western boundary current is estimated to carry 10 40 times 106 m3 s 1 of water2 3 4 5 transporting north atlantic deep water from the overflow regions between greenland and scotland and from the labrador sea into the south atlantic and the antarctic circumpolar current here we present direct velocity and water mass observations obtained in the period 2000 to 2003 as well as results from a numerical ocean circulation model showing that the atlantic deep western boundary current breaks up at 8 s southward of this latitude the transport of north atlantic deep water into the south atlantic ocean is accomplished by migrating eddies rather than by a continuous flow our model simulation indicates that the deep western boundary current breaks up into eddies at the present intensity of meridional overturning circulation for weaker overturning continuation as a stable laminar boundary flow seems possible

ground motions on rocky cliffed and sandy shorelines generated by ocean waves 1 we compare ground motions observed within about 100 m of the waterline on eight sites located on shorelines with different morphologies rock slope cliff and sand beaches at all sites local ocean waves generated ground motions in the frequency band 0 01 40 hz between about 0 01 and 0 1 hz foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent in phase ground flexing motions mostly oriented cross shore that decay inland at higher frequencies between 0 5 and 40 hz breaking ocean waves and wave rock impacts cause ground shaking overall seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings however specific site response varied and was influenced by a combination of tide level incident wave energy site morphology ground composition and signal decay flexing and shaking increased with incident wave energy and was often tidally modulated consistent with a local generation source flexing magnitudes were usually larger than shaking and flexing displacements of several mm were observed during relatively large incident wave conditions hs 4 5 m comparison with traffic noise and earthquakes illustrate the relative significance of local ocean generated signals in coastal seismic data seismic observations are not a simple proxy for wave cliff interaction

identifying and removing noise from the monterey ocean bottom broadband seismic station mobb data when compared to quiet land stations the very broadband monterey ocean bottom seismic station mobb shows increased long period background as well as signal generated noise both sources of noise are unavoidable in shallow ocean bottom installations and postprocessing is required to remove them from seismic observations the long period background noise observed for periods longer than 20 s is mainly due to infragravity waves and ocean currents the shorter period signal generated noise on the other hand is due to reverberations of the seismic waves in the shallow sedimentary layers as well as in the water layer we first present the steps that were taken prior to and during the instrument deployment to minimize instrument generated noise as well as to avoid noise due to water flow around the instrument we then present results from two postprocessing methods that can be used to remove the long period background noise which both utilize the ocean bottom pressure signal locally recorded on a differential pressure gauge dpg one consists of subtracting the locally recorded ocean bottom pressure from the vertical seismic acceleration signal in this case the frequency independent scale factor is linearly estimated from the data the other one makes use of the transfer function between the vertical seismic and pressure signal to predict the vertical component deformation signal the predicted signal is then removed from the vertical seismic data in either frequency or time domain we also present two methods that can be used to remove the signal generated noise one employs the empirical transfer function constructed from mobb data and nearby land station data that do not show the signal generated noise the other one uses a synthetic transfer function computed by modeling the response of shallow layers at the mobb location using either of the two transfer functions most of the signal generated noise can be removed from the mobb data by deconvolution

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

synthetic seismograms for a complex crustal model the algorithm of the original reflectivity method has been vectorized and implemented on a cdc cyber 205 computer calculation times are shortened by a factor of 20 to 30 compared with a general purpose computer with a capacity of several million floating point operations per second mflop the rapid calculation of synthetic seismograms for complex models high frequency sources and all offset ranges is a provision for modeling not only particular phases but the whole observed wavefield as an example we model refraction data of the black forest southwest germany and are able to derive rather tight constraints on the physical properties of the lower crust

shear wave structure of the southern volcanic plateau of oregon and idaho and the northern great basin of nevada from surface wave dispersion fundamental mode rayleigh wave phase velocities to 100 s period have been measured for two paths across the northern great basin of nevada and utah and southern volcanic plateau of oregon and idaho the average dispersion for these regions is similar to that previously observed for the central great basin of nevada and utah average structural models were derived for these paths from the observed dispersion data and existing refraction data the model for the southern volcanic plateau and western snake river consists of a three layer 40 km thick crust and a 10 10 km thick high velocity mantle lid above a broad low velocity zone for shear waves higher phase velocities are observed at long periods 40 s for the path through the northern great basin than for parallel paths in the central great basin or volcanic plateau indicating higher average mantle shear wave velocities the model for the northern great basin consists of a three layer 30 km thick crust and a 30 10 km thick high velocity mantle lid above a low velocity zone for shear waves the average shear wave velocity within the low velocity zone beneath the northern great basin is 4 3 km s compared with 4 1 km s within the low velocity zone beneath the central great basin these higher mantle shear wave velocities postulated for the northern great basin are at odds with the observed heat flow but in agreement with teleseismic p wave results both the higher velocities and the high heat flow may be the result of upper mantle differentiation during a recent volcanic event

seismic observations of sea swell on the floating ross ice shelf antarctica 1 a seismometer operating on the floating ross ice shelf near its seaward ice front nascent iceberg for 340 days out of 730 days during the 2004 2005 and 2006 antarctic field seasons recorded the arrival of 93 distantly sourced ocean swell events displaying frequency dispersion characteristic of surface gravity waves propagating on deep water comparison of swell event dispersion with the noaa wave watch iii nww3 ocean wave model analysis reveals that 83 of these events were linked to specific storms located in the pacific southern and indian oceans nearly all major storms in the nww3 analysis of the pacific ocean were linked to signals observed at the nascent site during the period of seismometer operation swell induced motion of the ross ice shelf is found to increase by several orders of magnitude over the time period that sea ice surrounding antarctica decreases from its maximum extent october to its minimum extent february the amplitude of vertical vibration of the ice shelf in the frequency band between 0 025 and 0 14 hz varies between tens of micrometers to millimeters as sea ice decays to its minimum seasonal extent this suggests that climate influence on sea ice extent may indirectly modulate swell energy incident on the calving margins of the antarctic ice sheet the largest swell signals observed on the ross ice shelf come from storms in the tropical pacific and gulf of alaska these remote events emphasize how the iceberg calving margin of antarctica is connected to environmental conditions well beyond antarctica

swash oscillations on a natural beach run up swash oscillations were measured on a gently sloping beach face for a variety of incident wave conditions run up energy spectra at wind wave frequencies show an 3 dependence and energy levels that are independent of incident wave height this suggests saturation in contrast run up energy at surf beat periods increase approximately linearly with increasing incident wave energy thus in the inner surf zone where wave breaking limits the energy at wind wave frequencies the principal manifestation of large incident wind waves is energetic surf beat

alongshore variability in wave energy transfer to coastal cliffs abstract the alongshore distribution of wave energy is believed to be an important control on the spatial variability of coastal erosion there is however a lack of field data quantifying the alongshore variability in wave energy on rock coasts whereby the relative control of coastline geometry versus foreshore characteristics on wave energy delivery remains unclear a number of studies have identified high frequency cliff top ground shaking to be generated by wave impacts at the cliff toe during high tides ht to capture the variability of wave cliff impact energy along coast we installed an array of cliff top seismometers along a 1 km stretch of coastline in north yorkshire uk our aim is to constrain how wave energy transfer to the cliff toe varies and to examine the relative energy transfer around typical coastline features including a bay and headlands whilst the greatest ht ground motion energy is recorded at a headland and the lowest at the centre of the bay 5 of that observed at the headland we identify no systematic alongshore variation in the ht ground motion energy that can be related to coastline morphology we also note considerable variation between features of similar form the total ht ground motion energy at one headland is only 49 of the next headland 1 km alongshore between neighbouring sites within the bay separated by only 100 m we observe up to an order of magnitude difference in ground motion energy transfer our results demonstrate the importance of the foreshore in driving the variations in energy delivery that we observe local alterations in water depth and foreshore topography control the alongshore distribution of wave energy available to generate cliff ht ground motions importantly this apparently local effect overrides the influence of macroscale coastal planform morphology which has previously been assumed to be the dominant control the results show that foreshore characteristics that hold influence over wave energy transfer vary significantly over short 100 m distances and so we expect erosion controlled by wave impacts to vary over similar scales

a discussion on the 410 km depth discontinuity a sharpness estimate from near critical reflections by vidale et al vidale et al 1995 presented a convincing evidence of a fairly sharp 410 km seismic discontinuity uncjer the western united states by examining clear noise free reflected arrivals from this discontinuity in the near critical distance range of 11 5 to 14 fig ia they reconstructed the p velocity depth model from the arrival times of the 410 km reflection and initial p waves across the distance range 8 14 the prominent features of the upper mantle p velocity model given by them include a low velocity layer lvl in the depth range of about 110 200 km with a broad transitional bottom a fairly large velocity gradient 0 4 km s velocity increase from 200 to 410 km depth above the 410 km discontinuity which is sharp and associated with a 5 5 velocity increase seismic estimates of sharpness as well as velocity contrast at the 410 km and 660 km discontinuities in the mantle transition zone provide important constraints to plausible models of composition temperature and convective processes in the deep earth the rapid increases of seismic wave velocities inferred in the transition zone at depths of 410 km and 660 km are classically associated ringwood 1975 with the pressure induced phase transitions in olivine which is considered to be the predominant mineral in the upper mantle recent observations of high quality coherent seismic reflections from the transition zone benz and vidale 1993 vidale et al 1995 conclusively reveal that the 410 km discontinuity is fairly sharp contrastingly the experimental results from mineral physics akaogi et al 1989 bina and wood 1987 katsura and ito 1989 predict a substantially larger transition width on the order of 6 19 km for the olivine beta spinel phase transition at pressures corresponding to 410 km depth discontinuity similar inconsistencies in the magnitude of velocity contrast at the 410 km discontinuity are also found duffy et al 1995 jeanloz 1995 by comparison of results from modern seismic measurements and the new experimental models of the olivine beta spinel phase transition the latter revealing a relatively large contrast in view of these apparently contradicting results it is certainly critical to evaluate the high quality seismic data vidale et al 1995 for reliable estimates of both sharpness and velocity contrast of the 410 km discontinuity in order to consider its traditional association with the simple phase transition in the olivine dominated compositional model

using a genetic algorithm to model broadband regional waveforms for crustal structure in the western united states in this study we analyze regional seismograms to obtain the crustal structure in the eastern great basin and western colorado plateau adopting a for ward modeling approach we develop a genetic algorithm ga based parameter search technique to constrain the one dimensional crustal structure in these regions the data are broadband three component seismograms recorded at the 1994 95 iris passcal colorado plateau to great basin experiment cpgb stations and supple mented by data from u s national seismic network usnsn stations in utah and nevada we use the southwestern wyoming mine collapse event m 5 2 that occurred on 3 february 1995 as the seismic source we model the regional seis mograms using a four layer crustal model with constant layer parameters timing of teleseismic receiver functions at cpgb stations are added as an additional constraint in the modeling ga allows us to efficiently search the model space a carefully chosen fitness function and a windowing scheme are added to the algorithm to prevent search stagnation the technique is tested with synthetic data both with and without random gaussian noise added to it several separate model searches are carried out to estimate the variability of the model parameters the average colorado plateau crustal struc ture is characterized by a 40 km thick crust with velocity increases at depths of about 10 and 25 km and a fast lower crust while the great basin has approximately 35 km thick crust and a 2 9 km thick sedimentary layer

tilts in strong ground motion most instruments used in seismological practice to record ground mo tion are pendulum seismographs velocigraphs or accelerographs in most cases it is assumed that seismic instruments are only sensitive to the translational motion of the instrument s base in this study the full equation of pendulum motion including the inputs of rotations and tilts is considered it is shown that tilting the accelerograph s base can severely impact its response to the ground motion the method of tilt evaluation using uncorrected strong motion accelerograms was first suggested by graizer 1989 and later tested in several laboratory experiments with different strong motion instruments the method is based on the difference in the tilt sensi tivity of the horizontal and vertical pendulums the method was applied to many of the strongest records of the mw 6 7 northridge earthquake of 1994 examples are shown when relatively large tilts of up to a few degrees occurred during strong earthquake ground motion residual tilt extracted from the strong motion record at the pacoima dam upper left abutment reached 3 1 in n45e direction and was a result of local earthquake induced tilting due to high amplitude shaking this value is in agreement with the residual tilt measured by using electronic level a few days after the earthquake the method was applied to the building records from the north ridge earthquake according to the estimates residual tilt reached 2 6 on the ground floor of the 12 story hotel in ventura processing of most of the strongest records of the northridge earthquake shows that tilts if happened were within the error of the method or less than about 0 5

assimilating coastal wave observations in regional swell predictions part i inverse methods abstract inverse methods are used to assimilate wave observations into numerical predictions of ocean swell 0 04 0 12 hz surface waves propagating over complex continental shelf bathymetry model predictions of swell on the shelf can be degraded by the limited accuracy and resolution of the initializing offshore unsheltered deep water frequency directional spectra so usually derived from buoy measurements or meteorological hindcasts the authors use a spectral refraction wave propagation model to find improved estimates of so that are consistent with both unsheltered and sheltered altered by coastal bathymetry observations and vary smoothly in direction and time in part i linear and nonlinear inverse assimilation methods are developed their potential and limitations are illustrated qualitatively using a scenario where no a priori knowledge of so is used in the inverse estimates inverse estimates of so based solely on sheltered wave data routinely collected in the southern california bight are

seismic precursory patterns before a cliff collapse and critical point phenomena 1 we analyse the statistical pattern of seismicity before a 1 2 103 m3 chalk cliff collapse on the normandie ocean shore western france we show that a power law acceleration of seismicity rate and energy in both 40 hz 1 5 khz and 2 hz 10khz frequency range is defined on 3 orders of magnitude within 2 hours from the collapse time simultaneously the average size of the seismic events increases toward the time to failure these in situ results are derived from the only station located within one rupture length distance from the rock fall rupture plane they mimic the critical point like behavior recovered from physical and numerical experiments before brittle failures and tertiary creep failures our analysis of this first seismic monitoring data of a cliff collapse suggests that the thermodynamic phase transition models for failure may apply for cliff collapse

surface wave studies of the sierra madre occidental of northern mexico abstract seismograms originating from earthquakes in the gulf of california and recorded in west texas txar were used to construct rayleigh wave group velocity dispersion curves for propagation paths in northern mexico these paths were approximately orthogonal to boundaries of several different tectonic provinces including the gulf of california the sonoran basin and range the central plateau of mexico and the sierra madre occidental smo thus the effects of horizontal refraction on the rayleigh waves were neglected prior surface wave studies have determined velocity structures for the crust and upper mantle for all of these provinces except the smo and the results of these studies were used to generate rayleigh wave dispersion curves for each segment of the path the group delays associated with each province were calculated and subtracted from the observed dispersion curve for the entire path thus isolating the effects of the smo on group velocity dispersion between periods of 12 and 40 sec linearized inversions showed that the most realistic geophysical model that fits the smo dispersion data consisted of a 55 km thick crust the crustal velocity structure for the smo consists of three layers a thin 5 km low velocity 2 8 km sec 1 l upper layer a middle layer approximately 20 km with a mean shear velocity near 3 6 km sec 1 l and a third lower crustal layer 30 km with shear velocity of about 4 0 km sec 1 l the mantle has shear velocities between 4 55 and 4 7 km sec 1 l but the thickness of the mantle lid is poorly resolved

coastal cliff ground motions from local ocean swell and infragravity waves in southern california 1 ground motions atop a southern california usa coastal cliff are compared with water level fluctuations observed at the cliff base and with ground motions observed 10 km inland at high tide cliff top ground motions in three frequency bands were generated locally by ocean waves at the cliff base 1 high frequency 0 3 hz shaking caused by waves impacting the cliff and 2 gravitational loading induced swaying at the frequency of the incident sea swell waves 0 05 0 1 hz and 3 slow swaying at infragravity frequencies 0 006 0 05 hz at high tide at infragravity and incident sea swell wave frequencies cliff top vertical ground displacement and cliff base water level fluctuations are coherent and oscillate in phase with occasional deviation at sea swell frequencies and spectral levels at the cliff top are much higher than at the inland seismometer in contrast at double frequencies 0 1 0 3 hz spectral levels of vertical motions are nearly identical inland and at the cliff top consistent with a common distant or spatially distributed source at low tide when ocean waves did not reach the cliff base power levels of vertical ground motions at the cliff top decreased to inland levels at incident wave frequencies and higher and only infragravity band motions were noticeably forced by local ocean waves

do fracture zones define continental margin segmentation evidence from the french guiana margin abstract plate reconstructions suggest that the french guiana margin in the west equatorial atlantic is a highly segmented margin with both rift and transform style features we describe here the results of modelling coincident multi channel and wide angle seismic gravity and magnetic data acquired along two transects of this margin the resulting models not only highlight the degree of structural segmentation but also demonstrate the effect of trans tension on margin evolution as a whole the margin is characterised by 35 37 km thick pre rift continental crust which is separated from unusually thin oceanic crust 3 4 km by thinned continental and or transitional regions to the north the margin exhibits a 320 km wide zone of thinned continental crust adjacent to a narrow ocean continent transition and is interpreted as a transform margin where the wide zone of thinned crust is a result of profile orientation being highly oblique to the direction of rifting approximately 240 km to the south the margin is characterised by a 70 km wide zone of thinned continental crust which is wider than typical for transform and narrower than typical for rifted margins this crustal structure is interpreted to reflect a leaky transform formed by trans tensional extension these observations suggest that fracture zone influenced geometry of equatorial atlantic rifting did not produce a well defined margin crustal structure but instead resulted in margin segments which display characteristics of both rift and transform tectonic processes the associated abundance of fracture zones has likely also affected the post rift evolution of the margin and provided topographic basement highs which acted as sediment dams to the northwards flux of sediment from the amazon

the role of beach morphology on coastal cliff erosion under extreme waves erosion of hard rock coastal cliffs is understood to be caused by a combination of both marine and sub aerial processes beach morphology tidal elevation and significant wave heights especially under extreme storm conditions can lead to variability in wave energy flux to the cliff toe wave and water level measurements in the nearshore under energetic conditions are difficult to obtain and in situ observations are rare here we use monthly cliff face volume changes detected using terrestrial laser scanning alongside beach morphological changes and modelled nearshore hydrodynamics to examine how exposed cliffs respond to changes in extreme wave conditions and beach morphology the measurements cover the north atlantic storms of 2013 2014 and consider two exposed stretches of coastline porthleven and godrevy uk with contrasting beach morphology fronting the cliffs a flat dissipative sandy beach at godrevy and a steep reflective gravel beach at porthleven beach slope and the elevation of the beach cliff junction were found to influence the frequency of cliff inundation and the power of wave cliff impacts numerical modelling xbeach g showed that under highly energetic wave conditions i e those that occurred in the north atlantic during winter 2013 2014 with hs 5 5 m dissipative site and 8 m reflective site the combination of greater wave height and steeper beach at the reflective site led to amplified wave run up subjecting these cliffs to waves over 4 times as powerful as those impacting the cliffs at the dissipative site 39 kwm 1 compared with 9 kwm 1 this study highlighted the sensitivity of cliff erosion to extreme wave conditions where the majority over 90 of the annual value of cliff face erosion ensued during the winter the significance of these short term erosion rates in the context of long term retreat illustrates the importance of incorporating short term beach and wave dynamics into geomorphological studies of coastal cliff change

coastal cliff ground motions and response to extreme storm waves coastal cliff erosion from storm waves is observed worldwide but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs limiting our understanding of cliff processes over january february 2014 during the largest atlantic storms in at least 60 years with deepwater significant wave heights of 6 8 m cliff top ground motions showed vertical ground displacements in excess of 50 100 m an order of magnitude larger than observations made previously repeat terrestrial laser scanner surveys over a 2 week period encompassing the extreme storms gave a cliff face volume loss of 2 orders of magnitude larger than the long term erosion rate the results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts

fine structure of p nl waves from explosions the long period character of p nl waves from many tectonic regimes has been modeled in the past using a simple homogeneous layer over a half space crust model scant attention has been paid to the short period wave form character in this study the p nl waves from nevada test site explosions as recorded on a regional digital seismic array have been modeled in the period range 1 10 s the fine structure of the p nl waveform has been carefully analyzed the effects of a realistic velocity gradient at the free surface or a velocity transition zone at the crust mantle boundary have been calculated a free surface gradient of even a moderate nature has a major effect on the waveforms whereas a finite crust mantle transition apparently does not we have developed an efficient scheme to implement the wavenumber integration theory for computing short period p nl waves at regional distances we utilized both the wavenumber integration and a generalized ray theory synthetic seismogram code for use in our analysis the former was used to compute exact though band limited synthetics the latter was used to determine which generalized ray paths contributed the primary energy to the major features of the waveforms for the simple one layer crust model the dominant energy to the critically reflected p wave portion of the wave comes from the primary ray reflected from the mantle we refer to this as pmp similar to the notation of pcp for the primary core reflection the next high amplitude energy is associated with a group of ray paths with at least one converted mode i e p converting to s and vice versa if the wave velocities are gradientlike within the top few kilometers of the model 6 km in this study the contribution from 2pmp a ray reflecting twice from the crust mantle interface ray path becomes significant the converted group of rays still contributes but not strongly free surface reflections become significant with the surface gradient present whereas they are not important for the simple one layer model besides the direct pn four major ray groups have been specifically identified in the observed waveforms and shown to dominate the wave shape these are the pmp and 2pmp groups the converted group and the 2pn head wave group the 2pmp and 2pn groups are portions of the same generalized rays since the converted group of rays loses significance in the presence of a realistic free surface gradient the onset of the critically reflected portion of the pnl waveform can be modeled as primarily an interaction between pmp and 2pmp the increased importance of depth phases in this part of the waves implies that it may be useful in improving source discrimination capabilities low q surface layers have been explored as a possible physical mechanism for the resolving power of regional spectral discriminants such a mechanism appears plausible if this is the dominant mechanism in differentiating earthquake and explosion spectra then earthquakes should have a much more energetic pmp phase with later arrivals being comparable in frequency content for the two types of sources

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

coastal cliff top ground motions as proxies for environmental processes 1 a two year dataset of coastal cliff microseismic ground motions is used to explore energy transfer to a cliff the long term dataset enables us to characterise cliff motion responses to a wide range of environmental processes and examine whether short term characteristics are representative of the long term we examine whether cliff top motions are reliable proxies for environmental processes to inform future investigations into the drivers of erosion the study is based at an actively eroding macrotidal hard rock cliffed coast where considerable intra annual variability in wave tide and storm conditions permit the examination of a full range of environmental permutations three frequency bands of ground motion are identified that represent wind and wave processes that transfer energy to the cliff examining mean energy transfer by aggregating the frequency bands by sea water elevation reveals a notable departure from tidal inundation duration alone of relevance to understanding the timing duration and intensity of effective processes of erosion peak energy transfer to the cliff face occurs during the largest storms where water levels significantly exceed those of tidal inundation rather than at locations most frequently inundated by tides we anticipate it is therefore these conditions that are likely to be most effective in eroding hard rock coasts rather than periods which accrue energy transfer associated with still or calm waters and hence tidally modulated inundation may not relate well to coastal erosion promisingly despite signal overlap and noise cliff top motions can be used as proxies for the processes that transfer energy to the coast

inversion of far regional broadband p waves for the estimation of source parameters from shallow depth earthquakes 1 attempts in separating the earthquake source effect from complex upper mantle wave propagation effects have been unsuccessful due to band limited world wide standardized seismograph network data and limitations in the computation of accurate seismograms in this study we examine the potential for estimating source parameters using broadband p waves observed between distances of 10 and 30 we used the reflectivity method which retains all of the rays to compute synthetic green s functions from the earth flattened global ak135 and regional t7 isotropic velocity models we applied the moment tensor inversion and iterative dislocation grid search methods to estimate seismic moment moment tensor focal mechanism and focal depth for three example seismic events the 1995 m w 5 7 west texas 1999 m w 5 6 scotty s junction nevada and 1999 southern iran m w 4 8 earthquakes the west texas and scotty s junction earthquakes were well recorded and they had independently established source parameters independent estimates from different data sets and agencies were used to validate the inversion results we selected the southern iran earthquake to show the utility of the method at lower magnitudes selected vertical and radial component seismograms were windowed about the p wave arrival corrected for instrument response and converted to velocity preserving the absolute amplitudes and periods within approximately 0 5 to 100 s both inverse methods were successful in separating the source effect with the use of the ak135 velocity model the inversion results using the t7 model appear slightly biased and had worse waveform fits compared to ak135 more importantly the use of two different velocity models resulted in biases in focal depths that were less than 2 km thereby providing a robust inverse method for focal depth utilizing far regional p waves would be most useful for remote earthquakes not adequately recorded locally and too small in magnitude to be recorded beyond epicentral distances of 30 for teleseismic analysis

loading and gravitational effects of the 2004 indian ocean tsunami at syowa station antarctica the 2004 indian ocean tsunami reached syowa station antarctica approximately 12 5 hr after the december sumatra andaman earthquake we have analyzed the tsunami signals recorded on ocean bottom pressure gauges broadband seismometers sts 1 and a superconducting gravimeter sg we calculated the sea level variation tilt and gravity changes induced by the tsunami and compared these results to observations from this comparison we confirmed the loading and gravity effects of the tsunamis on the sts 1 horizontal components and the sg records at syowa station the magnitudes of these effects given as root mean square amplitudes are as follows for the tilt effects obtained from 20 hr long sts 1 records at frequencies in the range 0 3 0 6 mhz 5 and 8 gal 10 8 m sec 2 in the east west and north south directions respectively and for the gravity effect obtained from the sg records for the same time period of 20 hr at frequencies in the range 0 1 0 2 mhz 0 2 gal by using detailed bathymetry around syowa station the synthetic amplitudes similar to the observed were obtained although the waveforms of synthetic and observation are not always consistent

a comparison of two spectral wave models in the southern california bight abstract two models a spectral refraction model longuet higgins and a parabolic equation method pem refraction diffraction model kirby are used to simulate the propagation of surface gravity waves across the southern california bight the bight contains numerous offshore islands and shoals and is significantly larger 300 km by 300 km than regions typically studied with these models the effects of complex bathymetry on the transformation of incident wave directional spectra s0 f 0 which are very narrow in both frequency and direction are difficult to model accurately as s0 f 0 becomes broader in both dimensions agreement between the models improves and the spectra predicted at coastal sites become less sensitive to errors in the bathymetry grid to tidal changes in the mean water depth and to uncertainty in s0 f 0 itself the smoothing associated with even relatively narrow 0 01 hz 5 bandwidth s0 f 0 is usually sufficient to bring the model predictions of shallow water energy into at least qualitative agreement however neither model is accurate at highly sheltered sites the importance of diffraction degrades the predictions of the refraction model and a positive bias o 10 of the deep ocean energy in the refraction diffraction model estimates believed to stem from numerical noise kirby may be comparable to the low wave energy the best agreement between the predicted spectra generally occurs at moderately exposed locations in deeper waters within the bight away from shallow water diffractive effects and in the far field of the islands in these cases the differences between the models are small comparable to the errors caused by tidal fluctuations in water depth as waves propagate across the bight the accuracy of predicted energies at these sites is likely to be limited by the uncertainty in specifying s0 f 0

are microseismic ground displacements a significant geomorphic agent this paper considers the role that microseismic ground displacements may play in fracturing rock via cyclic loading and subcritical crack growth using a coastal rock cliff as a case study we firstly undertake a literature review to define the spatial locations that may be prone to microseismic damage it is suggested that microseismic weakening of rock can only occur in damage accumulation zones of limited spatial extent stress concentrations resulting from cliff height slope angle and surface morphology may nucleate and propagate a sufficiently dense population of microcracks that can then be exploited by microseismic cyclic loading we subsequently examine a 32 day microseismic dataset obtained from a coastal cliff top location at staithes uk the dataset demonstrates that microseismic ground displacements display low peak amplitudes that are punctuated by periods of greater displacement during storm conditions microseismic displacements generally display limited preferential directivity though we observe rarely occurring sustained ground motions with a cliff normal component during storm events high magnitude displacements and infrequently experienced ground motion directions may be more damaging than the more frequently occurring reduced magnitude displacements characteristic of periods of relative quiescence as high magnitude low frequency events exceed and then increase the damage threshold these extremes may also render intervening reduced magnitude microseismic displacements ineffective in terms of damage accumulation as a result of crack tip blunting and the generation of residual compressive stresses that close microcracks we contend that damage resulting from microseismic ground motion may be episodic rather than being continuous and in quasi proportional and cumulative response to environmental forcing a conceptual model is proposed that describes when and where microseismic ground motions can operate effectively we hypothesise that there are significant spatial and temporal limitations on effective microseismic damage accumulation such that the net efficacy of microseismic ground motions in preparing rock for fracture and hence in enhancing erosion may be considerably lower than previously suggested in locations where high magnitude displacements punctuate standard displacement conditions determining and measuring the exact effects of microseismic ground displacement on damage accumulation and as a trigger to macro scale fracture in the field is not currently possible though our model remains consistent with field observations and conceptual models of controls on rockfall activity

regional mb ms lg pg amplitude ratios and lg spectral ratios as criteria for distinguishing between earthquakes and explosions a theoretical study summary theoretical seismograms for point explosion and double couple sources in a uniform plane layered earth are used to evaluate the likely effectiveness of three criteria that have been proposed for distinguishing between earthquakes and explosions the criteria are regional ms ms lg pg amplitude ratios and lg spectral ratios for explosions in material with a high wave speed the near regional mb ms discriminant gives only marginal separation between the two types of source ranging from zero for strike slip earthquakes to on average 0 4 magnitude units for 45d dip slip mechanisms only for explosions in material with a low wave speed do the theoretical data show an overall separation lg pg amplitude ratios successfully separate the source types except for strike slip earthquakes where there is overlap with shallow explosions theoretical lg spectra for deep 1 5 km explosions are depleted in high frequencies when compared with those for earthquakes and shallow explosions discrimination between earthquakes and these deep explosions is therefore possible using the spectral ratio method an important mechanism underlying these lg based discriminants is the interaction of the spherical p wavefront from an explosion with the free surface which generates shear waves with amplitude depending both on frequency and source depth of burial

nearshore wave induced cyclical flexing of sea cliffs 1 evolution of a tectonically active coast is driven by geomorphically destructive energy supplied by ocean waves wave energy is episodic and concentrated sea cliffs are battered by the geomorphic wrecking ball every 4 25 s we measure the response of sea cliffs to wave assault by sensing the ground motion using near coastal seismometers sea cliffs respond to waves in two distinct styles high frequency motion 20 hz reflects the natural frequency of the sea cliff as it rings in response to direct wave impact low frequency motion in the 0 1 0 05 hz 10 20 s band consistently agrees with the dominant nearshore wave period integrating microseismic velocities suggests 50 m and 10 m displacements in horizontal and vertical directions respectively displacement ellipsoids exhibit simultaneous downward and seaward sea cliff motion with each wave video footage corroborates the downward sea cliff flex in response to the imposed water load on the wave cut platform gradients in displacement amplitudes documented using multiple seismometers suggest longitudinal and shear strain of the flexing sea cliff on the order of 0 5 4 strains during each wave loading cycle as this sea cliff flexure occurs approximately 3 million times annually it has the potential to fatigue the rock through cyclical loading local sea cliff retreat rates of 10 cm yr imply that a given parcel of rock is flexed through roughly 109 cycles of increasing amplitude before exposure to direct wave attack at the cliff face

implications for upper mantle structure in the western united states from complete far regional seismograms abstract nuclear explosions from the nevada test site and earthquakes in southern and central california are recorded with offsets of 800 to 2000 km at the lajitas seismic station in texas these broadband far regional data are from a single high dynamic range station with three component instruments at an exceptionally quiet site and bridge the distance range between regional refraction studies of the crust and uppermost mantle and teleseismic investigations with long period data seismograms from 15 events were used to constrain the upper mantle structure to a depth of about 250 km by matching the complete waveforms including body and surface waves a simple one dimensional model is proposed that is consistent with the broadband body and surface waveforms as well as arrival times while the p wave velocity structure is well constrained by a model similar to that proposed by olsen et al 1980 the shear wave velocity structure is less controlled since the only identifiable shear arrivals are the l g phase trapped in the crustal wave guide there are no identifiable s n or mantle s waves below a distance of 1900 km in contrast mantle p waves turning in the depth range below 120 to 150 km are the p wave arrivals that dominate beyond 1200 km although p n is observed in cases of good signal to noise ratios to distances of 1400 to 1500 km as an emergent phase preceding these mantle arrivals due to the emergent p n wave packet observed at all distances the mantle lid p wave velocities are believed to exhibit a negative gradient zone as proposed by olsen et al 1980 in contrast to the model developed by burdick and helmberger 1978 the medium parameters for s waves can only be constrained by the observed dominant l g energy by introducing a strong velocity contrast across the crust mantle boundary including a high velocity s lid the l g energy can be efficiently trapped in the crust this effect is further enhanced by including a laminated structure for the lower crust surface waves are most sensitive to the velocities in the uppermost crust which consists of low velocity gradient layers typical for sediments starting at 4 and 2 km sec for p and s waves respectively for the basin and range province low q values 20 to 50 in the shallow crustal layers are further required to match these waves

the effects of spall on regional seismograms the effects of spall on regional signals are investigated using synthetic seismograms to frequencies of 20 hz depending on the scaling relationships used it is found that spall may have an important effect on regional body waves and especially surface waves the frequency range in which the spall effect dominates is dependent upon the characteristic times of the spallation process but generally occurs in the frequency range of about 0 2 to 2 hz because of the peaked nature of the radiated spall spectra effects at frequencies outside the 0 2 to 2 hz frequency range will be dominated by the explosion source the frequency range and strength of the spall effect depend in a complicated manner upon the yield depth of burial near source structure and material strength uncertainties in the spall scaling relationships need to be better understood before the effects of spall on regional discrimination and yield estimation can be properly quantified copyright american geophysical union 1989

cross shore decay of cliff top ground motions driven by local ocean swell and infragravity waves 1 ground motions at the frequencies between 0 01 and 0 1 hz of ocean infragravity and swell waves were observed on a cross shore transect extending landward from the edge of a southern california coastal cliff cliff top ground motions are coherent and in phase with water level fluctuations at the cliff base vertical ground motions at infragravity and single frequencies decay rapidly with inland distance from the cliff edge e folding scale is about 12 m and at the edge decrease by several orders of magnitude between high tide when waves reach the cliff base and low tide when the waterline is about 50 m from the cliff base the observed cross shore decay scales are qualitatively consistent with gravitational loading and attraction of water waves at tidally modulated distances from the cliff base at approximately constant distance from the waterline ground motions vary roughly linearly with nearshore swell wave energy in contrast to these locally forced ground motions double frequency band 0 1 0 2 hz cliff top vertical ground motions are remotely generated with spatially uniform magnitudes approximately equal to those observed 14 km inland near the cliff edge ground tilt dominates the observed large relative to vertical cross shore acceleration at infragravity frequencies contributes significantly to cross shore acceleration at swell frequencies and is a small fraction of cross shore acceleration at higher frequencies

the stability of rms lg measurements and their potential for accurate estimation of the yields of soviet underground nuclear explosions data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the soviet union and china observations of root mean square rms lg wave signals for soviet underground nuclear explosions at the shagan river test site in east kazakhstan show that the relative amplitudes of the rms signals at stations in norway the ussr and china are very similar for different explosions the standard deviation of the differences being only about 0 03 in logarithmic units i e magnitude units this is consistent with earlier observations comparing norsar and graefenberg array data and the observed scatter is significantly lower than has been reported for lg data from nevada test site explosions in view of the excellent correspondence found by nuttli 1986 and patton 1988 for lg versus yield at nevada this indicates that rms lg has a potential for yield estimation with very high accuracy at shagan river our study has shown that a selected stations in the ussr and china situated at regional distances provide a much improved signal to noise ratio of the lg phase for events at shagan river as compared to norsar array data b the scaling of rms lg amplitudes between different sized events recorded at the same single station site appears to be consistent with that of norsar indicating a remarkable degree of precision in single station measurements of lg signal c rms lg amplitude measurements for the best of these stations may be made at 1 5 to 2 0 magnitude units lower than at norsar or graefenberg allowing a much lower threshold for lg based yield determination and d the p wave detection capabilities of these single stations do not match those of the noress and arcess arrays thus teleseismic signals continue to be important for detection of small nuclear explosions our conclusion is that lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high quality digital in country seismic stations and when calibrated by access to independent nonseismic yield information for a few nuclear explosions at the test sites of interest in the context of monitoring a low yield threshold test ban treaty it will in addition be important to take into consideration various environmental conditions in the testing area such as the possible presence of cavities and to devise appropriate procedures for on site observations in this regard

structure and evolution of the demerara plateau offshore french guiana rifting tectonic inversion and post rift tilting at transform divergent margins intersection we present the structure and evolution of the eastern part of the demerara plateau offshore french guiana from the analysis of geophysical data collected during guyaplac cruise this area is located at the intersection of a transform segment and a divergent segment of a continental margin related to the early cretaceous opening of the equatorial atlantic the main structures are nne ssw to nnw sse trending normal faults on the eastern edge of the plateau and wnw ese to nw se trending acoustic basement ridges on its northern edge when replaced in their albian position these structures appear to be parallel to the coeval oceanic accretion axis and transform faults respectively the most striking structures are related to a post rift but syn transform tectonic inversion producing e w to wnw ese trending folds sealed by a regional unconformity this shortening can not be related to ridge push but is probably related to a plate kinematic change 105 my ago that modified the deformation in the vicinity of the transform fault late post rift evolution also includes a significant tertiary oceanward tilt of the edge of the demerara plateau the driving mechanism of this late tilt is unclear but may be related to a lithospheric flexure resulting from the loading of the abyssal plain by the orinoco and amazon deep sea fans

source scaling of contained chemical explosions as constrained by regional seismograms quantification of source coupling and characterization parameters for contained single fired chemical explosions observed at a regional seismic array are quantified the explosions were conducted in a mine in northeast wyoming where delay fired explosions occur regularly the primary observational data sets consist of close in measurements in the mine and regional observations at the international monitoring system primary array at pinedale wyoming pdar the single fired explosions ranged in size from 5500 to 50 000 lb and were separated from one another from 30 m to over 4 km peak amplitude measures at a single element of the regional array are well matched with a power law dependence on explosive weight similar scaling constants were determined for each of the dominant regional phases p n 0 84 0 14 p g 0 84 0 09 and l g 0 91 0 08 peak amplitudes across pdar show a factor of 3 variation for an individual explosion across all array elements this amplitude variation is accompanied by a decrease in spatial correlation with increasing station separation indicating the importance of near receiver structure the regional signals were further characterized by computing frequency dependent envelope functions at each array element consistent source scaling factors at a single array element were obtained from the envelope functions a high degree of spatial variability as a function of frequency was documented for the envelope functions spectral ratios are used to investigate source scaling relations for the different explosions four similarly prepared shots with total explosive weights between 5500 and 6000 lb were detonated to investigate source repeatability spectral ratio analysis identified two of the four shots as only partially detonating resulting in a reduction of long period spectral level by factors of 10 and 50 these long period reductions were accompanied by increases in source corner frequency consistent with a smaller source size spectral ratios of waveforms from the larger explosions that fully detonated illustrate that p g and l g source functions are similar the empirical source ratio is well modeled with a mueller murphy source model these experiments and the resulting data analysis suggest that simple single fired explosions of modest explosive weight can be used to calibrate regional seismic arrays networks and individual stations

seismic observations of glaciogenic ocean waves micro tsunamis on icebergs and ice shelves seismometers deployed over a 3 year period on icebergs in the ross sea and on the ross ice shelf antarctica reveal that impulsive sources of ocean surface waves are frequent e g 200 events per year in the ross sea in the ice shelf and iceberg covered environment of coastal antarctica the 368 events recorded by our field deployment suggest that these impulsive events are generated by glaciological mechanisms such as 1 small scale calving and edge wasting of icebergs and ice shelf fronts 2 edge on edge closing and opening associated with iceberg collisions and 3 possibly the impulsive opening of void space associated with ice shelf rifting and basal crevasse formation the observations described here provide a background of glaciogenic ocean wave phenomena relevant to the ross sea and suggest that these phenomena may be exploited in the future using more purposefully designed observation schemes to understand iceberg calving and ice shelf disintegration processes

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

constraints for upper mantle shear wave models of the basin and range from surface wave inversion several earthquakes in a limited region on the coast of northern california and off the coast of oregon have provided a set of broadband regional seismograms at lajitas ltx the significant love and rayleigh waves contained in these waveforms have repetitively sampled the same source receiver path within the basin and range province previous studies for this path using a subset of these sources of mantle s waves suggest a smoothly varying s velocity structure above 400 km followed by a strong gradient between 400 and 700 km these data are unable to uniquely constrain the shear velocity at shallower depths surface wave inversions are performed in order to refine the upper mantle s wave model using group and phase velocity dispersion for periods between 10 and 100 sec this period range gives good resolution for sub moho depths extending into the low velocity zone group velocities are extracted by multiple filter analysis and show significant differences for events on and off shore at periods around 50 sec this effect can be shown to be an interference pattern with the mantle s body wave arrivals as single station data were used phase velocities are estimated by phase matched filtering the recovered surface wave dispersion data are used in an inversion procedure to recover a shear wave structure for the basin and range path to ltx that consists of a relatively thin mantle lid underlain by a low velocity channel extending to a depth of 200 km structure below 200 km is poorly resolved and trades off with shallower structure the rayleigh wave group velocity data favor shear velocity models with a ridge within the low velocity zone with velocities 0 05 to 0 2 km sec higher than the background

sea cliff retreat and shore platform widening steady state equilibrium we challenge the notion of steady state equilibrium in the context of progressive cliff retreat on micro tidal coasts ocean waves break at or close to the abrupt seaward edge of near horizontal shore platforms and then rapidly lose height due to turbulence and friction conceptual models assume that wave height decays exponentially with distance from the platform edge and that the platform edge does not erode under stable sea level these assumptions combine to a steady state view of holocene cliff retreat we argue that this model is not generally applicable recent data show that 1 exponential decay in wave height is not the most appropriate conceptual model of wave decay 2 by solely considering wave energy at gravity wave frequencies the steady state model neglects a possible formative role for infragravity waves here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances and longer timescales than imaginable under the established conceptual model copyright 2013 john wiley sons ltd

crustal structure of the northwestern basin and range province from the 1986 program for array seismic studies of the continental lithosphere seismic experiment the basin and range province of the western united states is characterized by active east west extension at strain rates of 1 cm yr 1 high regional heat flow of 90 mw m 2 and widespread late cenozoic bimodal rhyolitic basaltic magmatism the 1986 program for array seismic studies of the continental lithosphere basin and range seismic experiment imaged a portion of northwestern nevada to determine the crustal structure and to assess reported differences between refraction versus reflection determinations of moho depth and how the crustal composition and structure has been influenced by volcanic and extension mechanisms our interpretation of the refraction wide angle reflection data suggests that the crust is fairly uniform in thickness and varies by less than 5 km over the 280 km east west profile and 3 km over its 220 km north south length we characterize the velocity structure by five layers 1 an upper most crust composed of sedimentary rocks and basement that has an average velocity of 5 7 km s i 2 a middle crust that extends to a depth of 18 22 with an average velocity of 6 1 km s 1 3 a 10 12 km thick lower crust with an average velocity of 6 6 km s 1 4 a 2 5 km thick transitional crust mantle boundary defined by a 7 6 km s l velocity and 5 an upper mantle with an average pn velocity of 7 9 8 0 km s 1 these data show a uniformily thick crust of 28 km 5 km beneath northwestern nevada and a lack of evidence for significant low velocity crustal layers in general the entire crustal column exhibits uniform positive velocity gradients of 0 02 0 04 s the midcrustal discontinuity is interpreted as a small velocity increase of 0 2 km s l at 18 km depth the absence of a significant midcrustal reflection and the presence of large velocity gradients throughout the crust arises either from 1 a systematic increase in mafic composition with depth or 2 possibly high lower crustal pore pressure that acts to decrease the velocity contrast across the midcrustal boundary our interpreted seismic velocity structure is consistent with a broad range of bulk compositions for the crust upper crustal velocities are consistent with bulk compositions that range from metasediments and granites at shallow depth to diorites at midcrustal levels while lower crustal velocities suggest bulk compositions that range from diorites and amphibolities at midcrustal depths to mafic granulites and gabbros at the base of the crust the uniform crustal thickness of 30 34 km in northwestern nevada is close to the crustal average for the basin and range province but is thin when compared to surrounding regions such as the sierra nevada and colorado plateau where crustal thickness is greater than 40 kin similarily northwestern nevada pn velocities of 7 9 8 0 km s 1 are near the province wide average of 7 9 km s l temperature corrected pn velocities from a 90 mw m 2 geotherm for the basin and range to 60 mw m 2 for the stable interior of the united states are within one standard deviation of the continental average of 8 05 km s i and suggest a uniform upper mantle composition across the basin and range in addition to these observations the homogeneity of the velocity structure beneath the western basin and range argues for a youthful moho and crust that has been reworked by province wide late cenozoic extension episodic magmatism and underplating

a physical model for seismic noise generation from sediment transport in rivers measuring sediment flux in rivers remains a significant problem in studies of landscape evolution recent studies suggest that observations of seismic noise near rivers can help provide such measurements but the lack of models linking observed seismic quantities to sediment flux has prevented the method from being used here we develop a forward model to describe the seismic noise induced by the transport of sediment in rivers the model provides an expression for the power spectral density psd of the rayleigh waves generated by impulsive impacts from saltating particles which scales linearly with the number of particles of a given size and the square of the linear momentum after incorporating expressions for the impact velocity and rate of impacts for fluvially transported sediment we observe that the seismic noise psd is strongly dependent on the sediment size such that good constraints on grain size distribution are needed for reliable estimates of sediment flux based on seismic noise observations the model predictions for the psd are consistent with recent measurements and based on these data a first attempt at inverting seismic noise for the sediment flux is provided

mass transport deposits and fluid venting in a transform margin setting the eastern demerara plateau french guiana abstract the eastern demerara plateau offshore french guiana was surveyed in 2003 during the guyaplac cruise multibeam bathymetry and acoustic imagery 6 channel seismic reflection and 3 5 khz echo sounding the data show the post transform cenozoic that the series located on the outer part of the plateau below c 2000 m contain at least twelve stacked mass transport deposits mtds that have recorded a history of large scale slope failure as well as two main normal fault sets that provide possible pathways for upward fluid migration through the series reaching at high as the uppermost mtds seabed data show that the area above the failures is characterized by circular to elongate slope parallel depressions interpreted as fluid seeps pockmarks some of them have been modified by along slope currents we suggest that the development of the mtds to results from the combinaiton of the presence of fluid overpressure at depth the geometry of the margin s deep structure in particular the existence of a free borderlateral border on the outermost plateau our results also emphasise the role of stratigraphic decollements within the cenozoic series

mechanism of thin skinned detachment in the amazon fan assessing the importance of fluid overpressure and hydrocarbon generation abstract since about 10 ma a wedge of clastic sediment up to 10 km in thickness has accumulated near the mouth of the amazon river forming the amazon fan thin skinned extensional and contractional structures root into a common basal detachment hundreds of kilometers long extensional faults have formed landward of the prograding delta slope and contractional folds and faults have formed seaward of it by plan view restoration we show that extension and contraction balance we therefore infer that slope instability has provided the driving force for thin skinned deformation on seismic data the detachment appears as a sharp surface within late cretaceous strata however there is no evidence at that level for soft layers such as evaporites or muds abnormal fluid pressure provides a more reasonable mechanism for the detachment at depths of several thousand meters deep wells have encountered fluid overpressures amongst the possible causes of abnormal fluid pressures are compaction and hydrocarbon generation although compaction may have contributed to fluid overpressures encountered in wells we argue that hydrocarbon generation provides the best explanation for detachment in cretaceous rocks which were old and lithified when it occurred in particular the broadly triangular area of detachment coincides with an inferred pod of cenomanian turonian source rock which is interpreted to have been in the gas window during detached deformation we have developed new techniques of sandbox modelling to investigate the geometries of fault patterns produced by fluid flow through porous media for the amazon fan we have been able to reproduce the structural pattern on the assumption that fluid overpressures existed over a broadly triangular area beneath the detachment

identifying and removing tilt noise from low frequency 0 1 hz seafloor vertical seismic data low frequency 0 1 hz vertical component seismic noise can be reduced by 25 db or more at seafloor seismic stations by subtracting the coherent signals derived from 1 horizontal seismic observations associated with tilt noise and 2 pressure measurements related to infragravity waves the reduction in effective noise levels is largest for the poorest stations sites with soft sediments high currents shallow water or a poorly leveled seismometer the importance of precise leveling is evident in our measurements low frequency background vertical seismic spectra measured on a seafloor seismometer leveled to within 1 10 4 radians 0 006 degrees are up to 20 db quieter than on a nearby seismometer leveled to within 3 10 3 radians 0 2 degrees the noise on the less precisely leveled sensor increases with decreasing frequency and is correlated with ocean tides indicating that it is caused by tilting due to seafloor currents flowing across the instrument at low frequencies this tilting generates a seismic signal by changing the gravitational attraction on the geophones as they rotate with respect to the earth s gravitational field the effect is much stronger on the horizontal components than on the vertical allowing significant reduction in vertical component noise by subtracting the coherent horizontal component noise this technique reduces the low frequency vertical noise on the less precisely leveled seismometer to below the noise level on the precisely leveled seismometer the same technique can also be used to remove background noise due to the seafloor pressure field up to 25 db noise reduction near 0 02 hz and possibly due to other parameters such as temperature variations

seismic monitoring of the indian ocean tsunami the 26 december 2004 sumatra andaman earthquake of mw 9 3 triggered a massive tsunami in the indian ocean we here report on observations of the indian ocean tsunami at broadband seismic stations located on islands in the area the tsunami induces long period 1000 s signals on the horizontal components of the sensor frequency time analysis shows that the long period signals cannot be due to seismic surface waves but that it arrives at the expected time of the tsunami the waveforms are well correlated to tide gauge observations at a location where both observations are available to explain the signals we favour tilt due to coastal loading but we cannot at the present stage exclude gravitational effects the density of broadband stations is expected to increase rapidly in the effort of building an earthquake monitoring system they may unexpectedly become useful tsunami detectors as well

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

wave runup during extreme storm conditions 1 video measurements of wave runup were collected during extreme storm conditions characterized by energetic long swells peak period of 16 4 s and offshore height up to 6 4 m impinging on steep foreshore beach slopes 0 05 0 08 these conditions induced highly dissipative and saturated conditions over the low sloping surf zone while the swash zone was associated with moderately reflective conditions iribarren parameters up to 0 87 our data support previous observations on highly dissipative beaches showing that runup elevation estimated from the variance of the energy spectrum can be scaled using offshore wave height alone the data is consistent with the hypothesis of runup saturation at low frequencies down to 0 035 hz and a hyperbolic tangent fit provides the best statistical predictor of runup elevations

spectral analysis of seismic noise induced by rivers a new tool to monitor spatiotemporal changes in stream hydrodynamics to 20 db relative to m s 2 hz for all the stations located along a steep 30 km long narrow and deeply incised channel of the trisuli river a major trans himalayan river the early summer increase in high frequency energy is modulated by a 24 h periodicity where the minimum of seismic noise level is reached around noon and the maximum is reached late in the evening a detailed study of seismic noise amplitude reveals a clear correlation with both regional meteorological and hydrological data along the trisuli river seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period of rapid melting of snow and ice in the high elevations the observed 24 h cyclicity is consistent with the daily fluctuation of the precipitation and river discharge in the region river induced seismic noise is partly generated by stream turbulence but this mechanism fails to explain the observed clockwise hysteresis of seismic noise amplitude versus water level this pattern is better explained if a significant part of the observed seismic noise is caused by ground vibrations generated by bed load transport this points out the potential of using background seismic noise to quantify in continuous river bed load and monitor its spatial variations which remain difficult with classical approaches

field evidence of beach profile evolution toward equilibrium an equilibrium framework is used to describe the evolution of the cross shore profile of five beaches medium grain size sand in southern california elevations were observed quarterly on cross shore transects extending from the back beach to 8 m depth for 3 10 years transects spaced 100 m in the alongshore direction are alongshore averaged into nineteen 700 900 m long sections consistent with previous observations changes about the time average profile in many sections are captured by the first mode empirical orthogonal function eof the first eof poorly describes sections with hard substrate less than roughly 80 sandy bottom and also fails near the head of a submarine canyon and adjacent to an inlet at the 12 well described sections the time varying amplitude of the first eof the beach state a describes the well known seasonal sand exchange between the shoreline and offshore roughly between 4 and 7 m depth we show that the beach state change rate da dt depends on the disequilibrium between the present state a and wave conditions consistent with the equilibrium concepts of wright and short 1984 and wright et al 1985 empirically determined optimal model coefficients using the framework of yates et al 2009a 2011 vary between sections but a single set of globally optimized values performs almost as well the model implements equilibrium concepts using ad hoc assumptions and empirical parameter values the similarity with observed profile change at five southern california beaches supports the underlying model equilibrium hypotheses but for unknown reasons the model fails at duck nc

quantifying the environmental controls on erosion of a hard rock cliff linking hard rock coastal cliff erosion to environmental drivers is challenging with weak relationships commonly observed in comparisons of marine and subaerial conditions to the timing and character of erosion the aim of this paper is to bring together datasets to explore how best to represent conditions at the coast and to test relationships with erosion which on this coast is primarily achieved via rockfalls on the n yorkshire coast in the uk we compare a continuously monitored microseismic dataset regionally monitored coastal environmental conditions modelled at cliff conditions and periodic high resolution 3d monitoring of changes to the cliff face over a 2 year period cliff top microseismic ground motions are generated by a range of offshore nearshore and at cliff sources we consider such ground motions as proxies for those conditions that promote the occurrence of rockfalls and erosion both these data and modelled at cliff water levels provide improved insight into conditions at and wave energy transfer to the cliff the variability in microseismic modelled and regionally monitored environmental data derives statistically significant relationships with increases in the occurrence of rockfalls the results demonstrate a marine control on the total volume and size characteristics of rockfalls the strongest relationships found are with rockfalls sourced from across the entire cliff rather than just at the toe indicating that the marine influence albeit indirectly extends above and beyond the area inundated these results identify failure mechanisms driving erosion where a range of processes unique to the coast trigger failure but in a manner beyond purely wave action at the cliff toe greater erosion occurs at the cliff toe however comparing water level inundation frequency microseismic energy transfer and erosion we observe that heights up the cliff that correspond with water levels associated with low frequency high energy storms or more frequent inundation do not experience increased erosion our results describe the relationship between inundation duration energy transfer and erosion of hard rock cliffs and illustrate the relative intensity of erosion response to variations in these conditions implicitly our data suggests that in future cliffed rocky coasts may be relatively quick to respond to changes in environmental forcing